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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
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163
presentation control Text, graphics, images
Electronic newspaper moving
pictures+sound Video signal distribution
Video TV programme distribution
With user presentation control
Text, graphics, sound, images
Electronic newspaper Tele-advertising
12.1.2. B-ISDN User-Network Interface
In addition to the narrowband channels defined for ISDN, B-ISDN supports the following three User-Network Interfaces UNIs:
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Symmetric full-duplex 155.52 Mbps
. This interface provides the basis for interactive services. This will therefore be the most common interface offered. It
is commonly referred to as the 150 Mbps interface. The effective payload of this interface is 149.76 Mbps.
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Symmetric full-duplex 622.08 Mbps . This interface is suitable for situations
which involve very high traffic volumes. It is commonly referred to as the 600 Mbps interface. The effective payload of this interface is 599.04 Mbps or
600.768 Mbps, depending on how it is structured.
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Asymmetric full-duplex 622.08155.52 Mbps
. This is a hybrid interface which combines the earlier two. It uses bit rates of 622.08 in the network-to-subscriber
direction and 155.52 Mbps in the subscriber-to-network direction. It is suitable for situations where the traffic volume in the network-to-subscriber direction is
much higher than in the opposite direction.
The functional groupings and reference points for B-ISDN UNI closely follow those of the narrowband, as illustrated by Figure 12.137. Their role remains identical
to those of narrowband ISDN. To highlight the broadband nature of the functional groupings and reference points, the letter ‘B’ is added e.g., B-TE1. The R
reference point is an exception because it may or may not have broadband capabilities. Accordingly, it may support a B-TE2 or TE2.
Figure 12.137 B-ISDN functional groupings and reference points.
B-NT1 B-ISDN Network
T S
R B-TE1
B-TE2 Functional groupings
Reference points B-NT2
B-TA
B B
or TE2
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12.1.3. B-ISDN Protocol Architecture
Figure 12.138 shows the reference model for the B-ISDN protocol architecture. The architecture is partitioned by three planes. The User Plane facilitates the
transfer of user information and associated control signals. The Control Plane is responsible for connection control functions such as call setup and release. The
Management Plane
is responsible for management functions relating to the system as a whole and coordination between the planes Plane Management, and for
management functions related to resources and parameters residing in its protocol entities Layer Management.
Figure 12.138 B-ISDN protocol architecture reference model.
Higher layers Higher layers
ATM Adaptation Layer ATM Layer
Physical Layer Control Plane
User Plane Management Plane
Plane Management Layer Management
The Physical Layer is responsible for the physical transmission of ATM cells.
To achieve some degree of physical medium independency, this layer is divided into two sublayers. The Physical Medium Sublayer covers the medium-dependent
aspects of the physical layer and provides bit transmission and bit timing functions. The Transmission Convergence Sublayer is independent of the physical medium
and provides five functions:
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Generation and recovery of transmission frames similar to frame structures described in Chapter 11 for narrowband ISDN.
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Transmission frame adaptation which involves the packing of cells into transmission frames and their extraction upon arrival.
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Cell delineation to enable the receiving-end identify the boundaries of cells whose information fields have been scrambled prior to transmission and are
descrambled by the receiver.
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HEC sequence generation by the transmitter, and verification by the receiver.
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Cell rate decoupling through insertion of idle cells by the transmitter in order to adapt the cell rate to the playload capacity, and their removal by the receiver.
