Building Blocks for IP Telephony

The global telephony infrastructure is rapidly evolving from circuit-switching to IP-based packet-switching. Voice over IP (VoIP) is becoming common and is the intended base technology for corporate giants such as AT&T and Qwest. The marketing research firm, IDC, states “IP telephony is poised to become the fastest-growing, network services market of the decade” [1]. Reference [2] reviews the motivations behind the move toward Internet telephony. The internet already provides sufficient service quality for one-way voice transmission (such as for recording voice messages, listening to messages, etc.). For these purposes, VoIP surpasses the audio quality of the PSTN. It is likely that in the near future the Internet will also provide sufficient service quality for two-way voice transmission. Nevertheless, there is a large investment in the PSTN infrastructure which will not go away overnight. However, this infrastructure, with its complex interfaces, is increasingly difficult to manage and control. In order to smoothly transition from the current PSTN infrastructure, while simultaneously leveraging it to create new services, we believe that there is a need to rapidly prototype multimodal applications, that is, applications that span the telephone network and the Internet [3]. At Cornell, the ITX project has created an open-source, portable, programmable platform for developing multimodal applications. The ITX platform allows these applications to span the telephone and IP networks, or run only on one of these networks. Our main design philosophy was to create a small set of core components that could be composed to create non-trivial multimodal applications. We have not only used this to create some example applications, but have also made the code widely available, in source form, for others to use (see Appendix A for details). In this paper, we describe the design of the ITX platform, present a simple application built using this platform, and present preliminary performance measurements.