IBM OPTIONS ATM OC-3c User Manual

8271 Nways Ethernet LAN Switch
ATM OC-3c Module

User’s Guide

Before using this inform ation an d the prod uct i t supports, b e sure

to read the general information under Appendix A,“Safety Infor-

mation” and Appendix F, “Notices, Trademarks, and Warranties”.

First Edition (October 1997)

This e ditio n ap pl ies t o the IB M 82 71 Nw ays Eth er net L A N Swi tch ATM

3C-Oc Module with agent software version 1.05 and IBM 8271 Nways

Ethernet LAN Switch Models 524, 612, 624, 712 with agent software

version 3.1.

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C

ONTENTS

A

BOUT THIS GUIDE

Introduc tion 1
Terminology 1

AT M Te rmino logy 1
Finding Information in This Guide 2
Conventions 2
Related Documentation 3

1

F

EATURES AND BENEFITS

ATM Benefits 1-1
ATM Module Features 1-2

2

N

ETWORK LAYER CONCEPTS

The Layered Network Architecture 2-1
Upper Layer Protocols 2-2
What is LAN Emulation (LANE)? 2-2

LAN Emulation Components 2-3

LAN Emulation Client (LEC) 2-3
LAN Emulation Server (LES) 2-3
Broadcast and Unknown Server (BUS) 2-3
LAN Emulation Configuration Server (LE C S) 2-3

LAN Emulation Components in Your Network 2-4

LAN Emulation and IBM Dev ices 2-4

Joining th e ELAN 2- 5

Locating the LECS 2-5

Mapping Ethernet and ATM Addresses 2-6

Address Resolution 2-6
LAN Emulation Address Resolution Protocol (LE_ARP)

2-7
What Happens to Unic ast Frames? 2-7
What Happens to Broadcast and Mult icast Frames? 2-7

AT M Adaptation Layer (AAL) 2-8
Asynchronous Transfer Mode (ATM) Layer 2-8

ATM is Cell-based 2-8
AT M i s Service Transparent 2-9
AT M is Connection-oriented 2-9

Switched Virtual Circuits (SVCs) 2-12
Permanent Virtual Ci rcuits (PVCs) 2-12

ATM Interfaces 2-12

Interim Local Man agem ent Interface ( ILMI) 2-13
ATM Address Registration 2-13

The A TM Layer and Cell Stru cture 2-14

Physical Layer 2-15

SONET STS-3c 2-15
SDH STM-1 2-15

3

V

IRTUAL

LAN C

ONCEPTS

What is a Virtual LAN (VLAN)? 3-1
Creating Inter-switch VLANs 3-1
Extending VLANs into the AT M N e tw o rk 3-2

4

P

UTTING YOUR

ATM N

ETWORK TOGETHER

Planning Your Network 4-1
ATM Configuration Rules 4-2
Extending VLANs Through the A TM Network 4-2
A TM Connections Within Your Network 4-3

5

N

ETWORK CONFIGURATION EXAMPLES

A TM Backbone in the Buildi ng 5-1
Campus Configuration 5-2
Making a Building Resilient to Network Failure 5-4

6

I

NSTALLING AND SETTING UP THE MODULE

Following Saf ety Information 6-1
Device Support 6-3
Pre-installation Procedure 6-3

Check the Power Supply 6-3

Installa tion 6-4

Connecting a cable to the ATM Port 6-5
Powering Up the Switch 6-5

Power On Sel f Test (POST) 6-5

Post-Installation Checks 6-5

LED Summary 6-6
Checking the Power Supply 6-7
Checking that the ATM Module is Installed Cor rectly 6-7
Checking the Physical Connections 6-7

7

A

CCESSING MANAGEMENT FEATURES

Screen Map 7-1
Keyboard Shortcuts 7-1
Correcting Text Entry 7-1

Logging On 7-3
Logging Off 7-4

Automatic Logout 7-4

8

M

ANAGING THE

ATM M

ODULE

Configuring an ATM Port 8-2
Extending VLANs into the AT M N e tw o rk 8-4

Displaying all VLANs 8-5
AT M Por t Setup 8-6
Mapping Far End MAC Addresses 8-8

Creating a MAC Addre ss to ATM Ent ry 8-9

Finding an Addre ss Entry 8-10

Updating Addres s Entries 8-10

Deleting an Address Entry 8-10
Displaying an ATM Connecti on 8-10

Finding an ATM Connectio n 8-11

Updating Addres s Entries 8-11
Setting Up Resilient Links 8-11
Upgrading Software 8-12

Error Messages 8-13

Status Messa ges 8-14

9

M

ONITORING THE

ATM M

ODULE

Statisti cs O verview 9-2
ATM Port Statistics 9-3
AT M VLAN LEC Status 9-5
AT M Physical Layer Statistics 9-10

Using Physical Layer Statistics to Troubleshoot 9-12

A

S

AFETY INFORMATION

Safety Notices A-1

World Trade Safety Information A-1

B

S

CREEN ACCESS RIGHTS

C

ATM M

ODULE TECHNICAL SPECIFICATIONS

Environm ental Specifications C-1
ATM Cable Specification C-1

Does the Cable Provide Sufficient Bandwidth? C-2

D

T

ROUBL ESHOOTING

How to Use this Guide to Troubleshoot D -1
Using LEDs D-2
Identifying the Problem D-3

