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What is the full form of ISDN in telecommunications?
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Answer: Option D — Integrated Services Digital Network
Detailed Solution
ISDN stands for "Integrated Services Digital Network", a set of communication standards for transmitting voice, video and data digitally over ordinary telephone (copper) lines.
About ISDN:
- It was standardised by the International Telegraph and Telephone Consultative Committee (CCITT), now part of the International Telecommunication Union (ITU-T), in 1988.
- Before ISDN, telephone lines carried analog signals; ISDN made it possible to send digital signals end to end.
- It allowed voice calls, fax, data and video conferencing on the same line at the same time.
Types of ISDN service:
Basic Rate Interface (BRI): two "B" (bearer) channels of 64 kbps each and one "D" (data/signalling) channel of 16 kbps ("2B+D"), giving a total of 144 kbps. It was meant for homes and small offices.
Primary Rate Interface (PRI): 23 B channels plus one D channel (in North America and Japan, about 1.544 Mbps), or 30 B channels plus one D channel (in Europe and India, about 2.048 Mbps). It was meant for businesses.
ISDN in India:
- BSNL and MTNL offered ISDN services in major cities from the late 1990s, mainly for businesses, video conferencing and internet access.
- It has now been largely replaced by faster technologies such as DSL broadband, optical fibre (FTTH) and mobile data (4G and 5G).
Related telecom abbreviations:
- DSL: Digital Subscriber Line; ADSL: Asymmetric DSL.
- PSTN: Public Switched Telephone Network.
- FTTH: Fibre to the Home.
- VoIP: Voice over Internet Protocol.
- LTE: Long-Term Evolution (4G).
- ITU: International Telecommunication Union (founded 1865, Paris; headquarters Geneva).
- BharatNet: a project to connect all gram panchayats with optical fibre.
Why not the other options?
- ✗"Internet Service Data Network" is not the correct expansion.
- ✗"International Satellite Digital Network" is not the correct expansion.
- ✗"Integrated Signal Data Node" is not the correct expansion.
Quick tip
Remember: ISDN = Integrated Services Digital Network (digital voice and data over telephone lines; BRI = 2B+D = 144 kbps; PRI = 23B+D or 30B+D); replaced by DSL, fibre and mobile data; ITU = Geneva.
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Abbreviations & Full Forms — Preparation
This question tests your understanding of Abbreviations & Full Forms, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers the full forms of common abbreviations used in government, banking, science, technology, defence, international relations and everyday life, such as ISRO, NABARD, SEBI, GDP, GST and UNICEF. These questions are quick marks if you have revised the most common abbreviations. Group them by field (banking, government bodies, science and technology, international organisations) and pay attention to small words such as 'of', 'for' and 'and', since wrong options often change just one word. Practise the abbreviations and full forms questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.