[OT] aal5 pdu CRC
Harti Brandt
hartmut.brandt at dlr.de
Thu Jan 27 07:07:29 PST 2005
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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