How to develop Windows Forms softphone using Visual Basic .NET?

1. Download and extract the sample program.
2. Load the sample program into Visual Studio.
3. For the proper operation of the program a minimal configuration is required:
   In the telephone initialization section of the PhoneForm.vb 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 PhoneForm.vb file:

   	    Private Sub InitializeSoftPhone()
   	        Try
   	            Dim ip As IPAddress = SoftPhoneFactory.GetLocalIP()
   	            softPhone = SoftPhoneFactory.CreateSoftPhone(ip, 5700, 5750)
   	            AddHandler softPhone.IncomingCall, New EventHandler(Of VoIPEventArgs(Of IPhoneCall))(AddressOf softPhone_IncommingCall)
   	            phoneLine = softPhone.CreatePhoneLine(New SIPAccount(True, "oz878", "oz878", "oz878", "oz878", "192.168.115.103", 5060))
   	            AddHandler phoneLine.RegistrationStateChanged, New EventHandler(Of RegistrationStateChangedArgs)(AddressOf phoneLine_PhoneLineInformation)
   	            softPhone.RegisterPhoneLine(phoneLine)
   	        Catch ex As Exception
   	            MessageBox.Show("You didn't give your local IP adress, so the program won't run properly.")
   	        End Try
   	    End Sub
   		

   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".
   
   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))
   		

   Where "true" is the registrationRequired parameter: this is a true value and it allows to receive calls (not just to initiate them) in case the registration is successful. (In case of "False" value registration, calls can only be initiated).
   
   In the sample program "oz891" marks the SipAccount displayname, the username, the registername and the registerpassword.
   
   The following two parameters are the IP address or domain address and the port of the SIP PBX.
4. When you are finished you only need to build and run the program.

Public Class PhoneForm  

    ' Fields  
    Private phoneCall As IPhoneCall  
    Private phoneLine As IPhoneLine  
    Private phoneLineInformation As PhoneLineState  
    Private softPhone As ISoftPhone  
    Private microphone As Microphone = microphone.GetDefaultDevice()  
    Private speaker As Speaker = speaker.GetDefaultDevice()  
    Private connector As MediaConnector = New MediaConnector  
    Private mediaReceiver As PhoneCallAudioReceiver = New PhoneCallAudioReceiver  
    Private mediaSender As PhoneCallAudioSender = New PhoneCallAudioSender  
    Private inComingCall As Boolean  

		Private Sub InitializeSoftPhone()
	        Try
	            Dim ip As IPAddress = SoftPhoneFactory.GetLocalIP()
	            softPhone = SoftPhoneFactory.CreateSoftPhone(ip, 5700, 5750)
	            AddHandler softPhone.IncomingCall, New EventHandler(Of VoIPEventArgs(Of IPhoneCall))(AddressOf softPhone_IncommingCall)
	            phoneLine = softPhone.CreatePhoneLine(New SIPAccount(True, "oz878", "oz878", "oz878", "oz878", "192.168.115.103", 5060))
	            AddHandler phoneLine.RegistrationStateChanged, New EventHandler(Of RegistrationStateChangedArgs)(AddressOf phoneLine_PhoneLineInformation)
	            softPhone.RegisterPhoneLine(phoneLine)
	        Catch ex As Exception
	            MessageBox.Show("You didn't give your local IP adress, so the program won't run properly.")
	        End Try
	    End Sub

• Handling outgoing calls: for establishing an outgoing call, enter the number you wish to dial. Then click the 'Pick Up' button and the call starts. The surface buttons are assigned to triggers so let's look at the "Pick Up" button for details:

  		Private Sub buttonPickUp_Click(ByVal sender As Object, ByVal e As EventArgs) Handles buttonPickUp.Click
  	        If inComingCall Then
  	            inComingCall = False
  	            phoneCall.Answer()
  	        ElseIf ((phoneCall Is Nothing) AndAlso Not String.IsNullOrEmpty(labelDialingNumber.Text)) Then
  	            If ((phoneLineInformation <> RegState.RegistrationSucceeded) AndAlso (phoneLineInformation <> RegState.NoRegNeeded)) Then
  	                MessageBox.Show("Phone line state is not valid!")
  	            Else
  	                phoneCall = Me.softPhone.CreateCallObject(phoneLine, labelDialingNumber.Text)
  	                WireUpCallEvents()
  	                phoneCall.Start()
  	            End If
  	        End If
  	    End Sub
  		

  Since you can make and pick up the call with the very same button first you need to decide if it is an incoming or an outgoing call with the help of a simple bool variable truth verification (Incoming calls will be detailed later).
  
