Appendix: What is the ISDN?
MicroLink ISDN/PCC-16
Manual © 1997 ELSA GmbH
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The D channel protocol controls only the establishment of communications between the user and his
local exchange, and thus the communications between users is completely independent of the ISDN
protocol. DSS1 devices and 1TR6 devices are fully able to communicate with one another.
Data transfer takes place over the B channel, which are controlled by the B channel protocols. These
will be covered here in brief only: X.75 (bit rate 64,000 bps, data security controlled by the HDLC (High
Level Data Link Control), V.110 (bit rate asynchronous 300...38,400 bps, synchronous 600...64,000 bps,
permanent data structure, no data security), V.120 (used mainly in the USA, similar to X.75 but with
just 56,000 bps).
Software Interface to ISDN Adapter Boards
The software interface between ISDN adapter boards and communications applications is called the
CAPI (Common ISDN Applications Interface). This software makes all of the ISDN services available.
CAPI was developed in a cooperation between the manufacturers of ISDN adapters and software, and
the German FTZ (Telecommunications Technology Central Office), and is available in two versions:
CAPI 1.1 and CAPI 2.0. The two versions are not compatible with one another.
EuroFileTransfer
This is an internationally standardized transfer protocol (ETS 300075) which enables a platform-
independent data transfer via ISDN. The EuroFileTransfer protocol must be supported by the
application software and the ISDN adapter board must fulfill the international standard ISO 8208.