From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Richard Scheffenegger" Subject: (unknown) Date: Tue, 21 Dec 2010 11:35:39 +0100 Message-ID: <20101221103539.137960@gmx.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE To: netdev@vger.kernel.org Return-path: Received: from mailout-de.gmx.net ([213.165.64.22]:44842 "HELO mail.gmx.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with SMTP id S1751240Ab0LUKfm (ORCPT ); Tue, 21 Dec 2010 05:35:42 -0500 Sender: netdev-owner@vger.kernel.org List-ID: Hi guys, You may be interested in this draft I recently posted: http://tools.ietf.org/html/draft-scheffenegger-tcpm-sack-loss-recovery-= 00 It addresses a minor nit-pick fix in the SACK specs, and is a sender-on= ly modification.=20 Basically, with SACK a sender following RFC3517 will ignore partial ACK= s as signal that some segments running up to the end-of-stream are lost= =2E SACK will only recover "known" holes - which means that at least on= e segment after the lost segment has to be received (and the ACK/SACK f= or this has to get to the sender). Under certain circumstances - when the sender is regularly limited in t= he amount of data to send, either by the application, network (cwnd) or= receiver (rwnd), loss of the last segment before RecoveryPoint leads t= o avoidable RTOs - if the sender would use the partial ack (ACK without= any SACK entries, but below RP / snd.max) also as loss indication just= as NewReno does. In comparison, using NewReno (disabling SACK), one ca= n get improved delivery latencies, as partial ACKs trigger a retransmis= sion with NewReno. =46or the public internet, I received reports by a major player indicat= ing a shift between 0.1 and 0.8% from RTOs to fast retransmission (at a= overall RTO vs. FastRetransmit ratio of ~60%) =46or private LANs, which run different applications such as NFS and ve= ry often stall until one such transaction finishes, I can not provide s= olid data, but it appears that the impact is more pronounced - but the = RTO/FR ratio there is typically only 20-40%. Please let me know what you think about this change. Richard Scheffenegger --=20 GMX.at - =C3=96sterreichs FreeMail-Dienst mit =C3=BCber 2 Mio Mitgliede= rn E-Mail, SMS & mehr! Kostenlos: http://portal.gmx.net/de/go/atfreemail