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Re: [AVT] RFC 2833 questions: Intervals, durations, and lost packets.

Please read the updated version (draft-ietf-avt-rfc2833bis, issued a few days ago) and see if it answers your questions.

Lubbs, Stephen wrote:
Hi Folks,
I have a few questions related to RFC 2833, to wit:

   1. Is the intent of the spec that RFC 2833 packets should
      be transmitted every 50 ms or is it that they should be
      transmitted at the interval represented by the duration of audio
      packets sent prior to RFC 2833 events?

See the draft.


   2. If both audio packets and RFC 2833 packets are transmitted
      concurrently, is it allowable for the duration of each RFC packet
      be different from that of the packet interval of the audio
      packets. Is there a recommendation with respect to this?
The spec can't spell all allowable permutations. If nothing is said, normal RTP rules apply. Since every RTP packet even with the same PT could, conceivably, cover a different time interval, this is certainly possible. I would expect that this would test the robustness of most implementations, so maybe we should add this to a torture test...

   3. If both audio packets and RFC 2833 packets are transmitted
      concurrently and an RFC 2833 packet is missing, is the intent that
      the last RFC 2833 packet received should be extended or should the
      audio packet be played out in its stead? Should the ability of the
      codec to represent the event be considered?
This is an implementation decision since it does not affect correct interoperation. Consider it product differentiation.

   4. If both audio packets and RFC 2833 packets are transmitted
      concurrently and an RFC 2833 packet is missing, assuming that the
      last RFC 2833 packet should be extended for a period that would
      represent up to 3 lost packets, which should be used to calculate
      the duration of the extension: the duration of the previously
      received RFC 2833 packet or the packet interval of the previously
      received audio packets?

See above; you can only guess at what you might have received.


   5. If both audio packets and RFC 2833 packets are transmitted
      concurrently which takes precedence? There seem to be
      contradictory statements in the RFC.
Please point out contradictory statements by citation in the I-D. In general, this is one of million of possible failure cases which should only occur if somebody goofs. Depending on the application, you could justify any approach, including dropping the packet, since the sender is obviously confused and may not mean either.


Regards,
Steve Lubbs
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