ing their software code to a small "kernel." The "computer-like" part of a PBX is analogous to the com- bined capabilities of a media gateway controller and an applications server in the newer softswitch environment. The PBX circuit board for outside lines is analogous to the media gateway. An open and public operating system will mean that people other than the manufacturer can program the communications servers, making them do things that the manufacturer never thought of or did not have time to address. The communica- tions server can be programmed do what the customer wants it to do. This is the premise of the trend towards more open telecommunications systems. This openness still requires the skill of experienced and tal- ented programmers to design and test the new applications. The more ubiquitous and flexible the programming languages (like Java and C++), the more likely that new applications can be prac- tically developed, as there will be programmers available to design and support them. The situation driving communications server development today is clear. The average traditional PBX contains three to five million lines of software code. Central office switches such at The Telecom Handbook 30 155 CONVERGENCE OF VOICE & DATA Northern Telecom's DMS 100 also contain several million lines of code. Adding a few new features requested by a customer re- quires regression testing. The new software code is tested in combination with all of the old code, simulating conditions of the telephone system under normal day-to-day use. This can be a prohibitively lengthy process and in many cases, can never be completed. It is further complicated because it is unlikely that the pro- grammers writing the new code are the same programmers who wrote the original code. (Code refers to the sequence of instruc- tions in software.) Traditional PBX manufacturers respond to this phenom- enon by releasing new system features infrequently. When they do, a whole collection of new features is introduced, resulting in a very long ti