RFC 2174 (rfc2174) - Page 3 of 22

A MAPOS version 1 Extension - Switch-Switch Protocol

RFC 2174                         MAPOS                         June 1997


3.1 Address Structure of MAPOS version 1

   In a multiple switch environment, a node address consists of the
   switch number and the port number to which the node is connected. As
   shown in Figure 1, the address length is 8 bits and the LSB is always
   1, which indicates the end of the address field. A MSB of 0 indicates
   a unicast address. The switch and the port number fields are
   variable-length. In this document, a unicast address is represented
   as "0 ".  Note that a port number
   includes EA bit.

   MSB of 1 indicates multicast or broadcast. In the case of broadcast,
   the address field contains all 1s (0xff in hex). In the case of
   multicast, the remaining bits indicate a group address.  The switch
   number field is variable-length. A multicast address is represented
   as "1 ".


           Switch Number(variable length)
               |
               |      +--- Port Number
               |      |
               V      V
             |||
           +-------------+-+
           | | | | | | | | |
           | |           |1|
           +-+-----------+-+
            ^             ^
            |             |
            |             +------- EA bit (always 1)
            |
            1 : broadcast, multicast
            0 : unicast

                        Figure 1 Address Format

   Figure 2 shows an example of a SONET LAN that consists of three
   switches.  In this configuration, two bits of a node address are used
   to indicate the switch number. Node N1 is connected to port
   0x03(000011 in binary) of the switch S2 numbered 0x2.  Thus, the node
   address is 01000011 in binary. Node N4 has an address 01101001 in
   binary since the connected switch number is 0x3 and the port number
   is 0x09.







Murakami & Maruyama          Informational