Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
37
Configuring Data Rates
It is recommended to disable rates below 12 Mbps for 802.11a and below 12 Mbps for 802.11b/g deployments where capacity
and range are factored in for best results.
If 802.11b clients are not allowed in the wireless LAN, then it is recommended to disable the 1, 2, 5.5, 11 Mbps data rates.
When 802.11b clients exist in the wireless network, then an 802.11b rate must be enabled and only an 802.11b rate can be
configured as a basic rate. In this case, is suggested to enable the data rates 11 Mbps and higher.
If using Coexistence where 802.11b/g and Bluetooth are being used simultaneously, then the data rates below 11 Mbps should
be disabled. If 802.11b clients are not allowed in the wireless network, then it is strongly recommended to disable the data rates
below 12 Mbps. This will eliminate the need to send CTS frames for 802.11g protection as 802.11b clients can not detect these
OFDM frames.
The recommended data rate configuration is the following:
802.11 Mode
Basic (Mandatory)
Data Rates
Supported (Optional)
Data Rates
Disabled
Data Rates
802.11a
12 Mbps
18 - 24, <36-54> Mbps
6, 9, <36-54> Mbps
802.11b
11 Mbps
None
1, 2, 5.5 Mbps
802.11g
12 Mbps
18 – 24, <36-54> Mbps
6, 9, <36-54> Mbps
802.11b/g
11 Mbps
12 – 24, <36-54> Mbps
1, 2, 5.5, 6, 9, <36-54> Mbps
Data rates higher than 24 Mbps (36, 48 and 54 Mbps) can optionally be enabled or disabled, but there is no advantage from a
capacity or throughput perspective to enable these rates for a voice application.
Enabling these rates could potentially increase the number of retries for a data frame.
Other applications may be able to benefit from having these higher data rates enabled.
Note:
Some environments may require that a lower data rate be enabled due to use of legacy clients, environmental factors or
maximum range is required.
Set only the lowest data rate enabled as the single basic rate. Multicast packets will be sent at the highest basic data rate
enabled.
Note that capacity and throughput are reduced when lower rates are enabled.
If Call Admission Control (TSPEC) is enabled then the Traffic Stream Rate Set (TSRS) feature will also be enabled, which will
allow lower rates to be enabled for legacy devices, but prevent the Cisco Unified Wireless IP Phone 7925G Series to transmit at
rates below 12 Mbps for 802.11a and 11 Mbps for 802.11b/g, while also allow set the ceiling data rate to a more reliable data
rate (24 Mbps). Disallowing packets to be transmitted at lower rates preserves capacity. Sending voice frames at a more
reliable rate initially can potentially reduce the number of retries of a data frame to ensure the packet transmission is successful
on the first try.
See the “
Product Specific Configuration Options
” section for information on how to configure the Restricted Data Rates
options on the Cisco Unified Wireless IP Phone 7925G Series in order to utilize the TSRS feature.
Call Capacity
Design the network to accommodate the desired call capacity.
The Cisco Access Point can support up to 27 bi-directional RTP streams for both 802.11a and 802.11g at a data rate of 24 Mbps
or higher. To achieve this capacity, there must be minimal wireless LAN background traffic and radio frequency (RF)
utilization.
