JVC AV IPTEL IMP Service Manual

Avaya IP Telephony Implementation Guide

Communication Manager 2.1 Avaya Labs

ABSTRACT

This application note gives implementation guidelines for the Avaya MultiVantage™ Communications Applications. Configurations and recommendations are given for various Avaya Media Servers and Gateways, as well as Avaya 4600 Series IP Telephones. This document also provides information on virtual local area networks (VLANs), and guidelines for configuring Avaya and Cisco networking equipment in VoIP applications.

The intent of this document is to provide training on IP telephony, and to give guidelines for implementing Avaya solutions. It is intended to supplement the product documentation, not replace it.

This document covers the Avaya Communication Manager 2.0 and 2.1, and the Avaya 4600 Series IP Telephone 1.8 and 2.0, with limited information regarding previous and future versions.

External posting: www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

Application Note

August 2004 COMPAS ID 95180

Avaya IP Telephony Implementation Guide

All information in this document is subject to change without notice. Although the information is believed to be accurate, it is provided without guarantee of complete accuracy and without warranty of any kind. It is the user’s responsibility to verify and test all information in this document. Avaya shall not be liable for any adverse outcomes resulting from the application of this document; the user accepts full responsibility.

The instructions and tests in this document regarding Cisco products and features are best-effort attempts at summarizing and testing the information and advertised features that are openly available at www.cisco.com. Although all reasonable efforts have been made to provide accurate information regarding Cisco products and features, Avaya makes no claim of complete accuracy and shall not be liable for adverse outcomes resulting from discrepancies. It is the user’s responsibility to verify and test all information in this document related to Cisco products, and the user accepts full responsibility for all resulting outcomes.

Avaya and the Avaya Logo are trademarks of Avaya Inc. or Avaya ECS Ltd., a wholly owned subsidiary of Avaya Inc. and may be registered in the US and other jurisdictions. All trademarks identified by ® and ™ are registered trademarks or trademarks, respectively, of Avaya Inc. All other registered trademarks or trademarks are property of their respective owners.

SM Avaya IP Telephony Implementation Guide

Foreword

Several benefits are motivating companies to transmit voice communications over packet networks originally designed for data.

Cost saving is one factor. By eliminating a separate circuit-switched voice network, businesses avoid the expenses of buying, maintaining and administering two networks. They may also reduce toll charges by sending long distance voice traffic over the enterprise network, rather than the public switched telephone network.

Another benefit is the potential to more tightly integrate data and voice applications. Because they use open programming standards, Avaya ECLIPS products make it easier for developers to create, and for companies to implement, applications that combine the power of voice and data in such areas as customer relationship management (CRM) and unified communications. A converged multi-service network can make such applications available to every employee.

These benefits do not come free, however. Voice and data communications place distinctly different demands on the network. Voice and video are real-time communications that require immediate transmission. Data does not. Performance characteristics that work fine for data can produce entirely unsatisfactory results for voice or video. So networks that transmit all three must be managed to meet the disparate requirements of data and vo ice /video.

Network managers are implementing a range of techniques to help ensure their converged networks meet performance standards for all three payloads: voice, video and data. These techniques include the strategic placement of VLANs, and the use of Class of Service (CoS) packet marking and Quality of Service (QoS) network mechanisms.

For an overview of IP telephony issues and networking requirements, see the “Avaya IP Voice Quality Network Requirements” white paper at www1.avaya.com/enterprise/resourcelibrary/applicationnotes.

Professional consulting services are available through The Avaya Business Communication Solutions and Integration group. One essential function of this professional serv ices g roup is to prov ide pre- deployment network assessments to Avaya customers. This assessment helps to prepare a customer’s network for IP telephony, and also gives critical network information to Avaya support groups that will later assist with implementation and troubleshooting. Arrange for this essential service through an Avaya account team.

SM Avaya IP Telephony Implementation Guide

Avaya IP Telephony Implementation Guide

Table of Contents

1 Introduction to VoIP and Avaya Products.............................................................................................7

1.1 Servers, Gateways, Stations, and Trunks Defined......................................................................7

Servers ........................................................................................................................................7

Gateways.....................................................................................................................................7

Stations........................................................................................................................................7

Trunks.........................................................................................................................................8

1.2 Avaya Server-Gateway and Trunk Architectures.......................................................................8

Traditional DEFINITY System ...............................................................................................8

IP-enabled DEFINITY System...................................................................................................9

S8700 Multi-Connect................................................................................................................10

S8500 Media Server..................................................................................................................10

S8700 IP-Connect.....................................................................................................................11

S8300/G700/G350....................................................................................................................11

S8700 Multi-Connect with remote G700/350 gateways...........................................................12

S8700 IP-Connect with remote G700/350 gateways................................................................13

S8100/G600..............................................................................................................................13

Trunks.......................................................................................................................................14

1.3 VoIP Protocols and Ports..........................................................................................................15

2 IP Network Guidelines........................................................................................................................16

2.1 General Guidelines....................................................................................................................16

Ethernet Switches......................................................................................................................16

Speed/Duplex............................................................................................................................17

2.2 Bandwidth Considerations........................................................................................................18

Calculation................................................................................................................................18

Ethernet Overhead ....................................................................................................................19

WAN Overhead ........................................................................................................................19

L3 Fragmentation (MTU).........................................................................................................19

L2 Fragmentation......................................................................................................................20

2.3 CoS and QoS.............................................................................................................................20

General......................................................................................................................................20

CoS............................................................................................................................................20

802.1p/Q ...................................................................................................................................21

Rules for 802.1p/Q Tagging .....................................................................................................21

DSCP ........................................................................................................................................23

QoS on an Ethernet Switch.......................................................................................................24

QoS on a Router........................................................................................................................24

QoS Guidelines.........................................................................................................................25

Traffic Shaping on Frame Relay Links.....................................................................................26

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3 Guidelines for Avaya Servers and Gateways ......................................................................................27

3.1 S8700/8500 Servers..................................................................................................................27

S8700/8500 Speed/Duplex........................................................................................................27

S8700/8500 802.1p/Q and DSCP Tagging...............................................................................28

3.2 S8300 Server.............................................................................................................................28

3.3 S8100 Server (IP600)................................................................................................................29

S8100 Speed/Duplex.................................................................................................................29

S8100 802.1p/Q and DSCP Tagging........................................................................................29

3.4 G700 Media Gateway...............................................................................................................29

P330 L2 Switch.........................................................................................................................30

Media Gateway Processor (MGP)............................................................................................30

SAT Media-Gateway Form.......................................................................................................31

G700 802.1p/Q and DSCP Tagging..........................................................................................31

G700 in Octaplane Stack vs. Standalone..................................................................................32

3.5 G350 Media Gateway...............................................................................................................32

3.6 G600/650, MCC1, and SCC1 Gateways...................................................................................33

C-LAN Capacity and Recommendations..................................................................................33

C-LAN and MedPro Protocols and Ports..................................................................................34

C-LAN and MedPro Network Placement.................................................................................34

C-LAN and MedPro Speed/Duplex..........................................................................................34

C-LAN and MedPro 802.1p/Q and DSCP Tagging..................................................................35

Extreme Measures for MedPro and Other IP Boards on Cisco Switches.................................35

IP Server Interface (IPSI) Board...............................................................................................35

3.7 General IP-Telephony-Related Configurations (SAT Forms)..................................................36

ethernet-options.........................................................................................................................36

node-names ip...........................................................................................................................36

ip-interface................................................................................................................................36

data-module...............................................................................................................................37

ip-codec-set...............................................................................................................................37

ip-network-region.....................................................................................................................37

ip-network-map.........................................................................................................................39

station........................................................................................................................................40

trunk-group and signaling-group ..............................................................................................40

system-parameters ip-options ...................................................................................................41

SAT Troubleshooting Commands ............................................................................................42

4 Guidelines for Avaya 4600 Series IP Telephones...............................................................................43

4.1 Basics........................................................................................................................................43

4606/12/24 Speed/Duplex.........................................................................................................43

30A Base Switch.......................................................................................................................43

Legacy Models vs. Current Mode ls..........................................................................................44

DHCP Option 176.....................................................................................................................44

DHCP Lease Duration ..............................................................................................................45

SM Avaya IP Telephony Implementation Guide

Boot-up Sequence.....................................................................................................................46

Call Sequence............................................................................................................................47

Keepalive Mechanisms.............................................................................................................47

4.2 Connecting a PC to the Phone ..................................................................................................48

IP Phone and Attached PC on Same VLAN.............................................................................49

IP Phone and Attached PC on Different VLANs......................................................................50

4.3 Gatekeeper Lists and DHCP Option 176..................................................................................51

Main Site...................................................................................................................................52

Branch Site................................................................................................................................52

Two Methods of Receiving the Gatekeeper List ......................................................................53

Verifying the Gatekeeper Lists.................................................................................................54

Appendix A: VLAN Primer........................................................................................................................55

Appendix B: Cisco Auto-Discovery...........................................................................................................60

Appendix C: RTP Header Compression.....................................................................................................62

Appendix D: Access List Guidelines..........................................................................................................64

Appendix E: Common IP Commands.........................................................................................................66

Appendix F: Sample QoS Configurations..................................................................................................68

Appendix G: IP Trunk Bypass – TDM Fallback Q&A...............................................................................70

References...................................................................................................................................................73

SM Avaya IP Telephony Implementation Guide

1 Introducti on to VoIP and Avaya Products

This section provides a foundation to build upon for the rest of this document. Voice over IP (VoIP) terminology and Avaya products and architectures are introduced here.

1.1 Servers, Gateways, Stations, and Trunks Defined

Servers

Most of the intelligence in a voice system is in the call server. From servicing a simple call to making complex decisions associated with large contact centers, the call server is the primary component of an IP telephony system. Avaya Communication Manager is the call processing software that runs on Avaya server platforms.

The following are some common terms for a call server. Some are generic and some are specified by a protocol, but all are generally used throughout the industry.

- Call Server – generic term

- Call Controller – generic term

- Gatekeeper – H.323 term

- Media Gateway Controller – H.248 term

Gateways

A gateway terminates and converts various media types, such as analog, TDM, and IP. A gateway is required so that, for example, an IP phone can communicate with an analog phone on the same telephony system, as well as with an external caller across a TDM trunk.

The following are some common terms for a gateway, and they are generally used throughout the industry.

- Gateway – generic and H.323 term

- Media Gateway – H.248 term

- Port Network – Avaya term

A gateway requires a call server to function, and some common Avaya server-gateway architectures are illustrated later.

Stations

There are several technical terms for what most would call a phone, and some that are generally used throughout the industry are listed below.

- Endpoint – H.323 general term that includes IP phones and other endpoints

- Terminal – H.323 specific term to mean primarily IP phones (also an Avaya term)

- Station – Avaya term, and possibly a generic term

- Set – Avaya term, and possibly a generic term

Avaya gateways have port boards or media modules that terminate various types of stations.

SM Avaya IP Telephony Implementation Guide

Trunks

Trunks connect independent telephony systems together, such as PBX to PBX, or PBX to public switch, or public switch to public switch. In traditional telephony there are various types of circuit-switched trunks, using various protocols to signal across these trunks. IP telephony introduces another trunk type – the IP trunk. Like circuit-switched trunks IP trunks connect independent telephony systems together, but the medium is an IP network and the upper-layer protocol suite is H.323.

Avaya gateways have port boards or media modules that terminate various types of trunks, including IP trunks.

1.2 Avaya Server-Gateway and Trunk Architectures

The following figures illustrate some common Avaya server-gateway architectures in succession, from established to most recent technologies. Also included in the diagrams are the protocols used to communicate between the various devices.

Traditional DEFINITY System

Adjunct Location

Analog

EPN

MCC

CCMS and bearer over TDM or ATM

CCMS from pr ocessor

to port boards across

backplane

SCCDCP

Medium/Large Enterprise - Main Location

PPN

Procr

EPN

TDM busTDM bus

MCC

Center St age

or ATM PNC

MCC

EPN

DCP

Analog

Figure 1: Traditional DEFINITY System architecture

- The single- (SCC1) and multi-carrier cabinets (MCC1) are called port networks (Avaya term) or

media gateways (VoIP term). They house port boards, which, among other things, terminate stations and trunks. (These port boards are not the focus of this document.)

- The DEFINITY® call servers are the processor boards inserted into the processor port network

(PPN).

- The other cabinets, without processors, are called expansion port networks (EPN) and are controlled

by the DEFINITY servers in the PPN.

- The port networks are connected together via a port network connectivity (PNC) solution, which can

be TDM-based (Center Stage PNC) or ATM-based (ATM PNC). Both bearer (audio) and port network control are carried across the PNC solutions.

- Control Channel Message Set (CCMS) is the Avaya proprietary protocol used by the DEFINITY

servers to control the port networks (cabinets and port boards).

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IP-enabled DEFINITY System

Adjunct Location Medium/Large Enterprise - Main Location

IP IP

RTP

audio

Enterprise

IP Network

DCP

Analog

IP Net

DCP

Analog

RTP

H.225

C-LAN

MedPro

MCC

EPN

CCMS and bearer over TDM or ATM

CCMS from processor

to port boards across

backplane

EPN

SCC

PPN

Procr

MCC

Center Stage

or ATM PNC

H.225 - RAS &

Q.931 signaling

C-LAN

MedPro

TDM busTDM bus

MCC

EPN

Figure 2: IP-enabled DEFINITY System

- IP-enabled DEFINITY System is the same architecture as before, but with IP port boards added.

- The Control-LAN (C-LAN) board is the call servers’ interface into the IP network for call signaling.

H.225, which is a component of H.323, is the protocol used for call signaling. H.225 itself has two components: RAS for endpoint registration, and Q.931 for call signaling.

- The IP Media Processor (MedPro) board is the IP termination point for audio. It performs the

conversion between TDM and IP. The audio payload is encapsulated in RTP, then UDP, then IP.

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S8700 Multi-Connect

Adjunct Location Medium/Large Enterprise - Main Location

IP Net

DCP

Analog

RTP

H.225

C-LAN

MedPro

MCC

CCMS over

TCP/IP

CCMS and bearer over TDM or ATM

s8700 s8700

L2 switch L2 switch

IPSI

SCC

Center St age

or ATM PNC

IPSI

MCC

H.225 - RAS &

Q.931 signaling

Control

IP Network

IPSI

C-LAN

MedPro

TDM busTDM bus

MCC

IP IP

RTP

audio

Enterprise

IP Network

DCP

Analog

Figure 3: S8700 Multi-Connec t

- S8700 Multi-Connect is the same underlying DEFINITY architecture, except that the processor

boards are replaced with much more powerful Avaya S8700 Media Servers.

- Port networks get IP Server Interface (IPSI) boards to communicate with the S8700 call servers.

- CCMS exchanges between the call servers and port networks now take place over the control IP

network.

- Not all port networks require IPSI boards, because Center Stage PNC and ATM PNC are still present

to connect the port networks.

S8500 Media Server

Figure 4: Avaya S8500 Media Ser ver

The Avaya S8500 Media Server is the simplex equivalent of the S8700 server pair. The S8500 gives the same call processing capability without the redundancy and added reliability of duplicated servers. The S8500 can be substituted in any configuration in this section where the S8700 servers are shown. Such a substitution would necessitates the removal of a duplicated IPSI board, where applicable.

SM Avaya IP Telephony Implementation Guide

S8700 IP-Connect

IPSI

C-LAN

MedPro

G650

IPSI

C-LAN

MedPro

G650

S8300/G700/G350

Medium/Large Enterprise

s8700 s8700

Enterprise

IP Network

CCMS over

TCP/IP

H.225

Analog

RTP

audio

DCP

Figure 5: S8700 IP-Connect

C-LAN

MedPro

G650

IPSI

- With S8700 IP-Connect the

traditional port networks – MCC1 and SCC1 – are replaced with new, 19-inch rack-mountable Avaya G600 or G650 Media Gateways.

- All G600/650s require IPSI

boards; no more Center Stage or ATM PNC.

- Everything is done on the

enterprise IP network; no more control IP network.

- G600/650 media gateways still

use C-LAN and MedPro boards, as well as the other traditional port boards used in the MCC1 and SCC1.

- The Avaya G700 and G350 Media Gateways are based on the

H.248 protocol.

- The G700 is tailored for medium size offices, and the G350 is

tailored for small offices. (Refer to current product offerings for exact specifications.)

- Both gateways have built-in Ethernet switches. The G700

supports IP routing and IP WAN connectivity with an expansion module, and the G350 supports them natively.

- The G700 is built on the Avaya P330 Stackable Switching

System, with similar CLI. The G350 is built on a new IP platform, also with similar CLI.

- Both gateways use compact media modules instead of

traditional port boards.

- The VoIP media module serves the same function as the

MedPro board.

- There are other media modules equivalent to traditional port

boards (analog, DCP, DS1).

- The Avaya S8300 Media Server in internal call controller (ICC)

mode is the call server.

- The S8300 is a Linux platform, similar to the S8700, but in a

compact form factor that fits into either gateway.

- The S8300 is not front-ended by C-LANs; it terminates the call

signaling natively.

Small/Mediu m Enterprise

H.225

g700 with

IP IP

H.248 media

gateway control

Ent IP Net

IP IP

DCP

RTP

Analog

s8300 ICC VoIP mod

g700 with

VoIP mod

g350 with

VoIP mod

g700 with

VoIP mod

DCP mod

Analog mod

T1/E1 mod

Figure 6: S8300/G700/G35 0

architecture

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S8700 Multi-Connect with remote G700/350 gateways

backup H.225

IP Net

Remote Office

backup

H.248

RTP

Analog

L2 switch L2 switch

CCMS

IPSI

SCC

CCMS and bearer over TDM or ATM

Medium/Large Enterprise

s8700 s8700

IPSI

MCC

Center Stage or ATM PNC

H.225 - RAS &

Q.931 sig naling

Control

IP Network

IPSI

C-LAN

MedPro

C-LAN

MCC

IP IP

H.225

RTP

audio

Enterprise

IP Network

IP IP

DCP

Figure 7: S8700 Multi-Connec t with rem ote G700/ 350s

- Remote gateways and stations are controlled by the S8700 servers via the C-LAN boards.

- The remote S8300 is in local survivable processor (LSP) mode to take over as call server if

connectivity to the S8700s is lost.

g700 with

s8300 LSP

VoIP mod

g700 with

VoIP mod

g350 with

VoIP mod

g700 with

VoIP mod DCP mod

Analog mod

T1/E1 mod

SM Avaya IP Telephony Implementation Guide

S8700 IP-Connect with remote G700/350 gateways

Medium/Large Enterprise

s8700 s8700

IPSI

C-LAN

MedPro

G650

C-LAN

MedPro

G650

CCMS over

TCP/IP

IPSI

Analog

Enterprise

IP Network

H.225

DCP

RTP

audio

IPSI

C-LAN

MedPro

G650

H.225

IP IP

DCP

backup H.225

IP Net

Remote Office

backup

H.248

RTP

Analog

Figure 8: S8700 IP-Connect with remote G700/350s

- Remote gateways and stations are controlled by the S8700 servers via the C-LAN boards.

- The remote S8300 is in local survivable processor (LSP) mode to take over as call server if

connectivity to the S8700s is lost.

S8100/G600

g700 with

s8300 LSP

VoIP mod

g700 with

VoIP mod

g350 with

VoIP mod

g700 with

VoIP mod

DCP mod

Analog mod

T1/E1 mod

Small/Medium Enterprise

H.225

Analog

Enterprise

IP Network

DCP

RTP

audio

CCMS from S8100

to port boards

across backplane

S8100 can control

multiple G600s

connected together

S8100 C-LAN

MedPro

G600

Admin

Figure 9: S8100/G600

SM Avaya IP Telephony Implementation Guide

- The Avaya S8100 Media

Server is a PC board that fits into the G600 gateway.

- Multiple G600s can be

connected together and controlled by the same S8100 server.

- The S8100 server is a

Windows 2000 Server platform.

- The upgrade path for the

S8100/G600 is S8500 IPConnect using G650 gateways. There is no S8100/G650 combination.

Trunks

QSIG

H.323 (Q.931)

I P

Call

Manager

DCP

S8300 / G700

Q.931

PRI

DCP

Q.931

PRI

PSTN

Public Switch

SS7

Public Switch

I P

Loop Start

Analog

H.225

Vendor X PBX

H.225

I P

Inband

S8700

G650

QSIG or DCS

Inband

QSIG

Q.931

PRI

QSIG or DCS H.323 (Q.931)

I P

Q.931

PRI

DEFINITY Sy s tem

Figure 10: Trunks

This figure illustrates a broad picture to put trunks into context.

- PSTN trunks use the Signaling System 7 (SS7) signaling protocol. This protocol is not relevant to

private, enterprise telephony systems.

- Private systems, such as the S8700 IP-Connect and DEFINITY servers in this illustration, commonly

connect to public switches using ISDN PRI trunks with Q.931 signaling.

- Two private systems commonly connect to one another using T1 trunks with inband signaling, or

ISDN PRI trunks with Q.931 signaling. This is illustrated in the trunks connecting the DEFINITY server to the S8700 IP-Connect, and to the Vendor X PBX.

- QSIG is a standard, feature-rich signaling protocol for private systems, and it “rides on top of” Q.931

as illustrated between the DEFINITY server and Vendor X PBX. DCS is The Avaya proprietary equivalent to QSIG, which also rides on top of Q.931 as illustrated between the S8700 IP-Connect and DEFINITY server.

- Gatekeepers, such as the S8700, S8300, and Cisco Call Manager in this illustration, can connect to

one another using IP trunks. The medium is IP and the signaling protocol is H.323, but Q.931 is still the fundamental component of H.323 that does the call signaling. And, as with ISDN PRI trunks, QSIG or DCS can be overlaid on top of Q.931.

QSIG is the standard signaling protocol that provides the feature-richness expected in enterprises. Generally speaking, traditional telephony systems support a broad range of QSIG features, while pure IP telephony systems support a very limited range. Due to the history and leadership of Avaya in traditional telephony, all Avaya call servers – whether traditional, IP-enabled, or pure IP – support virtually the same broad range of QSIG features.

SM Avaya IP Telephony Implementation Guide

1.3 VoIP Protocols and Ports

The following figure illustrates the protocol stacks relevant to VoIP. The contents of the upper-layer protocol messages are important to those who develop VoIP applications. However, those who implement these applications are typically not concerned with decoding the upper-layer messages. Instead, they are concerned primarily with the transport mechanism – TCP and UDP ports – so that they can verify and filter these message exchanges.

H.245

CODEC

negotiation

TCP 1720 (gatekeeper)

Q.931 Signaling

L2 - Ethernet, PPP, frame relay, ATM, ...

H.323

H.225

RAS

Registration

UDP 1719

(gatekeeper)

L3 - IP

Audio CODEC

G.711, G.729

RTP

RTCP

UDP pseudo-

random port

H.248

Media Gateway

Control

TCP 2945

(MG controller)

CCMS

Port Network

Control

TCP 5010

(port network)

Figure 11: VoIP protocol stacks

- H.323 is the prevalent VoIP protocol suite. It is used for signaling from gatekeeper to terminals

(stations), and gatekeeper to gatekeeper (trunks).

