Filter
Top Products
Challenges of integrating voice applications 27
because handsets are roaming around and rate scaling up and down as
necessary. Handsets are moving, and as they do, the engineering target of
call capacity becomes a moving target.
Power adjustments and variable capacity
A WLAN has dynamic mechanisms in place for adjusting channels,
adjusting power, and filling coverage holes, all in response to changes in
the Radio Frequency (RF) environment. All of these mechanisms present
challenges to the engineering of voice networks.
Dynamic adjustments work well for guaranteeing minimum coverage and
connectivity of devices, particularly data devices. Voice requires more
planned engineering.
Usually, the number of calls per area (square foot) and calls per AP
determines the number of APs required to support the voice applications
and devices. Power adjustments affect these parameters. If an AP
increases power, it provides coverage for a larger area, meaning a greater
call demand for the AP. Doubling the power of an AP can quadruple its
coverage area, which means up to four times as much call demand as
originally engineered. That increased coverage area also has substantial
portions of lower data rate coverage. In addition, the added cochannel
interference to other cells using the same channel degrades their call
capacity. The net effect is that a network previously tuned for voice is
now less capable of meeting the demands of voice than it was before the
dynamic power adjustment.
Automatic RF changes do not always have a negative impact on
voice-engineered networks. Admission control techniques help with the
oversubscription problems related to increasing cell sizes dynamically.
Hole filling, after an AP failure occurs, also provides substantial value to
a voice solution.
When VoWLAN drives the engineering of the network both in scale and
capacity, sometimes automatic RF features create more challenges than
they resolve.
Quality of Service
802.11 is a shared media technology, but only one device can use the
media at a time. The AP abides by this rule as well.
Because the transmitting device cannot detect collisions, 802.11 uses
a statistical mechanism to reduce the possibility of collisions when two
devices are ready to transmit at the same time. After the medium becomes
available, the mechanism requires the devices to wait a random amount
Nortel Communication Server 1000
WLAN IP Telephony Installation and Commissioning
NN43001-504 03.04 Standard
23 September 2008
Copyright © 2004–2008 Nortel Networks
.