'Huge' number of wireless clients..

In article , Russ Gimple wrote: :I originally posted this to alt.internet.wireless but was advised to repost :it here because some of you guys here have experience with similar :scenarios.

I'm a bit surprised -- usually Jeff would have a good answer in a question such as this.

:We plan to introduce wireless LAN in a couple of student's dorm areas for :web based classroom management software (interaction teachers - students, :knowledge bases etc..) Filesharing and other bandwidth consuming ports will :be blocked.

:Which equipment do we need to handle *many* clients, say 200 simultaneous :connections?

In the past, Jeff (I think it was) has posted information on the number he has managed to connect to one AP. The WRT54GS is not even in the running, as best I recall. Whipping my memory cells, I -seem- to recall him finding that Buffalo was the lowest-end vendor that made an AP that could handle 50, and that to go much beyond that you needed to go up the food chain a fair bit.

:Would it be better to think smaller 'cells'?


In dorm and classroom areas, there are a *lot* of obstructions. Wiring, walls, metal rods in the concrete, water pipes -- and *books* are pretty hard on wireless signal.

In an ampitheatre-style lecture hall, you would need several APs just to cover the one room.

The alternative longer-distance more-penetrating technology is known as WiMax -- but it's pretty expensive, -partly- because the production volume isn't up there [but there are other reasons too.]

If you want to stick with WiFi, 802.11a (54 Mb/s, channels do not overlap, more common in Europe), 802.11b (11 Mb/s, most common, the 11 channels overlap leaving you with 3 or 4 effective channels), or 802.11g (54 Mb/s, 3 channels that do not overlap each other but overlap 802.11b heavily), then for that scale of a project, you

*really* need a "managed" wireless system.

I'm sure there are a number of worthwhile managed products out there, but the only one I know anything about is Cisco's 11x0/12x0 series AP's when integrated with their WLSE. With Cisco wireless cards, or with select Linksys wireless cards, the cards themselves send signal strength and quality feedback information to the WLSE, and the WLSE can dynamically adjust signal strength on the APs in order to provide the needed coverage whilst trying to minimize cross-channel interference. The WLSE has built-in site-survey capability. It's interesting technology -- but it's not SOHO pricing, that's for sure!

:What about many WRT54GS installed in different corners of the area...?

Unless you are planning to replace the firmware on the WRT, then I would avise great caution before investing heavily in that solution. Read the reviews of the WRT54GS; read the user ratings. It is a device that -sells- well, but the user ratings top out as "fair" with a number of people saying they would never buy another one. No one particular problem that might be worked around; I gather that it can behave quite differently in different situations.

When I was trying to decide what to buy a couple of months ago,

*none* of the consumer 54G devices I found had well-satisfied customers... except for the customers who replaced the firmware. It was quite discouraging.

In a situation such as yours, I think it would be better for you to consider dual-radio APs, possibly with WDS ("Wireless Distribution System"), and with that many users around and the nature of the users (and the ability of strangers to wander up...) give serious thought to going 802.1x authentication. WEP should not even be -considered- in your case (unless as a layer overtop a different encryption layer such as IPSec.)

A site that tends to have a fair bit of useful WiFi information is tomsnetworking.com . (It isn't a WiFi oriented site, but they do some good reviews and tutorials on WiFi.)

Reply to
Walter Roberson
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I originally posted this to alt.internet.wireless but was advised to repost it here because some of you guys here have experience with similar scenarios. here goes:

We plan to introduce wireless LAN in a couple of student's dorm areas for web based classroom management software (interaction teachers - students, knowledge bases etc..) Filesharing and other bandwidth consuming ports will be blocked.

Which equipment do we need to handle *many* clients, say 200 simultaneous connections?

Would it be better to think smaller 'cells'?

What about many WRT54GS installed in different corners of the area...?

Thanks for tips and hints for this scenario


Reply to
Russ Gimple

Rather extensive but not comprehensive, based on my memory, which is not perfect, and my experience, which is for a slightly different scenario. Here you go:

For equipment, think "administration" and "robustness". The answer I come up with is Cisco. They handle the DoS attacks we have had better than our other bases (one rogue user is all it takes, and you're in trouble), and the options for filtering, VLAN and authentication on those are more than sufficient. A bit pricey, but you will probably find it worth the expense, at least if you need more than 3 base stations.

For placement, experiment with different setups. A pc with proper software (netstumbler or Cain&Abel) can be used for analyzing coverage, or "cell size". Building materials and construction/architecture can play a major role.

- Try "even distribution" with power turned way down on all the bases, versus "clustered distribution", where you'd probably use medium power output. With 802.11b/g, make sure the bases in each cluster don't overlap channels. (Spread spectrum with 5 channels overlap, so failsafe setup must use channels 1,6 and 11).

- Going out to the corners of the house is generally not a good idea. That way you move 75% of the coverage outside the building. If you are thinking of internal "corners", you are more on the right track. Some walls (particularly with steel reinforcing) form radio barriers.

Don't expect to serve more than 60 simultaneous clients from each base station. (That's if the traffic is mostly client-server, with mainly peer-to-peer traffic on the infrastructure i'd guess 35-40 simultaneous users would represent a practical limit.)

Offer basic services (web access, local SMTP, print, files shared readonly), nothing that requires heavy administration (like distributing applications or providing traditional file services). The planned "web classroom service" should work fine (we use something like that). Network authentication should be lightweight, such as RADIUS, if used at all. (We have an open network, with authentication on the external line and on the web "classroom" service only. Local info and print services are more or less freely available). Logging into domains such as MS network (Active Directory) or Novell (Netware tree/bindery) seem to load down the connections with housekeeping. Works fine when you're testing it, but full scale use shuts the base stations down.

Keep the WLAN on a separate network segment, with no or limited traffic allowed to pass into the production/teaching network. Use a different IP subnet for the WLAN segment.

If the students use their own PCs, demand that they have proper security (at least updated antivirus), and that they don't use network administration or server/sharing software when they are within the WLAN cells. (You definitely don't want several DHCP servers on the network, and just a few KaZaa clients can saturate the network, so you don't want that either.) Ban the use of all network administration and server tools/daemons, such as

- DHCP server (often enabled when you share your internet connection)

- Steam (games service)

- P2P file sharing, such as KaZaa, LimeWire, Napster

- Web, chat, ftp or other server software

- Creation of "adhoc" or "peer to peer" networks. (That jams the radio channels. The students should use the existing infrastructure to transfer files over network shares.)

- Automatic search for shared resources (default *on* in Windows!). Switch it off! (Consider 200 PCs with 2 shared resources each, That's

400 shared resources, with 199 possible clients for each. Autoconnect will give nearly 80000 active connections to be maintained on the network, probably resulting in a noticeable load both on the network and on each computer involved.)

As for the "rogue user" I mentioned, you may want to check out

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(and a few others I don't quite recall) to get some idea of what you should be ready for.

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