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

Magnus Westerlund <> Thu, 11 April 2019 12:12 UTC

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From: Magnus Westerlund <>
To: Lou Berger <>, "Ratliff, Stanley" <>, The IESG <>
CC: "" <>, "" <>, "" <>
Thread-Topic: [manet] Magnus Westerlund's Discuss on draft-ietf-manet-dlep-pause-extension-06: (with DISCUSS)
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Date: Thu, 11 Apr 2019 12:12:05 +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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I don't have a text proposal. I think if you work with Bob to detail out
the use case and
clarifications on the limitations with the protocol that should solve my
issue here.



On 2019-04-11 13:47, Lou Berger wrote:
> 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


Magnus Westerlund 

Network Architecture & Protocols, Ericsson Research
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