User Manual

Yealink Skype for Business HD IP Phones Administrator Guide
420
Step
Action
Description
notifies User A that the connection has
been made.
F21
ACK— User A to Proxy Server
User A sends a SIP ACK to the proxy server.
The ACK confirms that User A has received
the 200 OK response. The call session is
now active.
F22
ACK—Proxy Server to User C
The proxy server sends the ACK message to
User C. The ACK confirms that the proxy
server has received the 200 OK response.