From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from g1t5424.austin.hp.com (g1t5424.austin.hp.com [15.216.225.54]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "smtp.hp.com", Issuer "VeriSign Class 3 Secure Server CA - G3" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id D817A21F31B for ; Tue, 3 Mar 2015 10:27:35 -0800 (PST) Received: from g2t2360.austin.hp.com (g2t2360.austin.hp.com [16.197.8.247]) by g1t5424.austin.hp.com (Postfix) with ESMTP id 6969E9C; Tue, 3 Mar 2015 18:27:34 +0000 (UTC) Received: from [16.103.148.51] (tardy.usa.hp.com [16.103.148.51]) by g2t2360.austin.hp.com (Postfix) with ESMTP id 38DA74B; Tue, 3 Mar 2015 18:27:34 +0000 (UTC) Message-ID: <54F5FD15.1030605@hp.com> Date: Tue, 03 Mar 2015 10:27:33 -0800 From: Rick Jones User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: divya singla References: <5EDCCC18D27F4F039FA971B3C834A466@srichardlxp2> <20150226151457.75fc898b@urahara> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: codel@lists.bufferbloat.net Subject: Re: [Codel] About Packet Drop in Codel X-BeenThere: codel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: CoDel AQM discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Mar 2015 18:28:04 -0000 On 03/03/2015 10:12 AM, divya singla wrote: > But Sir i heard that UDP does not respond to congestion.Even though its > packets are lost, it keeps sending packets at the same rate(unlike tcp) UDP does not and never has. All it has ever done is send what the application has told it to send as the application tells it to. The *application* using UDP is expected to respond to congestion. rick jones > > -- please answer this too: > Does codel implement concept of marking(ECN) in ns2? > > > On Tue, Mar 3, 2015 at 12:37 AM, Jonathan Morton > wrote: > > With UDP, you're at the mercy of the application using it. With TCP, > you're merely at the mercy of the operating system. > > AQM acts on UDP packets in the same way as TCP packets - in fact it > can't tell them apart. So any application which detects and responds > to UDP packet loss in the same way as TCP does, will back off just > the same. > > In practice, UDP is used for several different types of application: > > - simple request response, such as DNS and NTP, where eliminating > TCP's connection setup overhead is important. In any case, TCP's > congestion control doesn't get a chance to do any good on such s > short-lived connection. Packet loss in this situation is tolerated > by retry, with exponential backoff as an alternative congestion > control measure. > > - latency sensitive and often isochronous (inelastic) flows like > VoIP. Packet loss may lead to a loss of quality, but there is little > the application can do to reduce its loss except dropping the call > completely. > > - as a way to implement delay sensitive and pacific congestion > control algorithms, as in uTP. > > A flow isolation system, such as that in fq_codel, will often leave > UDP flows alone completely, because they tend not to be the ones > using the bulk of the bandwidth. Conversely, if a single UDP flow > was responsible for the congestion, it would let the other traffic > bypass it. This is why fq_codel is better than just plain codel, if > you can get it. > > - Jonathan Morton > > > > > _______________________________________________ > Codel mailing list > Codel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/codel >