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The World's Entering the Era of the Integrated Services Digital Network.

ISDN--the Integrated Service Digital Network--is becoming reality.

In the past year, ISDN has moved from a concept toward reality: the I-series of standards was adopted by the Consultative Committee for International Telegraph and Telephone (CCITT) in October 1984: many major manufacturers have announced aggressive plans to offer ISDN products (for example, AT&T Technologies and Northern Telecom); and carriers and public telecommunications administrations around the world have announced trials of ISDN" standard services" (for example, Illinois Bell for 1986).

ISDN is an international telecommunications architecture meant to provide widespread availability (comparable with telephony) of a wide variety of telecommunications capabilities for numerous applications, including voice, high-quality audio, alarms, telemetry, interactive data, bulk data, images and video.

From a user's perspective, the integration is accomplished through a small set of multi-purpose interfaces using common signaling and control for different applications. A user can have a single multi-application ISDN workstation, a cluster of ISDN terminals, or one or more non-ISDN terminals working through terminal adapters. The same terminals, with the same standard interfaces, can connect directly to a public or private ISDN or through an ISDN-compatible PBX. LAN and cluster controller to an ISDN. This permits users' equipment configurations to change with the current need, without having to change interfaces or other arrangements with the ISDN (unless, of course, additional interfaces are needed for added capacity).

The user-network interfaces play a key role in defining ISDN and establishing many of its characteristics. The "basic interface" carries two 64-kb/s B (bearer) channels and a 16-kb/s D channel. The D channel carriers signaling for all of the services using the interface. In addition, the D-channel protocol provides for carrying packet data in separate logical links. The basic interface provides all of the capabilities needed by a typical ISDN workstation and most existing terminals. Standards are currently being established to support the basic interface over approximately 80 percent of the loops in the US using the existing wire pairs. The remaining loops can be economically served by digital carrier systems out to a remote point from the central office.

For connecting PBXs, LANs and other concentrated-traffic devices, a "primary rate interface" is provided at 1.544 Mb/s (2.048 Mb/s in Europe) carrying 23 B channels and a 64-kb/s D channel. For higher bit-rate applications, channels of 384 kb/s and 1.536 Mb/s can be carried across this interface. Plans are being made for a wideband ISDN, fiber-optic interface for even higher bit-rate applications.

These capabilities should lead to considerable savings when compared with a variety of single-application terminals, each requiring a separate interface corresponding to only a single communications service. Savings accrue through reduced equipment costs due to mass production and standardization, sharing of interfaces by several applications, and reduced operations, administration and maintenance costs through standardization and interchangeability.

One mechanism for introducing ISDN terminals may be the use of an "ISDN card" in personal computers. This card and accompanying software would permit communication over an ISDN in much the same way that am existing modem card works with the telephone network. This will permit existing applications to use ISDN for communications, and will also foster a whole new range of communicating applications to take advantage of the many ISDN capabilities.

For example, suppose that you're making some changes to your budget using your spreadsheet application, and you have a question about your computer charges. You go to your ISDN communications "window" and place a voice call to George, your budget coordinator. George wants to see your spreadsheet results, so you add a packet data connection to your voice call and jointly work on the spreadsheet.

As you're finishing up, your terminal signals an urgent incoming call from your boss, Jim, with the following message: "Calling from San Francisco about the ISDN talk." You say goodbye to George, disconnect the call, and pick up Jim's call. He wants to see the three new slides you have prepared for his ISDN talk, so you add a 64 kb/s connection to the call and transmit an image of the first slide from your disk. You work through changes to each slide and finally finish. These are only some of the many capabilities possible through ISDN.

The I-series of CCITT recommendations contains not only the interface and protocol specifications, but also includes an overview of ISDN, service capability specifications, network and protocol architecture models, ISDN numbering plans, internetwork considerations, and maintenance and operation considerations (although much work remains in these last areas).

Inside the network, integration can occur in several areas. Of course, the local loops or access lines provide several services over the same pair of wires (or other transmission medium), along with common switch terminations and signaling. In addition to saving transmission media and equipment, and switching and signaling equipment, there's no special engineering, administration, operations or maintenance required for each of the different services provided. As integrated ISDN switches become available, similar sharing and savings will become possible further inside the network.

Good Digital Track Record

Digital technology has been economically proving out over specific analog systems for more than 20 years for voice communications. This began with metropolitan transmission, and then moved to toll switching and signaling, local switching and loops, and now long-haul transmission and local signaling. ISDN completes this replacement by bringing digital transmission, switching and signaling directly to the user.

For example, for a small business or residence location where telecommunications service might include voice, packet and circuit data, for the next several years, a single POTS (plain old telephone service) line will be less expensive to provide than an ISDN loop, although this will eventually change over also. However, for any two or more services, an ISDN access line will be less expensive than individually provided services. For a larger location, where services could also include PBX-CO circuits, voice-grade private lines and higher-speed data, the primary rate access will prove economical for as few as five to 10 lines, depending on the mix of services, the distance to the office and the type of transmission. Again, the savings are in both capital and expense categories.

Manufacturers are actively building equipment to comply with the CCITT recommendations and the further specifications of the carriers and administrations around the world. For example, both AT&T Technologies and Northern Telecom have announced aggressive plans to support ISDN standards in their product lines.

In many areas, additional details are needed to complete the specifications required to actually build equipment. In the US, the newly formed ANSI standards group TI is providing a focus for this specification. Detailed standards for the internal network signaling called Signaling System 7, are being finalized right now. Bellcore is completing the further details that can be used by the operating companies in a complete specification. Similar work is in progress on ISDN interfaces and protocols, service features and loop transmission systems.

Many carriers and administrations have announced plans for ISDN trials, including ones in England, Germany, Italy and Japan. Announcements prior to 1985 were for "pre-ISDN" or "nearly ISDN" capabilities, because the standards were not finalized until October 1984. Now, however, true ISDN standards trials are being introduced. For example, Illinois Bell recently announced an ISDN trial outside of Chicago, using the AT&T Technologies 5ESS-TM switch to provide ISDN Centrex service in 1986.

In summary, all of the necessary parts of ISDN are rapidly coming into being: standards, detailed specifications, semi-conductor chips, equipment for both networks and terminals, and the fact that the carriers and administrations are moving aggressively to install and test the systems with "live" customers. The economics are compelling to introduce ISDN capabilities, even just for cost reduction, without considering the additional capabilities, which can lead to additional service revenues. Customers will share in both the reduced costs and the increased capabilities. Thus, assuming successful trials and market acceptance, ISDN will be introduced as rapidly as equipment can be manufactured and installed, beginning in 1986.

We are entering the ISDN information
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Author:Gifford, W.
Publication:Communications News
Article Type:transcript
Date:Jun 1, 1985
Words:1335
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