From owner-freebsd-net@FreeBSD.ORG Thu Jan 27 15:32:30 2005 Return-Path: Delivered-To: freebsd-net@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id AB43316A4CF; Thu, 27 Jan 2005 15:32:30 +0000 (GMT) Received: from 212.106.239.101.adsl.jazztel.es (212.106.239.101.adsl.jazztel.es [212.106.239.101]) by mx1.FreeBSD.org (Postfix) with ESMTP id 89CB043D3F; Thu, 27 Jan 2005 15:32:27 +0000 (GMT) (envelope-from josemi@freebsd.jazztel.es) Received: from orion.redesjm.local (orion.redesjm.local [192.168.254.16]) j0RFWOwt076679; Thu, 27 Jan 2005 16:32:25 +0100 (CET) (envelope-from josemi@freebsd.jazztel.es) From: Jose M Rodriguez Organization: Redes JM To: freebsd-net@freebsd.org, Harti Brandt Date: Thu, 27 Jan 2005 16:32:37 +0100 User-Agent: KMail/1.7.1 References: <200501271600.42408.josemi@freebsd.jazztel.es> <20050127160658.K55581@beagle.kn.op.dlr.de> In-Reply-To: <20050127160658.K55581@beagle.kn.op.dlr.de> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Message-Id: <200501271632.37457.josemi@freebsd.jazztel.es> X-AntiVirus: checked by AntiVir Milter (version: 1.1.0-3; AVE: 6.29.0.8; VDF: 6.29.0.75; host: antares.redesjm.local) cc: net@freebsd.org Subject: Re: [OT] aal5 pdu CRC X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.1 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 27 Jan 2005 15:32:31 -0000 El Jueves, 27 de Enero de 2005 16:10, Harti Brandt escribi=F3: > On Thu, 27 Jan 2005, Jose M Rodriguez wrote: > > JMR>Hi, > JMR> > JMR>get some free time to work in uadsl, but have a problem. Hope someone > that JMR>can read ITU I.363 can answer this. > JMR> > JMR>Every usb adsl modem implementation I see doesn't obey aal5 pdu > encoding JMR>standards, which requires that the PDU trailer come at the > begin of a fresh JMR>cell. > > That is not true. The trailer must be on the END of a cell. Before the > trailer there will be padding bytes so that this happens. If, for example, > you have a one byte PDU the AAL5 PDU will consist of 1 byte information, > 39 bytes padding and 8 bytes trailer. > At last, rfc1483 and the received logic side seems to point that this is tr= ue.=20 Most implementations sync the begin of a new PDU after detect the last cell= =20 by header test. Also, PDU lenght and crc is decode from a fixed ptr on the= =20 ENDPDU cell (lenght=3Dcell[2]..cell[3], crc=3Dcell[4]..cell[7]). > JMR> > JMR>So, I think that the modem must rework this and generate two cells on > the JMR>wire. Due how this modems works, I doubt that the modem > recalculate PDU CRC JMR>itself, So... > JMR> > JMR>Can someone confir if the CRC covers the PAD? I'm begin to think that > the CRC JMR>only covers the playload and the pdu-trailer. > > The CRC covers everything but the CRC. The PAD must be filled with zeros > though. > This is not so clean. This pad may be take as a cell pad or as a PDU pad. = If=20 this is take as a cell pad, it may not be part of the CRC (the ENDPDU cell = is=20 also paded from 8 to 48). My first guest is that the pad is part of the PDU, but I really doubt that = the=20 modem may be able to do a full CRC reclaculation. > harti =2D- josemi