At present there are many overlapping information networks (e.g., telephone, telegraph, data, cable TV), and new networks are emerging rapidly (paging, personal communications services, etc.). Each of the current information networks was engineered to provide a particular type of service and the added value provided by each different type was sufficient to overcome the fixed costs of building overlapping physical networks.
However, given the high fixed costs of providing a network, the economic incentive to develop an ``integrated services'' network is strong. Furthermore, now that all information can be easily digitized separate networks for separate types of traffic are no longer necessary. Convergence toward a unified, integrated services network is a basic feature in most visions of the much publicized ``information superhighway'' (e.g., [National Academy of Sciences1994]). The migration to integrated services networks will have important implications for market structure and competition.