Maximum SU per sector

I have 3 2.4 AP and 3 5.7 AP connected in CMM micro. The site is on a mountain witch is 400 meters higher then the city where are all the SM-s.

I have 30 5.7 Subscriber Modules and they work excellent.

The problem witch I have is with 2.4 AP. In the moment I have 140 2.4 SMs, and 60 waiting to be installed. On sector 1 I have 60 SM, sector 2 54 and sector 3 36. Every Monday to Friday in about 12 PM I have latency of average 400 ms with AP on sector 2. Rarely a have the same problems with sector 1.

The question is, what is the real number of subscribers per AP witch will have QoS with average 40 ms. Should I install one more AP?

Erkan,
This is a tough question to answer without viewing actual data numbers. Do you have any monitoring devices put in place (MRTG or custom graphs) which show your throughput at the AP? A granular (less than 5 minutes) chart showing IN and OUT packets on both the RF link and the Ethernet interface would help to show how much the AP is being used. Then, using actual numbers and an over subscription ratio, we can develop a target number for the AP load.

I have MRTG.
Here are the graphs for today. If you like I can sand you email with url to my MRTG.

These are iamges for AP on sector 1 withch is the bigest problem. You can notice some weird peaks wich I have no idea where do they come from:

Radio

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This is sector 2, also troubles, but not that often.

Radio

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This is the third sector, no troubles at all, never. Here I have 36 SMs.

Radio

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I forgot to mention that when the problem with latency begins the web management page of AP is opening very slowly. Also I have timeouts when I try to connect trough FTP.

I have MRTG for CMM ports, and the results there are quite normal. Total bandwidth usage on MRTG on CMM ports for each AP never goes above 3-4 mbps per AP.