From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.17.21]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (Client CN "mout.gmx.net", Issuer "TeleSec ServerPass DE-1" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id F146B21F0B3 for ; Sat, 4 Jan 2014 12:23:15 -0800 (PST) Received: from hms-beagle-3.fritz.box ([87.240.240.144]) by mail.gmx.com (mrgmx002) with ESMTPSA (Nemesis) id 0LlESk-1VS88Y2O50-00b0rD for ; Sat, 04 Jan 2014 21:23:00 +0100 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 6.6 \(1510\)) From: Sebastian Moeller In-Reply-To: <01558084-B7D8-448A-A4ED-CE36D18AAA97@gmail.com> Date: Sat, 4 Jan 2014 21:22:59 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <9628EA9A-E5AD-4D6B-A8E3-30AFECB2FC2E@gmx.de> References: <01558084-B7D8-448A-A4ED-CE36D18AAA97@gmail.com> To: Rich Brown X-Mailer: Apple Mail (2.1510) X-Provags-ID: V03:K0:Y5kC3cP+PTk9gLRk1657Pq9W7SKxIquIv0GzEtzBZ9mGj9mnmgZ vrffVR5LImv9D5w8+taxkKXr1BkDt4U/Bd9zi1ZF3qR1/Km6eUCXSxsd7QIiPshLFeZ9xYZ jRjZnXhZIEqgZC0m5P+TK/iqaUTGPr37/rf9w8X1EI7WS3mR1u7sSlxYOfFuO9fmV1cOID9 Wt17j7/lpZStMPwrXBrkw== Cc: cerowrt-devel Subject: Re: [Cerowrt-devel] SQM Question #5: Link Layer Adaptation Overheads 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: Sat, 04 Jan 2014 20:23:24 -0000 Hi Rich, On Jan 4, 2014, at 19:16 , Rich Brown wrote: > QUESTION #5: I still don=92t have any great answers for the Link Layer = Adaptation overhead descriptions and recommendations. In an earlier = message, (see = https://lists.bufferbloat.net/pipermail/cerowrt-devel/2013-December/001914= .html and following messages), Fred Stratton described the overheads = carried by various options, and Sebastian Moeller also gave some useful = advice. >=20 > After looking at the options, I despair of giving people a clear = recommendation that would be optimal for their equipment. Consequently, = I believe the best we can do is come up with =93good enough=94 = recommendations that are not wrong, and still give decent performance. =20= Not wanting to be a spoilsport, but IMHO the issue is = complicated hence no simple recommendations. I know that my last word = was that 40bytes would be a good default overhead, but today I had the = opportunity to measure the overhead on fast ADSL connection in = Luxembourg and found that in this double-play situation (television and = internet via DSL) that an other wise invisible VLAN was further = increasing the overhead (from the 40 expected to 44 bytes). At least on = faster links these combo packets (internet, phone and potentially = telephone) are becoming more and more common, so maybe the = recommendation should be 44 (hopping that FCS are truly rare). >=20 > In this spirit, I have changed Draft #3 of the =93Setting up SQM=94 = page to reflect this understanding. See = http://www.bufferbloat.net/projects/cerowrt/wiki/Setting_up_AQM_for_CeroWr= t_310 >=20 > ADSL/ATM link: Choose =93ADSL/ATM", and set Per Packet Overhead = to 40 While I prefer ATM, I think all deployed ADSL is on ATM so these = are synonyms for our purpose. I prefer ATM since the most critical part = of the link layer adjustments is caused by the impedance mismatch = between what ATM offers and what the data transport layer requires. I = have the impression that ADSL might still evolve to a different carrier, = while ATM is basically in maintenance mode (not much new deployment if = any). > VDSL2 link: Choose =93VDSL=94, and set Per Packet Overhead to 8 There are several issues with this; VDSL is not the direct = predecessor of VDSL2 (rather VDSL2 is the successor of ADSL2+ with some = similarities to VDSL). Lumping VDSL with VDSL2 will require us figuring = out whether both behave the same. =46rom my cursory reading of the = standards of both I think VDSL is not unlikely to be using an ATM link = layer, VDSL2 is unlikely to do the same, both seem technically able to = use ATM.=20 > Other kind of link (e.g., Cable, Fiber, Ethernet, other not = listed): Choose =93None (default)=94, and set Per Packet Overhead to 0 This is not going to be worse than today, so sounds fine (it = would be good to know whether there is truly no overhead on these links = in practical useage).=20 Quick vote: anyone on this list using ceroWRT on an VDSL/VDSL2 = link or cable fiber whatnot that could do some quick testing for us?=20 >=20 > NB: I have changed the first menu choice to =93ADSL/ATM=94 and the = second to =93VDSL=94 in the description. I am fine with changing names, just see what the consensus is = for the names. > I would ask that we change to GUI to reflect those names as well. This = makes it far easier/less confusing to talk about the options.=20 Agreed. >=20 > As always, I welcome help in setting out clear recommendations that = work well for the vast majority of people who try CeroWrt. Thanks. I guess, we need a new wiki page detailing the procedure to = figure out the link layer (and overhead if on ATM). Best Sebastian >=20 > Rich > _______________________________________________ > Cerowrt-devel mailing list > Cerowrt-devel@lists.bufferbloat.net > https://lists.bufferbloat.net/listinfo/cerowrt-devel