Programmable Voice

  1. Home
  2. Docs
  3. Programmable Voice
  4. Tutorials
  5. IVR with Transfer

IVR with Transfer

This tutorial is a walk-through explanation of the IVR with Transfer sample solution that can be downloaded from your demo dashboard. If you haven’t already, sign up for a demo account and get 100 minutes of free call time for the next 30 days with the Voice Elements servers. This tutorial covers the basics of how to take an incoming call and route it to a different phone number.

It is important to note that this project is set up to run either as a windows service or as a Windows form.  While you are debugging, you will want to simply start the application using the default Windows form.  Once you are ready to deploy for production, we recommend that you install as a Windows Service. See the documentation for .net windows services here.

Download the Sample Solution

You will find this sample solution in your demo dashboard.  Once you have the project downloaded, unzip it and open IVRTransfer.sln with Visual Studio. This application is already complete and ready to go, so you can test it out to see what it does before you start to read through the code to see how it works.  When you first compile the solution, it will automatically get the Voice Elements Client from NuGet.

Three Main Classes in this Project

This project contains three main classes that you should pay attention to: IvrApplicationInboundCall, and TransferCall.


The core class of this project is IvrApplication. This class contains a lot of logic that sets up the application as a windows service so you can ignore a lot of the code in it for now. The most important method here is MainCode().


When the application is run, it starts a new thread which runs MainCode(). This connects to the Voice Elements servers in the cloud. Then loops indefinitely checking for new tasks to run, and inbound call events.


Note that Log.Write() is used frequently to log call progress and help with debugging. It is recommended that you continue to do this as you program your own Voice Elements applications.

The first thing MainCode() does is connect to the Voice Elements servers. This is done by constructing a new TelephonyServer object passing in server IP, username, and password as parameters. These values have already been generated for your account but you can change them in your Settings.settings file.

MainCode() also sets the CacheMode on the TelephonyServer object. ClientSession mode means that the server will stream and cache the files to and from your client machine. These files are flushed after you disconnect. Server mode means that the files reside on the server and will use the full path name to find them there. Note that Server mode can only be used on your own dedicated Voice Elements server.

After connecting to the server and setting its cache mode the new call event should be subscribed to. This sets a method to be called when an incoming call is received. In this example, TelephonyServer_NewCall() is the method to be called on new incoming call events.


RegisterDNIS() is then called on the TelephonyServer to tell the server which phone numbers the application will handle. This method can be called with no parameters to instruct Voice Elements to handle calls from all phone numbers on your account. Otherwise you can specify numbers to handle as parameters.

    Log.Write("Connecting to: {0}", Properties.Settings.Default.PhoneServer);

    m_telephonyServer = new TelephonyServer("gtcp://" + Properties.Settings.Default.PhoneServer, Properties.Settings.Default.UserName, Properties.Settings.Default.Password);

    m_telephonyServer.CacheMode = VoiceElements.Interface.CacheMode.ClientSession;

    // SUBSCRIBE to the new call event.
    m_telephonyServer.NewCall += new VoiceElements.Client.NewCall(TelephonyServer_NewCall);

    // Subscribe to the connection events to allow you to reconnect if something happens to the internet connection.
    // If you are running your own VE server, this is less likely to happen except when you restart your VE server.
    m_telephonyServer.ConnectionLost += new ConnectionLost(TelephonyServer_ConnectionLost);
    m_telephonyServer.ConnectionRestored += new ConnectionRestored(TelephonyServer_ConnectionRestored);

Inbound Call

The InboundCall class is designated to handle most of the logic for an inbound call. When an inbound call event is generated and the TelephonyServer_NewCall method in IvrApplication is called.


An object of the InboundCall class is constructed with the TelephonyServer and ChannelResource objects as parameters. The RunScript() method is then called on the new InboundCall object.

static void TelephonyServer_NewCall(object sender, VoiceElements.Client.NewCallEventArgs e)
        Log.Write("NewCall Arrival! DNIS: {0} ANI: {1} Caller ID Name: {2}", e.ChannelResource.Dnis,
        e.ChannelResource.Ani, e.ChannelResource.CallerIdName);

        if (string.IsNullOrEmpty(TransferNumber))
        Log.Write("WARNING - You have not entered a transfer number so the call will go to voicemail!!");

        // Handle The New Call Here
        InboundCall inboundCall = new InboundCall(m_telephonyServer, e.ChannelResource);
    catch (Exception ex)
        Log.WriteException(ex, "IvrApplication::NewCall");

The RunScript() method contains the logic for handling this inbound call. This method first checks to see if the number that is calling is blocked.


