I work at a metro hospital with about 2000 cisco APs and a high-density design with Apple iPhones providing voice to our staff. Cisco had us use RRM to set all APs to 40MHZ for better data rates, but i continue to get a LOT of tickets regarding dropped VOIP calls on these iPhones. Using Ekahau to survey the routes of dropped calls, there are a few things going on.
1. (according to Ekahau) Primary signal strength mostly healthy, 90% of the path is -64db or better, with a few spots dropping to -67dBm
2. (according to Ekahau) Secondary signal strength fails in some areas (we try for -67 or better, but reach some areas at about -70dBm)
3. When standing in a spot that has reported to fail both primary AND secondary coverage, my Netscout adapter packet capture shows the RSSI of the iPhone i'm testing with to have an RSSU of -53dBm (effectively contradicting what Ekahau says the coverage is)
4. At this spot, i am getting a failure on my co-channel interference maximum of 1. I am seeing 4 broadcasting antennas on this channel...2 of which are Cisco APs and 2 of which are medical devices.
Conclusion: I believe what actually is causing these drops is the fact that we're running 40MHz rather than 20MHz in very dense and very diverse wireless space. I spoke to our cisco wireless contact about this, and he refuses to believe that moving to a 20MHz setup would help us create a healthier wireless space, so i come to the community for your thoughts.
