FEC for getstream

[Denis Lackovic]

On Thu, Sep 30, 2010 at 2:05 PM, Florian Lohoff <f at zz.de> wrote:
> On Thu, Sep 30, 2010 at 01:26:40PM +0200, Frederik Kriewitz wrote:
>>
>> I prefer RTP retransmissions over FEC too. Especially because it's
>> similar to RTP Bursts for rapid channel changing.
>> I looked into this topic some time ago, for me cisco's VQE seems to be
>> the way to.
>
> Okay - so basically in the SDP you see the definition of the history
> buffer on the streaming source. Once you see gaps in the RTP sequence
> numbers you request the retransmission of those sequence numbers.
>
> I guess this request is done unicast to the source address of the
> multicast stream. Or is the VQE server listed in the SDP?

I believe this depends on the implementation. Almost certainly in
large (expensive) IPTV installations VQE server is not listed in the
SDP - because there is not just one VQE server (due to redundancy),
and there are redundant receivers going into redundant encoders and
then they go into (in some cases)  redundant streamers. They have
existed  for a few years when you add your first bunch of VQE servers
- which run independent on the rest of the hardware.

Probably configuration of which VQE servers are responsible for which
channel streams is info transfered to STB during boot process
(probably in proprietary way).



> Doesnt seem to be too complicated.
>
> Does anyone have a comparison on fec/vqe induced receiver delay?
> I mean the VQE delay has to be something like 2*rtt between multicast
> source and receiver. Or will the receiver buffer for the amount of time
> listed in the SDP to be shure?

I believe  STB buffer has to be big enough. I will have one of the
implementations (Edgeware) on test next month, so then I wil be able
to see how it's implemented.

> fec will have some delay too especially when done with large
> packet interleave.
>
> Flo
> --
> Florian Lohoff                                                 f at zz.de
>                 Professionell gesehen bin ich zu haben ....
>
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-- 
Denis Lackovic