what's the main function of the WCS
If you have a controller-based environment, the WCS can manage one or more WLC. Aside from that, the WCS can generate reports that the WLC can't.
1240 or 1200 for indoor?
Depends on alot of factors. Firstly you can no longer buy 1200 or 1240. Next, the 1200-series is designed to use optional external antennas. For built-in, the can purchase the 1040, 1130, 1140 and 3500i. Only the 1130 will support 802.11a/b/g. The rest will support 802.11a/b/g/n.
If yes, how large area can be covered by AP for client?
This depends on alot of factors. In a wide open space (no walls) you can get up to 40 meters in a single direction. I'd recommend you get a wireless site survey done.
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