ELAN Configuration Problems D-15

Solving Known Problems D-17

Power Supply Problems D-18
Power On Self Test (POST) Failure D-19
Cable Connection Problems D-20
ATM Problems D-21
VLAN or ELAN Problems D-22

Cleaning Dirty Fiber Optic Connectors D-24

E

T

ECHNICAL SUPPORT AND SERVICE

Electr onic Support E-1

WWW E-1
FTP E-1
IBM Bulletin Board System E-1

Vo ice Support E-1

F

N

OTICES

, T

RADEMARKS, AND WARRANTIES

T rademarks F-1
Statement of Limited Warranty F-2

Production Status F-2
The IBM Warranty for Machines F-2
Warranty Service F-3
Exten t of Warr a nt y F -3
Limitation of Liability F-4

Electronic Emission Notices F-5

Federal Communications Commission (FCC) Statement

F-5

Canadian Department of Comm unications (DOC)

Compliance Statement F-5

Avis de confor mite aux normes du ministere des

Communications du Canada F-5
European Union (EU) Statement F-6
Japanese Voluntary Control Council for Inter ference

(VCCI) Statement Class B F-7
Korean Communications Statement F-7
Information To The User F-7

G

LOSSARY

B

IBLIOGRAPHY

Asynchronous Transfer Mode (ATM) 1
LAN Emulation (LANE) 1

I

NDEX

A

BOUT THIS

G

UIDE

Introduction

This guide provides the information that you need to
install and configure the IBM 8271 Nways Ethernet
LAN Switch ATM OC-3c Module (agent software
version 1.05) within an IBM 8271 Nways Ethernet
LAN switch which has version 3.1 agent software
installed.

This guide is intended for use by network administrators
who are responsible for installing and setting up
networking equipment. It assumes a basic working
knowledge of Local Area Networks.

This guide explai ns Asynchronous Transfer Mode (ATM)
and LAN Emulatio n (LANE) concepts, and provides a
Bibliography for further reading.

The Release Notes shipped with the ATM Module may
contain information that updates or overrides
information in this guide. You should always follow
the informa t ion in t he Rel ea se N ot es if it is dif f e rent
from the information given in this guide.

Terminology

In this User’ s Guide the term ATM Module is used when
referring to the IBM 8271 Nways Ethernet LAN Switch
ATM OC-3c Module.

The device into which the ATM Module is fitted, is
known simply as the Switch. An example of a Switch
is the IBM 8271 Nways Ethernet LAN Switch
Model 624.

This type of Switch is often referred to as an
edge-device, edge-switch or boundary switch.

The term ATM S witch is used to identify the ATM
device to which the edge-switch is connected.

Switches in IBM’s 8271 Nways Ether net LAN Switc h
device range provide support for the ATM Module.

ATM Terminology

This user guide uses the term Network-To-Network
Interface (NNI). You may know this protocol by its

alternative name, Network-to-Node Interface (NNI).
Additional ATM definitions can be found in the
Glossary at the end of this guide.

2 A

BOUT THIS GUIDE

Finding Information in This Guide

The following table shows you where to find specific
information within this guide.

Convent ions

Table 1 and Table 2 list conventions that are used
throughout this guide.

Task Location

Learning
concepts

Chapter 1, ‘Features and Benefits”
Chapter 2, ‘Network Layer Concepts”
Chapter 3, ‘Virtual LAN Concepts”

Planning your
network

Chapter 1, ‘Features and Benefits”
Chapter 4, ‘Putting Your ATM Network Together”
Chapter 5, ‘Network Configuration Examples”
Appendix C, ‘ATM Module T echnical Specifications”

Upgrading
Software

Chapter 8, ‘Managing the ATM Module”

Installing the
A TM Mo dule

Chapter 6, ‘Installing and Setting Up the Module”
Appendix A, ‘Safety Information”

Accessing screens Chapter 7, ‘Accessing Management Features”

Appendix B, ‘Screen Access Rights”

Managing
the ATM Module

Chapter 8, ‘Managing the ATM Module”

Monitoring
the ATM Module

Chap ter 9, ‘Monit oring t he ATM Modu le”

Troubleshooting Appendix D, ‘Troubleshooting”
Getting Technical

Support

Appendix E, ‘Technical Support and Service”

Identifying terms ‘Glossary”
Further reading ‘Bibliography”

Table 1

Notice Icons

Icon Notice Type Alerts you to...

Information
note

Important features or instructions

ATTENTION Risk of system damage or data loss

CAUTION Conditions or procedures that can cause

personal injury that is neither lethal nor
extremely hazardous

DANGER Conditions or proce dures that can result in

death or severe personal injury

Table 2

Text Conventions

Convention Description

Screen
display

This typeface represents information as it appears on
the screen.

The words
“Enter” and
“Type”

The word “enter” means type something and then
press the Retu rn or En ter k ey. Do not press the Return
or Enter key when an instruction simply says “type.”

