

Is it just me or does wi-fi seem to break down above 20-30 computers in a room? Why? - niels_olson

This may seem like it's coming from left field, but stick with me. The US Medical Licensing Exams are computerized. Many schools, including ours, are exploring administering computerized exams also. Building computer lab facilities to support conducting a computerized test with 180 people seems a bit over-the-top. The often suggested alternative is to administer the test over wireless. Virtual machines and other security concerns aside, when students pile into any of the auditoriums, just for class, it seems like we never get more than 20 or 30 of us connected. I have also noticed this in other venues, thousands of miles away. Is this a sideband or bit-rate issue? Can't have too many red flashlights blinking at the same time? Is this a solvable configuration issue with 802.11G? Sunspots?
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jwilliams
Basically it'll be a limitation of the Access Point, and the actual spectrum.

All of those clients will be connecting using the same frequency band - and
Wifi uses a spread spectrum approach (basically), which means that whilst you
can connect more clients, the quality degrades each time you add another.

The most I've ever seen connected was 30. I've heard of commercial grade AP's
that claim to handle 60-120 clients (for airports and such).

This interference also depends on how the clients are actually using the
network - if they're all downloading at once, I'd guess it would get saturated
very quickly. Maybe as low as 10 (just a guess). If they are all relatively
idle you could probably get a lot of clients on.

It's also not helped by the fact that certain clients and AP's do not interact
well with one another (due to slightly different interpretations of the
spec)... It's also not helped by other devices operating in the 2.4Ghz range.
e.g. Cordless phones and such. I think microwaves also put out a of 2.4Ghz
noise too.

However, you can run multiple access points - you just run each access point
on a different channel. The trick here is that wifi channels actually overlap
with one another, so pick ones next to each other and they'll interfere with
each other (i.e. slow each other down). However, you can pick channels that
don't overlap. IIRC in the US these are 1,6,11.

(p.s. This is also a good tip if you're in an appt building. If there are lots
of other AP's take a look at the channel they're on and try and get on a clear
band).

Theoretically you could also run (one or more) 5ghz wireless N network in
parallel with this. Modern macs will be able to connect to this.

