Term

Description

B channel

A 64kbps data channel that can be used for voice/fax/modem  calls at the same call charges as a conventional analogue telephone line  (or for data calls at a slightly higher cost).

D channel

A 16kbps control channel used for setting up calls, DDI  info, call cost info, etc.

BRI

Basic Rate Interface: a twisted pair copper connection  which uses the same wires as analogue lines. It has 2 B channels and one  D channel (2B+D). BT's service is called ISDN-2. In the UK both DDI and  MSN are available over BRI. In some countries MSN is not available, and  DDI is only available over PRI or multiple BRIs.

PRI

Primary Rate Interface: a fibre connection. Traditionally  30B+D, it is now also available from BT as 15B+D and even 8B+D. Note that  the service is called ISDN-30 (even if only 15 or 8 channels are purchased).

Bundling

If greater capacity is needed, more B channels can be  used at once (sometimes called bundling).Group 464kbps fax at 300dpi. Its use is reasonably widespread  use in Germany, but practically nowhere else.

Group III bis

Faster (64kbps) Group III fax.

CAPI

An API standard for interfacing PC software to ISDN controllers  or terminal adapters. Zetafax supports active ISDN controllers by making  use of the CAPI interface.

Protocols

ISDN provides a raw channel for passing data, it does  not specify what protocols you should use for passing information across  it securely. Common examples are digitized analogue data (voice/fax/modem),  X.25 (packet switched data), V.14 (async chars to 57.6kbps), V.120 (more  sophisticated, often with compression and bundling), V.110 (American, similar  to V.120), Group 4 (fax). It is believed that the ZyXEL and SpartaDIS hardware can do all of the list except V.110 (SpartaDIS) and Group 4 (SpartaDIS and  ZyXEL). Above these sit network layer protocols such as IP or IPX (used  by remote ISDN routers) and proprietary protocols used by remote bridges  and programs such as file transfer packages (eg 4Sight).