Cisco Unified Wireless IP Phone 7925G Series Deployment Guide
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Roaming Admission Control
During a call, the Cisco Unified Wireless IP Phone 7925G Series measures Received Signal Strength Indicator (RSSI) and
Packet Error Rate (PER) values for the current and all available access points to make roaming decisions.
If the original access point where the call was established had Call Admission Control (TSPEC) enabled, then the wireless IP
phone will send an ADDTS request during the roam to the new access point.
For more information about Call Admission Control and QoS, refer to the “Cisco Unified Wireless Quality of Service” chapter
in the
Enterprise Mobility Design Guide
at this URL:
http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/emob41dg/eMob4.1.pdf
Traffic Classification (TCLAS)
Traffic Classification (TCLAS) helps to ensure that the access point properly classifies voice packets.
Without proper classification, voice packets will be treated as best effort which will defeat the purpose of TSPEC and QoS in
general.
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.
