[Sugar-devel] GSoC Proposal: Multimedia Broadcasting

[Martin Langhoff]

On Sat, Apr 11, 2009 at 1:37 AM, Geza Kovacs <gkovacs at mit.edu> wrote:
> According to http://ieeexplore.ieee.org/search/wrapper.jsp?arnumber=4292735
> then the slowest transmission speed, Mode1 (6 Mbps) is only beneficial
> for multicasting over very large distances; in the case of the AWGN

I am sure they did their tests in quiet RF environments. In crowded
environments nodes can tell the AP that they're having trouble hearing
the frames, please transmit slower.

You've calculated 1.6Mbps but that's only the stream. You need to get
each to the AP, and _then_ it'll be broadcast. The frame to the AP may
be transmittedfast if the XO is close to the AP. The datarate for the
broadcast frame from the AP to all the nodes is set by the AP based on
the nodes it has registered...

> In terms of airtime consumption, this of course depends on the
> airtime-fairness mechanisms used by the wireless network. However,

Which just don't exist (not in the QoS sense that you seem to be
picturing at least), and deal rather badly with dense networks. There
is a backoff mechanism that avoids collisions (rather than detect
them) ... in very dense environment this means that the available
bandwidth is significantly reduced.

The tools that you want to reuse work well in a switched network with
ample capacity. The workload of video streaming -- however "light" you
might thing 1.6Mbps is -- in a saturated shared medium with "slowest
client sets the speed" broadcast and conservative backoff strategies
is AFAIK an unsolved problem.

There's surely a complex research project there -- can it be made to
work? What strategies can work on that complex problem? But if you
start by assuming you can reuse existing high level tools, it'll be a
disaster. It might work in a test environment. But it will never ever
work in a real life school.

cheers,



m
-- 
 martin.langhoff at gmail.com
 martin at laptop.org -- School Server Architect
 - ask interesting questions
 - don't get distracted with shiny stuff  - working code first
 - http://wiki.laptop.org/go/User:Martinlanghoff