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 9.1(1) release, the Cisco Unified IP Phone 9971 supports CCKM with WPA2 (AES or TKIP), WPA (TKIP or AES)
and 802.1x (WEP) authentication, where WPA2 (AES) with CCKM is recommended.
The Cisco Unified IP Phone 9971 manages 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 or video interruptions).
Unexpected roams are triggered either by missing contiguous 802.11 acknowledgements (Max Tx retransmissions) or missing
beacons from the access point.
For seamless roaming to occur, the Cisco Unified IP Phone 9971 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 IP Phone 9971 does 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.
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