IBM International ISDN User Manual page 198

Appendix C: A Brief ISDN Glossary
Glossary
a/b interface
Adapter types There are three categories of ISDN adapters avail-
198 ISDN PC Card – 17 Appendix C: A Brief ISDN Glossary
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.
able for use in computers:
•
Passive adapters are the cheapest and gen-
erally the best choice among today's ISDN
adapters. Passive ISDN adapters work pri-
marily on OSI Layer 1. The IBM International
ISDN PC Card is a passive ISDN device.
semi-active These adapters support proto-
cols 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 cases this capability can
also be implemented in the device drivers of
passive ISDN adapters. active Active ISDN
adapters are top-of-the-line ISDN cards, and
the most expensive.
•
Active ISDN adapters handle all ISDN proto-
cols on OSI Layers 1, 2 and 3. These cards
have one or more on-board microprocessors
and a certain amount of RAM. Active ISDN
adapters relieve the host system's CPU of all
ISDN communication processing. Their pri-
mary area of application is in RAS servers,
for which many manufacturers offer a spe-
cial line of active adapters.
Note: ISDN adapters cover OSI Layer 1, but differ
in the higher-layer protocols that they provide!