Programming Internet Telephony Services

The Intelligent Network (IN) was created to satisfy an increasing need for programmability of telephone network services. It provided a means by which intelligence could be removed from the switch, and placed in general purpose computers (Service Control Points), where services were more easily created. This model has enabled services such as 800-numbers, call-forwarding, credit card calling, and follow-me. In this paper, we consider the issue of programmability when applied to internet telephony. We discuss the models used for programming in both the web and the IN, and analyze their relevance to IP telephony services. We then present the Session Initiation Protocol (SIP), used for IP telephony signaling, focusing on why it is useful as a platform for service creation. We then present two mechanisms for programming IP telephony services: an extension of HTTP-CGL, called SIP-CGI, primarily targeted at service creation for administrators, and a Call Processing Syntax aimed primarily at end users.