SRP, Spatial Reuse Protocol

Description Glossary RFCs Publications Obsolete RFCs


Protocol suite:
Type:MAC layer protocol.

Packet format:

00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
TTL R Mode PRI P Destination address :::
Source address ::: Protocol
Data :::

TTL, Time To Live. 8 bits.
A hop count that must be decremented every time a node forwards a packet. If the TTL reaches zero it is stripped off the ring. This allows for a total node space of 256 nodes on a ring. However, due to certain failure conditions (e.g. when the ring is wrapped) the total number of nodes that are supported by SRP is 128. When a packet is first sent onto the ring the TTL should be set to at least twice the total number of nodes on the ring.

R, Ring Identifier. 1 bit.
Identifies which ring this packet is designated for.

0 Outer Ring.
1 Inner Ring.

Mode. 3 bits.
Mode of the packet.

3 ATM cell.
4 Control message (Pass to host).
5 Control message (Locally buffered for host).
6 Usage message.
7 Packet data.

PRI. 3 bits.

P, Parity. 1 bit.
This bit is used to indicate the parity value over the 15 bits of the SRP header to provide additional data integrity over the header. Odd parity is used (i.e. the number of ones including the parity bit shall be an odd number).

Destination address. 48 bits.

Source address. 48 bits.

Protocol. 16 bits.

0x0800 IP.
0x0806 ARP.
0x2007 SRP control.



[RFC 2892] The Cisco SRP MAC Layer Protocol.

Description Glossary RFCs Publications Obsolete RFCs