An Overview of ATM Signalling

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An Overview of An Overview of ATM SignallingATM Signalling

Carey WilliamsonCarey Williamson

University of Calgary

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Introduction Introduction

ATM is a connection-oriented ATM is a connection-oriented protocol, which means that virtual protocol, which means that virtual channels must be set up before channels must be set up before any data cells can be sent on the any data cells can be sent on the channelchannel

Connection setup is done using a Connection setup is done using a signalling protocolsignalling protocol

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ATM Signalling ProtocolATM Signalling Protocol

Protocol consists of two partsProtocol consists of two parts User-Network Interface (UNI)User-Network Interface (UNI)

• defines how hosts talk to switchesdefines how hosts talk to switches Network-Network Interface (NNI)Network-Network Interface (NNI)

• defines how switches talk to other defines how switches talk to other switchesswitches

Cell formats slightly differentCell formats slightly different

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ATM UNI Cell FormatATM UNI Cell Format

GFC VPI

Payload(48 bytes)

VPI VCI

VCI

HEC

PT CLPVCI RES

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ATM NNI Cell FormatATM NNI Cell Format

VPI VPI

Payload(48 bytes)

VPI VCI

VCI

HEC

PT CLPVCI RES

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ATM NNI Cell FormatATM NNI Cell Format

VPI VPI

Payload(48 bytes)

VPI VCI

VCI

HEC

PT CLPVCI RES

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Basic Signalling Operation Basic Signalling Operation

Connection requests proceed hop-Connection requests proceed hop-by-hop through the switches of the by-hop through the switches of the network en route to destinationnetwork en route to destination

Switches perform Call Admission Switches perform Call Admission Control (CAC) based on traffic Control (CAC) based on traffic descriptor, QOS requirements, and descriptor, QOS requirements, and available resources at that switchavailable resources at that switch

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Basic Operation (Cont’d)Basic Operation (Cont’d)

If connection is acceptable, then If connection is acceptable, then request is forwarded on, request is forwarded on, otherwise “reject” is returnedotherwise “reject” is returned

If destination accepts connection, If destination accepts connection, then “accept” is returnedthen “accept” is returned

VPI and VCI assignedVPI and VCI assigned

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Example: ATM SignallingExample: ATM Signalling

ATMNetwork

1010


ATM Switch

1111


UNI

1212


UNI

NNI

1313


UNI

UNINNI

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Example 1: ATM SignallingExample 1: ATM Signalling

CR

CR: Connection Request

1515


CR


1616


CR


1717


CR


1818


CR


1919


CR

CR: Connection RequestOK : Connection Accept

OK(VCI = 12)

2020


CR


OK(VCI = 12)

(VCI = 4)

2121


CR


OK(VCI = 12)

(VCI = 4)

(VCI = 104)

2222


CR


OK(VCI = 12)

(VCI = 4)

(VCI = 104)

(VCI = 4)

2323


CR


OK

OK(VCI = 12)

(VCI = 4)

(VCI = 104)

(VCI = 4)(VCI = 77)

2424


CR


2525


CR

NO: Connection Reject

NO


2626


CR


2727


CR


2828


CR


2929


CR


NO


3030


CR


NO


3131


CR


NO


NO

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SummarySummary

ATM UNI and NNI signalling ATM UNI and NNI signalling specifications define the protocols specifications define the protocols for connection setup and for connection setup and teardown between ATM teardown between ATM equipment (Version 4.0 soon)equipment (Version 4.0 soon)

Can support point to point and Can support point to point and multipoint connectionsmultipoint connections

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Where to get more informationWhere to get more information

ATM UNI 3.0 Specification ATM UNI 3.0 Specification (now obsolete!) (now obsolete!)

ATM ForumATM Forum Fore Systems SPANS protocol Fore Systems SPANS protocol

specification (Simple Protocol specification (Simple Protocol for ATM Network Signalling)for ATM Network Signalling)

An Overview of ATM Signalling

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