[Iccrg] TFRC and RTP

[Ingemar Johansson S]

Hi

I am in the process where I try to understand TFRC (and the modifications like TFRC-SP and MulTFRC) better and in particular how they can be used with RTP.
RTP is assumed to use RTCP as feedback protocol. The rate of the RTCP feedback is given by the alloacted RTCP bandwidth, I would expect that in the majority of cases the time between RTCP is considerably longer than RTT.

This gives as I see it two potential problems
+ Estimation of RTT, RTT will be subsampled.
+ Loss events. The traditional RTCP report blocks does not make it possible to determine this reliably. The ECN for RTP draft (http://tools.ietf.org/id/draft-ietf-avt-ecn-for-rtp-02.txt) specifies a NACK feedback packet that can be transitted in early or immediate mode. This should make it possible to determine the loss events but the accuracy will then depend on the estimate of RTT.

Does anybody have an idea about how the limitations above (esp the subsampled RTT) will affect TFRC ?

Regards
/Ingemar

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INGEMAR JOHANSSON  M.Sc. 
Senior Research Engineer 

Ericsson AB
Multimedia Technologies
Labratoriegränd 11
971 28, Luleå, Sweden
Phone +46-1071 43042
SMS/MMS +46-73 078 3289
ingemar.s.johansson at ericsson.com
www.ericsson.com 
Visit http://labs.ericsson.com !
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