An ActiveX-Control SIP Softphone based on the Microsoft Real Time Communications (RTC) API

back to SIP phones

This work was done by Wolfgang Hatzinger. This work is an ActiveX-Control written in Visual Basic. Parts of the code are taken from an sample programm which is part of the RTC SDK. It uses the Microsoft RTC API as SIP stack. The ActiveX-Control runs in the Internet Explorer.

Requirements: The RTC API must be installed. The RTC API is included in Windows XP. For Windows 2000, you can donwload it from

The documentation is in german - sorry!
Update: Thanks to Christoph Wernli, the source code comments in chapter 8 are now also available in english.

You can start the applet directly from here. As the ActiveX control is not signed, you have to add this site to your trustet sites first. Another possibility is, to download the whole programm and start it local by opening the file MyActXPcToPcPhone.HTM in your browser.

You can try the SIP phone by calling a "echo server" at: - maybe currently offline :(

It was tested under Windows 2000. I heard from other people that they had to recompile the application to use it on Windows XP. Be aware: there might be some problems on Windows XP Service 2 due to the new security features! The software comes without any warranties.

This application requires Microsoft Internet Explorer. Other browsers like Firefox, Mozilla ... will not work!

If you find some bugs or added new features, please send it back to me and I will add the newer versions to this site.

Microsoft RTC SDK 1.2:
Microsoft Platform SDK:
This application is similar to the one from Free World Dialup: