Date: Thu, 27 Jan 2005 16:10:59 +0100 (CET) From: Harti Brandt <hartmut.brandt@dlr.de> To: Jose M Rodriguez <josemi@freebsd.jazztel.es> Cc: net@freebsd.org Subject: Re: [OT] aal5 pdu CRC Message-ID: <20050127160658.K55581@beagle.kn.op.dlr.de> In-Reply-To: <200501271600.42408.josemi@freebsd.jazztel.es> References: <200501271600.42408.josemi@freebsd.jazztel.es>
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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. 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. harti
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