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Appendix C. A brief ISDN glossary
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This chapter gives a brief overview of technical terms used in the world of ISDN
as well as a few computer-related terms.
Historical survey
The first steps in the development of ISDN –the Integrated Services Digital
Network– took place in the early 1980s in France. Many other European countries
soon joined in the development work, however. ISDN was considered the logical
successor to the analog telephony technology commonly used in Europe at that
time. ISDN offered the potential for high speed bi-directional data
communications at 64 kbit/s or 128 kbit/s. The ISDN specifications were
submitted to the ITU and have since been standardized. However, ITU standards
are only recommendations, and some countries have implemented their own
versions of ISDN. Thus ISDN protocols are not exactly the same in every country.
However, the IBM International ISDN PC Card supports all major D-channel
switching protocols, so that this adapter can be used in a great number of
countries throughout the world.
Today ISDN is very easily implemented, since telephone companies in most
countries use only digital interfaces within their networks. The difference
between an analog telephone line and an ISDN line today lies in the wire used
from the telephone company's exchange to the subscriber's access interface, the
type of signals traveling on these lines, and the voltage. Hence you cannot
connect an analog device to an ISDN line, nor vice versa.
Glossary
• a/b interface - Copper interface of the analog telephone network for use of
analog telephones or other equipment such as modems or fax machines. The
term a/b interface is derived from the designation of the two wires in the
analog subscriber line.
• Adapter types - There are three categories of ISDN adapters available for use
in computers:
— Passive adapters are the cheapest and generally the best choice among
today's ISDN adapters. Passive ISDN adapters work primarily on OSI
Layer 1. The IBM International ISDN PC Card is a passive ISDN device.
semi-active These adapters support protocols on OSI Layer 2.
— Semi-active adapters have a DSP (digital signal processor) on board that is
primarily used to provide fax capabilities over ISDN. However, in most
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