SONET is the American National Institute standards for synchronous data transmission and the international equivalent is synchronous digital hierarchy. The standards are comprised so networks are able to interconnect, both nationally and internationally. Conventional transmission systems also are able to utilize the optical media through tributary attachments. SONET provides standards for a number of line rates. The maximum line rate is 9.953 gigabits per second with possible line rates of 20 gigabits.
             SONET is the base for the physical layer of broadband integrate network. Above the SONET a layer called asynchronous transfer mode runs and SONET fixes the limits of a base rate of 51.84 Mbps. Broadband Integrated Services Digital Network (BISDN) is both a concept and it is also a set of services and developing standards for integrating digital transmission services in a broadband network of fiber optic and radio media. BISDN encompasses frame relay service for high-speed data that can be sent in large bursts, the Fiber Distributed-Data Interface.
             SONET allows various kinds of formats to be transmitted on one line. Before SONET was used, communication between the various localized networks was expensive because the digital signals were different. SONET was developed to deal with this problem and it standardized the rates and formats, with the Synchronous Transport Signals (STS) as the fundamental building block. The STS is divided into two parts, the payload that carries the data and the overhead that transports signal and protocol data. SONET has more powerful capabilities than the asynchronous systems. SONET enables integrated network, where one connection reaches all network elements within a given structure. It also provides centralized maintenance and reduced travel maintenance personnel and thus provides a cost effective method.
             Different formats and rates are converted into STS and they are carried ...