[Key] names Key names appear in text in one of two ways:

■

Referred to by their labels, such as “the Return
key” or “the Escape key”.

■

Enclosed within brackets, such as [Return] or [Esc].

If you must press two or more keys simultaneously,
the key names are linked with a plus sign (+). For
example: Press [Ctrl]+[Alt]+[Del].

Related Documentation 3

Related Documentation

The ATM OC-3c Module documetation set includes:

■

IBM 8271 Nways Ethernet LAN Switch ATM OC-3c
Module Quick Reference Guide.

Part Number 02L1333

■

IBM 8271 Nways Ethernet LAN Switch ATM OC-3c
Module Release Notes.

Part Number 02L1334

Words in

Italics

Italics emphasize a point or denote new terms at the
place where they are defined in the text.

Words in

bold

Bold text denotes key features.

Table 2

Text C onventions (continued)

Convention Description

4 A

BOUT THIS GUIDE

1

F

EATURES AND

B

ENEFITS

This chapter describes the main features of the IBM
8271 Nways Ethernet LAN Switch ATM OC-3c
Module and the benefits of ATM within your
network.

The ATM Module provides a high-speed ATM
connection between your IBM 8271 Nways Etherne t
LAN Switch and the ATM network.

Positioned within a workgroup or departmental LAN,
the A TM Module p ro vides a fas t ATM downlink to the
building or ATM campus.

Resilient links protect your Switch from network and
equipment failure, while the software upgrade
feature future-proofs your Switch by allowing you to
add new features as they become available.

Additional featur es ar e provided by the Switch, and
you should refer to the guide that accompanies y our
Switch for mor e details. The Release Notes that
accompany the ATM Module list the IBM 8271 Nways
Ethernet LAN Switches that support the ATM Module.

ATM Benefits

ATM is the only technology specifically designed to
carry voice, video and data traffic simultaneously and
to provide the required level of service that these
different applications need in order to run effectively
across a network. ATM provides the following
benefits:

■

It is easy and low cost to add additional services to
the ATM network.

■

Services can be added as and when they are
needed. It is easier to scale ATM networks
compared to other network technologies.

■

ATM devices interoperate with your existing
network. LAN Emulation (LANE) is a standards
based technology specifically designed to provide
interoperability between existing Ethernet/Fast
Ethernet networks and ATM networks. LANE
allows users to interoperate with ATM or
traditional LAN based servers over ATM for higher
performance and functionality.

1-2 C

HAPTER

1: F

EATURES AND BENEFITS

ATM Module Features

The following list summarizes the ATM Module
featu re s . These feat u res are d escrib ed in more detail
in this guide.

■

Conforms to ATM Forum Standards

■

OC-3c 155Mbps Interface

■

SONET (STS 3c) and SDH (STM-1) compliant

■

Multi-mode Fiber, SC connectors

■

LAN Emulation (LANE)

version 1.0

■

16 Emulated LAN Clients

■

512 Virtual Circuits

■

1024 remote MAC Addresses

■

User -To-Network Interf ace (UN I)

version 3.0 and 3.1

■

Interim Local Management Interface (ILMI)

■

AAL5 ATM Adaptation Layer

■

16 Virtual LANs (VLANs)

■

RMON per Em ul ate d L AN. R MON Gr ou ps su pp ort e d:

■

Alarms

■

Events

■

Statistics

■

History

■

Data buffer to store 40,000 ATM cells

■

High performance with fast data transfer

■

Wire Rate Transmission

on ATM port

■

Low Latency (68 microseconds when using
Store and Forward traffic management between
ATM and Ethernet components)

■

Resilient Links protect your network against cable
and equipment failure

■

SNMP management

■

Telnet and local management (using VT100
screens)

Cabling and environmental specifications are listed in
Appendix C, ‘ATM Module Technical Specifications”.

2

N

ETWORK LAYER

C

ONCEPTS

This guide contains several chapters that describe the
basic concepts behind ATM technology, and
integrating ATM into your existing network:

■

This chapter describes some of the concepts
behind the network layer architecture of a typical
AT M network.

■

Chapter 3, “Virtual LAN Concepts” describes how
Virtual LANs (VLANs) are extended into the ATM
network.

■

Chapter 4, “Putting Y our ATM Network Together”
describes how to plan your ATM network.

■

Chapter 5, “Network Configuration Examples”
provides some examples of how you can use the
AT M Module within an ATM networks.

If you are already familiar with these concepts, refer
to Chapter 6, “Installing and Setting Up the Module”.

If you have read the concepts chapters and still
requir e a more in-depth explan ati on , refer to the
technical publications listed in the Bibliography.

The Layered Network Architecture

Asynchronous Transfer Mode (ATM) is on ly part of a
layered net wo rk arch ite ct u re. Th is ar chit e c ture is
shown in Figure 2-1.

Each of the layers in discussed in turn; starting with
the Upper Layer and working down to the Physical
Layer.

Figure 2-1

Network Layer Architecture

2-2 C

HAPTER

2: N

ETWORK LAYER CONCEPTS

Upper Layer Protocols

The

Upper Layer

is the layer in the network architecture
that rel a tes to user applications and service requ ests.
For example, an application could be fi l e transfer
softwar e, and t he ser vic e reque st c ould be a req uest t o
transfer a file from a user’s PC to a shared file server.