- H.225 is the endpoint registration (RAS) and call signaling (Q.931) component of H.323.

- H.225 call signaling messages are transported via TCP with port 1720 on the gatekeeper side.

- H.225 registration messages (commonly referred to simply as RAS message) are sent via

UDP with port 1719 on the gatekeeper side.

- H.245 is the multimedia control component of H.323.

- Audio is digitally encoded prior to transmission and decoded after transmission using a coder/decoder

(codec).

- G.711 is the fundamental codec based on traditional pulse-code modulation (PCM), and it is

generally recommended for LAN transport.

- G.729 is a compressed codec, and it is generally recommended for transport over limited-

bandwidth WAN links.

- Encoded audio is encapsulated in RTP (real-time protocol), then UDP, then IP.

- RTP has fields such as Sequence Number and Timestamp that are designed for the transport and

management of real-time applications.

- On Avaya solutions the UDP ports used to transport RTP streams are configured on the call

server.

- Most protocol analyzers can identify RTP packets, making it easy to verify that audio streams are

being sent between endpoints.

- H.248 is a protocol for media gateway control. It is transported via TCP with port 2945 on the media

gateway controller side.

- CCMS is an Avaya proprietary protocol for port network control (same as media gateway control). It

is transported via TCP with port 5010 on the port network (IPSI board) side.

SM Avaya IP Telephony Implementation Guide

2 IP Network Guidelines

This section gives general guidelines and addresses several issues related to IP networks (LAN/WAN) and device configurations.

2.1 General Guidelines

Because of the time-sensitive nature of VoIP applications, VoIP should be implemented on an entirely switched network. Ethernet collisions – a major contributor to delay and jitter – are virtually eliminated on switched networks. Additionally, VoIP endpoints should be placed on separate subnets or VLANs (separated from other non-VoIP hosts), with preferably no more than 500 hosts per VLAN. This provides for a cleaner design where VoIP hosts are not subjected to broadcasts from other hosts, and where troubleshooting is simplified. This also provides a routed boundary between the VoIP segments and the rest of the enterprise network, where restrictions can be placed to prevent unwanted traffic from crossing the boundary. When a PC is attached to an IP telephone, even if they are on separate VLANs, all traffic (including broadcasts) to/from the PC and to/from the phone traverse the same uplink to the Ethernet switch. In such a case the uplink should be a 100M link, and the recommended subnet/VLAN size is no larger than 250 hosts.

Sometimes customers are unable to follow these guidelines, and Avaya solutions can be made to work in some less-than-ideal circumstances. If IP telephones share a subnet with other non-VoIP hosts, they should be placed on a subnet of manageable size (24-bit subnet mask or larger; 254 hosts or less) with as low a broadcast rate as possible. If the broadcast level is high, keep in mind that 100M links are less likely to be overwhelmed by broadcast traffic than 10M links.

On the subject of broadcasts, Avaya media servers and gateways and IP telephones utilize very low amounts of broadcast traffic to operate. Therefore, a subnet/VLAN with only these Avaya hosts has a very low level of broadcasts. There are two cases where Avaya hosts can be subjected to high levels of broadcasts: 1) Avaya hosts and other broadcast-intensive hosts share a subnet/VLAN; and 2) broadcastintensive PCs are attached to Avaya IP phones. Case 1 is one of the reasons for the recommendation to use separate voice subnets/VLANs. Case 2 is unavoidable, and the result is that broadcasts used by the PC must pass through the phone, even if the phone and PC are on different VLANs. For this reason Avaya IP phones are designed to be very resilient against broadcasts, with lab tests showing the phones operating satisfactorily even with 1000+ broadcasts per second. Nevertheless, high-broadcast environments are very strongly

discouraged for IP telephony.

Ethernet Switches

The following recommendations apply to Ethernet switches to optimize operation with Avaya IP telephones and other Avaya VoIP endpoints, such as IP boards. They are meant to provide the simplest configuration by removing unnecessary features.

- Enable spanning tree fast start feature or disable spanning tree at the port level – The spanning tree

protocol is a layer 2 (L2) protocol used to prevent loops when multiple L2 network devices are connected together. When a device is first connected (or re-connected) to a port running spanning tree, the port takes approximately 50 seconds to cycle through the Listening, Learning, and Forwarding states. This 50-second delay is not necessary and not desired on ports connected to IP hosts. Enable a fast start feature on these ports to put them into the Forwarding state almost immediately. Avaya P550 calls this fast-start and Cisco calls it portfast. If this feature is not available, disabling spanning tree on the port is an option that should be considered. Do not

disable

spanning tree on an entire switch or VLAN.

SM Avaya IP Telephony Implementation Guide

- Disable Cisco features – Cisco features that are not required by Avaya endpoints are auxiliaryvlan

(except for IP phones in a dual-VLAN setting as described in appendices A and B), channeling, cdp, inlinepower, and any Cisco proprietary feature in general

. Explicitly disable these features on ports connected to Avaya devices, as they are non-standard mechanisms relevant only to Cisco devices and can sometimes interfere with Avaya devices. The CatOS command set port host <mod/port> automatically disables channeling and trunking, and enables portfast. Execute this command first, and then manually disablec cdp, inlinepower, and auxiliaryvlan. For dual-VLAN implementations see Appendices A and B for more information and updates regarding trunking and auxiliaryvlan.

- Properly configure 802.1Q trunking on Cisco switches – When trunking is required on a Cisco CatOS

switch connected to an Avaya IP telephone, enable it for 802.1Q encapsulation in the nonegotiate mode (set trunk <mod/port> nonegotiate dot1q). This causes the port to become a plain 802.1Q trunk port with no Cisco auto-negotiation features. When trunking is not required, explicitly disable it, as the default is to auto-negotiate trunking.

Speed/Duplex

One major issue with Ethernet connectivity is proper configuration of speed and duplex. There is a significant amount of misunderstanding in the industry as a whole regarding the auto-negotiation standard. The following table is provided as a quick reference for how speed and duplex settings are determined and typically configured. It is imperative that the speed and duplex settings be configured properly.

Device1

Configuration

auto-negotiate

100/full 100/full 100/full stable. Typical configuration for server connections and

10/half

100/half

Device2

Configuration

auto-negotiate

100/half

10/half

100/full

10/half

100/half

Result

100/full expected and often achieved, but not always stable. Suitable for user PC connections, but not suitable for server connections or uplinks bet we en network devices. Suitable for a single VoIP call, such as with a softphone or single IP telephone. Not suitable for multiple VoIP calls, such as through a MedPro board.

100/half stable. Device1 senses the speed and matches accordingly. Device1 senses no duplex neg otiation, so it goe s to half duplex. 10/half stable. Device1 senses the speed and matches accordingly. Device1 senses no duplex neg otiation, so it goe s to half duplex.

Device1 goes to 100/half, resulting in a duplex mismatch – undesirable. Device1 senses the speed and matches accordingly. Device1 senses no duplex neg otiation, so it goe s to half duplex.

uplinks between network devices. Stable at respective speed and duplex. Some enterprises do this on user ports as a matter of policy for various reasons.

Table 1: Speed/duplex matrix

Layer 1 (L1) errors such as runts, CRC errors, FCS errors, and alignment errors often accompany a duplex mismatch. If these errors exist and continue to increment, there is probably a duplex mismatch or cabling problem or some other physical layer problem. The show port <mod/port> command on Catalyst switches gives this information. The Avaya P550 commands are show port status <mod/port>, show port counters <mod/port>, and show ethernet counters <mod/port>. The Avaya P330 switch command is show rmon statistics <mod/port>.

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2.2 Bandwidth Considerations

Calculation

Many VoIP bandwidth calculation tools are available, as well as pre-calculated tables. Rather than presenting a table, the following information is provided to help the administrator make an informed bandwidth calculation. The per-call rates for G.711 and G.729 are provided under the “Ethernet Overhead” and “WAN Overhead” headings below, and all calculations are for the recommended voice packet size of 20ms.

- Voice payload and codec selection

– The G.711 codec payload rate is 64000bps. Since the audio is encapsulated in 10-ms frames, and there are 100 of these frames in a second (100 * 10ms = 1s), each frame contains 640 bits (64000 / 100) or 80 bytes of voice payload. The G.729 codec payload rate is

8000bps, which equates to 80 bits or 10 bytes per 10-ms frame.

Voice Payload 1 frame – 10ms 2 frames – 20ms 3 frames – 30ms 4 frames – 40ms

G.711 80 B 160 B 240 B 320 B G.729 10 B 20 B 30 B 40 B

Table 2: Voice payload vs. number of frames

- Packet size and packet rate

– Because the voice payload rate must remain constant, the number of voice frames per packet (packet size) determines the packet rate. As the number of frames per packet increases, the number of packets per second decreases to maintain a steady rate of 100 voice frames per second (64000bps or 8000bps).

Packet Rate 1 frame/packet

10ms

G.711 100pps 50pps 33pps 25pps G.729 100pps 50pps 33pps 25pps

Table 3: Packet rate vs. packet size

2 frames/packet

20ms

3 frames/packet

30ms

4 frames/packet

40ms

- IP, UDP, RTP overhead – Each voice packet inherits a fixed overhead of 40 bytes.

20 B

UDP

8 B

Figure 12: IP/UDP/RTP overhead

RTP 12 B

Voice Payload

Variable

To this point the calculation is simple. Add up the voice payload and overhead per packet, and multiply by the number of packets per second. Here are the calculations for a G.711 and a G.729 call, both using 20-ms packets. (Remember that there are 8 bits per byte.)

G.711: (160 voice payload + 40 overhead)B/packet * 8b/B * 50packets/s = 80kbps

G.729: (20 voice payload + 40 overhead)B/packet * 8b/B * 50packets/s = 24kbps

The calculations above do not include the L2 encapsulation overhead. L2 overhead must be added to the bandwidth calculation, and this varies with the protocol being used (Ethernet, PPP, HDLC, ATM, Frame Relay, etc).

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header

20 B

UDP

8 B

RTP

12 B

Figure 13: L2 overhead

Voice Payload

Variable

trailer

Ethernet Overhead

Ethernet has a header of 14 bytes and a trailer of 4 bytes. It also has a 7-byte preamble and a 1-byte start of frame delimiter (SFD), which some bandwidth calculation tools do not take into

G.711 20-ms call over Ethernet = 90.4kbps G.711 30-ms call over Ethernet = 81.6kbps

G.729 20-ms call over Ethernet = 34.4kbps G.729 30-ms call over Ethernet = 25.6kbps

consideration. Nevertheless, the preamble and SFD consume bandwidth on the LAN, so the total Ethernet overhead is 26 bytes. When transmitting 20-ms voice packets, the Ethernet overhead equates to 10.4kbps (26 * 8 * 50), which must be added to the 80kbps for G.711 or 24kbps for G.729. For full-duplex operation the totals are 90.4kbps for G.711 and

34.4kbps for G.729. For half-duplex operation these figures are at least doubled, but effectively the load

is higher due to the added overhead of collisions.

WAN Overhead

The WAN overhead is calculated just like the Ethernet overhead, by determining the size of the L2 encapsulation and figuring it into the calculation. L2 headers and trailers vary in size with the protocol being used, but they are typically much smaller than the Ethernet header and trailer. For example, the PPP overhead is only 7 bytes. However, to allow for a high margin of error, assume a 14-byte total L2 encapsulation size, which would add an overhead of 5.6kbps (14 * 8 * 50), assuming 20-ms voice

packets. This would result in approximately 86kbps

G.729 20-ms call over PPP = 26.8kbps G.729 30-ms call over PPP = 20.5kbps

G.729 20-ms call over 14-B L2 = 29.6kbps G.729 30-ms call over 14-B L2 = 22.4kbps

for G.711 and 30kbps for G.729 over a WAN link. Significant bandwidth savings are realized by using a compressed codec (G.729 recommended) across a WAN link. Note that in today’s data networks most, if

not all, WAN links are full duplex.

L3 Fragmentation (MTU)

Related to bandwidth, there are two other factors that must be considered for operation across WAN links, and they both involve fragmentation. The first factor, maximum transmission unit (MTU), involves fragmenting the layer 3 (L3) payload. The MTU is the total size of the L3 packet (IP header + IP payload), which is 200 bytes for G.711 and 60 bytes for G.729 (assuming 20-ms voice packets). If the MTU on an interface is set below these values the IP payload (UDP + RTP + voice payload) must be fragmented into multiple IP packets, each packet incurring the 20-byte IP overhead. For example, suppose the MTU on an interface is set to 100 bytes, which is an extremely low value. The 20-ms G.711 IP packet is 200 bytes, consisting of a 20-byte IP header and a 180-byte IP payload. The 180-byte payload must be divided into three fragments of 80 bytes, 80 bytes, and 20 bytes. Each fragment incurs a 20-byte IP header to make the packets 100 bytes, 100 bytes, and 40 bytes. A single 200-byte IP packet must be fragmented into three separate IP packets to meet the 100-byte MTU. In addition, the L2 overhead also increases because each L3 packet requires L2 encapsulation.

MTU should not be an issue for VoIP because most interfaces have a default MTU of 1500 bytes. However, it is possible to intentionally set the MTU to low levels. Even if the MTU is not set to a level that would fragment VoIP packets, the principle of fragmenting the L3 payload and incurring additional L3 and L2 overhead applies universally. Changing the MTU requires a thorough understanding of the

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traffic traversing the network. A low MTU value, relative to any given IP packet size, always increases L3 and L2 overhead as illustrated with the VoIP example. Because of this inefficiency, it is generally not advisable to lower the MTU.

L2 Fragmentation

The second factor involves fragmenting the L2 payload, or the entire IP packet. This process of fragmenting a single IP packet into multiple L2 frames incurs additional L2 overhead, but no additional IP overhead. For example, the fixed cell size for ATM is 53 octets (bytes), with 5 octets for ATM overhead and 48 octets for payload. Without header compression there is no way to get a voice packet to fit inside one ATM cell. Therefore, the L3 packet (not just the IP payload, but the entire IP packet) is fragmented and carried inside multiple ATM cells. A 200-byte G.711 IP packet would require five ATM cells (25 octets of ATM overhead), whereas a 60-byte G.729 IP packet would only require two ATM cells (10 octets of ATM overhead). Refer to Appendix C for information regarding RTP header compression.

Keep in mind, however, that the same precautions apply to RTP header compression as to QoS (see the next section on CoS and QoS). The router could pay a significant processor penalty if the compression is done in software.

Inter-LATA (typically interstate) Frame Relay is also affected by this ATM phenomenon. This is because most carriers (ATT, Worldcom, Sprint) convert Frame Relay to ATM for the long haul, between the local central offices. This is done through a process called frame-relay-to-ATM network interworking and service interworking (FRF.5 and FRF.8). In this process the Frame Relay header is translated to an ATM header, and the Frame Relay payload is transferred to an ATM cell. Since the Frame Relay payload can be a variable size but the ATM payload is a fixed size, a single Frame Relay frame can be converted to multiple ATM cells for the long haul. Therefo re, it is b enef ic ial to lim it the siz e of the voice pa ck et even when the WAN link is Frame Relay.

2.3 CoS and QoS

General

The term “Class of Service” refers to mechanisms that tag traffic in such a way that the traffic can be differentiated and segregated into various classes. The term “Quality of Service” refers to what the network does to the tagged traffic to give higher priority to specific classes. If an endpoint tags its traffic with L2 802.1p priority 6 and L3 DSCP 46, for example, the Ethernet switch must be configured to give priority to value 6, and the router must be configured to give priority to DSCP 46. The fact that certain traffic is tagged with the intent to give it higher priority does not necessarily mean it receives higher priority. CoS tagging does no good without the supporting QoS mechanisms in the network devices.

CoS

802.1p/Q at the Ethernet layer (L2) and DSCP at the IP layer (L3) are two CoS mechanisms that Avaya products employ. These mechanisms are supported by the IP telephones and most IP port boards. In addition, the call server can flexibly assign the UDP port range for audio traffic transmitted from the MedPro board or VoIP module. Although TCP/UDP source and destination ports are not CoS mechanisms, they are inherently used to identify specific traffic and can be used much like CoS tags. Other non-CoS methods to identify specific traffic are to key in on source and destination IP addresses and specific protocols (ie, RTP).

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802.1p/Q

The figure below shows the IEEE 802.1Q tag and its insertion point in the Ethernet and 802.3 frames. Note that in both cases the 802.1Q tag changes the size and format of the comprehensive Ethernet and

802.3 frames. Because of this, many intelligent switches (ones that examine the L2 header and perform some kind of check against the L2 frame) must be explicitly configured to accept 802.1Q tagged frames. Otherwise, these switches may reject the tagged frames. The Tag Protocol Identifier (TPID) field has hex value x8100 (802.1QTagType). This value alerts the switch or host that this is a tagged frame. If the switch or host does not understand 802.1Q tagging, the TPID field is mistaken for the Type or Length field, which results in an erroneous condition.

Figure 14: 802.1Q tag

The two other fields of importance are the Priority and Vlan ID (VID) fields. The Priority field is the “p” in 802.1p/Q and ranges in value from 0 to 7. (“802.1p/Q” is a common term used to indicate that the Priority field in the 802.1Q tag has significance. Prior to real-time applications 802.1Q was used primarily for VLAN trunking, and the Priority field was not important.) The VID field is used as it always has been – to indicate the VLAN to which the Ethernet frame belongs.

Rules for 802.1p/Q Tagging

There are two questions that determine when and how to tag:

1. Is tagging required to place the frame on a specific VLAN (VLAN tagging)?

2. Is tagging required to give the frame a priority level greater than 0 (priority tagging)?

Based on the answers to these questions, tagging should be enabled following these two rules.

1. Single-VLAN Ethernet switch port (default scenario).

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- On a single-VLAN port there is no need to tag to specify a VLAN, because there is only one

VLAN.

- For priority tagging only, the IEEE 802.1Q standard specifies the use of VID 0. VID 0 means

that the frame belongs on the port’s primary VLAN, which IEEE calls the “port VLAN,” and Cisco calls the “native VLAN.” Some Ethernet switches do not properly interpret VID 0, in which case the port/native VID may need to be used, but this is not the standard method.

- For single devices, such as a call server or port board, a simpler alternative is to not

tag at all, but to configure the Ethernet switch port as a high-priority port instead. This treats all incoming traffic on that port as high-priority traffic, based on the configured level.

- For multiple devices on the same VLAN, such as an IP telephone with a PC attached, the high-

priority device (IP telephone) should tag with VID 0 and the desired priority. The low-priority device (PC) would not tag at all. No tag at all is the same as priority 0 (default).

2. Multi-VLAN Ethernet switch port.

- A multi-VLAN port has a single port/native VLAN and one or more additional tagged VLANs,

with each VLAN pertaining to a different IP subnet.

- In general, do not configure multiple VLANs on a port with only one device attached to it (unless

that device is another Ethernet switch across a trunk link).

- For the attached device that belongs on the port/native VLAN, follow the points given for rule 1

above. Clear frames (untagged frames) are forwarded on the port/native VLAN by default.

- An attached device that belongs on any of the tagged VLANs must tag with that VID and the

desired priority.

- The most common VoIP scenario for a multi-VLAN port is an IP telephone with a PC attached,

where the phone and PC are on different VLANs. In this case the PC would send clear frames, and the IP telephone should tag with the designated VID and desired priority.

As stated previously, an Ethernet switch must be capable of interpreting the 802.1Q tag, and many must be explicitly configured to receive it. The use of VID 0 is a special case, because it only specifies a priority and not a VLAN. Avaya switches accept VID 0 without any special configuration. However, some Ethernet switches do not properly interpret VID 0. And some switches require trunking to be enabled to accept VID 0, while others do not. The following table shows the results of some testing performed by Avaya Labs on Cisco switches.

Catalyst 6509 w/ CatOS 6.1(2)

Catalyst 4000 w/ CatOS 6.3(3)

Catalyst 3500XL w/ IOS 12.0(5)WC2 Conclusion Note the hardware platfor m and OS version and consult Cisco’s

Accepted VID 0 for the native VLAN when 802.1Q trunking was enabled on the port. Would not accept VID 0 for the native VLAN. Opened a case with Cisco TAC, and TAC engineer said it was a hardware problem in the 4000. Bug ID is CSCdr06231. Workaround is to enable 802.1Q trunking and tag with native VID instead of 0. Accepted VID 0 for the native VLAN when 802.1Q trunking was disabled on the port.

documentation, or call TAC.

Table 4: Sample VID 0 behaviors for Cisco switches

See Appendix A for more information on VLANs and tagging.

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DSCP

Figure 15: IP header

The figure above shows the IP header with its 8-bit Type of Service (ToS) field. The ToS field contains three IP Precedence bits and four Type of Service bits as follows.

Bits 0-2

IP Precedence

Bit 3

Delay

Bit 4

Throughput

Bit 5

Reliability

Bit 6

Monetary Cost

Bit 7

Reserved

Figure 16: Original scheme for IP ToS field

000 001 010 011 100 101 110 111

0 1 0 1 0 1 0 1

Always set to 0

Routine Priority Immediate Flash Flash Override CRITIC/ECP Internetwork Control Network Control Normal Low Normal High Normal High Normal Low

This original scheme was not widely used, and the IETF came up with a new CoS tagging method for IP called Differentiated Services Code Points (DSCP, RFC 2474/2475). DSCP utilizes the first six bits of

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the ToS field and ranges in value from 0 to 63. The following figure shows the original ToS scheme and DSCP in relation to the eight bits of the ToS field .

8-bit Type of Service field

IP Precedence bits Type of Service bits 0

0 1 2 3 4 5 6 7

DSCP bits 0 0

Figure 17: Compare DSCP w/ origin al ToS

Ideally any DSCP value would map directly to a Precedence/ToS combination of the original scheme. This is not always the case, however, and it can cause problems on some legacy devices, as explained in the following paragraph.

On any device, new or old, having a non-zero value in the ToS field cannot hurt if the device is not configured to examine the ToS field. The problems arise on some legacy devices when the ToS field is examined, either by default or by enabling QoS. These legacy devices (network and endpoint) may contain code that only implemented the IP Precedence portion of the original ToS scheme, with the remaining bits defaulted to zeros. This means that only DSCP values divisible by 8 (XXX000) can map to the original ToS scheme. For example, if an endpoint is tagging with DSCP 40, a legacy network device can be configured to look for IP Precedence 5, because both values show up as 10100000 in the ToS field. However, a DSCP of 46 (101110) cannot be mapped to any IP Precedence value alone. Another hurdle is if the legacy code implemented IP Precedence with only one ToS bit permitted to be set high. In this case a DSCP of 46 still would not work, because it would require two ToS bits to be set high. When these mismatches occur, the legacy device may reject the DSCP-tagged IP packet

or exhibit

some other abnormal behavior. Most newer devices support both DSCP and the original ToS scheme.

QoS on an Ethernet Switch

On Avaya and Cisco Catalyst switches, VoIP traffic can be assigned to higher priority queues. The number and sizes of queues and how they function are device-dependent and beyond the scope of this document. However, generally speaking, there is a fixed number of queues and they are typically not configurable. If they are configurable, it is typically not recommended. Older or lower end switches commonly have only two queues or none at all. Newer or higher end switches commonly have four or eight queues – eight being the maximum because there are only eight L2 priority levels. An Ethernet switch can identify the high priority traffic by the 802.1p/Q tag and assign that traffic to a high priority queue, but only if this is a default feature or it is explicitly configured

. On many switches a specific port can be designated as a high priority port, causing all incoming traffic on that port to be assigned to a high priority queue. This frees the endpoint from having to tag its traffic with L2 priority.

QoS on a Router

It is generally more complicated to implement QoS on a router than on an Ethernet switch. Unlike Ethernet switches, routers typically do not have a fixed number of queues. Instead, routers have various queuing mechanisms. For example, Cisco routers have standard first-in first-out queuing (FIFO), weighted fair queuing (WFQ), custom queuing (CQ), priority queuing (PQ), and low latency queuing (LLQ). LLQ is a combination of priority queuing and class-based weighted fair queuing (CBWFQ), and it is Cisco’s recommended queuing mechanism for real-time applications such as VoIP. Each queuing mechanism behaves differently and is configured differently and has its own set of queues. First the desired traffic must be identified using DSCP, IP address, TCP/UDP port, or protocol. Then the traffic must be assigned to a queue in one of the queuing mechanisms. Then the queuing mechanism must be applied to an interface. [2 p.1-7, 3-4, 3-5, 5-2]

SM Avaya IP Telephony Implementation Guide

The interface itself may also require additional modifications, independent of the queuing mechanism, to make QoS work properly. For example, Cisco requires traffic shaping on Frame Relay and ATM links to help ensure that voice traffic is allotted the committed or guaranteed bandwidth (see “Traffic Shaping on Frame Relay Links” below in this section). Cisco also recommends link fragmentation and interleaving (LFI) on WAN links below 768kbps, to reduce serialization delay. Serialization delay is the delay incurred in encapsulating a L3 packet in a L2 frame and transmitting it out the serial interface. It increases with packet size but decreases with WAN link size. The concern is that large, low priority packets induce additional delay and jitter, even with QoS enabled. This is overcome by fragmenting the large, low priority packets and interleaving them with the small, high priority packets, thus reducing the wait time for the high priority packets. The following matrix is taken directly from the “Cisco IP Telephony QoS Design Guide” [2 p.1-3].

L3 Packet Size WAN

Link Speed

56 kbps 9 ms 18 ms 36 ms 72 ms 144 ms 214 ms

64 kbps 8 ms 16 ms 32 ms 64 ms 128 ms 187 ms 128 kbps 4 ms 8 ms 16 ms 32 ms 64 ms 93 ms 256 kbps 2 ms 4 ms 8 ms 16 ms 32 ms 46 ms 512 kbps 1 ms 2 ms 4 ms 8 ms 16 ms 23 ms 768 kbps 640 us 1.28 ms 2.56 ms 5.12 ms 10.24 ms 15 ms

64 bytes 128 bytes 256 bytes 512 bytes 1024 bytes 1500 bytes

Table 5: Cisco seralization delay matrix

Consult Cisco’s documentation for detailed information regarding traffic shaping and LFI, and be especially careful with LFI. On one hand it reduces the serialization delay, but on the other it increases the amount of L2 overhead. This is because a single L3 packet that was once transported in a single L2 frame, is now fragmented and transported in multiple L2 frames. Configure the fragment size to be as high as possible while still allowing for acceptable voice quality.

Instead of implementing LFI, some choose to simply lower the MTU size to reduce serialization delay. Two possible reasons for this are that LFI may not be supported on a given interface, or that lowering the MTU is easier to configure. As explained in section 2.2 under the heading “L3 Fragmentation (MTU),” lowering the MTU (L3 fragmentation) is much less efficient than LFI (L2 fragmentation) because it incurs additional L3 overhead as well as additional L2 overhead. Lowering the MTU is generally not advisable and may not provide any added value, because it adds more traffic to the WAN link than LFI. The added congestion resulting from the increase in traffic may effectively negate any benefit gained from reducing serialization delay. One should have a thorough understanding of the traffic traversing the WAN link before changing the MTU.

Because of all these configuration variables, properly implementing QoS on a router is no trivial task. However, it is on the router where QoS is needed most, because most WAN circuits terminate on routers. Appendix F contains examples of implementing QoS on Cisco routers. This appendix does not contain configurations for all the issues discussed in this document, but it gives the reader a place to start.

QoS Guidelines

There is no all-inclusive set of rules regarding the implementation of QoS, because all networks and their traffic characteristics are unique. It is good practice to baseline the VoIP response (ie, voice quality) on a network without QoS, and then apply QoS as necessary. Conversely, it is very bad practice to enable multiple QoS features simultaneously, not knowing what effects, if any, each feature is introducing. If voice quality is acceptable without QoS, then the simplest design may be a wise choice. If voice quality is not acceptable, or if QoS is desired for contingencies such as unexpected traffic storms, the best place

SM Avaya IP Telephony Implementation Guide

to begin implementing QoS is on the WAN link(s). Then QoS can be implemented on the LAN segments as necessary.

One caution to keep in mind about QoS is regarding the processor load on network devices. Simple routing and switching technologies have been around for many years and have advanced significantly. Packet forwarding at L2 and L3 is commonly done in hardware (Cisco calls this fast switching [2 p.5- 18], “switching” being used as a generic term here), without heavy processor intervention. When selection criteria such as QoS and other policies are added to the routing and switching function, it inherently requires more processing resources from the network device. Many of the newer devices can handle this additional processing in hardware, resulting in maintained speed without a significant processor burden. However, to implement QoS, some devices must take a hardware function and move it to software (Cisco calls this process switching [2 p.5-18]). Process switching not only reduces the speed of packet forwarding, but it also adds a processor penalty that can be significant. This can result in an overall performance degradation from the network device, and even device failure.

Each network device must be examined individually to determine if enabling QoS will reduce its overall effectiveness by moving a hardware function to software, or for any other reason. Since most QoS policies are implemented on WAN links, the following very general points for Cisco routers are offered to increase the level of confidence that QoS remains in hardware. Consult Cisco to be sure.

- Newer hardware platforms are required: 2600, 3600, 7200, and 7500.

- Newer interface modules (WIC, VIP, etc.) are required: Consult Cisco to determine which hardware

revision is required for any given module.

- Sufficient memory is required: Device dependent.

- Newer IOS is required: 12.0 or later.

Several things should be examined whenever QoS is enabled on a network device. First, the processor level on the device should be examined and compared to levels before QoS was enabled. It is likely that the level will have gone up, but the increase should not be significant. If it is significant, then it is likely that the QoS process is being done by software. The processor load must remain at a manageable level (max 50% average, 80% peak). If the processor load is manageable, the VoIP response should be examined to verify that it has improved under stressed conditions (ie, high congestion) compared to performance before QoS was implemented. There is no added value in leaving a particular QoS mechanism enabled if VoIP response has not improved under stressed conditions. If VoIP response has improved, then the other applications should be checked to verify that their performances have not degraded to unacceptable levels.

Traffic Shaping on Frame Relay Links

Experience to date supports Cisco’s requirement to use traffic shaping on frame relay links [2 p.5-22]. Simply stated, VoIP traffic must be sent within the committed information rate (CIR) and not in the burst range. This means that everything traversing a specific interface or sub-interface must be sent within CIR, because there is no mechanism to dictate that VoIP be sent within CIR while data is sent in the burst range on the same interface. Under this constraint one solution for maximizing bandwidth is to make the CIR as large as possible, and this is dictated by the end of the PVC that has the smaller access circuit. Consult each router vendor’s documentation to see if other methods are available.

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3 Guidelines for Avaya Servers and Gateways

This section gives guidelines for Avaya servers and gateways, and covers most of the IP-telephonyrelated configurations. Refer back to section 1 for an overview of IP telephony components and Avaya architectures.

Avaya Communication Manager is the call processing software that runs on Avaya servers, and it is configured via the Switch Administration Terminal (SAT) interface. Although the server platforms themselves may be configured in various ways, SAT is the universal interface for Communication Manager.

The Avaya Site Administrator (SA) is a client software application used to access the SAT interface on all Avaya servers. Additionally, on all but the DEFINITY servers, SAT can also be accessed by telnet-ing to the server.

3.1 S8700/8500 Servers

The S8700 and S8500 are 19-inch rack-mountable Red Hat Linux server platforms. S8700 servers operate in a redundant pair, whereas the S8500 is a simplex server. Each server is configured and managed via a variety of web interfaces, with the Maintenance Web Interface being the most comprehensive. The web interfaces are designed to facilitate all anticipated configuration and management requirements, and there is little or no need for a customer to access the Linux shell.

In an S8700 pair one of the servers is active and the other is standby. SAT administration is performed on the active server, and it is automatically carried over to the standby server. Either of the servers could be active or standby at any given time, and there are different ways to determine which is active. If the two servers are on the same subnet there is a virtual IP address, which is labeled the active server address in the Configure Server – Configure Interfaces screen of the Maintenance Web Interface. Whichever server is active takes control of the active server address, and telnet-ing or browsing or pointing Avaya SA to that address accesses the active server. If the two S8700 servers are not on the same subnet (server separation), there is no virtual active server address. The Status Summary web screen shows the status of the servers.

The S8700 SAT interface may be accessed using Avaya SA or by telnet-ing to port 5023: telnet <active server address> 5023. This could also be done by telnet-ing to the active server and typing sat from the Linux shell. The standby server does not permit access to SAT.

SAT access to the S8500 is similar to that of the S8700 server pair, except that there is only one server.

S8700/8500 Speed/Duplex

Speed and duplex for the various S8700/8500 Ethernet interfaces are configured using the Configure Server – Configure Interfaces web admin screen. It is critical to configure the speed and duplex

correctly on the server interfaces used to communicate with the gateway IPSI boards. A speed/duplex mismatch between these interfaces and the Ethernet switch causes severe call processing problems.

The web admin screen has a pull-down menu for the various speed/duplex settings. This pull-down menu does not indicate the current configuration, but only the available options. A “current speed” description next to this pull-down menu indicates the current speed and duplex, but it does not indicate whether these settings were manually configured or reached via auto-negotiation. Follow these steps to properly configure the speed and duplex.

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- Start with the server and the Ethernet switch port set to auto-negotiate (default). The server should

show “(Current speed : 100 Megabit full duplex)” on the web admin screen, and the Ethernet switch port should show that the negotiated speed/duplex is 100/full. When in doubt always return to this base state.

- On the server manually configure the interface to 100/full. With the Ethernet switch port still at auto-

negotiate, it should now show that the negotiated speed/duplex is 100/half. This is expected.

- Manually configure the Ethernet switch port to 100/full. After a screen refresh the server should still

show the “current speed” to be 100/full. Both sides are now optimally configured for 100/full operation.

- If either side reverts back to auto-negotiate for any reason, it will show the negotiated speed/duplex to

be 100/half, which is a duplex mismatch and must be corrected.

- Following the instructions in section 2.1, heading “Speed/Duplex,” examine the error counters on the

Ethernet switch port and verify that the link is healthy (no errors).

S8700/8500 802.1p/Q and DSCP Tagging

On a Multi-Connect system, the port network control traffic between the S8700/8500 server(s) and IPSI boards traverses a closed control IP network. On this network there is no need to configure QoS, because all traffic is port network control traffic and has equal priority. QoS is required when there is the potential for contention for resources such as bandwidth, queue space, and processing power between various classes of traffic. This does not apply on the control IP network.

On an IP-Connect system the port network control traffic traverses the enterprise IP network, which services various classes of traffic. If QoS is desired and properly configured on this network, it may be necessary to have the S8700/8500 server(s) tag the port network control traffic. This is only required on the interfaces that communicate with IPSI boards, as they are the only ones that participate in real-time IP telephony. Traffic is tagged from these interfaces on a per destination basis for each IPSI board, as administered on the SAT ipserver-interface form (see section 3.6, heading “IP Server Interface Board”). For the 802.1p priority from the SAT form to be applied to the S8700/8500 server(s), L2 tagging must be enabled on the appropriate server interfac es via the Configure Server – Configure Interfaces web admin screen. The interfaces that communicate with IPSI boards have this option, and the others do not. The VLAN ID is always 0 for the S8700/8500 servers (follow the instructions in section 2.3, heading “Rules for 802.1p/Q Tagging”).

3.2 S8300 Server

The S8300 is a Red Hat Linux server platform, similar to the S8700, but on a compact media module that fits into a G700/350 gateway (always in media module slot 1

). The S8300 is similar to the S8700 in many ways. It is configured and managed via the same web interfaces as the S8700, and, as with the S8700, there is little or no need for a customer to access the Linux shell.

In a G700

the S8300 must have an IP address on the same IP subnet as the MGP, with the same mask and default gateway (see G700 section below). This is because all media module slots in a G700 inherit the VLAN of the MGP, and therefore all VoIP media modules and the S8300 must be on the same IP subnet as the MGP. In a G350

a VLAN must be designated as the ICC VLAN, and the S8300 must have an IP

address on the IP subnet pertaining to that VLAN (see G350 section below).

An S8300 server can be in one of two modes: internal call controller (ICC) or local survivable processor (LSP). In ICC mode the S8300 is a standalone call server. In LSP mode it is a backup to the primary call

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server and must be activated. An LSP does not accept station registrations or assume call processing responsibilities until it becomes active, which occurs when a gateway registers to it.

The S8300 SAT interface may be accessed using Avaya SA or by telnet-ing to port 5023: telnet <S8300 address> 5023. This could also be done by telnet-ing to the S8300 and typing sat from the Linux shell. S8300 ICC permits SAT configuration (changes and displays), but S8300 LSP does not (displays only) because it receives its Avaya Communication Manager translations from the primary server.

The S8300 connects to the G700/350 via a backplane 100M Ethernet interface, for which early software versions have a speed/duplex configuration parameter on the Configure Server – Configure Interfaces web admin screen. This parameter is a carryover from the S8700 and is not necessary, because there is no need to configure the backplane Ethernet interface. Do not change the settings for this parameter; it must be left at auto-negotiate. In later S8300 Avaya Communication Manager versions, this is a display only field and is not configurable.

3.3 S8100 Server (IP600)

The S8100 is a Windows 2000 Server platform on a PC board that slides into the G600 Media Gateway. The S8100’s interface module, which is placed on the back of the G600 adjacent to the processor slot, contains interfaces for a monitor, keyboard, mouse, and Ethernet. The Ethernet interface and associated networking parameters are configured just like any other Windows 2000 PC by right-clicking on My Network Places and selecting Properties, or by accessing the Network and Dial-up Connections icon from the Control Panel.

The S8100 has a terminal server that allows one to web browse to the server and emulate the Windows Desktop environment in the web browser. The S8100 also has DHCP and TFTP servers pre-installed. However, it is better to use the enterprise DHCP and TFTP servers for large-scale production use, and reserve the S8100 processing resources for Communication Manager.

The S8100 SAT interface may be accessed using Avaya SA or by telnet-ing to the S8100 and typing

definity at the LAC> prompt.

S8100 Speed/Duplex

Speed and duplex configuration on the S8100 is not as critical as with other servers, because the S8100’s native interface is used primarily for administrative access and not real-time IP telephony. The S8100 and its associated Ethernet switch port can be configured to auto-negotiate, but it is better to configure both sides to 100/full.

S8100 802.1p/Q and DSCP Tagging

There is no need to enable either L2 or L3 tagging on the S8100 native interface, because it is used primarily for administrative access and not real-time IP telephony.

3.4 G700 Media Gateway

The G700 is built on the Avaya P330 L2 switching platform, and has a form factor similar to the P330 L2 switch. Although the G700 is one physical unit, it is made up of several logical components.

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P330 L2 Switch

The P330 L2 switch is the base platform for the G700. All other logical components are connected to the P330 L2 switch. The asynchronous port (9600/8/N/1) marked CONSOLE on the face of the G700 connects the user to the P330 CLI. The IP expansion slot on the lower left corner of the chassis accepts the same X330 expansion modules used by the P330 switch. The most common ones are probably the WAN router module and the 16-port Ethernet module. The two Ethernet ports marked EXT1 and EXT2 are L2 switch ports. There is also an Octaplane® slo t on the back of the chassi s, just lik e the P330. For practical purposes the L2 switching portion of the G700 is equivalent to a 2-port P330 switch, which has a CLI similar to Cisco’s CatOS and is configured using various set commands.

Three components of the P330 should be configured: the inband management interface, the default route, and the switch itself. The inband management interface is displayed and configured using the commands show interface inband and set interface inband, respec tively. The inband interface requires a VLAN, an IP address, and a mask. The VLAN can be any of the VLANs active on the P330, and the IP address and mask must correspond to the IP subnet associated with that VLAN.

Once configured, the inband interface should be thought of as a host attached to the P330. This may seem non-intuitive, because the inband interface is

the P330 and the way to administer the P330 remotely. However, like most L2 switch management interfaces, the inband interface is associated with a specific VLAN. As such, it is accessed just like any other host attached to the switch on a given VLAN – either directly from another host on the same VLAN/subnet, or by routing to it from a host on a different VLAN/subnet. Many mistakenly think that any host attached to the P330 should be able to access the inband interface directly, and this is not necessarily true. Hosts on different VLANs/subnets must route to the inband management interface via a L3 router.

Like any other IP host, the inband interface needs a default route if it is to route off of its VLAN/subnet. The default route for the inband interface is displayed and configured using the commands show ip route and set ip route, respectively. If there is more than one router on the inband VLAN/subnet, the inband interface may have additional routes based on destination subnets or hosts. These are displayed and configured using the same commands.

Finally, the P330 L2 switch itself has various configuration parameters, such as spanning tree, VLANs, trunking, and speed/duplex. These are configured just like on the P330 switch (see appendix E). The EXT1 and EXT2 ports are most likely going to be used as uplinks to other Ethernet switches, and both ends of any uplink should be fixed at 100M/full-duplex (see section 2.1, heading “Speed/Duplex”).

Media Gateway Processor (MGP)

The media gateway processor (MGP) is the media gateway portion of the G700. The MGP manages the various media modules inserted into the G700. These media modules include analog port modules for analog phones, DCP port modules for DCP phones, DS1 modules for TDM trunks, and others. The media module associated specifically with IP telephony is the VoIP module. Each VoIP module is equivalent to a MedPro board and has 64 audio resources. A single VoIP module is built in to the MGP, and external VoIP modules can be added as necessary.

Like the P330 inband management interface, the MGP should be thought of as a host on the P330 L2 switch. The command session mgp from the P330 CLI puts the user into the MGP CLI. The MGP requires a VLAN, IP address, and mask. These are displayed and configured using the MGP CLI commands show interface mgp and set interface mgp (type configure to enter configuration mode for the set commands). The MGP may be on the same VLAN as the inband interface, or on a different VLAN. If on a different VLAN, a L3 router is required to route between the two VLANs. Like the

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inband interface, the MGP also needs at least a default route to route off of its VLAN/subne t. The MGP CLI commands are show ip route mgp and set ip route to display and configure MGP routes.

Each VoIP media module also requires an IP address using the set interface voip v# command. The VoIP modules inherit the VLAN, mask, and configured routes of the MGP, so there is no need to explicitly configure them for each VoIP module. The internal VoIP module is voip v0. An external VoIP module would be voip v1 or voip v2 or voip v3 or voip v4, depending on which slot it is in. show mm shows all the media modules and their slot numbers.

Finally, the MGP must know the IP address(es) of the media gateway controller(s) (MGC), so that the MGP can register with a call server. This is displayed and configured using the MGP CLI commands show mgc list and set mgc list. An MGC is either an S8300 server or a C-LAN, and multiple MGCs can be listed.

See the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html for detailed instructions on configuring the MGC list with primary controllers and LSP. This guide also gives instructions on configuring the associated recovery mechanism to send the media gateway to the LSP.

SAT Media-Gateway Form

A G700 media gateway is administered on a call server via the SAT media-gateway form, which has commands change media-gateway #, display media-gateway #, and list media-gateway. Number numeric identifier used to sort the list of gateways. Name

is an arbitrary descriptor. Identifier is the

is a

gateway’s serial number, which is displayed by typing show system at the MGP CLI. A gateway must be administered on the call server before it can register to that server, and the serial number is what uniquely identifies a valid gateway. Network Region Communication Manager network region. Site Data

assigns the gateway VoIP resources to a particular

can be used to note the G700’s address (ie, if it is located at a remote branch office). The IP and MAC addresses, as well as the module types are automatically populated when the gateway registers with the call server.

G700 802.1p/Q and DSCP Tagging

The G700 can receive its audio and call signaling priority values from the call server’s ip-networkregion form or from local configuration. The MGP CLI command show qos-rtcp shows the locally set

values and the values downloaded from the call server, along with which set of values is in effect. The command set qos control determines which set of values is used. The simplest implementation is to use the values from the call server. If configured locally, the set qos commands are used to administer the settings. There is no need, and no parameter, to set the VLAN ID because the MGP is already assigned to a VLAN via the set interface mgp command, and all modules inherit that VLAN ID.

The L3 DSCP value in an IP packet is carried end to end from source to destination across the IP network. The L2 802.1p value in the Ethernet frame is only carried from switch to switch, and this only if a trunk link is in place between switches. Therefore, the uplink from the G700 EXT port to the next Ethernet switch must be a trunk link, with matching VLANs at both ends of the link, if the L2 tag is to be forwarded. Subsequent links upstream must also be trunk links to forward the tag. For the link between the G700 and the connected Ethernet switch, an alternative method is to use an access (non-trunk) link, and set the upstream Ethernet switch port as a high-priority port. Then all incoming traffic on that port receives the configured priority.

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G700 in Octaplane Stack vs. Standalone

The G700 can be placed within an Avaya P330 Octaplane stack, which provides 4Gib/full-duplex uplinks between the Avaya switches in the stack. There are pros and cons to this. The pros are that the entire stack can be managed as one unit via a single IP address, there is abundant bandwidth between the switches in the stack, and the entire stack can be uplinked to other network equipment without uplinking each individual switch in the stack. The cons are that the initial configuration can be a little more complex, and a problem associated with the stack can adversely affect the G700. Many factors can drive the decision to use or not use the Octaplane.

Device and uplink management are key factors. If several G700 gateways are co-located in the same rack, it makes practical sense to use the Octaplane stacking feature. This allows the P330 components of all the G700s to be managed via a single inband interface. But more importantly, it eliminates the need for each G700 to be uplinked to the next network device individually.

