[Sugar-devel] GSoC Proposal: Multimedia Broadcasting

[Martin Langhoff]

On Fri, Apr 10, 2009 at 6:47 PM, Geza Kovacs <gkovacs at mit.edu> wrote:
> Assuming I'm using Farsight2 to broadcast MJPEG video over multicast UDP,

As I've posted earlier, for multicast frames you'll see the AP
switching to the slowest transmission speed to increase the chances
that all the nodes will get the frame reliably, which hogs airtime.

And airtime is what really matters in wireless networking.

So, if one session of your proposed application is the *only* thing
running on the whole network, you can do some rough math. You'll need
to

  - Send the stream to the AP. If the 'broadcasting' node is close to
the AP, and sees no interference, it may be able to transmit
relatively fast (let's assume 36Mbps).

  - Broadcast the framesfrom the AP at 1Mbps.

What's the bits-per-second of your stream? What % of the airtime do
you thing it will consume?

This of course assumes 802.11abg. With 802.11s, sending a stream over
broadcast will mess up the network completely because of the funny
rebroadcasting rules in the 's' standard.

All OLPC deployments are a very busy wifi environment. If you build
tools that assume that they are the only thing in the air, or that it
can take a significant portion of the RF airtime... would be just like
assuming that your program is the only thing in the hard disk.

cheers,



m
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