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Re: [mpls] MPLS_RT review of draft-mirsky-mpls-residence-time-06.txt

Gregory Mirsky <gregory.mirsky@ericsson.com> Mon, 08 June 2015 05:01 UTC

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From: Gregory Mirsky <gregory.mirsky@ericsson.com>
To: Markus Jork <mjork@juniper.net>, "draft-mirsky-mpls-residence-time@tools.ietf.org" <draft-mirsky-mpls-residence-time@tools.ietf.org>, "mpls-chairs@tools.ietf.org" <mpls-chairs@tools.ietf.org>
Thread-Topic: MPLS_RT review of draft-mirsky-mpls-residence-time-06.txt
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Date: Mon, 08 Jun 2015 05:00:59 +0000
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Subject: Re: [mpls] MPLS_RT review of draft-mirsky-mpls-residence-time-06.txt
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Hi Markus,
thank you for your thorough review and very helpful comments. We're working on the next version and will share with the reviewers by week's end. Please find couple notes in-line and tagged GIM>>.

	Regards,
		Greg

-----Original Message-----
From: mpls [mailto:mpls-bounces@ietf.org] On Behalf Of Markus Jork
Sent: Monday, May 18, 2015 8:07 PM
To: draft-mirsky-mpls-residence-time@tools.ietf.org; mpls-chairs@tools.ietf.org
Cc: mpls@ietf.org
Subject: Re: [mpls] MPLS_RT review of draft-mirsky-mpls-residence-time-06.txt

I was asked to review draft-mirsky-mpls-residence-time-06.txt as part of the review team process.

The document provides justification for why residence time measurement for MPLS LSPs may be useful and coherently describes the procedure for performing it. However, I could not understand the 2-step process from reading this document.
GIM>> We'll keep on improving the text.

The proposed rsvp extensions look technically sound. Though I do question the extra complexity introduced for keeping track of the RTM capable LSRs (using the RTM_SET object). While I generally understand the value in supporting incremental deployment of new features, I do wonder how much value there is in doing partial residence time measurements for random sub-sections of an LSP? Are the incomplete measurements done in such a scenario really worth the added protocol complexity?
GIM>> We believe that incremental improvements are improvements nevertheless and bring better quality of clock synchronization.

The document talks about the difficulties of applying the measurement procedure to LDP networks due to ECMP. Maybe it should also discuss potential difficulties with rsvp when there is link aggregation/bundling which could lead to load-balancing over multiple egress interfaces?
GIM>> LAG may be better handled by the Conversation-sensitive frame collection and distribution section 6.6 in new revision of 802.1AX as likely to be the case for PTP data. Will look into the link bundling.

I can't really comment on the usefulness of the document as I'm not familiar with the time synchronization protocols and use cases.
Under the assumption that partial residence time measurements for an LSP are useful, I think the document is ready for WG adoption.

-Markus
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