Lecture 9

Integrated Services Digital Network

(ISDN)

A Quick Glance To History of Transmission

Voice Communication Over An Analog Telephone Network

Voice and Data Communication over an Analog Telephone Network

Analog and Digital Services over the Telephone Network

Integrated Digital Network (IDN)

ISDN

Digital Pipes : TDM channels with very high transmission speed with one or two pairs of copper wires

ISDN incorporates all communication connections in a home or building into a single interface

• Integrated Services Digital Network(ISDN) was developed by ITU-T in 1976

• The purpose of the ISDN is to provide fully integrated digital services to the users

• It is a set of protocols that combines digital telephony & data transfer/transport services

• The whole idea is to digitize the telephone network to permit the transmission of audio, video, images & text over existing telephone lines

ISDN

• It is an effort to standardize subscriber services & provide usage of internet services over it

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

• And, this can be done by integrating all of the separate transmission services into one without adding new links or subscriber lines.

Definition of ISDN

An integrated Service Digital Network (ISDN) is a communication technology that combines digital telephony & data transport services. The idea is to digitize the telephone network to allow the transmission of audio(like voice etc), video, images & text over existing telephone lines.

Types of ISDN• Narrowband ISDN

– uses data transmission speed upto 64 kbps using circuit switching technology

– Narrowband ISDN provides 144kbps and 2.048Mbps data rates.

• Broadband ISDN (B-ISDN)– It supports very high data rate (in range of 100 mbps)– It uses packet switching orientation– It uses 2B/1Q digital coding– It uses Asynchronous Transfer Mode (ATM) technology– Broadband ISDN provides 155.52Mbps and 622.08Mbps data rates.

• Given figure is a conceptual view of the ISDN from a user or customer point of view.

• User has access to ISDN via a local interface to a digital pipe.• Pipes of various sizes are available to satisfy different needs.

Each pipe may contain 1 or two twisted pair of wires.• Pipe to the user’s premises has a fixed capacity but the traffic on

the pipe may be a variable mix up to the capacity limit.• ISDN requires control signals to instruct how to sort out the

time multiplexed data and provide the required services.

ISDN User Interface

• Control signals are multiplexed onto the same digital pipe.

• A user may employ less than the maximum capacity of the pipe and will be charged according to the capacity used.

• Figure shows ISDN user interface example.

Figure : Conceptual View of ISDN Connections

ISDN

Objectives of ISDN• The objectives of the activities for developing

a worldwide ISDN are:• Standardization• Transparency• Separation of competitive functions• Leased and switched services• Cost related tariffs• Smooth migration• Multiplexed support

Standardization• To provide access to the network.• Movable ISDN-standard equipment and use of layered protocol.• To allow users to select equipment from multiple suppliers.

Transparency• Digital transmission service is independent of the contents of

data.• Users can develop new applications and protocols.• User provided encryption methods can be employed simply.

Separation of competitive functions• ISDN does not preclude competitive functions from basic

ones.• Some countries desire certain enhanced services be offered

competitively (e.g. videotex, electronic mail).

Leased and switched services• ISDN should provide both leased and switched services.• To allow users to optimize on the basis of cost and

performance.

Cost-related tariff• One type of service does not subsidize others.• Price distinctions related to the cost of providing specific

performance and functional characteristics of a service.

Smooth migration

• ISDN evolution must coexist with existing equipment and services specific capabilities required: pre-ISDN terminals to interface to ISDN inter-network protocols and protocol converters.

Multiplexed support

• Accommodating user-owned PBX and LAN equipment.

Benefits of ISDN• The principle benefits of ISDN to the customers can

be expressed in terms of cost saving, flexibility and speed.

• Integrated voice and data means that the user does not have to buy multiple services to meet multiple needs.– Access charges are made to a single access line only.– Purchasing services based on actual needs.– Product diversity, low price and wide availability of

equipment.

ISDNOthers

Single ISDN

terminal Multiple ISDN

terminal Installation

PBX LAN,

private network

Specialized storage and information processing

centers

Figure : User Network Interface