Frequently Asked Questions
IS
DN

What is ISDN?
ISDN stands for Integrated Services Digital Network. ISDN is a high speed, high capacity digital communication line. Basic Rate ISDN is comprised of 3 communications paths called channels. Two of the B channels communicate at 64 kilobits per second (kbps) and the third, the D channel communicates at 16 kbps. The third channel is primarily used for signaling.

ISDN can be configured with virtually any of the features available with a standard telephone line, such as Call Forwarding, Three Way Calling, etc. However, it also has the capability to do things not feasible with a standard line, such as Video Conferencing.

Can I communicate with people and locations that don't have ISDN?
ISDN is designed to work smoothly with traditional telephone service. Customers who subscribe to ISDN can make voice calls to and receive voice calls from customers who subscribe to traditional telephone service.

How do I know if ISDN is available in my area?
There are 2 stages of qualification to determine if ISDN is available at your location. The first stage is to verify that your serving central office -- which provides telephone service to your locations -- has ISDN capability. Most central offices are equipped with ISDN or can be "linked" with a Central Office that is ISDN equipped.

The second stage is to determine if your local loop is qualified. This loop is the connection from the Central Office to your home or business. If you live more than 3.5 miles from the central office, you may not qualify, but the local ISDN provider may be able to make special arrangements to get ISDN to you. Most telcos are continually expanding ISDN availability.

What if my central office does not have ISDN capability?
You still may be able to obtain ISDN service from a nearby central office that is equipped with ISDN. There may be an additional charge for both of these services.

Will ISDN work over my existing phone wires?
ISDN works over the copper wires that run to your location, but it may require special jacks and connections. Some inside wiring changes may be required.

Will ISDN work with my existing equipment?
In almost all cases, ISDN requires special equipment. If connecting ISDN to a PC, a terminal adapter is required. Many of the terminal adapters come with 1 or 2 standard jacks (RJ-11), so standard (analog) phones and/or facsimile machine scan be connected also. This equipment is often sold where PC and PC equipment are sold.

If ISDN is being used for voice applications, a special telephone set may be desirable in order to take full advantage of the many calling features such as caller number identification. This equipment is often sold in office supply stores and PC stores.

Why is ISDN better than a standard (analog) line with a modem?
If you transmit very large data files, ISDN provides speed and capacity that may not be possible over an analog line, regardless of the modem speed. For example, video conferencing is difficult over an analog line, but is close to full motion over ISDN. Some terminal adapters have the capability to use both of the two 64 kbps channels to allow you to communicate at 128 kbps. ISDN is an end to end digital connection which provides cleaner data and clearer voice. Analog telephone sets convert the sound waves of your voice to analog electrical waves (analog transmission). ISDN sets convert your voice into voltages representing a string of 0s and 1s (digital transmission), similar to those on a compact disc recording. In both cases, these converted electrical signals are sent over the telephone network. However, as an analog transmission travels through the telephone network, it can pick up noise from power lines, moisture in telephone cables, lightning, or cross talk from other lines. These noise sources do not contaminate ISDN transmission. Therefore ISDN sound quality and transmission reliability is far better than traditional voice service.

What is the cost of ISDN?
The prices vary depending on various issues such as the configuration you select the minimum service period that you select and the state in which you are ordering the service. In Massachusetts, contact Verizon for exact rates.

Why is it more expensive than a standard phone line?
ISDN is a very high-feature, high-speed, high-capacity and high-quality communication line. It is comprised of two channels for communication, giving it the functionality of two standard lines. In addition, ISDN includes some features such as Caller ID, Call Waiting, and Call Hold. Providing these capabilities is costly. But, remember that ISDN will help improve your productivity through increased speed (possibly reducing your Internet access usage charges), expanded applications (such as video conferencing and real-time application sharing), and improved customer service -- you know when that important call is arriving.

Why do ISDN prices vary in other states around the country?
As is often the case when a technical service is first embraced by a market, ISDN still has a wide variety of pricing plans available across the nation. Just as we are beginning to see on-line service, cellular and long distance prices begin to "settle down" and stabilize, ISDN pricing will also. Rates are reflective of the ISDN demand, customer usage in our region and the state and federal regulations within which phone companies must currently operate. In some states ISDN is much higher priced, while in others it is currently lower. You will continue to see pricing plans introduced and withdrawn across the nation as ISDN grows in mass market appeal.

Why is the hardware associated with ISDN so expensive?
Telcos do not manufacturer hardware for ISDN. Similar to any new technology, such as VCRs, and personal computers, prices are often initially high, but often come down as more units are sold and economies of scale take place. Some ISDN hardware manufacturers have already significantly lowered their prices.

Does ISDN need its own power back-up?
Traditional telephone sets receive electrical power from the copper wires that link your home to the local central office. When there is a power failure in your neighborhood, traditional telephone service is not interrupted because backup generators in the Central Office send power to your telephone over your line. ISDN requires more power than your phone line can carry, so ISDN equipment must be powered from electrical outlets in your home or business.

In the event of a power failure, ISDN will not operate unless it has a power back-up such as a Uninterruptible Power Supply (UPS). Just as a PC requires power back-up in case of a power failure, ISDN equipment may run off of the same back-up. Battery back-up is available where PCs and PC equipment are sold.

Should ISDN be the only line to my location?
While this is a matter of choice, an ISDN line can serve as the only phone line to your home and business -- if you have a backup power supply (as mentioned above) in the event of a power failure. You may want to keep your existing lines and add ISDN for specific purposes that cannot be accommodated by your present line (e.g., higher transmission speed).

What services does Verizon offer in our area?
Verizon ISDN Basic Service consists of two 64-Kbps (Kilobytes) B channels to carry voice, data and image communications, and one 16-Kbps D channel for packet data and call management. The two Basic Service B channels can be combined to transmit data or images at 128-Kbps.

