Yealink SIP-T2XP Administrator's Manual page 567

Step Action
F7 ACK—User A to Proxy Server
F8 ACK—Proxy Server to User B
F9 REFER—User B to Proxy Server
202 Accepted—Proxy Server
F10
to User B
REFER—Proxy Server to User
F11
A
202 Accepted—User A to
F12
Proxy Server
F13 BYE—User B to Proxy Server
F14 BYE—Proxy Server to User A
200OK—User A to Proxy
F15
Server
200OK—Proxy Server to User
F16
B
INVITE—User A to Proxy
F17
Server
Description
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 sends a REFER message to the
proxy server. User B performs a blind
transfer of User A to User C.
The proxy server sends a SIP 202 Accept
response to User B. The 202 Accepted
response notifies User B that the proxy
server has received the REFER
message.
The proxy server forwards the REFER
message to User A.
User A sends a SIP 202 Accept response
to the proxy server. The 202 Accepted
response indicates that User A accepts
the transfer.
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 BYE
request to User A.
User A sends a SIP 200 OK response to
the proxy server. The 200 OK response
confirms that User A has received the
BYE request.
The proxy server forwards the SIP 200
OK response to User B.
User A sends a SIP INVITE request to the
proxy server. In the INVITE request, a
unique Call-ID is generated and the
Appendix
549