  Before initiating a phone call, check if the phoneline has successfully registered to the server when registration is required. If an inappropriate result is returned the user is informed about the reason of the failure.
  
  If the phoneline is registered, create a IPhoneCall object representing a call via the "softPhone.Call" method and its parameters. The first parameter is the telephone line on which we would like to initiate calls, the second parameter is the phone number to be called. In order to make your calls successful, wire up to some Call Events. Therefore, the audio data arriving from the remote end, the DTMF signal or changes in call status can be processed effectively. The wire up process is demonstrated in the sample as follows:

  		Private Sub WireUpCallEvents()
  	        AddHandler phoneCall.CallStateChanged, New EventHandler(Of CallStateChangedArgs)(AddressOf phoneCall_CallStateChanged)
  	        AddHandler phoneCall.DtmfReceived, New EventHandler(Of VoIPEventArgs(Of DtmfInfo))(AddressOf phoneCall_DtmfReceived)
  	    End Sub
  		

  CallStateChanged: this event is for displaying the changes in the call status.
  
  MediaDataRecived: the audio data from the remote end arrive via this event.
  
  DtmfReceived: this event is responsible for processing DTMF signals arriving from the remote end.
  
  To wire up to these necessary events you only need to actually start a call. You can do it with the Start() function of the call object. In this example it is the "call.Start()" line.
• Handling incoming calls: Ozeki VoIP SIP SDK publishes the incoming calls through the "ISoftPhone" InComingCall event.

  	Private Sub softPhone_IncommingCall(ByVal sender As Object, ByVal e As VoIPEventArgs(Of IPhoneCall))  
  		InvokeGUIThread(Sub()  
  	        labelCallStateInfo.Text = "Incoming call"  
  	        labelDialingNumber.Text = String.Format("from {0}", e.Item.DialInfo)  
  	        phoneCall = e.Item  
  	        WireUpCallEvents()  
  	        inComingCall = True  
  	    End Sub)  
  	End Sub  
  	

  The code sample above is for handling this. It displays incoming calls on the display and registers onto the necessary events of the object representing incoming calls which was mentioned above. The incoming call variable notifies the Pick Up button if the call is an outgoing or an incoming one.
• Ending calls: there are three different ways for ending a call that is in progress:
  • the user (this softphone) ends the call
  • the remote party ends the call
  • there is a break in network connection (error occurs and ends the call)
  You need to take care of ending the call only if you want to end it. Just like the "Pick Up" button the "Hang Up" button is also connected to the event manager.
  
  If you use the "Hang Up" button the following event manager is responsible for ending the call:

  			Private Sub buttonHangUp_Click(ByVal sender As Object, ByVal e As EventArgs) Handles buttonHangUp.Click  
  			If (Not phoneCall Is Nothing) Then  
  			    If (phoneCall.CallState = CallState.Ringing AndAlso inComingCall) Then  
  			        phoneCall.Reject()  
  			    Else  
  			        phoneCall.HangUp()  
  			    End If  
  			    inComingCall = False  
  			    phoneCall = Nothing  
  			End If  
  			    labelDialingNumber.Text = String.Empty  
  			End Sub  
  		

  Now it needs to be checked if there is an active call. If there is an active call you need to end it and delete the information related to dialing.
• Displaying call status: Ozeki VoIP SIP SDK provides the following information about the call status: ringing, InCall, Completed, Rejected etc. These call statuses are displayed via the CallStateChange event of "call" object. In this sample program I only focused on the essential options for being simple but demonstrative. Based on these essential options you can easily create further options.

  		Private Sub phoneCall_CallStateChanged(ByVal sender As Object, ByVal e As CallStateChangedArgs)
  	        InvokeGUIThread(Sub()
  	                            labelCallStateInfo.Text = e.State.ToString
  	                        End Sub)
  	        Select Case e.State
  	            Case CallState.Answered
  	                microphone.Start()
  	                connector.Connect(microphone, mediaSender)
  	                speaker.Start()
  	                connector.Connect(mediaReceiver, speaker)
  	                mediaSender.AttachToCall(phoneCall)
  	                mediaReceiver.AttachToCall(phoneCall)
  	
  	                Return
  	            Case CallState.Completed
  	                microphone.Stop()
  	                connector.Disconnect(microphone, mediaSender)
  	                speaker.Stop()
  	                connector.Disconnect(mediaReceiver, speaker)
  	                mediaSender.Detach()
  	                mediaReceiver.Detach()
  	                WireDownCallEvents()
  	
  	                phoneCall = Nothing
  	                InvokeGUIThread(Sub()
  	                                    labelDialingNumber.Text = String.Empty
  	                                End Sub)
  	                Return
  	            Case CallState.Rejected
  	                Exit Select
  	            Case CallState.Cancelled
  	                WireDownCallEvents()
  	                phoneCall = Nothing
  	                Exit Select
  	            Case Else
  	                Return
  	        End Select
  	    End Sub
  		

