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What is ISDN ? Integrated Services Digital Network (ISDN) is the next generation of communication service, and is available right now. ISDN brings affordable, high-speed digital communication - up to 128 Kbps - to millions of people like yourself for the first time. Verizon pipes ISDN into your home just like POTS (Plain Ordinary Telephone Service).

The main difference between your existing line and an ISDN line is that your current line is analog whereas ISDN line is digital. Why is this important? The line is designed to support data! It can carry up to 128 Kbps of data, plus it allows for greater connection stability and faster set-up times.

How Does It Work ?
Verizon divides the POTS wiring between your premises and the phone company into three separate logical channels. The term logical refers to the fact that these three channels are not three separate wires, but are defined by the logic of how the ISDN systems operates.

Advantages of ISDN
The modem was a big breakthrough in computer communications. It allowed computers to communicate by converting their digital information into an analog signal to travel through the public phone network. There is an upper limit to the amount of information that an analog telephone line can hold. Currently, it is about 56 kbps, using special equipment. Commonly available modems have a maximum speed of 33.6 kbps, but are limited by the quality of the analog connection and routinely go no faster than 26.4 or 28.8 kbps.

ISDN allows multiple digital channels to be operated simultaneously through the same regular phone wiring. The change comes about when the telephone company's switches can support digital connections. Therefore, the same physical wiring can be used, but a digital signal, instead of an analog signal, is transmitted across the line. This scheme permits a much higher data transfer rate than analog lines. BRI ISDN, using a channel aggregation protocol such as bonding or Multilink-PPP, supports an uncompressed data transfer speed of 128 kbps.

Multiple Devices
Previously, it was necessary to have a phone line for each device you wished to use simultaneously. For example, a separate line was required for a telephone, fax, computer, bridge/router, and live video conference system. Transferring a file to someone while talking on the phone or seeing their live picture on a video screen would require several expensive phone lines.

It is possible to combine many different digital data sources and have the information routed to the proper destination. Since the line is digital, it is easier to keep the noise and interference out while combining these signals. ISDN technically refers to a specific set of digital services provided through a single, standard interface. Without ISDN, multiple distinct interfaces may be required.

Signaling
Instead of the phone company sending a ring voltage signal to ring the bell in your phone ("in-band signal"), it sends a digital packet on a separate channel ("out-band signal"). The out-of-band signal does not disturb established connections, and call setup time is very fast. For example, a V.34 modem typically takes 30-60 seconds to establish a connection; an ISDN connection usually takes less than 2 seconds to establish.

The signaling also indicates who is calling, what type of call it is (data, voice), and what number was dialed. Available ISDN phone equipment is then capable of making intelligent decisions on how to direct the call.

Basic Rate Interface (BRI) The three channels of a residential ISDN connection include two 64 Kbps B (Bearer) channels and one 16 Kbps D (Delta) channel. This standard configuration is referred to as 2B+D. The two B channels are the workhorse of an ISDN connection because they deliver the bulk of the digital information that's transmitted. This digital information can include voice, files, video and sounds. You can also combine multiple BRI lines to add more bandwidth power.
Primary Rate Interface (PRI) ISDN Primary Rate Interface (PRI) is an all digital networking service that consists of a 23B+D connection. Configuration: Twenty three 64 Kbps "Bearer" (B) channels One 64 Kbps "Delta" (D) channel.
Bandwidth: With a total bandwidth of 1.544 Mbps, it is designed for transmission through a standard North American T-1 trunk. Flexibility: Most of today's new high-capacity telephony, data communications and video conferencing equipment are built to be ISDN PRI capable. This includes PBX's, mainframe and distributed systems, LANs and WANs, multiplexers and ISDN controllers, video conferencing units and more. Expandability: Most PRI equipment can flexibly utilize and aggregate B channels to build as big a pipe as needed for medium to large applications. The B channels on PRI are fully compatible with the B channels on BR

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ISDN Benefits In A Nutshell
OK, enough of the vision: let's look at the specifics of what ISDN offers in practical terms. ISDN is an integrated voice and data network that offers an impressive collection of benefits.

