Yealink SIP-T48G Administrator's Manual page 586

Administrator's Guide for SIP-T2_Series_T4_Series IP Phones
Step
F9 ACK—User A to Proxy Server
F10 ACK—Proxy Server to User B
F11 BYE—User B to Proxy Server
F12 BYE—Proxy Server to User A
200 OK—User A to Proxy
F13
Server
200 OK—Proxy Server to User
F14
B
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.
572
Action
response notifies User A that the
connection has been made.
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.
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.
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.
The proxy server forwards the SIP BYE
request to User A to notify that User B
wants to release the call.
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.
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.
Description