From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.15]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "mout.gmx.net", Issuer "TeleSec ServerPass DE-1" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 9EDB621F1F9 for ; Mon, 18 May 2015 01:41:37 -0700 (PDT) Received: from hms-beagle-6.lan ([134.2.89.70]) by mail.gmx.com (mrgmx002) with ESMTPSA (Nemesis) id 0LdHqj-1Zbocu35dp-00iTVx; Mon, 18 May 2015 10:41:33 +0200 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) From: Sebastian Moeller In-Reply-To: Date: Mon, 18 May 2015 10:41:39 +0200 Content-Transfer-Encoding: quoted-printable Message-Id: References: <554F64E1.6000609@gmail.com> <554F9594.60808@gmail.com> <7B7986E7-49A1-4EE1-B8D0-B55A6C2660A1@gmx.de> To: Jonathan Morton X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:FYxxPvHHnoxCrSeNVFqyZb36OM9cRdECKM7oi6KbLtHpag9C85+ 2RVrHgoGEFq9i7IKugNynm2sUHqpu+bibDzR+iGTsHpMeHJA+ma2IbJLqckTE/ZudmDEDqL y/VJkVG0sMkW1nlgzdrAhKyjNu0A4oWwzzCn/aaq1UQgaD9Aj0tBwlZxund20heO78gkC7f N7spsXi3DMWc1kOvR5tMQ== X-UI-Out-Filterresults: notjunk:1; Cc: cake@lists.bufferbloat.net Subject: Re: [Cake] More overhead keywords X-BeenThere: cake@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Cake - FQ_codel the next generation List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 18 May 2015 08:42:07 -0000 Hi Jonathan, On May 18, 2015, at 10:13 , Jonathan Morton = wrote: > Hmm. Looks like that document I found was really out of date, then. = But it got me fairly close. >=20 > For me, the overhead starts at the IP packet (so for your example, at = the 1492 byte level), and excludes optional parts of the spec like FCS = (since I have a separate flag for that). So I need to take the 8 bytes = for PPPoE, the 14 for Ethernet and the 4 for PTM, total 26 - one less = than my existing figure. >=20 > Presumably the bridged version is also one byte smaller than my = calculation, 18 rather than 19. Is there also a version which transmits = IP without Ethernet framing? Not as far as I know, but I do not claim to be an expert here. >=20 > You would then specify "pppoe-ptm ether-vlan via-ethernet" to set your = example connection up the friendly way, or just "overhead 16" for the = terse way (and you can already do that in the current version). >=20 > The 64/65 sync overhead is something we'll have to discover by = experiment. Luckily, it's pretty easy to tell whether we're filling up a = dumb FIFO or not. That is what I had thought as well, before realizing my ISP = actually throttles my connection at the BRAS so that the VDSL link = itself never becomes the bottleneck=85 >=20 > I've gone for the technical labels for three reasons. First, it = reflects what's actually happening, which generally reduces confusion in = the long run. I am not sure that wielding term as vcmix and llcsnap reduces = confusion ;) just kidding. > Second, you might underestimate the number of ADSL ISPs worldwide, as = well as the difficulty of keeping such a database up to date. Fair enough. > Third, every DSL modem and ISP I know of has made it reasonably easy = to discover at least the base encapsulations - autodetection of vcmux vs = llc isn't absolutely reliable, for example. Well ,not in Germany were it is all detective work and no clear = documentation from the ISPs. > They might be less forthcoming about vlan and FCS, but one can make = intelligent guesses here, based on whether it's a converged services = ISP. True >=20 > Ideally, we could do with a tool (at dslreports?) which makes = detecting the actual overhead easier. This would be doable using small = packets to magnify the differences. I happen to have a very hacky implementation of such a tool = available, but that only works for ATM carriers, I am not sure whether = this really can be done for VDSL2 at all (for example, some ISPs limit = the number of packets per second so one never can saturate the link with = small packets). But for ATM it just takes a few hours of collecting data = and a bit of processing ;)=20 >=20 > And if the user really can't work it out, they can always throw up = their hands and specify "conservative". >=20 > - Jonathan Morton