[linux-dvb] Re: Which CRC-code is used in TS of DVB?

[Johannes Stezenbach <js@convergence.de>]

Andrew de Quincey wrote:
> On Monday 27 October 2003 22:46, Emard wrote:
> > Soma idea about CRC and network problems associated with it;
> >
> > can we verify that the crc calculation arithmetic is carried
> > out properly (i.e. take a look at another's author code doing the
> > same thing).
> >
> > Typical error in CRC's is improper usage of signed and unsigned
> > arithmetic, shifts with and without sign or bit rotations with carry
> > and similar stuff regarding boundary conditions.
> >
> > From the experience I have seen, if crc is enabled, some
> > packets that should have passed are rejected.
> 
> But lots do work with CRC enabled.... sounds like a boundary condition.

Maybe the CRC check fails because some TS packets have errors?
We could add a check for the transport_error_indicator to
dvb_dmx_swfilter_section_packet().

I'm not a network specialist and could be wrong here, but IIRC
ethernet has a CRC for the full packet, but IP only has a header
checksum. So without CRC you could silently get wrong data.
Sometimes wrong data is better then no data, so maybe we should
add a flag to NET_ADD_IF which allows one to specify if the
CRC check is wanted. (Not that this would solve any real problems, but
it might be nice for testing.)

Johannes


-- 
Info:
To unsubscribe send a mail to ecartis@linuxtv.org with "unsubscribe linux-dvb" as subject.