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.
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