Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #2
John Leslie <john@jlc.net> Thu, 02 May 2013 16:44 UTC
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Date: Thu, 02 May 2013 12:43:58 -0400
From: John Leslie <john@jlc.net>
To: Wesley Eddy <wes@mti-systems.com>
Message-ID: <20130502164358.GF23227@verdi>
References: <8C48B86A895913448548E6D15DA7553B82A5E5@xmb-rcd-x09.cisco.com> <517FF171.4010306@mti-systems.com> <4A95BA014132FF49AE685FAB4B9F17F645B16159@dfweml509-mbx.china.huawei.com> <5181D8E2.1040306@mti-systems.com>
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Cc: aqm@ietf.org, Linda Dunbar <linda.dunbar@huawei.com>
Subject: Re: [aqm] Question re draft-baker-aqm-recommendations recomendation #2
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Wesley Eddy <wes@mti-systems.com> wrote: > On 4/30/2013 6:17 PM, Linda Dunbar wrote: >> >> Do you mean that downstream nodes treat packets with ECN bits marked >> differently than that packets whose ECN bits are not marked? >> In another words, is "congestion experienced (CE)" encoded in the packets? > >... all that it's saying is that the congested queue set the CE bit > (when ECT is set), per normal ECN protocol. It isn't saying anything > new about the downstream nodes that see CE has already been set. A downstream node _could_ treat the packet differently: it wouldn't matter much for what we're interested in. Note that a downstream node could reasonably drop a packet already CE-marked if that node _also_ is congested. It wouldn't actually help IMHO if the flow containing the marked packet is well-behaved; but there's really no way to tell whether the flow is well-behaved. With room for doubt, it's arguably right to drop it at an even lighter level of congestion: in all reasonable cases of two or more nodes congested on the path, we should expect another packet to come along _not_ already CE-marked. (I'm not actually proposing this -- least of all proposing to _standardize_ this; but perhaps it will help folks to think through the issue.) In some future "perfect world", where CE can mark packets _before_ there is any reason to drop any, I might talk about standardizing such a practice. ;^) -- John Leslie <john@jlc.net>
- [aqm] Question re draft-baker-aqm-recommendations… Fred Baker (fred)
- Re: [aqm] Question re draft-baker-aqm-recommendat… Linda Dunbar
- Re: [aqm] Question re draft-baker-aqm-recommendat… Fred Baker (fred)
- Re: [aqm] Question re draft-baker-aqm-recommendat… John Leslie
- Re: [aqm] Question re draft-baker-aqm-recommendat… John Leslie
- Re: [aqm] Question re draft-baker-aqm-recommendat… Linda Dunbar
- Re: [aqm] Question re draft-baker-aqm-recommendat… Fred Baker (fred)
- Re: [aqm] Question re draft-baker-aqm-recommendat… Wesley Eddy
- Re: [aqm] Question re draft-baker-aqm-recommendat… Dave Taht
- Re: [aqm] Question re draft-baker-aqm-recommendat… Fred Baker (fred)
- Re: [aqm] Question re draft-baker-aqm-recommendat… Wesley Eddy
- Re: [aqm] Question re draft-baker-aqm-recommendat… Linda Dunbar
- Re: [aqm] Question re draft-baker-aqm-recommendat… Wesley Eddy
- Re: [aqm] Question re draft-baker-aqm-recommendat… John Leslie
- Re: [aqm] Question re draft-baker-aqm-recommendat… Bob Briscoe
- Re: [aqm] Question re draft-baker-aqm-recommendat… Fred Baker (fred)
- Re: [aqm] Question re draft-baker-aqm-recommendat… Bob Briscoe
- Re: [aqm] Question re draft-baker-aqm-recommendat… Dave Taht