Packets used by (SRP Spatial Reuse Protocol) can be sent over any point-to-point
link layer (e.g., SONET/SDH, ATM, point to point Ethernet connections). The
maximum transfer unit (MTU) is 9216 octets; the minimum MTY for data packets
is 55 octets.
The overall SRP packet format is as shown in the following illustration:
11 bits
1
1
3 bits
Time to Live
R
D
Mode
Usage
P
Destination Address (6 bytes)
Source Address (6 bytes)
Protocol Type (2 bytes)
Payload
SRP packet
structure
Time to live
11 bit field representing the hop-count. It is decremented every time a node
forwards a packet. If the TTL reaches zero it is stripped off the ring,
thus allowing for a total node space of 2048 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 1024. 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.
Ring identifier (R)
1-bit field which identifies to which ring this packet is designated, as follows:
Inner ring 0
Outer ring 1
Designation strip (D)
1-bit field used to indicate whether or not the destination node should strip
the packet. This bit is almost always set to 1.
Priority field (PRI)
3-bit field that indicates the priority level of the SRP packet (0-7). Higher
values indicate higher priority.
Mode
3-bit field used to identify the mode of the packet as follows:
000 Reserved
001 Reserved
010 Reserved
011 Reserved
100 Control message (pass to host)
101 Control message (locally buffered for host)
110 MAC keep alive
111 Packet data
Usable bandwidth (Usage)
12-bit field which indicates the current usable bandwidth this node sees according
to the SRP Fairness Algorithm (SRP-fa).
Parity bit (P)
Indicates the parity value over the last 31 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 is an odd number).
Destination address
Globally unique 48-bit address assigned by IEEE.
Source address
Globally unique 48-bit address assigned by the IEEE.
Protocol type
2-octet field similar to EtherType field. Possible values are as follows:
0x2007 SRP Control
0x0800 IP version 4
0x0806 ARP
Interested in more details about testing
this protocol?
