<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I'm taking the liberty of forwarding this to ICCRG because it is as relevant to the group as it gets, I suppose...<br><div><br><div>Begin forwarded message:</div><br class="Apple-interchange-newline"><blockquote type="cite"><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1);"><b>From: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Bob Briscoe <<a href="mailto:bob.briscoe@bt.com">bob.briscoe@bt.com</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1);"><b>Date: </b></span><span style="font-family:'Helvetica'; font-size:medium;">March 9, 2011 12:30:25 PM GMT+01:00<br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1);"><b>To: </b></span><span style="font-family:'Helvetica'; font-size:medium;">Caitlin Bestler <<a href="mailto:cait@asomi.com">cait@asomi.com</a>><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1);"><b>Cc: </b></span><span style="font-family:'Helvetica'; font-size:medium;"><a href="mailto:conex@ietf.org">conex@ietf.org</a><br></span></div><div style="margin-top: 0px; margin-right: 0px; margin-bottom: 0px; margin-left: 0px;"><span style="font-family:'Helvetica'; font-size:medium; color:rgba(0, 0, 0, 1);"><b>Subject: </b></span><span style="font-family:'Helvetica'; font-size:medium;"><b>[conex] More precision than 1 bit ECN (was: Re: WG energy)</b><br></span></div><br><div>Caitlin,<br><br>Still catching up on parts of past threads...<br><br>At 04:41 23/02/2011, Caitlin Bestler wrote:<br><br><blockquote type="cite">On Feb 17, 2011, at 10:04 AM, John Leslie wrote:<br></blockquote><blockquote type="cite"><br></blockquote><blockquote type="cite">> Caitlin Bestler <<a href="mailto:cait@asomi.com">cait@asomi.com</a>> wrote:<br></blockquote><blockquote type="cite">The other area where convergence would be useful is coming up with an abstract way to report "congestion<br></blockquote><blockquote type="cite">detected" with more precision than just an ECN bit, so that L4 can utilize this information wihtout having to<br></blockquote><blockquote type="cite">learn the specifics of L2 congestion control protocols.<br></blockquote><br>This as relevant to tsvwg & iccrg as to ConEx, but I'll keep it to ConEx for now...<br><br>Matt Mathis taught me something important in respect of how many bits you need per frame/packet for congestion control. The critical metric is the amount of signalling information per *window*, not per packet/frame. You can maintain the same amount of signalling information per window with just 1 bit per packet as long as the congestion control keeps the packet rate proportional to 1/p, where p is the marking probability.<br><br>Intuition: with a window of 100 frames, if the marking probability is 1% you will get one mark per round trip. If when the marking probability reduces /100 to 0.01% you speed up x100 to 10,000 frames per window, you will still get one mark per RTT. So you will still have the same rate of control information per time.<br><br>See slide 8 of this Anaheim ICCRG presentation jointly from Matt & I:<br><<a href="http://www.bobbriscoe.net/present.html#1003iccrg">http://www.bobbriscoe.net/present.html#1003iccrg</a>><br><br><br>DCTCP, Relentless TCP and Scalable TCP all aim for 1/p (this is why Scalable TCP was called scalable). TCP NewReno's window is proportional to 1/sqrt(p), but more modern algorithms like these are moving closer to 1/p.<br><br><br>Bob<br><br><br>________________________________________________________________<br>Bob Briscoe, BT Innovate & Design <br>_______________________________________________<br>conex mailing list<br><a href="mailto:conex@ietf.org">conex@ietf.org</a><br>https://www.ietf.org/mailman/listinfo/conex<br></div></blockquote></div><br></body></html>