PRI Phone Line Connections

Traditional analog business phone lines are useful in very small retail and office locations and any business where just a few outside lines are all you need. Once you accumulate more than half a dozen, it’s time to look at a telephone trunk like option like ISDN PRI.

ISDN PRI stands for Integrated Services Digital Network Primary Rate Interface. Now you know why they abbreviate it. ISDN is a set of standards for how to transmit phone calls digitally on ordinary telephone wire. PRI is the larger of two major options. The other, BRI or Basic Rate Interface, provides two telephone lines, one telephone and one 64 Kbps data line, or a 128 Kbps data line. It’s mostly used for low speed data connections or to transmit high quality audio for broadcast and production.

PRI is the business telephone trunk service that is highly popular for use with PBX phone systems. PRI is transmitted on a T1 line using two twisted copper pair. Chances are you are already familiar with T1 lines for dedicated Internet access at 1.5 Mbps. ISDN PRI, also called T1 PRI, uses the same T1 line technology. In fact, T1 lines were originally designed to transport telephone conversations in bulk between telco switching offices.

What do you get with ISDN PRI service? A single trunk can support up to 23 separate phone conversations, each in its own time division multiplexed channel. Think of these as the equivalent of 23 outside lines. Each line can be set up for local, long distance, incoming only, outgoing only, toll free or some combination. There are actually 24 channels on the T1 line. The last one is reserved for switching signals to support the other 23 plus data such as Caller ID.

ISDN PRI lines almost always plug into an interface card made especially for this purpose. There’s at least one in most PBX phone systems. Some have four or more ISDN PRI connectors so that you can add dozens of outside lines if your operation is large enough to need them. Call centers are big users of ISDN PRI, as are large business offices.

PRI pricing has been getting better over the years, following the declining cost of T1 lines. A few years ago, PRI became more cost effective when you exceeded 10 or 12 outside phone lines. Today, that number is more like 6 or 10 lines, depending on where you are located.

Other than analog phone lines, the direct competitor to ISDN PRI is SIP Trunking. PRI is a traditional telephone technology that connects your PBX system to the public switched telephone network. SIP Trunking is a packet based technology originally designed to support enterprise VoIP telephone systems. SIP Trunks connect directly to converged networks for enterprise VoIP support and can supply both phone and Internet service for smaller companies. SIP Trunks can also be ordered with analog, IP or PRI handoffs to connect to any PBX telephone system.

What type of telephone trunk line is best for your particular situation? Consider the interfaces you have available and get competitive prices and availability for business telephone lines and trunks to make a good decision.

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.