Avaya IP Voice Quality Network Requirements User Manual

AVAYA IP VOICE QUALITY NETW O R K REQ UI R E M E NTS

White paper

Issue 3.2

August 2009

Developed by: Avaya, Inc.

Westminster, Colorado

Printed in U.S.A.

TRADEMARK NOTICE

Avaya and the Avaya Logo are trademarks of Avaya Inc. and may be registered in certain jurisdictions. All trademarks identified by

® or ™ are registered trademarks and trademarks respectively of

Avaya Inc. All other trademarks are the property of their respective owners.

NOTICE

While reasonable efforts were made to ensure the information in this document was complete and accurate at the time of printing, Avaya can assume no responsibility for any errors. Changes and corrections to the information contained in this document may be incorporated

into future releases.

Contents

1 Document Summary ............................................................................................ 4

Avaya IP Voice Quality Network Requirements ............................................................... 7

Explanations ............................................................................................................ 7

2 Introduction ........................................................................................................ 7

3 Defining Quality .................................................................................................. 8

3.1 What is Quality? ............................................................................................. 8

3.2 What is Voice Quality? ..................................................................................... 8

4 Prioritizing Voice Traffic ........................................................................................ 8

4.1 Understanding the difference between CoS and QoS ........................................... 8

4.2 Using Ports .................................................................................................... 9

4.3 Using DSCP (or TOS) ....................................................................................... 9

4.4 Using IEEE 802.1 p/Q ...................................................................................... 9

4.5 Using VLANs ................................................................................................. 10

5 Network Parameters .......................................................................................... 10

5.1 Network Packet Delay .................................................................................... 10

5.2 Network Jitter ............................................................................................... 11

5.3 Packet Loss .................................................................................................. 12

5.4 Network Packet Mis-Order .............................................................................. 12

5.5 Transcoding ................................................................................................. 13

5.6 Echo ............................................................................................................ 13

5.7 Silence Suppression and Voice Activity Detection .............................................. 13

5.8 Network Duplex ............................................................................................ 14

5.9 Codec Selection ............................................................................................ 14

6 Bearer Bandwidth .............................................................................................. 14

6.1 WAN Bandwidth Comparison .......................................................................... 15

6.2 LAN Bandwidth Comparison ........................................................................... 15

7 Network Assessment .......................................................................................... 16

8 PC Considerations using Avaya’s One X Communicator ........................................... 18

9 Bandwidth Requirements .................................................................................... 19

9.1 Bandwidth Requirements using IP SoftPhone (or IP Agent) ................................ 19

10 Other Elements that Affect VoIP ....................................................................... 20

10.1 WAN Considerations ................................................................................... 20

10.2 VPN (Virtual Private Network) ..................................................................... 20

10.3 Frame Relay ............................................................................................. 20

10.4 Multi Protocol Label Switching (MPLS) .......................................................... 21

10.5 Network Address Translation (NAT) ............................................................. 21

Appendix A .............................................................................................................. 22

Network Design Recommendations ........................................................................... 22

Best practices .......................................................................................................... 22

Common issues ........................................................................................................ 23

Appendix B .............................................................................................................. 25

Overview................................................................................................................. 25

Issue and Alternatives .............................................................................................. 26

Additional Frame Relay Information ............................................................................ 26

Appendix C .............................................................................................................. 27

VoIP without using NAT ........................................................................................... 27

Avaya IP Voice Quality Network Requirements

1 Document Summary

This document contains basic network requirements that are foundational for good voice quality when using Avaya IP products and solutions over a data network. No document can satisfy the detailed needs of every network, and therefore, this paper serves only as a starting point. The document summary provides a short list of networking requirements, allowances and recommendations. Use this page as a checklist to determine if the network meets the minimum requirements for implementing Voice over Internet Protocol (VoIP) with acceptable quality. The rest of the document contains basic networking and telephony

concepts for those who haven’t been exposed to a converged implementation. It also explains why VoIP applications can yield poor results when data traffic on the same network doesn’t

seem to have problems.

Voice quality is always a subjective topic. Defining ―good‖ voice quality varies with business

needs, cultural differences, customer expectations, etc. The requirements below are based on the ITU-T, EIA/TIA guidelines and extensive testing at Avaya Labs. Note that while

Avaya’s requirements will meet or exceed most customer quality expectations, the final determination of acceptable voice quality lies with the customer’s definition of quality and the

design, implementation and monitoring of the end to end data network.

