The Linux Telephony Kernel API

Herlein explains the integration of the telephony device driver into the Linux kernel.
Open-Source Programs Available Now

There are many open-source programs available now that use this API. However, the most well-known and widely used program is ohphone, a console application using the open-source OpenH323 library. Ohphone is part of the OpenH323 Project ( and is in daily use by thousands of people to make free, high-quality phone calls over the Internet. Ohphone not only fully supports the Linux telephony API, but it is also compatible with other H.323-based products like Microsoft NetMeeting<+H>tm<+H> and Cisco voice-enabled routers. A more detailed discussion of this fine software is too much for this article, but you're encouraged to look at its web site to catch the latest news. The company that developed the OpenH323 library was recently acquired by Quicknet Technologies, Inc. as part of Quicknet's efforts to ensure continued major development effort of this open-source project. With such full commercial backing and a commitment to open source, I expect the OpenH323 Project software to become even better in the near future.


The Linux telephony API provides a common and consistent interface for developing telephony software on Linux. While there is currently only one vendor (Quicknet Technologies, Inc.) with fully compliant drivers for this API, several others are working toward compliant drivers. The API is lean, well designed, will not conflict with the existing API for sound cards and provides the ability to support multiple vendors behind the same interface. There's sure to be some exciting new telephony software developed for Linux in the coming year.


Greg Herlein has been an avid Linux developer since 1994. His company, Herlein Engineering, currently offers Linux/UNIX consulting, especially in the areas of telephony software development. He lives and works in San Francisco, California. He can be reached at



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