When determining whether or not a single G700 should be added to an existing Octaplane stack of P330 switches, the relative importance of the G700 to the other devices is another factor. A G700’s primary role is that of IP telephony, specifically media conversion. A P330 switch’s primary role is that of L2 switching – processing and forwarding Ethernet frames, managing broadcast domains (VLANs), participating in spanning tree, etc. Depending on the implementation, especially if there are no dependencies between the G700 and the P330 stack, it may be prudent to keep the two roles separate so that a problem with either the G700 or the P330 stack does not adversely affect the other. These points are mentioned to provoke thought in design and implementation. Whatever the decision, a G700 can fully participate in Octaplane stacks, with other G700s or with P330 switches.

Bandwidth is another key factor for using or not using the Octaplane stack. The G700 components (P330 inband, MGP, VoIP modules, S8300) require a certain amount of bandwidth to communicate off the chassis. Each VoIP module consumes a maximum of approximately 6Mbps to service 64 G.711 calls using 20-ms packets. With up to five VoIP modules on a single G700, the maximum bandwidth consumption is approximately 30Mbps. Other than firmware and translation downloads the bandwidth consumed by the other components is negligible. Therefore, a single 100M uplink from EXT1 or EXT2 to another Ethernet switch is sufficient for the G700 itself.

The added bandwidth of the Octaplane stack might be required when the 16-port X330 Ethernet expansion module is used in the G700, and the hosts attached to that module communicate mostly to other hosts not on the G700. If the hosts on the expansion module are IP telephones, a 100M uplink is sufficient. But if PCs are attached to the phones and the PCs frequently communicate off the G700, a 100M uplink may not be sufficient.

3.5 G350 Media Gateway

The G350 is similar to the G700 in many ways. Therefore, this section details the differences while referring to the G700 explanations for similarities.

Two significant differences between the G350 and G700 are capacity and architecture. The G350 supports much fewer users than the G700. As such, the G350’s internal VoIP module has only 32 audio resources, as opposed to 64 in the G700’s internal VoIP module, and in the external VoIP media module and MedPro board. The G350 also cannot presently accept external VoIP modules.

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The primary architectural d iff er ence between the G350 and G700 is that the G350 is an integrated platform. The L2 switch, MGP, and internal VoIP module all share the same processing engine and same IP address. In addition, a L3 router is integrated into the G350, whereas the G700 can accept a L3 router as an expansion module. The resulting G350 CLI has two components. The L2 switch and MGP commands are practically the same as on the G700, using set commands similar to the P330 switch and Cisco’s CatOS. The L3 router commands are practically the same as on the X330WAN and P330R routers, using commands similar to Cisco’s IOS. The G350 utilizes both command sets in a single CLI.

The G350 can have several physical and logical interfaces, and there is no inband interface as on the G700’s P330 switch component. One of the G350’s IP interfaces must be designated the primary management interface (PMI). There is a default designation, but it can be changed by inserting the command pmi under the desired interface. The PMI, among other things, is the interface used by the MGP and internal VoIP module. This means that H.248 media gateway control signaling and RTP audio are sourced by and terminated on the PMI. When an S8300 media server is inserted into a G350, one of the VLANs on the G350 must be designated the ICC VLAN. This is done by inserting the command icc- vlan under the desired VLAN interface.

The remaining G350/G700 similarities and differences are as follows. Refer to the G700 section above for more details on each subject.

- Like the G700, the G350 needs at least a default route to route off of its connected VLANs/subnets.

But there is a single default route for the whole unit, as opposed to a route for the P330 component and a route for the MGP component. This is configured using the ip route command.

- The G350 and G700 L2 switch configurations (spanning tree, VLANs, trunking, speed/duplex ) are

very similar.

- The G350 and G700 MGC List configuration are very similar.

- The G350 and G700 SAT administration are very similar.

- The G350 and G700 802.1p/Q and DSCP configurations are very similar.

- The G350 does not have an Octaplane interface.

3.6 G600/650, MCC1, and SCC1 Gateways

The G600/650, MCC1, and SCC1 media gateways share the same port boards. The two most significant boards related to IP telephony are the C-LAN (TN799DP) and MedPro (TN2302AP) boards. Boards with these specific codes are required for Communication Manager; previous board revisions cannot be used.

C-LAN Capacity and Recommendations

The Control LAN (C-LAN) board is the IP interface for many functions, including H.225 call signaling for IP stations and IP trunks, H.248 media gateway control signaling, connectivity to various adjuncts, and SAT administrative access via TCP/IP. Each connection for one of these functions requires at least one TCP socket on the C-LAN board. The C-LAN board can support over 400 sockets under typical usage conditions. However, the heavier the usage the greater the load on the CLAN and the worse the performance. Furthermore, regardless of usage it is highly discouraged to operate the C-LAN near maximum capacity in a production environment. The following conservative recommendations are offered for typical environments, and can vary based on usage levels.

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- Adjuncts such as CMS, CDR, AUDIX Messaging System, and others should be placed on separate

C-LAN boards that are not used for call signaling or media gateway control signaling. This is common practice primarily due to business impact of the adjunct and the consequent need to isolate the adjunct, as well as to quickly troubleshoot any problems related to the adjunct.

- In a typical call center environment, design for a normal operating load of 200-250 IP stations plus 6

media gateways per C-LAN.

- In a typical non-call center business environment, design for a normal operating load of 250-300 IP

stations plus 8 media gateways per C-LAN.

- The number of signaling groups (IP trunks) per CLAN depends greatly on the configuration and

usage of each signaling group. Configuring the signaling group to have “calls share IP signaling connection” – an option between Avaya systems – requires less C-LAN resources than if each individual call has its own connection. The greater the usage of the signaling group (frequency of calls, features utilized during calls, number of simultaneous calls, etc.), the greater the C-LAN resource consumption. As a very general rule

, based on anecdotal evidence of typical IP trunk usage and assuming calls share IP signaling connection, substitute one signaling group for ten IP stations in the two preceding bullet items.

C-LAN and MedPro Protocols and Ports

Call signaling and media conversion between analog, TDM, and IP are key IP telephony functions. The S8700, S8500, S8100, and DEFINITY servers use distributed C-LAN boards to front-end the call signaling, and distributed MedPro boards to perform the media conversion. The following table lists the protocols and ports used by both boards. Section 3.7, heading “ip-network-region” gives instructions on how to configure the MedPro UDP port range. See Appendix D for guidelines on configuring access lists.

C-LAN

MedPro UDP 2048 – 65535 (configurable) RTP-encapsulated audio

UDP 1719 H.225 RAS – IP station registration

TCP 1720 H.225 Q.931 – call signaling TCP 2945 H.248 media gateway control signaling

Table 6: C-LAN and MedPro protocols and ports

C-LAN and MedPro Network Placement

Place both the C-LAN and MedPro boards on highly reliable subnets as close as possible to the majority of IP endpoints (ie, IP phones and softphones). Keep in mind that both call signaling and audio from all IP endpoints require these boards. Therefore, it may not be good practice to place these boards on a subnet containing many enterprise resources – such as a server farm – where there is heavy traffic both on the subnet and on the uplink(s) to the subnet. On the other hand, a server farm is typically where the most reliable and redundant network resources are deployed. A thorough understanding of the network and network traffic is required to ultimately determine the best placement of these critical boards.

C-LAN and MedPro Speed/Duplex

Use the SAT ip-interface form to configure the speed and duplex for the C-LAN and MedPro boards. It should be standard procedure to properly set the speed and duplex on all C-LAN and MedPro boards, and to configure the associated Ethernet switch ports accordingly. This results in much better system stability and audio quality than if the boards and Ethernet switch ports are left to auto-negotiate. See section 2.1 under the “Speed/Duplex” heading.

The default speed/duplex setting on the MedPro board is auto-negotiate. The default speed/duplex setting on the TN799DP C-LAN board is 10/half, to make it backwards compatible with the previous TN799C board, which could only do 10/half. When a C-LAN or MedPro is inserted into one of the gateways, the

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board receives its speed/duplex programming from Communication Manager, per the appropriate form. If for any reason a board loses this programming, it reverts back to the board’s default.

The maximum MedPro throughput is

5.8Mbps for 64 G.711 20-ms calls.

The maximum throughput for a MedPro board is

5.8Mbps, which is what is required for 64 G.711 20ms calls over Ethernet. The maximum throughput for a C-LAN board is much less than this. Therefore, the

minimum speed/duplex requirements are 100/half for the MedPro and 10/half for the C-LAN.

If there is poor audio quality on calls going through a particular MedPro board, follow these steps to determine if a speed/duplex mismatch between the MedPro and the Ethernet switch is the cause.

- Check both the MedPro (get ethernet-options <slot #>) and the Ethernet switch port and verify that

they are set to the same speed/duplex or have auto-negotiated to the same speed/duplex.

- Check for L1 errors as instructed in section 2.1 under the “Speed/Duplex” heading.

- Send a continuous ping (ping -t) to the MedPro from a Windows machine. If the pings intermittently

fail and the failures coincide with periods of poor audio quality, then there is probably a speed/duplex problem between the MedPro and the Ethernet switch.

C-LAN and MedPro 802.1p/Q and DSCP Tagging

See section 3.7, headings “ip-interface” and “ip-network-region.” L2 and L3 tagging on the C-LAN requires the TN799DP board with firmware v5 or later.

Extreme Measures for MedPro and Other IP Boards on Cisco Switches

This information is intentionally placed here and not in section 1.1 “General Guidelines,” because it is a last-resort

measure. On rare occasions a MedPro board’s Cisco switch port may flap up and down continuously. This is manifested by bridge join/leave messages for CatOS-based switches, and interface up/down messages for IOS-based switches. Sometimes this problem is caused by the backplane I/O cable not being Cat5 compliant, and Avaya Tier 3 support can determine whether or not this is the case. Sometimes this problem is a compatibility issue between the MedPro and the Cisco switch. After the instructions in section 2.1, headings “Etherne t Switch es” and “Speed/Duplex” have been followed, if the Cisco switch port continues to flap up and down, consider the options described in the next paragraph.

The Cisco white paper “Troubleshooting Cisco Catalyst Switches to Network Interface Card (NIC) Compatibility Issues [4 p.6]” describes the flapping problem mentioned above and offers a suggestion to adjust the jitter tolerance (not rela ted to audi o jitte r) on Cisco switches. The CatO S global com m and (which is hidden) is set option debounce enable (disable to undo). This command increases the jitter tolerance to 3.1 nsec from the 1.4-nsec default. The IOS interface command is carrier-delay 4 (no carrier-delay to undo). This adjusts the carrier transition delay to 4 seconds. If these commands do not correct or improve the flapping condition, put the switch back to its original state and try operating at 10/half until the problem can be resolv ed.

IP Server Interface (IPSI) Board

The IP Server Interface (IPSI) board is installed in a G600/650, MCC1, or SCC1 gateway, and it is the gateway’s interface to communicate with the S8700 servers. Most of the programming for an IPSI board is done on the SAT ipserver-interface form, which has commands change ipserver-interface #, display ipserver-interface #, and list ipserver-interface. Location IP address, or the hostname if DHCP is used. DHCP ID

is the board slot #. Host is the board’s static

is the hostname. Socket Encryption, if the

parameter is present, allows the control link between the IPSI and call server to be encrypted. When QoS

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is enabled the 802.1p and DiffServ parameters contain the values to be applied to the call server when communicating with this IPSI board (values are not applied to the IPSI board itself).

The IPSI’s speed/duplex and L2/L3 tagging parameters are configured on the board itself, instead of via SAT forms. From the IPSI board type ipsilogin at the [IPSI]: prompt, and enter the login name and password to access the [IPADMIN]: prompt. The commands to display and configure the control port speed and duplex are show port 1, set port negotiation 1, set port speed 1, and set port duplex 1. The commands to display and configure the L2 and L3 priority values are show qos, set vlan tag, set vlan priority, and set diffserv. Be sure to understand what these values do before setting them (see all of section 2.3, particularly the heading “Rules for 802.1p/Q Tagging”).

3.7 General IP-Telephony-Related Configurations (SAT Forms)

The SAT interface has various “forms” that are used to configure specific features. This section covers the forms used to configure general IP telephony. Most of the forms have a display option to view the current configurations, and a change option to change them. Some also have a list option to view, for example, a broad list of stations without seeing in detail how each station is configured.

ethernet-options

As of Avaya Communication Manager 2.0 each IP board’s speed and duplex settings are configured using the ip-interface form. The ethernet-options form now has the list and get options to verify configurations and actual settings for all boards and individual boards respectively. With each new system or IP board installation, one standard procedure should be to apply matching speed/duplex settings to each IP board and its corresponding Ethernet switch port. Then this form can be used to verify the configured settings.

node-names ip

Options are change and display. This form is used to define arbitrary names and associate an IP address with each name. For example, the name “c-lan_80” could be defined to describe a C-LAN board on the 80 subnet with address 192.168.80.10, and the name “medpro_80” could be defined to describe a MedPro board on the 80 subnet with address 192.168.80.11.

ip-interface

Options are change, display, and list. This form is used to configure individual IP boards. The first step is to associate a board type

and slot # to a previously defined node name, and to give the board a subnet mask and default gateway and assign it to a network region. For example, the board type C-LAN in slot 01A05 can be associated with the node name “c-lan_80” defined earlier. This assigns the IP address

192.168.80.10 to the C-LAN board in slot 01A05. Then the board can be given the mask 255.255.255.0 with default gateway 192.168.80.254. The board can also be assigned to network region 1.

802.1p/Q tagging for an IP board is also enabled or disabled on this form. A number (including 0) in the VLAN

field indicates the VID, and it means that tagging is enabled on the board with that VID. Although most implementations should use VID 0, other VIDs are permitted as well. The letter ‘n’ in this column means that tagging is disabled on the board, and a blank means that tagging is not supported on the board. To properly enable L2 tagging on the C-LAN and MedPro boards, follow the instructions in section 2.1 under the heading “Rules for 802.1p/Q Tagging.”

The speed and duplex settings for an IP board are configured on this form under the Ethernet Options heading.

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data-module

Options are change, display, and list. This form is used to assign an extension (required for call processing) to a C-LAN board, and to specify other parameters. The extension in the dial plan, and does not have to be a DID extension. The type # appended with the number 17 (ie, 01A0517). The link

number can be any available number from the

is Ethernet. The port is the board slot

output of the display communication-interface links command. The name

can be any valid extension

is the previously defined

node name (ie, “c-lan_80”).

ip-codec-set

Options are change, display, and list. This form is used to define the codec sets that are referenced by other IP telephony forms. Up to 7 codec sets may be defined with 5 codecs, listed in order of preference, in each set. G.711 (uncompressed) and G.729 (compressed) are the recommended codecs for LAN and WAN, respectively. No silence suppression and 20-ms voice packets are also recommended.

Note about silence suppression:

Although silence suppression conserves bandwidth by not transmitting audio packets during periods of silence, its use typically results in audio clipping, which most users consider unacceptable. The G.729B codec may be a better alternative to silence suppression. Rather than not transmitting during silence, this codec transmits silence in a condensed format that requires less bandwidth.

Larger packet size = less bandwidth Smaller packet size = more bandwidth

Larger packet size → low loss, high jitter

network Smaller packet size → high loss, low jitter network

20-ms packet size recommended

Note about voice packet size:

increments called frames, w ith the ty pica l fram e size being 10ms. The packet size, or number of frames per packet, is a measure of how much audio is sent in each IP packet. Experience has shown that a 20-ms packet is a good compromise between audio quality and bandwidth consumption. Reducing to 10ms doubles the number of packets put onto the network, but only 10ms of audio can be lost when a packet fails to reach

Audio is encoded in

its destination or arrives out of order. Going beyond 20ms reduces the number of packets put onto the network, but there is greater potential for poor audio quality when there is high packet loss.

Larger packets work better in low loss, high jitter networks. Smaller packets work better in high loss, low jitter networks. 20-ms packets are a good compromise.

The Media Encryption

portion of this form is an ordered list of preferred media encryption options. For example, an ordered list of AES, AEA, and none means that AES encryption is preferred first, then AEA encryption if AES is not possible, then no encryption if neither AES nor AEA is possible. This list may contain one or more items.

ip-network-region

Options are change, display, and list. This form is used to define the characteristics of an Avaya Communication Manager network region. While this section desc rib es the conf ig urat ion par ameters of the ip-network-region form, the overall explanation of network regions and guidelines for network region design are covered in detail in the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

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The name

is an arbitrary string to describe the network region.

The codec set

is one of the seven codec sets defined using the ip-codec-set form, and it specifies which

codec(s) are used by the endpoints in this network region.

The UDP port range

is the range used by MedPro boards in this network region for RTP audio. Use the

following points to configure a more narrow UDP port range (to set up security filters, for example).

- 2048 is the beginning of the range by default.

- The MedPro supports 64 uncompressed audio streams (G.711 codec) or 32 compressed audio streams

(G.729 codec) or any combination using the following formula: [uncompressed str eams + 2(compressed streams)] = 64.

- Per the RTP standard, each audio stream requires an even-numbered UDP port for the RTP audio, and

the subsequent odd-numbered UDP port for the RTCP control exchange.

- Therefore, to support 64 audio streams, the end of the UDP port range should be no less than 2175 for

the default beginning of 2048, or any other range containing 64 sequential even- and odd-numbered ports (128 ports total).

The DiffServ

(DSCP) and 802.1p/Q parameters are the L3 and L2 priority values for call signaling from C-LANs in this network region, and audio from MedPros in this network region. The L2 values are only applied to boards that have L2 tagging enabled via the ip-interface form. The reason for the two forms is that tagging and VID can vary per board across a network region, but the priority values are typically uniform throughout the region.

Although two different sets of L3/L2 values can be specified for signaling and audio, it is common to use the same set of values for both, and appendix F gives examples of how the L3 values are used in conjunction with QoS on routers. L2 and L3 tagging on the C-LAN requires the TN799DP board with firmware v5 or later.

The H.323 Link Bounce Recovery connectivity matrix beginning on page 3

parameters, the LSP list on page 2 of this form, and the inter-region

of this form are covered in detail in a separate document. For these configurations, see the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

Direct IP-IP Audio

(shuffling) and IP Audio Hairpinning within a network region and across different network regions are enabled and disabled on this form. Direct IP-IP audio permits calls between IP endpoints to “shuffle” directly to each other, instead of speaking through the MedPro board or VoIP module. If a feature that requires the media gateway, such as conferencing, is activated during the call, the endpoints shuffle back to the MedPro board or VoIP module. If then the conference ends and only two parties remain, the IP stations shuffle back to one another.

Hairpinning permits calls between IP endpoints to speak through the MedPro board or VoIP module, but without any transcoding. This is essentially a relay feature for IP endpoints that are not capable of redirecting their audio streams. None of the Avaya IP telephones have this limitation.

Direct IP-IP Audio and IP Audio Hairpinning are generally enabled, unless there is an Avaya R300 or MultiVOIP gateway in this network region, in which case hairpinning should be disabled. Also, for direct IP-IP audio to function across different network regions, an inter-region codec set must be specified and the regions must be connected via the inter-region connectivity matrix beginning on page 3 of this form.

SM Avaya IP Telephony Implementation Guide

NAT shuffling. Since Avaya Communication Manager 1.3, Avaya has permitted shuffling between endpoints that are separated by network address translation (NAT). NAT has been a hurdle for VoIP due to the fact that the address in the IP header is translated, but embedded IP addresses in the H.323 messages are not translated. This hurdle has been overcome to some extent with the “NAT shuffling” feature in Communication Manager, without the need for H.323-aware NAT devices. See “NAT Tutorial and Avaya Communication Manager 1.3 NAT Shuffling Feature” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_security.html.

Note: In addition to the ip-network-region form, shuffling and hairpinning must be enabled on two other forms: the system-parameters features form, page 10; and the station form, page 2, for each station. Communication Manager has direct IP-IP audio enabled on all these forms by default.

The RTCP

monitoring feature is used with the Avaya VoIP Monitoring Manager (VMM). Enabling this feature causes the audio endpoints in this region to send periodic RTCP reports to VMM. VMM uses these reports to keep a history of audio quality for all reporting endpoints. The default server parameters are configured on the system-parameters ip-options form. If the default settings are not desired in any given network region, specific settings can be applied on a per region basis.

The RSVP

feature requires careful integration with the IP network and must not be enabled without the supporting IP network configurations. These configurations can be cumbersome and require a significant amount of network overhead. A better call admission control (CAC) mechanism is native to Communication Manager 2.0 and is explained in detail in the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

ip-network-map

Options are change and display. This form is used to assign stations to Communication Manager network regions by IP address range or subnet. If a station’s IP address does not fall into any of the ranges configured on this form, the station is assigned to the same network region as the gatekeeper it registers with. Whether by assignment on this form or by inheritance, it is very important to assign IP stations to the proper network region. To understand how these methods of network region assignment affect the station, see the “Avaya Communicat ion Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

The VLAN

column is used to send a VID to IP phones. This field should only be used if DHCP option 176 is not available. If such is the case, then two rows are required on this form: one row for the data subnet/VLAN the phone passes through, and another row for the voice subnet/VLAN on which the phone finally resides, with both rows containing the voice VID. The resulting functionality would be as follows.

- IP phone boots and obtains address on data VLAN.

- IP phone registers with Communication Manager from data VLAN.

- ip-network-map shows phone assigned to a specific network region on a specific voice VLAN.

- Communication Manager directs phone to that voice VLAN.

- IP phone releases data VLAN address and obtains address on voice VLAN.

- IP phone registers with Communication Manager from voice VLAN.

- ip-network-map shows phone assigned to a specific network region on a specific voice VLAN.

- Communication Manager directs phone to that voice VLAN, but phone is already on it.

The Emergency Location Extension

is part of the E911 features of Communication Manager and is not

within the scope of this document.

SM Avaya IP Telephony Implementation Guide

station

Options are add, change, display, and list. This form is used to define stations. To specify an IP station the type

must be an IP model. The port is automatically set to X for an IP phone when the station is first added. This is changed to S##### – an automatically assigned internal port number – when the phone registers with the call server. The IP softphone

inquiry is regarding whether or not a softphone is permitted to take over the extension. This field applies to non-IP stations as well, as an IP softphone can take over an analog or DCP extension and emulate that set type. Survivable GK Node Name

provides an option for the station to fail over to a MultiVOIP gateway when no other gatekeeper is available. Direct IP-IP Audio and IP Audio Hairpinning for the individual station is configured on page 2 of this form.

trunk-group and signaling-group

Options are add, change, display, and list. These forms are used to define trunks, including H.323 IP trunks. This document is concerned only with the IP-specific configuration parameters.

In the trunk-group form, the group type member’s port

designation (beginning on page 6 of the form) should also be IP. Once the members are

should be isdn, the carrier medium should be IP, and each

used for active calls the call server automatically changes the port designations to T#####, which are internal port numbers. The number of members determines the number of simultaneous calls.

The signaling-group parameters are as follows.

