How to create a Callback form using the Ozeki C# SIP VoIP softphone source

1. Download and extract the sample program.
2. Load the sample program to Visual Studio 2010 or to .Net compatible development environment.
3. Only a minimal configuration is needed to setup the example efficiently.
   In the telephone initialization section of the FormCallback.cs file you need to replace the local IP address of the PC on which the system runs instead of "your local IP Address". Below you can find this step in details. This is the telephone initialization section of the FormCallback.cs file:

   		private void InitializeSoftPhone()  
   		    {  
   		        try  
   		        {  
   		            var account = new SIPAccount(true, "oz875", "oz875", "oz875", "oz875", "192.168.115.103", 5060);
   					softPhone = SoftPhoneFactory.CreateSoftPhone(SoftPhoneFactory.GetLocalIP(), 5700, 5750);
   		            softPhone.IncomingCall += softPhone_IncomingCall;
   		            phoneLine = softPhone.CreatePhoneLine(account);
   		            phoneLine.RegistrationStateChanged += phoneLine_PhoneLineInformation;
   		
   		            softPhone.RegisterPhoneLine(phoneLine);
   		
   		            connector.Connect(operatorReceiver, customerSender);
   		            connector.Connect(customerReceiver, operatorSender);
   		        }  
   		        catch (Exception ex)  
   		        {  
   		        	//
   		        }  
   		    }  
   		

   In this section search for the following line:

   		softPhone = SoftPhoneFactory.CreateSoftPhone("your local IP Address", 5700, 5750);
   		

   In this line replace the local IP address of the PC on which the system runs instead of "your local IP Address".
   
   As a next step you also need to provide the user data of your selected SIP PBX as the SIP account object values. Then you need to provide the user data of your selected SIP PBX as the SIP account object values similarly to the following line:

   		phoneLine = softPhone.CreatePhoneLine(new SIPAccount(true, "oz891", "oz891", "oz891", "oz891", "192.168.91.212", 5060));
   		

4. Finally, you only need to build and run the program.

public partial class FormCallback : Form  
{  
    const bool OperatorCall = false;  
    const bool CustomerCall = true;  
    ISoftPhone softPhone;  
    IPhoneLine phoneLine;  
    PhoneLineState phoneLineInformation;  
    IPhoneCall calloperator;  
    IPhoneCall callcustumer;  
    Timer countDownTimer;  

    private PhoneCallAudioSender operatorSender = new PhoneCallAudioSender();  
    private PhoneCallAudioReceiver operatorReceiver = new PhoneCallAudioReceiver();  
    private PhoneCallAudioSender customerSender = new PhoneCallAudioSender();  
    private PhoneCallAudioReceiver customerReceiver = new PhoneCallAudioReceiver();  
    private MediaConnector connector = new MediaConnector();

		private void InitializeSoftPhone()
        {
            try
            {
                var account = new SIPAccount(true, "oz875", "oz875", "oz875", "oz875", "192.168.115.103", 5060);
                softPhone = SoftPhoneFactory.CreateSoftPhone(SoftPhoneFactory.GetLocalIP(), 5700, 5750);
                softPhone.IncomingCall += softPhone_IncomingCall;
                phoneLine = softPhone.CreatePhoneLine(account);
                phoneLine.RegistrationStateChanged += phoneLine_PhoneLineInformation;

                softPhone.RegisterPhoneLine(phoneLine);

                connector.Connect(operatorReceiver, customerSender);
                connector.Connect(customerReceiver, operatorSender);
            }
            catch (Exception ex)
            {
                MessageBox.Show(String.Format("You didn't give your local IP adress, so the program won't run properly.\n {0}", ex.Message), string.Empty, MessageBoxButtons.OK,
                MessageBoxIcon.Error);
				
                var sb = new StringBuilder();
                sb.AppendLine("Some error happened.");
                sb.AppendLine();
                sb.AppendLine("Exception:");
                sb.AppendLine(ex.Message);
                sb.AppendLine();
                if(ex.InnerException != null)
                {
                    sb.AppendLine("Inner Exception:");
                    sb.AppendLine(ex.InnerException.Message);
                    sb.AppendLine();
                }
                sb.AppendLine("StackTrace:");
                sb.AppendLine(ex.StackTrace);

                MessageBox.Show(sb.ToString());				
            }
        }

• Initiate a call: initiation of calls is made in a set time instant. I make the examination of this time instant with the help of the timer offered by .Net Framework. This timer examines in every seconds if it is the time for making the call. When it is time for call, the BeginCall(bool IsCustomerCall) method is called. This method dials the operator or the customer according to the value of the bool parameter. Meanwhile, it informs us about this procedure on the user interface.

