TELECOMMUNICATION SYSTEMS - studentsfounder.com · 6 Telecommunication Systems INTEGRATED SERVICES DIGITAL NETWORKS (ISDN) Integrated Digital Network (IDN) – Next, customer began

Telecommunication Systems 1

TELECOMMUNICATION SYSTEMS

By

Syed Bakhtawar Shah Abid

Lecturer in Computer Science

INTEGRATED SERVICES DIGITAL NETWORKS (ISDN)

The original concept of ISDN dates back to the early

1970s.

Its design, in the context of the period, was built

around the copper distribution plant (subscriber loop

and local trunk plant).

The designers saw and understood that by the early

1980s there would be a digital network in place

controlled by CCITT Signaling System No. 7




Voice Communication over Analog Networks

Initially, telecommunication networks were entirely analog networks and were used for the transmission of analog information in the form of voice.

The local loop connecting the subscriber’s handset to the telephone company’s central office were also analog.



Voice and Data Communication over Analog Networks

– With the advent of digital processing, subscriber needed to

exchange data as well as voice.

– Modem were developed to allow digital exchanges over existing

analog lines.



Analog & Digital Services to Subscribers

– To reduce cost and improve performance, the telephone companies gradually began to add digital technologies while continuing their analog services to their customers.

– Three types of customers were identified that time:

Traditional customers using local loops only for analog purposes;

Customers using analog facilities to transmit digital information via modem; and

Customer using digital services to transmit digital information.



Integrated Digital Network (IDN) – Next, customer began to require access to a variety of networks,

such as packet switched networks, and circuit switched networks.

– To meet these needs, the telephone companies created Integrated Digital Networks (IDNs).

– An IDN is a combination of networks available for different purposes.

– Access to these networks is by digital pipes, which are time multiplexed channels sharing very high speed paths.

– Customer can use their local loops to transmit both voice and data to their telephone company’s central office.

– The office then directs these call to the appropriate digital networks via digital pipes.





To receive the maximum benefits from the integrated digital networks, the next step is to replace the analog local loops with digital subscriber loops.

ISDN was developed by ITU-T in 1976.

It is a set of protocols that combines digital telephony and data transport services.

The whole idea is to digitize the telephone network to permit the transmission of audio, video, and text over the existing telephone lines.

ISDN is an effort to standardize subscriber services, provide user/network interface, and facilitate the internetworking capabilities of existing voice and data network.



The goal of ISDN is to form a wide area network that provides universal end-to-end connectivity over digital media.

This can be done by integration all of the separate transmission services into one without adding new links or subscriber lines.

Most important, ISDN will allow all communication connection in a home or building to occur via a single interface.


It was revolutionary for its time by bringing 64-kbps

digital channels right into the home and office. With

the ISDN design, the 64-kbps digital channel

handles:

– Voice telephony (digital)

– Digital data, both packet switched and circuit switched

– Teletext

– Facsimile (e.g., CCITT Group 4) and

– Conference television (56, 64, or 128 kbps).




The goal of ISDN is to provide an integrated facility to incorporate each of the services listed above on a common 64-kbps channel.

These services fall into three categories: – Bearer Services

– Teleservices

– Supplementary Services




Bearer Services provides the means to transfer

information (voice, data, and video) between users

without the network manipulating the content of that

information.

The network does not need to process the information

and therefore does not change the content.

Bearer services belongs to the first three layers of the

OSI reference model and are well defined in the ISDN

standard.

They can be provided using circuit switched, packet

switched, frame switched, or cell switched networks.

Bearer Services


In Teleservices, the network may change or process the

contents of the data. These services corresponds to

layers 4-7 of the OSI reference model.

Teleservices rely on the facilities of bearer services and

are designed to accommodate complex user needs

without the user having to be aware of the detail of the

process.

Teleservices include telephony, teletex, telefax, telex, and

teleconferencing.

Although the ISDN defines these services by name, they

have not yet become standards.

TeleServices


Supplementary services are those

services that provide additional

functionality to the bearer services and

teleservices.

Example of these services are call waiting,

and message handling, all familiar from

today’s telephone company services.

Supplementary Services

ISDN STRUCTURES

ISDN STRUCTURES – ISDN User Channels

B-channel: 64 kbps;

D-channel: 16 kbps or 64 kbps

H-Channel: 384 kbps; 1536 kbps and 1920 kbps.

– Basic and Primary User Interfaces Basic Rate Interface (BRI)

– 2 B-Channels

– 1 D-Channel

Primary Rate Interface (PRI)

– 1.544 Mbps = 23B + D (from the North American T1 configuration)

– 2.048 Mbps = 30B + D (from the European E1 configuration).



ISDN STRUCTURES

A B-channel is defined at a rate of 64 Kbps.

It is the basic user channel and can carry any type of digital

information in full duplex mode as long as the required

transmission rate does not exceed 64 Kbps.

For example, a B channel can be used to carry digital data,

digitized voice, or other low data rate information.

H channels are available with the data rates of 384 Kbps

(H0), 1536 Kbps (H11), or 1920 Kbps (H12).

These rates suit H channels for high data-rate applications

such as video, teleconferencing, and so on.


