From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-x232.google.com (mail-pg0-x232.google.com [IPv6:2607:f8b0:400e:c05::232]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by lists.bufferbloat.net (Postfix) with ESMTPS id 5B3D63B29E for ; Tue, 5 Sep 2017 21:45:56 -0400 (EDT) Received: by mail-pg0-x232.google.com with SMTP id d8so12561116pgt.4 for ; Tue, 05 Sep 2017 18:45:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mounce.com.au; s=google; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc; bh=VtqsV7/rZfpzEyCeLxB33eT0TumA8OVyexjpwLFOHbw=; b=alYG7zbFujhP1G4EdHk7bpNenDDkoy65wIy+CEwmwkKnxrmmEtnfDzgFhoxwdlIk7w TeHKVlFguLfFVJD32CUeryXGT75m3YjmmsbIQTUwh/h7oe2v/j7HQBJirWO4LtWz9xpU kXskpQu6Q9N5CcvL8nuZrYxEYvEbQMaubjFZDlR/8fc0jkKKjaMbXnKjTxDQA0+GM0ZG FIq7/8DxuAdMUfpnDYu3K6B8DEV+sj/WBzq/N97bk2OgRd23I3D83UA5eidzIY85Jck6 I3wGGeJ/HIy+jAx/GrhUdJ0v+J4Xbe3uYrAbkZ3veACBlnplZ0JMyNflBWLvqAv29BcI nALg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc; bh=VtqsV7/rZfpzEyCeLxB33eT0TumA8OVyexjpwLFOHbw=; b=s+AgXqtRAzTfAF7qJx7cb+P+sdi6SIgDeIJfUr9QLXFZdm9chpgTTNKmFtBIb3Ymbn 1SpUQUhCFvWV22Z9cnRGcZkvz4fzOeNNzploBN9XnasskLirnQxmhelJ8TGYo0kMcOSY kkmn6+tiLWYlv5NtwGn+P7pRXrKz0uOXvjflOMnFw7vVCY1Ahk62Is2Ta2q/ta7NvC9U gfmP1YHTgUeL3Gbc0PtSX2AKWYLHtsBO0FGVNfTnoZfpnmKMj6pi2QUsc6RXTh0bkN2e yj617/oaXb7Ml80Wm0oIPJ2lMy+bwCtR2t1aI8NyIIBIz6W3FvdcEkoHZvAKvcxGvVxR Digg== X-Gm-Message-State: AHPjjUizpVf/oeB1e4j3cHt1WQhLM2chY5Qm42pRD0oDFSCc/FrKkg7y hXrkegE3a1c/2TXzFz/UUbydXDWcJ4HG X-Google-Smtp-Source: ADKCNb7wb2uM2W5pEOhoKXVcwJcCrKfKhITvMPuJ2nurGN6qgWZASZ3cnzqWouZPumzqq7I893ljeqsbHsj2FBwGrFQ= X-Received: by 10.84.132.13 with SMTP id 13mr6346161ple.235.1504662355386; Tue, 05 Sep 2017 18:45:55 -0700 (PDT) MIME-Version: 1.0 Received: by 10.100.189.72 with HTTP; Tue, 5 Sep 2017 18:45:39 -0700 (PDT) X-Originating-IP: [101.166.225.7] In-Reply-To: <915b0913-0ac5-c6b6-3771-752a9e41dff2@gmail.com> References: <915b0913-0ac5-c6b6-3771-752a9e41dff2@gmail.com> From: Ryan Mounce Date: Wed, 6 Sep 2017 11:15:39 +0930 Message-ID: To: Dennis Fedtke Cc: Jonathan Morton , Cake List Content-Type: text/plain; charset="UTF-8" Subject: Re: [Cake] overhead and mpu X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.20 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 06 Sep 2017 01:45:56 -0000 On 6 September 2017 at 05:49, Dennis Fedtke wrote: > Hi! > > Thank you for all answers. > But for me this still makes no sense. > Assuming we have an ethnernet connection running over a docsis line. > docsis is able to transmit full 1500byte ethernet packets. > Lets say it is an 50 Mbit/s Line. (I dont know now how exactly docsis works) > So to reach the 50Mbit/s ethernet speed the docsis link rate needs to be > higher 50,6 Mbit/s (50*1518/1500 ??) > But when running a speedtest it will still not show the full speed. because > of other overhead from underlying protocols (tcp/ip for example) > So the ISP will set the sync rate even higher to compensate for that. > > But does this matter for the end user? There is only one speed that matters for an end user configuring cake. You need to know the rate of the shaper defined in the CM config file for your plan, or otherwise determine this rate. As I have said CMs don't 'sync' in the way you are used to with xDSL so this terminology isn't really correct, however in terms of being the significant bottleneck immediately 'upstream' of cake the configured rate of this shaper is equivalent to the 'sync' speed for xDSL. Simply ignore the speed that your ISP advertises, this is a bogus number for just about every DOCSIS ISP. Also ignore the speed reported by speedtest.net unless you are confident that there is no other activity on your link and that you know what TCP options are in use by your operating system. If you get a very consistent result on speedtest.net, it is possible to estimate the rate of the CMTS's shaper. This is a relationship between the TCP payload size and full Ethernet frame size. For example, on an OS that uses TCP timestamps and you get a result of 100Mbps on speedtest.net the L2 rate may be 100 * (1518 / 1448) ~= 104.8Mbps. By now you can see where 1518 comes from (1500 bytes Ethernet payload (IP packet) + 14 bytes Ethernet header + 4 bytes Ethernet FCS). 1448 is (1500 bytes IP packet (Ethernet payload) - 20 bytes IPv4 header - 20 bytes TCP header - 12 bytes TCP timestamps option). You should use Wireshark to confirm which TCP options and MTU your system is using with the speedtest.net server and use these values instead of my above example. Once you have your estimate, round it down a couple of percent. If your estimate is too high then it will be as if you don't have cake at all. Too low and cake will still be effective, you will just sacrifice a small amount of speed. > In case of docsis does it make sense to account for 18 overhead? Whatever the speed may be, you must always configure 'overhead 18 mpu 64' or the equivalent 'docsis' keyword to correctly compensate for the Ethernet framing seen by the shaper in the CM/CMTS, otherwise cake may underestimate the link utilisation when smaller packets are being sent and its benefits will be defeated. > The user will enter 50mbit and it will work. If the isp has provided a > sligher higher syncrate. This 50Mbps figure is suspiciously round, where is it actually from? This is the advertised speed of your plan by the ISP? > and the mpu setting. i don't know how cake handles this in detail. > How the overhead gets added. > lets i enter mpu 46. > And cake we set 18 as overhead. > Will this result in mpu 46 or 64? > Can someone debug the code maybe please? :> This has already been answered and the relevant snippet of code has been posted. Overhead is first added (relative to IP), and packets that are still below the MPU *after* the overhead is added will be rounded up to the MPU of 64. > I have the feeling with mpu 46 my pages lot a bit snappier. but could be > placebo. Correct, this is a placebo. You need to configure 'overhead 18 mpu 64' or equivalently 'docsis', no ifs no buts. Focus your attention on estimating the rate of your shaper. The framing compensation for DOCSIS is a solved problem whereas the rate of a given link varies from ISP to ISP, and from plan to plan. > > Thank you. > > > > > > _______________________________________________ > Cake mailing list > Cake@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cake