What Is a PRI Line?

PRI lines are popular for providing multi-line phone service to businesses. But just what is a PRI line and what options are available?

PRI is part of a telephone technology standard called ISDN (Integrated Services Digital Network). It was envisioned as a digital line service that would replace analog telephone lines for both residential and business users. At the time that ISDN was being introduced, connections to the Internet were mostly dial-up using 56 Kbps modems at best. Many of those 56K modems really connected at something around 30 to 40 Kbps due to noise and other limitations on most phone lines. All-digital lines offered basic ISDN service with 64 Kbps data plus one standard telephone service on a single line.

This basic service is called BRI for Basic Rate Interface. It consists of 3 channels. There are two “B” or Bearer channels at 64 Kbps each that can be configured as either voice or data. That can be a 64K digital Internet connection and a phone line, 2 phone lines, or 2 combined data lines for 128 Kbps Internet. The third channel is called a “D” or Delta channel. It has only 16 Kbps, but is used for signaling and control.

If you’ve never heard of ISDN BRI it’s because it never took off. By the time it was starting to be deployed in a big way, technology had moved on and broadband over DSL and Cable was taking over the role of Internet access.

The second standard introduced with ISDN is PRI for Primary Rate Interface. This much higher bandwidth service offers 24 channels configured as 23 B + D. In this case the D channel bandwidth has increased to 64 Kbps just like the B channels. Why stick with 64K channels? It’s because 64 Kbps is just the right amount of bandwidth to transport one digitized telephone conversation using the industry standard G.711 coding standard.

You can configure a PRI circuit to carry voice, data or a combination. Some ISPs used these to connect to modem banks in the dial-up days. Today, the most popular use of ISDN PRI is for PBX telephone trunking with 23 outside voice lines and one control channel that also handles Caller ID for the other 23. Most PBX switches come already configured for at least one PRI line or can be interfaced with a plug-in card.

BRI was designed to be provisioned over the same twisted pair cable that brings in analog phone service. PRI is provisioned over T1 lines because of its higher capacity. T1 was designed to use 2 twisted pair of telco cable and is almost universally available as a standard business-grade digital telecom service.

Recently, another PRI option has become available. That is business grade telephone trunking provided by Cable companies, such as Comcast. The coaxial cable used to bring in television has tremendous capacity and easily supports broadband services up to 100 Mbps. The same cable can transport individual analog telephone lines or ISDN PRI to support a business PBX phone system. With Cable PRI, you may have the option to order fractional PRI service with as few as 6 phone lines. You can then add more, even one at a time, as your business needs increase.

Are you interested in lower cost multi-line business telephone service to support your in-house phone system? If so, get prices and availability for PRI line service options. Single line service and VoIP SIP trunking are also often available.

VoIP is For Smaller Companies Too

Enterprise VoIP solutions are generally seen as too sophisticated and way too expensive for small business. For the most part, that's true. In exceptional cases you may find that the feature rich IP PBX systems available today are a productivity booster for your sophisticated, if small, operation. For everyone else who just wants good voice quality telephone calls at a modest cost, SMB (Small and Medium Business) VoIP solutions may well fit the bill.

VoIP ranges from using your computer as a telephone all the way up to systems that are indistinguishable from standard network switched technologies. The home business user may be very happy with a VoIP telephone service that piggy-backs on the Cable or DSL broadband they already have for Internet access. These services don't require you to buy a special telephone. Instead, they provide an adaptor, sometimes called an ATA or Analog Telephone Adaptor, that works with the phone you have now. You simply plug your phone into the adaptor, connect the adaptor to your router or broadband modem, and you're set.

When you pick up the phone you get dial tone just like you have now. The phone rings just like it always has. The difference is that the bundled price of local and long distance service is often much less than you pay for traditional analog telephone service. Are you interested in VoIP as a replacement telephone service or for a second phone line? If so, you can use the service finder at Affordable VoIP to compare service offers and pick the one that's right for you.

Businesses that are large enough to have multiple employees and their own business address usually need a multi-line system so that more than one person can be on the phone at a time. Typical of these small businesses are real estate offices, insurance sales, warehouses, restaurants, retail stores and so on. What's also typical these days is that most businesses have a need for both telephone and Internet service. There are two good solutions that will give you both phone and Internet service with the voice quality and reliability you need.

The first solution is called Integrated T1. The integration comes from a combination of telephone and Internet on the same standard T1 line. Usually T1 is set up for either voice or data. But an integrated solution gives you both. A dynamic T1 line goes even further and automatically assigns any bandwidth not being used for telephone calls to broadband Internet. Even a heavily loaded Integrated T1 line with a dozen calls in progress will still give you Internet access similar to may DSL services. Being a combined service, you get a price break by ordering a single T1 line instead of two separate ones for telephone and Internet.

The second solution is call SIP Trunking. This is a fairly new service and works very much like a dynamic T1 line. Both voice and data packets travel on the same SIP Trunk from your business to your service provider, where they are separated into phone calls destined for the public telephone system and Internet access routed to the Internet backbones. The term SIP refers to Session Initiation Protocol, the term used for signaling in a VoIP telephone system.

Would an Integrated T1 or SIP Trunking solution be best for your company? The way to find out is to get pricing for each approach and compare cost and benefits. A simple online query will get the ball rolling and a friendly consultant will help you pick the right service for your business needs.