RE: [AVT] Request for WG Last-Call for draft-ietf-avt-rtp-3gpp-timed-text-07.txt

["Rey Jose" <Rey at panasonic.de>]

Colin,

> Section 3.1.2 (first paragraph on page 21) states that a 
> maximum of 64 dynamic SIDX are allowed at any moment, but 
> allows a range of 0-127.  
> Suggest either allowing 127 active values, or reducing the 
> allowable range, or adding an explanatory note to clarify.

This has the following reason: If you allow 127 values, then when a reordered packet with a new sample description arrives, it is discarded.  E.g. last packet received is SIDX=5, thus the only invalid value would be SIDX=6, e.g. Now a reordered packet arrives with a new description, SIDX=9. It will be mistakingly discarded, because the SIDX=9 is marked "valid" at that moment and the valid sample descriptions shall not be re-written.  Therefore, a "guard interval" is introduced. Agreed it should be rare to use so many sample descriptions but nevertheless, a mechanism is provided for that case. As for the "guard interval" value, we found 64 as 128/2 simple enough while still meeting the expected maximum number of sample descriptions. Besides that, there's no other motivation for choosing 64 or other value. I'll add a similar explanation if that's fine with you into the Annex.  Comments?

Thanks,

José





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