Re: [AVT] Generic FEC how many packets can be recovered

[Ross Finlayson <finlayson at live.com>]

> This may be well understood to FEC experts, but I'm new to this area.
> The FEC proposal provides protection for a set of RTP packets, lets say 
> sequence numbers 2 through 10.

More precisely: In your example, a "source block" of original data is 
encoded into a sequence of RTP packets: 2 through 10.

> If packets, 4, 5, and 6 are lost.  Can this FEC scheme recover ALL the 
> lost packets?

Depending on the particular FEC scheme that is being used (which, BTW, is 
specified within the RTP payload format), either the entire original 
"source block" will be recovered, or none of it will be.

> If so, the recovery text in the draft could be enhanced to detail how this 
> would be accomplished.

The "RTP payload format for generic FEC" Internet Draft does not describe 
specific FEC encoding schemes.  Instead, that is done by separate RFCs that 
define instantiations of the "FEC building Block" (see RFC 3452).

(For more information on the use of FEC in general, see RFC 3453.)

        Ross.



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