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Re: UPC and AAL5 PDUs

> Today I have been trying to use the UPC (just rate control) implemented
> in the PCA200-E NIC. I simply changed the values in the driver to 
>   tpd->rc_stream_desc.data_cells = 10;
>   tpd->rc_stream_desc.empty_cells = 343;
> to get an approximate rate of 10,000 cells per second, but it doesn't
> work. Any ideas?
> I guess the problem is in the size of the PDU. I changed the PDU size to
> different values using the max_sdu QoS parameter, but it did not work
> anyway. There is something even more strange: using a different PDU size
> for transmission and reception (set by max_sdu) does not cause any
> errors. I though that since the CRC is computed on different data, the
> PDU would be discarded.
> How can this happen? 
> I also would like to know if it is possible to set the size of the AAL5
> PDUs, and if not, what size is used by default?

I think the Rate Control Mechanism is used on PDUs effectively larger than
one cell (-> when more than 40 byte are being sent). max_sdu isnīt evaluated
in the PCA200E driver. The driver itself doesnīt perform any CRC checks.
Using ttcp_atm with -a (AAL5) the PDU size is equal to the packet size given
with option -l. In general the PDU size is the MTU size of the interface beeing
used (9180 for Classical IP over SVCs) plus 8.  The maximum SDU/PDU size in
AAL5 is 65535.


Uwe Dannowski, student, Dresden University of Technology, Dept. of CS, OS group
email:  WWW:
tel: +49-351-2848091/+49-172-3736772 addr: Gamigstr. 20, 01239 Dresden, Germany

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