Average Clients Simultaneously Accessing a WAP?

Question

We have two (sometimes three in that area) mobile carts of ~20 MacBooks accessing the network using Cisco Access Points, the model numbers of which I don't have handy at the moment. But we're trying to track down issues with timeouts and access issues to the local network servers as well as web access. It seems right now that the issue is network timeouts on the Macs. I know that the access points are managed through a special wireless controller on the rack, so these aren't the typical small business or SOHO wireless access point hardware.

The users have home directories set up through Active Directory and the Macs are bound to the Active Directory system.

The access issues seem to get better and worse through the course of the day and I'm not the primary troubleshooter on this issue, but I'm the only one that thought maybe SF might have some input on the issue. I'm wondering if the WAPs may be having trouble handling traffic for between 20 and 40 systems simultaneously, or if even at lower numbers of simultaneous connections it's choking bandwidth. I've been assured that these are high quality Cisco access points that should have no trouble handling this kind of traffic.

Any experiences with this? Typical numbers that a WAP should be able to handle before choking?

Answer 1

I have some Cisco Aironet 1131G access points bolted to a cart in a K12 school w/ 35 Windows XP-based laptop computers with 802.11g radios. They APs are configured for non-overlapping channels. I see the laptops distribute themselves roughly evenly between the APs when they're all running.

Trying to support all of the clients w/ one of these APs didn't work (logon failures, random inability to access network resources), so we bought another one. Both of them together work fine. The students are mainly using them for web-based assessment applications, but they do access their home directories over the WiFi and, to my knowledge, it's been working fine. (I'll put it this way-- the Customer hasn't let me know there have been any problems... smile).

I'd be hesitant to put more than about 20 clients on a single 802.11b/g AP, and even then it needs to be an "enterprise" class AP.

Answer 2

While I don't have any "typical" numbers for you, it seems that that is a lot of clients. How many WAP's do you have. How many clients connected per WAP. Are the WAP's A, B, or G?

Wirelss is a shared medium so even at B or G speeds, all the clients connected to a particular WAP are sharing the same 54Mbps channel. Can you monitor the utilization between the WAP and the core network to determine how much data is being pumped through?

Answer 3

I do wireless at a major University, and in some lecture halls we've had over 100 clients on one AP. Granted, these are some pretty fancy APs (Meru Networks) running GigE back to the controllers (and we're also rolling out N).

How many APs do you have, and what data rates are they running at?

My tentative plan of action would be:

1. Do other users of the same setup (AP model and controller) report good results with that many clients? If not, you'll need more APs.
2. Go through whatever troubleshooting docs Cisco has.
3. Go out to the site in question with a spectrum analyzer (Wi-Spy is inexpensive, Cisco makes expensive ones) and see what's going on... could be a wireless phone or rogue AP causing interference.
4. Setup the APs on a full, non-overlapping channel (1,6,11). Experiment with disabling the low data rates if you're sure the clients should have a good connection.
5. Try a packet capture and see what's going on.