RFC 2173 (rfc2173) - Page 2 of 6
A MAPOS version 1 Extension - Node Switch Protocol
Alternative Format: Original Text Document
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
header.
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
1" for a unicast address, "all 1" for
the broadcast address, and "1 1" for a multicast
address.
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 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
