Subject: [Pce] comments on draft-leroux-pce-backup-comp-frwk-00.txt

From: Cristel Pelsser <[email-masked]>
Date: Wed, 17 Nov 2004 17:31:16 +0100

Hi Jean-Louis and all,

Here are some comments on draft-leroux-pce-backup-comp-frwk-00.txt

1. Could you replace the occurences of PCS by PCE

2. In the draft, you consider two cases. Either there is a single PCE that
computes all the bypass tunnels paths or each LSR behaves as a PCE and
computes the paths for the bypass tunnels protecting its own failure or the
failure of one of its links. What about the case where not all nodes have
the PCE capability but there are mutliple PCEs for request balancing and
resilience purposes? Maybe you could say that in this case there needs to
be synchronisation between the PCEs or a way to determine which PCE is
responsible for the protection of a given facility.

3. Paragraph 3 of section 6.3.1 is not clear. What approach do you propose
to determine the backup-bandwidth pool? If you take the same pool as for
the primary LSPs then you need to update this primary-bandwidth pool when
a new bypass tunnel is established depending on the resources that it
protects.

4. Paragraph 1 of section 6.3.1.2, replace "to tell" by "to distinguish"
in sentence: "... additional signaling extensions need to be implemented
to enable an LSR to tell a primary LSP from a bypass LSP ..."

5. What happens if the PCE elected to compute the bypass tunnels paths for
a given facility fails? For example: if the PCE elected to compute paths
for a SRLG fails, it looses all the information about the bypass tunnels
established to protect the SRLG. Thus it looses the information concerning
the resources allocated to these bypass tunnels. How can this PCE compute
subsequent bypass tunnels paths protecting the SRLG?

Best regards,

Cristel

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From: "LE ROUX Jean-Louis RD-CORE-LAN" <[email-masked]>
Date: Wed, 17 Nov 2004 18:30:55 +0100

Hi Cristel,

Thanks a lot for these really valuable comments.

Please see inline,

JL

>-----Message d'origine-----
>De : Cristel Pelsser [mailto:[email-masked]] 
>Envoyé : mercredi 17 novembre 2004 17:31
>À : LE ROUX Jean-Louis RD-CORE-LAN; [email-masked]
>Objet : comments on draft-leroux-pce-backup-comp-frwk-00.txt
>
>
>Hi Jean-Louis and all,
>

Right, I though I had removed all PCS occurences, but it seems that 
there is some "resistance" in the SDLG section...
Anyway, we will kill them.

>
>2. In the draft, you consider two cases. Either there is a 
>single PCE that computes all the bypass tunnels paths or each 
>LSR behaves as a PCE and computes the paths for the bypass 
>tunnels protecting its own failure or the failure of one of 
>its links. What about the case where not all nodes have the 
>PCE capability but there are mutliple PCEs for request 
>balancing and resilience purposes? Maybe you could say that in 
>this case there needs to be synchronisation between the PCEs 
>or a way to determine which PCE is responsible for the 
>protection of a given facility.

You raised a good point.
Basically the set of bypass tunnels protecting a given facility (link, node SRLG or SDLG) must be computed by the same PCE, and as you mention there must be a way to determine which PCE is responsible for the protection of a given facility. We will fix that for the next revision.

>
>3. Paragraph 3 of section 6.3.1 is not clear. What approach do 
>you propose to determine the backup-bandwidth pool? If you 
>take the same pool as for the primary LSPs then you need to 
>update this primary-bandwidth pool when a new bypass tunnel is 
>established depending on the resources that it protects.

In this section we address  the case where both primary and backup LSPs 
are computed by the same PCE. That is the PCE is aware of all primary and backup LSPs.
In such case, we just have to tell the PCE the amount of link bandwidth it can use for backup
and there is actually no need to explicitely define a backup pool. 
Does that make sense ?

>
>4. Paragraph 1 of section 6.3.1.2, replace "to tell" by "to 
>distinguish" in sentence: "... additional signaling extensions 
>need to be implemented to enable an LSR to tell a primary LSP 
>from a bypass LSP ..."

OK, will update

>
>5. What happens if the PCE elected to compute the bypass 
>tunnels paths for a given facility fails? For example: if the 
>PCE elected to compute paths for a SRLG fails, it looses all 
>the information about the bypass tunnels established to 
>protect the SRLG. Thus it looses the information concerning 
>the resources allocated to these bypass tunnels. How can this 
>PCE compute subsequent bypass tunnels paths protecting the SRLG?

Actually after a PCE restart, all PLRs will have to re-send a PC request to the PCE,
potentially indicating the previous computed path (kind of PCE graceful restart approach)
We will clarify that in next revision.

Again thanks a lot for these useful comments

Regards,

JL