From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mout.gmx.net (mout.gmx.net [212.227.15.19]) (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 8D98921FB6D for ; Thu, 3 Sep 2015 06:58:35 -0700 (PDT) Received: from u-089-d091.biologie.uni-tuebingen.de ([134.2.89.91]) by mail.gmx.com (mrgmx003) with ESMTPSA (Nemesis) id 0MO7ee-1ZczDP18zs-005dFf; Thu, 03 Sep 2015 15:58:31 +0200 From: Sebastian Moeller Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Date: Thu, 3 Sep 2015 15:58:28 +0200 Message-Id: To: cake@lists.bufferbloat.net Mime-Version: 1.0 (Mac OS X Mail 7.3 \(1878.6\)) X-Mailer: Apple Mail (2.1878.6) X-Provags-ID: V03:K0:XNbNXMqyf4UrlT0HsZjk0YBdsypihVaVaDUhgY/wmI/rvcwPEMr G7h8iCMj5pbvu5VS8XnX8NmTbDQc/x9+RW/pddnGwfFmP/8lK72j/F3vrCwYSRW9II1LkLs ybDibFbV2beZy2ZZJKuZubKyirLt1AhOrIpZaNx5R5XvTFV7AwhHrZs7yJsaZdMy3Qc48Hm J+jXWYTko+KDd031QBHrQ== X-UI-Out-Filterresults: notjunk:1;V01:K0:0IoMhEJevjw=:BQlYB07TYlHrugg7rBkbbi 6ySq6q1xXbFMd2QFlEZV8f0wl4KwvRPAFc4AVs+poiooKxR7CyoUJsIuZpuJMOSdHJpJXxQs3 /LUwvCHfUDd2In1abaoh89zkmrDPYA/LMfNU1KpJWcSHflw/qUigmbL1XYcXgis03m8taDO7+ BHFlXoDWsocH+lkKJZilUaz1RBgCHg1R7hwn4Zbf10NcVqbCEUAHJk8U/Qbfvaj01qLNvziI9 KMA+fze3aj+YnLuvzbpgxCSsTbqRt0SiHgh9m8/rqqrzv4cFAiCKfpGlLAoSYUOq8kjKuxHmN JGUUHIEnUSl74mB3laKaAtE8OQuWr+QK/05OGWQlOnnajLBOmqOzXR5hrtu+wsqdka5fDT6sN xO/Lil+lzfppFdznTCcr7bIL3svRylfd/hP4ZIHphmQLQOLn9TX0KsA95tWmnfslWqSv/2F0T WIOaJqWAz3/ISCHUdCbrkBXklEZ8MImaaVGHQSJv7PrJwc7s/EbpzcUrf0orCuE1/1f9bU+13 RrACVrf/iqH0tXp51V8ELq/lNrYEdhCWMrVo5iA4IVBburxDYoVZ9mqNvwjDLDNR3LAnXB9g7 tpTNTeEFGUDzCiKqFbuN6qSYywCgQnZO+7FLkx79ZMZ24iqXrV/+fzHhI2k0o/ydHeozX/C1q bgNOEepJqySgItBdMMKsTD16leD45ZMOlsplsQXBG66abLcpVpD6vERULrZv7PihqzHWCCKj/ CdJGwguDhkcDkaHMfbdta8mLnw/0IqXqcf8K0lhAeBV5Fofhk/MLRBCpMKg= Subject: [Cake] pppoe-ptm overhead calculation question 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: Thu, 03 Sep 2015 13:58:58 -0000 Hi Jonathan, I just stumbled over the following snippet in tc/q_cake.c = (https://github.com/dtaht/tc-adv/commit/853558f94968fe849ddd51e0ca395688af= f1d940): + /* Typical VDSL2 framing schemes */ + /* NB: PTM includes HDLC's 0x7D/7E expansion, adds extra = 1/128 */ + } else if (strcmp(*argv, "pppoe-ptm") =3D=3D 0) { + atm =3D 0; + overhead =3D 27; + } else if (strcmp(*argv, "bridged-ptm") =3D=3D 0) { + atm =3D 0; + overhead =3D 19; Now the comment might be irrelevant, but I believe it to be actually not = quite roght; VDSL2 does not (typically) use HDLC on the bearers used for = data paths, but those are the ones we care about when thinking about per = packet overhead and on-the-wire-bandwidth. According to Rec. ITU-T G.993.2 (12/2011) HDLC is used on the = ManagementTPS-TC(MPS-TC) (see section 8.2); but neither the user data = TPS-TC section (8.1) nor the referenced annex L.3 mention HDLC = encapsulation at all.=20 They do however reference Rec. ITU-T G.992.3 (04/2009) Annex N, = which in turn describes the 64/65 encapsulation scheme used in VDSL2.=20 So VDSL2 in contrast to VDSL1 uses 64/65 encapsulation and no = HDLC expansion is required. Which is great as for HDLC the 1/128 is just = stochastic approximation that can be gamed by manipulating packet = payload to consist only out of to-be-expanded-bytes. The 64/65 = encapsulation of VDLS2, IMHO, is best dealt with as a generic rate = reduction of 100-100*64/65 =3D 1.54%, but I digress. I also believe the correct overhead for pppoe-ptm over vdsl2 to be: VDSL2 (IEEE 802.3-2012 61.3 relevant fuer VDSL2): 2 Byte PPP + 6 Byte = PPPoE + 1 Byte Start of Frame (S), 1 Byte End of Frame (Ck), 2 Byte = TC-CRC (PTM-FCS), =3D 12 Byte With a high probability that on-the-wire an ethernet header including = frame-check-sequence (4 Byte Frame Check Sequence (FCS) + 6 (dest MAC) + = 6 (src MAC) + 2 (ether type) + 18 bytes) needs to be added (and = depending on ISP potentially several VLAN tags); I realize that cake = handles all of those as discrete entities that need to be specified in = their own right I really do not see how you get to 27 for pppoe-ptm, so most likely I am = overlooking something, so I would be delighted if you could explain what = I am missing. Thanks in advance... Best Regards Sebastian=