Re: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions

[Nic Neate <[e-mail]>]

Hi Saquib,

In S2L sub-path diversity, it is allowed for the sub-path to leaf A in the first tree to share resources with the sub-path to leaf B in the second tree.  So the complete trees are not (necessarily) diverse.

Nic

-----Original Message-----
From: saquib khan [mailto:[e-mail]]
Sent: 21 November 2008 03:09
To: Nic Neate; 'Quintin Zhao'; Aria - Adrian Farrel Personal
Cc: [e-mail]; 'Mohamad CHAITOU'; [e-mail]; [e-mail]
Subject: RE: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions



Hi Nic,
If we consider S2L diversity for all the leaves in the tree, automatically the complete tree will become diverse, then why do we require a new diversity option?


-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf Of Nic Neate
Sent: Thursday, November 20, 2008 10:04 PM
To: Quintin Zhao; Aria - Adrian Farrel Personal
Cc: [e-mail]; 'Mohamad CHAITOU'; [e-mail]; [e-mail]
Subject: Re: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions

Hi Quintin,

I don't think "partial path diversity for certain leaves" is quite the point I was suggesting.

The idea of S2L sub-path diversity is that, when you're doing 1+1 protection, you don't need complete tree diversity.  It is sufficient just to ensure that, for any given leaf, the S2L sub-paths to that leaf in the two trees are diverse.  Then, following some network failure, traffic will still be delivered to all leaves on at least one of the two trees.

Two P2MP LSPs going in opposite ways around a ring is the easiest way to picture this.

Nic

-----Original Message-----
From: Quintin Zhao [mailto:[e-mail]]
Sent: 20 November 2008 16:16
To: Aria - Adrian Farrel Personal; Nic Neate
Cc: [e-mail]; [e-mail]; [e-mail]; 'Mohamad CHAITOU'; [e-mail]; [e-mail]; [e-mail]
Subject: RE: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions

Nic and Adrian,

Thanks for your suggestions!

By using the existing SVEC functionality, PCC can request the secondary P2MP LSP path computation to protect the whole P2MP path tree by specifying the S/N/L bit in the SVEC object.

If we understand the new requirements you suggested for S2L sub-path diversity, you want the PCC to be able to ask the PCE to compute secondary P2MP path tree with partial path diversity for certain leaves or certain S2L sub-path.

We will address these new requirements in our next version of the draft.

Quintin

-----Original Message-----
From: Adrian Farrel [mailto:[e-mail]]
Sent: Wednesday, November 19, 2008 3:49 PM
To: Nic Neate; [e-mail]; [e-mail]
Cc: [e-mail]; [e-mail]; [e-mail]
Subject: Re: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions

Ah, that is an interesting and valid point, Nic.

And I think one might also consider "directional diversity" for your ring example.

A
----- Original Message -----
From: "Nic Neate" <[e-mail]>
To: <[e-mail]>; <[e-mail]>
Cc: <[e-mail]>; <[e-mail]>; <[e-mail]>
Sent: Wednesday, November 19, 2008 8:28 PM
Subject: [Pce] Comment on draft-ietf-pce-pcep-p2mp-extensions


Hi,

I have a suggestion for a small extension to the PCEP P2MP draft.

I believe the base PCEP specification currently has three options for calculating diverse protection paths: link diverse, node diverse and SRLG diverse (draft-ietf-pce-pcep section 7.13.2).

In P2MP, S2L sub-path diverse is another important case.  I think it would be good to allow the PCC to request computation of S2L sub-path diverse protection paths.

This is useful when doing 1+1 protection in a ring topology, for example.

Nic




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