Specifications

Cisco Unified Wireless IP Phone 7921G Series Deployment Guide 28
TCP and UDP port information will be used to set the UP (User Priority) value.
The previous method of classification depends upon preservation of DSCP value throughout the network, where the DSCP
value maps to a particular queue (BE, BK, VI, VO).
However, the DSCP values are not always preserved as this can be viewed as a security risk.
TCLAS is supported in the Cisco Unified Wireless LAN Controller release 5.1.151.0 and later.
Using port based QoS policies is inadequate as all data packets use the same UDP port (LWAPP = 12222; 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
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 7921G 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 7921G 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 7921G 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 7921G 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 7921G 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),