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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?