User data and control information is passed down the
network layers in the source device, and passed up
the layers at the destination device.

What is LAN Emulation (LANE)?

LAN Emulation (LANE)

allows users on Ethernet,
Token Ring, and other traditional LAN networks, to
communicate with each other over an ATM network.

LANE emulates the broadcast nature of traditional
LANs. Each LANE broadcast domain is known as an

Emulated LAN (ELAN)

.

Each ELAN can only carry one type of traffic. For
example, an ELAN could carry either Ethernet frames
or Token Ring frames, but not both.

There can be several ELANs on a single ATM network.
Some of these ELANs could be carrying Ethernet
traffic and others could be carrying Token Ring traffic.

T raffic from one ELAN is not seen on another ELAN, as
they are logically separate broadcast domains. If devices
from different ELANs need to communicate with each
other, t hey must do so using an ATM ro uter.

LAN emulation software is contained within ATM
devices which can be added to your existing network.

LANE allows you to add ATM to your network
without having to replace or upgrade the whole of
your underlying technology. LANE allows you to do
this because it is completely transparent to the ATM
network and to the traditional LAN network,
end-users, operating systems and applications.

LAN Emulation allows users on traditional LANs to
communicate over ATM by performing the following
tasks:

■

Emulates the broadcast nature of LANs.

■

Maps MAC addresses to ATM addresses.

■

Maps upper layer connection-less technologies to
the

connection-oriented

ATM network.

Although LAN Emulation emulates a range of
network technologies, all examples in this guide are
be based on an Ethernet network.

What is LAN Emulation (LANE)? 2- 3

LAN Emulation Components

Each

Emulated LAN (ELAN)

is composed of a set of
LAN Emulation components. This section describ es
each of these components.

LAN Emulation Client (LEC)

Each ATM de v ic e has a number of LAN Emul at i on
clients. Each

LAN Emulation Client (LEC)

is responsibl e
for tak i ng Ethernet fr am e s and passing them through
the ATM network to the LEC se rving the destination
address. The dest ination LEC is r esponsible for re ceiving
the frame from the ATM network and passing it to the
local Ethernet network, where it can be delivered to the
destination address.

LAN Emulation Server (LES)

Each

LAN Emulation Server (LES)

controls a single

Emulated LAN (ELAN)

. The purpose of the LES is to
store address and control information for the ELAN it
is serving, and to pass this information onto the
clients and other components within the ELAN.

The LES, therefore, needs to know the address of
every client and component in the ELAN.

Broadcast and Unknown Server (BUS)

Each ELAN has a

Broadcast and Unknown S erver (BU S)

.
The BUS fo rward s frames that it receiv es fro m a n y
client to all of the clients in the ELAN. The BUS is used
to forward broadcast and multicast frames so that they
are

flooded

throu ghout the ELAN . The BUS also

floods

unicast frames if the location of the destination MAC
address is u nkn own.

LAN Emulation Configuration Ser ver (LECS)

The

LAN Emulation Configuration Server (LECS)

is an
optional component, and is not essential for the
normal running of an ELAN

.

The LECS stores the names of all th e ELA Ns that ha ve
been set up on the ATM network, and the address of
the

LAN Emulation Server (LES)

that serves each of

these ELANs.
If there is an LECS on the network, any client can

interrogate the LECS to find the address of the server
associated with the ELAN they wish to join. The
clients may also get ELAN configuration information
from the LECS.

If a LECS is not present on the A TM network, the server
addres s to be used by the clie nt must be specif ied using
the management software on that client’s ATM d evice.

2-4 C

HAPTER

2: N

ETWORK LAYER CONCEPTS

LAN Emulation Components in Your Network

Each Emulated LAN consists of a single

LANE Service

,

and a number of LAN Emulation clients.
A LANE Service consists of:

■

A

LAN Emulation Server (LES)

■

A

Broadcast and Unknown Server (BUS)

■

Optional

LAN Emulation Configuration Server (LECS)

.

Figure 2-2 shows a logical view of a typical ELAN.

Figure2-2

LAN Emulation Components

The router shown in Figure 2-2 is not a LAN
Emulation component, but would be required should
a device on one Emulated LAN need to communicate
with a device on another Emulated LAN.

You may wish to have more than one LECS on your
network for security reasons. For example, you may
wish the Finance department to be controlled by one
LECS and the rest of your network to be controlled by
a different LECS.

LAN Emulation and IBM Devices

LAN Emulation components are implemented in ATM
dev ic e s . The L A N Emulatio n standards ( re f erence d i n
the Bibliography) do not specify how each vendor
implements each of these components.

What is LAN Emulation (LANE)? 2- 5

Joining the ELAN

Before a LAN Emulation Client (LEC) can transmit any
Ethernet frames onto the ATM network it must first
join an ELAN . To join the ELAN:

1

The LEC must know the name of the ELAN it is to
join.

The ELAN name is specified through the management
software on the Switch.

2

The LEC must communicate with the LAN
Emulation Server (LES) that is serving that ELAN.

