The rapid proliferation of the Internet in the last few years has given rise to a strong interest in carrying telephony over the Internet. Because the Internet supports data communications, a range of other services can be bundled together with Internet telephony. The Internet, however, was designed for non-real-time data communications, and hence it poses several technical challenges that must be overcome before the Internet can be successfully used for carrying telephone services. This article discusses new services we can expect from Internet telephony, the technical challenges and solutions, and the emerging products that promise to support Internet telephony. INTRODUCTIONCircuit switching and packet switching are the two main technologies for computer and telecommunications networks. The current telephone system is based on circuit switching, which offers a guaranteed quality of service (QoS) to customers. A circuit has to be set up between two endpoints before the start of communication. On the contrary, data communications have so far been considered non-real-time, and hence have been carried over packet-switched networks such as the Internet, which is based on the TCP/IP protocol suite.The proliferation of the Internet in the last few years has given rise to a strong interest in the possibility of carrying real-time voice traffic over the Internet. Since the Internet was not initially designed for real-time communications, carrying voice over the Internet presents a number of challenges and technical issues that need to be solved prior to successful deployment of telephony over the Internet. Some of these technical challenges include the lack of guarantee in terms of bandwidth, packet loss, delay, and jitter which affect the quality of voice over the Internet.However, telephony over the Internet brings in a number of services and their integration which are not possible using traditional circuitswitched telephone networks. It allows the integration of voice, fax, and data over the same network, transport of intracompany voice communications between remote sites of an enterprise, and others. Services such as Web-based call centers, real-time billing, remote teleworking, and enhanced teleconferencing using shared whiteboard and shared applications are some of the services possible using IP telephony.A number of products have been developed by commercial vendors which allow voice communications over the Internet. These products can be divided into three groups according to the end user: carrier, enterprise, and individual users. The objective of this article is to bring together a survey of the new services possible with IP telephony, the technical challenges of IP telephony, and products that facilitate IP telephony. The above topics will be described in detail. APPLICATIONS AND SERVICESA major difference between the conventional public switched telephone network (PSTN) and IP telephony is that IP telephony is a voice service built on top of existing data communications services. As a result, IP te...