Specifications

Cisco Unified Wireless IP Phone 7921G Series Deployment Guide 36
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 7921G 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 7921G 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.
The number of calls may vary depending on the data rate, initial channel utilization, and the environment.
Max # of Streams
802.11 Mode
Data Rate
13
802.11a, 802.11g
6 Mbps
20
802.11a, 802.11g
12 Mbps
27
802.11a, 802.11g
24 – 54 Mbps