7/16/2007 IEEE 802.17 RPRWG Mike Takefman

PIRC Architecture

July 2007 Plenary SessionSan Francisco

Mike TakefmanCisco Systems

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

My PIRC High Level Goals

• Built on top of 802.17b MAC• Assumption is an L2 switched network

• PIRC has to provide loop-free dual connectivity• Multiple Load-Balancing methods

• Compatible with non-PIRC stations• ideally no MAC or operational changes needed for other nodes

• usable with existing standard product chips

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

Where To Put Filtering

• PIRC is essentially adding new filtering rules to the system• assumption is that ingress and egress filter rules exist

• Our scope requires that these filtering rules exist in the MAC level, but the actual position is implementation dependant• side effect on whether 802.17b learning occurs• no easy way to arbitrarily allow or not allow learning• question is one of compliance

• Tributary support requires egress filtering rules in addition to ingress rules

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

Hash Filtering

• Previous presentations have pointed out that certain constraints must be followed in order to insure connectivity • net result is that the basic hash function is based on outer VLAN

• hence this form of hash filtering is essentially VLAN filtering and any other hashing function is by definition proprietary

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

• It has been suggested that PIRC support both 1 and 2 span failures• it must be assumed that the network is otherwise loop free

• 2 cuts on a leaf ring is trivial as a loop cannot be created

• 2 cuts on an intermediate ring is more interesting and has a few cases

DC

BA

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

BA

• Isolated Node• no connectivity to that node• no loops created

• Nothing can be done, and there are no PIRC issues

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

BA

• Isolated Neighbour Ring• no connectivity to that sub-tree• no loop created

• Nothing can be done, and there are no PIRC issues

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

BA

• Isolated Partial Ring• full connectivity possible• no loop created

• PIRC could restore connectivity• A&B operated normally• D&C both do full forwarding

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

BA

• Split Ring• full connectivity possible BUT• loop created with current suggested PIRC filtering

• PIRC could restore connectivity • A&B, C&D forward everything from neighbour ring to “broken ring”

• one of A|B, C|D forward to neighbour ring

• never forward back from mate• done with egress filtering if tribs are needed else ingress

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

BA

• How to recognize split ring? Nodes on affected ring observe• mate has disappeared on one ring but not the other

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

2 Span Failure Scenarios

DC

A

B

• Does the split ring scenario scale to 3 PIRC pairs?• A&B,C&D are partially isolated from B&E

• A&B is split from C&D• the problem is that the split rules are different from the partially isolated rules

• implies you need to apply rules based on ringSA -> YUCK

E

F

7/16/2007 IEEE 802.17 RPRWG Mike Takefman

Conclusions

• Dual Failure scenario can only be handled for limited cases• likely not worth doing