Re: [Pce] stateful-HPCE

Leeyoung <leeyoung@huawei.com> Fri, 19 August 2016 19:23 UTC

From: Leeyoung <leeyoung@huawei.com>
To: weiw <weiw@bupt.edu.cn>, "pce@ietf.org" <pce@ietf.org>
Thread-Topic: [Pce] stateful-HPCE
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Date: Fri, 19 Aug 2016 19:22:43 +0000
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Subject: Re: [Pce] stateful-HPCE
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Hi Wei,

Thanks for your comment on Stateful H-PCE draft. Please see my comment on some of your questions. Dhruv might also have his comments.

Best regards,
Young

From: weiw [mailto:weiw@bupt.edu.cn]
Sent: Friday, August 19, 2016 9:13 AM
To: Leeyoung; pce@ietf.org
Cc: Jonathan.Hardwick
Subject: Re: [Pce] stateful-HPCE

Hi Young and PCE GW,

I am now implementing a ACTN control framework for transport networks, which is a usecase for stateful HPCE. In the coding process, I find some problems about this draft, as follows.

In the beginning of section 3, it states that "In the hierarchical PCE architecture, a P-PCE maintains a domain topology map that contains the child domains (seen as vertices in the topology) and their interconnections (links
in the topology. The P-PCE has no information about the content of the child domains.)". I think it means that P-PCE only has some abstracted information about physical network elements.

YOUNG>> Yes, when it says vertices in the topology, it implies that it is an abstraction. We can make it more clear on this in the next revision.

According to the considerations above, I think the stateful related messages (PCUpd, PCRpt, PCInitiate) and PCRep should be used in a different way between P-PCE and C-PCE, because we need to do some abstraction processing on these message to report the abstracted information so that P-PCE can match them to the abstracted topology and TE information it has. For example, in the condition where C-PCE only report the border nodes to its P-PCE, it also need to report a abstracted path (whose RRO feild is composed of border nodes) to its P-PCE. Also, in the perspective of security, it not reasonable for C-PCE to forward the physical network specific information carried in PCRep and PCRpt message to P-PCE without any abstraction processing. It is a kind of information leaking in the condition where C-PCEs do not want to provide detailed information about their physical networks to P-PCE.

YOUNG>> It is correct that the there is a level of difference between MPI and SBI (in ACTN terms) as to how much details should be disclosed. But the basic stateful (and stateless) PCEP messages will be applicable as is across PCE-PCC (SBI) and P-PCE-C-PCE (MPI). The current PCEP messages/Objects/TLVs allow expressing TE information (which is basically, nodes, links, b/w, etc.) in an abstracted way. I think you are talking about how to abstract RRO of an LSP for instance. You can use “loose hop” notion to hide internal details, simply giving the source border node and the destination border node.

Consequently, I suggest to add one section to clarify the abstraction processing requirment for the stateful related messages (PCUpd, PCRpt, PCInitiate) and PCRep.

YOUNG>> This can be done.
If the abstraction processing is mandatory, there would be another problem, as follows.

This draft provide two usecases for LSP initiation in stateful HPCE context, as section 3.3. One can be concludes as "initiated by P-PCE", and the other "Per Domain Stitched LSP".
For the first case, the P-PCE can choose an optimal abstracted E2E path according to the Hierarchical End-to-End Path Computation Procedure in section 4.6.2 of [RFC6805]. While, the P-PCE cannot initiate a LSP by sending this abstrated path info to the Ingress PCC via ingress C-PCE, becuse the ingress PCC would be confused by the abstracted hop information. How to deal with this case?

YOUNG>> P-PCE should know the border nodes domain networks when it computes an E2E path across multiple domains. P-PCE would express the C-PCEs to create LSP between a pair of border nodes (source and destination) for each domain. Do you see any issue with this? Then each C-PCE will setup an LSP that connects the border nodes. I don’t think C-PCE would be confused with this method.

The draft is OK for the second usecase, where each C-PCE is responsible for initiating its own intra-domain LSP.

Thanks,
Wei Wang

________________________________
发件人：Leeyoung <leeyoung@huawei.com<mailto:leeyoung@huawei.com>>
发送时间：2016-07-21 23:58
主题：[Pce] stateful-HPCE
收件人："pce@ietf.org<mailto:pce@ietf.org>"<pce@ietf.org<mailto:pce@ietf.org>>
抄送：

Hi PCE WG,

https://datatracker.ietf.org/doc/draft-dhodylee-pce-stateful-hpce/

We’d like to solicit WG’s comment on this draft. As Dhruv presented today in the PCE WG meeting, this draft does not add any new protocol work. It is informational only and the co-authors believe this draft can move to the next step.

Thanks in advance for your comments, suggestions, etc for this draft.

Young (on behalf of co-authors and contributors).