Other network design considerations 57
Example
The channel reuse factor for 802.11b networks is fixed at three (three nonoverlapping channels in the 2.4 GHz range), corresponding to channels 1, 6, and 11. The transmit power is fixed at 50 mW, which establishes the radius of the cell.
Now the effects of cell size, based on the other fixed parameters, can be compared.
If the deployed cells have a radius of anywhere from 33 ft to 75 ft, the call capacity per square foot is essentially the same. This means that packing cells in tighter than a 75 ft radius per AP is a waste of money. This example shows that in a typical office environment with APs at half power, you can deploy APs anywhere from 100 ft to 150 ft from each other. More walls mean there must be less distance between APs, and lowering the power of the AP lessens the required distance between APs, both of which also serve to increase the net call density.
SSID options and limitations
The traditional WLAN deployment requirement was to implement separate SSIDs for voice and for data. This requirement no longer exists, though it is still a useful deployment option in some circumstances.
If all devices implement common security encryption mechanisms (for example,
If data devices do not use the same encryption mechanism as WLAN handsets, it is best to implement multiple
If necessary, one way to ensure that multiple handset SSIDs on the same AP still work without oversubscribing the medium is to cut in half the number of calls per AP configured on the WLAN IP Telephony Manager 2245.
Nortel does not recommend a closed system for VoWLAN installations that use more than one SSID, including converged data and voice WLANs. The reason is that the SSID serves a valuable purpose in roaming. When it is hidden by not being included in the beacon, roaming devices must attempt to try all closed system APs. This result can dramatically impact call handoff times.
Nortel Communication Server 1000
WLAN IP Telephony Installation and Commissioning
Release 5.0 15 June 2007
