Roaming - Cisco 7925G Deployment Manual

Using port based QoS policies is inadequate as all data packets use the same UDP port (LWAPP = 12222; or CAPWAP = 5246)
and the access point uses the outside QoS marking to determine which queue the packets should be placed in.
With TCLAS, DSCP preservation is not a requirement.
Call Admission Control (TSPEC) must be enabled on the access point in order to enable TCLAS.
TCLAS will be negotiated within the ADDTS packets, which are used to request bandwidth in order to place or receive a call.

Roaming

CCKM is the recommended deployment model for all environment types where frequent roaming occurs.
802.1x authentication is required in order to utilize CCKM.
802.1x without CCKM can introduce delay during roaming due to its requirement for full re-authentication. WPA and WPA2
introduce additional transient keys and can lengthen roaming time.
When CCKM is utilized, roaming times can be reduced from 400-500 ms to less than 100 ms, where that transition time from
one access point to another will not be audible to the user.
As of the 1.3(4) release, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G support CCKM with WPA2 (AES
or TKIP), WPA (TKIP or AES), and 802.1x (WEP) authentication.
Authentication
WPA/WPA2 Personal
WPA/WPA2 Enterprise
CCKM
The scanning mechanism was enhanced in the 1.4(2) release to provide seamless interband roaming in the most challenging
environments, including pico cell deployments.
The Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G manage the scanning and roaming events; Client Roaming
parameters in the Cisco Unified Wireless LAN Controller are not utilized.
Roaming can be triggered for either of the following reasons.
RSSI Differential
•
Max Tx Retransmissions (not receiving 802.11 acknowledgements from the access point)
•
Missed Beacons
•
Call Admission Control
•
The roaming trigger for the majority of roams should be due to meeting the required RSSI differential based on the current
RSSI, which results in seamless roaming (no voice interruptions).
Unexpected roams are triggered either by missing contiguous 802.11 acknowledgements (Max Tx retransmissions) or beacons
from the access point.
For seamless roaming to occur, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G must be associated to an
access point for at least 3 seconds, otherwise roams can occur based on packet loss (max tx retransmissions or missed beacons).
Roaming based on RSSI may not occur if the current signal has met the strong RSSI threshold.
Note: The Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G do not utilize the RF parameters in the Client
Roaming section of the Cisco Unified Wireless LAN Controller as scanning and roaming is managed independently by the
phone itself.
Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G Deployment Guide
Roaming Time
150 ms
300 ms
< 100 ms
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