Quality is not measured by one discrete value where a number where 8 is good and 9 is bad. There is a tradeoff between real-world limits and acceptable voice quality. Lower delay, jitter and packet loss values can produce the best voice quality, but may also come with a cost to upgrade the network infrastructure to get to the lower network values. Another real-world limit is the inherent WAN delay over a trunk linking, for example, the U.S. West coast to India. This link could easily add a fixed 150ms delay into the overall delay budget and is beyond the control of an enterprise. Perfectly acceptable voice quality is attainable but will not be ―toll‖ quality. Therefore, Avaya presents a tiered choice of values that make up the requirements.

Voice quality is made up of both objective and subjective contributors. The objective elements in assessing VoIP quality are delay, jitter and packet loss. These elements are defined and influenced in the transport of IP both within and outside an enterprise. To ensure good and consistent levels of voice quality, Avaya suggests the following network parameters. Note that these suggestions hold true for LAN only and LAN/WAN connectivity. All requirement values listed are measured between endpoints because this document assumes

that IP telephony has not yet been implemented. All values therefore reflect the network’s

performance without endpoint consideration. This is why there is, seemingly, a discrepancy between the well-known ITU-T value for one-way delay and the values listed. The ITU-T values are end-to-end values; from the mouth of the transmitter to the ear of the receiver. The network requirements listed are meant for the network only – between endpoints - so that your business data network can be assessed and modified, if need be, for successful deployment of real time applications like voice and video. The requirement values are also useful for ongoing network monitoring by IT staff. Upward trends in delay, jitter or packet loss serve as a warning of potential voice quality problems.

Also, please note that ―Business Communication Quality‖ is defined as slightly less than toll

but far better than cell-phone quality. This is the tier where most businesses experience the best trade-off between voice quality and network infrastructure costs.

Requirements for objective factors:

 Network delay: One-way Between endpoints,

o 80ms (milliseconds) delay or less can, but may not, yield toll quality. o 80ms to 180ms delay can give business communication quality. This is far

better than cell-phone quality and in fact is very well suited for the majority of businesses.

o Delays exceeding 180ms may still be quite acceptable depending on customer

expectations, analog trunks used, codec type, etc.

(See section 4.1 for more information)

 Network jitter: Jitter is a measure of the variability of delay. Between endpoints:

o Toll quality suggests average jitter be less than ½ the packet payload. This

value has some latitude depending on the type of service the jitter buffer has in

relationship to other buffers, packet size used, etc.

(See section 4.2 for more information)

 Network packet loss: The maximum loss of packets (or frames). Between

endpoints:

o 1% or less can yield toll quality depending on many factors. o 3% or less should give Business communications quality. Again, this quality is

much better than cell-phone quality.

o More than 3% may be acceptable for voice but may interfere with signaling.

(See section 4.3 for more information)

Recommendations: Avaya highly recommends consideration of the following list of Best Practices when implementing VoIP.

 QoS/CoS: Quality of Service (QoS) for voice packets is obtained only after a Class of

Service (CoS) mechanism tags and Network elements treat voice packets as having priority over data packets. Networks with periods of congestion can still provide excellent voice quality when using a QoS/CoS policy. Switched networks may use IEEE 802.1p/Q. Routed networks should use DSCP (DiffServ Code Points). Mixed networks may use both as a best practice. Port priority can also be used to enhance DiffServ and IEEE 802.1p/Q. Even networks with plentiful bandwidth should implement CoS/QoS to protect voice communications from periods of unusual

congestion such as from a computer virus. See sections 3.1 - 3.4 for more information.

 Switched Network: A fully switched LAN network is a network that allows full duplex

and full endpoint bandwidth for every endpoint that exists on that LAN. Although VoIP systems can work in a shared (hubs or bussed) LAN, Avaya recommends the

consistently high results a switched network lends to VoIP.

 Network Assessment: A Basic Network Readiness Assessment Offer from Avaya is

vital to a successful implementation of VoIP products and solutions. Contact the Avaya

representative or authorized dealer to review or certify your network. Section 7 ―Network Assessment‖ explains the options available with this offer.

 VLANs: Placing voice packets on a separate VLAN (subnet) from data packets is a

generally accepted practice to reduce both broadcast and data traffic from contending for the same bandwidth as voice. Other benefits become available when using VLANs, but there may be a substantial cost for initial administration and maintenance. Section

3.5 ―Using VLANs‖ further explains this concept.

