Re: IP over DVB-S2 - crc usage?

[Gorry Fairhurst <gorry@erg.abdn.ac.uk>]

Fausto,

I'm trying to understand the main outstanding issues.

I agree there are a set of DVB-S.2 BB header fields that may be re-used to
carry the protocol control information for the encapsulation layer. This
seems like the correct way to go. Many BB header fields are not defined/used
for the Generic Mode, but I don't yet know (maybe others are wiser) exactly
which fields may be safely (re)used and for a S.2 generic encapsulation and
still remain compatible the DVB-S.2 spec.  This is probably an area that
needs to be cleared with the DVB S.2 group.

My main query relates to your comment about the optional CRC fields. I'm
puzzled by your suggestion that requirements for CRC usage may be related to
the presence of padding in the BB frame.  My thoughts were that the CRC
requirement stemmed from:

    (i) The need to verify the integrity of the payload (PDU) before
    passing to the IP layer - to mitigate the impact of link errors
    and low level errors in data movement.

    (ii) To verify the framing (length) of PDUs - ensuring the next
    SNDU header was correctly located within the BB frame payload.

    (iii) To verify the integrity of reassembled SNDUs.

    (iv) To allow a receiver to monitor the quality of the
    received bitstream.

- I can see how (i) relates to worst case expected link error
characteristics, but don't see yet how this can be related to the presence
or absence of padding bytes.

Thoughts?

Gorry