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ISDN PRI over Cable Advantages
Comcast business class telephone service offers ISDN PRI service at a cost savings.

By: John Shepler

Many businesses use ISDN PRI trunking to provide phone service for their organizations. The original motivation to move from analog business lines to PRI was the cost savings that T1 technology offered. Now there is a newer and even better cost option called PRI over Cable.

The Origins of ISDN PRI
Regardless of the delivery technology, ISDN PRI is a well-established standard for bundling up to 23 business telephone lines on a single digital cable. Why 23? It’s because T1 lines were designed to have 24 channels, each capable of transporting one high quality digitized telephone conversation. One channel is reserved for signaling and Caller ID, leaving 23 channels available for phone calls. Each channel is equivalent to one analog phone line. By bundling them, you can almost always save money over ordering 23 individual phone line.

Works With Most PBX Systems
What’s more, nearly all modern PBX telephone systems and many key telephone systems support the ISDN PRI standard. There is a PRI jack on the back of the system or a plug-in accessory card. Many larger business phone systems accommodate multiple PRI lines so you can have 46, 69, 92 or more outside phone lines if your company is large enough to need this many.

Transport Via T1 or Other Networks
ISDN was designed around T1 lines, but there is no reason that more modern packet switched networks can’t also provide phone lines to meet the ISDN specification. It’s all a matter of hardware and firmware on circuit cards to get the signals formated properly.

The Comcast Cable System
Comcast, the largest cable operator in the US, is now offering PRI telephone trunking over their Hybrid Fiber Cable (HFC) system. If you are only familiar with Comcast as a provider of Cable TV service or broadband, you may be surprised to learn that Comcast is the third largest telephone company in the country. The other possible surprise is that Comcast is a business as well as residential service provider.

The Immense Bandwidth of Coaxial Cable
Coaxial cable has bandwidth capabilities far beyond those of twisted pair copper telephone wiring. This is especially true when most of the network is built on fiber optic cabling and only the last mile or less uses coax. Coax is cheap, reliable and well-proven technology. There is plenty of room on that coax to delivery television, broadband and telephone services, including ISDN PRI.

This Is NOT Internet Phone
But isn’t broadband telephone fraught with performance issues? The Internet often isn’t up to traditional telephone standards when it comes to voice distortion and latency, the annoying time delay that makes you pause during two-way conversations. That’s why Comcast keeps their broadband and telephone signals separate. They’re both riding the same cable, but in different channels so they don’t interfere. TV signals are also on the same cable in their own assigned channels.

Cable Delivers Phone and Broadband
What makes PRI over Cable a great option for a small to medium size business? Consider that you can get a 6 channel telephone trunk capable of serving up to 24 employees plus 22/5 Mbps broadband Internet service for less than the cost of many T1 lines. Most companies need both telephone and Internet service, and Comcast’s business class Business Class Trunks and Internet with broadband speed up to 22 Mbps download easily fits the need.

Add Channels One at a Time
Do you need a larger phone system capacity or are concerned that you will in the future? No problem. Comcast lets you add to your PRI service in single channel increments. Many ISDN PRI services now come with a full 23 lines even if you don’t need that many. Having a system that is scalable for both phone lines and Internet bandwidth gives you the ability to buy just what you need now and be able to easily upgrade in the future.

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