panded to include data transport, video conferencing, e-mail, instant messaging, Web browsing, and various forms of distributed collaboration, enabled by transmission media that have also expanded (from traditional copper wires) to include microwave, terrestrial wireless, satellite, hybrid fiber/coaxial cable, and broadband fiber transport.
Today consumers think of telecommunications in terms of both products and services. Starting with the Carterphone decision by the Federal Communications Commission in 1968,1 it has become permissible and increasingly common for consumers to buy telecommunications applications or equipment as products as well as services. For example, a customer-owned and customer-installed WiFi local area network may be the first access link supporting a voice over Internet Protocol (VoIP) service, and a consumer may purchase a VoIP software package and install it on his or her personally owned and operated personal computer that connects to the Internet via an Internet service provider.
The technologies used for telecommunications have changed greatly over the last 50 years. Empowered by research into semiconductors and digital electronics in the telecommunications industry, analog representations of voice, images, and video have been supplanted by digital representations. The biggest consequence has been that all types of media can be represented in the same basic form (i.e., as a stream of bits) and therefore handled uniformly within a common infrastructure (most commonly as Internet Protocol, or IP, data streams). Subsequently, circuit switching was supplemented by, and will likely ultimately be supplanted by, packet switching. For example, telephony is now routinely carried at various places in the network by the Internet (using VoIP) and cable networks. Just as the PSTN is within the scope of telecommunications, so also is an Internet or cable TV network carrying a direct substitute telephony application.
Perhaps the most fundamental change, both in terms of technology and its implications for industry structure, has occurred in the architecture of telecommunications networks. Architecture in this context refers to the functional description of the general structure of the system as a whole and how the different parts of the system relate to each other. Previously the PSTN, cable, and data networks coexisted as separately owned and operated networks carrying different types of communications, although they often shared a common technology base (such as point-to-point digital communications) and some facilities (e.g., high-speed digital pipes shared by different networks).
How are the new networks different? First, they are integrated, meaning that all media— be they voice, audio, video, or data—are increasingly communicated over a single common network. This integration offers economies of scope and scale in both capital expenditures and operational costs, and also allows different media to be mixed within common applications. As a result, both technology suppliers and service providers are increasingly in the business of providing telecommunications in all media simultaneously rather than specializing in a particular type such as voice, video, or data.
Second, the networks are built in layers, from the physical layer, which is concerned with the mechanical, electrical and optical, and functional and procedural means for managing network connections to the data, network, and transport layers, which are concerned with transferring data, routing data across networks between addresses, and ensuring end-to-end