Analogy to railroads apt in many ways

Although there weren’t any ponies or free beer, the ceremonial cross-country ISDN link-up at TRIP ‘92 near Washington, DC, had everything else: famous men, politicians and schoolchildren. Bob Metcalfe, the inventor of Ethernet, served as the event’s master of ceremonies. The U.S. Commerce Secretary and Virginia’s lieutenant governor made speeches that were more-or-less focused on the subject at hand. The kids showed their drawings depicting various benefits of ISDN and spoke their well-memorized lines.

The occasion was the first public transcontinental voice-and-picture phone call over ISDN basic-rate lines. From a Hyatt Regency hotel ballroom in Reston, VA, ISDN calls quartered the nation to Redstone Arsenal (Huntsville, AL), Jet Propulsion Laboratory (Pasadena, CA) and the Ameritech Center (Chicago, IL). In a reference to the driving of the Golden Spike linking the transcontinental railroad in 1869, this symbolic linking of the heretofore separate central switches was designated the “Golden Splice.”

The ceremony was marred by technical difficulties; during the first half of the presentation, the audio kept breaking up. After a while, technicians tracked the problem — not to the ISDN hookup, but to an intermittent ground connection in the hotel’s wiring closet. Metcalfe reminded the audience that the Golden Spike Ceremony had its glitches too: The ceremony was delayed two days because of rain, and the first dignitary to swing a sledgehammer missed the spike entirely.

WHAT EXACTLY IS ISDN, ANYHOW?

ISDN, which stands for Integrated Services Digital Network, provides several independent 64-Kbps data channels, along with a digital control channel that handles call setup and takedown, over a single physical connection between the phone company and the subscriber. The phone company’s switching gear can connect each channel to a different destination. A channel can carry computer data, digitized voice, fax transmissions, video or any other digital data.

A standard voice line (POTS, for Plain Old Telephone Service) usually carries analog signals. Transmission quality varies widely depending on the distance the signal must travel and the number of intermediate central switches it must cross. However, the typical quality is usually equivalent to a bandwidth of 10 Kbps or so. On long-distance calls, echo-canceling filters limit the audio bandwidth to about 3 Kbps for each direction, or 6 Kbps for the conversation. (Modems and fax machines emit tones that suppress the echo-canceling mechanism, because they only transmit one way at a time.)

APPLICATION DEMOS COVER A BROAD RANGE

On the trade show floor adjoining the ceremony, two dozen vendors touted equipment and software to take advantage of ISDN lines. Common applications included:

• Home office. Telecommuting is being touted as one way to meet commuter-restriction laws by having staffers work at home a few days each week. The at-home office needs a voice line (probably with call-waiting features), a fax line and a computer link to the corporate LAN. Fortunately, most workers don’t use all of these services all the time, so they can share a low-bandwidth 2½-channel ISDN line. The telephone receiver contains the logic to route the data and fax calls appropriately.

In one press kit, we saw a detailed cost comparison between an ISDN-equipped office and a POTS-equipped office. The total costs of equipment and operation are remarkably similar.

• Wide-area networks. By joining several 64-kilobit channels together, you can obtain greater bandwidth. Note, though, that there is no standard protocol for interleaving the data across the channels, so you must use the same brand of router at both ends. A standard, known as H0, has been proposed but is far from adoption.

We saw the same technique of linking several channels being used for video conferencing. By combining moderate frame rates, modest amounts of on-the-fly compression and multiple ISDN lines, a fairly credible moving image can be presented.

• Graphic image databases. Kodak showed its Photo CD image library concept (see Vol. 2, No. 4, p. 5), pointing out that an ISDN link would obviously be better than a slow 9,600-bps link for sending pictures.

• Remote medical consultations. This would enable doctors to simultaneously talk and view diagnostic images in real time across a phone connection. The best specialists in the land would be available to small-town GPs everywhere (for a nominal fee, no doubt).

Conference attendees were told that 22 central offices in the U.S. have interLATA (i.e., long distance) ISDN connections. Another 84 exchanges have installed ISDN-capable gear and will shortly be linking them to the national network. By the end of 1993, Bellcore estimates that 1,700 exchanges will be ISDN-equipped, and by the end of 1994, half of the exchanges in the land will be able to offer the service.

The service that Bellcore is talking about is the Basic Rate Interface, which provides two 64-Kbps signal channels plus one 16-Kbps control channel. (The control channel can also carry a 9,600-bps fax or data link.) Together with a limited set of central office features such as billing and the conversion to and from ordinary analog lines, it makes up the National ISDN-1 (NI-1) standard. NI-1 also allows some optional features, such as caller identification, call waiting and call forwarding.

From the user’s perspective, NI-1 has two advantages. First, it can be carried on the copper pairs that are already installed; no need to run new, expensive fiber or dedicated wires. Second, all conforming equipment is interoperable throughout the U.S. You will be able to buy telephones, Group IV faxes, computer interfaces and so on from many vendors and simply plug them in, no matter what kind of switchgear your local phone company has installed.

A GLOBAL MARKET IN A YEAR OR TWO …

Waiting in the wings is the proposed NI-2 standard, which will be upward compatible with NI-1. The principle reason that NI-2 has not already been promulgated is that its sponsors are coordinating its development with CCITT, the organization that sets the international standards for telecommunication.

Thus, when NI-2 is adopted, conforming equipment will plug in anywhere in the world — which means a global market and global competition among vendors.

NI-2 also standardizes the Primary Rate Interface, which provides 23 64-Kbps signal channels and one 64-Kbps control channel. This is equivalent to today’s T1 service (the same 1.5 Mbps total bandwidth), except that it is divided into independent channels. American businesses cannot get Primary Rate service from their local phone companies today, but they can buy it directly from Bell, MCI and Sprint. However, customers must verify that their equipment is compatible with the central switch that serves their location.

WHEN IS A STANDARD NOT A STANDARD?

One up-and-coming alternative to ISDN, called Asynchronous Transfer Mode or ATM, is something that no one at the TRIP ‘92 conference wanted to discuss, presumably because that’s not what they were selling. Proponents of ATM say that ISDN has long been bypassed by superior technologies, and as a result should never be allowed to catch on.

However, the regional Bell companies, as well as long-distance carriers such as Sprint and MCI, are in the driver’s seat; they already have businesses and homes wired for ISDN-1 and are busily installing central switches that handle ISDN. Since this is what they’re peddling, and we don’t have anything else to buy today, ISDN is likely to become the de facto digital telephony standard even if it’s already obsolete.

Peter Dyson