To communicate with the LES, the LEC must first
locate the LES. The LEC can find the ATM address of
the LES in one of the following ways:

■

If there is a LAN Emulation Configuration Server
(LECS) on the networ k, the LE C gets the ad dr ess of
the LES from the LECS.

The way in which the LECS determines which LES
the LEC needs to communicate with, depends on
the

policy

that the LECS is running. Refer to the
user guide that accompanies your LECS for more
details of the policies your LECS uses.

■

If the network does not have a LECS, the LEC gets
the LES address from the management software
on the ATM device.

3

The LEC must have a connection to the
Broadcast and Unknown Server (BUS).

When the LEC has joined the LES, the LES helps the
LEC locate the

Broadcast and Unknown Server

(BUS)

associated with that ELAN.

Locating the LECS

Before the LEC can ask the LECS for the address of
the LES, the LEC must first locate the LECS. There are
three ways i n w h ich th e LEC can locat e the LECS, and
the LEC tries these methods in the following order:

■

The LEC can ask the adjacent ATM Switch using
the

Interim Local Management Interface (ILMI)

.

■

The LEC can use a well known ATM addr es s that is
reserved for the LECS. The well known address is
pre-programmed into most LECS devices. The well
known address is:

47007900000000000000000000:00A 03E000001:00

■

The LEC can use a reserved

Permanent Virtual

Circuit (PVC)

which the ATM Switch has already
routed to the LECS. The reserved PVC is
VPI 0, VCI 17.

2-6 C

HAPTER

2: N

ETWORK LAYER CONCEPTS

Mapping Ethernet and ATM Addresses

Each device connected to an Ethernet port has one or
more MAC addresses.

Each ATM device has a number of LAN Emulation
clients, and each

LAN Emulation Client (LEC)

has an

A TM address . A n exa mpl e of t hi s i s s how n in F i gur e2-3.

Figure2-3

LAN Emulation Clients and Ethernet Hosts

These clients represent (act as a proxy) for devices
connected to the Ethernet ports.

Whenever an Ethernet device wants to communicate
with another device over the ATM network, the LEC
must first discover the ATM address of the LEC that is
acting as a proxy for the destination MAC address.
The LEC must do this for each unicast Ethernet fram e
sent. The process is known as

Address Resolution.

Address Resolution

The process by which a LEC associates a LAN
destination address with the ATM address of another
LEC (or the BUS) is known as

Address Resolution

.

Each LEC keeps a LAN Emulation

ARP Table

(which
should not to be confused with the IP ARP Table). The
ARP T able lists the remote destination MAC addresses
and the ATM address of the LEC though which each
destination MAC address can be reached.

Prior to sending a frame with a known destination,
the LEC checks th e ARP Table to s ee if the dest inati on
MAC address of the frame is listed in the ARP Table.
The action the LEC then takes depends on whether
the MAC address is listed in the ARP Table:

■

If the destination MAC address is listed in the
ARP Table:

■

and there is an A TM connection to that LEC, the
frame is sent directly to that LEC.

■

and an ATM connection has not already been
set up, the LEC sets up an ATM connection.

■

If the destination MAC address is not listed in
the ARP Table

, the LEC sends the frame to the
BUS. The BUS then sends the frame to all LECs on
the Emulated LAN.

Sending a frame to every LEC is an inefficient use
of resources, so the LEC also tries to locate the
MAC address for future use.

To discover the correct address, the LEC uses a
process called

LAN Emulation Address Resolution

Protocol (LE_ARP)

.

What is LAN Emulation (LANE)? 2- 7

LAN Emulation Address Resolution Protocol
(LE_ARP)

An LE_ARP request is sent to the LES to locate the
destination MAC address. The LES in turn sends the
LE_ARP request to all of the LECs in the E mulated LAN.

LECs represent (act as a proxy) for MAC address
devices connected to the Ethernet ports. When a LEC
receives an LE_ARP request it checks whether the
MAC address is on its Switch. It does this by checking
the entries in the Switch database.

If the MAC address belongs to one of the devices
connected to an Ethernet port, the LEC sends an
LE_ARP response to the LEC that sent the original
LE_ARP request.

The LEC that sent the LE_ARP request adds this
information to its ARP Table. The LEC then sets up a
direct connection through the ATM network to the
appropriate LEC, so that subsequent frames are
forwarded more efficiently.

What Happens to Unicast Frames?

The path a unicast frame takes through the ATM
network depends on whether the location of the
destination address is known to the sending LEC.

■

If the location of the destination address is
known

, the LEC sets up a direct connection to the

LEC serving the destination address.

■

If the location of the destination address is
unknown

, a unicast frame is sent to the

Broadcast

and Unknown Server (BUS)

; where it is treated in

the same way as a broadcast or multicast frame.

In addition the sending LEC attempts to locate the
LEC serving the destination address. It does this
using the LE_ARP process, described in “LAN
Emulation Address Resolution Protocol (LE_ARP)”.

What Happens to Broadcast and Multicast Frames?

Each

Emulated LAN (ELAN)

acts as a broadcast
domain. When a broadcast or multicast frame is
passed to the LEC for transmission, the frame is sent
to the

Broadcast and Unknown Server (BUS)

.

