Source code explanation for using the C# SIP softphone source of Ozeki VoIP SDK for creating a SIP SMS example

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SIP_SMS_Example.zip

This page includes the detailed source code explanation for using the C# SIP softphone source of Ozeki VoIP SDK for creating a SIP SMS example.

Graphical User Interface

The sample program has been made by the Microsoft Windows Forms Presentation technology that is well known for Microsoft .Net developers. The basic aspect of the created interface was to demonstrate the services that Ozeki VoIP SIP SDK offers so it omits the visual elements. It has all the functions that a softphone needs like call initiation, receiving calls, sending and receiving DTMF signals, event display on the display screen.

For being demonstrative, the interface of the sample program includes a section for SMS sending (Figure 1). This section would probably be hidden in a real environment but for sake of representativeness it has been visualized in this sample program.

Now let's see the interface. In IPAddress field the IP address of the SMS server needs to be entered with which you wish to send SMS messages. Below this edit box, the User name and Password can be specified that are related to the SMS server. In SIP text field you can specify the SIP message part that will trigger the SMS sending. In Recipient filed you can enter the telephone number of the recipient. In SMS text field you can compose the body of the SMS message.

Figure 1 - SMS sending interface

Running the program

After running the program the telephone automatically registers to the given SIP PBX with the given SIP account. If the registration process is ended successfully we can see Registration succeeded on the display. From this point the softphone is ready to establish and receive calls, to send and receive DTMF signals during calls for navigating in IVR systems. (The source code of the sample program includes settings that depend on the environment so after the download do not forget to customize it. After ending the call a notification is also received about the mentioned keywords.

Code

PhoneMain.cs code-behind file belonging to the program interface describes the control events related to the interface and connects the GUI with the logics. The sample program focuses on simplicity and representativeness. The PhoneMain.cs file includes the full logic of the sample program. By opening this PhoneMain.cs file, you can see a few lines of declaration right the beginning that are needed for the use of Ozeki VoIP SIP SDK.

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

ISoftphone:
It represents a telephone, and its telephone line is represented by an IPhoneLine object. It is also possible to develop a multiline phone.

Iphoneline:
It represents a telephone line that we can register to a SIP PBX, for example, Asterisk, 3CX, or to other PBXs that are offered by free SIP providers. Registration is made via a SIP account.

PhoneLineState:
It is an enum type that represents the telephone line status related to the PBX. For example registered, not registered, successful/unsuccessful registration.

IphoneCall:
It represents a call: the status of the call, the direction of the call, on which telephone line it was created, who is the called person, etc.

The softphone is initialized after loading the GUI

By subscribing to the 'Loaded' event of the Windows Form windows, it is possible to start the initialization and registration of Ozeki SDK softphone right after 'PhoneMain' window is loaded.

private void InitializeSoftPhone()
{
                try
                {
                        softPhone = SoftPhoneFactory.CreateSoftPhone(SoftPhoneFactory.GetLocalIP(), 5700, 5750, 5700);
                        softPhone.IncomingCall += new EventHandler<VoIPEventArgs<IPhoneCall>>(softPhone_IncomingCall);
                        SIPAccount sipAccount = new SIPAccount(true, "o875", "oz875", "oz875", "oz875", "192.168.112.100", 5060);
        phoneLine = softPhone.CreatePhoneLine(sipAccount, new NatConfiguration(NatTraversalMethod.None, ""), TransportType.Udp);
                        phoneLine.PhoneLineStateChanged += new EventHandler<VoIPEventArgs<PhoneLineState>>(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());
                }
}

Create an instance of the phone via the ’softPhone’ object and give the IP address of your computer and the port domain that can be used by the phone. Finally specify the port, at which the SIP messages arriving from the PBX are listened, as the last parameter.

Subscribe to the event that handles incoming calls of the telephone (’softPhone.IncomingCall’) that occurs when there is an incoming call from the remote end.

Create a phoneLine with a SIP account that can be the user account of your corporate SIP PBX or a free SIP provider account. To display the status of the created telephone line, sign up to its ’phoneLine.PhoneLineInformation’ event.

When these things are done you only need to register the created ’phoneLine’ to the ’softPhone’. In this example only one telephone line is registered but of course multiple telephone line registration is also available.

After these steps you only need to deal with the handling of the calls and to display them onto the GUI.

Handling the calls

Ozeki SDK represents the incoming and outgoing calls through the IpPhoneCall interface. This interface includes the status of the given call, on which line it was created and who the called person is. On this object we can pick up or hang up calls. Let’s see the event of the sample program.

a. Outgoing Call

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.Accept();
        return;
    }

    if (call != null)
        return;

    if (string.IsNullOrEmpty(labelDialingNumber.Text))
        return;

    if (phoneLineInformation != PhoneLineState.RegistrationSucceeded && phoneLineInformation != PhoneLineState.NoRegNeeded)
    {
        MessageBox.Show("Phone line state is not valid!");
        return;
    }

    call = softPhone.CreateCallObject(phoneLine, labelDialingNumber.Text);
    call.CallStateChanged += new EventHandler<VoIPEventArgs<CallState>>(call_CallStateChanged);
    call.CallErrorOccured += new EventHandler<VoIPEventArgs<CallError>>(call_CallErrorOccured);
    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 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. Via the CallErrorOccured event above you can receive information about the reasons why the call was not created. For example: the called party is busy, the call is rejected, the called number does not exist or the called number is not available.

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.

b. Handling incoming calls

The 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 += new EventHandler<VoIPEventArgs<CallState>>(call_CallStateChanged);
                call.CallErrorOccured += new EventHandler<VoIPEventArgs<CallError>>(call_CallErrorOccured);
                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.

c. Ending a call in progress

There are three different ways for ending a call that is in progress.

• We end the call
• The remote end ends the call
• There is a break in network connection

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.

d. 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, VoIPEventArgs<CallState> e)
{
    InvokeGUIThread(() => { labelCallStateInfo.Text = e.Item.ToString(); });

    switch (e.Item)
    {
        case CallState.Completed:
            call.CallStateChanged -= new EventHandler<VoIPEventArgs<CallState>>(call_CallStateChanged);
            call.CallErrorOccured -= new EventHandler<VoIPEventArgs<CallError>>(call_CallErrorOccured);
            call = null;
            InvokeGUIThread(() => { labelDialingNumber.Text = string.Empty; });
            break;
        case CallState.Cancelled:
            call.CallStateChanged -= new EventHandler<VoIPEventArgs<CallState>>(call_CallStateChanged);
            call.CallErrorOccured -= new EventHandler<VoIPEventArgs<CallError>>(call_CallErrorOccured);
            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 we can send our audio data to the other party. Moreover it initializes the devices that are necessary for playing incoming audio data.

e. Handling audio data arriving from the remote end

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.

f. Forwarding incoming audio from the microphone to the remote end via the SDK

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.

g. Sending 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);

h. 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 only 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();
 }

Further development possibilities

This sample program is only for handling one telephone line. However, Ozeki VoIP SIP SDK offers the opportunity to develop and handle multiple telephone lines simultaneously. Moreover further functions can also be implemented effectively like call forwarding and chat function. If the above mentioned functions have called your attention contact us at info@voip-sip-sdk.com!


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