[tcpm] Fwd: I-D Action:draft-ietf-tcpm-ecnsyn-07.txt

Sally Floyd <sallyfloyd@mac.com> Tue, 18 November 2008 19:32 UTC

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From: Sally Floyd <sallyfloyd@mac.com>
To: tcpm <tcpm@ietf.org>
Date: Tue, 18 Nov 2008 11:32:51 -0800
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Subject: [tcpm] Fwd: I-D Action:draft-ietf-tcpm-ecnsyn-07.txt
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This is just a reminder that, though I won't be at the tcpm meeting  
we have made a revision to the draft-ietf-tcpm-ecnsyn draft, and it
needs another round of working group review before moving back
to the IESG for the final stages.


Many thanks,
- Sally

Begin forwarded message:

> From: Sally Floyd <sallyfloyd@mac.com>
> Date: November 5, 2008 4:04:56 PM PST
> To: tcpm <tcpm@ietf.org>
> Cc: "K. K. Ramakrishnan" <kkrama@research.att.com>, Amit Mondal <amitmondal2010@u.northwestern.edu 
> >, Aleksandar Kuzmanovic <akuzma@cs.northwestern.edu>
> Subject: Re: [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.txt
> We have (finally) revised draft-ietf-tcpm-ecnsyn, on "Adding Explicit
> Congestion Notification (ECN) Capability to TCP's SYN/ACK Packets",
> and are finally ready for it to complete the standardization process.
> Here is the story:
> The draft had finished Working Group Last Call, and been forwarded
> to the IESG for review.  As a final step in revising the draft
> after the AD Evaluation, we (the authors) reran the simulations
> with an updated version of the ns-2 simulator, and found that in
> some highly congested scenarios, ECN+ would significantly increase
> the packet drop rate even further.  (I am appending the 5/26/08
> email below.)
> In response to this, we have added a change to ECN+, which in
> the new draft we call "ECN+/TryOnce".  With ECN+/TryOnce, when
> an ECN-Capable SYN/ACK packet is ECN-marked, the TCP responder
> sends another SYN/ACK packet that is not ECN-Capable, and also
> reduces the initial window to one packet.  ECN+/TryOnce
> shows most of the performance benefit of ECN+, and avoids the
> problem of increasing the packet drop rate in times of high
> congestion.
> I think it makes sense to pass this through the working group
> before going back to the IESG.  However, I won't be at IETF
> in Minnesota, and am hoping that this can be done by email.
> The new version of the draft is at:
> "http://tools.ietf.org/html/draft-ietf-tcpm-ecnsyn-07",
> and that web page also gives the differences with earlier
> versions of the draft.  Any feedback would be appreciated.
> Many thanks,
> - Sally
> http://www.icir.org/floyd/

>> From: Internet-Drafts@ietf.org
>> Date: November 3, 2008 12:30:01 PM PST
>> To: i-d-announce@ietf.org
>> Cc: tcpm@ietf.org
>> Subject: [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.txt
>> A New Internet-Draft is available from the on-line Internet-Drafts  
>> directories.
>> This draft is a work item of the TCP Maintenance and Minor  
>> Extensions Working Group of the IETF.
>> 	Title           : Adding Explicit Congestion Notification (ECN)  
>> Capability to TCP's SYN/ACK Packets
>> 	Author(s)       : S. Floyd, I. Property
>> 	Filename        : draft-ietf-tcpm-ecnsyn-07.txt
>> 	Pages           : 33
>> 	Date            : 2008-11-03
>> This draft specifies a modification to RFC 3168 to allow TCP SYN/ACK
>> packets to be ECN-Capable.  For TCP, RFC 3168 only specifies setting
>> an ECN-Capable codepoint on data packets, and not on SYN and SYN/ACK
>> packets.  However, because of the high cost to the TCP transfer of
>> having a SYN/ACK packet dropped, with the resulting retransmit
>> timeout, this document specifies the use of ECN for the SYN/ACK
>> packet itself, when sent in response to a SYN packet with the two ECN
>> flags set in the TCP header, indicating a willingness to use ECN.
>> Setting the initial TCP SYN/ACK packet as ECN-Capable can be of great
>> benefit to the TCP connection, avoiding the severe penalty of a
>> retransmit timeout for a connection that has not yet started placing
>> a load on the network.  The TCP responder (the sender of the SYN/ACK
>> packet) must reply to a report of an ECN-marked SYN/ACK packet by
>> resending a SYN/ACK packet that is not ECN-Capable.  If the resent
>> SYN/ACK packet is acknowledged, then the TCP responder reduces its
>> initial congestion window from two, three, or four segments to one
>> segment, thereby reducing the subsequent load from that connection on
>> the network.  If instead the SYN/ACK packet is dropped, or for some
>> other reason the TCP responder does not receive an acknowledgement in
>> the specified time, the TCP responder follows TCP standards for a
>> dropped SYN/ACK packet (setting the retransmit timer).  This document
>> updates RFC 3168.
>> A URL for this Internet-Draft is:
>> http://www.ietf.org/internet-drafts/draft-ietf-tcpm-ecnsyn-07.txt
>> Internet-Drafts are also available by anonymous FTP at:
>> ftp://ftp.ietf.org/internet-drafts/
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