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Posted 15 Jul 2005


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TAPI 3.0 Application development using C#.NET

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15 Jul 20054 min read
This is a sample telephony application which will help you to develop applications using TAPI 3.0 API and C#.NET. Here basic knowledge about TAPI is assumed.

Sample Image


This is a C# program which will exemplify the procedure which needs to be followed while doing TAPI programming using TAPI 3.0. Hence it can also be useful for VB.NET developers seeking TAPI 3.0 sample code for .NET. Here basic knowledge about TAPI and other related terms is assumed. To have more knowledge on TAPI 3.0, contact me on my email address or refer to the help provided in MSDN.


Hello, myself Gohel Devang M., 20 years old, Information Technology student. This is my first attempt to put some sample code on any site so if you do have any problems mail me at

This is a sample code to interface TAPI 3.0 API using .NET platform and C# as language. So people interested in developing telephony applications using C# will find this very useful. I was inspired to do this because I was not able to find such code on this site.

Initial steps

The first thing you need to start working on TAPI 3.0 API is to add the references to your project. To do that first create a new project or open an existing project, then right click on the solution file in Solution Explorer. This will open a dialog box showing three tabs as below:

Image 2

Then click on Browse button and select the tapi3.dll file from your windows\system32 or windows\system directory and click OK. Then press OK in the dialog box that had popped when you select Add references from the right click popup menu of the Solution Explorer.

Now you are ready to work with TAPI 3.0.

Using the code

The second thing you need to do is create the TAPI objects to initialize the TAPI 3.0 TSP (TAPI Service Providers). To have more information on TSP and what TAPI is all about, please refer to help provided in the MSDN .NET documentation. The code below is a declaration of the TAPI object and addresses the interfaces that will hold the addresses which are responsible for call handling, and basic call control interface which will hold the reference to the object that will be responsible for handling basic operations of the call.

private TAPIClass tobj;
private ITAddress[] ia=new TAPI3Lib.ITAddress[10];
private ITBasicCallControl bcc;

The code below is responsible for initializing a TAPI object so that it can be used by our application. The main functions are:

  • Initialize() will initialize TAPI.
  • EnumerateAddresses() will give the list of available TSPs.
void initializetapi3()
        tobj = new TAPIClass();
        IEnumAddress ea=tobj.EnumerateAddresses();
        ITAddress ln;
        uint arg3=0;
        cn=new callnotification();
        cn.addtolist=new callnotification.listshow(this.status);
        tobj.ITTAPIEventNotification_Event_Event+= new 
        for(int i=0;i<10;i++)
            ea.Next(1,out ln,ref arg3);
    catch(Exception e)

The code below is responsible for registering incoming calls so that they can be handled by our application. For that you need to select the line on which you want to receive calls and press the Register button.

    MessageBox.Show("Registration token : "+ 
                 "Registration Succeed for line "+line);
catch(Exception ein)
    MessageBox.Show("Failed to register on line "+line,"Registration for calls");

The class given below is to be added depending upon your TAPI event handling requirements. This is specially designed according to the requirements of the application.

class callnotification:TAPI3Lib.ITTAPIEventNotification
    public delegate void listshow(string str);
    public listshow addtolist;
    public void Event(TAPI3Lib.TAPI_EVENT te,object eobj)
                addtolist("call notification event has occured");
                TAPI3Lib.ITDigitDetectionEvent dd = 
                addtolist("Dialed digit"+dd.ToString());
                TAPI3Lib.ITDigitGenerationEvent dg = 
                MessageBox.Show("digit dialed!");
                addtolist("Dialed digit"+dg.ToString());
                addtolist("A phone event!");
                addtolist("Gather digit event!");
            case TAPI3Lib.TAPI_EVENT.TE_CALLSTATE:
                TAPI3Lib.ITCallStateEvent a= 
                TAPI3Lib.ITCallInfo b=a.Call;
                case TAPI3Lib.CALL_STATE.CS_INPROGRESS:
                case TAPI3Lib.CALL_STATE.CS_CONNECTED:
                case TAPI3Lib.CALL_STATE.CS_DISCONNECTED:
                case TAPI3Lib.CALL_STATE.CS_OFFERING:
                    addtolist("A party wants to communicate with you!");
                case TAPI3Lib.CALL_STATE.CS_IDLE:
                    addtolist("Call is created!");

How to handle H.323 or IP calls?

To do IP calls or H.323 calls, you need to make a checkbox named H.323 call(IP call) enabled and enter the IP address of the destination and press the Call button. Otherwise it will not succeed in calling to the remote destination. To receive H.323 calls or IP calls, you need to first register on the line on which you want to receive IP calls and check the checkbox named h.323 call(IP call).

How to answer an incoming call

The incoming calls will give notification in the call status area. Then according to whether you want to accept or reject the call, you check the checkbox named Reject to reject incoming calls, and press Answer or simply press Disconnect. To accept calls, do not check Reject checkbox and simply press Answer button which will connect to the call.

