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

Lou Berger <lberger@labn.net> Thu, 11 April 2019 11:47 UTC

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To: Magnus Westerlund <magnus.westerlund@ericsson.com>, "Ratliff, Stanley" <sratliff@idirect.net>, The IESG <iesg@ietf.org>
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From: Lou Berger <lberger@labn.net>
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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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Magnus,

On 4/5/2019 5:11 AM, Magnus Westerlund wrote:
> 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.

I think Stan's response already covered the above. From my perspective, 
I agree with stan that a modem that reports DSCPs should be expected to 
honor them like any other transit IP device (router, middlebox, etc.).  
I think that the following is possible in the non-diffserv modem aware 
case - but another approach would be to not deploy such limited modems 
in a network that requires DSCP support - just like you wouldn't deploy 
a router that doesn't support a particular PHB in network that expects 
to support it.

>
> 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?

Quite likely -- I think this is not the flow control you'd want with 
DetNet (I can't speak to L4S), i'd personally use something like what's 
covered in ietf-manet-dlep-da-credit-extension.


> 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?

I certainly have no objection to such, particularly given 
ietf-manet-dlep-da-credit-extension.  If you have any suggested text, 
that would be helpful.  Otherwise, as I mentioned in response to Bob, if 
really needed I can work with the Shepherd/WG on some applicability text.

Lou

> Cheers
>
> Magnus
>
>