CONCEPTS OF ISDN

1) Principle of ISDN
2) Evolution of ISDN
3) The user interface
4) Objectives
5) Benefits
6) Services
7) Architecture

1. PRINCIPLE OF ISDN:

a) Support of voice and non voice applications using a limited set of standardized facilities.

• This principle defines the purpose of ISDN and the means of achieving it.
• ISDN support voice communication (telephone calls) and non voice communication (digital data exchange).

b) Support for switched and non switched applications:

• ISDN will support for circuit switching and packet switching.
• ISDN will support for non switched services in the form of dedicated lines.

c) Reliance on 64 kbps connection:

• ISDN provides circuit switched and packet switched connection at 64 kbps.

d)Intelligence in the network:

• ISDN provides network management and maintenance capabilities.

e)Layered protocol architecture:

• ISDN protocols exhibit a layered architecture and can be mapped to OSI model(open system interconnections).
• This allows gradual implementation of ISDN services to a given customer base.

f)Variety of configurations:

• More than one physical configuration is possible for implementing ISDN and provides the usage of existing equipment of the customer base.

2. EVOLUTION OF ISDN:

a) Evolution from telephone IDN’s:

• The ISDN evolve from the existing telephone networks.
• Existing telephone network forms the foundation for the services to be provided by ISDN.

b) Transition of one (or) more decades:

• The introduction of ISDN services will be done in the context of existing digital facilities and services.
• Protocol conversion will be needed between alternative facilities and/or services.

c) Use of existing networks:

• If an ISDN will provide a packet switched service, for the time being the interface to that service will be X.25 (fast packet switching) may need to be a new interface in the future.

d) Interim user-network interface:

• With the lack of digital subscriber lines might delay introduction of digital services in developing countries.
• With the use of modems and other equipment existing analog facilities can support to some countries.

e)Connection at other than 64 kbps:

• The 64 kbps data rate was chosen as the basic channel for circuit switching.
• For digital data application the data rate is too low.
• Thus other data rates will be needed.

 

3. USER INTERFACE:

#) The user has access to the ISDN by mean of a local interface to a digital “pipe” of a certain bit rate.

(i)A residential customer may require only sufficient capacity to handle a  telephone and a personal customer.

(ii)An office may wish to connect digital PBX,LAN to the ISDN and this will require higher capacity pipe.

4. OBJECTIVES:

#)National governments, data processing and communication companies, standards organizations and others are leading to the development of worldwide ISDN.

#)They are in need of certain common objectives.

#)They are,

a. Standardization
b. Transparency
c. Separation of competitive functions
d. Lost related tariffs
e. Smooth migration
f. Multiplexed support

a)Standardization:

• Standards will provide for universal access to the network.
• ISDN – standard equipment can be moved from one location to another(eg. From one country to another) and be plugged into the network.
• The cost of such equipment will be minimized because of the competition among many vendors to provide the same type of functionality.

b)Transparency:

• The service is independent of and does not affect the content of the user data to be transmitted.
• This permits users to develop application and protocols with the confidence that they will not be affected by the underlying ISDN .
• Once a circuit (or) virtual circuit is setup, the user should be able to send information without the provider being aware of the type of information being carried.

c) Separation of competitive functions:

• It must be  possible to separate out functions that could be provided competitively as opposed to those that are fundamentally part of the ISDN.
• A single, government will provide all services in many countries.
• In some countries require certain enhanced services be offered competitively.E.g. Videotex, electronic mail.

d) Leased and switched services:

• This is used to configure the network services and allow the user to optimize on the basis of cost and performance.

e) Cost related tariff:

• The price for ISDN service should be related to cost and independent of the type of data being carried.
• The price is related to specific performance and functional characteristics of a service.

f) Smooth migration:

• To provide for a smooth migration to ISDN, ISDN interface should evolve from existing interfaces and inter working arrangements must be designed.E.g. adapter equipment, internetwork protocols and protocol converters.

g) Multiplexed support:

• Providing low capacity support to individual users multiplexed support must be provided to accommodate user owned PBX and local area network (LAN) equipment.

 

5. BENEFITS:

• The principle benefits of ISDN to the customer can be cost savings and flexibility.
• The integration of voice and a variety of data on a ingle transport system means that the user does not meet multiple needs.

 

6. SERVICES:

Facsimile:

• Service for the transmission and reproduction of graphics and hand written and printed material.
• This can be used to transmit a page of data at 64 kbps in 5 seconds.

Teletex:

• This service is for exchange correspondence. Used to prepare, edit, transmit and print messages.
• Transmission is at a rate of one page in two seconds at 9.6 kbps.

Videotex:

• An interactive information retrieval service.
• A page of data can be transmitted in 1 second at 9.6 kbps

 

7. ARCHITECTURE:

#)ISDN will support physical connector for users.

• A digital subscriber line.
• Transmission services.
• Common physical interface provides telephone interface, personal computer and video tex terminal.
• The terminal equipment is the customer equipment and network termination is the device on the customer premises.
• Subscriber line is the physical signal path from the subscribers NT to the ISDN central office.
• ISDN central office connects numerous subscriber lines to the digital network which provides,

a) Circuit switched capabilities:

• Operating at 64 kbps provided by other digital switched telecommunication network.

b) Non switched capabilities:

• 64 kbps dedicated link provided by broadband ISDN used for asynchronous transfer mode transmission.

c) Switched capabilities:

• High speed >64 kbps switched connections using ATM as a part of broadband ISDN.

d) Packet switched capabilities:

• this facility resembles packed switched service provided by other networks.

e)Frame mode capabilities:

• a service that supports frame relay.

f) Common channel signaling capabilities:

• These are used to control network and provide call management. It uses SS7 signaling system number-7.

g) It has a capability of user to network control dialogue.

 

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