Yealink SIP-T48G Administrator's Manual page 874

Administrator's Guide for SIP-T2 Series/T19(P) E2/T4 Series/CP860 IP Phones
Step
180 Ringing—Proxy Server to
F4
User A
200 OK—User B to Proxy
F5
Server
200 OK—Proxy Server to User
F6
A
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
854
Action
alerted.
The proxy server forwards the 180
Ringing response to User A. User A
hears the ring-back tone indicating that
User B is being alerted.
User B 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 200 OK
message 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 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
Description