It's a bit hard to assist remotely, but I can make some suggestions. Was the site survey done as a 'predictive' survey, or did you have one done after all the access points were installed and configured. If you haven't had an active site survey done since the installation you should really do that to understand what the RF looks like. You should also do a new site survey if there have been any changes in neighboring buildings or their occupancy (new tenants can mean they're generating new interference). You also need to look at the capability of the devices you're using. If they can all make use of 802.11a/g/n (i.e. no 802.11b) then you should be setting a minimum bitrate of 12Mbps - this disables 802.11b which will improve overall performance of the network, which you need for VoIP (802.11b is unsuitable for wireless VoIP). What's the approximate distance between access points? Are they mounted on steel beams or similar?
... View more