When the LEC receives a broadc as t, mul tic as t, or
unicast frame it checks to see if it originally sent the
frame, and then does the following:

■

If the LEC sent the frame, it discards the frame.

■

If the LEC did not send the frame, the LEC passes
the frame to the Ethernet device so that it can be
forwarded to the appropriate port(s).

Unlike broadcast and multicast frames, the number of
unicast frames that can be sent to the BUS every
second is limited so as not to overload the BUS and
LECs with too much traffic.

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ATM Adaptation Layer (AAL)

Ethernet frames can be between 64 and 1514 bytes
in length. ATM transmits data in fixed length

cells

.

Each cell contains 48 bytes of user data. The

ATM

Adaptation Layer (AAL)

converts data between the

Ethernet and A TM formats.
The AAL has a

Segmentation and Reassemb ly (SAR)

sub-layer that does the conversion.
In the sending device the LEC passes the Ethernet

frames to the SAR. The SAR converts the user data
into fixed length cells, and passes these cells to the
ATM Layer for transmission across the ATM network.

In the receiving device, the SAR converts the ATM
cells back into the appropriate user data again, and
passes this data to the LEC.

As ATM can carry different traffic types (for example,
voice, video, and other data), several Adaptation
Layer protocols have been defined. These protocols
operate simultaneously within the Adaptation Layer,
and allow the ATM Layer to support different
applications and traffic types.

The IBM 8271 Nways Ethernet LAN Switch ATM
OC-3c Module uses the AAL5 ATM Adaptation Layer
protocol, which is a data-oriented protocol. The ATM
Module will only work with other AAL5 devices.

Asynchronous Transfer Mode (ATM) Layer

Asynchronous Transfer Mode (ATM)

is a connection­oriented transmission protocol that has the following
features:

■

ATM us es the

Signalling Protocol (Q.2931)

to
dynamically create, maint ain and clear ATM
connections between end-systems.

■

ATM uses fixed length packets known as

cells

, and

each cell identifies the connection to be used.

■

ATM is transparen t to the m ul t ip l e se rv i ces it
supports and c a n c arry cells f rom diffe rent
applications over the same physical connection.

■

ATM has well-defined user and network interfaces.

ATM is Cell-based

ATM uses fixed length packets called

cells

. The first

five bytes of the cell is the

cell header

. The cell he ader
contains the information necessary to deliver the cell
to the correct destination.

Fixed-length cells offer smaller and more predictable
switchin g d e la ys, be ca u se ce ll switching is le ss
complex than variable-length packet switching.

Having all the data in the same cell format also
dramatically increases the speed of transmission, by
eliminating the need for protocol recognition and
decoding. A good analogy is containerized shipping,
where uniform shape and weight containers with
standardized labelling, ease and speed up processing.

Asynchronous Transfer Mode (ATM) Layer 2-9

ATM is Service Transparent

ATM allows for the high speed transfer of a wide range
of user traffic, inc l uding voice, v ideo and other da ta.

The cell format means that more than one service
(traffic type) can be

multip lexed

over the same

physical line, see Figure 2-4.

Figure2-4

Service Processing

Cells ar e

de-multiplexed

at the other end of the
connection and forwarded to the correct service
destination.

Multi-service processing promotes scalability by
significantly reducing the number of changes needed
to add new service traffic types to your network.

ATM is Connection-oriented

ATM is a

connection-oriented

transport service that
requires a communication channel to be set up
between the ATM source and destination end-systems
before ATM cells can pass between them.

Before a direct data connection can be set up
between two end-systems, a number of control
connections are set up. These control connections are
beyond the scope of this guide. If you require further
information about control connections, refer to the
ATM Forum’s “LAN Emulation Over ATM” document.

Figure 2-5 shows the logical structure of a
communication channel.

Figure 2-5

Communication Channels

Several communication channels can operate over the
same physical link. Each

Virtual Path Connection (VPC)

contains several communication channels known as

Virtual Channel Connections (VCCs)

.

The ATM Module only manages Virtual Channel
Connections (VCC).

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A VCC is defined as spanning end-to-end, whereas a

Virtual Channel (VC)

is the name given to a section of

the VCC, refer to Figure 2-6.

Figure2-6

Connection Terminology

Many virtual channels can exist on the same physical
link. Each virtual channel is identi fie d by a pair of
numbers:

■

The

Virtual Path Identifier (VPI)

and

■

The

Virtual Channel Identifier (VCI)

.

Any end-system that wishes to communicate with
another end-system must first use the

Signalling

protocol to set up the VCC.
The

Signalling

protocol negotiates with each ATM
device between the end-systems to set up a series of
virtual channels. Each of these virtual channels is
identified u sing the VPI and VCI values.

Figure 2-7 on page 2-11 shows how ATM cells are
switched through the A TM network using the VPI/VCI
values.

Instead of containing the ATM address of the final
destination device, each cell header contains the
VPI/VCI values associated with the virtual channel it is
going to take to get to the next ATM Switch in the
connection.

Each ATM switch kno w s th at when it r eceives a cel l
with a particular VPI/VCI value on one port that it must
transmit the cell on another port with another VPI/VCI.

