This was a presentation by a fellow from Bell Northern Research, a research arm shared by Bell Canada and Northern Telecom. He talked about ISDN standards, facilities, and some pilot projects. The audience was already fairly knowledgable about ISDN - which made me feel like a fish out of water. I'm afraid that I cannot even tell you what ISDN stands for. I am convinced that it's going to be neat, though.

ISDN is the Phone Company's all-digital network, being tested in about a hundred sites throughout the world. The speaker was certain that ISDN would become a part of your life sometime in the 1990s. ISDN standardization has turned into a hot button for U.S. telephone companies since divestiture took place - there is no larger Bell organization to enforce a common standard, so organizations such as EIA and ANSI have become very active in recent years.

In order to connect to the ISDN network, you need an ISDN node engine at your site. The engine performs packet switching, multiplexing and bandwidth allocation. Both sides of the engine are firmly standardized; there is a well-defined interface to the Phone Company's circuits, and a well-defined interface to terminals. By "terminal", I mean standard tubes, telephones, facsimile and high-fidelity audio. There is also a provision to attach "non-ISDN" terminals, using a method I'll describe in a second.

When you place a "call", you can use either a "packet-switched" channel, or a "circuit-switched" channel. Packet-switched channels use the X.25 standard. Circuit-switched channels are essentially point-to-point audio channels, sampled at either 3.5 or 7 KHz. If you want to attach a "non-ISDN" terminal to the net, you are obligated to use a circuit-switched logical channel, since ISDN has no control over the content or format of a circuit-switched channel. Note that ISDN makes no provision for multidropped circuit-switched channels; they are all point-to-point.

IBM is known to be working on ISDN interfaces. There exists a NETBIOS implementation for personal computers (which means that you will be able to transparently implement a wide-area LAN using the ISDN facilities). It will not be as fast as conventional LANs, however.

ISDN has lots of goodness associated with it: it requires only a small number of standard interfaces, it is all digital (and therefore reliable), and it will be ubiquitous.