problem for private networks, but it does become problematic for service providers who wish to interconnect PSTNs and provide national service among a cluster of providers. As a result of this, many service providers have chosen to deploy SIP instead of H.323 in their national networks. SIP is designed to establish peer-to-peer sessions between Internet routers. The protocol defines a variety of server types, including feature servers, registration servers, and redirect servers. SIP supports fully dis- tributed services that reside in the actual user devices and, because it is based on existing IETF protocols, provides a seamless integration path for voice/data integration. Ultimately, telecommunications, like any industry, revolves around profitability. Any protocol that allows new services to be deployed inex- pensively and quickly immediately catches the eye of service providers. Like TCP/IP, SIP provides an open architecture that can be used by any vendor to develop products, thus ensuring multivendor interoperability. And because SIP has been adopted by such powerhouses as Lucent, Nor- tel, Cisco, Ericsson, and 3Com, and is designed for use in large carrier networks with potentially millions of ports, its success is reasonably assured. Originally, H.323 was to be the protocol of choice to make this possible. And while H.323 is clearly a capable suite of protocols and is indeed quite good for VoIP services that derive from ISDN implementations, it is still incomplete and is quite complex. As a result, it has been relegated to use as a video-control protocol and for some gatekeeper-to-gatekeeper com- munications functions. The intense interest in moving voice to an IP infrastructure is driven by simple and understandable factors: cost of service and enhanced flex- ibility. However, in keeping with the "Jurassic Park Effect" (Just because you can, doesn't necessarily mean you should), it is critical to understand the differences that exist between simple voice and full-blown telephony with its many enhanced fea