Administrator’s Guide for SIP-T5 Series Smart Media Phones834Step Action DescriptionF13 200OK—User C to Proxy ServerUser C sends a SIP 200 OK response to theproxy server. The 200 OK response notifiesUser A that the connection has been made.F14 200OK—Proxy Server to User A The proxy server forwards the SIP 200 OKresponse to User A.F15 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.F16 ACK—Proxy Server to User C The proxy server sends the ACK message toUser C.No Answer Call ForwardThe following figure illustrates successful call forwarding between Yealink SIP IP phones in whichUser B has enabled no answer call forward. The incoming call is forwarded to User C when UserB does not answer the incoming call after a period of time. In this call flow scenario, the endusers are User A, User B, and User C. They are all using Yealink SIP IP phones, which areconnected via an IP network.The call flow scenario is as follows:1. User B enables no answer call forward, and the destination number is User C.2. User A calls User B.3. User B does not answer the incoming call.4. User B forwards the incoming call to User C.5. User C answers the call.