Verizon ISDN Primary Service consists of 23 64-Kbps B channels and one 64-Kbps D channel and allows users to combine the B channels for speeds up to 1.5 Mbps.

In some areas where local ISDN service is not available, Verizon can provide service from the closest central office that has ISDN equipment. This arrangement is called Virtual ISDN Service, and there is an additional one-time installation charge, as well as a monthly surcharge.

What equipment will I need with an ISDN line?
In addition to an ISDN line you'll need to buy a terminal adapter and a network termination device (NT-1) with a power supply to connect the equipment at your location to the Verizon ISDN network.

Tell me more about the B and D channels (The technical stuff!) Through standard telephone lines, an ISDN-capable digital switch at a local telephone company office generates two different types of "electronic channels."

Some of these channels, B channels, are designed to carry a full range of circuit-switched voice, circuit-switched data, and packet-switched data transmissions. Others, the D channels, carry call-signaling and set-up information for the network, plus a range of lower-speed packet transmissions.

There are no protocol or other restrictions for B channels. They are defined as transparent, circuit-switched, 64Kbps connections capable of carrying digital voice or digital data transmissions. B channels can also be inverse multiplexed, or "bonded" by customer equipment (or the local Verizon switch) into single n x 64Kbps data channels.

Call signaling and set-up information traveling on the D channel is also unique, designed to travel through a separate communications network dedicated to call set-up and control. This network is called Signaling System 7 (SS7).

The primary advantage of a separate, out-of-band signaling network is the speed with which calls can be connected - about 1-3 seconds from the last digit dialed to the first ring, compared to some 10-30 seconds without it.

In addition to transmitting call signaling and set-up information, the D channel can also be simultaneously interconnected to the worldwide X.25 packet network for user messaging, small file transfer, transaction processing, remote telemetry and a host of other applications. Using combinations of these B and D channels, a digital switch at the user's central office generates two types of ISDN interfaces. These are called the Basic Rate Interface (BRI) and the Primary Rate Interface (PRI).

What is the "Basic Rate Interface?"
The Basic Rate Interface - the BRI - consists of two 64Kbps B channels, and one 16Kbps D channel. Often called 2B+D connections, they link the end user directly to either a telephone company switch, or to a private branch exchange (PBX) or other ISDN call controller, which is itself linked to the telephone company's central office.

The Basic Rate Interface represents ISDN in its simplest form - a dialed, high-speed digital connection capable of carrying virtually any type of voice, data, video, image, sound or other transmission.

It should be noted that in some areas of the country where Signaling System 7 is not yet fully operational, D channel signaling information is carried in-band, that is within the main flow of voice or data. The result is that B channels are reduced to a speed of 56Kbps on calls from one telephone company central office to another. Nonetheless, D-channel interconnections to the X.25 packet network are still possible.

What is the "Primary Rate Interface?"
The Primary Rate Interface - the PRI - typically contains 23 64Kbps B channels, coupled to one 64Kbps D channel. Transmitted through a standard, dedicated North American 1.544Mbps (megabit per second) DS1 line or trunk, the PRI is also known as a 23B+D connection. PRIs link medium and large locations directly to a telephone central office ISDN switch.

PRIs add valuable new capabilities to a standard DS1 (T1) digital line. A key benefit is call-by-call service selection, with dynamic channel allocation. This means that a PRI lets a company flexibly allocate bandwidth as demands for that bandwidth change. A telecommunications or MIS manager can adjust the inbound and outbound calling flow on the PRI's 23 B channels to respond to specific time-of-day or day-of-week needs.

A group of six B channels, for example, could be combined - bonded - by customer equipment for a studio-quality, full-color, full-motion video conference, and afterward returned to the general pool of B-channels supporting internal and external voice and data communications. These same channels might be combined again after-hours into even larger channels for high-speed file transfers to locations around the nation and around the world.

Bandwidth control can either be preprogrammed into the central office digital switch serving a location, or can be allocated on demand through a growing range of telephone and computer systems designed for the purpose. These devices include PBXs, mainframes and minicomputers, LAN and WAN gateways, multiplexers, video units and a growing breed of ISDN bandwidth-on-demand controllers.

ISDN Glossary

Channel: A channel is a communication path that can carry a voice or data conversation. ISDN has multiple channels [a maximum of two (2) "B"s and one (1)"D".]

B Channel: This is an ISDN communication channel that bears or carries voice, circuit-switched data, or packet-switched data conversations.

D Channel: This is an ISDN communication channel used for sending information between the ISDN equipment and the ISDN central office switch. This channel can also carry "user" packet data at rates up to 9.6 kilobits.

Circuit Switched Data: A conversation between two devices (usually computers) where the devices have total use of the channel connecting them.

Packet mode data: In this type of conversation between two devices (usually computers), each device's "dialogue" is broken into small chunks called packets before being sent to the receiver. Unlike voice and circuit switched data calls, one communication channel can carry multiple packet conversations at the some time.

SPID: The ISDN central office needs to have a unique identification number for each ISDN set to which it sends calls and signals. This identification is called a Service Profile Identifier or SPID.

NT1: The NT1 (Network Termination 1) is a user owned device that provides an interface between your line from the telephone company and the ISDN wiring inside your home. This device can be a stand-alone device or can be integrated with other ISDN equipment. Your ISDN service will not work if the NT1's plug is not connected to a working electrical source.

Signaling: Your central office knows that you wish to make, take, or interrupt a call when it receives special signals from picking up a hand set, dialing, depressing buttons on your set, etc. Before ISDN, you frequently had to interrupt or terminate your conversation to signal the central office. ISDN lets you talk and signal at the same time.

Return to FAQ Home Page