Cells are switched through the network based on
these VPI/ VC I va lues, and swit c hin g is p e rf o rme d
independently for every cell. Each cell can be thought
of as taking a virtual channel connection.

The VPI/VCI values are only meaningful in the c onte xt
of that user-to-switch, or switch-to-switch, interface.
Identica l VP I/ VCI values ca n e xist on differ e nt
interfaces within the network.

Connections t ha t ar e e stabl ishe d d ynamica lly usi ng the
Signalling protocol are known as

Switched Virtual

Circuits (SVCs). Switche d V irtual C i rc uits

are described

in “Switched Vir tual Circu i ts (SVCs)” on pa ge 2-12.
ATM connections can also be established via

management, and these type of connections are
known as

Permanent Virtual Circuits (PVCs)

.

Permanent Virtual Circuits

are described in

“Permanent Virtual Circuits (PVCs)” on page 2-12.

Asynchronous Transfer Mode (ATM) Layer 2-11

Figure2-7

Switching Cells using VPI and VCI values.

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Switched Virtual Circuits (SVCs)

SVCs use the signalling protocol to dynamically define
connections as they are needed and to release them
when they are no longer needed.

SVCs use signalling for:

■

Connections initiated by the user/application.

■

Connections established and dropped dynamically.

■

Varied connection time.

■

Connections not automatically re-established after
network failure.

Permanent Virtual Circuits (PVCs)

The most basic connection setup requires the
definition of each connection via management. These
type of connections generally remain established for
long periods of time.

PVC attributes include:

■

Connections initiated by network management.

■

Long-term connection duration.

■

Automatically re-established after network failure.

■

Supported by MIB or other management entity.

The ATM Module does not support PVCs.

ATM Interfaces

ATM technology is implemented in A TM edge-devices
and ATM Switches.

ATM provides a

User-to-Network I n terface

(UNI). The
User-to-Netw o rk Interfac e (UNI) is us ed to con nect an
ATM edge devic e to an ATM switch that is managed
as part of the same network.

ATM al so provides a

Network-to-Network Interface (NNI)

that is typically used to interconnect two ATM switches
managed as part of the same network.

The ATM Interfaces are shown in Figure 2-8.

Figure 2-8

ATM Interfaces

The User-to-Network Interface (UNI) is managed by the

Interim Loca l Management Interface (ILMI)

protocol.

Asynchronous Transfer Mode (ATM) Layer 2-13

Interim Local Management Interface (ILMI)

The ATM Forum produced the

Interim Local

Management Interface (ILMI)

to increase monitoring
and diagnostic facilities, and to provide ATM address
registration at the

User-to-Network Interface (UNI)

.

ILMI uses a

Management Information Base (MIB)

and

the

SNMP

protocol.

Each device that provides ILMI support contains a

UNI Management Entity (UME)

, which uses SNMP to
access management information stored in the ILMI
MIB of the adjacent switch, see Figure 2-9.

Figure2-9

UNI Management Enti ti es

ATM Address Registrati on

In order to establish an ATM connection, both the
user and the network must know the ATM addresses
used at that

User -to-Ne twork Int erfac e (UNI)

. An

example of an ATM address is shown below.
47007900000000000000000000:00A03E000001:00
An ATM address consists of three sections of

information and is 20 bytes in length:

network:host:identifier

Where

network

is a network prefix assigned to the

device by the ATM Switch, and is 13 bytes long.
Where

host

is the edge-device identifier, and is 6

bytes long.
Where

identifier

identifies the client within the

edge-device, and is 1 byte long.
ILMI provides a mechanism for the edge-device (in

this case the ATM Module) to inform the ATM Sw i tch
of the addresses it represents.

When the ATM Module initializes, the ATM Switch
sends a network prefix to th e ATM Module. The ATM
Module then tries to register itself with the ATM
Switch by attaching the prefix to the front of its MAC
address, and an identifier to the end of the address. It
then sends this back to the A TM switch. If a cceptable,
the ATM Switch registers the address as the ATM
Module’s ATM address.

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The ATM Layer and Cell Structure

This section describes the cell structure, and how the
ATM Layer uses the information stored in the cell
header to perform each of its task s.

The ATM Layer’ s primary responsibility is to manage
the sending and receiving of cells between the user
and the network.

The A TM Layer acc ept s the user data and control
information from the ATM Adaptation Layer , adds the
cell header, and passes the resulting 53 byte cell to
the physical layer.

In addition, it also receives cells from the physical
layer, strips off the cell header and passes the
remaining 48 bytes to the higher layer protocols.

The ATM cell has 48 bytes of payload (information to
be carried) and five bytes of header information,
making the cell 53 bytes in length.

The cell header contains the information used by the
network to forward each cell to its destination. The
AT M cell structure is shown in Figure 2-10.

Figure2-10

ATM Cell Structure

The ATM cell header consists of the following fields:

Generi c Flow Control (GFC)

— Provides local

functions, such as flow control over the

User- to Network I nterface (UNI)

. The valu e enco ded i n
the GFC is not carried end-to-end and can be
overwritten by the ATM Switch.

