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Understanding ATM Signalling Protocol: UNI and NNI Overview

This overview delves into the Asynchronous Transfer Mode (ATM) signalling protocols, highlighting the User-Network Interface (UNI) and Network-Network Interface (NNI). ATM is a connection-oriented protocol requiring virtual channels to be established for data transfer. It involves a two-part signalling system where UNI facilitates communication between hosts and switches, while NNI governs switch-to-switch interactions. The document outlines basic signalling operations, connection requests, call admission control, and the cell formats used. Detailed examples demonstrate the practical application of ATM signalling operations.

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Understanding ATM Signalling Protocol: UNI and NNI Overview

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  1. An Overview of ATM Signalling Carey Williamson University of Calgary

  2. Introduction • ATM is a connection-oriented protocol, which means that virtual channels must be set up before any data cells can be sent on the channel • Connection setup is done using a signalling protocol

  3. ATM Signalling Protocol • Protocol consists of two parts • User-Network Interface (UNI) • defines how hosts talk to switches • Network-Network Interface (NNI) • defines how switches talk to other switches • Cell formats slightly different

  4. ATM UNI Cell Format GFC VPI VPI VCI VCI VCI PT RES CLP HEC Payload (48 bytes)

  5. ATM NNI Cell Format VPI VPI VPI VCI VCI VCI PT RES CLP HEC Payload (48 bytes)

  6. ATM NNI Cell Format VPI VPI VPI VCI VCI VCI PT RES CLP HEC Payload (48 bytes)

  7. Basic Signalling Operation • Connection requests proceed hop-by-hop through the switches of the network, route to destination • Switches perform Call Admission Control (CAC) based on traffic descriptor, QOS requirements, and available resources at that switch

  8. Basic Operation (Cont’d) • If connection is acceptable, then request is forwarded on, otherwise “reject” is returned • If destination accepts connection, then “accept” is returned • VPI and VCI assigned

  9. ATM Network Example: ATM Signalling

  10. Example: ATM Signalling ATM Switch

  11. Example: ATM Signalling UNI

  12. Example: ATM Signalling NNI UNI

  13. Example: ATM Signalling UNI NNI UNI

  14. Example 1: ATM Signalling CR CR: Connection Request

  15. Example 1: ATM Signalling CR CR: Connection Request

  16. Example 1: ATM Signalling CR CR: Connection Request

  17. Example 1: ATM Signalling CR CR: Connection Request

  18. Example 1: ATM Signalling CR CR: Connection Request

  19. Example 1: ATM Signalling OK (VCI = 12) CR CR: Connection Request OK : Connection Accept

  20. Example 1: ATM Signalling OK (VCI = 12) CR (VCI = 4) CR: Connection Request OK : Connection Accept

  21. Example 1: ATM Signalling OK (VCI = 12) CR (VCI = 104) (VCI = 4) CR: Connection Request OK : Connection Accept

  22. Example 1: ATM Signalling OK (VCI = 12) CR (VCI = 104) (VCI = 4) (VCI = 4) CR: Connection Request OK : Connection Accept

  23. Example 1: ATM Signalling OK (VCI = 12) CR (VCI = 104) (VCI = 4) OK (VCI = 4) (VCI = 77) CR: Connection Request OK : Connection Accept

  24. Example 2: ATM Signalling CR CR: Connection Request

  25. Example 2: ATM Signalling CR NO CR: Connection Request NO: Connection Reject

  26. Example 3: ATM Signalling CR CR: Connection Request

  27. Example 3: ATM Signalling CR CR: Connection Request

  28. Example 3: ATM Signalling CR CR: Connection Request

  29. Example 3: ATM Signalling CR NO CR: Connection Request NO: Connection Reject

  30. Example 3: ATM Signalling CR NO CR: Connection Request NO: Connection Reject

  31. Example 3: ATM Signalling CR NO NO CR: Connection Request NO: Connection Reject

  32. Summary • ATM UNI and NNI signalling specifications define the protocols for connection setup and teardown between ATM equipment (Version 4.0 soon) • Can support point to point and multipoint connections

  33. Where to get more information • ATM UNI 3.0 Specification (now obsolete!) • ATM Forum • For Systems SPANS protocol specification (Simple Protocol for ATM Network Signalling)

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