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RE: draft-ietf-rtgwg-segment-routing-ti-lfa Table 1 questions

Alexander Vainshtein <Alexander.Vainshtein@ecitele.com> Wed, 24 July 2019 12:05 UTC

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From: Alexander Vainshtein <Alexander.Vainshtein@ecitele.com>
To: Stewart Bryant <stewart.bryant@gmail.com>, "rtgwg@ietf.org" <rtgwg@ietf.org>, "draft-ietf-rtgwg-segment-routing-ti-lfa@ietf.org" <draft-ietf-rtgwg-segment-routing-ti-lfa@ietf.org>
Subject: RE: draft-ietf-rtgwg-segment-routing-ti-lfa Table 1 questions
Thread-Topic: draft-ietf-rtgwg-segment-routing-ti-lfa Table 1 questions
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Date: Wed, 24 Jul 2019 12:05:49 +0000
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Hi all,
I concur with Stewart.
>From my POV, it would be nice if the tables in Section 8 of draft-ietf-rtgwg-segment-routing-ti-lfa were aligned with those in Section 9 of RFC 7490,
This would facilitate meaningful comparison between the two sets of networks.

One of the differences between RFC 7490 and what the TI-LFA draft calls "repair with 1 SID" is that the former restricts computation of the PQ nodes to just one per failed link ("the Q-space of E with respect to link S-E is    used as a proxy for the Q-space of each destination" the latter leaves it "be up to each implementation to determine the good tradeoff between scaling and accuracy of the optimization". It would be nice if the authors could indicate whether per destination computation of PQ nodes has been used in the analysis each specific network or not.

My 2c,
Sasha

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-----Original Message-----
From: rtgwg <rtgwg-bounces@ietf.org> On Behalf Of Stewart Bryant
Sent: Monday, July 22, 2019 7:00 PM
To: rtgwg@ietf.org; draft-ietf-rtgwg-segment-routing-ti-lfa@ietf.org
Subject: draft-ietf-rtgwg-segment-routing-ti-lfa Table 1 questions

I would like to understand what Table 1 in draft-ietf-rtgwg-segment-routing-ti-lfa is telling us.

It uses the terms links and circuits without distinguishing between the two. I could speculate that a circuit is a group of links, but then the ratio of nodes to circuits in T1 seems far too low at less than 1:1 in network T1.

Then the node to link ratio sounds quite high with fan outs of 84:1 in T2.

Please could you explain what you mean by circuits and links in this table.

What I would like to know is the average ratio of nodes to neighbours, and the number of parallel links per neighbour.

Best regards

Stewart


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