Yealink SIP-T2XP Administrator's Manual page 422

Administrator's Guide for SIP-T2xP IP Phones
Step
486 Busy Here—Proxy Server
F6
to User A
F7 ACK—User A to Proxy Server
F8 ACK—Proxy Server to User B
406
Action
The proxy server forwards the 486 Busy
Here response to notify User A that User
B is busy.
User A sends a SIP ACK to the proxy
server. The SIP ACK message indicates
that User A has received the 486 Busy
Here message.
The proxy server forwards the SIP ACK to
User B to indicate that the 486 Busy Here
message has already been received.
Description