Cautions: Avaya also recommends caution when using the following:

 NAT: Be cautious when using NAT (Network Address Translation). Some

implementations using VoIP endpoints behind NAT fail because H.323 messages contain multiple instances of the same IP address in a given message, and NAT can fail

to find and translate all of them. Avaya’s Communication Manager will work

seamlessly with any static NAT application even if that NAT is not H.323 aware. See section 10.4, "Network Address translation" and Appendix C for more information on using NAT.

 Analog Dial-Up: Be careful using analog dial-up (bandwidth  56K) to connect two

locations. Upstream bandwidth is limited to a maximum of 56K, but in most cases is less. This results in insufficient bandwidth to provide toll-quality voice. Some codecs and network parameters provide connections that are acceptable, but consider each

connection individually.

 VPN: Use Virtual Private Network (VPN) cautiously with VoIP applications. Older

systems can have large delays due to encryption, decryption and additional encapsulation. Many hardware-based products encrypt at near wire speed and can be used. Additionally, if the VPN routes over the Internet without SLAs in place, sufficient quality for voice cannot be guaranteed unless delay, jitter and packet loss adhere to the parameters listed above. See section 9.2 ―VPN (Virtual Private Network)‖ for more information.

Avaya IP Voice Quality Network Requirements

 Delay

 Jitter

 Packet loss

 Packet mis-order

 Available

bandwidth

 Packet prioritization

 Network design

 Endpoint audio characteristics

(sound card, microphone, earpiece, etc.)

 Duplex

 Transcoding

 Echo

 Silence suppression

 Codec selection

 Router and data-switch

configuration

 Reliability

 Scalability

 Manageability

 WAN protocols

 QoS/CoS policy

 Encryption/Decryption

Explanations

2 Introduction

Voice over Internet Protocol (VoIP) is the convergence of traditional voice onto an IP data network to provide better application integration by using a common protocol and to lower costs by using ISPs and melding separate support staffs. Other real-time traffic, such as uncompressed video and streaming audio, is also converging onto data networks.

VoIP is very complex because it involves components of both the data and voice worlds. Historically, these worlds have used two different networks, two different support organizations and two different philosophies. The voice network has always been separate from the data network because of the protocols used and the characteristics of voice applications are very different from those of data applications.

Traditionally, voice calls have had their own dedicated bandwidth throughout the circuit switched network. This provided an environment where ―five nine‖ of reliability became the standard. Interactive voice traffic is sensitive to delay and jitter but can tolerate some packet loss, problems that were rarely an issue with circuit switching.

The data network, on the other hand, is packet switched. Data is less sensitive to delay and jitter, but cannot tolerate loss. The data philosophy has centered on providing reliable data transmission over unreliable media, almost regardless of delay. Bandwidth in the data world is largely shared, so congestion and delay are often present and can cause problems for multimedia applications such as voice.

The factors that affect the quality of data transmission are different from those affecting the quality of voice transmission. For example, data is generally not affected by delay. Voice transmissions, on the other hand, are degraded by relatively small amounts of delay and cannot be retransmitted. Additionally, a tiny amount of packet (data) loss does not affect voice quality at the receiver’s ear, but even a small loss of data can corrupt an entire file or application. In some cases, introducing VoIP to a high performing data network can yield very poor voice quality.

Therefore, implementing VoIP requires attention to many factors, including:

This document provides basic network guidelines to ensure good voice quality when implementing VoIP. This document also examines some of the more important components that affect VoIP and gives suggestions to help avoid problems during implementation.

3 Defining Quality

3.1 What is Quality?

Quality is a word that is used by almost all manufacturing and service providers. Quality, however, is an ambiguous term representing superiority of that product or service. But quality can mean different things to different people.

Consider Bill, a person who wants to buy a quality vehicle. Bill goes to a dealership and sees a luxury sports sedan. It is a quality vehicle. The stitching on the leather seats is uniformly

0.2‖ apart on all seams. The finish consists of 10 color coats and 2 high-polymer sealant coats. The fit between the doors and the body is consistently 0.167‖. Bill buys the luxury sports sedan and is happy with the ―quality‖.

Now consider Trish, a person who also wants to buy a quality vehicle. Trish lives in rugged mountain terrain, miles from anyone and must cross a boulder field just to get to work. Trish is looking for a vehicle that has high ground clearance, a stiff suspension and 4-wheel drive to get her to town and back – consistently without breaking down. Trish buys a Sport Utility Vehicle and is happy with the ―quality‖. Trish doesn’t care about the stitching on the seats, the gloss of the paint or the extreme exactness of the fit of the doors to the body. Trish knows the paint will soon have chips, the body will get dents and the interior will stain.

