Outbound call Response State

I make an outbound call  and can understand if  connection is established.

 private void EndEstablish(IAsyncResult ar)
        {
            AudioVideoCall avcall = ar.AsyncState as AudioVideoCall;

         
            try
            {
                avcall.EndEstablish(ar);

                log.Debug("Connection is Established");
            }

            catch (FailureResponseException frex)
            {
                log.Error("Failure response Code: "+ frex.ResponseData.ResponseCode);
                log.Error("Failure response Text: " + frex.ResponseData.ResponseText);

            }

            catch (RealTimeException ex)
            {
                log.Error(ex);
            }


        }

The problem is that how can i understand that user "answer" my call or "reject" it.

Hippias Minor