1. 802.17c Protected Inter-Ring Connection
Rafi Ram - Corrigent Systems
July 2007

2. PIRC Suggestion Highlights
Stations A & B are members of a protection group (PG) for interconnect between two rings
Station A and station B are protection group members (PGM)
One of the interconnected rings shall be provisioned as the “primary” ring and the other as “secondary” ring
The station on the secondary ring with the lower MAC address is designated as the “0” member, and the other as the “1” member

3. Network Diagram Stations A & C are “peer” stations
Stations B & D are “peer” stations
Stations A & B are “mate” stations
Stations C & D are “mate” stations
Stations A & B are protection group members on the primary ring
Station A is the “0” member and station B is the “1” member
Stations C & D are protection group members on the secondary ring
Station C is the “0” member and station D is the “1” member

4. Station-OK State Variable
Station-OK = (adminStatus==UP) AND (mateVisable==TRUE) AND

5. Peer Stations Communication
Peer stations exchange messages which are also used as “keep-alive”
The messages consist the following information (per protection group):
Station-OK state variable
Peer keep-alive timer expired
The peer messages are sent :
periodically
after a protection event
after change of admin-status
after peer keep-alive timer expires

6. Self-OK State Variable
Self-OK = (my_Station-OK==TRUE) AND (my_KA_Timer_Expired==FALSE) AND (peer_Station-OK==TRUE) AND (peer_KA_Timer_Expired==FALSE)

7. Mate Stations Communication
Mate stations exchange messages which are also used as “keep-alive”
Mate stations exchange the value of the Self-OK state variable (per protection group) :
The mate messages are sent :
periodically
after a protection event
after change Self-OK state variable value
The messages could be new control type or new OAM type

8. PIRC Stations Communication

9. Mate-OK State Variable
Mate-OK = (mateVisable==TRUE) AND (mate_Self-OK==TRUE) AND (mate_KA_Timer_Expired==FALSE)

10. PGM State Machine

11. MAC Table Flush
802.17b – When an interconnecting station no longer appears in the topology, the MAC entries associated with that stations are deleted
When a PIRC station it sends SAS_Group_Notify message when :
it changes PG state to “FWD-None”
it changes PG state from “FWD-All” to “FWD-mine”

12. myFlow(frame) Function
The function could be used to implementation of the load-balancing functionality
On of the possible implementations of the myFlow function could be :
myFlow(frame) = (hashing(frame) modulo 2) == member-type
The hashing could be on the service class and/or VLAN
“member-type” equals to 0 if the station is the 0 member, and equals to 1 if the station is the 1 member

13. PIRC Sublayer Logic on the Path Client  MAC as State Table
Row
Condition
Action 1
MAC is on primary ring
Forward 2
PG state is “fwd-none”
Discard 3
PG state is “fwd-all” 4
myFlow(frame) 5 -

14. PIRC Sublayer Logic on the Path Client  MAC as Pseudo-Code
if (MAC is on primary ring)
forward frame
else
if (((PG state is “fwd-mine”) and myFlow(frame)) or (PG state is “fwd-all”)) then
discard frame

15. PIRC Sublayer Logic on the Path MAC  Client as State Table
Row
Condition
Action 1
(MAC is on primary ring) and (RPR SA is the mate MAC address) and (PG state is “fwd-all”)
Discard 2
MAC is on primary ring
Forward 3
RPR SA is the mate MAC address 4
PG state is “fwd-none” 5
PG state is “fwd-all” 6
myFlow(frame) 7 -

16. PIRC Sublayer Logic on the Path MAC  Client as Pseudo-Code
if (MAC is on primary ring)
if ((PG state is “fwd-all”) and (RPR SA is the mate MAC address))
discard frame
else
forward frame
if (RPR SA is the mate MAC address)
if (((PG state is “fwd-mine”) and myFlow(frame)) or (PG state is “fwd-all”)) then

17. Local Tributaries at PIRC Stations
According to the suggested algorithm, if the PIRC station are isolated on the primary ring, then their local tributaries are also disconnected
Complicating the algorithm to allow forwarding through the secondary ring is not critical because :
isolation on the primary ring is a DUAL failure
if the primary ring has isolation, the local tributaries at the PIRC stations are usually not the biggest problem