The Integrated Services Digital Network

The present state of development of communication technology is characterized by two features, namely the digital representation of all signals transrnitted and processed, irrespective of information type - voice, text, data or images - and the integration of systems and services, this integration only being completely possible using digital technology. The boundaries between switching and transmission are shifting, and functions are being redefined and redistributed between terminals and communication networks. Multiservice terminals - unlike telephones, teleprinters, video data terminals - are designed to handle more than one information type. Lastly, the communication network allows voice, text, data and video information to be transmitted on the same circuit; the user obtains access to this network via a non dedicated "communication socket". The essential features of this Integrated Services Digital Network (ISDN) have been standardized over the last eight years by experts from all over the world under the aegis of the CCITT 1), the international standardizing body of the carriers of public communication networks. All the leading network carriers are working towards ISDN implementation because of the substantial benefits it will offer to users, network carriers and manufacturers alike: Users will obtain additional and advanced services, most of them designated to cater for the growth in non-voice traffic. The ISDN subscriber access will also enable users to operate existing systems more cost-effectively than via various dedicated networks.

An introduction to "ISDN" which brings the technology up-to-date, incorporating developments in "ATM", "SDH" and Broadband "ISDN". This book is suitable for self-learning communications professionals and applied courses in communications management and technology, and advanced undergraduates and graduates in computing and electronics.

What is "digital telephony"? To the authors, the term digital telephony de notes the technology used to provide a completely digital point-to-point voice communication system from end to end. This implies the use of digital technol ogy from one end instrument through the transmission facilities and switching centers to another end instrument. Digital telephony has become possible only because of the recent and ongoing surge of semiconductor developments allowing microminiaturization and high reliability along with reduced costs. This book deals with both the future and the present. Thus, the first chapter is entitled, "A Network in Transition." As baselines, Chapters 2, 3, and 10 provide the reader with the present status of telephone technology in terms of voice digitization as well as switching principles. The book is an outgrowth of the authors' continuing engineering education course, "Digital Telephony," which they have taught since January, 1980, to attendees from business, industry, government, common carriers, and tele phony equipment manufacturers. These attendees come from a wide variety of educational backgrounds. but generally have the equivalent of at least a bachelor's degree in electrical engineering. The book has been written to provide both the engineering student and the practicing engineer a working knowledge of the principles of present and future voice communication systems based upon the use of the public switched network. Problems or discussion questions have been included at the ends of the chapters to facilitate the book's use as a senior level or first year graduate level course text.

The present state of development of communication technology is characterized by two features, namely the digital representation of all signals transrnitted and processed, irrespective of information type - voice, text, data or images - and the integration of systems and services, this integration only being completely possible using digital technology. The boundaries between switching and transmission are shifting, and functions are being redefined and redistributed between terminals and communication networks. Multiservice terminals - unlike telephones, teleprinters, video data terminals - are designed to handle more than one information type. Lastly, the communication network allows voice, text, data and video information to be transmitted on the same circuit; the user obtains access to this network via a non dedicated "communication socket". The essential features of this Integrated Services Digital Network (ISDN) have been standardized over the last eight years by experts from all over the world under the aegis of the CCITT 1), the international standardizing body of the carriers of public communication networks. All the leading network carriers are working towards ISDN implementation because of the substantial benefits it will offer to users, network carriers and manufacturers alike: Users will obtain additional and advanced services, most of them designated to cater for the growth in non-voice traffic. The ISDN subscriber access will also enable users to operate existing systems more cost-effectively than via various dedicated networks.