Yealink SIP-T2 SERIES Administrator's Manual page 1013

Step
Server
200 OK—Proxy Server to User
F16
A
F17 ACK—User A to Proxy Server
F18 ACK—Proxy Server to User B
200 OK—User A to Proxy
F19
Server
F20 200 OK—Proxy Server User C
F21 ACK—User C to Proxy Server
F22 ACK—Proxy Server to User A
The following figure illustrates a successful call between Yealink SIP IP phones in which
two parties are in a call and then one of the parties transfers the call to a third party
without consultation. This is called a blind transfer. In this call flow scenario, the end
users are User A, User B, and User C. They are all using Yealink SIP IP phones, which are
connected via an IP network.
Action
that the INVITE was successfully
processed.
The proxy server forwards the 200 OK
response to User A. The 200 OK
response notifies User B is successfully
placed on hold.
User A sends an ACK message to the
proxy server. The ACK confirms that
User A has received the 200 OK
response. The call session is now
temporarily inactive. No RTP packets
are being sent.
The proxy server sends the ACK
message to User B. The ACK confirms
that the proxy server has received the
200 OK response.
User A sends a 200 OK response to the
proxy server. The 200 OK response
notifies that the connection has been
made.
The proxy server forwards the 200 OK
message to User C.
User C sends a SIP ACK to the proxy
server. The ACK confirms that User C
has received the 200 OK response. The
call session is now active.
The proxy server forwards the SIP ACK
to User A to confirm that User C has
received the 200 OK response.
Appendix
Description
991