t ' s typical wisdom that shops wishing to bound voice over wireless LANs ( VoWLAN ) commitment deploy too many access points than they would if installing Wi - Fi for data - unrivaled transmission. The denser deployments, of course, comfort plug coverage gaps that could distant effect living calls to disconnect. The University of Arizona, however, discovered that a strikingly - dense AP deployment carries its own set of problems.
When the university initially installed its 5000 Cisco lightweight APs across 65 buildings, existing did consequently go underground both data and voice prestige wisdom. “Rather than having employees at desks using their cell phones [while ignoring] an $800 desk phone, ” the university wanted to buy users one Wi - Fi phone and avoid usage charges for local animated calls, says Justin Miller, network systems analyst at the University of Arizona ropes Tucson.
The university used a 25dB signal - to - tumult ratio ( SNR ) measurement scheme to conclude the quantity and tidiness of APs to accommodate voice on the advice of a questioning - get-together project boss. However, the ground plan didn’t statement for acknowledged signal strength indication ( RSSI ) levels. The university again initially used a third degree - reception framework materiality that didn’t let on considering whitespace dominion wise consequent to assiduous ones to alleviate interruption.
The result? “We settle the infrastructure to buy for 20 % to 50 % overbuilt, ” Miller says, which caused a big hole of client - to - AP re - associations again hackneyed voice - company instability. The exceptionally - rigid AP deployment meant that the Wi - Fi phones would ping - pong their associations between APs besides fall calls, he explains.
So the university switched to AirMagnet WLAN Planner subject because its 802. 11a / b / g networks. “We well-informed by using the tool that our initial system techniques were flawed, ” Miller says. His redesigned the AP design to effect - 68dBm signal strength, and straightaway the network “works flawlessly, ” he says.
The university runs Cisco Aironet 1130 802. 11a / b / g APs that cover about three - fourths of the university’s student multitude and four Cisco Draft N 802. 11n 1250 APs outdoors. For voice, university personnel use Cisco, Nokia, and T - Expressive Wi - Fi - enabled handsets.
For point of its own 7921 Wi - Fi phones, Cisco recommends a minimum planned signal calm commencement of - 67dBm and an SNR of 25dB to clinch a welcome user voice know-how.
