How to implement SIP SMS using C#?

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 PhoneMain.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 PhoneMain.cs file:

   		private void InitializeSoftPhone()  
   		{  
   		    softPhone = SoftPhoneFactory.CreateSoftPhone("your local IP Address", 5700, 5750);  
   		    softPhone.IncomingCall += softPhone_IncomingCall;
   		    phoneLine = softPhone.CreatePhoneLine(new SIPAccount(true, "oz891", "oz891", "oz891", "oz891", "192.168.91.212", 5060));
   		    phoneLine.PhoneLineInformation += phoneLine_PhoneLineInformation;
   		  
   		    softPhone.RegisterPhoneLine(phoneLine);  
   		} 
   		

   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));
   		

4. When you are finished you only need to build and run the program.

public partial class PhoneMain : Form  
{  
    ISoftPhone softPhone;  
    IPhoneLine phoneLine;  
    PhoneLineState phoneLineInformation;  
    IPhoneCall call;  
    bool inComingCall;  
    SIPMessageLogger sipMessageLogger;  
...  

private void InitializeSoftPhone()  
{  
    try  
    {  
        softPhone = SoftPhoneFactory.CreateSoftPhone(SoftPhoneFactory.GetLocalIP(), 5700, 5750);  
        softPhone.IncomingCall += softPhone_IncomingCall;  
        SIPAccount sipAccount = new SIPAccount(true, "o875", "oz875", "oz875", "oz875", "192.168.112.100", 5060);  
    	phoneLine = softPhone.CreatePhoneLine(sipAccount);  
        phoneLine.RegistrationStateChanged += phoneLine_PhoneLineInformation;  

        softPhone.RegisterPhoneLine(phoneLine);  

	    sipMessageLogger = new SIPMessageLogger();  
	    sipMessageLogger.SIPMessageReceived += (sipMessageLogger_SIPMessageReceived);  
	    Logger.Attach(sipMessageLogger);  
	    Logger.Open(LogLevel.Information);  
    }  
    catch(Exception ex)  
    {  
	    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());  
    }
}  

• Handling outgoing calls: for establishing an outgoing call, enter the number you wish to dial. Then press 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 void buttonPickUp_Click(object sender, EventArgs e)  
  		{  
  		    if (inComingCall)  
  		    {  
  		        inComingCall = false;  
  		        call.Answer();  
  		        return;  
  		    }  
  		  
  		    if (call != null)  
  		        return;  
  		  
  		    if (string.IsNullOrEmpty(labelDialingNumber.Text))  
  		        return;  
  		  
  		    if (phoneLineInformation != RegState.RegistrationSucceeded && phoneLineInformation != RegState.NoRegNeeded)  
  		    {  
  		        MessageBox.Show("Phone line state is not valid!");  
  		        return;  
  		    }  
  		  
  		    call = softPhone.CreateCallObject(phoneLine, labelDialingNumber.Text);  
  		    call.CallStateChanged += call_CallStateChanged;
  		    call.Start();  
  		}  
  		

  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 an IPhoneCall object representing a call via the "softPhone.Call" method and its parameters. The first parameter is the telephone line on which you 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.
  
  To subscribe for these necessary events you only need to actually start a call. You can do it with the Start() method 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 void softPhone_IncomingCall(object sender, VoIPEventArgs<IPhoneCall> e)  
  		{  
  		    InvokeGUIThread(() =>  
  		        {  
  		                labelCallStateInfo.Text = "Incoming call";  
  		                labelDialingNumber.Text = String.Format("from {0}", e.Item.DialInfo);  
  		                call = e.Item;  
  		                call.CallStateChanged += call_CallStateChanged;
  		                inComingCall = true;  
  		        });  
  		}
  		

  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 can take care of ending the call by pressing the Hang Up button. Just like the "Pick Up" button the "Hang Up" button is also connected to the event manager.
  
  If you press the "Hang Up" button the following event manager is responsible for ending the call:

  		private void buttonHangUp_Click(object sender, EventArgs e)  
  		{  
  		if (call != null)  
  		{  
  		    inComingCall = false;  
  		    call.HangUp();  
  		    call = null;  
  		}  
  		labelDialingNumber.Text = string.Empty;  
  		} 
  		

  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 option you can easily create further options.

  		private void call_CallStateChanged(object sender, CallStateChangedArgs e)  
  		{  
  		    InvokeGUIThread(() => { labelCallStateInfo.Text = e.State.ToString(); });  
  		  
  		    switch (e.State)  
  		    {  
  		        case CallState.Completed:  
  		            call.CallStateChanged -= call_CallStateChanged;
  		            call = null;  
  		            InvokeGUIThread(() => { labelDialingNumber.Text = string.Empty; });  
  		            break;  
  		        case CallState.Cancelled:  
  		            call.CallStateChanged -= call_CallStateChanged;
  		            call = null;  
  		            break;  
  		    }  
  		}  
  		

  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 you 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 we 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. Beside, audio data is also stored for later keyword analysis.
• Outgoing DTMF signals: DTMF signals can be sent after the call is established for - for example - navigating in 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 void buttonKeyPadButton_MouseDown(object sender, MouseEventArgs e)  
  		{  
  		    if (call != null && call.CallState == CallState.InCall)  
  		    {  
  		        var btn = sender as Button;  
  		        if (btn != null)  
  		        {  
  		            int id;  
  		  
  		            if (btn.Tag != null && int.TryParse(btn.Tag.ToString(), out id))  
  		            {  
  		                call.StartDTMFSignal((DtmfNamedEvents)id);  
  		            }  
  		        }  
  		    }  
  		}  
  		

  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):

  		call.StopDTMFSignal((DtmfNamedEvents)id);
  		

• Monitoring SIP messages: Ozeki VoIP SIP SDK transforms the content of SIP messages in a very simple way. For this purpose you only need to sign up to an event:

  		sipMessageLogger.SIPMessageReceived += (sipMessageLogger_SIPMessageReceived);
  		

  Now you need to check the content of messages:

  		void sipMessageLogger_SIPMessageReceived(object sender, GenericEventArgs<string> e)  
  		    {  
  		        if (e.Item.Contains(txb_SIPText.Text))  
  		        {  
  		            SendSMS();  
  		        }  
  		    }  
  		

  If there is a match for the searched SIP text section, an SMS will be sent. Sending of messages is done by an SMS gateway software. An HTTP request is sent to the HTTP API of the SMS gateway software. Finally, the SMS gateway sends out the SMS message to the recipient.
  
  For this purpose it is recommended to use a stable and reliable SMS gateway software. Such a stable SMS gateway is Ozeki NG SMS Gateway software. You can download it from http://www.ozekisms.com.

  		private void SendSMS()  
  		{  
  		    string url =  
  		    string.Format(@"http://{0}/api?action=sendmessage&username={1}&password={2}&recipient={3}&messagetype=SMS:TEXT&messagedata={4}",  
  		        Txb_IpAddress.Text, txb_UserName.Text,  
  		        Txb_Password.Text, Txb_recipient.Text,  
  		        Txb_SmsText.Text);  
  		
  		    WebRequest request = WebRequest.Create(url);  
  		
  		    request.GetResponse();  
  		}
  		

• 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