- Group Type

- Remote Office

- Trunk Group for Channel Selection

- Near-end Node Name

: h.323.

: ‘n’ in most cases, ‘y’ if the far end is an R300 or MultiVOIP gateway.

: Specify the trunk group configured as described above.

: The node name of the local gatekeeper (C-LAN or S8300) terminating the

H.323 signaling link, as defined in the local call server’s node-names ip and ip-interface forms.

- Near-end Listen Port

: 1720 by default. This is the default TCP port used by the gatekeeper for H.225

call signaling.

- Far-end Node Name

: The node name of the far-end gatekeeper terminating the H.323 signaling link,

as defined in the local call server’s node-names ip form.

- Far-end Listen Port

: 1720 by default if far-end gatekeeper is an Avaya server or Cisco Call Manager.

May vary from device to device if configured to listen on a different TCP port.

- Far-end Network Region

: The numeric identifier of the locally defined network region with which the far-end gatekeeper is associated. That is, the far-end gatekeeper is treated as if it were an endpoint in the locally defined network region specified in this field.

- Calls Share IP Signaling Connection

: ‘y’ if the far-end is an Avaya device, ‘n’ if it is another vendor’s device. ‘y’ means that a single H.225 signaling connection is used for all trunk members (all calls), and ‘n’ means that each trunk member (each call) uses a separate signaling connection. The R300 and MultiVOIP gateways require this to be set to ‘y’.

- Bypass if IP Threshold Exceeded

: Part of a feature commonly referred to as “TDM fallback” or “IP trunk bypass.” This parameter has to do with whether or not a TDM fallback trunk is utilized when the IP network fails or performs poorly between the near-end and far-end gatekeepers. The thresholds for this fail- ov er are config ured in the system-parameters ip-options form, as described in Appendix G. Appendix G is a Q&A discussion on the IP trunk bypass feature and associated issues related to IP trunks.

- Media Encryption

: New to Avaya Communication Manager 2.1. This parameter permits media encryption between the two systems joined by this IP trunk. Selecting ‘y’ invokes a passphrase, and both ends of the IP trunk must have the identical passphrase. This facilitates a key exchange between the systems, which makes media encryption possible between endpoints on the two systems, as long as the ip-codec-set forms on both systems are configured with matching encryption options. In other words, enabling encryption on the ip-codec-set form permits encryption within a system. Media

SM Avaya IP Telephony Implementation Guide

encryption between two systems is possible when they have compatible codec sets and encryption options, and are connected by an IP trunk with this feature enabled.

- DTMF over IP

- Direct IP-IP Audio Connections

- IP Audio Hairpinning

: See the section below for the system-parameters ip-options form.

: ‘y’ typically, same as with endpoints.

: ‘y’, unless R300s or MultiVOIP gateways can talk across the trunk.

The LRQ Required

parameter allows IP trunk availability to be determined on a per call basis. When this option is enabled a RAS-Location Request (LRQ) message is sent to the far-end gatekeeper prior to each call over the IP trunk. The far-end gatekeeper responds with a RAS-Location Confirm (LCF) message and the call proceeds. The absence of an LCF from the far-end gatekeeper indicates that the call cannot proceed. If this occurs and the near-end gatekeeper is configured with the necessary route pattern, the next preferred trunk in the route pattern is used for that call as follows.

- send LRQ

- wait 2 seconds for LCF

- send LRQ

- wait 2 seconds for LCF

- go to next preferred trunk in route pattern (4 seconds total per call)

The LRQ feature affects individual calls, whereas the IP trunk bypass feature affects entire IP trunks. The IP trunk bypass feature takes some time to detect a problem in the IP network and put the signaling-group into bypass state. When this happens, with the appropriate route pattern in place, it results in all calls being routed onto the next preferred trunk. The LRQ feature speeds up per call re-routes until IP trunk bypass is established.

When LRQ is enabled the near-end listen port must be 1719. This means that the far-end gatekeeper must have its far-end listen port set to 1719. If the far-end gatekeeper is an Avaya call server and also has LRQ enabled (near-end listen port is 1719), then the near-end gatekeeper must have its far-end listen port set to

1719. Also, when LRQ is enabled calls cannot share the IP signaling connection, so this parameter must be set to ‘n’. Each call establishes signaling across the IP trunk after a successful LRQ/LCF exchange.

For information about IP trunking with the Cisco Call Manager, see “How to configure an IP Trunk between an Avaya IP600 Communication Server and Cisco Call Manager” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_interop.html. Despite the title, this document applies to more than just the S8100 (IP600).

system-parameters ip-options

Options are display and change. This form is used for miscellaneous IP settings.

IP Media Packet Performance Thresholds

: These parameters, detailed in Appendix G, are for the IP trunk

bypass feature described in the section covering the signaling-group form.

RTCP Monitor Server

: These are the VoIP Monitoring Manager server settings applied to all network

regions, unless specified otherwise in th e ip-network-region form.

IP DTMF Transmission Mode

: The intra-system parameter determines how DTMF tones are passed within a system between G600/650 gateways where the port network connectivity is IP (as opposed to TDM between MCC1 and SCC1 gateways using Center Stage or ATM PNC). The inter-system parameter, configured on the signaling-group form, determines how DTMF tones are passed between systems across IP trunks. Note that both ends of the IP trunk must be configured the same.

SM Avaya IP Telephony Implementation Guide

The primary issue driving these parameters is the fact that DTMF tones are not accurately reproduced using compressed codecs. This is particularly an issue for systems that rely on DTMF tones for functionality. The options operate as follows.

- in-band

: If the configured codec is G.711 or G.729, the tones are passed in-band. Otherwise, the tones are passed out-of-band via call signaling. G.711 accurately passes DTMF tones, while G.729 can pass the tones but is susceptible to error.

- in-band-g711

: If the configured codec is G.711, the tones are passed in-band. Otherwise, the tones

are passed out-of-band via call signaling. This option removes the uncertainty of G.729.

- out-of-band

: The digits represented by the tones are always passed out-of-band. If H.245 messages are exchanged, the H.245 UserInputIndication message is used to pass the digits. Otherwise, the Keypad Information Element of an H.225/Q.931 INFO message is used to pass the digits.

- rtp-payload

: The digits represented by the tones are sent via the RTP payload format specified in RFC

2833. This is required by SIP but also applicable to H.323.

The last two options require the MedPro board and VoIP media module to detect the tones and remove them from the outgoing audio stream. Then a message is sent to the call server for each dig it to be sent out-of-band, or a separate RTP packet with the specified payload format is created for each digit.

H.248 Media Gateway

and H.323 IP Endpoint: See the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

SAT Troubleshooting Commands

The following table lists some common SAT troubleshooting commands.

status station <ext> list trace station <ext> list trace ras ip-stations <ext>

status signaling-group status trunk-group

status clan-port <slot #17> (ie, 01a0517)

status clan-usage status media-processor <slot #>

status ip-network-region <#>

get ethernet-options <slot #>

ping and trace-route

Table 7: Common SAT troubleshooting commands

Gives a static view of a station’s current status (multiple pages). Gives a real-time view of a station’s activities – good for tracing calls. Traces a station’s registration events (GRQ, GCF, RRQ, RCF).

Gives signaling-group’s current status. Gives trunk-group’s current status.

Gives C-LAN board statistics (multiple pages). Gives C-LAN socket usage. Gives MedPro board’s current status.

Gives status o f inter-region connectivity.

Gives administered vs. actual speed/duplex settings for a board. Sends pings and trace-route from a board or from a station. If board, specify board <slot #>. If station, specify source <port #>, where port # is from status station form. Use Help feature.

SM Avaya IP Telephony Implementation Guide

4 Guidelines for Avaya 4600 Series IP Telephones

This section covers some general information regarding various Avaya 4600 Series IP Telephone models. More specific information is available in the “4600 Series IP Telephone LAN Administrator's Guide” and other IP telephone guides at support.avaya.com. The current GA firmware releases can be obtained at the same site. Be sure to read the “readme” files that accompany each firmware package.

The most widely deployed Avaya Communication Manager loads at the time of this writing are Communication Manager 1.3 and 2.0. The minimum recommended IP telephone firmware loads

for Communication Manager 1.3 and 2.0 are those found in the April 2004 package at support.avaya.com, which are listed below. While earlier firmware loads may be used, they are not recommended.

- 2.01 for the 4610/20 models

- 1.82 for the 4606/12/24 models

- 1.81 for the 4601/02 models

Note: For simplicity in many IP telephone applications a C-LAN is often called a gatekeeper, although the call server is the gatekeeper and the C-LAN is only a front end to the gatekeeper.

4.1 Basics

4606/12/24 Speed/Duplex

The integrated hub in the 4606/12/24 models operates at 10M or 100M half duplex. There are generally no speed/duplex issues with these models. When connected to an Ethernet switch port configured to auto-negotiate, the Ethernet switch port stabilizes at 100/half. The exception to this is if a PC is attached to the phone that is capable of only 10M, in which case all three devices stabilize at 10/half. If no PC is to be attached to the phone, or if the attached PC will always be capable of 100M operation, then it is good practice to lock down the Ethernet switch port to 100/half. If a PC may be attached to the phone, and there is a chance that it may have a 10M NIC, leave the Ethernet switch port in auto-negotiate mode.

Note about Single-Speed Bus:

Dual-speed hubs and switches must inherently buffer and discard traffic because of the inconsistent flows (one port receives at 100M but the other can only send at 10M). The 4606/12/24 models are designed with a single-speed bus in the hub and do not perform these functions. Instead, these functions are transferred to the enterprise Ethernet switch, where they really belong. Although the IP telephone can accommodate a second user device (the phone itself being the first), its primary function is not that of an enterprise network device.

30A Base Switch

Figure 18: 30A base switch

The 30A base switch is a 3-port switch integrated into the base stand of 4612 and 4624 sets. The pigtail cable attaches to the IP phone’s uplink port. The other two ports are an uplink port to connect to the enterprise Ethernet switch and a user port to connect to a PC, just like the IP telephone. Both ports are

SM Avaya IP Telephony Implementation Guide

wired such that they require straight Ethernet cables, just like the IP telephone. Each port supports 10/100 operation at full or half duplex. The ports are in auto-negotiate mode and cannot be configured. Therefore, the attached devices must also be in auto-negotiate mode, or they must be fixed at 100/half or 10/half. Experience has shown that the 30A functions adequa te ly with the attached devices in autonegotiate mode. Because the 30A is not an enterprise-class switch, it is best to have the speed and duplex on both ports be the same. Otherwise the 30A will be required to buffer and discard frames, which it cannot do as well as an enterprise Ethernet switch.

The 30A has built-in QoS and gives strict priority to the IP phone’s traffic on the uplink port. That is, when the IP phone and PC are both transmitting, the phone’s traffic is given strict priority out the uplink port to the enterprise Ethernet switch. This is not at all an issue for the PC, because under normal conditions the IP phone transmits less than 100kbps of audio traffic. Prioritization of traffic downstream from the enterprise Ethernet switch to the 30A must be handled by the enterprise Ethernet switch.

The 30A also does something interesting in terms of 802.1Q tagging. It strips the tag from the IP telephone toward the PC. That is, tagged traffic from the phone is sent to the Ethernet switch (uplink port) with the tag, but to the attached PC (user port) without the tag. This allows the attached PC to communicate with the IP telephone when they are on the same VLAN and the phone is tagging. This is not the case when the PC is connected directly into the phone’s hub port, because the hub port does not strip the tag, and most PCs do not interpret the tag correctly.

Legacy Models vs. Current Models

Legacy IP telephone models are the 4606, 4612, and 4624. The firmware for these models ends with

1.8x, and they cannot load the newer 2.x firmware and beyond. The term “current models” in this document refers to the 4620 and 4610. One primary difference between the legacy and current models is that the current models have integrated switches instead of hubs. Another primary difference is that the current models have an updated look and a larger screen that facilitates additional features and functionality.

The built-in switch of the 4620 and 4610 operates much like the 30A base switch in terms of speed/duplex, QoS, and treatment of tagged traffic from the phone. Additionally, the built-in switch permits speed and duplex configuration if necessary. Other than the hub/switch difference between the legacy and current models, they are practically the same with respect to implementation.

The additional features and function al ity of the curren t m odels are covered in I P telephon e spec if ic documentation found at support.avay a.com.

DHCP Option 176

Just the basics of DHCP option 176 are covered here. See the “4600 Series IP Telephone LAN Administrator's Guide” for more details.

The DHCP specification has what are called options, numbered from 0 through 255. Each option is associated with a specific bit of information to be sent to the client. For example, option 1 is the subnet mask option and is used to send the subnet mask to the client. Option 3 is the router option and is used to send the default gateway address and other gateway addresses to the client. Some options are defined – such as options 1 and 3 – and others are not. The defined options are found in RFC 2132.

Options 128 through 254 are site-specific options. They are standard options that are not defined, and vendors may use these options and define them to be whatever is necessary for a specific application.

SM Avaya IP Telephony Implementation Guide

Avaya IP telephones use site-specific option 176 as one of the methods to receive certain parameters from the DHCP server.

For The Avaya application of option 176, it is defined as a string. The string contains parameters and values separated by commas, as illustrated after the following table. The most prevalent parameters and values are as follows.

Parameter Value MCIPADD Address(es) of gatekeeper(s) – at least one required MCPORT The UDP port used for registration – 1719 default TFTPSRVR Address(es) of TFTP server(s) – at least one required L2QVLAN 802.1Q VLAN ID – 0 default VLANTEST The number of seconds a phone will attempt to return to the

previously known voice VLAN

Table 8: DHCP option 176 parameters and values

The typical option 176 string looks like this.

MCIPADD=addr1,addr2,addr3, … ,MCPORT=1719,TFTPSRVR=addr

At least one gatekeeper (C-LAN or S8300) address must be present after MCIPADD to point the phones to a call server. MCPORT specifies which UDP port to use for RAS registration. IP telephone firmware

1.61 and later already have 1719 as the default value, but it is prudent to include it for phones that might have older code. A TFTP server address is necessary so that phones know where to go to download the necessary script files and binary codes (see “Boot-up Sequence” heading below). L2QVLAN and VLANTEST would be included if 802.1Q tagging were required (see section 4.2).

Other parameters may be added to option 176, such as L2QAUD, L2QSIG, DSCPAUD, and DSCPSIG, which are used to specify the L2 and L3 priority values for audio and signaling. These values are configured on the call server (ip-network-region form) and are sent automatically to the phones, but they can be included in option 176.

An administrator must create option 176 on the DHCP server and include this string with the appropriate values. Option 176 could be applied globally or on a per scope basis. The recommendation is to configure option 176 on a per scope basis, because the values themselves or the order of the values could change on a per scope basis. As part of the DHCP process at boot-up, the IP telephone requests option 176 from the DHCP server.

DHCP Lease Duration

A DHCP server gives out an IP address with a finite or infinite lease, and The Avaya recommended lease duration for IP phones is 2 to 4 weeks. The DHCP specification calls for the client to renew the lease at determined intervals, typically beginning at half-life of the lease. If the first renewal attempt fails, there are allowances in the specification for further renewal attempts, dependent on the length of the lease. Too short a lease requires too many renewals, which not only taxes the DHCP server but can also disrupt service to the IP phones if renewals cannot be accomplished for whatever reason. On the other hand, too long a lease can result in IP address exhaustion if hosts are unplugged from the network without properly shutting them down to invoke a release of the IP address lease.

SM Avaya IP Telephony Implementation Guide

Boot-up Sequence

The following are key boot-up events, listed in order, which may help to verify proper operation of the IP phone. This list may not be comprehensive, as only key events are listed. The packets described here can be captured using a protocol analyzer, and one with H.323 capability is required to properly decode the H.225 RAS messages. On 4606/12/24 models the analyzer can be attached to the phone’s user port. But because the 4620 and 4610 have a built-in switch instead of a hub, the analyzer must be attached to a mirrored Ethernet switch port, or to a tap or hub in line between the phone and the Ethernet switch.

- Initial startup – At power-up or manual reset, the phone goes through a short initial startup procedure.

The display shows Restarting… (if the phone was intentionally restarted w/ Hold RESET#), and then Loading… and Starting…

- DHCP – The phone queries the DHCP server for an IP address and other needed information. The

following packets can be captured with a protocol analyzer: DHCP Discover from phone to broadcast; DHCP Offer from server to broadcast, or relay agent to phone; DHCP Request from phone to broadcast; and DHCP ACK from server to broadcast, or relay agent to phone. Note that this step is bypassed if the phone is manually configured with all the necessary information.

- Request file “46xxupgrade.scr” and others from TFTP server – This is a text script file that tells the

phone which boot code and application code are needed. If the phone does not have the current codes, it requests them from the TFTP server. A brand new phone makes all three requests, as phones typically come from the factory with outdated code. In addition, the “46xxupgrade.scr” script may instruct the phone to download the “46xxsettings.scr (or .txt)” file, which is an optional method to send configurations to the phone. When captured using a protocol analyzer, all requests and transfers show up as intuitive TFTP messages that reveal the file name. Note that there is a loading period

after each .bin code is received for the first time. Note also that the file names are case sensitive on some servers (Unix/Linux) and not on others (Microsoft).

- Ext and Password prompts – The phone prompts for the extension and password if there are no

previously stored values.

- Registration with gatekeeper – The phone registers with a gatekeeper (C-LAN or S8300) after the

extension and password are entered. This registration happens very quickly and does not show up on the display. However, the following packets can be captured using a protocol analyzer: RAS-

Gatekeeper Request (GRQ) from phone to gatekeeper; RAS-Gatekeeper Confirm (GCF) from

gatekeeper to phone; RAS-Registration Request (RRQ) from phone to gatekeeper (not necessarily the same one GRQ was sent to); RAS-Registration Confirm (RCF) from gatekeeper to phone.

- H.225 call signaling connection – The phone opens a TCP session with the gatekeeper and sends an

H.225 Setup message, which is answered with H.225 Call Proceeding and H.225 Connect messages

from the gatekeeper.

- Phone is operational – The administered display shows up on the phone (and the extension LED

illuminates on 4606/12/24 models).

- Unregistration messages – If the gatekeeper intentionally unregisters a set, or if the set intentionally

unregisters itself, the message sent by either the gatekeeper or the set is a RAS-Unregistration

Request (URQ) with a reason code that is deciphered in the hex decode of most protocol analyzers.

The acknowledgment message is a RAS-Unregistration Confirm (UCF).

SM Avaya IP Telephony Implementation Guide

Call Sequence

It is not feasible to give a standard packet-by-packet call sequence, because of the many possible variations on any given call. Instead, a higher level description of the process is offered here. Depending on which features are enabled and executed during a call the packet-by-packet sequence may vary, but the fundamental functions described here apply overall. All call signaling functions go through the gatekeeper, either via the C-LAN or natively (S8300), and the gatekeeper dictates what the IP stations do during a call.

- Calling phone contacts gatekeeper on TCP 1720, the H.225 call signaling port. TCP 1720 is always

the gatekeeper port. The phone's TCP port varies.

- There are some call signaling exchanges on this TCP session.

- Calling phone establishes an audio stream with an audio resource (MedPro board or VoIP module), as

directed by the gatekeeper.

- Gatekeeper contacts called phone on TCP 1720.

- There are some call signaling exchanges on this TCP session.

- Called phone also establishes an audio stream with an audio resource, as directed by the gatekeeper,

but this stream is one-way until the call completes.

- Called phone answers, resulting in more call signaling activity on TCP 1720, and the call completes.

The call could remain in this state, but…

- In most cases, unless configured otherwise, the gatekeeper contacts both phones on TCP 1720 and

instructs them to direct their audio streams to each other.

- Phones direct audio streams to each other, as instructed by the gatekeeper.

- One of the phones hangs up, resulting in more call signaling activity on TCP 1720.

- Gatekeeper contacts both phones on TCP 1720 and instructs them to tear down audio streams.

- Phones tear down audio streams.

Keepalive Mechanisms

There are two types of keepalive mechanisms: RAS and TCP.

- RAS keepalive – The IP telephone sends RAS keepalive messages to the gatekeeper at a time-to-live

(TTL) interval specified by the gatekeeper. On a protocol analyzer a RAS keepalive message shows up as a RAS-Registration Request (RRQ) with the keepalive bit set in the RAS decode. Each request message is acknowledged by the gatekeeper with a RAS-Registration Confirm (RCF). This exchange takes place over the RAS socket, which has UDP port 1719 on the gatekeeper side.

- TCP keepalive – The IP telephone sends TCP keepalive messages to the gatekeeper at a regular

interval determined by the phone, or as administered on the ip-network-region form. The keepalive is an empty TCP datagrams with a sequence number that is 1 to 5 less than the sequence number of the previous real TCP message or ACK sent by the phone. The gatekeeper acknowledges each keepalive from the phone with a similar empty TCP datagram. This exchange takes place over the call signaling socket, which has TCP port 1720 on the gatekeeper side.

- Regular and retry intervals – Each keepalive mechanism has a regular interval as described above.

If a regular interval keepalive is not acknowledged, more keepalives are sent at a faster retry interval. If all the retry keepalives are unanswered, the phone effectively unregisters and moves on to the next gatekeeper in its gatekeeper list (obtained via DHCP and/or the gatekeeper).

- TTL – As stated above, the gatekeeper sends a TTL for the RAS keepalive mechanism. The TTL is

the greater of 60 seconds or a multiplier times the number of registered endpoints

. The multiplier for a DEFINITY server is approximately 1.4 seconds, which means that anything above 42 registered endpoints would exceed the minimum 60-sec TTL. The multiplier for the other servers described in this document is .1 second, which means that more than 600 registered endpoints are required to exceed the minimum 60-sec TTL.

Independent of the mechanism (RAS or TCP), the keepalive flow follows this pattern.

SM Avaya IP Telephony Implementation Guide

regular interval regular interval retry int retry int retry int retry int retry int retry int

discovering

ACK

failure

no ACK

Figure 19: Keepalive pattern

retry KA

no ACK

retry KA

no ACK

time to unregister

retry KA no ACK

retry KA

no ACK

retry KA no ACK

The discovering at the end of the flow means that the phone has effectively unregistered and is searching for another gatekeeper. Effectively unregistered means that the phone has not sent an explicit RAS-

Unregistration Request (URQ) message, but it considers itself unregistered from that gatekeeper and is

moving on to the next. Even if the phone did send a URQ, chances are the gatekeeper would not receive it because the failure condition could still exist.

The final retry interval prior to discovering would appear to give extra time for the failure to recover. And indeed if the phone did receive a KA acknowledgment within that final retry interval it would stay registered to the same gatekeeper. However, the reality is that if the phone doesn’t receive an acknowledgment within a second or two after the final retry KA, it won’t receive one. Therefore, the final retry interval really does not factor into the time to unregister. Time to unregister answers the question, “How long must the failure (ie, network outage) last before the IP telephone unregisters?” If the failure recovers just before the final retry KA is sent, the phone remains registered to the same gatekeeper. If the failure recovers a couple seconds after the final retry KA is sent, the phone most likely unregisters and moves on to the next gatekeeper after the final retry interval.

