When the access point supports the Cisco Client Extensions (CCX) proxy ARP information element, the idle battery life will be optimized. Proxy ARP (It is enabled by default & cannot disable it) allows the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G to remain in sleep mode longer versus waking up at each Delivery Traffic Indicator Message (DTIM) period to check for incoming broadcasts.

To optimize battery life, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will utilize either U-APSD or PSPOLL power save methods depending on whether Wi-Fi MultiMedia (WMM) is enabled in the Access Point configuration or not.

U-APSD will be utilized when WMM is enabled on the Access Point.When on call U-APSD, PS-POLL, or active mode will be utilized depending on the Cisco Unified Wireless IP Phone 7925G,7925G-EX, and 7926G call power save mode configuration and the access point configuration. When in idle (no active call), the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G depending on the Access Point configuration will utilize U-APSD or PS-POLL.

Unscheduled Auto Power Save Delivery (U-APSD):
The Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will utilize U-APSD (Unscheduled Auto Power Save Delivery) for power management as long as Wi-Fi MultiMedia (WMM) is enabled in the access point configuration and the call power save mode on the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G is set to U-APSD/PS-POLL. U-APSD helps optimize battery life and reduces management overhead.

Below is a sample packet sequence when using U-APSD

Power Save Poll (PS-POLL):
If WMM is disabled (disabling U-APSD support) or U-APSD support is not available on the access point, then the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will utilize PS-POLL for power management when the call power save mode on the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G is set to U-APSD/ PS-POLL.
Below is a sample packet sequence when using PS-POLL.

Delivery Traffic Indicator Message (DTIM):
The Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G 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 Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G do not have to wake up at DTIM. 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. If multiple multicast streams exist on the wireless LAN frequently, then it is recommended to set the DTIM period to 1.

Scan Modes:
There are three different scan modes (Auto, Continuous, Single AP), which can be configured for the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G in the Cisco Unified Communications Manager.

When using multiple access points where seamless roaming is required, Auto (default) or Continuous scan mode should be enabled (Single AP scan mode should not be used if multiple access points exist).Auto scan mode is the default scan mode, which will optimize idle battery life as well as offer seamless roaming.

When on an active call with Auto scan mode enabled, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will continuously be scanning. If in idle (not on an active call) and Auto scan mode is enabled, then the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will only start to scan once the scan threshold is met for the currently connected access point.

Continuous scan mode is recommended for environments where frequent roams occur or where smaller cells (pico cells) exist.Continuous scan mode can also help with location tracking. With Continuous scan mode, scans occur regardless of the current call state (idle or on call) or current access point signal level (RSSI). There will be a slight decrease in idle battery life when using Continuous scan mode in comparison to using Auto scan mode.

If using only one access point, select Single AP mode on the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G to reduce scanning and optimize battery life.

Ref: Cisco 7925G Deployment Guide (page 25-28)

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