Eagle: FAPSI Academy,2003. 87 s. The manual covers a wide range of issues of construction and operation of narrowband digital networks with service integration (ISDN) and is intended for students in the specialties 200900 - "Communication Network and Communication Systems" , 201000 - "Multichannel telecommunications systems" , 075600 - "Information security of telecommunications systems" , 167700 - "Government Communications Organization" . This manual can also be useful for students studying automatic switching systems, telecommunications networks, as well as for a wide range of specialists interested in the network aspects of building narrow-band digital networks with the integration of services.