Call Capacity - Cisco 8821 Manual

Delivery Traffic Indicator Message (DTIM)
The Cisco Wireless IP Phone 8821 and 8821-EX can use the DTIM period to schedule wakeup periods to check for broadcast
and multicast packets as well as any unicast packets.
If proxy ARP is enabled, then the Cisco Wireless IP Phone 8821 and 8821-EX do not have to wake up at DTIM.
For optimal battery life and performance, is recommended to set the DTIM period to 2 with a beacon period of 100 ms.
The DTIM period is a tradeoff between battery life and multicast performance.
Broadcast and multicast traffic will be queued until the DTIM period when there are power save enabled clients associated to
the access point, so DTIM will determine how quickly these packets can be delivered to the client. If using multicast
applications, a shorter DTIM period can be used.
When multiple multicast streams exist on the wireless LAN frequently, then it is recommended to set the DTIM period to 1.
Dynamic Transmit Power Control (DTPC)
To ensure packets are exchanged successfully between the Cisco Wireless IP Phone 8821 or 8821-EX and the access point,
Dynamic Transmit Power Control (DTPC) should be enabled.
DTPC prevents one-way audio when RF traffic is heard in one direction only.
If the access point does not support DTPC, then the Cisco Wireless IP Phone 8821 and 8821-EX will use the highest available
transmit power depending on the current channel and data rate.
The access point's radio transmit power should not have a transmit power greater than what the Cisco Wireless IP Phone 8821
and 8821-EX can support.

Call Capacity

Design the network to accommodate the desired call capacity.
The Cisco Access Point can support up to 27 bi-directional voice streams for both 802.11a/n/ac and 802.11g/n at a data rate of
24 Mbps or higher. To achieve this capacity, there must be minimal wireless LAN background traffic and initial radio frequency
(RF) utilization.
The number of calls may vary depending on the data rate, initial channel utilization, and the environment.
Audio Only Calls
Below lists the maximum number of audio only calls (single bi-directional voice stream) supported per access point / channel.
Max # of Audio Codec
Streams
13 G.722 / G.711
20 G.722 / G.711
27 G.722 / G.711
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
Audio 802.11 Mode
Bit Rate
64 Kbps 802.11a/n or 802.11g/n +
Bluetooth Disabled
64 Kbps 802.11a/n or 802.11g/n +
Bluetooth Disabled
64 Kbps 802.11a/n/ac or 802.11g/n
+ Bluetooth Disabled
Data Rate
6 Mbps
12 Mbps
24 Mbps or higher
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