Interband Roaming; Scanning; Power Management - Cisco 8821 Manual

Interband Roaming

The Cisco Wireless IP Phone 8821 and 8821-EX default to Auto for the frequency band mode, which enables interband
roaming and currently gives preference to the strongest signal. Typically, this will give preference to 2.4 GHz over 5 GHz due
to 2.4 GHz having a stronger signal in general assuming the power levels are the same.
At power on, the Cisco Wireless IP Phone 8821 and 8821-EX will scan all 2.4 and 5 GHz channels when in Auto mode, then
attempt to associate to an access point for the configured network if available.
If configured for 5 GHz only or 2.4 GHz only mode, then just those channels are scanned.
It is recommended to perform a spectrum analysis to ensure that the desired bands can be enabled in order to perform interband
roaming.

Scanning

There are three different scan modes (Continuous, Auto, Single AP), which can be configured for the Cisco Wireless IP Phone
8821 and 8821-EX in the Cisco Unified Communications Manager.
When using multiple access points where seamless roaming is required, Continuous (default) or Auto scan mode should be
enabled (Single AP scan mode should not be used if multiple access points exist).
Continuous scan mode is the default scan mode, which enables seamless roaming while also conserving battery life.
When on an active call with Continuous or Auto scan mode enabled, the Cisco Wireless IP Phone 8821 and 8821-EX will be
continuously scanning regardless of the current call state (idle or on call) or current access point signal level (RSSI).
When in idle (not on an active call) and Continuous scan mode is enabled, then the Cisco Wireless IP Phone 8821 and 8821-
EX will also be continuously scanning.
When in idle with Auto scan mode, scans will only occur when the pre-defined RSSI threshold is held for the pre-defined
duration.
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.
If using only one access point, select Single AP mode on the Cisco Wireless IP Phone 8821 and 8821-EX to reduce scanning
and optimize battery life.

Power Management

When the access point supports the Cisco Client Extensions (CCX) proxy ARP information element, the idle battery life will be
optimized. Proxy ARP allows the Cisco Wireless IP Phone 8821 and 8821-EX 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 Wireless IP Phone 8821 and 8821-EX will utilize either U-APSD or PS-POLL power save
methods depending on whether Wi-Fi MultiMedia (WMM) is enabled in the Access Point configuration or not.
If the access point does not support CCX or proxy ARP is not enabled, then the idle battery life will be up to fifty percent less.
The Cisco Wireless IP Phone 8821 and 8821-EX primarily use U-APSD when in idle or on call.
Null Power Save (PS-NULL) frames are utilized for off-channel scanning.
Wireless LAN is automatically disabled temporarily when Ethernet is connected by docking the Cisco Wireless IP Phone 8821
or 8821-EX when a USB to Ethernet dongle is attached, but will be automatically re-enabled once Ethernet is disconnected.
Use of a supported USB to Ethernet dongle is for initial provisioning purposes only and not to convert the Cisco Wireless IP
Phone 8821 or 8821-EX to a wired IP phone.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
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