Yealink SIP-T46G - Page 390

Appendix
377
Step
Action
Description
F6
486 Busy Here—Proxy Server
to User A
The proxy server forwards the 486 Busy
Here response to notify User A that User
B is busy.
F7
ACK—User A to Proxy Server
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.
F8
ACK—Proxy Server to User B
The proxy server forwards the SIP ACK
to User B to indicate that the 486 Busy
Here message has already been
received.