The TCP and RAS keepalive algorithms are as follows.

IP telephone TCP KA

regular intrvl

4606/12/24/20

1.61 thru 1.72 4620

1.73

4606/12/24

1.73 It was intended to make the TCP KA mechanism faster in the 4606/12/24 1.73 code. However, a bug in the code made it much faster than intended.

4606/12/24/20

1.8 and later 4620/10

2.x w/ CM 2.x

60sec 5 * 30sec 150 to 210sec TTL – 5sec 2 * 45sec 90 to

15sec 5 * 2.5sec 12.5 to 27.5sec TTL – 5sec 2 * 45sec 90 to

30sec 5 * 10sec 50 to 80sec TTL – 5sec 2 * 45sec 90 to

configurable configur-

TCP KA

retry intrvl

able

Table 9: TCP and RAS keepalive matrix

Time to

unregister

varies obsolete obsolete n/a

RAS KA

regular intrvl

RAS KA

retry intrvl

Time to

unregister

TTL + 85sec

4.2 Connecting a PC to the Phone

On the back of the phone, the port with the icon that looks like a terminal is the user port. (The port with the icon that looks like a network jack is the uplink port, which connects to the Ethernet switch.) Use discretion when connecting a PC to the phone, and remember that its primary function is not that of an enterprise network device. For example, do not connect an enterprise server to the phone. Such high-

SM Avaya IP Telephony Implementation Guide

traffic servers require their own separate connections to the enterprise Ethernet switch. Also, do not connect a PC to the phone with a 10M uplink to the network, if that PC routinely runs high-volume transactions. The phone itself operates well at 10M, and the PC itself may also operate adequately at 10M. But the two combined can result in the PC overwhelming the 10M link at the expense of audio quality. Connecting a user PC to the phone at 100M works very well.

IP Phone and Attached PC on Same VLAN

There are three variations of attaching a PC to the phone, and the first two involve having both the phone and the PC on the same VLAN, which is the port/native VLAN (refer to Appendix A for a primer on VLANs). In the first scenario, traffic from both the phone and the PC have no CoS tagging. In this case, no special configurations are necessary. Simply attach the phone to an access port (one with only the port/native VLAN configured) and attach the PC to the phone.

The second scenario is similar to the first, except that traffic from the phone is tagged with L2 and/or L3 priority while remaining on the port/native VLAN. See the instructions in section 2.3 under the heading “Rules for 802.1p/Q Tagging.” The phone must be configured to tag its Ethernet frames and/or IP packets with the desired priority. The Hold ADDR# menu is used to manually enable or disable 802.1Q tagging and to set the VLAN ID. The other parameters are configured via the Hold QOS# menu. The manual method is covered below, and an automated method is covered in the next paragrap h.

- 802.1Q

- VLAN ID

– On/off for 802.1Q tagging. Turn this on if L2 priority tagging is desired; off otherwise.

– Should be zero (0) for this scenario, per the instructions in section 2.3, heading “Rules

for 802.1p/Q tagging.” The VID has no effect when 802.1Q tagging is disabled.

- L2 audio

– Layer 2 CoS tag for Ethernet frames containing audio packets. The phone automatically receives this value from the call server, per the ip-network-region form. This value could also be set manually on a per phone basis.

- L2 signaling

– Layer 2 CoS tag for Ethernet frames containing signaling packets. The phone automatically receiv es thi s v alue from the call server, per the ip-network-region form. This value could also be set manually on a per phone basis.

- L3 audio

– Layer 3 DSCP for audio IP packets. The phone automatically receives this value from the call server, per the ip-network-region form. This value could also be set manually on a per phone basis.

- L3 signaling

– Layer 3 DSCP for signaling IP packets. The phone automatically receives this value from the call server, per the ip-network-region form. This value could also be set manually on a per phone basis.

The manual menus are covered here for explanatory purposes. However, a better alternative is to use DHCP option 176 and the built-in capabilities of the call server and IP telephone to automatically configure the phones. As stated previously, the call server sends the L2 and L3 priority values to the phones automatically, per the values con fig ured in the ip-network-region form. The 802.1Q on/off instruction and the VLAN ID can be configured automatically using the DHCP option 176 string as specified in the “LAN Administrator’s Guide.” Here is what that string should look like for 1.8 and later phones (see the appropriate “LAN Administrator’s Guide” for previous phone releases).

MCIPADD=addr1,addr2,addr3, … ,MCPORT=1719,TFTPSRVR=addr,L2QVLAN=0

The L2QVLAN=0 parameter instructs the phone to enable 802.1p/Q tagging with VLAN ID 0, which means that the phone’s traffic belongs on the port/native VLAN. The Ethernet switch port to which the phone is connected must be configured to accept 802.1Q tagging for this to work, and the switch must interpret VLAN ID 0 as the port/native VLAN ID, per the IEEE 802.1Q standard [6 p.69]. If the

SM Avaya IP Telephony Implementation Guide

Ethernet switch does not understand VLAN ID 0, the phone may need to tag with the port/native VLAN ID, although this is not the standard method.

Remember that in order for the CoS tags to have any effect, the corresponding QoS configurations must be implemented on the necessary network devices. Remember also that improperly enabling L2 and L3 tagging may break processes that were working without tagging. Read section 2.3 of this document for more information on CoS and QoS.

IP Phone and Attached PC on Different VLANs

The third scenario for attaching a PC to the phone (the first two were covered in the previous heading) is to have the phone and the PC on separate VLANs. This requires a multi-VLAN port on the Ethernet switch as described in section 2.3, heading “Rules for 802.1p/Q Tagging.” One of the VLANs is the port/native VLAN (the data VLAN), and the clear Ethernet frames (ones with no 802.1Q tag) from the PC are forwarded on this VLAN. The IP phone must tag its traffic with the proper VLAN ID to have it forwarded on the voice VLAN. The Hold ADDR# and Hold QOS# menu options are exactly the same as described in the previous heading, except that the VID must not be zero. The automated method using DHCP option 176 is also the same, except that L2QVLAN has a non-zero value and the VLANTEST parameter may be applied.

IP telephone 1.8 and forward has an auto-tagging feature and persistent memory. These allow the phone to detect whether or not it can use tagged frames, and to preserve the voice VLAN ID through a reboot or power cycle. The L2Q=0,1 parameter used in DHCP option 176 for earlier firmware is no longer required, although it may be restored in later releases. Instead a VLANTEST parameter dictates how long the phone should try the previously known voice VLAN before reverting back to no tagging.

The following scenario with arbitrary VLAN IDs details the steps a phone (1.8 and later) would go through in a typical dual-VLAN implementation. It also illustrates the recommended content of the option 176 string.

- Phone with no previously stored values boots up and obtains an address on the data VLAN.

- The data VLAN option 176 string directs the phone to go to voice VLAN 25.

MCIPADD=addr1,addr2, … ,MCPORT=1719,TFTPSRVR=addr,L2QVLAN=25,VLANTEST=600

- Phone releases the data VLAN address and obtains an address on the voice VLAN.

- The voice VLAN option 176 string is identical to the data VLAN string but without the L2QVLAN

parameter

, because a phone already on the voice VLAN doesn’t need to be directed to go there.

- Phone is operational on the voice VLAN.

- Reboot or power cycle occurs.

- Phone immediately returns to voice VLAN 25 upon recovery, and one of the following occurs.

- Phone obtains an address and option 176 string on the voice VLAN and all is well.

- Phone cannot obtain an address on the voice VLAN, due to network or DHCP problems. In this

case the VLANTEST=600 parameter directs the phone to continue trying for 600sec (finite range is 1-999). If the phone does not succeed in obtaining an address within 600sec, it marks VLAN 25 as invalid and returns to no tagging (back to the data VLAN).

The idea behind going back to the data VLAN after some time is that the phone may have changed ports and be on one with a different voice VLAN. In such a case the phone would have to start over and be directed to the proper voice VLAN. The idea behind marking VLAN 25 invalid in the previous scenario is that if the phone hasn’t changed ports, it is preferable to operate on the data VLAN than to be sent to a bad voice VLAN in a continuous loop. For cases where it is not preferable to operate on the data VLAN, the option VLANTEST=0 was added to legacy phone firmware 1.82 and current phone firmware 2.01. This instructs the phone to permanently remain on the previously known voice VLAN. Once the phone

SM Avaya IP Telephony Implementation Guide

accepts VLANTEST=0 or marks a VLAN invalid, the only way to clear out this state is by manually resetting the values via the Hold RESET# menu.

Note: DHCP option 176 is the preferred method for directing the phone to the voice VLAN. The method described previously using the VLAN field of the ip-network-map form is an alternative if DHCP option 176 is not available. The two methods should not

be used simultaneously.

Appendix A describes in much more detail how to configure a network for dual-VLAN operation.

4.3 Gatekeeper Lists and DHCP Option 176

An IP telephone can have a list of gatekeepers (C-LANs and/or S8300s) to which it may send the initial RAS-Gatekeeper Request (GRQ) message. This list is obtained via the DHCP option 176 string, which is covered briefly in section 4.1 and in detail in the “LAN Administrator’s Guide.”

Within the DHCP option 176 string, the comma-separated IP addresses that follow the MCIPADD parameter constitute a gatekeeper list, and this list provides redundancy at boot-up. If a given gatekeeper is unreachable for any reason, the phone attempts other gatekeepers in the gatekeeper list. The following hypothetical network diagram and the accompanying instructions explain how gatekeeper lists should be administered on DHCP servers.

DHCP Server w/

scopes for v80-90

Switch

Access

Switches

Access

Voice v40

Switch

DHCP Server w/

scopes for v10-40

Core

Switch

Distribution

C-LAN 1 C-LAN 2 C-LAN 3

Switch

Access

Switches

Access

Voice v10

Switch

Network Region 1

Distribution

Switch

Access

Switches

Access

Voice v20

Switch

Distribution

Switch

Access

Switches

Access

Voice v30

Switch

Core

Switch

Distribution

Router

g700 with

s8300 LSP

VoIP mod

C-LAN 4

Network Region 2

Access

Switches

Access

Voice v80

Switch

phones on v80 get info from DHCP

v80 scop e

Access

Switches

Access

Voice v90

Switch

phones on v90 get info from DHCP

v90 scope

phones on

v10 get info

from DHCP

v10 scope

phones on v20 get info from DHCP

v20 scope

phones on v30 get info from DHCP

v30 scope

phones on v40 get info from DHCP

v40 scope

Figure 20: Hypothetical con verge d net work

SM Avaya IP Telephony Implementation Guide

Main Site

The converged network depicted in the figure above could be an entire network, or a portion of a much larger network. The main site is implemented in a core-distribution-access architecture common to many enterprise networks. The IP phones are scattered across various voice VLANs, but the phones all belong to the same Communication Manager network region because they use the same codec set, share the same audio characteristics, and use the same resources specified by a network region. Network region 1 has four C-LANs scattered across four distribution switches, but there could be more depending on the number of IP telephones. The fact that there are four C-LANs and four voice VLANs is purely coincidental.

Suppose, for whatever reason, that a large number of IP phones are rebooted at once. Which gatekeeper(s) will they contact first? The correct answer is that they should contact all the gatekeepers in a distributed fashion. All the phones should not bombard the same gatekeeper at once with GRQs. There are various ways to configure the gatekeeper lists, and the following is possibly the simplest.

- v10 scope: “MCIPADD=clan1addr,clan2addr,clan3addr,clan4addr, …”

- v20 scope: “MCIPADD=clan2addr,clan3addr,clan4addr,clan1addr, …”

- v30 scope: “MCIPADD=clan3addr,clan4addr,clan1addr,clan2addr, …”

- v40 scope: “MCIPADD=clan4addr,clan1addr,clan2addr,clan3addr, …”

Based on how this particular network is implemented, here is anot her al te rna tiv e.

- v10 scope: “MCIPADD=clan1addr,clan2addr,clan3addr,clan4addr, …”

- v20 scope: “MCIPADD=clan2addr,clan1addr,clan4addr,clan3addr, …”

- v30 scope: “MCIPADD=clan3addr,clan4addr,clan1addr,clan2addr, …”

- v40 scope: “MCIPADD=clan4addr,clan3addr,clan2addr,clan1addr, …”

Regardless of how the lists are administered, the principle is important. DHCP scopes should have rotating/varying gatekeeper lists, so as to produce a uniform distribution of GRQs at boot-up. Most DHCP servers facilitate this by permitting the option 176 string to be created per scope. Even servers like Microsoft’s which allow the option 176 string to be created for the entire server, resulting in only one gatekeeper list, also permit the option 176 string to be created per scope. Note that this principle may also apply to multiple TFTP servers.

Branch Site

The branch site is just slightly different in terms of the DHCP scopes, but very different in terms of the failure scenario and other factors that affect the branch implementation.

The IP telephones at the branch site could access the same four C-LANs shown above, or there could be a different set of C-LANs (not shown) for the branch IP phones. In either case the DHCP scopes for v80 and v90 should have rotating lists, as at the main site. However, in addition to the list of C-LAN addresses, the v80 and v90 scopes should also include the S8300 LSP address at the end of the list. This is because the LSP can take over as the call server for the branch if the WAN link fails. The LSP only permits registrations when it is active, so having the LSP in the list does not result in inadvertent registrations to the LSP.

Because an extended WAN link failure is possible, the branc h site shou ld idea lly have its own DHCP server. It makes sense that if there is a redundant call server at the branch, there should also be a dedicated DHCP server, because the IP telephones require both services. For cost and administrative reasons, however, many will choose not to install a DHCP server at all branch locations. In such cases it

SM Avaya IP Telephony Implementation Guide

is very important that the IP telephones not be rebooted during a WAN link failure, because they would not be able to obtain IP addresses. The manual configuration option is available, but it is not always a viable option for various reasons.

Two Methods of Receiving the Gatekeeper List

In addition to receiving the gatekeeper list via DHCP option 176, as described above, a gatekeeper list is also received via the RCF message during registration. In other words, when an IP telephone registers with the call server, the call server sends a gatekeeper list in the RCF message. The H.323 standard calls this the Alternate Gatekeeper List. This means that a phone really only needs one gatekeeper address at boot-up, because the phone receives the gatekeeper list when it registers. This feature is useful for phones that are manually administered, as the manual method only permits the entry of one gatekeeper address. However, it is still preferable to administer a gatekeeper list in DHCP option 176 for redundancy during boot-up.

Here are some key points regarding the option 176 gatekeeper list and the RCF Alternate Gatekeeper List.

- IP telephone versions prior to 2.0 use both lists simultaneously. GK addresses received from either

method are merged into one list.

- IP telephone 2.0 and later maintains the two lists separately, with only one list active at any given

time. During boot-up the phone uses the list obtained from option 176. After registration the phone uses the Alternate Gatekeeper List received in the RCF. When a phone is logged off but not rebooted, it reverts back to the list obtained from option 176.

- The option 176 GK list is recommended, as opposed to manual entry or a single GK address in option

176, because the RCF list is received after boot-up. If the phone only knows of one GK at boot-up and that GK is out of service, the phone cannot register and hence cannot get an RCF.

- The Alternate Gatekeeper List sent in the RCF follows a specific algorithm. When an IP phone

registers and its network region is specified in the ip-network-map form, the call server delivers a list of all gatekeepers in that region, plus connected regions (specified in the ip-network-region form). If an IP phone’s network region is not administered in the ip-network-map form, it inherits the region of the gatekeeper that receives the registration, and the call server delivers a list of all gatekeepers only in that region.

- As of Avaya Communication Manager 1.3 the addresses of the LSPs in the same network region as

the IP phone are also sent in the RCF. As of Communication Manager 2.0, in addition to the LSPs, the address of the Survivable GK Node Name is also sent in the RCF, but only to phones that have a Survivable GK administered on the station form.

- The combination of Communication Manager 2.x and IP telephone 2.x facilitates a distinction

between primary and backup gatekeepers in the Alternate Gatekeeper List. During recovery after an outage, the primary gatekeepers are attempted first for a period of time called the H.323 Primary Search Time, specified in the system-parameters ip-options form. After this search time expires, the backup gatekeepers – LSPs and the Survivable GK – are also included in the search. For a more detailed discussion see the H.323 Link Bounce section of the “Avaya Communication Manager Network Region Configuration Guide” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

SM Avaya IP Telephony Implementation Guide

Verifying the Gatekeeper Lists

The table below gives a summary of how to view the gatekeeper and gatekeeper list in use.

Phone state

Method

MIB Object ID .1.3.6.1.4.1.6889.2.69.1.1.3 (endptMCIPADD)

MIB Object ID .1.3.6.1.4.1.6889.2.69.1.1.4

Registered phone Phone logged off via Hold

LOGOFF# keypad command

- 2.1 shows Alternate Gatekeeper

List received in RCF message, which is the list in use.

- 2.01 shows gatekeeper list

received from option 176, or manually configured gatekeeper, even though the list in use is the Alternate Gatekeeper List from RCF.

- 1.8x shows combined list from

RCF and option 176, or combined RCF list and manually configured

gatekeeper. Shows gatekeeper to which phone is currently registered.

- 2.1 shows gatekeeper list

received from option 176, or manually configured gatekeeper.

- 2.01 shows gatekeeper list

received from option 176, or manually configured gatekeeper.

- 1.8x shows combined list from

RCF and option 176, or combined RCF list and manually configured

gatekeeper. Shows gatekeeper to which phone was last registered.

(endptMCIPINUSE) Hold ADDR# keypad menu Shows gatekeeper to which phone is

N/A

currently registered.

SM Avaya IP Telephony Implementation Guide

Appendix A: VLAN Primer

This appendix is primarily concerned with configurations that require the Avaya IP Telephone to connect to an Ethernet switch (Eth-switch) port configured with multiple VLANs – the IP phone on one VLAN and a PC connected to the phone on a separate VLAN. Three sets of configurations are given: Avaya P3 30 v3.2.8 and later, Cisco CatOS, and some Cisco IOS.

VLAN Defined

With simple Eth-switches, the entire switch is one L2 broadcast domain that typically contains one IP subnet (L3 broadcast domain). Think of a single VLAN (on a VLAN-capable Eth-switch) as being equivalent to a simple Eth-switch. A VLAN is a logical L2 broadcast domain that typically contains one IP subnet. Therefore, multiple VLANs are logically separated subnets – analogous to multiple switches being physically separated subnets. A L3 routing process is required to route between VLANs, just as one is required to route between switches. This routing process can take place on a connected router or a router module within a L2/L3 Eth-switch. If there is no routing process associated with a VLAN, devices on that VLAN can only communicate with other devices on the same VLAN.

For a tutorial and more information on VLANs, see “LANs and VLANs: A Simplified Tutorial” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_general.html.

The Port or Native VLAN

Port VLAN and native VLAN are synonymous terms. The IEEE standard and most Avaya switches use the term port VLAN [6 p.11], but Cisco switches use the term native VLAN. Issue the command show trunk on P330s and CatOS Catalysts to see which term is used in the display output.

Every port has a port/native VLAN configured on a per port basis with the following commands.

Avaya P330 v3.2.8 and later

set port vlan <id> <mod/port> set vlan <id> <mod/port>

All clear Ethernet frames (ones with no 802.1Q tag, such as from a PC) are forwarded on the port/native VLAN. This is true even if the Eth-switch port is configured as an 802.1Q trunk, or otherwise configur ed for multiple VLANs (see VLAN binding heading below).

Configuring a Trunk

A trunk port on an Eth-switch is one that is capable of forwarding Ethernet frames on multiple VLANs via the mechanism of VLAN tagging. IEEE 802.1Q specifies the standard method for VLAN tagging. Cisco also uses a proprietary method called ISL. Avaya products do not interoperate with ISL

A trunk link is a connection between two devices across trunk ports. This can be between a router and a switch, between two switches, or between a switch and an IP phone. Some form of trunking or forwarding multiple VLANs must be enabled to permit the IP phone and the attached PC to appear on separate VLANs. The following commands enable trunkin g.

Avaya P330 v3.2.8 and later

set trunk <mod/port> dot1q

By default only the port/native VLAN is enabled on the trunk port. Another set of commands is required to specify other allowed VLANs.

. Unless otherwise configured, it is VLAN 1 by default. It can be

Cisco CatOS

set trunk <mod/port> nonegotiate dot1q

By default all VLANs (1-1005) are enabled on the trunk port. VLANs can be sele ctively removed with the command clear trunk <mod/port> <vid>.

SM Avaya IP Telephony Implementation Guide

Note that Avaya adds additional VLANs to a trunk port that has only one VLAN, while Cisco removes excess VLANs from a trunk port that has all VLANs. Either method achieves the de sired objective, which is to have only two VLANs configured on a trunk port connected to an IP phone. That is, broadcasts from non-essential VLANs are not permitted to bog down the link to the IP phone.

VLAN Binding Feature (P330 v3.2.8 and later)

On the Avaya P330, additional VLANs are added to a port using the VLAN binding feature. The port may be a trunk po rt (802.1Q tagging enabled) or an access port (no 802.1Q tagging). The port does not need to be a trunk to forward multiple VLANs, and for one application – connecting to an Avaya IP phone – it must not

be a

trunk (ie, do not issue the set trunk command). The following steps enable VLAN binding.

1. Verify that the port is configured with the desired port/native VLAN.

2. Add additional VLANs with one of the following vlan-binding-mode options.

Static option:

set port vlan-binding-mode <mod/port> static

set port static-vlan <mod/port> <vid>

Put the port in bind-to-static mode. Statically add another VLAN, in addition to the port/native VLAN.

----- OR -----

Configured option:

set vlan <id>

Add a VLAN to the configured VLAN list. Type show vlan to see entire list.

set port vlan-binding-mode <mod/port> bind-toconfigured

Apply the configured VLANs to the port and permit only those VLANs (bind-to-all permits all VLANs and not just the configured).

3. If the port is connected to a router or to another switch, trunking must be enabled with the command set trunk

<mod/port> dot1q, which causes all IP phone wit h an attached PC, trunking must not

egress frames to be tagged. However, if the port is connected to an Avaya

be enabled so that none of the egress frames are tagged. This

is necessary because most PCs do not understand tagged frames.

Setting the Priority without Trunking or VLAN binding (Single-VLAN Scenario)

With Avaya switches it is possible to set the L2 priority on the IP phone, even if the phone is not connected to a trunk or multi-VLAN port. That is, the Avaya switch does not need to be explicitly configured to accept priority-tagged Ethernet frames on a port with only the port/native VLAN configured. This is useful if the phone and the attached PC are on the same VLAN (same IP subnet), but the phone traffic requires higher priority. Simply enable 802.1Q tagging on the IP phone, set the priorities as desired, and set the VID to zero (0). Per the IEEE standard, a VID of zero assigns the Ethernet frame to the port/native VLAN.