  		private void BeginCall(bool IsCustomerCall)  
  		{  
  		    if (IsCustomerCall && !String.IsNullOrEmpty(textBoxCallbackPhone.Text))  
  		    {  
  		        callcustumer = softPhone.CreateCallObject(phoneLine, textBoxCallbackPhone.Text);  
  		        WireUpCallEvents(callcustumer);  
  		        InvokeGUIThread(() =>  
  		        {  
  		            listBoxEvents.Items.Add(String.Format("{0} call starts.", callcustumer));  
  		        });  
  		  
  		        customerReceiver.AttachToCall(callcustumer);  
  		        customerSender.AttachToCall(callcustumer);  
  		  
  		        callcustumer.Start();  
  		    }  
  		    else  
  		    {  
  		        if (string.IsNullOrEmpty(textBoxOperator.Text))  
  		            return;  
  		  
  		        if (phoneLineInformation != PhoneLineState.RegistrationSucceeded && phoneLineInformation != PhoneLineState.NoRegNeeded)  
  		        {  
  		            MessageBox.Show("Phone line state is not valid!");  
  		            return;  
  		        }  
  		  
  		        calloperator = softPhone.CreateCallObject(phoneLine, textBoxOperator.Text);  
  		        WireUpCallEvents(calloperator);  
  		        InvokeGUIThread(() =>  
  		        {  
  		            listBoxEvents.Items.Add(String.Format("{0} call starts.", calloperator));  
  		        });  
  		  
  		        operatorSender.AttachToCall(calloperator);  
  		        operatorReceiver.AttachToCall(calloperator);  
  		  
  		        calloperator.Start();  
  		    }  
  		}
  		

  To initiate a call, you need to create an "IPhoneCall" object representing a call by using teh "softPhone.Call" method and its parameters. The first parameter is the phone line via which you wish to initiate the call. The second parameter is the phone number to be called. To make a successful call, you need to subscribe to specific events. Therefore, the audio data and DTMF signals arriving from the remote end, or the changes of the call status can be processed efficiently. I made the subscription in the sample program as follows:

  		private void WireUpCallEvents(IPhoneCall call)  
  		{  
  		    call.CallStateChanged += (call_CallStateChanged);  
  		    call.DtmfReceived += (call_DtmfReceived);
  		}  
  		

  CallStateChanged: this event is for demonstrating the changes in the call status.
  
  MediaDataRecived: the audio data from the remote telephone device arrives via this event.
  
  DtmfReceived: this event is responsible for processing DTMF signals that are arrived from the remote end.
  
  After subscribing for these necessary events you only need to actually initiate the call with the Start() method of the "call" object. In this sample program it is the "call.Start()" line.
• Handling of incoming calls: Ozeki VoIP SIP SDK publishes incoming calls via "ISoftphone" "InComingCall" event. Since incoming calls are not determined in the sample program, optional incoming calls are rejected immediately.

  		private void softPhone_IncomingCall(object sender, VoIPEventArgs<IPhoneCall> e)  
  		{  
  		    e.Item.Reject();  
  		}  
  		

• Displaying call status: regarding the call status, Ozeki VoIP SIP SDK provides the following information: Ringing, InCall, Completed, Rejected etc. These statuses are displayed via the "CallStateChanged" event of "call" object. In this sample program I concentrated on the basic options. So the further possibilities can be easily created based on these basic ones.

  		private void call_CallStateChanged(object sender, CallStateChangedArgs e)
          {
              InvokeGUIThread(() => 
              {
                  labelCallStateInfo.Text = e.State.ToString();
                  listBoxEvents.Items.Add(String.Format("{0} call statechanged: {1}",sender,e.State.ToString()));
              });
  
              switch (e.State)
              {
                  case CallState.Answered:                   
                      if ((IPhoneCall)sender==calloperator)
                      {
                          BeginCall(CustomerCall);
                      }
                      break;
                  case CallState.Completed:
                  case CallState.Cancelled:
                      HangUpCall((IPhoneCall)sender);
                      calloperator = null;
                      callcustumer = null;
                      break;
              }
          }
  		

  In the code above you can see how the program reacts to the changes in the call event. In case of "Incall" status, if changes occur in the call object of the operator, the call is started toward the customer. If one of the calls is hanged up, the other call is also hanged up with HangupCall(IPhoneCall call) method. This will hang up the given call via the Stop() method of "IPhoneCall" object.
• Handling audio data sending and receiving:

  		customerReceiver.AttachToCall(callcustumer);  
  		customerSender.AttachToCall(callcustumer); 
  		

• Handling incoming DTMF signals: receiving DTMF signals works in similar way as receiving audio data. The program forwards incoming signals to the other call and displays the reference value of the DTMF signals on the interface in the following way:

  		private void call_DtmfReceived(object sender, VoIPEventArgs<DtmfInfo> e)  
  		{  
  		    DtmfInfo dtmfInfo = e.Item;  
  		  
  		    InvokeGUIThread(() =>  
  		    {  
  		        labelCallStateInfo.Text = String.Format("DTMF signal received: {0} ", dtmfInfo.Signal.Signal);  
  		        listBoxEvents.Items.Add(String.Format("{0} sended the following DTMF sign: {1}", sender, dtmfInfo.Signal.Signal));  
  		    });  
  		} 
  		

• How to use SIP REGISTER request
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• How to accept incoming call
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• Download Ozeki VoIP SDK
• Ozeki VoIP SIP SDK - Training guides and examples