ISDN Frequently Asked Questions

What is ISDN?
Can I communicate with people and locations that don't have ISDN?
How do I know if ISDN is available in my area?
What if my central office does not have ISDN capability?
Will ISDN work over my existing phone wires?
Will ISDN work with my existing equipment?
Why is ISDN better than a standard (analog) line with a modem?
What is the cost of ISDN?
Why is it more expensive than a standard phone line?
How competitive is BellSouth ISDN pricing?
Why is it less expensive in Tennessee?
Is the hardware associated with ISDN expensive?
Does ISDN need its own power back-up?
Should ISDN be the only line to my location?
Who do I call for more information?
Glossary of Terms

Q.   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. The two primary channels communicate at 64 kilobits per second (kbps) and the third at 16 kbps. The third channel is primarily used for behind-the-scenes 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.

Q.   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.

Q.   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. The majority of the central offices in BellSouth territory 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 miles from the central office, you may not qualify, but we may be able to make special arrangements to get ISDN to you. BellSouth is continually expanding ISDN availability.

Q.   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.

Q.   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 also be required.

Q.   Will ISDN work with my existing equipment?

In almost all cases, ISDN requires special equipment. If connecting ISDN to a PC, a terminal adapter (sometimes called an "ISDN modem") is required. Many of the terminal adapters come with 1 or 2 standard jacks (RJ-11), so standard (analog) phones and/or facsimile machines can be connected. BellSouth has now made it easier than ever for you to purchase ISDN equipment by forming alliances with ISDN equipment manufactures and distributors. Also, this equipment is often sold where PCs and PC equipment are sold.

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

Q.   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, videoconferencing is difficult over an analog line, but is close to full motion over ISDN. Many 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 crosstalk 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.

Q.   What is the cost of ISDN?

The price varies depending on issues such as the configuration you select, the minimum service period that you select, and the state in which you are ordering the service.

Installation charges vary by state and you may desire some wiring, additions of jacks or relocation of existing jacks to ensure that the service is installed where and how you can best use it.

Q.   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, expanded applications (such as video conferencing and realtime application sharing), and improved communications -- you know when that important call is arriving.

Q.   How competitive is BellSouth ISDN pricing?

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. BellSouth rates are reflective of the ISDN demand, customer usage in our region and the state and federal regulations. You will continue to see pricing plans introduced and withdrawn across the nation as ISDN grows in mass market appeal.

Q.   Why is it less expensive in Tennessee?

The residential rate for ISDN in Tennessee is approximately $20. This is because ISDN is part of a larger technology program specific to Tennessee where a "pool" of funds has been set aside to assist (or supplement) customer rates on certain technology (which includes ISDN). This rate has been set independent of the cost associated with providing ISDN and can exist only because the technology program covers the remaining costs.

Q.   Is the hardware associated with ISDN expensive?

Many ISDN hardware manufacturers have already lowered their prices significantly. Similar to any new technology, such as VCRs and personal computers, prices are often initially high, but come down as more units are sold and economies of scale take place. BellSouth does not manufacturer hardware for ISDN.

Q.   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 Uninteruptable 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.

Q.   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).

Q.   Who do I call for more information?

Call the BellSouth Regional ISDN Center: 1-800-858-9413

Q.   Glossary of Terms

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 behind-the-scenes 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 same 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 handset, 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.

back to top