Quality, in the above examples, consists of entirely different values. Therefore, what one person values in quality may be almost irrelevant to another. Both Bill and Trish purchased quality vehicles that have superior, but different features.

3.2 What is Voice Quality?

Defining voice quality is also difficult because the values of a small business can be greatly different than a business that is larger or located in another culture or country. This is why Avaya presents choices using a tiered system of network requirements. One number for delay or jitter or packet loss cannot satisfy all customers in all businesses and in all cultures. Ultimately, each business must decide if quality voice using VoIP requires the first tier of values or other tiered values specified in this paper.

4 Prioritizing Voice Traffic

In order for a VoIP solution to function well, the network must be able to give voice packets priority over ordinary data packets and sufficient bandwidth must always be available. Avaya’s products for VoIP—Communication Manager™ Software include several standard strategies to prioritize voice traffic. These strategies include using class of service (CoS), prioritizing ports, prioritizing services, and using IEEE 802.1p/Q to set the priority bits. Avaya products are designed to work with most other popular switches and routers using open standards to provide end-to-end voice prioritization.

4.1 Understanding the difference between CoS and QoS

Class of Service (CoS) is a classification method only. CoS does NOT ensure a level of Quality of Service (QoS), but is the method used by queuing mechanisms to limit delay and other

factors to improve QoS. Most CoS strategies assign a priority level, usually 0–7 or 0-63, to a frame or packet respectively. Common CoS models include the IP TOS (Type Of Service) byte, Differentiated Services Code Point (DiffServ or DSCP, defined in RFC 2474 and others) and the IEEE 802.1p/Q.

Quality of Service (QoS) involves giving preferential treatment through queuing, bandwidth reservation, or other methods based on attributes of the packet, such as CoS priority. A service quality is then negotiated. Examples of QoS are CBWFQ (Class Based Weighted Fair Queuing), RSVP (RESERVATION Protocol - RFC 2205), MPLS, (Multi Protocol Label Switching RFC 1117 and others).

CoS, or tagging, is totally ineffective in the absence of QoS because it can only mark data. QoS relies on those tags or filters to give priority to data streams.

4.2 Using Ports

One prioritization scheme assigns priority based on the UDP (User Datagram Protocol) port numbers used by the voice packets. This scheme allows the use of network equipment to prioritize all packets from a port range. UDP is used to transport voice packets through the LAN because, unlike TCP, it is not connection-based. Because of the human ear’s sensitivity to delay, it is better to drop packets rather than retransmit voice in a real time environment so a connectionless protocol is preferable to a connection-based protocol. By using Communication Manager Software, users can define a UDP port range for voice priority. Routers and layer 3 data switches can then use these ports to distinguish priority traffic. This priority traffic can be voice packets (UDP), signaling packets (TCP) or both. This is an OSI model layer-4 solution and works on data coming to and from the specified ports or a port range.

4.3 Using DSCP (or TOS)

The DSCP prioritization scheme redefined the original Type of Service (TOS) byte in the IP header by combining the first six bits into 64 possible combinations. This use of the TOS byte is used by Communication Manager Software, IP Telephones, and other network elements such as routers and switches in the LAN and WAN. A DSCP of 46 (101110) is suggested for the expedited forwarding of voice packets. However, with Communication Manager, one can set any DSCP value as desired to work with a company’s QoS scheme.

Note that older routers may require a DSCP setting of 40 (101000), which is backward compatible to the original TOS byte definition of critical. But again, Avaya products and software allows users to set any of the 64 possible DSCP values to work with your voice quality policy. The TOS byte is an OSI model layer-3 solution and works on IP packets on the LAN and possibly the WAN depending on the service provider.

4.4 Using IEEE 802.1 p/Q

Yet another prioritization scheme is the IEEE 802.1Q standard, which uses four bytes to augment the layer-2 header. IEEE 802.1Q defines the open standard for VLAN tagging. Two bytes house 12 bits used to tag each frame with a VLAN identification number. The IEEE 802.1p standard uses three of the remaining bits in the 802.1Q header to assign one of eight different classes of service. Again, with Communication Manager Software, users can add the 802.1Q bytes and set the priority bits as desired. Avaya suggests you use a priority of

+ 19 hidden pages