Administrator’s Guide for W60P DECT IP Phones502Step Action DescriptionINVITE was successfully processed.F16 200 OK—Proxy Server to User AThe proxy server forwards the 200 OKresponse to User A. The 200 OK responsenotifies User B is successfully placed onhold.F17 ACK—User A to Proxy ServerUser A sends an ACK message to theproxy server. The ACK confirms that UserA has received the 200 OK response. Thecall session is now temporarily inactive.No RTP packets are being sent.F18 ACK—Proxy Server to User BThe proxy server sends the ACK messageto User B. The ACK confirms that theproxy server has received the 200 OKresponse.F19 200 OK—User A to Proxy ServerUser A sends a 200 OK response to theproxy server. The 200 OK responsenotifies that the connection has beenmade.F20 200 OK—Proxy Server User C The proxy server forwards the 200 OKmessage to User C.F21 ACK—User C to Proxy ServerUser C sends a SIP ACK to the proxyserver. The ACK confirms that User C hasreceived the 200 OK response. The callsession is now active.F22 ACK—Proxy Server to User AThe proxy server forwards the SIP ACK toUser A to confirm that User C has receivedthe 200 OK response.Call Transfer without ConsultationThe following figure illustrates a successful call between Yealink SIP DECT IP phones in whichtwo parties are in a call and then one of the parties transfers the call to a third party withoutconsultation. 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 DECT IP phones, which are connected via an IPnetwork.
