Adaptation field

["Surtees, Abigail" <abigail.surtees@roke.co.uk>]

Hi,

I've just started looking ip-over-dvb and have a question about part of draft-clausen-ipdvb-enc-00.txt which I hope someone can answer.

On page 10 there is a table showing the meaning of the PUSI and AFC bits in the TS packet header, followed by 2 paragraphs of explanation.  The second paragraph says:
"
        The TS Packet that carries the last byte of a SNDU MUST always have 
        an adaptation field. In case this was the last SNDU (0/11 PUSI/AFC) 
        the TS Packet is filled with stuffing bytes. In case another SNDU 
        starts in this TS Packet, another 4-byte adaptation field is 
        inserted before the next SNDU. "

I think this means that the adaptation field is used as stuffing bytes when there are no more SNDUs, so there will be 184 - x bytes of stuffing where x is the length of the last part of the SNDU.  Is this correct?

If there is another SNDU does 'another 4-byte adaptation field' mean the one that is always carried or another one on top of that?  In other words, do you get
  ________________ ____________ ______________
  ... end of SNDU | adap field | next SNDU ...
  ________________ ____________ ______________

or 
  ________________ ____________ ____________ _____________
  ... end of SNDU | adap field | adap field | next SNDU...
  ________________ ____________ ____________ _____________

?

Thanks,

Abbie

Abbie Surtees
Engineer
Internet Applications and Mobility
Roke Manor Research Ltd
Tel:   +44 (0) 1794 833131

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