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Discussion on Overlapped IPGs in 802.1Qbf

Discussion on Overlapped IPGs in 802.1Qbf. wei.yuehua@zte.com.cn ao.ting@zte.com.cn. 2010-01. IPG overlap description. In 802.1Qbf draft 0.1, Several paragraphs discuss overlap topology:

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Discussion on Overlapped IPGs in 802.1Qbf

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  1. Discussion on Overlapped IPGs in 802.1Qbf wei.yuehua@zte.com.cn ao.ting@zte.com.cn 2010-01

  2. IPG overlap description • In 802.1Qbf draft 0.1, Several paragraphs discuss overlap topology: • (26.11.3.1) IPGs are said to overlap if a Segment associated with one IPG and a Segment associated with another IPG share a sequence of PNPs. • NOTE2—It is recommended that the values of HoldOffTime (26.11.5.3.9) associated with overlapping IPGs be provisioned such the failure of a common component results in IPS action associated with one of the IPGs that completes (i.e., the value of MAdefectIndication associated with that IPG returns to “false”) before a failure of the other IPG is signaled (i.e., the value of MAdefectIndication associated with that IPG is set to “true”).

  3. 3 possible topologies • IPG1 and IPG2 protect the same group of TESIs. • The green line indicates the overlapped part of working segment of the two IPGs. • Working segment of IPG2 is totally overlapped with working segment of IPG1 in figure(1) and figure(2), We say IPG2 is nested with IPG1. • In figure(3), two IPGs are partially overlapped (1) (2) (3)

  4. Expanded view of nested topology • Configure HoldOffTime(IPG1)=50ms, HoldOffTime(IPG2)=0. • When a failure of link between Pb3 and Pc3 occurs, IPG2 Monitoring CC will detect the failure then IPG2 switch all protected TESIs from B-C to B-E-C including IPG1 monitoring TESI. • After IPG2 switches, IPG1 monitoring CCM traverses A-B-E-C-D. So IPG1 WOULDN’T trigger switching after waiting an interval of HoldOffTime(IPG1)

  5. Expanded view of partially overlapped topology • Configure HoldOffTime(IPG1)=50ms, HoldOffTime(IPG2)=0. • When a failure of link between Pb2 and Pc2 occurs, IPG2 Monitoring CC will detect the failure then IPG2 switch all protected TESIs from B-C-D to B-F-D NOT including IPG1 monitoring TESI. • After IPG2 switches, IPG1 monitoring CCM STILL traverses A-B-C. So IPG1 WOULD trigger switching after waiting an interval of HoldOffTime(IPG1) • Both IPGs trigger switching due to failure of overlapped link, So configure different holdOffTime values don’t bring any benefits to this topology

  6. Conclusions & Proposals • Conclusion: • holdoff-timer can apply to nested topology. It can’t apply to partially overlapped topology. • Proposal: • Replace “overlapped IPGs” with “nested IPGs” • Suggest to use the following definition for “Nested IPGs” • Both SEPs of a working segment in one IPG share the same PNP with SIPs/SEPs of a working segment in another IPG • Add specification on how the nested IPGs work.

  7. Thank You！

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