On Mon, Jan 25, 2010 at 10:31 PM, <[email protected]> wrote: > I've read through these, and they have a lot of useful info. I do have > good RF experiance (and even some halfway decent tools for looking at > things), but I didn't know what, if any limits there were on the number of > clients other than what can be supported by the available airtime.
Lots of very subtle protocol limits, having to do with all sorts of random mostly-timing related parameters where the 802.11 spec gives implementers a lot of freedom to choose arbitrary values. *Plus* the details of all your clients. There are all sorts of fancy algorithms you can use to tune your AP, but all it takes is one bad client and everything goes to hell. And that's completely apart from the arbitrary software limits that some access point manufacturers include, in order to differentiate their "consumer" and "professional" product lines. *And* not accounting for stupid software which decides to use the broadcast features of 802.11, which chew up bandwidth 50x faster than normal data does. So, basically: theory is no substitute for experience. It's not really the protocol that's the limit, it's the particular choices that particular access point makes and the choices that "common" clients and "common" software make. So your best bet is really to (a) find someone who's done it before, and slavishly copy their setup (variations that you think are trivial, like between firmware revisions, may in fact be critical), or (b) find a company who's invested the time and money to figure out all the variables and do the real world testing, and fork over the $$$ for the "commercial quality" or "pro grade" or whatever-they-call-it access point with a guarantee about the number of clients it can support. And a couple of accessible wired switches and wired internet kiosks will go a long way toward mitigating your downside if it turns out that your wireless totally melts down under load. I've attempted a couple of mystery hunts (http://en.wikipedia.org/wiki/Mystery_Hunt) with ~50 clients on one access point and can vouch that that's above the workable capacity of even consumer-grade access points. (We had a fancy commercial grade access point this year with 10s of compact antennas and it did much better.) As Chris noted, we did testing at OLPC and found that even 30 clients was pushing for most access points. At the time, I backed that up with a literature search and could cite the various parts of the 802.11 collision-avoidance algorithm which melted down in the 10s of clients. I can't cite chapter and verse any more, sadly. --scott -- ( http://cscott.net/ ) _______________________________________________ Devel mailing list [email protected] http://lists.laptop.org/listinfo/devel
