[AVT] Commetns on draft-luby-avt-rtp-generic-fec-00.txt

[Magnus Westerlund <magnus.westerlund at ericsson.com>]

Hi,

I have looked at the Generic FEC draft, I have some comments:

1. My first comment is that this draft is totally lacking any discussion 
on how the source blocks should be constructed to contain the necessary 
information that is needed for each Application Data Unit (ADU). If one 
consider that this should be a solution of providing FEC protection for 
what is normal RTP packets, then both RTP payload parts and RTP header 
information needs to be preserved and possible to reconstruct at the 
receiving end. This is not simple, and a step that also the UXP draft 
have not satisfactory solved yet.

2. Secondly, by using the RMT building block there is huge question of 
how to ensure interoperability. To be able to use this in either a 
streaming session one can only pray that the receiver will support the 
FEC decoder that is needed. Certain application specification, like ISMA 
or 3GPP would need to specify this to get it to work. For SIP there will 
be need to define a way to actually perform negotiation of these in a 
suitable way.

3. I am also interested to learn how the source block construction is 
affected by the selection of the FEC encoder. Will it be possible to 
build a implementation, that actually can manage delays and make 
encodings over variable number of source blocks in real-time, thus being 
able to take feedback into account?

I think there is potential here, however it must be shown that this can 
actually work, and also be possible to interoperate. There is also need 
to communicate with the UXP authors, because I think we have much more 
overlap between this and UXP than with ULP.

Cheers

Magnus Westerlund

Multimedia Technologies, Ericsson Research EAB/TVA/A
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Ericsson AB                | Phone +46 8 4048287
Torshamsgatan 23           | Fax   +46 8 7575550
S-164 80 Stockholm, Sweden | mailto: magnus.westerlund at ericsson.com


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