Pre-Call Admission Control - Cisco 7925G Series Deployment Manual

In releases prior to 1.3(3), the Cisco Unified Wireless IP Phone 7925G Series would use the static minimum PHY rate
configured locally.
If 12 Mbps is not enabled on the access point, then the next highest enabled data rate must be 24 Mbps. For example, if 12
Mbps is disabled but 18 Mbps is enabled, the phone will try the next highest rate of 18 Mbps and fail because that minimum
PHY rate for CAC is not supported by the Cisco access point.
The dynamic minimum PHY rate is useful for deployments that require higher capacity where 24 Mbps and higher data rates
are only enabled. For this high capacity deployment configuration and with release 1.3(3), the minimum PHY rate would be
adjusted to 24 Mbps automatically even if the phone is configured statically for a minimum PHY rate of 12 Mbps. In releases
prior to 1.3(3), the minimum PHY rate would have to be changed to 24 Mbps manually from the default of 12 Mbps in order for
CAC to work correctly for this deployment configuration.
If an 802.11b AP is used, the highest available date rate would be 11 Mbps, so 12 Mbps can not be used as the minimum PHY
rate. For this 802.11b (11 Mbps) deployment configuration and with release 1.3(3), the minimum PHY rate would be adjusted
to 11 Mbps automatically even if the phone is configured statically for a minimum PHY rate of 12 Mbps. In releases prior to
1.3(3), the minimum PHY rate would have to be changed to 11 Mbps manually from the default of 12 Mbps in order for CAC
to work correctly for this deployment configuration.
There is no support for load-based CAC or multiple streams on the autonomous access points therefore it is not recommended
to enable CAC on autonomous access points.
If CAC is enabled on the autonomous access point, then SRTP and barge calls will fail.

Pre-Call Admission Control

If Call Admission Control (TSPEC) is enabled on the access point, the Cisco Unified Wireless IP Phone 7925G Series sends an
Add Traffic Stream (ADDTS) to the access point to request bandwidth in order to place or receive a call. If the AP sends an
ADDTS successful message then the Cisco Unified Wireless IP Phone 7925G Series establishes the call. If the call is rejected
by the access point and the wireless IP phone has no other access point to roam to, then phone displays "Network Busy". If the
admission is refused, there is no messaging from the Cisco Unified Wireless IP Phone 7925G Series to inform the remote
endpoint that there is insufficient bandwidth to establish the call, so the call can continue to ring out within the system until the
remote user terminates the call.
Cisco Unified Wireless IP Phone 7925G Series Deployment Guide 28