If so then the RejectCall() method is called. If the call is not rejected the method proceeds to answer the call and play a recorded message.


The TerminationCodeFlag() method is called on the ChannelResource to determine if the message has completed playing. If so then a tone is played.


The ReceiveDigits() method is then called. A switch statement is then used to determine what to do based on the caller’s input.

StartTransfer() and RecordVoicemail()

It will either choose to transfer the call to another number by calling StartTransfer() or to record a voicemail using the RecordVoicemail() method.

    // Reject calls from blocked numbers
    if (string.IsNullOrEmpty(m_channelResource.Ani) || m_channelResource.Ani == "0000000000")

    // Answer the call
    Log.WriteWithId(m_channelResource.DeviceName, "Answering...");

    // Play a recorded message
    Log.WriteWithId(m_channelResource.DeviceName, "Playing prompt...");

    // If the entire message played to the end, play a tone so the user knows they are at the end of the message
    if (m_voiceResource.TerminationCodeFlag(TerminationCode.EndOfData))
        m_voiceResource.PlayTone(1000, 100, 500);

    // Get digits from the caller
    string digits = ReceiveDigits();

    // If no phone number was entered on the form yet, we can't transfer the call
    // so we will send it to voicemail instead
    if (string.IsNullOrEmpty(IvrApplication.TransferNumber))
        Log.WriteWithId(m_channelResource.DeviceName, "No phone number has been entered on the form yet, so call will go to voicemail");

    // If a number was entered, we will handle the option selected by the caller
    switch (digits)
        case "1":
        case "2":
        case "3":

RejectCall(), RouteHalf(), and RouteFull()

The RejectCall() method and the use of RouteHalf() and RouteFull():

private void RejectCall()
    Log.Write("Rejecting call...");

    // Half route the channel to the voice resource

    Log.Write("Playing busy");
    // Play a busy sound file

    // Disconnect the call

    // Route the channel back to its voice resource

    Log.Write("Call rejected");


Voice Methods


The ReceiveDigits() method accepts numeric input from the inbound caller and returns that input as a string. The first step to getting numeric input is to instruct the VoiceResource object not to clear the digit buffer on the next voice function. In this way, if the user began pressing digits during the previous play, those digits will not get lost.

You must then instruct the VoiceResource object as to how many digits to return. In this case the maximum number of digits that will be recorded is 1. You can then set a maximum wait time for the digits to be input. You can also set a termination digit that when pressed no more digits will be recorded.


You then call the GetDigits() method on the VoiceResource object. This will record the input digits into the DigitBuffer of the VoiceResource object when the above conditions are met. You can then store this string into a variable to be returned after instructing the VoiceResource object to start clearing the digit buffer again.

private string ReceiveDigits()
    string digits = string.Empty;

    // Use the log file often to help with debugging.
    Log.Write("Receiving digits...");

    // Instruct the voice resource NOT to clear the digit buffer on the next voice function.
    // In this way, if the user began pressing digits during the previous play, those digits will not get lost.
    m_voiceResource.ClearDigitBuffer = false;

    // Instruct the voice resource to return a maximum of 1 digit
    m_voiceResource.MaximumDigits = 1;

    // Only wait 5 seconds to get digits
    m_voiceResource.MaximumTime = 5;

    // Instruct the voice resource to terminate the next voice function on just a "#" DTMF digit.
    // If the user presses this key, it will not be included in the digit buffer.
    m_voiceResource.TerminationDigits = "#";

    // Wait until the above condition are met.

    digits = m_voiceResource.DigitBuffer;
    // Log the response
    Log.Write("Digits Returned: " + m_voiceResource.DigitBuffer);

    // On the next voice function, clear the digit buffer.
    m_voiceResource.ClearDigitBuffer = true;

    return digits;

RecordVoicemail() and PlayTTS()

The RecordVoicemail() method contains the basic structure for recording a voice mail. The caller is first prompted to record a message with the PlayTTS() method. A filename is also created and stored as a string.

