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

Lou Berger <lberger@labn.net> Mon, 06 May 2019 10:49 UTC

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To: Magnus Westerlund <magnus.westerlund@ericsson.com>, "Ratliff, Stanley" <sratliff@idirect.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>, Bob Briscoe <ietf@bobbriscoe.net>, "manet-chairs@ietf.org" <manet-chairs@ietf.org>
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From: Lou Berger <lberger@labn.net>
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Date: Mon, 6 May 2019 06:49:13 -0400
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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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Thanks Magnus.   I'll upload a rev with the change today (was waiting on 
AD/Shepherd, but now assume they will ask for the upload)...

Lou

On 5/6/2019 3:56 AM, Magnus Westerlund wrote:
> Thanks Lou,
>
> I think that clarifies my issue. I will clear with the assumption that
> you will include this.
>
> Thanks
>
> Magnus
>
> On 2019-05-06 02:40, Lou Berger wrote:
>> Hi Magnus/Bob,
>> 	I've updated the intro to try to address your points, while also trying
>> to bring in Stan's point, :
>>
>>     The base DLEP specification does not include any data plane flow
>>     control capability.  The extension defined in this document supports
>>     flow control of data traffic based on explicit messages sent via DLEP
>>     by a modem to indicate when a router should hold off sending traffic,
>>     and when it should resume.  This functionality parallels the flow
>>     control mechanism found in PPP over Ethernet (PPPoE) per [RFC5578].
>>     The extension also optionally supports DSCP (differentiated services
>>     codepoint) aware flow control for use by DiffServ-aware modems.  (For
>>     general background on Differentiated Services see [RFC2475].)  This
>>     functionality is very similar to that provided by Ethernet Priority
>>     flow control, see [IEEE.802.1Q_2014].  The extension defined in this
>>     document is referred to as "Control Plane Based Pause".  Other flow
>>     control methods are possible with DLEP, e.g., see
>>     [I-D.ietf-manet-dlep-da-credit-extension] and
>>     [I-D.ietf-manet-dlep-credit-flow-control].
>>
>> Please let me/us know what you think.
>>
>> Lou
>>
>>
>> On 4/11/19 8:12 AM, Magnus Westerlund wrote:
>>> Hi,
>>>
>>> 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.
>>>
>>> Cheers
>>>
>>> Magnus
>>>
>>> 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
>>>>>
>>>>>