MAPOS, Multiple Access Protocol over SONET/SDH

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite:
Type:Link layer protocol.

RFC 2176:

A component called "Frame Switch" allows multiple nodes to be connected together in a star topology to form a LAN. Using long haul SONET/SDH links, the nodes on such a "SONET-LAN" can span over a wide geographical area.

MAPOS is a link layer protocol for transmitting HDLC frames over SONET/SDH.

MAPOS header Data ::: MAPOS trailer

MAPOS frame format:

0001020304050607 0809101112131415 1617181920212223
Flag Address Control
Protocol Data :::
FCS Flag

Flag. 8 bits. Always set to 0x7E.
This field is used for frame synchronization. Each frame begins and ends with one or more Flag fields. If a frame immediately follows another, one flag sequence may be treated as the end of the preceding frame and the beginning of the immediately following frame. When the line is idle, the flag sequence is to be transmitted continuously on the line.

Address. 8 bits.
This field contains the destination HDLC address. A frame is forwarded by a switch based on this field. Address 0xFF indicates that the frame is a broadcast frame. Address 0x01 is reserved to identify the control processor inside a switch. Frames with an invalid address should be silently discarded.

M Node 1

M, Multicast. 1 bit.
If set, the frame is a multicast frame. Otherwise, this is a unicast frame.

Node, Destination node address. 6 bits.

Control. 8 bits. Always set to 3.
In HDLC nomenclature this indicates that the frame is an Unnumbered Information (UI) with the Poll/Final (P/F) bit cleared to zero. Frames with any other control field values should be silently discarded.

Protocol. 16 bits.

0x0021 IP, Internet Protocol version 4.
0x0057 IPv6, Internet Protocol version 6.
0xFE01 ARP, Address Resolution Protocol.
0xFE03NSP, Node Switch Protocol.
0xFE05SSP, Switch Switch Protocol.

Data. Variable length. 1 to 65280 bytes.
Contains the encapsulated datagram.

FCS, Frame Check Sequence. 16 or 32 bits.
By default, this field is 16 bits long. Optionally, 32 bit FCS may be used instead. The FCS is calculated over all bits of the address, control, protocol and information fields prior to escape conversions. The least significant byte of the result is transmitted first as it contains the coefficient of the highest term.



[RFC 2171] MAPOS - Multiple Access Protocol over SONET/SDH Version 1.

[RFC 2172] MAPOS Version 1 Assigned Numbers.

[RFC 2173] A MAPOS version 1 Extension - Node Switch Protocol.

[RFC 2174] A MAPOS version 1 Extension - Switch-Switch Protocol.

[RFC 2175] MAPOS 16 - Multiple Access Protocol over SONET/SDH with 16 Bit Addressing.

[RFC 2176] IPv4 over MAPOS Version 1.

[RFC 3186] MAPOS/PPP Tunneling mode.

[RFC 3422] Forwarding Media Access Control (MAC) Frames over Multiple Access Protocol over Synchronous Optical Network/Synchronous Digital Hierarchy (MAPOS).

[RFC 3572] Internet Protocol Version 6 over MAPOS (Multiple Access Protocol Over SONET/SDH).

Description Glossary RFCs Publications Obsolete RFCs