Re: [manet] Magnus Westerlund's Discuss on draft-ietf-manet-dlep-pause-extension-06: (with DISCUSS)

Magnus Westerlund <magnus.westerlund@ericsson.com> Fri, 05 April 2019 09:12 UTC

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From: Magnus Westerlund <magnus.westerlund@ericsson.com>
To: "Ratliff, Stanley" <sratliff@idirect.net>, Lou Berger <lberger@labn.net>, The IESG <iesg@ietf.org>
CC: "draft-ietf-manet-dlep-pause-extension@ietf.org" <draft-ietf-manet-dlep-pause-extension@ietf.org>, "manet@ietf.org" <manet@ietf.org>, "manet-chairs@ietf.org" <manet-chairs@ietf.org>
Thread-Topic: [manet] Magnus Westerlund's Discuss on draft-ietf-manet-dlep-pause-extension-06: (with DISCUSS)
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Date: Fri, 5 Apr 2019 09:11:57 +0000
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Subject: Re: [manet] Magnus Westerlund's Discuss on draft-ietf-manet-dlep-pause-extension-06: (with DISCUSS)
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Hi,

Thanks for the replies. 

I think the main point here is if one should treat router + modem as one
common queue when it comes to meeting PHBs or treat them as two in
sequence queues. If one treat them as two queues then you get the same
behavior as two routers in sequence. And that is acceptable from one
angle, but it also results in additional jitter and latencies.

If we take the Expedited Forwarding PHB (RFC 3246) treating this as two
queue results in that the error is E_a1 (router) + E_a2 (mode) rather
than a E_a for the combined queue. The question is if E_a actually will
be smaller than E_a1+E_a2 when one uses this type of control? In the
combined case if the modem queue is so shallow that E_a2 << E_a1 as well
as that time for performing the DLEP signalling is so short that the
main variations ends up being in the router queue where one can apply
suitable policies to control queue load to prevent violation of the
targets.

I think my main concern will be what happens if one attempts to
implement L4S dual queues or DETNET and have DLEP in the path. Will this
require additional extensions to provide more detailed flow control
information so that lower latency or more deterministic behavior can be
achieved?

I noticed that TSVART reviewer Bob Briscoe asked for a use case
description of the case when the main queue is pushed to the router. I
think that appears to be a good idea. I think what I am wondering is if
there need to be some applicability statement here due the limitations
of the technology?

Cheers

Magnus


-- 

Magnus Westerlund 

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Network Architecture & Protocols, Ericsson Research
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