The Cisco SRP MAC Layer Protocol
RFC 2892

Document Type RFC - Informational (August 2000; No errata)
Was draft-tsiang-srp (individual)
Last updated 2013-03-02
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Network Working Group                                          D. Tsiang
Request for Comments: 2892                                     G. Suwala
Category: Informational                                    Cisco Systems
                                                             August 2000

                    The Cisco SRP MAC Layer Protocol

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2000).  All Rights Reserved.

Abstract

   This document specifies the MAC layer protocol, "Spatial Reuse
   Protocol" (SRP) for use with ring based media. This is a second
   version of the protocol (V2).

   The primary requirements for SRP are as follows:

   -  Efficient use of bandwidth using:
          spatial reuse of bandwidth
          local reuse of bandwidth
          minimal protocol overhead
   -  Support for priority traffic
   -  Scalability across a large number of nodes or stations attached to
      a ring
   -  "Plug and play" design without a software based station management
      transfer (SMT) protocol or ring master negotiation as seen in
      other ring based MAC protocols [1][2]
   -  Fairness among nodes using the ring
   -  Support for ring based redundancy (error detection, ring wrap,
      etc.) similar to that found in SONET BLSR specifications.
   -  Independence of physical layer (layer 1) media type.

   This document defines the terminology used with SRP, packet formats,
   the protocol format, protocol operation and associated protocol
   finite state machines.

Tsiang & Suwala              Informational                      [Page 1]
RFC 2892            The Cisco SRP MAC Layer Protocol         August 2000

Table of Contents

    1.  Differences between SRP V1 and V2 .......................  3
    2.  Terms and Taxonomy ......................................  4
        2.1.  Ring Terminology ..................................  4
        2.2.  Spatial Reuse .....................................  5
        2.3.  Fairness ..........................................  6
        2.4.  Transit Buffer ....................................  7
    3.  SRP Overview ............................................  8
        3.1.  Receive Operation Overview ........................  8
        3.2.  Transmit Operation Overview .......................  8
        3.3.  SRP Fairness Algorithm (SRP-fa) Overview ..........  9
        3.4.  Intelligent Protection Switching (IPS) Protocol
              Overview ..........................................  9
    4.  Packet Formats .......................................... 13
        4.1.  Overall Packet Format ............................. 13
        4.2.  Generic Packet Header Format ...................... 14
             4.2.1.  Time To Live (TTL) ......................... 14
             4.2.2.  Ring Identifier (R) ........................ 15
             4.2.3.  Priority Field (PRI) ....................... 15
             4.2.4.  MODE ....................................... 15
             4.2.5.  Parity Bit (P-bit) ......................... 16
             4.2.6.  Destination Address ........................ 16
             4.2.7.  Source Address ............................. 16
             4.2.8.  Protocol Type .............................. 16
        4.3.  SRP Cell Format ................................... 16
        4.4.  SRP Usage Packet Format ........................... 17
        4.5.  SRP Control Packet Format ......................... 18
             4.5.1.  Control Ver ................................ 19
             4.5.2.  Control Type ............................... 19
             4.5.3.  Control TTL ................................ 19
             4.5.4.  Control Checksum ........................... 19
             4.5.5.  Payload .................................... 20
             4.5.6.  Addressing ................................. 20
        4.6.  Topology Discovery ................................ 20
             4.6.1.  Topology Length ............................ 22
             4.6.2.  Topology Originator ........................ 22
             4.6.3.  MAC bindings ............................... 22
             4.6.4.  MAC Type Format ............................ 22
        4.7.  Intelligent Protection Switching (IPS) ............ 23
             4.7.1.  Originator MAC Address ..................... 23
             4.7.2.  IPS Octet .................................. 24
        4.8.  Circulating packet detection (stripping) .......... 24
    5.  Packet acceptance and stripping ......................... 25
        5.1.  Transmission and forwarding with priority ......... 27
        5.2.  Wrapping of Data .................................. 28
    6.  SRP-fa Rules Of Operation ............................... 28
        6.1.  SRP-fa pseudo-code ................................ 30
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