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.

T1 Line Cost At A New Low

Over the years, most companies have come to own T1 lines either sooner or later. Larger companies got them for dedicated Internet connections back when business was just getting acquainted with the Internet. Small operations often get into T1 lines after becoming frustrated with shared bandwidth information services, such as DSL and Cable. There’s only one thing not to like about T1 lines and that’s the cost... or is it?

If you think that T1 lines cost a small fortune, you probably remember getting a quote some time ago. Yes, less than a decade ago it wasn’t uncommon to pay $1,000 a month for a typical T1 line. I say typical because there are different flavors of T1 service and pricing has been very location dependent. Today, you might pay about a third of that in most locations nationwide.

Costs have plunged due to maturity of the service, deregulation that has opened the market to many more competitive carriers, and new technologies that now compete directly for your bandwidth dollar.

It’s never been a better time to get into T1 line service if it will meet your needs. Let’s take a look at how T1 lines work, what you can use them for, and how to decide if T1 or something else is the right service for your company.

T1 is one of the most mature telco technologies, developed by the Bell System for telephone trunking. T1 formed the basis of digital telephone service and later was pressed into service to transport data also. A half-century of experience means that T1 is well understood, almost universally available and well supported. As a tariffed telecom service, carriers take T1 seriously. Most are sold with an SLA or Service Level Agreement that spells out what you can expect in the way of availability, time to respond to an outage and mean time to repair.

T1 lines were designed to be provisioned on two pair of ordinary telephone wire. One pair is for transmit or upload. The other is for receive or download. This is a symmetrical bandwidth service. You get the same bandwidth in both directions and it is full duplex. You can transmit and receive at the same time. That was designed-in to support telephone conversations that are also full duplex.

The original use for T1 lines was telephone trunking. A trunk line supports multiple phone conversations. A T1 telephone line supports up to 24 separate conversations, each with its own synchronized channel. Think of these as individual business phone lines. A device called a channel bank can convert the 24 channels back and forth to 24 analog phone lines.

A more popular configuration of T1 telephone line is called ISDN PRI or T1 PRI. This also divides the T1 line into 24 channels but only 23 of them are used as phone lines. The last one is reserved for switching signals and data, such as Caller ID. ISDN PRI is very popular as a telephone trunk line that plugs directly into many PBX phone systems.

When used to transport data, the idea of channels is dispensed with and the entire payload of the line service is used to carry data packets. T1 has a payload of 1.536 Mbps. The actual line speed itself is 1.544 Mbps. The difference of 8 Kbps is overhead used to keep the line synchronized and for maintenance. A T1 line is typically said to provide 1.5 Mbps of bandwidth.

That bandwidth can be used to connect to the Internet in what is called DIA or Dedicated Internet Access. Dedicated means that you have exclusive use of the bandwidth at all times. Use as little or as much of it as you need. The remainder will still be available and not shared by other users.

T1 lines are also popular as point to point connections to link two business locations. A specialized use is to transmit digitized audio from radio station studios to rurally located transmitter sites. T1 is also the most popular backhaul technology that connects cellular wireless towers to telephone switching systems.

Has the cost of a T1 line come down enough to make it attractive for your business use? If so, you may also want to compare T1 against the newer Ethernet over Copper that typically offers twice the bandwidth for the same money. If EoC is available, it's an even better bargain. Get quotes now for EoC and T1 line services at your business locations.