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What You Will Need
To have ISDN at your home or office you will need the following:

Are You A Candidate ?
The combined voice and data capabilities of ISDN offer a broad range of applications for all kinds of people, including telecommuters, small office/home office (SOHO) workers, Internet surfers, consultants, contract workers, business executives, researchers, teachers, and customer service representatives. You are a candidate for ISDN service if you:

Getting Wired For ISDN
ISDN uses the same wiring as that used for your existing analog telephone service, but wiring configurations for ISDN operate differently. You need to understand several important wiring issues before dealing with your ISDN equipment.

Converting an Existing Line or Getting a New Line
One of the first ISDN wiring issues is whether you want to convert an existing telephone line to ISDN service or to add a completely new line. Older homes or offices may be wired for only one line, while newer ones may have come pre-wired for up to four lines. The standard four-wire cable allows for two lines. One line uses the red and green wires, while the other lines uses the yellow and black wires. Most buildings in metropolitan areas can add additional lines beyond two. Verizon can help you find out if you can bring an additional line in before deciding whether to convert an existing analog line.

If you can't bring another line in, you'll need to convert an existing line to ISDN. Don't worry, you can use an ISDN line for analog communications. For example, if you use a second analog line for telephone, fax, or modem communications, you can still use these devices with an ISDN line for high-speed digital communications.

In most cases, you don't want to convert your primary analog voice line to ISDN service. Unlike your existing analog service, ISDN is disrupted if you experience a power outage. Additionally, you may want to use your ISDN line exclusively for data transmission and not tie it up with incoming voice calls.

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Wiring from Verizon to your Premises
The U reference point covers the wiring from Verizon to your premises as well as your home's internal wiring up to the NT1. In the United States, the division of telephone wiring responsibility between the telephone company and the end user is different from the U-interface. The telephone company is responsible for any wiring to your doorstep, but from that point it's your responsibility.

The demarcation point (demarc) is the dividing line between the telephone company's wiring and the premises wiring. The physical device that provides the means to connect the telephone company's wire to the premises wire is the Network Interface (NI). The demarcation point and Network Interface box are the same for your existing regular telephone service and ISDN service. However, if your building is an older one, you may not have a network Interface box. As a result, the incoming telephone line connects directly to a device called a Protector Block.

The FCC places a restriction commonly referred to as the 13-inch rule on both the customer and the telephone company. Basically, this rule states that the Network Interface box must be located within 12 inches of the Protector Block. If your building doesn't have a Network Interface box, you must have the telephone company install one. The FCC prohibits customers from working at the Protector Block. Only the telephone company can install the Network Interface device or any device wired to the telephone line.

Wiring Your Premises
From the demarcation point, your telephone wiring is your responsibility. You can have AMERICOM INC. do your wiring from a new line, or you can do it yourself. If you are using one of two pairs of wires in a line, you need to know which pair is used for which line. If you have a choice, bring in your ISDN line as a separate line and use just one of the wires from the ISDN line. It makes it easier to install and set up ISDN equipment.

Link to additional technical information on ISDN

Additional Resources

• North American ISDN Users' Forum
• National ISDN Council (NIC)

General ISDN Information

• Dan Kegel's ISDN Homepage
• Papers on ISDN at the University of Wisconsin's Gopher


ISDN Books and Publications

• ISDN for Dummies

Revised excerpt from "ISDN for Dummies(R)" by David Angell. Copyright © 1995 by IDG Books Worldwide, Inc. All rights reserved. Revised and reprinted here by permission of the publisher. No part of this text may be reproduced or transmitted in any form, by any means (electronic, photocopying, recording, or otherwise) without prior written permission of IDG Books Worldwide. "ISDN for Dummies" is a registered trademark under exclusive license to IDG Books Worldwide, Inc. from International Data Group.

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