ATM Signalling

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Copyright © Monash University

ATM Signalling

Philip BranchCentre for Telecommunications and Information

Engineering (CTIE)

Monash Universityhttp://www.anspag.monash.edu.au/~pbranch/masters.ppt

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Signalling Overview

• Description of Signalling

• Signalling between the User and Network

• Signalling within Private ATM Networks

• Signalling between ATM networks

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What is Signalling?

• Call and Connection Control • Means by which calls are

– established, maintained, terminated

• In Channel Signalling– in and out of band

• Common Channel Signalling– One shared, dedicated signalling channel– N-ISDN and ATM

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Requirements of ATM Signalling

• Establish connection– Routing– Quality of Service– Point to point, multipoint

• Clear connection

• Status information

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Establishment of a Connection

• Find destination node

• Determine path through network

• Establish connection between each node

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Signalling Standards

• User-Network Interface– UNI 3.0, UNI 3.1, UNI 4.0– Q.93B, Q.2931– ILMI

• Network to Network Interface– IISP, P-NNI, IPNNI, AINI, BICI, B-ISUP

• Other important standards– LANE, MPOA

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ATM Signalling Standards Evolution

• Q.931 - Q.93B - UNI 3.0

• Q.931 - Q.2931 - UNI 3.1

• Q.931 - Q.2931 - UNI 4.0

• Q.931 - Q.2931 - IISP - PNNI

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Signalling within Private ATM Networks

• Private and public network standards

• ATM Forum, ITU-T main standards bodies

• Connection of CPE to network

• Connection across the network

• Passing of reachability information between switches

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ATM Addressing

• Two formats– OSI NSAP for private networks– E.164 for public networks (ISDN numbers)

• Format– Network part– User part

• Network part hierarchical structure• User part similar to Ethernet MAC address

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ILMI and Addressing

• Interim Local Management Interface Specification

• Management plane of ATM protocol stack

• Built around SNMP

• Management Information Base

• Monitoring and Control across the UNI

• Key function is address registration

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User-Network Interface

• Access Signalling

• Connection between CPE and network

• UNI 3.0, 3.1, 4.0

• Q.2931

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UNI 3.1

• ATM Forum Standard

• Similar to N-ISDN Q.931

• Signalling between CPE and network

• Specify point to point and multipoint

• Signalling ATM Adaptation Layer

• Signalling over PVC– VPI = 0, VCI = 5

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Signalling Protocol Stack

• UNI,

• UNI SSCF,

• SSCOP Q.2110,

• AAL5

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UNI 3.1 Signalling Messages

• Fewer messages than Q.931

• Call establishment– setup, proceeding, connect, connect

acknowledge

• Call Clearing– release, relase complete

• Status– status, status enquiry

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SETUP Signalling Message

• Similar to SETUP in N-ISDN Q.931

• Additional functions in SETUP– AAL type– Bearer (CBR, VBR-nrt, Unkown)– ATM traffic descriptor– QoS parameter

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Traffic Descriptor in SETUP

• Forward and backwards traffic

• CLP priorities

• Token Bucket Parameters– Peak Cell Rate– Sustainable Cell Rate– Maximum Burst Size

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Quality of Service Parameter

• Predefined in 3.1

• Parameterised in 4.0

• Parameters– Cell Loss Ratio– Maximum Cell Delay Time– Maximum Cell Delay Variation

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Call Progression

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Calling Party ATM Network/Switch

SETUP (Call Ref, AAL, Address, Cell Rates, QoS)

CONNECT (Call Ref, AAL, Connection ID - VPCI, VCI)

CONNECT ACK (Call Ref)

Various timersused during callconnection phase

Various timersused during callconnection phase

ActiveState

VPI 0, VCI 5

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Switch to Switch Signalling

• Routing– How to find destination

• Resource allocation– Quality of Service guarantees– Connection Admission Control

• Signalling Protocol

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Interim Inter-Switch Protocol (IISP)

• Precursor to PNNI– PNNI phase 0

• Based on UNI 3.1

• Static Routing

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P-NNI Standard

• Private Network to Network Interface

• ATM Forum Standard

• Communications between switches in a private network

• Scalability

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P-NNI Protocol Stack

• PNNI

• UNI SSCF (Q.2130) and SSCOP (Q.2110)– Signalling Specific Coordinating Functions– Service Specific Connection-oriented Control– Data Link protocol

• AAL5

• SSCF, SSCOP, AAL5 = SAAL

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Functions of P-NNI

• Signalling protocol– Based on UNI 3.1

• Routing– Most important function of P-NNI– Designated Transit List(DTL)

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Routing in P-NNI

• Source based routing protocol

• Source specifies route to destination– Designated Transit List

• Transfer of topology information between switches

• Uses hierarchy and summarisation

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Source Routing

• Source needs complete topology information

• Broadcast id on all paths

• Copy and transfer other nodes

• Scales poorly

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P-NNI Topology Construction

• Hierarchy of Peer Groups– overcomes scalability problems of Source

Routing

• Every member of Peer Group knows route to every other member– DTL in Setup message

• New DTL constructed whenever message leaves peer group

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Exchange of information at first level within a PG

• PNNI topology state packets (PTSP)– reachable destinations within PG– current capabilities of nodes and links

• All members of Peer group flooded with PTSPs

• New PTSPs exchanged when– major events– information aged

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Topology State Information

• Information transferred in PTSPs

• Attributes of Switch– total capacity

• Metrics– number of connections– used capacity

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Reachability Information

• Based on Address prefixes

• Designated Transit List– Source route at each level

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Exchange of information at higher level PGs

• Designated Peer Group Leader– Elected by other nodes– Election ongoing– Represents PG at next layer

• PGL summarises topology state and reachability information

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GCAC and Crankback

• Generic Connection Admission Control (GCAC)– Indication only as to whether connection can be

admitted

• Crankback enables alternate path to be found without abandoning complete call

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Example of P-NNI connection establishment

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Summary of Functions of PNNI Routing

• Discovery of neighbours and link status

• Synchronisation of topology databases

• Flooding of PTSPs

• Election of PGLs

• Summarisation of topology information

• Construction of routing hierarchy

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Broadband ISDN User Part

• ITU-T standard

• Public carrier standard

• Connectionless, Hop-by-hop routing– similar to IP

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Signalling between ATM Networks

• Interconnection between both public and private networks

• Private to private eg. Monash University / Melbourne University

• Private to public eg. Monash / Telstra

• Public to Public eg. Telstra / Optus

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Issues with signalling between ATM networks

• Different network signalling standards

• Large amounts of topology information

• Confidential information– topology, metrics

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Standards for Signalling between ATM Networks

• Broadband Inter-Carrier Interface – ATM Forum– Based on SS7, B-ISUP– Interworking between B-ISUP networks

• ATM Internetwork Interface (AINI)– Interworking between PNNI, B-ISUP– PNNI signalling with static routing– Connecting non-PNNI / PNNI networks

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Conclusion

• Signalling functions

• User network interface signalling– UNI 3.0, 3.1

• Switch to switch signalling– IISP, P-NNI

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Questions

• Why is there no contention algorithm for access to the signalling channel in ATM?

• In the worked example of PNNI routing, what is the next DTL to be pushed onto the stack?

Documents

ATM Signalling