A MAPOS version 1 Extension - Node Switch Protocol
RFC 2173

Document Type RFC - Informational (June 1997; No errata)
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Network Working Group                                        K. Murakami
Request for Comments: 2173                                   M. Maruyama
Category: Informational                                 NTT Laboratories
                                                               June 1997

           A MAPOS version 1 Extension - Node Switch Protocol

Status of this Memo

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


   This document describes a MAPOS extension, Node Switch Protocol, for
   automatic node address assignment. MAPOS is a multiple access
   protocol for transmission of network-protocol datagrams, encapsulated
   in High-Level Data Link Control (HDLC) frames, over SONET/SDH. NSP
   automates the HDLC address configuration of each node. Using NSP, a
   node retrieves its HDLC address from the switch to which it is

1. Introduction

   MAPOS[1], Multiple Access Protocol over SONET(Synchronous Optical
   Network)/SDH(Synchronous Digital Hierarchy)[2][3][4][5], is a
   protocol for transmission of HDLC frames over SONET/SDH. A SONET
   switch provides multiple access capability to each node. In MAPOS,
   each node has a unique HDLC address within a switch. The address is
   equivalent to the port number of the switch to which the node is
   connected.  This document describes an extension to MAPOS, Node
   Switch Protocol, which enable automatic HDLC address assignment.
   First, it explains the addressing of MAPOS. Then, it describes the
   NSP protocol for automatic HDLC node address assignment.

2. Node Address Format

   This section describes MAPOS Version 1 address format in single and
   multiple switch environment.

Murakami & Maruyama          Informational                      [Page 1]
RFC 2173                         MAPOS                         June 1997

2.1 Address Format

   In MAPOS network, each end node has a unique HDLC address. As shown
   in Figure 1, the address length is 8 bits. The LSB is always 1 which
   indicates the end of the field.  When a SONET switch receives an HDLC
   frame, it forwards the frame based on the address in the frame

   In unicast, MSB is 0 and the rest of the bits are the port number to
   which a node is connected. Since the LSB is always 1, the minimum and
   maximum addresses are 0x01 and 0x7F, respectively.  Address 0x01 is
   reserved and is assigned to the control processor in a SONET switch.

   In broadcast, MSB is 1 and the rest of the bits are all 1s. In
   multicast, MSB is 1 and the rest of the bits, except for the LSB,
   indicate the group address.

           | | | | | | | | |
           | |port number|1|
            ^             ^
            |             |
            |             +------- EA bit (always 1)
            1 : broadcast, multicast
            0 : unicast

                              Figure 1 Address format

2.2 Address in multi-switch environment

   In a multi-switch environment, variable-length subnet addressing is
   used. Each switch has a switch number that is unique within the
   system. Subnetted node addresses consist of the switch number and the
   port number to which a node is connected. The address format is "0
   <switch number> <node number> 1" for a unicast address, "all 1" for
   the broadcast address, and "1 <group address> 1" for a multicast

   The address 0x01 is reserved and is assigned to the control processor
   in the "local" switch. That is, it indicates the switch itself to
   which the node is connected. The addresses of the form "0 <switch
   number> <all 0> 1" are reserved, and indicates the control processor
   of the switch designated by the switch number.

   In Figure 2, the switch numbers are two bits long. Node N1 is
   connected to port 0x3 of switch S1 numbered 0x1 (01 in binary). Thus,

Murakami & Maruyama          Informational                      [Page 2]
RFC 2173                         MAPOS                         June 1997

   the node address is 0 + 01 + 00011, that is, 00100011(0x23). Node N3
   has an address 01001001(0x49), since the switch number of S2 is 0x2
   (10 in binary) and the port number is 0x09. Note that all the port
   numbers are odd because the LSBs are always 1.

                           | node |
                           |  N1  |
                               | 00100011(0x23)
                               |0x3             |0x3
               +------+    +---+----+       +---+----+     +------+
               | node +----+ SONET  +-------+ SONET  +-----+ node |
               |  N2  | 0x5| Switch |0x9 0x5| Switch |0x9  |  N3  |
               +------+    |   S1   |       |   S2   |     +------+
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