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Stateful PCE

Kexin Tang

Xuerong Wang

Yuanlin Bao

ZTE Corporation

draft-tang-pce-stateful-pce-01.txt

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Problems without Stateful PCE

Receive PCReq

Path computation complete (per-PCE)

End-to-end path computation complete

RSVP signalling complete

OSPF flooding update

Time

T 1 T 2 T 3 T 4 T 5

In network failure, a large number of LSPs need to be restored within very short time:During restoration, same resource maybe assigned to two or more

different requests (from T2 to T5), retry is needed.Within the time window (T4 to T5), PCE will not know the LSPs

failed to be created or the released LSPs, if the bandwith change below the bandwith threshold of IGP (this time window may last for half an in the IGP aging case). The restoration LSP may not succeed.

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Realization of stateful PCE

PCC discovers

stateful PCE

PCE reserves

resources

Notify PCE the end-to-end path

computation result

Notify PCE the LSP

setup result

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PCED Extension

Bit Capabilities

0 Path computation with GMPLS link constraints

1 Bidirectional path computation

2 Diverse path computation

3 Load-balanced path computation

4 Synchronized path computation

5 Support for multiple objective functions

6 Support for additive path constraints (max hop count, etc.)

7 Support for request prioritization

8 Support for multiple requests per message

9 Stateful PCE

10-31 Reserved for future assignments by IANA

New PCE Capability Flag of PCE-CAP-FLAG

Extended PCED TLV(RFC 5088), defined a new capability flag

With the stateful PCE capability flag, the PCC can select which PCE to be used.

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PCEP Extensions• Notification-type=3: end-to-end path computation result

– Notification-value=1: end-to-end path computation success.– Notification-value=2: end-to-end path computation failure.

• <PCNtf Message>::=<Common Header><notify-list> <notify-list>::=<notify> [<notify-list>] <notify>::=[<request-id-list>]<notification-list> <request-id-list>::=<RP>[<path-list>][<request-id-list>] <path-list>:=<path>[<path-list>] <path>:=<ERO><attribute-list> <notification-list> ::=<NOTIFICATION>[<notification-list>]

– Both type 3 and type 4 Notification can carry the <path>in the PCNtf Message.

• Notification-type=4: path delete– Notification-value=1: path delete

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Centralized PCE

• After path computation, stateful PCE will save the computed result and reserve resources immediately

• If LSP signaling failed, PCC should notify PCE to release resources from its TED:

– Notification-type=4, Notification-value=1

– PCNtf optinally carries <path> to indicate which path should delete

– A timer maybe needed according to local policy

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BRPC compute Inter-area/AS path

For each PCE•Compute potential paths•Reserve resources for each potential path in local TED

HFDB

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After end-to-end path computation•PCE of the first domain Sends PCNtf to each PCE in the PCE chain

•Notification-type=3•PCNtf carries <path> to indicate the end-to-end path

•Each PCE released resources except those belong to the <path> carried in the PCNtf

1. PCNtfLSP is

created

2. PCNtfLSP is

created

4. PCNtfLSP is

created

3. Release reserved

resource: EF

5. Release reserved

resource: IJ

BRPC compute Inter-area/AS path(Cont)

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H-PCE compute Inter-area/AS path

After end-to-end path computation•Parent PCE sends PCNtf to each child PCE

•Notification-type=3•PCNtf carries <path> to indicate the end-to-end path

For each child PCE and parent PCE•saves the computed result•reserves resources

In multi-domain path computation, if LSP signaling failed, PCC should also notify PCE to release resources from its TED.

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Next Steps

• Refine it according to the feedback from the meeting or mailing list.

• Maybe more scenarios of stateful PCE need to be identified.

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Thank You！

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