The book was written by Oleg Konstantinovich Sklyarov, one of the well-known experts in the field of fiber-optic communications. This is his second major work on FOCL - the most important technology of modern information transmission systems. Unfortunately the last one. As soon as he finished working on the manuscript, the author died suddenly.O.K. Sklyarov's first book, Modern Fiber Optic Transmission Systems, Equipment and Elements, was published in 2001. In recent years, fiber-optic transmission systems have developed so rapidly both qualitatively and quantitatively that it took the author great efforts to convey to the reader the main trends in the progress of the industry. The book contains material on the main protocols used in optical networks, on system testing, on methods for transmitting information flows. Much attention is paid to digital hierarchy equipment, sealing issues, and optical access networks. Of particular interest are the chapters devoted to new passive and active elements of networks, new domestic and foreign cables. The principles of operation of optical Raman (RMA) amplifiers, an electroabsorptive light modulator widely used in modern high-speed transmission systems, are covered.The book is intended for students, specialists in fiber-optic communication systems, it will help in the technical training of maintenance personnel.< /p>