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ISDN PRI Pricing

Primary Rate Interface service is booming for PBXs and dial-up Internet access.

Telecom TrackerSome people may say that ISDN is dead, but that's news to the millions who rely on ISDN Primary Rate Interface service for connecting PBXs and dial-up modem banks to the public network.

While it's true that sales of ISDN Basic Rate Interface service aren't as high as those of competing broadband technologies, PRI sales are going through the roof.

As a PBX platform, PRI's offer more flexibility than traditional analog trunks. PRI's are good for ISPs because they let users connect via 56K bit/sec modems or 128K bit/sec ISDN BRI service.

Behind the scenes
Comparing costs
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A PRI offers 23 B channels for voice, video and data traffic via a 1.544M bit/sec T-1 line. The 24th channel, the D channel, is used for signaling. When you combine multiple PRI's, you only need to use one signaling channel for the group of lines, freeing at least one additional B channel for regular traffic. Because of their digital nature, PRI's are equally good at handling voice or data traffic. What's more, PRI will certainly be the access method of choice for connecting voice-over-IP traffic to the public switched telephone network.

Breaking down the costs

The cost of PRI service comprises four components: the T-1 line; the B and D channel arrangements; the trunking arrangements; and special features.

The T-1 charge covers the cost to connect your network to the carrier's switch. In the case of some PRI service providers, you can actually collocate your equipment in the same building with the switch, thus eliminating this charge.

The channel arrangement refers to the way in which you multiplex the B and D channels over a T-1, such as 23B + D, 24B and so on. The trunking element covers services such as Direct Inward Dialing, which lets you give each employee his own direct-dial phone number.

Finally, the special features include options such as calling line ID. When you combine all these elements, you arrive at the true cost of PRI service.

Where to buy

One of the most difficult aspects of buying PRI service is determining if a particular carrier has the service in your area. There's no question that regional Bell operating companies provide the greatest coverage of any PRI provider. Interexchange carriers such as AT&T, WorldCom and Sprint also offer PRI's, but these circuits are typically sold for access to long- distance service.

Competitive local exchange carriers (CLEC) are another source for PRI in larger metropolitan areas of the country - what some people refer to as the NFL cities. A search on the carrier's Web site or a telecom portal such as will tell you if the CLEC serves your area, but then you'll need to call the carrier to confirm that it can serve your address. If you have to deploy PRI across the U.S., you should choose a CLEC - such as Focal, Teligent and Winstar - that offers national service.

Regardless of what type of carrier you choose, be prepared for extensive installation delays in areas with heavy demand. It's common for your order to sit in a reservation queue until new facilities become available.

What it costs

PRI pricing varies depending on which carrier you choose and the configuration of your service. As you might expect, the RBOCs are generally the most expensive and the CLECs tend to offer more competitive prices to win your business. A dial-up modem PRI configuration is the least expensive and generally costs between $300 and $1,000 depending on the region. A more full-featured PBX PRI configuration costs about $1,000 to $2,000. See the graphic on page 48 for sample pricing for PRI deployment in various cities.

Thanks to approved tariffs and lack of competition, RBOCs haven't had to lower their prices much. However, some carriers negotiate discounts based on high volume orders or a combination of long-term contracts and volume commitment. Carriers are also likely to waive installation charges in competitive markets. As competition intensifies, you can expect carriers to reduce their monthly charges as well.

No matter what you hear about ISDN, it's not going away. PRI's are the foundation of today's worldwide switched digital network, and deployment is taking off. Every time another million people get on the Internet, ISPs have to order another 3,000 PRI's. Some ISPs order circuits in quantities of 100 at a time to keep up with customer demand for dial-up services.

As for PBXs, most corporations are moving away from analog trunks to PRI configurations. PRI's may seem expensive when you compare them with analog trunks, which cost between $30 and $80 per month. However, when you factor in the flexibility, ease of maintenance and advanced features of PRI, it's hard not to justify moving to avoice/data/video telecom infrastructure based on PRI service.

Behind the scenes

Back to top

Comparing costs
Here's what you can expect to pay per month for two types of ISDN service: ISP PRI inward dialing lowest cost, and PBX PRI inward and outward dialing for 1,000 phone numbers and 23 trunks. In some cases, carriers may waive installation charges.
  Month-to month contract Multi-year contract Month-to-month contract Multi-year contract
New York
Verizon $1,153 $1,083 $1,254 $1,184
CLEC $495 $495 $600 $600
Bell South $1,210 $1,040 $2,464 $2,464
CLEC $1,195 $1,195 $1,195 $1,195
Ameritech $789 $543 $889 $543
CLEC $516 $516 $516 $516
San Francisco
SBC $618 Not applicable $1,063 Not applicable
CLEC $420 $390 $1,200 $1,000
CLEC = competitive local exchange carrier
Source: Telco Exchange, Fairfax, Va.

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Dunetz is vice president of engineering with Telco Exchange, an online marketplace for high-bandwidth communications services. He can be reached at

Figuring frame costs
Network World, 09/18/00.

Demystifying T-1 pricing
Network World, 05/08/00.

Winstar Communications

Net2000 Communications



XO Communications


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