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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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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 1: ATM SignallingExample 1: ATM Signalling
CR
CR: Connection RequestOK : Connection Accept
OK(VCI = 12)
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Example 1: ATM SignallingExample 1: ATM Signalling
CR
CR: Connection RequestOK : Connection Accept
OK(VCI = 12)
(VCI = 4)
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Example 1: ATM SignallingExample 1: ATM Signalling
CR
CR: Connection RequestOK : Connection Accept
OK(VCI = 12)
(VCI = 4)
(VCI = 104)
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Example 1: ATM SignallingExample 1: ATM Signalling
CR
CR: Connection RequestOK : Connection Accept
OK(VCI = 12)
(VCI = 4)
(VCI = 104)
(VCI = 4)
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Example 1: ATM SignallingExample 1: ATM Signalling
CR
CR: Connection RequestOK : Connection Accept
OK
OK(VCI = 12)
(VCI = 4)
(VCI = 104)
(VCI = 4)(VCI = 77)
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Example 2: ATM SignallingExample 2: ATM Signalling
CR
NO: Connection Reject
NO
CR: Connection Request
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Example 3: ATM SignallingExample 3: ATM Signalling
CR
CR: Connection Request
NO
NO: Connection Reject
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Example 3: ATM SignallingExample 3: ATM Signalling
CR
CR: Connection Request
NO
NO: Connection Reject
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Example 3: ATM SignallingExample 3: ATM Signalling
CR
CR: Connection Request
NO
NO: Connection Reject
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)