One thing that was clear to everyone from the start was that if each vendor designed its own protocol stack, the system would never work. To avoid this problem, a number of interested parties got together under ITU auspices to work out standards. In 1996 ITU issued recommendation H.323 entitled ‘‘Visual Telephone Systems and Equipment for Local Area Networks Which Provide a Non- Guaranteed Quality of Service.’’ Only the telephone industry would think of such a name. The recommendation was revised in 1998, and this revised H.323 was the basis for the first widespread Internet telephony systems. H.323 is more of an architectural overview of Internet telephony than a specific protocol. It references a large number of specific protocols for speech coding, call setup, signaling, data transport, and other areas rather than specifying these things itself. The general model is depicted . At the center is a gateway that connects the Internet to the telephone network. It speaks the H.323 protocols on the Internet side and the PSTN protocols on the telephone side. The communicating devices are called terminals. A LAN may have a gatekeeper, which controls the end points under its jurisdiction, called a zone.