Cisco switches behave differently in this scenario, depending on the hardware platforms and OS versions. Here are Avaya Labs test results with a sample of hardware platforms and OS versions.

Catalyst 6509 w/ CatOS 6.1(2)

Accepted VID zero for the native VLAN when 802.1Q trunking was enabled

on the port. In this case, all but the native VLAN should be cleared

off the trunk.

Catalyst 4000 w/ CatOS 6.3(3)

Would not accept VID zero for the native VLAN. Opened a case with Cisco TAC, and TAC engineer said it was a hardware problem in the 4000. Bug ID is CSCdr06231. Workaround is to enable 802.1Q trunking and tag with native VID instead of zero. Again, clear all but the native VLAN off the trunk.

SM Avaya IP Telephony Implementation Guide

Catalyst 3500XL w/ IOS 12.0(5)WC2

Accepted VID zero for the native VLAN when 802.1Q trunking was disabled

on the port.

Conclusion Note the hardware platfor m and OS version and consult Cisco’s

documentation, or call TAC.

Note that setting a L2 priority is only useful if QoS is enabled on the Eth-switch. Otherwise, the prioritytagged frames are treated no differently than clear frames.

Sample Multi-VLAN Scenario for Avaya P330 Code 3.2.8 and Cisco CatOS and IOS

Here is a sample multi-VLAN scenario. Suppose there is a Cisco router connected to a P330 switch that contains two VLANs, one for the VoIP devices and one for the PCs. To conserve ports and cabling, the PCs are connected to the phones and the phones are connected to the P330 switch.

S8100/G600

C-LAN

vlan 10

192.168.10.1

f0/1

1/1 1/5

Cisco Router

192.168.1.254

192.168.10.254 vlan 1

192.168.1.100

DHCP Server

TFTP Server

interface FastEthernet0/1 description 802.1Q trunk interface ! interface FastEthernet0/1.1 encapsulation dot1q 1 ip address 192.168.1.254 255.255.255.0 ! interface FastEthernet0/1.10 encapsulation dot1q 10 ip address 192.168.10.254 255.255.255.0 ip helper-address 192.168.1.100

P330 configuration (bind-to-static option)

set port vlan-binding-mode 1/1 static set port static-vlan 1/1 10 set trunk 1/1 dot1q set port spantree disable 1/1

set port vlan 10 1/2 set port spantree disable 1/2

MedPro

vlan 10

192.168.10.2 vlan 10

1/2 1/3

Avaya

192.168.10.7

Cajun P330

1/12

vlan 1

192.168.1.7

Cisco Router configuration

To forward DHCP requests to the DHCP server.

All ports have port/native VLAN 1 by default. Port in static binding mode by default, but command shown. In addition to v1, v10 statically bound to port. Port connected to Cisco router is an 802.1Q trunk port. Spanning Tree disabled at the port level.

Port/native VLAN changed to 10 on this port. Spanning Tree disabled at the port level.

Avaya IP Phone

SM Avaya IP Telephony Implementation Guide

set port level 1/2 6

set port vlan 10 1/3 set port spantree disable 1/3 set port level 1/3 6

set port vlan-binding-mode 1/5 static set port static-vlan 1/5 10 set port spantree disable 1/5

set port spantree disable 1/12

P330 configuration (bind-to-configured option)

set vlan 1 set vlan 10

set port vlan-binding-mode 1/1 bind-to-

configured set trunk 1/1 dot1q

set port spantree disable 1/1

set port vlan 10 1/2

set port spantree disable 1/2 set port level 1/2 6

set port vlan 10 1/3 set port spantree disable 1/3 set port level 1/3 6

set port vlan-binding-mode 1/5 bind-to-

configured

set port spantree disable 1/5

If the P330 switch were a Cisco CatOS switch instead

set port host

set vlan 1005 1/1 set trunk 1/1 on dot1q clear trunk 1/1 2-9,11-1004

set vlan 10 1/2

set port qos 1/2 cos 6

set vlan 10 1/3 set port qos 1/3 cos 6

set trunk 1/5 nonegotiate dot1q clear trunk 1/5 2-9, 11-1005

set port auxiliaryvlan 1/5 10

Port L2 (802.1p) priority set to 6.

Port in static binding mode by default, but command shown. In addition to v1, v10 statically bound to port, but not a trunk port. Spanning Tree disabled at the port level. Port 1/12 for the DHCP/TFTP server already has port/native VLAN 1. Spanning Tree disabled at the port level.

All ports have port/native VLAN 1 by default. v1 configured v10 configured

Port bound to configured VLANs 1 and 10.

Port connected to Cisco router is an 802.1Q trunk port. Spanning Tree disabled at the port level.

Port/native VLAN changed to 10 on this port. Spanning Tree disabled at the port level. Port L2 (802.1p) priority set to 6.

Bound to configured VLANs but not a trunk po rt.

Spanning Tree disabled at the port level.

All ports have port/native VLAN 1 by default. First invoke this command o n all user ports. Cisco switches do not tag the native VLAN, but the router expects a tag on v1, so the native VLAN i s changed to some unused VLAN. Port connected to Cisco router is an 802.1Q trunk port. Unnecessary VLANs removed; 1, 10, and 1005 remain.

Port/native VLAN changed to 10 on this port. Port L2 (802.1p) priority set to 6.

Plain 802.1Q trunk port with no Cisco negotiation features. Unnecessary VLANs removed; 1 and 10 remain.

Optional

command using auxiliaryvlan on the phone port instead of explicit trunking. v10 is the auxiliaryvlan; only v1 and v10 on this port; port is an

802.1Q trunk port, though not explicitly configured.

SM Avaya IP Telephony Implementation Guide

If the P330 switch were a Cisco IOS switch instead

interface FastEthernet0/1 switchport trunk encapsulation dot1q switchport trunk native vlan 1005

switchport trunk allowed vlan 1,10,1005 switchport mode trunk spanning-tree portfast

interface FastEthernet0/2 switchport access vlan 10 spanning-tree portfast switchport priority default 6

interface FastEthernet0/3 switchport access vlan 10 spanning-tree portfast switchport priority default 6

interface FastEthernet0/5 switchport trunk encapsulation dot1q switchport trunk native vlan 1

switchport trunk allowed vlan 1,10 switchport mode trunk spanning-tree portfast

All ports have port/native VLAN 1 by default.

Port connected to Cisco router is an 802.1Q trunk port. Cisco switches do not tag the native VLAN, but the router expects a tag on v1, so the native VLAN i s changed to some unused VLAN. VLANs 1, 10, and 1005 allowed on trunk. Port is in trunk mode. Spanning Tree fast start feature.

Port/native VLAN changed to 10 on this port. Spanning Tree fast start feature. Port native VLAN L2 (802.1p) priority set to 6.

802.1Q trunk port. Since most PCs do not understand the tag, the PC’s VLAN must be the native VLAN. v1 is already the native, but command shown. VLANs 1 and 10 allowed on trunk. Port is in trunk mode. Spanning Tree fast start feature.

IP phone configuration

This procedure applies regardless of the Eth-switch being used. Initially placing the IP phone on VLAN 10 requires two DHCP scopes – one for VLAN 1 and another for VLAN 10. Both scopes should have identical DHCP option 176 parameters, with one exception. The VLAN 1 scope must have the L2QVLAN parameter, and the VLAN 10 scope should not. The following strings apply to phone firmware 1.8 and beyond

v1: MCIPADD=addr1,addr2,addr3, … ,MCPORT=1719,TFTPSRVR=addr,L2QVLAN=10,VLANTEST=600 v10: MCIPADD=addr1,addr2,addr3, … ,MCPORT=1719,TFTPSRVR=addr,VLANTEST=600

Run the phone through its normal boot-up sequence. It obtains an IP address on VLAN 1 – the port/native VLAN. When the phone receives the option 176 string above from the VLAN 1 scope, it releases the VLAN 1 address and enters a second DHCP sequence with tagging enabled to obtain a VLAN 10 address. After the phone is operational on VLAN 10, subsequent reboots result in the phone returning to VLAN 10 directly, instead of passing through VLAN 1. If an address is not obtained on VLAN 10 for 10min (VLANTEST=600), the phone reverts back to no tagging (VLAN 1). With legacy phone firmware 1.82 and current phone firmware 2.01, VLANTEST=0 could be used to make the phone stay on VLAN 10 indefinitely. See section 4.2, heading “IP Phone and Attached PC on Different VLANs” for a full explanation of how the phone operates between the data and voice VLANs, including the use of the VLANTEST parameter.

The L2QVLAN parameter should not

be added to the VLAN 10 DHCP scope. This is so that in the event a phone is connected to a port that has VLAN 10 as the port/native VLAN, it will not receive instructio ns from the DHCP scope to enable tagging. In such a case the phone would not require tagging to function on VLAN 10, and tagging could result in an incompatibility with the Eth-switch.

PC configur ation

: The PC can be statically addressed with a VLAN 1 address, or it can receive a VLAN 1 address

via DHCP. No special configurations are required.

SM Avaya IP Telephony Implementation Guide

Appendix B: Cisco Auto-Discovery

This appendix describes Cisco’s proprietary auto-discovery feature using CDP and the auxiliaryvlan. Some customers have requested that Avaya IP phones be put on the auxiliaryvlan. The previous position was that it was believed to work but was not recommended. However, recent tests have shown successful interop e rab ility with both the auxiliaryvlan (CatOS) and the voice vlan (IOS). This testing was initiated because of the inability to enable portfast on older Catalyst 6500 code (pre 5.5.14, 6.3.2, 7.2.2) when the port is in trunk mode. The resulting request was to use the auxiliaryvlan instead of explicit trunking, because portfast can be enabled on auxiliaryvlan ports, even on the older code releases. auxiliaryvlan and voice vlan were successfully tested on the following platforms, with no known issues to date.

auxiliaryvlan on Catalyst 6509 w/ CatOS version 7.2.2 auxiliaryvlan on Catalyst 6509 w/ CatOS version 6.3.7 auxiliaryvlan on Catalyst 6509 w/ CatOS version 5.5.15 auxiliaryvlan on Catalyst 6509 w/ CatOS version 5.5.7a auxiliaryvlan on Catalyst 6509 w/ CatOS version 5.5.3a auxiliaryvlan on Catalyst 4000 w/ CatOS version 7.2.2 auxiliaryvlan on Catalyst 4000 w/ CatOS version 6.3.3 auxiliaryvlan on Catalyst 4000 w/ CatOS version 5.5.15 auxiliaryvlan on Catalyst 4000 w/ CatOS version 5.5.7a voice vlan on Catalyst 3524 with IOS version 12.0.5

Therefore, the current Avaya position is that both the auxiliaryvlan (implicit 802.1Q trunking) and explicit

802.1Q trunking appear to be viable options when a dual-VLAN environment is required (see Appendix A). It is left to the user to choose the method. The benefits of using the auxiliaryvlan are simpler configuration and no known issues with the ability to enable portfast. However, auxiliaryvlan is a Cisco proprietary mechanism and is not subject to constraint by a standards body or by Avaya. 802.1Q trunking is well tested, successfully deployed , and defined by a standards body. But the inability to enable portfast on some CatOS versions is an obstacle that merits the use of the auxiliaryvlan instead. For IOS-based Catalyst switches the voice vlan is roughly equivalent to the auxiliaryvlan, but there appear to be no configuration or functionality benefits to using the voice vlan

Note that Avaya IP phones still do not interoperate with CDP. Therefore, although the auxiliaryvlan can be used, the mechanism of discovering the auxiliaryvlan via CDP is not supported. The Avaya IP phone can learn the auxiliaryvlan designation via DHCP option 176, as explained below and in Appendix A.

How it Works

At the heart of this feature are Cisco-proprietary mechanisms. The first proprietary mechanism is CDP (Cisco Discovery Protocol). This is a layer 2 protocol, which means that it works at the Ethernet level, without requiring IP addresses. Cisco devices identify themselves to other Cisco devices using CDP packets that contain device- and port-specific information. (CDP packets can be captured and decoded using protocol analyzers that support CDP.) With certain devices the CDP packets contain information that is specific to VoIP and other realtime applications. This VoIP information exchange requires CatOS (Catalyst Operating System) version 5.5 or higher on Catalyst 4000, 5000, 6000, and 6500 series switches and 2948G and 2980G switches. The voice vlan is supported on the Catalyst 2900XL and 3500XL series switches running IOS 12.0.5XU and higher. [1 p.2-22]

Using CDP, the Catalyst sends the Cisco IP phone an auxiliaryvlan ID, if auxiliaryvlan is enabled phone tags its frames to be forwarded on that VLAN. The auxiliaryvlan is the second Cisco-proprietary mechanism, and it must be enabled

on the port that connects to the IP phone. It is VLAN 200 by default or can be arbitrarily

assigned as any number between 1 and 1000. According to Cisco’s documentation the auxiliaryvlan is just another

802.1Q VLAN. The only difference is the proprietary method of assigning it to a Cisco IP phone. The port with the auxiliaryvlan also has a port/native VLAN (VLAN 1 by default or any arbitrarily assigned VLAN). This implies that the port is an 802.1Q trunk port with two VLANs, and can accept 802.1p/Q tagged frames. This is similar to the VLAN binding feature on the Avaya P330 v3.2.8 and later. [1 p.2-22, 2-23]

, and the

SM Avaya IP Telephony Implementation Guide

The information passed from the Cisco phone to the Catalyst is not of concern. The phone communicates its specific power requirements to the Catalyst, and the phone can also trigger the Catalyst to send its CDP packet immediately instead of waiting for the transmit period (60 seconds by default) to recycle. [1 p.2-23]

Avaya IP Phones on Cisco Auxiliaryvlan

The auxiliaryvlan is a modified method of implementing 802.1Q trunking, and it may be nothing more than this. Although testing to date has been positive, Avaya does not know what other mechanisms are or will be incorporated with this feature, or if they could have any adverse effects on Avaya IP phones. Assuming that an auxiliaryvlan-enabled port is truly a standard 802.1Q trunk port, the following steps allow Avaya I P phones to work on Cisco’s auxiliaryvlan.

1) Verify that the auxiliaryvlan is enabled.

a) For example, the command set port auxiliaryvlan 2/4-8 500 would make ports 2/4 through 2/8

auxiliaryvlan-capable with auxiliaryvlan ID 500.

b) The command set port auxiliaryvlan 2/4-8 (w/o the 500) would make ports 2/4 through 2/8 auxiliaryvlan-

capable with the default auxiliaryvlan ID 200.

c) The command show port auxiliaryvlan reveals the ports that have been made auxiliaryvlan-capable, and

their respective auxiliaryvlan ID(s). The command show port reveals each port’s port/native VID.

2) Bring up the phones on the auxiliaryvlan using the same procedures that would be used on a regular trunk port.

a) Verify that a L3 router interface exists for both the port/native VLAN and the auxiliaryvlan, with an

associated subnet and gateway IP address. Both interfaces must be configured to forward DHCP requests

(ip helper-address <IP addr. of DHCP server>) to the DHCP server if the server is on a different subnet.

b) Follow the instructions at the end of appendix A to get the IP phone on the auxiliaryvlan (voice VLAN). c) After the phone boots up, press Hold ADDR # to verify that the phone received an IP address and

associated information for the auxiliaryvlan.

3) For call servers, IP boards (ie, C-LAN and MedPro), and other VoIP resources, configure their ports on the Eth-

switch to be native to the auxiliaryvlan. That is, these ports do not require both a port/native VLAN and an auxiliaryvlan. Just make the auxiliaryvlan the port/native VLAN on these ports (set vlan 200 <mod/port>, assuming 200 is the auxiliaryvlan ID). Then disable the auxiliaryvlan feature on these ports (set port auxiliaryvlan <mod/port> none).

4) Always verify network connectivity between devices using pings and trace-routes.

SM Avaya IP Telephony Implementation Guide

Appendix C: RTP Header Compression

RTP header compression is a mechanism that reduces the protocol overhead associated with VoIP audio packets. It is a function of the network RTP header compression there are also cautions, and this appendix discusses both.

Application Perspective

Here is the anatomy of a 20-ms G.729 audio packet, which is recommended for use across limited bandwidth WAN links. Notice that two-thirds of the packet is consumed by overhead (IP, UDP, and RTP), and only one-third is used by the actual audio.

IP Header

20 B

It is important to understand that all Not only is the structure of the packet the same, but the method of encoding and decoding the audio itself is also the same. This sameness is what allows an Avaya IP phone to communicate directly with a Cisco IP phone, or any other IP phone, when using matching codecs. The packets from the application perspective are identical.

Network Perspective

RTP header compression is a mechanism employed by routers to reduce the 40 bytes of protocol overhead to approximately 2 to 4 bytes [7 p.1] [2 p.5-14]. Cisco routers employ this mechanism, as does the Avaya X330WAN router, which is a module for the P330 chassis. RTP header compression can drastically reduce the VoIP bandwidth consumption on a WAN link when using 20-ms G.729 audio. When the combined 40-byte header is reduced to 4 bytes, the total IP packet size is reduced by 60% (from 60 bytes to 24 bytes). This equates to reducing the total VoIP WAN bandwidth consumption by roughly half, and it applies to all packets, regardless of the vendor.

Customers who deploy routers capable of this feature may be able to benefit from it. However, Cisco recommends caution in using RTP header compression because it can significantly tax the processor if the compression is done in software. Depending on the processor load before compression, enabling RTP header compression could significantly slow down or crash the router. For best results, use a hardware/IOS/interface module combination that permits the compression to be done in hardware [3 QC-333] [5 “RTP Header Compression and QoS”].

RTP header compression has to function with exactness or it will disrupt audio. If for any reason the compression at one end of the WAN link and decompression at the other end do not function properly, the result could be intermittent loss of audio or one-way audio. This has been very difficult to quantify, but there is some anecdotal evidence. One production site in particular experienced intermittent one-way audio whose cause was very difficult to troubleshoot and isolate. When RTP header compression was disabled, simply for experi me ntation purposes, the audio problems went away.

The Test

This section details the results of a simple RTP header compression te st conducted in a lab environment. Although this t est was conduc t ed using Cisco routers, the expected behavior is the same for any router that performs this function as specified in RFC 2508 [7]. This test was performed in the following lab configuration.

and not a function of the VoIP application. Along with the benefits of using

UDP Hdr

8 B

RTP Header

12 B

20ms of G.729 Audio

20B

20-ms G.729 audio packets, regardless of the vendor, are constructed like this.

20-ms G.729 audio

SM Avaya IP Telephony Implementation Guide

- NetIQ Chariot v4.0 was used to simulate VoIP calls between the two endpoints. Chariot v4.0 accurately

simulates the characteristics of various codecs and uses a 40-byte IP/UDP/RTP header.

- Sniffer Pro v3.50.02 was used to capture the sent and received packets.

- The Cisco 3600 had IOS v12.1(2)T and the Cisco 1600 had IOS v12.0(12).

- The Fredericks Engineering Parascope WAN probe was tapped int o the V.35 serial l i nk to take bandwid th

measurements.

- This test was performed using PPP encapsulation on the WAN link.

A single call was placed between the Chariot endpoints using various codecs, all sending 20-ms voice packets. Be low are the results with and without RTP header compression. Note that these are rough measurements

Packets/sec

bytes/packet

Avg WAN BW consumption (kbps) Codec Payload w/o compression w/ compre ssion

% reduction

G.711 (64 kbps) 160 50 84 68.5 ~18 % G.729A (8 kbps) 20 50 27.5 13 ~53%

For each codec there was an attempt to verify that the audio packets were received in tact. This was done by spot-checking the audio packets before and after compression, using two Sniffer protocol analyzers. For every codec except G.711 the RTP header and payload were identical before and after compression. With G.711, however, the received packets had the PADDING flag set in the RTP header, although the flag was not set when the packets were transmitted. The PADDING flag indicates the presence of padding octets at the end of the RTP payload, which cannot be true for G.711. Why this occurred is unknown, but it does not really matter because there is no point in using the G.711 codec if bandwidth is scarce.

Configuration

To configure RTP header compression on a Cisco router,

1. Specify the number of RTP connections that can be compressed (cache allocation). In interface configuration

mode, the command is ip rtp compression-connections <number>. The default is 32, and each call requires two connections. The configurable range is 3 to 256 for PPP and HDLC using IOS v11.3 and later; and 3 to 1000 for PPP and HDLC using IOS v12.0(7)T and later. For Frame Relay the value is fixed at 256.

2. The command to turn on compression is ip rtp header-compression in interface configuration mode. It must

be implemented at both ends of the WAN link. For this experiment, when the command was entered into the router, ip tcp header-compression was also installed automatically. When either command was removed the other was automatically removed.

Consult Cisco’s documentation for more specific configurations on other types of WAN links (ie, Frame Relay and ATM) [2 p.5-14, 5-18, 5-26, 5-33] [3]. Configuration for the X330WAN router is very similar to Cisco and well documented in the X330WAN User Guides.

SM Avaya IP Telephony Implementation Guide

Appendix D: Access List Guidelines

This appendix gives guidelines for configuring access lists to facilitate basic Avaya IP telephony functionality. The ports used by the Avaya call server are fairly fixed and known. The ports used by the endpoints are more variable and random. As a result, it is simpler to tailor access lists based on call server ports.

Action From TCP/UDP port

or Protocol

The C-LAN uses UDP port 1719 for endpoint registration (RAS). Permit Any C-LAN UDP 1719 Any endpoint UDP any Permit Any endpoint UDP any Any C-LAN UDP 1719 The C-LAN uses TCP port 1720 for H.225 call signaling. Permit Any C-LAN TCP 1720 Any endpoint TCP any Permit Any endpoint TCP any Any C-LAN TCP 1720 This is to facilitate IP trunking between two Avaya call servers, and must be done for each IP trunk. Permit Near-end C-LAN TCP 1720 Far-end C-LAN TCP 1720 Permit Far-end C-LAN TCP 1720 Near-end C-LAN TCP 1720 This is one way to facilitate audio streams between MedPros and endpoints. Permit Any MedPro UDP port range

in ip-networkregion form

Permit Any endpoint UDP any Any MedPro UDP port range in

This is another way to facilitate audio streams between MedPros and endpoints. Permit Any MedPro RTP/RTCP Any endpoint -- Permit Any endpoint RTP/RTCP Any MedPro -This is to facilitate audio streams between direct IP-IP (shuffled) endpoints. Permit Any endpoint

UDP any

RTP/RTCP The R300 uses this default UDP port range for audio. However, the range is configurable. Permit Any R300

UDP 1900-2075

RTP/RTCP Permit Any MedPro or endpoint

UDP varies

RTP/RTCP Permit Any R300

UDP 1900-2075

RTP/RTCP These are a ll services used by the IP telephone. TFTP is tough to isolate to a po rt range. The GET and PUT requests from the client go to the server’s UDP port 69, but all other messages go between random ports. Permit Any IP telephone (hardphone) UDP an y DNS server(s) UDP 53 (dns) Permit DNS server(s) UDP 53 (dns) Any IP telephone (hardphone) UDP any Permit Any IP telephone (hardphone) UDP 6 8 (bootpc) DHCP server(s) UDP 67 (bootps) Permit DHCP server(s) UDP 67 (bootps) Any IP telephone (hardphone) UDP 68 (bootpc) Permit Any IP telephone (hardphone) TFTP TFTP server(s) -Permit TFTP server(s) TFTP Any IP telephone (hardphone) -Permit SNMP mana ge me n t station(s) UDP any Any IP telephone (hardphone) UDP 161 (snmp) Permit Any IP telephone (hardphone) UDP 161 (snmp) SNMP mana ge men t stati o n( s) UDP any Avaya devices ping other devices for various reasons. For example, C-LANs ping endpoints for management purposes; MedPros ping C-LANs to gauge network performance across an IP trunk; IP telephones ping TFTP servers for verification purposes. Permit Any Avaya device ICMP Echo Any -Permit Any ICMP Echo

To TCP/UDP port

or Protocol

Any endpoint UDP any

ip-network-region form

Any endpoint

UDP any

Any MedPro or endpoint

UDP varies

Any R300

UDP 1900-2075

Any R300

UDP 1900-2075

Any Avaya device --

SM Avaya IP Telephony Implementation Guide

The following table contains access list guidelines for Avaya media servers and media gateways. The S8700 enterprise interface, which is the one connected to the enterprise network (vs. the control network), is eth4 on Multi-Connect systems and eth0 on IP-Connect systems.

