Administrator’s Guide for SIP-T5 Series Smart Media Phones824Step Action DescriptionF22 200OK—Proxy Server to User A The proxy server forwards the SIP 200 OKresponse to User A.F23 ACK— User A to Proxy ServerUser A sends a SIP ACK to the proxy server.The ACK confirms that User A has receivedthe 200 OK response. The call session isnow active.F24 ACK—Proxy Server to User CThe proxy server forwards the ACK messageto User C. The ACK confirms that User A hasreceived the 200 OK response. The callsession is now active.Call Transfer with ConsultationThe following figure illustrates a successful call between Yealink SIP IP phones in which twoparties are in a call and then one of the parties transfers the call to the third party withconsultation. This is called attended 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 IPnetwork.The call flow scenario is as follows:1. User A calls User B.2. User B answers the call.3. User A calls User C.4. User C answers the call.5. User A transfers the call to User C.
