Roaming Admission Control; Traffic Classification (Tclas); Roaming - Cisco 8800 Series Deployment Manual

Wireless lan deployment guide

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If the admission is refused for an inbound call there is no messaging from the Cisco IP Phone 8800 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.

Roaming Admission Control

During a call, the Cisco IP Phone 8800 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 Cisco IP

Phone 8800 Series will send an ADDTS request during the roam to the new access point, which embedded in the reassociation

request frame.

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 as all data packets use the same UDP port (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.

The Cisco IP Phone 8800 Series defaults to Auto for frequency band mode, which allows the Cisco IP Phone 8800 Series to

connect to either 5 GHz or 2.4 GHz and enables interband roaming support.

Cisco IP Phone 8800 Series Wireless LAN Deployment Guide

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