Creating calls and conferences using 3CX Call Control API

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By default, 3CX provides the HTTP API to allow users to make calls on the PBX programmatically as well as changing some other extension settings. However, the HTTP API is pretty limited and a better way is to use the Call Control API to have more controls on how calls are created.

Although the Call Control API is available on both 3CX version 12 and 11, the library DLLs (3cxpscomcpp2.dll and sl.dll) used by the DLL are not interchangeable between the two versions. This means you will probably need to build two versions of your application referencing the different versions of the libraries if you wish to target both 3CX version 11 and 12. Also it is advised to keep a local copy of 3cxpscomcpp2.dll (and sl.dll) in your application and add a reference to the local copy, and not the version of the DLL found in the .NET Global Assembly Cache (GAC). In my test, referencing the GAC version may result in problems finding the 3CX assembly when the application is run on a different machine.

Making calls

To make a call connecting two extensions on the PBX, use the following method:

public void MakeCall(
string dn_from,
string number_to

The source number, dn_from can be any internal number on the PBX and number_to can be any internal or external number. 3CX will call dn_from waiting for the call to be answered, upon which number_to will be called. When number_to picks up the call, dn_from and number_to will be able to talk to each other. This process is also known as callback.

While number_to can be any internal or external number, dn_from can only be an internal number. This means you will not be able to use this method to connect two arbitrary PSTN numbers via 3CX.

Conferencing on 3CX version 11

To initiate the simplest conference you can use

MakeCall(701, 101)

where 701 is the first conference extension on the system and 101 is the extension number. If 701 does not currently have any conference in progress, this will make a call to 101 informing the extension that a new conference will be created with the extension being the first participant and other people calling 701 will be able to join this conference. If a conference is already in progress, extension 101 will be able to join the existing conference.

The number of maximum simultaneous conference can be configured inside Settings > Advanced:

The above settings will create 4 conference extensions 701-704 on the system, viewable from System Extension Status from the 3CX web portal. A default conference extension 700 will also be created but cannot be used to make conference calls programmatically. From the call control API, extension 700 will be treated as a ConferencePlaceExtension with IsGateway property set to TRUE. User can still call 700 to create a new conference.

To have more controls on the created conference, use the following method:

public void MakeCall(
string dnNumber,
Dictionary<string, string> parameters

where dnNumber is a conference extension which is not a gateway and parameters is dictionary containing the following parameters:

“tojoin” – number to dial. Specifies destination of call.
“PIN” – the pin of this conference. Can be empty.
“noname” – “0” or “1”. Only for initial call. Conference place will not ask new members to pronounce name before entering this conference call but will ask to confirm participation. Will inform participants about joining and leaving but without name.
“instant” – “0” or “1”. Only for initial call. Conference is instant. Conference place will not ask member to confirm participation

For example, to create a conference to extension 100 that begins immediately, does not ask members for name or PIN code, use the following set of parameters:

{“tojoin”:”100″, “PIN”:””, “noname”:”1″, “instant”:”1″}

Conferencing on 3CX version 12

On 3CX version 12, major changes have been implemented in the conference architecture and associated APIs. There are no longer separated conference extensions (e.g. 701-704) on the system. Rather, there is only a single conference extension (700) and each extension will have its own conference slot which can hold conference calls for that extension. The number of simultaneous conferences is also removed from 3CX settings:

To create a simple conference, you can use

MakeCall(700**101, 101)

to use the dedicated conference slot on extension 101 to initiate a new conference that has 101 as the first participant.

Unfortunately, according to 3CX support, the method

public void MakeCall(
string dnNumber,
Dictionary<string, string> parameters

is no longer supported as at 3CX version 12, despite still being mentioned inside the API documentation.

The ScheduleTheConference.cs sample provided with the API provides another method to create a new conference:

PhoneSystem ps = PhoneSystem.Root;
var stat = ps.CreateStatistics("S_SCHEDULEDCONF", args[1]);
stat["name"] = args[4];
stat["idstat"] = args[1];
stat["pin"] = args[3];
stat["startat"] = dt.ToUniversalTime().ToString(@"yyyy-MM-dd HH:mm:ss");
stat["target"] = args.Length > 5 ? args[5] : "";
stat["numbertocall"] = "";
stat["email"] = "";
stat["description"] = "";
stat["emailtext"] = "";

However, despite much effort, I could not get this method to work on my 3CX setup. No errors are returned and no related events are found inside the 3CX system activity log. Even if I could get it to work, it will not create a new conference effectively since the method intention is to schedule a new conference to run in the future, not to start it immediately and monitor its progress. This means there is currently no way to have full control over the created conference on 3CX version 12.

Surprisingly, the new version of 3CX Phone for Windows is able to support creating, scheduling and maintaining conference:

My guess is that it uses a proprietary communication protocol to communicate with the 3CX server directly. Knowing that the phone application is built as a .NET Silverlight application, I tried to use Reflector to decompile it and although the source code is not obfuscated, the decompiled code still looks far too complicated. At this point it is not worth the time and efforts for me to attempt to identify the conference mechanism this way. 

See also:
Using 3CX Call Control API in a .NET application

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A tough developer who likes to work on just about anything, from software development to electronics, and share his knowledge with the rest of the world.

5 thoughts on “Creating calls and conferences using 3CX Call Control API

  • March 17, 2016 at 3:48 am

    Thanks for the information, Do you know how to change the status of the call from free to busy line when you use Trasfearcall to transfer call.

  • March 17, 2016 at 9:23 pm


    I don't think there is a way. In fact the Call Control API in 3CX is extremely limited with no official support from 3CX, and beyond what is provided in the documentation on 3CX blog, there is little else you can do.

  • March 18, 2016 at 11:24 pm

    Can you inform me how to change phone extension status to busy using API, like when you transfer a call from one number to another I would like for example to keep the number as busy status using API.
    Hope you have solution for me.

  • March 18, 2016 at 11:30 pm

    OK, But can we use the API to change the BusyLampField and by doing that we change the status of the phone. can it be done.


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