Cisco 8861 Deployment Manual page 60

If the client uses TCP for SIP, then the access point will snoop the SIP packets when media session snooping is enabled on the
WLAN and will not forward the SIP frames upstream or downstream if there is not bandwidth available for the new voice
stream. This could potentially result in loss of registration to the Cisco Unified Communications Manager.
If the client uses UDP for SIP, then the access point will snoop the SIP packets when media session snooping is enabled on the
WLAN and will sent a 486 busy message to the client, which in turn can be interpreted as a Network Busy message and the
client could either roam to another access point or simply terminate the call setup for that session.
If the Cisco IP Phone 8861 and 8865 uses TCP for SIP communications and the channel is busy where another call can not be
allowed, then the Cisco IP Phone 8861 and 8865 could potentially lose registration to the Cisco Unified Communications
Manager if SIP CAC is enabled.
Admission Control Mandatory for Video should be disabled.
Cisco IP Phone 8861 and 8865 Wireless LAN Deployment Guide
60