The TerminationDigits property can be set. This sets the next voice function to terminate on the input of any of these digits.

The MaximumTime property can also be set. This sets the recording to terminate after a set amount of time.


The Record() method is then called on the VoiceResource with the desired file name as a parameter.

At this point the program is recording and will stop recording when on of the TerminationDigits is pressed by the caller.

private void RecordVoicemail()
    Log.WriteWithId(m_channelResource.DeviceName, "Playing voicemail prompt...");

    // Play voicemail prompt

    string filename = "VM_ " + DateTime.Now.ToString("yyMMdd.hh:mm:ss") + m_voiceResource.DeviceName + ".wav";

    // Log Often
    Log.WriteWithId(m_channelResource.DeviceName, "Recording to " + filename);

    // On the next voice function, stop on any DTMF digit.
    m_voiceResource.TerminationDigits = "ANY";

    // Let the voicemail record for up to 3 minutes
    m_voiceResource.MaximumTime = 180;

    // Record the caller's message to the local hard disk

    // On the next voice function, clear the digit buffer
    m_voiceResource.ClearDigitBuffer = true;


Let’s look at how transferring a call with Voice Elements works.


The InboundCall class contains the StartTransfer() method which, when called, constructs a new TransferCall object, passing in the TelephonyServer, ChannelResource, VoiceResource, and playMusicOnHold as parameters.


The TransferCall class contains all of the logic for handling call transfer. The ToPhone() method is then called on the new TransferCall object passing in the phone number to be transferred to and the server phone number as parameters.

private void StartTransfer(bool playMusicOnHold)
    Log.WriteWithId(m_channelResource.DeviceName, "Transferring call...");

    // We will create a new instance of the TransferCall and let it 
    // handle the transfer
    TransferCall call = new TransferCall(m_telephonyServer, m_channelResource, m_voiceResource, playMusicOnHold);
    call.ToPhone(IvrApplication.TransferNumber, Properties.Settings.Default.TestPhoneNumber);

ToPhone() contains all of the logic for transferring a phone call.

    // Subscribe to the disconnect events so e
    m_outboundChannelResource.Disconnected += new Disconnected(OutboundChannelResource_Disconnected);
    m_parentChannelResource.Disconnected += new Disconnected(ParentChannelResource_Disconnected);

    // Get the outbound voice resource
    m_outboundVoiceResource = m_outboundChannelResource.VoiceResource;

    if (m_playMusicOnHold)
        // Start playing music on hold to the caller
        m_musicOnHold = new MusicOnHold(m_parentVoiceResource, "..\\..\\AudioFiles\\Music.wav");
        // If we aren't playing music, we will route early so the caller can hear ringing

    m_outboundChannelResource.CallProgress = CallProgress.WaitForConnect;
    m_outboundChannelResource.OriginatingPhoneNumber = callerID;

    // Limit the amount of time for the phone to answer
    m_outboundChannelResource.MaximumTime = 60;

    // Place the call
    m_dialing = true;
    DialResult dr = m_outboundChannelResource.Dial(phone);
    m_dialing = false;

    Log.Write("The dial result for {0} was: {1}", phone, dr);

    switch (dr)
        case DialResult.Connected:
        case DialResult.HumanDetected:
        case DialResult.MachineDetected:
        case DialResult.Successful:
            connected = true;
            // If it wasn't answered properly, we won't let it continue

    // If we were playing music on hold, stop playing and route the 
    // two calls together
    if (m_playMusicOnHold && connected)
        m_musicOnHold = null;

        // This will let both legs hear each other 

    // If record the call is selected, we will start the recording now
    if (IvrApplication.RecordCall)
        string filename = "RC_" + DateTime.Now.ToString("yyMMddhhmmss") + m_outboundChannelResource.DeviceName + ".wav";

        // Start recording the conversation
        m_recordConversation = new RecordConversation(m_telephonyServer, m_parentChannelResource, m_outboundChannelResource, filename);

    // Let the call run until one of the channels disconnects
Was this article helpful to you? Yes 15 No

How can we help?