This article is a detailed guide about attended call transfer method
in relation with Ozeki VoIP SIP SDK. After reading through this page you will
be fully familiar with all the essential terms concerning attended call transfer
and what you will need for creating your own solution using Ozeki VoIP SIP SDK.
When an incoming call has to be transferred from the client that accepted it, for example in case of a call center,
the transfer can be made by using blind transfer, when the call is forwarded to a randomly chosen
end-point or by intentionally choosing a callee and notifying them about the transfer. This second method is called
attended call transfer (Figure 1) and it is basically made when the caller
asks for a special agent of some specialist to help them.
In case of an attended call transfer the call center agent who receives all the incoming calls
chooses between the possible agents according to the caller's needs and calls the agent and tells about the transfer before
actually performing it. Attended call transfers can be used
for directing the caller to the agent that is the best qualified for solving the given problem.
Figure 1 - Transferring a call using attended call transfer
The following example source code contains a basic implementation of attended
call transfer using the existing support of Ozeki VoIP SIP SDK. In the next sections
you will get all the information you need to be able to write your own
solution on this purpose.
The following program code uses the background support of Ozeki VoIP SIP SDK,
therefore you will need to download and install the SDK on your computer
before starting to use the program code. You will also need to have Visual
Studio 2010 or compatible IDE and .NET Framework installed on your system, as the program code below is written in C# language.
Figure 2 shows the user interface of the softphone application that is capable for
attended call transfer.
Figure 2 - The user interface for the example program
In case of an attended call transfer the simplest solution is to have a human
operator who makes the transfer directly by user interaction. The example program
that will be explained here is operating according to this logic.
In this example the incoming call is accepted by a human operator who asks about the
motive of the call. The operator then decides about the call transfer according to the answers
the caller gives.
In this example the operator can type in the number of the end-point where the
call will be transferred (Code 1). The operator can also extort blind transfer by pressing the Transfer button on the
blind transfer panel.
private void buttonAttendedTransfer_Click(object sender, EventArgs e)
IPhoneCall transferTo = cbAttendedTransfer.SelectedItem as IPhoneCall;
if (transferTo == null)
Code 1 - The event handler for attended call transfer
The transfer itself is made the same way as in case of a blind transfer
the only difference is that in this case the called number is get from the operator not from the
transfer list and the operator calls the addressee of the transfers and talks to them before the transfer.
This also means that the transfer needs two simultaneous calls to be performed.
When the operator wants to transfer a call, they call another party - the one they want to transfer the call to -
and when they have agreed about the transfer, the operator chooses the call to transfer and
exits the call. After that the line will only be established between the original caller and the end-point
where the call was transferred to.
This example program also contains solutions for call forwarding and
blind call transfer.
If you are interested in those technologies too, follow the links above and you will
find all the information you need.
This article introduced you the basic knowledge about attended call transfer technology and showed how Ozeki VoIP SIP SDK can help you to fulfill your wishes about this topic. If you have read through this page carefully, you already have all the knowledge you need to start on your own solution.
As you are now familiar with all the terms concerning this topic, now it is time to take a step further and explore what other extraordinary solution Ozeki VoIP SIP SDK can provide to you.