[Sugar-devel] GSoC Proposal: Multimedia Broadcasting

[Geza Kovacs]

On 04/03/2009 06:09 PM, Martin Langhoff wrote:
> On Fri, Apr 3, 2009 at 4:08 PM, Benjamin M. Schwartz
>> Agreed... which is why the correct solution is to use link-layer
>> broadcast/multicast.  That way, the bandwidth usage is independent of the
>> number of users, and only a single stream must be transmitted.  Farsight2
>> already supports link-layer multicast UDP.  I don't think Icecast does.
>
> Proposing broadcast/multicast over wireless is not _so_ obvious. It
> causes non-trivial problems on both the 802.11abg protocol family and
> 802.11s.
>

Assuming I'm using Farsight2 to broadcast MJPEG video over multicast 
UDP, to my understanding the primary issue with multicast over wireless 
is unreliable data transmission, which when compounded with the 3-5% 
packet loss rate, "bursty" packet loss, and lack of acks or error 
checking in UDP will mean that a few frames will be occasionally be lost 
or corrupted, leading to temporary but very short freezes in the video 
stream. However I don't think this unreliable data transmission is 
really much of an issue, at least with MJPEG, since the loss of video 
data over a short time interval will lead only to the loss of frames 
corresponding to that particular interval since it doesn't use 
predictive encoding or b-frames; therefore the effect of a burst of lost 
packets will still only lead to a second or so pause in the video stream.

Other than this issue, are there any other non-trivial problems that you 
were thinking of that I have missed?

> So there is a lot of work to be done in figuring out how to use
> broadcast frames over either type of wireless efficiently.
>
>   cheers,
>
>
> martin