Transcript bf-weiyh-overlap-0110-v0.ppt

Discussion on Overlapped
IPGs in 802.1Qbf
[email protected]
[email protected]
2010-01
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 possible topologies
IPG2
IPG1
• IPG1 and IPG2 protect the same
group of TESIs.
(1)
IPG2
IPG1
• 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.
(2)
IPG1
IPG2
(3)
• In figure(3), two IPGs are partially
overlapped
Expanded view of nested topology
E
A
Pa1
WS
IPG1
B
PS
IPG1 Monitoring TESI
E
C
D
A IPG1 B
IPG2
C
Pc2
Pb2
F
Pd1
Pb1 Pb3 IPG2
WS
Pc3
Pa2
Pc1
Pd2
F
PS
•
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 BC 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)
D
Expanded view of partially overlapped
IPG2 Monitoring TESI
topology PS
A
E
IPG1
C
D
Pc1
B
Pa1
E
IPG1
C
A
B
WS
F
Pc2 Pc3
Pd1
Pa2
Pb1 Pb2
Pb3
Pd2
WS
B
IPG1 Monitoring TESI
PS
B
F
IPG2
•
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
IPG2 D
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.
Thank You！