How to transfer a call

To transfer a call, first there should be one active call existing. Then you can specify the address to which the call is to be transferred to, as shown in the figure:

Image 3

Here I have specified the internet address since the call was an IP call. To provide this functionality, there is one function in IBasicCallControl named BlindTransfer(String transfferaddress). Refer the MSDN documents for more information on that!

Points of Interest

My interest is in developing more and more TAPI 3.0 applications using .NET as the platform. I am also interested in J2EE application development. My other areas of interest are:

  • VC++
  • Crystal Reports

and many other thing in my reach.


Latest revised version. This is the first release of this code so if you do have any suggestions they are always welcomed by me.


This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here


About the Author

Web Developer
India India
Hi,I am 21 year old student of information technology.I am interested to develop Computer telephony integeration softwares. I am also interested in deploying crystal reports, Directx programming and device driver implementation using VC++.Currently i am pursuing my degree at Nirma Institute of Technology,Gujarat(india).
Skills :,,VC++(MFC)

Comments and Discussions

QuestionIt is not displaying my service provider in the list Pin
Mahadevan Venkatesan2-Oct-19 19:52
MemberMahadevan Venkatesan2-Oct-19 19:52 
Questionwhat is Proper hardware for this code Pin
aref_it6-Sep-19 21:41
Memberaref_it6-Sep-19 21:41 
QuestionTAPI 3.0 Application development using C#.NET Pin
Member 1435936613-May-19 19:12
MemberMember 1435936613-May-19 19:12 
QuestionCouldn't register for any line of communication Pin
Member 137524694-Apr-18 1:48
MemberMember 137524694-Apr-18 1:48 
Questioncan you able to take project? Pin
Member 134402441-Oct-17 18:41
MemberMember 134402441-Oct-17 18:41 
QuestionCan i use this code with GSM Modem? If Yes Please share Modify Code. Pin
Member 1337933328-Aug-17 3:55
MemberMember 1337933328-Aug-17 3:55 
QuestionCall recording using TAPI Pin
nitin-aem26-Jul-17 0:22
Membernitin-aem26-Jul-17 0:22 
QuestionTapi don't sometimes answer or reject calls Pin
amagitech6-Apr-17 0:25
Memberamagitech6-Apr-17 0:25 
AnswerRe: Tapi don't sometimes answer or reject calls Pin
Member 1320383116-May-17 2:15
MemberMember 1320383116-May-17 2:15 
QuestionGetting following error on listbox Pin
Member 129875147-Feb-17 4:58
MemberMember 129875147-Feb-17 4:58 
QuestionHow to transfer call from in c# ?? Pin
Jignesh Patel 428225-Nov-16 0:08
MemberJignesh Patel 428225-Nov-16 0:08 
QuestionHow to GetCallInformation and Transfer call In with c# ? Pin
Jignesh Patel 42827-Nov-16 0:19
MemberJignesh Patel 42827-Nov-16 0:19 
QuestionDevelopment Environment Pin
pæperclip2-Aug-16 4:45
Memberpæperclip2-Aug-16 4:45 
QuestionNot able to fetch callerid Pin
sarath1er20-Jun-16 20:05
Membersarath1er20-Jun-16 20:05 
Questionregister failed values Pin
Pradeep Kadnor14-Nov-15 8:45
MemberPradeep Kadnor14-Nov-15 8:45 
AnswerRe: register failed values Pin
Member 1291214919-Dec-16 4:23
MemberMember 1291214919-Dec-16 4:23 
QuestionRegisterCallNotifications(..) and SetQOS(..) always failed Pin
zxmlxclyj23-Oct-15 10:36
Memberzxmlxclyj23-Oct-15 10:36 
Questiongot exception button2_click Pin
okansarica5-Aug-15 22:07
Memberokansarica5-Aug-15 22:07 
Questiondoes not work with win 7 or 8 Pin
Member 1152549214-Mar-15 14:28
MemberMember 1152549214-Mar-15 14:28 
AnswerRe: does not work with win 7 or 8 Pin
Naveed Yousaf13-May-15 23:50
professionalNaveed Yousaf13-May-15 23:50 
GeneralRe: does not work with win 7 or 8 Pin
Pratik19Chaudhari27-Nov-15 19:30
MemberPratik19Chaudhari27-Nov-15 19:30 
QuestionEvent Forwarding Pin
Member 1124369018-Nov-14 2:34
MemberMember 1124369018-Nov-14 2:34 
Questionhow can register H323 protocol in window7 os and use with tapi3.0 in c#? Pin
upendra205865-Oct-14 18:37
Memberupendra205865-Oct-14 18:37 
AnswerRe: how can register H323 protocol in window7 os and use with tapi3.0 in c#? Pin
upendra205865-Oct-14 18:41
Memberupendra205865-Oct-14 18:41 
QuestionProblem Pin
g@urav12328-Aug-14 2:04
Memberg@urav12328-Aug-14 2:04 

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