Yealink T46G Administrator's Manual page 413

Step Action
180 Ringing—Proxy Server to
F18
User A
F19 200OK—User C to Proxy Server
F20 200OK—Proxy Server to User A
F21 ACK— User A to Proxy Server
F22 ACK—Proxy Server to User C
F23 REFER—User A to Proxy Server
202 Accepted—Proxy Server to
F24
User A
F25 REFER—Proxy Server to User B
202 Accepted—User B to Proxy
F26
Server
F27 BYE—User A to Proxy Server
F28 BYE—Proxy Server to User B
Description
The proxy server forwards the 180 Ringing
response to User A. User A hears the
ring-back tone indicating that User C is
being alerted.
User C sends a SIP 200 OK response to the
proxy server. The 200 OK response notifies
User A that the connection has been made.
The proxy server forwards the SIP 200 OK
response to User A. The 200 OK 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 forwards the ACK message
to User C. The ACK confirms that the proxy
server has received the 200 OK response.
The call session is now active.
User A sends a REFER message to the proxy
server. User A performs a transfer of User B
to User C.
The proxy server sends a SIP 202 Accepted
response to User A. The 202 Accepted
response notifies User A that the proxy
server has received the REFER message.
The proxy server forwards the REFER
message to User B.
User B sends a SIP 202 Accept response to
the proxy server. The 202 Accepted
response indicates that User B accepts the
transfer.
User A terminates the call session by
sending a SIP BYE request to the proxy
server. The BYE request indicates that User
A wants to release the call.
The proxy server forwards the BYE request
to User B.
Appendix
399