Re: [conex] Friendly Reminder: ConEx TCP mods
Bob Briscoe <bob.briscoe@bt.com> Sun, 08 March 2015 15:42 UTC
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Date: Sun, 08 Mar 2015 15:42:18 +0000
To: Mirja Kühlewind <mirja.kuehlewind@tik.ee.ethz.ch>, Richard Scheffenegger <rs@netapp.com>
From: Bob Briscoe <bob.briscoe@bt.com>
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Subject: Re: [conex] Friendly Reminder: ConEx TCP mods
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Mirja, Richard, I've written my review comments into the XML. Sorry I didn't get this done earlier. .xml .txt and a diff from draft-07 are here: <http://bobbriscoe.net/projects/conex/draft-ietf-conex-tcp-modifications-07-bb.xml> <http://bobbriscoe.net/projects/conex/draft-ietf-conex-tcp-modifications-07-bb.txt> <http://bobbriscoe.net/projects/conex/draft-ietf-conex-tcp-modifications-07-DIFF-07-bb.html> * I've put all the editorial suggestions (mostly english grammar) directly into the XML. * I've made some changes I thought would be non-controversial directly in the text. Some involve moving paragraphs into sections that seemed more relevant. * I've added comments as <cref> elements within the XML. These appear as footnotes, which you can turn off with <?rfc comments="no"?> Feel free to reject any changes you don't like. My overarching suggestion is that, if you want to keep any algorithm that adds incremental precision, put it in an appendix. Then the base document will be really simple. I've added all my most significant concerns in my <cref> comments, rather than changing the text. I've summarised them here: 1) ConEx Loss marking: Just mark retransmissions. Simple. Rationale: TCP never retransmits less data than is lost. Any attempt to identify lost bytes more accurately or with less delay than the universe of TCP researchers and developers over the last two decades seems rather obsessive-compulsive. I know this seems harsh, but... if you want to keep the algo you've written, pls shift it to an appendix. But I would strongly urge removal. 2) The text in destopt says that the X flag will only be turned off "...if no congestion feedback is (currently) available e.g. in TCP if one endpoint has been receiving data but sending nothing but pure ACKs (no user data) for some time." draft-07 still says X is turned off if the packet in question has no payload, which I thought we agreed was wrong. 3) I've added a para saying that experimentation in credit algorithms is encouraged, and the ones given are mainly to be concrete. Nonetheless, I think the ones given need to be stated as absolute worst-case. They allow for the /absolute/ worst case, rather than the /likely/ worst case. E.g. the worst case during congestion avoidance is taken as "all packets in flight might suddenly be dropped". I know you're trying to say something concrete, so I suggest we keep these suggestions but make it clear that they cover the absolute worst-case. 4) The suggested test to detect a re-route onto an audit function with no flow state (i.e. at least a loss in two consecutive RTTs) is surely far too over-sensitive. Actually, I think no specific detection of this event is needed. I believe an audit function would drop a significant proportion of packets, but in the next round the normal rules you've specified will cause the sender to replenish the credit while responding to these losses. Perhaps I'm wrong though. 5) IMO, resetting negative balance after one RTT ought to be a MAY, not a SHOULD. I think we should care more about simplicity than precision. I also added some security considerations text you might want to use (and I suggested moving the existing para under security considerations to Classic ECN Support, because it was about protocol safety during heavy congestion, not security against attackers). Bob At 10:08 07/03/2015, Bob Briscoe wrote: >Mirja, > >Starting this now... > >Sorry I've delayed it until just before the IETF >deadline - BT and European project guff has just taken over my life since xmas. > > >Bob > >At 19:12 03/02/2015, Mirja Kühlewind wrote: >>Hi Bob! >> >>Can you please, please do the ConEx TCP mods review...? Please! >> >>Thanks, >>Mirja > >________________________________________________________________ >Bob Briscoe, BT ________________________________________________________________ Bob Briscoe, BT
- Re: [conex] Friendly Reminder: ConEx TCP mods Bob Briscoe
- Re: [conex] Friendly Reminder: ConEx TCP mods Mirja Kühlewind