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

Magnus Westerlund <> Mon, 06 May 2019 07:56 UTC

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From: Magnus Westerlund <>
To: Lou Berger <>, "Ratliff, Stanley" <>, The IESG <>
CC: "" <>, "" <>, Bob Briscoe <>, "" <>
Thread-Topic: [manet] Magnus Westerlund's Discuss on draft-ietf-manet-dlep-pause-extension-06: (with DISCUSS)
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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 Lou,

I think that clarifies my issue. I will clear with the assumption that
you will include this.



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

Magnus Westerlund 

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