Cisco 8821, Manual

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Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
38
Roaming
The Cisco Wireless IP Phone 8821 and 8821-EX default to Auto for the 802.11 mode, which allows the Cisco Wireless IP
Phone 8821 and 8821-EX to connect to either 5 GHz or 2.4 GHz and enables interband roaming support.
802.11r / Fast Transition (FT) 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 802.11r (FT) or 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 802.11r (FT) or 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.
The Cisco Wireless IP Phone 8821 and 8821-EX support 802.11r (FT) with WPA2 (AES) or WPA2-PSK (AES) and CCKM
with WPA2 (AES).
Authentication Roaming Time
WPA/WPA2 Personal 150 ms
WPA/WPA2 Enterprise 300 ms
802.11r (FT) < 100 ms
CCKM < 100 ms
The Cisco Wireless IP Phone 8821 and 8821-EX manage the scanning and roaming events.
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).
For seamless roaming to occur, the Cisco Wireless IP Phone 8821 and 8821-EX 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.
Fast Secure Roaming (FSR)
802.11r / Fast Transition (FT) is the recommended deployment model for all environment types where frequent roaming occurs.
Cisco Centralized Key Management (CCKM) is also supported, but requires 802.1x authentication.
802.11r (FT) and CCKM enable fast secure roaming and limits the off-network time to keep audio gaps at a minimum when on
call.
802.1x or PSK without 802.11r (FT) and 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.
802.11r (FT) and CCKM centralizes the key management and reduces the number of key exchanges.
When 802.11r (FT) or 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.
There are two methods of 802.11r (FT) roaming.