Specifications

Cisco Unified Wireless IP Phone 7921G Series Deployment Guide 22
Delivery Traffic Indicator Message (DTIM)
Increasing the DTIM period can also increase the battery life. The Cisco Unified Wireless IP Phone 7921G can use the DTIM
period to schedule wakeup periods to check for broadcast and multicast packets as well as any unicast packets.
For optimal battery life and performance, we recommend setting 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.
Scan Modes
When using only one access point, select Single Access Point Mode on the phone to reduce scanning and optimize battery life
for phones that do not roam.
When using multiple access points where roaming is required, “Single AP Mode” should not be enabled. Instead use the auto
(default) or continuous scan mode, which will allow for seamless roaming.
Continuous scan mode can be optionally enabled to allow for better location tracking.
Quality of Service (QoS)
Quality of Service enables queuing to ensure high priority for voice traffic. To implement appropriate queuing for voice traffic,
use the following suggestions:
• Ensure that WMM is enabled on the access point.
• Create a QoS policy on the access point giving priority to voice (RTP) and call control (SCCP) traffic and apply that
profile to the desired interfaces.
Traffic Type
DSCP
802.1p
WMM UP
Voice (RTP)
EF (46)
5
6
Call Control (SCCP)
CS3 (24)
3
4
• Be sure that RTP packets have the proper QoS markings and other protocols are not using the same QoS markings.
• Select the “Platinum” QoS profile for the voice wireless LAN when using Cisco Unified Wireless LAN Controller
technology and set the 802.1p tag to “6”.
• Enable Differentiated Services Code Point (DSCP) preservation on the Cisco IOS switch and/or use a QoS policy to set
DSCP to EF for RTP traffic (UDP port range 16384-32767) on the Cisco IOS router.
For more information about TCP and UDP ports used by the Cisco Unified Wireless IP Phone 7921G and the Cisco Unified
Communications Manager, refer to the Cisco Unified Communications Manager TCP and UDP Port Usage document at this
URL: