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12. Broadband ISDN and ATM
This chapter describes Broadband ISDN B-ISDN and the transfer mode designed for its implementation: Asynchronous Transfer Mode ATM. ATM provides a
means for fast switching and transmission at data rates required by B-ISDN services. It relies on the division of information into small fixed-size packets, called cells, and
their demand-based transmission over optical fiber – hence the term asynchronous.
We will first discribe some of the basic concepts underlying ATM, including its protocol architecture, and then discuss each of its layers in turn. We will also discuss
the organization of ATM networks and their potential applications.
12.1. Broadband ISDN
Increasing market demand for data rates substantially greater than those supported by ISDN has lead to the notion of Broadband ISDN B-ISDN. By relying on
optical fiber transmission systems, B-ISDN opens the door to a whole range of new applications e.g., high quality digital audio, real-time video, pay TV, video phone,
high speed LAN connection with emphasis on interactivity and high speed transfer services.
B-ISDN is developed as an evolution of ISDN and hence follows the same principles. This section provides an overview of B-ISDN, its services, and its
protocol architecture.
12.1.1. B-ISDN Services
B-ISDN services are clasified into interactive and distribution services. Interactive services involve the bidirectional flow of user information between two subscribers or
between a subscriber and a service provider. Interactive services are divided into three subcategories:
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Conversational services involve real-time exchange of information such as
sound, video, data, or entire documents. Typical examples include: video- telephony, video-conference, and high speed data transfer. Video-telephony is
like the normal voice telephony service but also includes video capture, transmission, and display capabilities. Video-conference provides voice and
video communication between two conference rooms or between a number of individuals.
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Messaging
services involve non-real-time exchange of information between subscribers in a store-and-forward fashion. Examples include: video mail and
document mail. Video mail supports the exchange and storage of moving video images and sound as messages. Document mail allows documents of different
types and formats to be exhanged and stored.
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Retrieval services provide subscribers with retrieval access to centrally-stored
public information. Examples include: broadband videotex retrieval of video imagessequences with sound, text, and graphics, video retrieval subscriber
access to video libraries of movies, and retrieval of high-resolution images and documents from various archives and information centres.
Distribution services involve the unidirectional flow of user information from a service provider to a subcriber. Distribution services are divided into two
subcategories:
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Distribution services without user presentation control involve the central broadcast of information to a large number of subscribers, where subscribers
have no control over the presentation of information. Examples include: broadcast of TV programmes, electronic newspapers, and electronic publishing.
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Distribution services with user presentation control are the same as the previous category except that here the information is offered as cyclically-
repeated frames, thereby enabling the subscriber to control the start and the order of the presentation of frames. Examples include: electronic newspaper and
tele-advertising.
Figure 12.136 summarizes the B-ISDN services.
Figure 12.136 Summary of B-ISDN services. Category
Subcategory Type of Information
Example
Interactive Conversational
Moving picture Broadband video-telephony
and sound Broadband video-conference
Video-surveillance Sound
Multiple sound prog. signal Data
High speed data transfer High volume file transfer
High speed teleaction Document
High speed telefax High resolution image comm.
Document communication Messaging
Moving picture+sound Video mail
Document Document mail
Retrieval Text, data, graphics,
Broadband videotex still images, moving
VideoImage retrieval pictures
DocumentData retrieval Distribution
Without user Data
Data distribution
Kategori