From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-x22e.google.com (mail-wi0-x22e.google.com [IPv6:2a00:1450:400c:c05::22e]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 9E87821F1D4 for ; Sun, 29 Dec 2013 00:54:57 -0800 (PST) Received: by mail-wi0-f174.google.com with SMTP id z2so15478115wiv.7 for ; Sun, 29 Dec 2013 00:54:55 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=ETrdrQMfDk464bmzbvxJM3ZMlzwRRfS+loL5WVKKLRE=; b=qbjgqTcL2Pu+6Bjvlu5p+hVcyUMxtNX+g059qnjU06sskf836gymUORzel6ueaOLIb FD158nwLf4tBx4t0yYkP84W6paZ+szH4/2B8R4jcEfmRkjYmasphgaGCvoDYR0f9rziB 0j8H7HJukx5QWDPCgpW8wURhi2lfxrnrkP6EMjlYZmVcm3jk01SeG7FXE0f6cBt2A5gp +Gg3K5eHmkK/ml/cHxjwxolrEjGf2hj5MvVCi0GfpBWA/HTpLVjmND7imNZ+xON091po 7j8qBB6EN+katly+J+EF9jVtyGJ3OQOkR26UV6i0cDbWQwgXu7OUkkN8PYaRsbls+CP/ GN6A== MIME-Version: 1.0 X-Received: by 10.180.95.162 with SMTP id dl2mr40034049wib.17.1388307295905; Sun, 29 Dec 2013 00:54:55 -0800 (PST) Received: by 10.217.123.69 with HTTP; Sun, 29 Dec 2013 00:54:55 -0800 (PST) In-Reply-To: <41ec2fd6-4fb8-4e17-8458-861e27c2c5ff@email.android.com> References: <3AE6C690-F53C-471F-9980-9E071B87D983@gmail.com> <41ec2fd6-4fb8-4e17-8458-861e27c2c5ff@email.android.com> Date: Sun, 29 Dec 2013 00:54:55 -0800 Message-ID: From: Dave Taht To: Sebastian Moeller Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Cc: cerowrt-devel Subject: Re: [Cerowrt-devel] SQM Question #2: How does CeroWrt use info gleaned from the link layer adaptation? X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 29 Dec 2013 08:54:58 -0000 I would like it if we had a couple per-provider recomendations and relevant discussion. On Sat, Dec 28, 2013 at 11:36 PM, Sebastian Moeller wrote= : > Rich Brown wrote: >>QUESTION #2: How does CeroWrt use info gleaned from the link layer >>adaptation? > > The link layer adaptations work in correcting the kernels estimate = of a packets behavior on the wire. In the tc_stab case the kernel calculate= s the effective size of the packet on the wire, that is it pretends the pac= ket is larger than it really is, so for a given bandwidth it estimates the = correct time it takes for that packet to be actually transmitted. In the ht= b_private case the kernel keeps the packet's size (more or less) intact but= adjusts its estimate of the packets transmit rate. Both methods boil down = to the same idea, make sure the packet scheduler will only send packet N+1 = after packet N has just cleared the wire. > >> >>Specifically, the link layer adaptation all seem to be designed to >>compute the actual time it takes to transmit a packet, accounting for >>Ethernet & PPPoE header bytes, other overhead, and ATM 48-in-53 >>framing. > > And the annoying size dependent padding of the last ATM cell. > >> >>How does CeroWrt use this time calculation? Does it simply make sure >>that the target time doesn=92t get too low for a particular flow=92s queu= e? > > Thanks to the link layer adjustments (lla) cero now estimates the= correct time each packet takes and will not send any faster than the shape= d rate allows. If no lla is performed cero would overestimate the link capa= city, send more than expected and potentially fill the modems bloated buffe= rs. Traditionally people tried to reduce their shaped rate by >10% to at le= ast account for the 48 in 53 framing, but failed miserably for small packet= s since overhead and padding can more than double the wire size of a packet= . Note that ACQ packets typically are small as are voice over IP packets. > > I hope this helps > Sebastian > >>(I could imagine that a short packet over ATM would take 2x the (naive) >>expected/calculated time for a packet of that length, and that flow >>would be penalized. Is there more to it?) >>_______________________________________________ >>Cerowrt-devel mailing list >>Cerowrt-devel@lists.bufferbloat.net >>https://lists.bufferbloat.net/listinfo/cerowrt-devel > > Hi Rich > -- > Sent from my Android phone with K-9 Mail. Please excuse my brevity. > _______________________________________________ > Cerowrt-devel mailing list > Cerowrt-devel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cerowrt-devel --=20 Dave T=E4ht Fixing bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.= html