Re: [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.txt
Sally Floyd <sallyfloyd@mac.com> Thu, 06 November 2008 00:05 UTC
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From: Sally Floyd <sallyfloyd@mac.com>
To: tcpm <tcpm@ietf.org>
Date: Wed, 05 Nov 2008 16:04:56 -0800
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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
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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/ Begin forwarded message: > From: Lars Eggert <lars.eggert@nokia.com> > Date: May 28, 2008 7:35:26 AM PDT > To: ext Sally Floyd <sallyfloyd@mac.com> > Cc: Mark Allman <mallman@icir.org>, Aleksandar Kuzmanovic <akuzma@northwestern.edu > >, "K. K. Ramakrishnan" <kkrama@research.att.com>, Ted Faber <faber@isi.edu > >, Amit Mondal <a-mondal@northwestern.edu> > Subject: Re: AD review: draft-ietf-tcpm-ecnsyn-05 > > Hi, > > thanks for the update. I'll move it back to a WG document in the > tracker in this case, and Ted and Mark will figure out what to do > with the new version when it comes out. > > On 2008-5-27, at 1:45, ext Sally Floyd wrote: >> We need to modify the mechanism in ECN+ to deal with severely >> congested networks. (I fixed a bug in the simulator some time ago, >> and the result was to uncover a problem with ECN+, in a few cases, >> in highly congested networks.) We are rerunning the simulations, >> and I will let you know as soon as we have a revised version of the >> draft. I think we will have to report back to the working group >> before moving on to the IESG. > > Thanks, > Lars Begin forwarded message: > 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/ > > Below is the data which will enable a MIME compliant mail reader > implementation to automatically retrieve the ASCII version of the > Internet-Draft.
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_______________________________________________ tcpm mailing list tcpm@ietf.org https://www.ietf.org/mailman/listinfo/tcpm
- [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.txt Internet-Drafts
- Re: [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.t… Sally Floyd
- Re: [tcpm] I-D Action:draft-ietf-tcpm-ecnsyn-07.t… Lars Eggert
- [tcpm] Fwd: I-D Action:draft-ietf-tcpm-ecnsyn-07.… Sally Floyd