Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
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Roaming
When using 802.1x type authentication, it is recommended to implement CCKM to enable fast roaming. 802.1x can introduce
delay during roaming due to its requirement for full re-authentication. CCKM centralizes the key management and reduces the
number of key exchanges. WPA introduces additional transient keys and can lengthen roaming time.
As of the 1.3(4) release, the Cisco Unified Wireless IP Phone 7925G Series supports CCKM with WPA2 (AES or TKIP), WPA
(TKIP or AES) and 802.1x (WEP) authentication.
Authentication
Roaming Time
WPA/WPA2 Personal
150 ms
WPA/WPA2 Enterprise 300 ms
CCKM
< 100 ms
Interband Roaming
Some deployments may use one band for indoor (i.e. 5 GHz) and the other for outdoor coverage (i.e. 2.4 GHz). In this case, set
the phone to either Auto-a or Auto-b/g mode, depending on the preferred band.
For Auto-a and Auto-b/g modes, this is giving preference to one band over another. At power on, the Cisco Unified Wireless IP
Phone 7925G Series will scan all 2.4 and 5 GHz channels then attempt to associate to an access point for the configured
network using the preferred band if available. If the preferred band is not available, then the Cisco Unified Wireless IP Phone
7925G Series will try to use the less preferred band if available. If the phone roams out of coverage of the preferred band,
where the less preferred band signal is available, then the phone will attempt to associate to that less preferred band.
As of the 1.3(4) release, seamless interband roaming between 5 Ghz and 2.4 Ghz bands is supported as both bands are now
scanned simultaneously when on call.
In order for the Cisco Unified Wireless IP Phone 7925G Series to roam from the preferred band to the less preferred band (i.e.
roam to 2.4 GHz when configured for Auto-a mode), all access points in the preferred band must have a signal low enough to
match the less preferred band roam threshold and the RSSI differential threshold for roaming must be met. In order to roam
back to the preferred band, there must be at least one access point with sufficient signal matching the preferred band roam
threshold.
Prior to the 1.3(4) release, the Cisco Unified Wireless IP Phone 7925G Series would have to roam out of range of the current
band before it would attempt to roam to the other band when configured for an Auto 802.11 mode (i.e. Auto-a, Auto-bg, Auto-
RSSI), where the user may experience choppy audio with the weak signal, followed up with a small second audio gap before
looking for the least preferred band. Then once it has failed over to a less preferred band (i.e. associated to 802.11b/g when
phone configured for Auto-a), there was no mechanism in place to check to see if the preferred band is available again or not in
order to roam back to the preferred band.
It is recommended to perform a spectrum analysis to ensure that the desired bands can be enabled in order to perform seamless
interband roaming.
Channel Parking
Channel Parking is a sub-feature of interband roaming, which is designed to conserve idle battery life when the Cisco Unified
Wireless IP Phone 7925G Series are configured for an Auto 802.11 mode and continuous scan mode is enabled in the Cisco
Unified Communications Manager.
Continuous scan mode enables constant scanning of all channels regardless of call state, which can also help with location.
When configured for auto scan mode, typically the phone is only scanning when on call and not in idle unless the current signal
drops below a certain RSSI threshold.
