Programming Internet telephony services

Internet telephony enables a wealth of new service possibilities. Tradition al telephony services, such as call forwarding, transfer, and 800 number se rvices, can be enhanced by interaction with e-mail, Web, and directory serv ices. Additional media types, like video and interactive chat, can be added as well. One of the challenges in providing these services is how to effec tively program them. Programming these Services requires decisions regardin g where the code executes, how it interfaces with the protocols that delive r the services, and what level of control the code has. In this article we consider this problem in detail. We develop requirements for programming In ternet telephony services, and we show that at least two solutions are requ ired - one geared For service creation by trusted users (such us administra tors), and one geared for service creation by untrusted users (such as cons umers). We review existing techniques for service programmability in the In ternet and in the telephone network, and extract the best components of bot h. The result is a common gateway interface that allows trusted users to de velop services, and the Call Processing Language that allows untrusted user s to develop services.