ISDN

(Integrated Services Digital Network)

What is ISDN?

Simply speaking, ISDN provides the customer with the 64kbit/s that PCM (Pulse Code Modulation) digital representation of speech occupies, but doesn't insist that it be used for speech. The simplest connection you can buy offers `2B+D' (BT's ISDN-2, or 'basic-rate' ISDN), which is 2x64kbit/s with a 16kbit/s signalling channel. In principle, you can send rather wimpy video with 128kbit/s, but it would have to be highly compressed, at low resolution and with a low frame rate (like in a picture-phone).

Say I want to access my University computer from home, using an ISDN connection, in order to get fast terminal access and file transfer. What would I need to connect a PC to a workstation over this?

You will need a terminal adaptor at the Unix end, and a PC card in the PC. Terminal adaptors are around UKP1000. Software is dependent upon what you wish to run over the link. An async terminal connection will probably not utilise the full bandwidth available. It is possible to run IP over the link.

Adaptors for Sun Microsystems currently available: [consult relevent comp.sys.sun and uk.sun lists for more upto date info]

Diehl have an Sbus card with SunOS-4.1.3 and UK approval. UK distributor is Controlware, Thatcham, UK, (01635 871636) or try info@diehl.de. They also have PC cards for DOS and Unix.

Bintec have a range of cards for different backplanes and operating systems, including an Sbus card, approved for UK usage and with drivers. Contact reinhard@bintec.de, Tel: (01911) 99675-0, Fax: (01911) 6880725

NetBlazer PN and an external TA, allowing ISDN access from Ethernet. The Controlware CITAM unit was also recommended in this context.

Sparc 10s, LXs and later models have on-board ISDN. However, Sun are not planning to release SunOS drivers for this at the moment. They say that BABT approval of the hardware is imminent and Solaris drivers will be released.

I am told some models of DEC AXP also have on-board ISDN. Driver status is unknown.

What's the difference in equipment at the exchange switch between an ISDN line and that for an analogue line?

The lines have an identical concentrator, but have different line termination. Instead of converting analogue signals to PCM format for transmisson to the switch, an ISDN Line Terminator will process the signal differently and pass it on directly to the switch.

The subscriber's ISDN unit can talk directly to the switch's control units; thereby reducing call setup times to an absolute minimum. Which is great for ethernet ISDN bridges as they can raise and drop the line on demand.