  The code above is only for reacting to the changes in the call status. For example: If the phone is picked up it starts the voice recording so we can send our audio data to the other party. Moreover it initializes the devices that are necessary for playing incoming audio data.
• Handling incoming audio data: since you've wired up to the MediaDataReceived event of the "call" in case of both outgoing and incoming calls, the incoming PCM audio data only needs to be forwarded to the sound system as it is demonstrated below.
• Handling outgoing audio data: the PCM audio data originating from the microphone is forwarded to the "call" object that represents the actual call via the process of SendMediaData. Then audio data is compressed by Ozeki SIP SDK with the right audio codecs and then sent to the intended person according to the built communication channel.
• Receiving DTMF signals: DTMF signals can be received similarly to audio data. Regarding processing, this sample program only displays the reference value of the received DTMF signal on the interface.

  		Private Sub phoneCall_DtmfReceived(ByVal sender As Object, ByVal e As VoIPEventArgs(Of DtmfInfo))  
  			InvokeGUIThread(Sub()  
  		        Me.labelCallStateInfo.Text = String.Format("DTMF signal received: {0} ", e.Item.Signal.Signal)  
  		    End Sub)  
  		End Sub  
  		

• Sending DTMF signals: DTMF signals can be sent after the call is established for - for example - navigating i n the IVR menu system of the called call center. Ozeki VoIP SIP SDK allows to send DTMF signals in a simple way: the "StartDTMFSignal" method is called in the object representing the given call in the following way:

  		Private Sub buttonKeyPad_MouseDown(ByVal sender As Object, ByVal e As MouseEventArgs) Handles button9.MouseDown, button8.MouseDown, button7.MouseDown, button6.MouseDown, button5.MouseDown, button4.MouseDown, button3.MouseDown, button2.MouseDown, button12.MouseDown, button11.MouseDown, button10.MouseDown, button1.MouseDown  
  			If ((Not phoneCall Is Nothing) AndAlso (phoneCall.CallState = CallState.InCall)) Then  
  			    Dim id As Integer  
  			    Dim btn As Button = TryCast(sender, Button)  
  			    If (((Not btn Is Nothing) AndAlso (Not btn.Tag Is Nothing)) AndAlso Integer.TryParse(btn.Tag.ToString, id)) Then  
  			        phoneCall.StartDTMFSignal(VoIPMediaType.Audio, id)  
  			    End If  
  			End If  
  		End Sub
  		

  According to RFC2833 the sending of the DTMF signal can represent how long the DTMF signal is being sent. In the sample program I would like to demonstrate this with the events of MouseDown and MouseUP buttons. By using MouseDown, the DTMF signal of the pressed button starts to be sent. By using MouseUP, the sending of the given DTMF signal is ended. The way of ending DTMF signal is similar to the way of start. On the object that represents the current call, the 'StopDTMFSignal' method is called in the following way (where the ID is the number-type DTMF signal according to the reference relating to the pressed button):

  			phoneCall.StopDTMFSignal(VoIPMediaType.Audio, id)
  		

• Volume control: Ozeki VoIP SIP SDK provides the possibility for controlling the volume of the microphone and the speaker. You can use a Trackbar element on the GUI for this purpose and set the actual volume according to the track bar value like in the following two functions.
  
  The volume is set every time you change the state of the tracker on the certain Trackbar. This can be implemented easily in the event handler functions for the Trackbar objects (see the following code).

  		Private Sub MicrophoneVolumeTrackbar_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MicrophoneVolumeTrackbar.Scroll  
  		    Dim volume As Single  
  		    volume = MicrophoneVolumeTrackbar.Value / 100  
  		    microphone.Volume = volume  
  		End Sub  
  		  
  		Private Sub SpeakerVolumeTrackbar_Scroll(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles SpeakerVolumeTrackbar.Scroll  
  		    Dim volume As Single  
  		    volume = SpeakerVolumeTrackbar.Value / 100  
  		    speaker.Volume = volume  
  		End Sub  
  		

  The example program sets the speaker and microphone volume according to the state of the Trackbar trackers using percentage values, but you can also use the actual value of the tracker if you want. In that case you need to delete the "/ 100" section from the code.

• How to use SIP REGISTER request
• How to make a SIP voice call
• How to accept incoming call
• How to implement Auto Answer
• Download Ozeki VoIP SDK
• Ozeki VoIP SIP SDK - Training guides and examples