you introduce a low power VoWLAN device like Vocera badges into your enviornment. If you are running your AP's at full power (100mW) and your devices can run at or around the same power levels. The Vocera badges for size and battery life only have 25mW of output power.
If AP's are running full power and the badges only have 25mW of power this creates an asynchronous power condition where the AP can talk to the badge, but the badge does not have enough transmit power to reach the AP. This is bad.
In this case you have the reverse situation than U of A. Very dense access point deployment, where the AP's run a half or lower power levels. This also fixes the client-to-AP re-association issues for normal VoWLAN phones.
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Just speculating
It sounds like the university is using UMA cellular/Wi-Fi handsets which are designed for the single-AP home or hotspot environment and not for a multi-AP environment. Could it be that those handsets were getting confused when they saw more than one AP? Don't UMA handsets fallback to the cellular network instead of handing off between Wi-Fi APs?
UMA and Wi-Fi
Aruba Networks did a paper on this:
http://www.arubanetworks.com/pdf/technology/whitepapers/wp_FMC_UMA.pdf
Hopefully the university configured these phones not stick to just one A by enabling inter-access point handover.
What is the point?
Joanie:
Is the point that Cisco wireless networks are over engineered?
Or is the point that Fat APs are troublesome?
Mike
Planning, that's what it is all about...
The truth is that WLAN vendors tout speed and coverage as the most important issue in WLANs. It is not.
First and foremost any VoWLAN must be planned, and yes, sometimes it is overcrowded with radio environment polluting APs - too many of them.
VoIP requires a completely different mentality from the current one: quality.
I work with WLANs in many situations and this is quite common with VoIP enabled WLANs, overcrowded radio space, be it from own APs or other networks.
Just remember, WLAN is a case-by-case beast: quality can be achieved with one AP for oa certain application, but may require six APs for another, and vice-versa...
EIRP and mobile devices
Since 802.11abgn is not a broadcast environment where the signal to noise ratio matters only at the client, client antenna gain as well as transmitter power needs to be considered. If you look at manufacturers' specifications for small embedded antennas, some have a peak gain as low as 1 dBi in the best direction. They often run 0 dBi to -4 dBi in some directions, with an efficiency around 60%. This means client EIRP would be 2-6 dB below an AP that uses 2 dBi antennas, at the same output power. If the client devices are rated in RF power, instead of EIRP, gain should be considered. Measurements from clients support this calculation. In a balanced WLAN environment where desirable SNR at each radio is close to the same, even lowering power to 20 mW from an AP with efficient antennas is not the same as 20 mW from a handset. Using higher power in a device used for long periods of time while touching someone's head or body may be increasing the health risk.
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