Subject: [Pce] More on draft-minei-pce-association-group

From: "Adrian Farrel" <[email-masked]>
Date: Thu, 23 Jul 2015 13:31:37 +0100

Hi Ina,

In the interest of time, moved from mic to list...

I'm struggling with the semantics of the Association object is used.

In signaling, when I mention an LSP I mention all of the Associations that are
relevant. If I mention the LSP again with a different set of Associations, this
set replaces the previous set.

Now, here you have a different semantic with the R-bit. This means that the set
of Associations for an LSP is the sum of all reported Associations, and they
only go away when the R-bit is set.

I think you have done this in order to allow for multiple PCCs/PCEs reporting
Associations.

But you have created a state synchronisation problem because the addition (and
more importantly the removal) of an Association is not a confirmed operation.
Thus, if the PCEP session goes down, we aren't sure whether the other end knows
about the Association state we think we sent it. This is OK for adding
Associations because we can re-send them. For removal of Associations we are now
in a mess and forced to retain removal state until we are sure our peer has
heard us. That seems icky. Have I missed something?

An alternative is to go to the signaling model and say that Associations
*in*PCEP* must be reported by the node that created them and that all
Associations created by a node must be reported in the same message. This allows
for recovery.

Adrian

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From: "Zhangxian (Xian)" <[email-masked]>
Date: Thu, 23 Jul 2015 19:48:07 +0000

Hi, Adrian, 

          Thank you for the question. A short answe to your question would be: we are following the same logic as how we handle the LSP delete/update as described in the stateful PCE base draft.

         To explain a bit more: in the version we are prensenting, both the PCE (with delegation enabled or initiation capability) and the PCC can create association groups, so we need a way to delete/update the association membership information for a LSP if it is PCE created. There are two options:

1) The one you propose below;
2) The one we use, by using a flag;

The advantage of this, as i can think of, is: instead of resending the remaining association groups which are still valid, in order to get rid of some, we just using a R flag to delete what association. So, it is an incremental change. As for PCC-created association, it can delete itself and report the update to the stateful PCE.  

As for the error handling part, I think you have made a good point. It is indeed somthing that we are discussing and will be included in the next version.  

Regards,
Xian & Ina

________________________________________
发件人: Pce [[email-masked]] 代表 Adrian Farrel [[email-masked]]
发送时间: 2015年7月23日 20:31
收件人: Ina Minei
抄送: [email-masked]
主题: [Pce] More on draft-minei-pce-association-group

Hi Ina,

Adrian

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