Appendix813Step Action DescriptionF4180 Ringing—Proxy Server toUser AThe proxy server forwards the 180 Ringingresponse to User A. User A hears thering-back tone indicating that User B isbeing alerted.F5CANCEL—User A to Proxy Server User A sends a SIP CANCEL request to theproxy server after not receiving anappropriate response within the timeallocated in the INVITE request. The SIPCANCEL request indicates that User A wantsto disconnect the call.F6CANCEL—Proxy Server to User B The proxy server forwards the SIP CANCELrequest to notify User B that User A wantsto disconnect the call.F7200 OK—User B to Proxy Server User B sends a SIP 200 OK response to theproxy server. The SIP 200 OK responseindicates that User B has received theCANCEL request.F8200 OK—Proxy Server to User A The proxy server forwards the SIP 200 OKresponse to notify User A that the CANCELrequest has been processed successfully.Successful Call Setup and Call HoldThe following figure illustrates a successful call setup and call hold. In this scenario, the two endusers are User A and User B. User A and User B are located at Yealink SIP IP phones.The call flow scenario is as follows:1. User A calls User B.2. User B answers the call.
