Pre-Call Admission Control - Cisco 7925G Deployment Manual

Enable a data rate that is enabled on the access point. (Default setting is 12 Mbps)
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Cisco Access Points will only accept a minimum PHY rate of 5.5, 6, 11, 12 or 24 Mbps, so ensure that at least one of
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these rates are enabled.
As of the 1.3(3) release, the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G will auto-negotiate the minimum
PHY rate to be used for TSPEC. By default it will try the locally configured minimum PHY rate (e.g. 12 Mbps) first, but if that
data rate is not enabled on the access point, then it will try the next highest enabled data rate on the access point. If there is not
a higher data rate enabled, then it will then try the next lowest data rate as the minimum PHY rate.
In releases prior to 1.3(3), the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G would use the static minimum
PHY rate configured locally, which required that rate to be enabled on the access point.
When using the 1.3(3) release or later and 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 data 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 Cisco Autonomous Access Points therefore it is not
recommended to enable CAC on Cisco Autonomous Access Points.
If CAC is enabled on the Cisco 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, 7925G-EX,
and 7926G will send 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, 7925G-EX, and 7926G
establishes the call.
If the access point rejects the call and the Cisco Unified Wireless IP Phone 7925G, 7925G-EX, and 7926G has no other access
point to roam to, then the phone will display Network Busy.
If the admission is refused for an inbound call there is no messaging from the Cisco Unified Wireless IP Phone 7925G, 7925G-
EX, and 7926G 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, 7925G-EX, and 7926G Deployment Guide
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