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ATM Signalling

ATM Signalling

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ATM Signalling

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  1. ATM Signalling Philip Branch Centre for Telecommunications and Information Engineering (CTIE) Monash University http://www.anspag.monash.edu.au/~pbranch/masters.ppt

  2. Signalling Overview • Description of Signalling • Signalling between the User and Network • Signalling within Private ATM Networks • Signalling between ATM networks

  3. 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

  4. Requirements of ATM Signalling • Establish connection • Routing • Quality of Service • Point to point, multipoint • Clear connection • Status information

  5. Establishment of a Connection • Find destination node • Determine path through network • Establish connection between each node

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. User-Network Interface • Access Signalling • Connection between CPE and network • UNI 3.0, 3.1, 4.0 • Q.2931

  12. 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

  13. Signalling Protocol Stack • UNI, • UNI SSCF, • SSCOP Q.2110, • AAL5

  14. 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

  15. 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

  16. Traffic Descriptor in SETUP • Forward and backwards traffic • CLP priorities • Token Bucket Parameters • Peak Cell Rate • Sustainable Cell Rate • Maximum Burst Size

  17. Quality of Service Parameter • Predefined in 3.1 • Parameterised in 4.0 • Parameters • Cell Loss Ratio • Maximum Cell Delay Time • Maximum Cell Delay Variation

  18. Call Progression VPI 0, VCI 5 ATM Network/Switch Calling Party SETUP (Call Ref, AAL, Address, Cell Rates, QoS) CONNECT (Call Ref, AAL, Connection ID - VPCI, VCI) Various timers used during call connection phase Various timers used during call connection phase Active State CONNECT ACK (Call Ref)

  19. Switch to Switch Signalling • Routing • How to find destination • Resource allocation • Quality of Service guarantees • Connection Admission Control • Signalling Protocol

  20. Interim Inter-Switch Protocol (IISP) • Precursor to PNNI • PNNI phase 0 • Based on UNI 3.1 • Static Routing

  21. P-NNI Standard • Private Network to Network Interface • ATM Forum Standard • Communications between switches in a private network • Scalability

  22. 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

  23. Functions of P-NNI • Signalling protocol • Based on UNI 3.1 • Routing • Most important function of P-NNI • Designated Transit List(DTL)

  24. 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

  25. Source Routing • Source needs complete topology information • Broadcast id on all paths • Copy and transfer other nodes • Scales poorly

  26. 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

  27. 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

  28. Topology State Information • Information transferred in PTSPs • Attributes of Switch • total capacity • Metrics • number of connections • used capacity

  29. Reachability Information • Based on Address prefixes • Designated Transit List • Source route at each level

  30. 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

  31. 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

  32. Example of P-NNI connection establishment

  33. 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

  34. Broadband ISDN User Part • ITU-T standard • Public carrier standard • Connectionless, Hop-by-hop routing • similar to IP

  35. 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

  36. Issues with signalling between ATM networks • Different network signalling standards • Large amounts of topology information • Confidential information • topology, metrics

  37. 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

  38. Conclusion • Signalling functions • User network interface signalling • UNI 3.0, 3.1 • Switch to switch signalling • IISP, P-NNI

  39. 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?