<html><head><style type="text/css"><!-- DIV {margin:0px;} --></style></head><body><div style="font-family:times new roman, new york, times, serif;font-size:12pt"><DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">The problem with ECN is that, as in any router assisted CC solution, it requires an all routers' support. If a single router is not ECN enabled, little can be guaranteed about CC's performance.</DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Of course, any ECN solution in a mix path environment should perform at least as well as when there is no ECN router support at all in the session path. That is why I am more infavor of CC schemes with implicit CC info, not explicit. I believe it is possible to differentiate between (b) and (c) cases below with implicit feedback information...</DIV>
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<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">Dirceu<BR><BR></DIV>
<DIV style="FONT-SIZE: 12pt; FONT-FAMILY: times new roman, new york, times, serif">----- Original Message ----<BR>From: Lachlan Andrew <lachlan.andrew@gmail.com><BR>To: Shivkumar Kalyanaraman <shivkuma@ecse.rpi.edu><BR>Cc: "RAMAKRISHNAN, KADANGODE K (K. K.)" <kkrama@research.att.com>; iccrg@cs.ucl.ac.uk; Vijay Subramanian <subrav@rpi.edu><BR>Sent: Wednesday, August 8, 2007 10:15:12 AM<BR>Subject: Re: [Iccrg] LT-TCP followup<BR><BR>
<DIV>Greetings Shiv,<BR><BR>If we use ECN to distinguish between congestion and loss, how can we<BR>detect that "there is loss that is caused due to congestion on the<BR>path (and ECN signals are absent)" and know to revert to TCP-SACK?<BR><BR>The problem is that the flow may be ECN-enabled, and there may be (a)<BR>some ECN packets, (b) some packets lost due to corruption, and (c)<BR>some packets lost due to congestion of a non-ECN queue. How can we<BR>distinguish (b) from (c)?<BR><BR>Thanks,<BR>Lachlan<BR><BR>On 08/08/2007, Shivkumar Kalyanaraman <shivkuma@ecse.rpi.edu> wrote:<BR>><BR>> If ECN is used, the likelihood of congestion related loss may be<BR>> minimized. However, if there is congestion related loss, because either<BR>> ECN is absent, or there are also end-systems that do not respond to ECN,<BR>> then LT-TCP will have a robust method for safely reverting back to<BR>> TCP-SACK behavior. When there is loss
that is caused due to congestion<BR>> on the path (and ECN signals are absent), LT-TCP will revert back to<BR>> TCP-SACK.<BR><BR>> best<BR>> -Shiv<BR>><BR>> On Mon, 6 Aug 2007, Michael Welzl wrote:<BR>><BR>> > in the presence of<BR>> > packet loss (which can always be due to an overflowing queue,<BR>> > ECN notwithstanding), the right thing to do is to assume congestion.<BR><BR><BR>-- <BR>Lachlan Andrew Dept of Computer Science, Caltech<BR>1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA<BR>Phone: +1 (626) 395-8820 Fax: +1 (626) 568-3603<BR><BR>_______________________________________________<BR>Iccrg mailing list<BR>Iccrg@cs.ucl.ac.uk<BR><A href="http://oakham.cs.ucl.ac.uk/mailman/listinfo/iccrg" target=_blank>http://oakham.cs.ucl.ac.uk/mailman/listinfo/iccrg</A></DIV></DIV>
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