Linux as a Telephony Platform

Using Linux as a base to implement advanced telphony applications.
TServer Applications

An interesting feature of the DBS is the ability to turn a large display telephone into a simple kind of terminal device. This allows the display content to be controlled by the application, and the application to receive input events when keys are pressed on the telephone. Another feature is a special “hot key” (also known as the ACD key), that functions as an “attention” key that generates an API event when pressed, regardless of the current telephone state.

One of the first DBS applications I created is a simple menu program for attaching “applets” to a telephone. When the attention key is pressed, a simple menu of applications appears from which one can be selected. One such application is used to immediately show status information for my server (how many users on-line, uptime, etc.) along with a soft key menu item to force a server reboot.

Another digital telephone application of mine is a more advanced speed dialer that has no capacity limit and is programmable from the telephone. This application resembles the Fujitsu “Dial-by-Name” server application in concept. The DBS has its own internal speed dialing directory. Since alphanumeric text is hard to enter through the phone, I wrote a simple Visual Basic program to connect to the SMDR programming protocol in order to program DBS speed dialing.

A possible future application that comes to mind is empowering users to program their own phones from the desktop or perhaps from web pages.


Many opportunities exist for the use of free and open systems in computer telephony, especially for those telephone vendors wise enough to expand their marketing opportunities by allowing third parties to freely address issues and applications beyond their own immediate scope. While I choose to use the Panasonic DBS and, with it, have accepted restrictions on disclosure and source publication, several other vendors have expressed interest in having their equipment featured in a follow-up article.

When I started this article, I became aware of the effort to create a standard and open Internet protocol for telephony integration, known as “stp”, Simple Telephony Protocol. After some debate, I have chosen to fully embrace stp, and the current software described in this article is being rewritten to support and comply with the evolving stp standard. The name “SwitchLink” has also been adopted for it (swilink for short). My intention is that swilink will become widely available as a free and open software package for release with all mainstream Linux distributions. Thus, free and open telephony will become the norm rather than the exception for Linux.

Recently, there has been considerable change in the attitudes of several key hardware vendors in the telephony business with regard to Linux. I now believe opportunities to write on the use of Linux as a general purpose and high performance Internet telephony platform may be possible much earlier than I anticipated.


Best known for WorldVU, a public BBS system for Linux, David Sugar is currently employed as Director of Software Engineering for Fortran Corp. and uses Linux for commercial telephony development. He maintains his own Internet server under Linux, and may be reached for comment via He can be reached via e-mail at



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