Yealink T27P - Page 586

Administrator’s Guide for SIP-T2_Series_T4_Series IP Phones
572
Step
Action
Description
response notifies User A that the
connection has been made.
F9
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.
F10
ACK—Proxy Server to User B
The proxy server sends the SIP ACK to
User B. The ACK confirms that the proxy
server has received the 200 OK
response. The call session is now active.
F11
BYE—User B to Proxy Server
User B terminates the call session by
sending a SIP BYE request to the proxy
server. The BYE request indicates that
User B wants to release the call.
F12
BYE—Proxy Server to User A
The proxy server forwards the SIP BYE
request to User A to notify that User B
wants to release the call.
F13
200 OK—User A to Proxy
Server
User A sends a SIP 200 OK response to
the proxy server. The 200 OK response
indicates that User A has received the
BYE request. The call session is now
terminated.
F14
200 OK—Proxy Server to User
B
The proxy server forwards the SIP 200
OK response to User B to indicate that
User A has received the BYE request.
The call session is now terminated.
The following figure illustrates the scenario of an unsuccessful call caused by the called
user’s being busy. In this scenario, the two end users are User A and User B. User A and
User B are located at Yealink SIP IP phones.
The call flow scenario is as follows:
1. User A calls User B.
2. User B is busy on the IP phone and unable or unwilling to take another call.