[AVT] Packet accumulation strategies in RFC 2833bis

[Tom Taylor <taylor at nortelnetworks.com>]

RFC 2833bis currently contains various pieces of advice about what packetization 
interval to use at the beginning, in the middle, or at the end of events or tones 
respectively.  A lot of this advice really depends on what sort of buffering the 
receiving end applies.  It occurs to me that buffer management should be solely 
the responsibility of the receiving end, hence there should not be suggestions for 
the sender to create a buffer by accumulating more in the initial report of an 
event or tone before sending it than in subsequent reports.

For the events payload, I therefore propose the following policy:

 - The sender SHOULD report the beginning of an episode of events as soon as the 
initial event is recognized or after one packetization period, whichever comes later.

 - The sender SHOULD continue reporting at the negotiated packetization interval 
until there are no more event reports or retransmissions of event reports to send.

 - The receiver will lag in playout by one packet length anyway.  It SHOULD add 
another packet length of delay to that, to handle the length of silences 
accurately.  (This is mainly a concern for data protocols where there is little 
tolerance on a typical 75 ms delay between preliminary signalling and the modem 
stream.)

Comments?

--
Tom Taylor
Carrier VoIP Standards Development
Nortel
Phone +1 613 763 1496  (ESN 393-1496)
E-mail: taylor at nortelnetworks.com

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