Virtual Path Identifier (VPI)

and

Virtual Channel

Identifier (VCI)

— The VPI/VCI values allow the
network to associate a cell with a given connection,
so that the cell can be switched to its destination.

Payload Type Identifier (PTI)

— The PTI is used to
indicate whether the cell contains user information,
or management information. The management
information is used for resource and network
congestion management.

Cell Loss Priority (CLP)

— The purpose of the

Cell

Loss Priority (CLP)

bit in the A TM cell is to i ndicate that
cells with this bit set should be discarded before cells
which do not have the CLP bit set. Cells can be
discarded based on CLP condition and according to
the network load. When the network overloads, a
discard mechanism, based on the value of the CLP bit
in the cell header, may come into operation.

Header Error Check (HEC)

— The HEC field is used
for detecting bit errors in the cell header. It is also
used for cell delineation, defining where the cell
begins in a SONET frame.

Physical Layer 2-15

Physical Layer

The physical layer is responsible for transmitting and
receiving ATM cells over a physical medium. It is also
responsible for checking the integrity of the bits being
transferred over a physical media, and for making
sure that they are error-free.

The ATM Module is compliant with both

SONET STS-3c

and

SDH STM-1

physical layer standard s.

These standar d s ar e similar, and most devices allow
you to use either framing standar d on each link in the
AT M network.The same framing standard must be
used at each end of the link.

Many users prefer to use the same framing st anda rd
throughout the ir ne twork (f or example SONET STS-3c ).

The physical layer is sub-divided into:

■

Path

— SONET and SDH are capable of carrying
traffic for a number of uppers layers, and ATM is
only one of those layers. Each upper layer uses its
own

Path

through the SONET/SDH layer.

■

Line

— A

line

is the whole path between one ATM
device and the adjacent ATM switch or ATM
end-station.

■

Section

— When ATM is used for telephone

networks, a

line

may cover a large distance,
requiring optical repeaters to boost the signal
along its way . The part of a

line

between an optical
repeater and the adjacent repeater or switch is
known as a

section

.

SONET STS-3c

Synchronous Optical N et w ork (SONET) is the phy sical
layer most often associated with ATM. SONET provides,
throug h a f raming struc ture, the mechanism for the
transport of AT M c ells. Data c a n be transferred at

155.52Mbps.

SDH STM-1

SDH STM-1 is a physical layer similar to the SONET layer,
but with some differences in frame fields. SDH STM-1 is
the physical layer commonly used in Europe.

The physical layer and ATM layers in the network
provide simple performance monitoring functions
between ATM devices; providing basic information
about the health of the link. These functions are
known as “Operation and Maintenance (OAM)”
functions.

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3

V

IRTUAL

LAN C

ONCEPTS

This chapter provides a brief overv i ew of
Virt ual LAN (VLAN) concepts, and describes how to
extend VLANs into the ATM network.

This user guide does not describe how to create or
configure VLANs. VLAN configuration is described in
the user guide that accompanies your Switch.

What is a Virtual LAN (VLAN)?

A V irtual LAN (VLAN) is a fle xibl e, loc ati on and t opolog y
independent group of end-stati ons communicating as
if they are on a common physical LAN.

You can create VLANs that closely correspond to how
your network and business functions. For example,
marketing personnel in different physical locations
could be part of one VLAN and finance personnel
could be in another VLAN.

VLANs provide the following benefits:

■

VLANs make mo ves an d cha nge s sim ple .

■

As each VLAN is a common broadcast domain, you
can erect firewalls against broadcast storms.

■

VLANs improve security.

For a full description of VLAN functionality, refer to
the user guide that accompanies your Switch.

Creating Inter-switch VLANs

You can create inter-switch VLANs using Virt ual LAN
Trunks (VLTs ) on Fast Etherne t connec tions, as shown

in Figure 3-1.

Figure 3-1

Inter-sw itch VLANs

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Extending VLANs into the ATM Network

You can use LAN Emulation to define and extend
VLANs seamlessly through the ATM network, as
shown in the example in Figure 3-3.

Traffic from one

Emulated LAN (ELAN)

is not seen on
another ELAN as they are logically separate domains.
For this reason, when you plan your network, you
should consider what ELANs you require, and how
the VLANs will map to these ELANs.

The A T M Module has a LE C for each of th e Switch ’s 16
VLANS, and each VL A N/ L EC c an be mapped onto an

Emulated LAN (ELAN)

. In this way , E thernet traffic is
mapped to an ELAN by a VLAN-to-LEC association. The
mapping of VLANs to ELANs is shown in Figure 3-2.

When an Ethernet device attached to a Switch
generates traffic, the Switch forwards the frames to
the appropriate port.

A unicast frame is only forwarded to a port if the
address of the destination device is known to be on
that port and the destination port is in the same
VLAN as the source port. If a unicast frame is
forwarded to the ATM port, the ATM port uses the
destination MAC addr es s to identify the ATM
connection to use.

A broadcast or multicast frame is forwarded to all
ports in the same VLAN as the source port. If a frame
is received by the ATM port, the ATM port forwards i t
to the BUS for the associated VLAN.

Figure 3-2

VLAN to ELAN M apping