Cisco Aironet 1142N at elementary school

Question

Hi. We're having a tough time at a couple of elementary schools that are using a number of Cisco products which we got through a deal with AT&T. I really hope you can give us some guidance. Here's our situation: We have an elementary school equipped with about eight Cisco Aironet 1142N access points. Signals go to 3 stacked switches (Cisco Catalyst 3750 PoE-48) and are managed via a Cisco wireless LAN controller (NME-AIR-WLC12-K9).
We are having significant bandwidth problems. If we get more than 12 laptops (we've got a "mobile Macintosh lab") simultaneously online, the network freezes.We can't even get more than 15 iTouches online simultaneously.
Here's the rest of the setup: our *elementary* school is connected via fiber (probably 10MB) to the *intermediary* school and then to the district office. The district office is connected to the Internet (county depart of Ed is officially the ISP; AT&T is the service provider).  The AT&T link may be 6MB.At the *intermediary* school the data traffic for the mobile Macs is    handled by an
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Apple Xserve workgroup server.
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The XServers are for Directory Services only (log in authentication for the MacBook Labs). There is one Open Directory Master at the intermediary school, and an Open Directory Replica at each site. A LightSpeed Total Traffic Control Server does content filtering for us. There are also about 5 Cisco (Windows-based) servers helping manage data at the intermediary school (VOIP and Wifi traffic only).The rest of the traffic (internal, wired ethernet) is handled by the Cisco switches and controllers; for external traffic - after the controllers it goes to the LightSpeed Traffic Control server then out the Cisco FireWall.
Sorry to dump all that on you, but candidly since we installed the Aironets in September we haven't really been able to effectively use the mobile Mac lab. Ideally we'd like to be able to run about 30 laptops simultaneously. They don't have to get video -- just google searches would be a start.
We should also note that at this elementary school, we have 4 wifi networks running different VLANs available through the Aironets. The one that has the most problems is the one I've described above -- it's supposed to be for student access. We have a teacher-only network that does NOT seem to have the same bandwidth constraints as the student network. We also Cisco VOIP phones all over the school, but use of the phones is modest.
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What we’d like to know:
1.     Is it likely that we have an insufficient number of access points or that that those access points can’t handle? If so, is the problem likely that we need more access points? (and if that's true, why is the teachers' network ok?)
2.     Is the problem more likely at the server or switch choke point?
3.     Is it likely that the problem involves Student accounts rather than teacher accounts? Why would this be so?
4.     What are the best ways to test what’s causing our choke points?
Thank you for your help!!!

Answer 1

Thanks all for your comments. Here are some responses as well as our current "plan of action." I'd VERY MUCH welcome any additional suggestions that you have about the test we're going to run (probably next Tue).
1. Channel: the site operates on Channel 1 (2.4 Ghz)
2. Professional site survey: no: AT&T is supposed to do it at some point as they're our ISP. But that hasn't yet happened. No idea when it might.
3. Aggressive load balancing?  We don't know as AT&T has that info.
4. 15th client... Once we exceed 15 clients, access for all clients grinds to a halt. The slowdown is a pretty steep curve (not quite a cliff) for 15 clients when we use iPods; it begins at 12 clients or so when we use Macbooks.
5.   
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Does your WLAN come to a halt or does the wired LAN gets affected too?
When we experience these problems, the teachers’ wireless LAN is unaffected. The only place we’re experiencing the slowdown is on the wireless LAN that’s used by the students. We have a “computer lab” with a wired network of about 30 PCs. (Ethernet CAT 5 to fiber on the way out of the building). This is a separate VLAN from the (student) wireless VLAN. When the student wireless VLAN stalls, it DOES NOT affect either the wired VLAN or teacher network. We do experience slowdowns on the WIRED student VLAN but no where as severe as on the WIRELESS VLAN. (In other words, we can run all 30 wired PCs on the wired LAN).
6. Could inability to get more computers on the network be due to an address limitation in the NAT server?
No. We have a big, big address range.
Here's our current plan: we're going to VERY CAREFULLY chronicle the drop off in usage at several points during the day:
8:00 am (no students)
10:00 am (busy school but probably not much student wifi usage)
noon: we'll run a test with +15 students using laptops and measure the bandwidth using a network speed checker at every point. That way, we figure we'll have a clearer chart of the usage breakdown.
Does anyone have any suggestions of addition things we should monitor during this test? We're going to do it next Tue (2/19).
In addition, if there are any specific questions that we should put to AT&T, I'd love to hear them.
Thank you all!!