Data Channels

A Data Channel (D Channel) can be either 16 or 64 Kbps,

depending on the needs of the user.

The primary function of a D channel is to carry signaling

information for the B channels. Control information (such as call

establishment, ringing, call interrupt) is carried.

The ISDN separates control signals onto a channel of their own,

the D channel.

A D channel carries the control signaling for all of the channels in

a given path, using a method called common-channel (Out-of-

band) signaling.


Basic Rate Interface

The basic rate interface (BRI) specifies a digital pipes consisting of two B channels and one 16 Kbps D channel.

Two B channels of 64 Kbps each, plus one D channel of 16 Kbps, equals 144 Kbps. In addition, the BRI service itself requires 48 Kbps of operating overhead. BRI therefore requires a digital pipe of 192 Kbps.

The BRI is designed to meet the needs of residential and small-office customers.

In most cases, there is no need to replace the existing local loop cable.

The same twisted-pair local loop that delivers analog transmission can be used to handle digital transmission.


Primary Rate Interface

The usual PRI specifies a digital pipe with 23 B channels and one 64 Kbps D channel.

Twenty three B channel of 64 Kbps each, plus one D channel of 64 Kbps equal to 1.536 Mbps.

In addition, the PRI service itself uses 8 Kbps of overhead. PRI therefore requires a digital pipe of 1.544 Mbps.


Primary Rate Interface

PRI can provide full duplex transmission between as many as 23 source and receiving nodes.

The individual transmission are collected from their source and multiplexed onto a single path (DSL) for sending to the ISDN office.

In North America and Japan, PRI offers 23 64-Kbps B channels and one 64-Kbps D channel.

PRI was designed to be compatible with existing T-1 lines.

In Europe and the rest of the world, PRI offers 30 B channels and 2 D channels, giving it a capacity of 2.048 Mbps


Broadband ISDN

To provide for the needs of the next generation of technology,

an extension of ISDN, called Broadband ISDN (B-ISDN).

The original ISDN is now known as narrowband ISDN.

B-ISDN provides subscribers the network with data rates in the

range of 600 Mbps, almost 400 times faster than the PRI rate.

Narrowband ISDN is an outcome of the logical evolution of the

telephone system.

Broadband ISDN, however, represents a revolution in thinking

that radically alter the entire aspects of communication.

B-ISDN is based on a change from metal to fiber-optic cable at

all levels of telecommunications.


B-ISDN Services

B-ISDN provides two types of services:

– Interactive Services

– Distributive Services


Interactive Services

Interactive Services are those services that require two-way exchanges between either two subscribers or between a subscriber and a service provide.

These services are of three types. – CONVERSATIONAL SERVICES:

Such as telephone call, that support real t ime exchanges. These real t ime services can be used for telephony, video conferencing, data transfer, and so on.

– MESSAGING SERVICES: Stored-and-forward exchanges.

These services are bidirectional, meaning that all part ies in an exchange can use them at the same t ime. The actual exchange, however, may not occur in real t ime.

One subscriber asking another for information may have to wait for an answer, even though both parties are available at the same time. E.g. voice mail, data mail, and video mail and so on.

– RETRIEVAL SERVICES: Services used to retrieve information from a central source, called information

center.

An example of retr ieval service is videotex that allow subscribers to select video data from an online library.


Distributive Services

Distributive services are unidirectional services sent

from a provider to subscribers without the subscriber

having to transmit a request each time a service is

desired.

The services can be with or without user control.

– Distributive services Without User Control: These services are broadcasted to the user without the user’s having requested them or having

control over either broadcast times or content.

User choice is limited to weather or not to receive the service at all.

An example of this type services is commercial TV.

– Distributive services With User Control: These services are broadcasted to the user in a round-robin fashion.

Services are repeated periodically to allow the user a choice of times during which to receive them.

Example of this type of services are educational broadcasting, teleadvertising.


Access Methods

B-ISDN defines three methods designed to provide for three levels of

user needs.

They are symmetrical 155.520 Mbps, asymmetrical 155.520/622.080

Mbps, and symmetrical 622.080 Mbps.


ACCESS METHODS

155.520 Mbps full duplex: – This rate matches that of an OC-3 SONET link.

– It is high enough to support customers who

need access to all narrowband ISDN services

and to one or more regular video transmission

services.

– It is designed to fill the needs of most

residential and many business subscribers.

ACCESS METHODS

155.520 Mbps output/622.080 Mbps input:

– This method provides asymmetrical full duplex

network access.

– The outgoing rate is 155.520 Mbps (the same as

an OC-3 SONET link),

– The incoming rate is 622.080 Mbps (the same as

an OC-12 SONET link).

– It is designed to fill the needs of business that

require the simultaneous recipient of multiple

services and video conferencing. Telecommunication Systems 28


ACCESS METHODS

622.080 Mbps full-duplex:

– This mechanism is designed for businesses that

provide and receive distributive services.

? Telecommunication Systems 30

Thank You


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TELECOMMUNICATION SYSTEMS - studentsfounder.com · 6 Telecommunication Systems INTEGRATED SERVICES DIGITAL NETWORKS (ISDN) Integrated Digital Network (IDN) – Next, customer began