Action From TCP/UDP port

or Protocol

To TCP/UDP port

or Protocol

This allows the S8500/8700 to synchronize translations with the S8300 LAN Spare Processor (LSP). A TCP session is initiated from the S8500/8700 to the S8300 TCP port 514. A second session is then initiated from the S8300 to the S8500/8700 TCP port range 512-1023. Permit S8700 enterprise interface TCP any S8300 LSP TCP 514 Permit S8300 LSP TCP 514 S8700 enterprise interface TCP any Permit S8300 LSP TCP any S8700 enterprise interface TCP 512-1023 Permit S8700 enterprise interface TCP 512-1023 S8300 LSP TCP any This allows an administrator to log in via Avaya SA to a call server (S8500/8700 and S8300). Permit Avaya SA workstation TCP any S8700-ent-intf or S8300 TCP 5023 Permit S8700-ent-intf or S8300 TCP 5023 Avaya SA workstation TCP any This allows secure and unsecure web access to a call server (S8500/8700 and S8300). The call server redirects unsecure sessions to https. Permit Web admin station TCP any S8700-ent-int or S8300 TCP 80 Permit S8700-ent-int or S8300 TCP 80 Web admin station(s) TCP any Permit Web admin station TCP any S8700-ent-int or S8300 TCP 443 Permit S8700-ent-int or S8300 TCP 443 Web admin station(s) TCP any Optional services used by S8500/8700 and S8300. Permit S8700-ent-int or S8300 UDP any DNS server(s) UDP 53 (dns) Permit DNS server(s) UDP 53 (dns) S8700-ent-int or S8300 UDP any Permit S8700-ent-int or S8300 UDP any NTP server(s) UDP 123 (ntp) Permit NTP server(s) UDP 123 (ntp) S8700-ent-int or S8300 UDP any H.248 signaling between G700 Media Gateway and S8300 or CLAN. G700 initiates session. Permit G700 TCP any S8300 or CLAN TCP 2945 Permit S8300 or CLAN TCP 2945 G700 TCP any Control network traffic and other traffic between S8500/8700 and IPSI board. Permit Call server IP any IP SI board IP any Permit IPSI board IP any Call server IP any

SM Avaya IP Telephony Implementation Guide

Appendix E: Common IP Commands

Cisco CatOS Switches (6500, 6000, 5000, 4000) set port speed <mod/port> ? set port duplex <mod/port> ? show port show port <mod/port> clear counters ?

set port host ? clear port host ?

set spantree portfast <mod/port> ? show spantree [<mod/port>]

set vlan <vlan id> <mod/port> set port auxiliaryvlan <mod/port> <vid> set port auxiliaryvlan <mod/port> none show port auxiliaryvlan ?

set trunk all off set trunk <mod/port> ? clear trunk <mod/port> clear trunk <mod/port> <vid(s)>

show trunk ? OR show port trunk ? show vlan ?

Cisco IOS Switches (3500XL, 2900XL)

Global commands

show running-config

show startup-config copy running-config startup-config

show interfaces status show interfaces [fast|gig <mod/port>] clear counters [fast|gig <mod/port>] show controllers ethernet-controller ? clear controllers ethernet-controllers ? show vlan

Interface commands

speed ? duplex ? spanning-tree portfast switchport access vlan <vid>

switchport mode trunk switchport trunk encapsulation dot1q switchport trunk allowed vlan ? switchport trunk native vlan

sets the speed for given port (s) sets the duplex for given port(s) displays settings and status for all ports displays settings, statistics, and err ors for given port clears statistics and error counters on all ports or given port(s)

disables channeling/trunking; enables portfast on all or given port(s) opposite of set port host

enables or disables spanning tree fast start feature on given port(s) displays spanning tree and portfast info for all ports or given port(s)

sets the nati ve vlan (default vlan) for given port(s) sets the auxiliary vlan for given port(s) removes auxiliary vlan from given port(s) displays auxiliary vlan information

disables trunking on all ports sets trunking mode for given port(s) puts given port in auto trunk mode with negotiating encapsulation removes specified vlans from given trunk port(s) (all vlans are permitted on trunk by default) displays trunking information for all ports or given port displays vlan configuration informatio n

displays all configurations currently running on switch displays all configurations in NVRAM to be used at next boot-up must be executed to save running configuration to NVRAM (not necessary on CatOS switches, except on router module)

displays settings and status for all ports displays port(s) status, statistics, and errors at the interface level clears show interfaces counters displays port(s) statistics and errors at the controller level clears show controllers counters displays vlan configuration informatio n

These commands are executed on a port by port basis. sets the port speed sets the port duplex enables spanning tree fast start feature (no to undo) sets the native vlan (default vlan) when port is in access mode (default is access mode, where there is only one vlan on port) puts port in trunk mode makes trunk 802.1Q (instead of ISL) specifies vlans permitted on trunk port (default is all vlans) sets the native vlan (default vlan) when port is in trunk mode

SM Avaya IP Telephony Implementation Guide

Avaya P550/580 and P880/882 Switches show running-config show startup-config copy running-config startup-config

set port auto-negotiation <mod/port> ? set port speed <mod/port> ? set port duplex <mod/port> ? show port status ? show port counters ? show ethernet counters ? clear port counters ?

set port fast-start <mod/port> ? show port [<mod/port>]

set port vlan <mod/port> <vid>

set port trunking-format <mod/port> ? set port vlan-binding-method <md/pt> ? show port [<mod/port>] show vlan ?

set port negotiation <mod/port> ? set port speed <mod/port> ? set port duplex <mod/port> ? show port [<mod/port>] show rmon statistics <mod/port>

set port spantree ? <mod/port> show spantree [<mod/port>]

set port vlan <vid> <mod/port>

set trunk <mod/port> ? set port vlan-binding-mode <mod/prt> ? show trunk [<mod/port>] show vlan ?

Avaya SAT and IPSI Interfaces

change ethernet-options

display ethernet-options

get ethernet-options <slot #>

IPSI commands

set port negotiation 1 enable|disable set port speed 1 100MB|10MB set port duplex 1 full|half show port 1

show control stats

enables or disables speed/duplex negotiation for given port(s) sets the speed for given port (s) sets the duplex for given port(s) displays settings and status for all ports or given port(s) displays high level TX and RX statistics for all po r ts or given port(s) displays detailed statistics and errors for all ports or given port(s) clears statistics and error counters on all ports or given port(s)

enables or disables spanning tree fast start feature on given port(s) displays spanning tree and fast start info for all ports or given port(s)

sets the port vlan (default vl an) for given port(s)

sets trunking mode for given port(s) sets the vlan binding method for given port(s) displays trunking and vlan-binding info for all ports or given port(s) displays vlan configuration informatio n

Avaya P330 Switches

enables or disables speed/duplex negotiation for given port(s) sets the speed for given port (s) sets the duplex for given port(s) displays settings and status for all ports or given ports(s) displays statistics and errors for given port(s) (must reset switch to clear these counters)

enables or disables spanning tree on given port (no fast start on P330) displays spanning tree information for all ports or given port

sets the port vlan (default vl an) for given port(s)

sets trunking mode for given port(s) sets the vlan binding mode for given port(s) displays trunking and vlan-binding info for all ports or given port(s) displays vlan configuration informatio n

sets the speed and duplex for IP boards (board must be disabled before change and enabled after change using ip-interface form) displays administered speed and duplex for IP boards compares administered vs. actual speed and duplex for given IP board

These commands are executed from the IPSI [IPADMIN] prompt. enables or disables IPSI control port (port 1) speed/duplex negotiation sets control port speed sets control port duplex displays control port status and configuration displays control port statistics and errors

SM Avaya IP Telephony Implementation Guide

Appendix F: Sample QoS Configurations

This appendix gives simple examples of configuring QoS on Cisco routers. It is only meant to give the

reader a starting point. Consult Cisco’s documentation for a full explanation of Cisco’s QoS implementation.

This rudi mentary network configuration is used as a refer ence point. The objective is to assure high quali ty

of service to VoIP applications across the congested WAN link.

Example 1

Suppose all endpoints are capable of tagging with DSCP 46 or 34 (the defaults for audio and signaling). This would be true in an Avaya Communication Manager system with TN799DP C-LAN boards running firmware v5 or later. Previous firmware versions and the T N799C board ca nnot tag at L2 or L3. A matching set of configura tions is applied to both routers.

class-map match-any VoIP match ip dscp 46 match ip dscp 34

policy-map voipQoS class VoIP priority 768 class class-default fair-queue random-detect dscp-based

interface Serial0 description T1 ip address 172.16.0.1 service-policy output voipQoS

create a class map called VoIP any packet with DSCP 46 or 34 is in the class VoIP

create a policy map called voipQoS give strict priority to packets in the class VoIP on up to 768k of this WAN link put everything else in the default class and transmit it out the default queue in a fair queue fashion if the default queue starts to get full, randomly discard packets in this queue based on DSCP (lower values get discarded first)

apply the voipQoS policy outbound on this interface In this example there is no distinction between DSCP 46 and 34, because they are treated the same by the routers. This being the case, it would be equally effective to use just one code point throughout. If, however, the class VoIP only included DSCP 46, the 34 packets would end up in the default queue, in which case the “dscp-based” discard method would be very significant.

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Example 2

Suppose now that C-LANs 192.168.1.10 and .11 cannot tag their traffic (pre-Communication Manager system). This set of configurations is applied only to the left router.

access-list 101 permit ip host 192.168.1.10 192.168.2.0 0.0.0.255 access-list 101 permit ip host 192.168.1.11 192.168.2.0 0.0.0.255

access list 101 permits any IP traffic from the two C-LANs to the 192.168.2.0/24 network there is an implicit deny any at the end of this access list

class-map match-any untaggedVoIP match access-group 101

policy-map setDSCP class untaggedVoIP set ip dscp 46

interface Ethernet 0/0 service-policy input setDSCP

create a class map called untaggedVoIP

packets matching access list 101 are in the class untaggedVoIP

create a policy map called setDSCP

for all packets in the class untaggedVoIP set the DSCP to 46

apply the setDSCP policy inbound on this interface Now the C-LAN traffic is also tagged with DSCP 46, as in example 1, and the example 1 configurations must be applied to both routers.

Example 3

This is the same as example 1, but with more restrictions on the traffic. In this example DSCP 46 is used throughout to simplify the access list. A somewhat matching set of configurations is applied to both routers.

access-list 101 permit ip 192.168.1.0 0.0.0.255 192.168.2.0 0.0.0.255 dscp 46 (left router) access-list 101 permit ip 192.168.2.0 0.0.0.255 192.168.1.0 0.0.0.255 dscp 46 (right router)

access list 101 permits any IP traffic that is tagged with DSCP 46 between the two VoIP subnets there is an implicit deny any at the end of this access list

class-map match-any VoIP match access-group 101

policy-map voipQoS class VoIP priority 768 class class-default fair-queue random-detect dscp-based

interface Serial0 description T1 ip address 172.16.0.1 service-policy output voipQoS

create a class map called VoIP

only packets matching access list 101 are in the class VoIP; this is

more restrictive than matching any packet with DSCP 46 or 34

the remainder of the configurations is identical to example 1

create a policy map called voipQoS

give strict priority to packets in the class VoIP on up to 768k of this

WAN link

put everything else in the default class and transmit it out the default

queue in a fair queue fashion

if the default queue starts to get full, randomly discard packets in this

queue based on DSCP (lower values get discarded first)

apply the voipQoS policy outbound on this interface If any of the endpoints were incapable of tagging, the “dscp 46” could be removed from access list 101. Then any traffic between the two VoIP subnets, regardless of the tag, would be in the class VoIP.

SM Avaya IP Telephony Implementation Guide

Appendix G: IP Trunk Bypass – TDM Fallback Q&A

Q1: How does the IP trunk bypass (aka TDM fallback) feature work, and how should the parameters be set on

the system-parameters ip-options form? How do these settings affect the IP trunk bypass feature?

The system-parameters ip-options form is used to define the thresholds that trigger a fallback to a TDM trunk, thus bypassing the IP trunk. For this feature to work, the ‘Bypass if IP Threshold Exceeded’ parameter must be set to ‘y’ in the signaling-group form for an IP trunk. The Avaya document, “How to Configure IP T runk Bypass to a PSTN Trunk…,” at www1.avaya.com/enterprise/resourcelibrary/applicationnotes/eclips_configuration.html explains this feature and configuration in more det ail. Simply stated, a near-end MedPro monitors network per formance by pin ging the farend C-LAN to measure network response against the configured thresholds.

One thing to note about the IP trunk bypass feature is that it is not fully platform. The VoIP module in the G700 does not behave exactly like the MedPro board, and it cannot perform the ping functions that a MedPro performs. The issues with an S8300/G700 are discussed throughout this appendix.

When a high threshold is reached the signaling group goes into bypass state, and a fallback TDM trunk is utilized. When the corresponding low threshold is re-established the signaling group comes back into service, and the IP trunk is utilized. Because networks and user preferences vary, there is no single set of optimal thresholds. This is a feature that must be tested and fine-tuned with each implementation. The parameters are as follows.

- Roundtrip Propagation Delay (ms) High: 400-500ms is a good starting point for this threshold. Many users

begin to notice performance degradation at around 200-250ms one-way delay.

- Roundtrip Propagation Delay (ms) Low: 200-300ms is a good starting point for this threshold. 100-150ms or

less one-way delay typically results in very acceptable audio quality.

- Packet Loss (%) High: 7-10% is a good starting point for this threshold. Avaya Labs testing has shown that

audio quality is acceptable even with 5% packet loss.

- Packet Loss (%) Low: 0-3% is a good starting point for this threshold.

- Ping Test Interval (sec): This is the frequency at which pings are sent out. The lower the interval the better for

measuring network performance. In loads prior to Avaya Communication Manager 2.1 the low limit is 10sec, which is sufficient for detecting a network outage but not for measuring network performance. With Communication Manager 2.1 and MedPro firmware v70 the minimum ping test interval is 1sec, which is granular enough to gauge network performance. 1-2 sec is a good starting point for this parameter.

- Number of Pings per Measurement Interval: This is the number of pings sent out before delay and loss are

calculated. 10 should be used here for a minimum ping test interval of 10sec, which results in calculations every 100sec to detect a network outage. With Communication Manager 2.1 and MedPro firmware v70, 20 to 30 pings at 1-second intervals results in calculations every 20 to 30 seconds, which provides the granularity required to gauge network performance.

Because pings are used to determine network performance, the IP network should ideally give the pings (ICMP Echoes and Echo Replies) between MedPros and C-LANs the same priority as audio traffic. To facilitate this it is important to know that the call server can select any MedPro in the near-end system’s network region to originate the pings. Depending on the network, it may be feasible to activate this feature without deploying any network policies for the pings, especially if the primary concern is to compensate for network outages and no t necessarily for poor performance.

Q2: Besides the IP trunk bypass feature, what other mechanisms are in place to detect an outage or severe congestion in the IP network, and how long does it take to detect it?

See section 3.7, heading “trunk-group and signaling-group” for details on the LRQ feature that applies to individual calls placed over an I P trunk. For the IP trunk as a whole the best method is the IP trunk bypass feature. In addition there is also a Maintenance Function. This function assesses the IP trunk every 15 minutes in a G3r or Linux platform, and every hour in a G3i platform. Without going into detail, the Maintenance Function determines

supported on the S8300/G700

SM Avaya IP Telephony Implementation Guide

whether the signaling group is in service or out of service. It can detect a network outage, but it does not assess network performance.

A third method was implemented as of Avaya Communication Manager 1.3. With this method a failure to set up a signaling link triggers the Maintenance Function t o assess the IP trunk immediately. Assuming the failure to set up the signaling link is the result of a network outage, the Maintenance Function detects this and puts the signaling group out of service within one minute. For example, suppose there is an IP trunk between an S8700 system and an S8300/G700. There is an outage in the IP network between the two systems and the S8700 discovers this after a measurement interval (IP trunk bypass feature). The S8700 puts the signaling group in bypass state and begins using the fallback TDM trunk. The S8300/G700 normally does not detect the outage until the next Maintenance Function cycle. However, if the S8300 attempts to place a call over the IP trunk and cannot establish a signaling link to the other end, this triggers the Maintenanc e Function immed i ately, which takes the signaling group out of service, causing the fallback TDM trunk to be used. So the S8300 detects the outage less than one minute after the first call attempt.

The scenario for severe congestion is different. In the case of severe congestion the S8700 detects the congestion and puts the signaling group in bypass state, the same as with a network outage. It then sends a message to the S8300 indicating this condition. (This message is also sent in the network outage case, but it doesn’t reach the far end because of the outage.) The status signaling-group command at the S8700 shows the signaling group in bypass state. The same command at the S8300 shows the signaling group in far-end bypass state. In this condition both sides use the fallback TDM trunk until the S8700 puts the signaling group back into service.

Q3: As a follow-up to the previous question, what are the effects of the two sides not detecting the outage at exactly the same time?

Both sides accept incoming calls on TDM trunks, regardless of the state of IP trunks. So if side A detects an IP network outage and calls side B via the TDM trunk instead of the IP trunk, side B accepts the call. Side B continues to attemp t using the IP trunk until it detects the outage, a t which time it utilizes the TDM trunk for its outbound calls.

In the case of severe congestion, side A detects the congestion first, goes to bypass state, and starts using the TDM trunk. This causes side B to go to far-end bypass state and also use the TDM trunk. Eventually side B detects the congestion and goes to bypass state as well.

Q4: When the IP network recovers after an outage or severe congestion, do both sides discover this at the same time and star t sending calls over the IP trunk at the same time? If not, what are the effects?

No, as with detecting the failure, detecting the recovery is also independent. But this is usually not a problem because both sides accept incoming calls on an IP trunk in bypass state. So if side A detects the IP network recovery first and calls side B while B is still in bypass state, side B accepts the call. However, the same is not true if side B is in out of service state.

The scenario for severe congestion is the same.

Q5: If the C-LAN or S8300 on one end of the IP trunk fails, does the IP trunk cover to a different C-LAN or S8300?

No, the IP t runk has fixed termination point s. If one of the points fails the IP trunk goes out o f service almost immediately at the local system where the failure occurred. This is especially true for an S8300 because it is the call server and not just a call signaling board like the C-LAN. At the remote system (the other end of the IP trunk) the IP trunk eventually goes out of service as follows. The IP trunk bypass feature puts the si gnaling group i n bypass state (unless the system is an S8300/G700). The Maintenance Function, either at the normal interval or

SM Avaya IP Telephony Implementation Guide

triggered by a call attempt, puts the signaling group out of service. Depending on which of these occurs first the signaling group may go into bypass and then out of service, or out of service directly. A way to compensate for this type of outage is to administer multiple IP trunks (signaling groups and trunk groups) across multiple C-LANs between the same systems.

Q6: What about a MedPro or VoIP module failure at either end of the IP trunk?

The IP trunk is not tied to any given MedPro or VoIP module . As long as there is at least one MedPro or VoIP module at each end with available DSP resources, the IP trunk is unaffected by MedPro or VoIP module failures. If all usable Medpros or VoIP modules fail, the IP trunk’s trunk group members go out of service, but the signaling group stays in service and can be used to send messages between the two systems. This essentially re sults in a bypass conditio n where the TDM trunk is utilized.

Q7: How is call processing affected in general by a C-LAN outage?

When configured properly t he stations and media gateways ha ve a list of alter nate gatekeepe rs. They discover if a C-LAN they are registered with has gone down, and re-home to a different C-LAN. If the C-LAN failure occurs during an active call, the H.323 and H.248 link bounce recovery features preserve active calls on stations and media gateways, respectively.

Q8: How is call processing affected in general by a MedPro or VoIP module outage?

The call server knows when a MedPro or VoIP module has gone out of service and stops directing calls to that device. As long as there are sufficient MedPros or VoIP modules to compensate for the outage, there is no adverse effect. If there is an outage during an active call, and that call is going through the affected MedPro or VoIP module, that call loses audio. Avaya is studying the concept of redirecting an active call to a different MedPro or VoIP module in this type of failure.

Q9: How is call processing affected in general by an IP trunk outage?

If the IP trunk outage is the result of a C-LAN/S8300 failure, direct IP-IP calls remain up until one of the IP phone users goes on hook. If the IP trunk outa ge is the result of a MedPro/VoIP failure, existing calls are affected as previously described. If the IP trunk outage is the result of the IP network goi ng down, the audi o is lost on active calls, and new calls are routed over the fallback TDM trunk if one is administered.

SM Avaya IP Telephony Implementation Guide

References

[1] Cisco Systems, Inc., “Cisco IP Telephony Network Design Guide,” www.cisco.com, Customer Order Number:

[2] Cisco Systems, Inc., “Cisco IP Telephony QoS Design Guide,” www.cisco.com, Customer Order Number:

[3] Cisco Systems, Inc., “Configuring Compressed Real-Time Protocol,” www.cisco.com, July 2002.

[4] Cisco Systems, Inc., “Troubleshooting Cisco Catalyst S w itches to Network Interface Card (NIC) Compatibility

Issues,” www.cisco.com, July 2002.

[5] Cisco Systems, Inc., “Understanding Compression (Including cRTP) and Quality of Service,” www.cisco.com,

July 2002.

[6] IEEE, Inc., “802.1Q: IEEE Standard for Local and Metropolitan Area Networks: Virtual Bridged Local Area

Networks,” www.iee.org, December 8, 1998.

[7] IETF, “RFC 2508: Compressing IP/UDP/RTP Headers for Low-Speed Serial Links,” www.ietf.org,

February 1999.

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