Monday, July 13, 2009

What is ISDN and Why Do I Want It?

You may have heard the term ISDN related to telephone services. So what is it and what can it do for you?

ISDN stands for Integrated Services Digital Network. It's a fancy term for digital telephone service. But not just any digital phone service. This one has very specific standards.

The story behind ISDN goes back to the days when the standard for Internet access was a dial-up modem using an ordinary analog telephone line. ISDN was envisioned as a way for users to have a combination of separate telephone service and Internet service on a single ISDN telephone line with three channels. Two of these are called "B" or bearer channels and are 64 Kbps each. The third is the "D" or delta channel that is used for switching and signaling. One B channel can be used for a telephone handset. The other can be used for a modem. Or both channels can be combined for 128 Kbps Internet service. This arrangement is called ISDN BRI. The BRI means Basic Rate Interface.

The telephone companies expected ISDN BRI to be a hit with consumers as an upgrade to their analog phone service. But by the time it was ready for mass deployment, Internet standards had moved on and everybody really wanted DSL or Cable broadband. After all, 128 Kbps may be impressive when compared to a dial-up modem, but it pales in comparison with always-on broadband at 512 Kbps or higher. Today, even mobile users want bandwidth above 1 Mbps, so ISDN BRI is of little interest to most users.

The exception is in the field of broadcasting and professional audio. ISDN BRI lines can be used to transmit high quality audio through the telephone network by using a CODEC (Coder / Decoder) to convert the audio to and from the ISDN format at each end of the call. Guests around the country can join a panel discussion and sound like they are right in the studio instead of hundreds or thousands of miles away. Voice over artists can contribute to a production from their home studios.

Where ISDN flourishes today is in its second standard, called PRI or Primary Rate Interface. ISDN PRI consists of 24 channels configured as 23 bearer channels plus 1 delta channel. The 23 bearer channels can each support 1 telephone call each. That's 23 digital phone lines, plus the delta channel used for signaling and Caller ID data.

ISDN PRI is the telephone service of choice for medium and large company telephone systems. Most PBX and IP PBX business phone systems offer built-in support for at least one ISDN PRI line. Other systems can be configured for one or more ISDN PRI trunks with a plug-in circuit card.

In addition to office PBX telephone, ISDN PRI is preferred by company contact centers and independent call centers. There is a significant cost reduction realized by using a single ISDN PRI instead of a dozen or more individual analog phone lines. Each channel on the PRI can be configured to be local and/or long distance, incoming and/or outgoing calls. If more than 23 lines are needed, more can be added to the system to double, triple or quadruple the number of active phone lines.

ISDN PRI is delivered on a T1 line in the United States. For this reason, it is sometimes known as T1 PRI or T1 telephone service. In other countries, an E1 line might be used to provide PRI service.

Now that you know what ISDN is good for, can this service help your business or organization to provide high quality voice communications for perhaps less than you are spending now? Find out by checking ISDN PRI service pricing now.

Click to check pricing and features or get support from a Telarus product specialist.

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