Appendix809Step Action Descriptionnow active.F10 ACK—Proxy Server to User BThe proxy server sends the SIP ACK to UserB. The ACK confirms that the proxy serverhas received the 200 OK response. The callsession is now active.F11 BYE—User B to Proxy ServerUser B terminates the call session bysending a SIP BYE request to the proxyserver. The BYE request indicates that UserB wants to release the call.F12 BYE—Proxy Server to User AThe proxy server forwards the SIP BYErequest to User A to notify that User Bwants to release the call.F13 200 OK—User A to Proxy ServerUser A sends a SIP 200 OK response to theproxy server. The 200 OK responseindicates that User A has received the BYErequest. The call session is now terminated.F14 200 OK—Proxy Server to User BThe proxy server forwards the SIP 200 OKresponse to User B to indicate that User Ahas received the BYE request. The callsession is now terminated.Unsuccessful Call Setup—Called User is BusyThe following figure illustrates the scenario of an unsuccessful call caused by the called user’sbeing busy. In this scenario, the two end users are User A and User B. User A and User B arelocated at Yealink SIP IP phones.The call flow scenario is as follows:1. User A calls User B.2. User B is busy on the IP phone and unable or unwilling to take another call.
