Convergence and fiber-optic technology in competitive long-distance networks has resulted in drastically lowered prices for long distance. The same fiber-optic lines that carried data now also carry voice, images, and video. This is done transparently to end users and is a major factor in the continuing decline of long-distance prices. Backbones of public networks carry vast amounts of voice, video, and data between cities and long-distance carriers, and between local telephone companies. These high-speed "backbone" networks, as well as the Internet, transmit data, voice, and video as converged traffic using either ATM or IP equipment.
Asynchronous Transfer Mode (ATM) carries digital information in fixed-sized packages called cells. Internet Protocol (IP) transmits information digitally in variable-sized packages called packets. ATM is currently used more extensively for voice because it provides better quality of voice. Both ATM and IP are used for the convergence of voice, video, images, and data in the backbone of public networks.
The next challenge for carriers is to extend convergence from the central, backbone portion of out networks to customer premises and facilities between customers and telephone companies' equipment.