【正文】 ication As can be inferred from the examples of videophone and HDTV, the evolution of future munications will be via broadband munication centered around video signals. The associated services such as video phone, video conferencing, video surveillance, cable television (CATV) distribution, and HDTV distribution to the highspeed data services such as highresolution image transmission, highspeed data transmission, and color facsimile. The means of standardizing these various broadband munication services so that they can be provided of standardizing these various broadband munication services so that they can be provided in an integrated manner is no other than the broadband integrated services digital work in an integrated services digital work (BISDN). Simple put, therefore, the future munications work can be said to be a broadband telemunication system based on the BISDN. For realization of the BISDN, the role of several broadband munication technologies is crucial .Fortunately ,the remarkable advances in the filed of electronics and fiber optics have led to the maturation of broadband munication technologies .As the BISDN bees possible on the optical munication technologies .As the BISDN bees possible on the optical munication foundation . the relevant manufacturing technologies for lightsource and passive devices and for optical fiber have advanced to considerable levels . Advances in highspeed device and integrated circuit technologies for broadband signal processing are also worthy of close attention. There has also been notable progress in software, signal processing, and video equipment technologies . hence, form the technological standpoint ,the BISDN has finally reached a realizable state . On the other, standardization activities associated with broadband munication have been progressing. The Synchronous Optical Network (SONET) standardization centered around the T1 mittee eventually bore fruit in the form of the Synchronous Digital Hierarchy (SDH) standards of the International Consultative Committee in Telegraphy and Telephony (CCITT), paving the way for synchronous digital transmission based on optical munication .The standardization activities of the integrated services digital work (ISDN), which menced in early 1980?s with the objective of integrating narrowband services ,expanded in scope with the inclusion of broadband services ,leading to the standardization of the BISDN in late 1980?s and establishing the concept of asynchronous transfer mode (ATM) munication in process . In addition, standardization of various video signals is being finalized through the cooperation among such anizations as CCITT, the International Radiomunications Consultative Committee (CCIR ) ,and the International Standards Organization (ISO),and reference protocols for highspeed packet munication are being standardized through ISO, CCITT, and the Institute of Electrical and Electronics Engineer (IEEE). Various factors such as these have made broadband munication realizable. Therefore, the 1990?is the decade in which matured broadband munication technologies will be used in cibhybctuib with broadband standards to realize broadband munication works. In the broadband munication work, the fiber optic work will represent the physical medium for implementing broadband munication, while synchronous transmission will make possible the transmission of broadband service signals over the optical medium. Also, the BISDN will be essential as the broadband telemunication work established on the basis of optical medium and synchronous transmission and ATM is the munication means that enables the realization of the BISN. The most important of the broadband services to be provided through the BISDN are high –speed data munication services and video munication services. Asynchronous Transfer Mode (ATM) Demand for rich media services such as Inter access ,video on demand ,digital television and voice over IP grows more clamorous every day .So ,too ,does the need for highperformic distribution technology . To meet this demand , service providers are turning to ATM technology – a flexible ,scalable way of moving highspeed video and data across works .ATM?s sophisticated bandwidth utilization capabilities enable providers to efficiently transport large ,plex video packets without taxing a work . The majority of traffic ported over the ATM infrastructure is voice and data, Video will soon be as prominent and will drive the need for more highcapacity ATM works .The basis of ATM technology is a highefficiency ,low –latency switching and multiplexing mechanism ideally suited to an environment in which there are specific bandwidth limitations. ATM allocates bandwidth on demand by construction virtual channels and virtual paths between source and destination points on the ATM work boundaries. These channels are not dedicated physical connections, but are permanent virtual connections or switched virtual connections that are deconstructed when no longer needed. The speed and reliability of ATM switched works can?t be matched by other popular WAN technologies, which are illequipped to transport highperformance data. However, even in an ATM environment, the nuances and peculiarities of digital video make it impractical to transport realtime video in its native unpressed format over ATM. Using MPEG2 sophisticated pression techniques, providers can alleviate technical roadblocks when managing and ensuring the integrity of large ,super –fast video streams over ATM. Local MPEG2 video streams are typically transported via an interface known as digital video broadcast asynchronous serial interface .ATM edge devise deconstruct either an MPEG2multiple program transport stream (MPTS) or single program transport stream to the program level a