Re: Antwort: Re: Antwort: IP over DVB-RCS

[Lloyd Wood <l.wood@eim.surrey.ac.uk>]

On Thu, 4 Apr 2002 Torsten.Jaekel@FTK.rohde-schwarz.com wrote:

> The 32 bit CRC is just used to recognize transmission (packet) errors. No way to
> correct missing or incorrect bits (is not a redundancy
> part or Reed Solomon code). The whole packet (many ATM cells) is discarded if
> the CRC is not matching.

data integrity is ensured by discards and retransmission.

limited amounts of redundancy or FEC can't guarantee data integrity,
though they can increase its likelihood.

L.

> On Wed, 3 Apr 2002 Torsten.Jaekel@FTK.rohde-schwarz.com wrote:
>
> > I am not (yet) so familiar with RCS but a bit with ATM.
> > There are different ATM Adaption Layers (AAL). AAL5 (using jumbo frames) has
> > just a 32 bit CRC, no approaches for data integrity (issue of
> > higher layers).
>
> ??? that's what the 32-bit CRC is for...
>
> > But if you use AAL1 (I do not know if intended for RCS, perhaps because this
> is
> > also used for MPEG-2 via ATM),
> > there is an ATM based FEC algorythm (Reed Solomon), in addition to MPEG-2 FEC.
> >
> > Is this similar to CableModems (DOCSIS) where the Uplink is also ATM-like ?

<L.Wood@surrey.ac.uk>PGP<http://www.ee.surrey.ac.uk/Personal/L.Wood/>