Traffic Classification (Tclas); Qos Basic Service Set (Qbss) - Cisco 8821 Manual

If the AP sends an ADDTS successful message then the Cisco Wireless IP Phone 8821 or 8821-EX establishes the call.
If the access point rejects the call and the Cisco Wireless IP Phone 8821 or 8821-EX 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 Wireless IP Phone 8821 or 8821-EX 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.
Roaming Admission Control
During a call, the Cisco Wireless IP Phone 8821 and 8821-EX measure 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 enabled, then the Cisco Wireless IP
Phone 8821 and 8821-EX will send an ADDTS request during the roam to the new access point, which embedded in the
reassociation request frame.

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.
Using port based QoS policies is inadequate for CAPWAP based wireless LAN solutions as all data packets use the same UDP
port (CAPWAP = UDP 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 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.

QoS Basic Service Set (QBSS)

There are three different versions of QoS Basic Service Set (QBSS) that the Cisco Wireless IP Phone 8821 and 8821-EX
support.
The first version from Cisco was on a 0-100 scale and was not based on clear channel assessment (CCA), so it does not account
for channel utilization, but only the 802.11 traffic traversing that individual access point's radio. So it does not account for
other 802.11 energy or interferers using the same frequencies.
QBSS is also a part of 802.11e, which is on a 0-255 scale and is CCA based. So this gives a true representation on how busy
the channel is. The max threshold is also defined on the client side, which is set to 105.
The second version from Cisco is based on the 802.11e version, but allows the default max threshold of 105 to be optionally
configured.
Each version of QBSS can be optionally be configured on the access point.
Cisco Wireless IP Phone 8821 and 8821-EX Wireless LAN Deployment Guide
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