When Only T1 Will Do

By: John Shepler

In the age of gigabit fiber connections, the venerable T1 line might be thought of as a relic of the past. Not at all. T1 service is alive and well. It might even be exactly what you need right now in the way of bandwidth and affordability.

Why Would Anyone Want a T1 Line?
T1 is the most mature, most deployed and most available of the telecom line services. You might think that Plain Old Telephone Service (POTS) would be the leader in that category. It was. POTS is giving way in many organizations to newer premises VoIP and telephony in the cloud. That still leaves what used to be the POTS lines connected. What are they good for? Think: T1

T1 lines are amazingly versatile. They make perfect telephone trunks for channelized T1 phone, ISDN PRI and even high quality VoIP. They are almost certainly available at your location, wherever you may happen to be. Plus, T1 is readily affordable by just about any size business.

The T1 Telephone Line
Did you know that T1 actually started out as a telephone trunking technology? If the telco companies didn’t have a burning desire to consolidate the mass of wiring that interconnected their switching centers, T1 might never have come about. In the beginning, it was one telephone conversation per pair of wires. Then the phone companies found a way to send multiple conversations down the same pair simultaneously using a method called carrier telephony. It works like the radio band. Each conversation had its own assigned carrier frequency separated from the others so they wouldn’t interfere. This is the analog way to get the job done.

The breakthrough that was T1 involved the conceptual change from analog to digital. By digitizing the phone conversations, you could send 24 of them down the same pair of wires and they wouldn’t interfere. What’s more, digital technology got rid of all that noise and crosstalk that analog long distance lines were famous for in the first part of the last century.

A channelized T1 telephone line consists of 24 time division multiplexed segments or channels that are synchronized at the transmitting and receiving end. Each analog phone signal is digitized into 8 bits by 64 Kbps, which preserves the call quality. What grade of wiring do you need to transmit these calls? Ordinary twisted pair telephone cable will do just fine. With signal regenerators every mile or so, a T1 line can be stretched as far as you like.

ISDN PRI Telephone Trunks
T1 telephone lines are used by in-house PBX business phone systems. In recent decades, that technology has been upgraded to something called ISDN PRI or Primary Rate Interface. It’s the same T1 line, but with a slightly different format. ISDN PRI provides 23 separate phone lines plus a control and signaling channel that runs the system. This is the preferred option for call centers because of its fast connection times and high voice quality. Multiple T1 lines can be installed to most PBX systems to match the number of outside lines needed.

T1 for VoIP
VoIP or Voice over Internet Protocol is a different method of achieving the same phone service. VoIP was designed to be compatible with computer networks rather than a unique telephone standard. Even so, VoIP trunks, called SIP trunks are needed to get the phone calls to the telephone service provider in the cloud. Unchannelized T1 lines work great for this because they are highly reliable and offer enough bandwidth to carry two dozen or more simultaneous telephone conversations.

T1 Internet Lines
T1 for Internet access, with its paltry 1.5 Mbps bandwidth might be considered laughable in this age of gigabit broadband. It’s not so funny when your business is on a farm or so far out in the wilderness that you are lucky to have a landline phone. Those landline phone wires can also carry T1. That means if you can get phone service, you can get at least T1 broadband where there is no fiber or even cell towers for miles.

Is 1.5 Mbps truly a problem? It likely is if you want to transfer HD video production. Not really, though, if you have a small business and need the line for credit card verification, a connection back to a franchise office, or just email and casual web browsing. You can increase this bandwidth by combining, called bonding, multiple T1 lines together. This will give you anywhere from 3 to 12 Mbps, depending on the number of lines you bond.

How About The Cost?
People who think T1 is expensive remember back a decade or two, when a single T1 line would set you back at least a grand a month. Today, that figure is more like $200 to $300 in most cases. It still depends on how much competing service is in your area and how far you are from the telco office. Is this expensive? Business grade cable broadband is also priced in that range, but with “up to” higher advertised bandwidth… if you happen to be next to where the cable line runs. Even then, cable is shared bandwidth while T1 is dedicated to your particular company.

If your need is for highly reliable PBX telephone lines, point to point private lines, dedicated Internet access or rural broadband applications, T1 might still be the optimum service for your company. Check out T1 and bonded T1 pricing and availability and compare with your alternative service options.



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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 a PRI in VoIP?

We tend to think of VoIP as a “new generation” phone service based on IP technology unrelated to the historical public switched telephone network. Well there’s some truth in that, but no matter what you implement you’ll still be dealing with the good old PSTN. The bigger your company or organization, the more “outside” phone lines you’ll need. You should take a close look at ISDN PRI to make the connection to all the phones that are not part of your enterprise VoIP telephone system.

What is a PRI? It stands for Primary Rate Interface. That’s telephony talk for a particular standard related to another telephone industry term, ISDN. ISDN is the Integrated Services Digital Network. There’s a history to the development of ISDN that relates to the once lofty ambition of replacing all analog home and business phone lines with digital versions. You may not have heard of this, as it fizzled when broadband Internet came along and usurped the data role intended for ISDN. Even so, the business version persists and is more popular now than ever. That’s what’s called PRI or ISDN PRI or even T1 PRI.

Why T1 PRI? It’s because ISDN PRI is physically transported on a T1 line. T1 is another telephone industry standard widely used in business for dedicated Internet and point to point data connections. T1 lines have the advantages of being provisioned on copper wires so you don’t need fiber optics installed. They can be extended to nearly any distance, are highly reliable and reasonably priced. The pricing has gotten really attractive lately due to all the competition in the industry. With all this going for it, T1 makes a great choice to carry PRI.

What’s different between a regular T1 line and a T1 PRI line? The line speeds and voltages are the same. What differentiates a PRI is how it is organized. Instead of a big chunk of bandwidth, ISDN PRI is set up as 23 channels that each represent one digital telephone line. A 24th channel is used for signaling and data such as Caller ID. It’s an upgrade to an older T1 telephone standard that was set up as 24 phone channels and no Caller ID.

The beauty of bringing in an ISDN PRI line or “trunk”, as it is called, is that you get 23 outside phone lines coming in on a single digital line. It’s a lot more compact and is almost always cheaper, usually a lot cheaper, than dealing with 24 individual analog business lines.

The interface is also generally very easy. Most PBX and IP PBX telephone systems either come with ISDN PRI capability or offer it through a plug-in module you can buy. All the circuitry to convert between 23 individual phone lines and the PRI digital trunk are implement on that circuit board. You simply plug-in one or more ISDN PRI lines and you have outside phone lines and a lot of them.

But why would you connect a T1 PRI to a VoIP phone system rather than keep it 100% VoIP? The simple explanation is that the rest of the world isn’t serviced by VoIP or at least the same VoIP provider. The only thing universal is the PSTN, where you can dial any number and get connected to any telephone in the world. Your enterprise VoIP phone system can save you a bundle on internal calls that stay on your own network. You can also buy a SIP Trunk that connects you to a telephone service provider completely in IP or Internet Protocol. But, guess what happens at that service provider when you want to call an outside number? That’s right. You’ll be switched through to the ISDN PRI lines that connect them to the public phone network.

Which is the best deal for your company when it comes to analog (POTS) phone lines, ISDN PRI or SIP trunking? Why not let an expert consultant get you competitive quotes for these various options so you make an informed decision? The service is fast, easy and free.

ISDN's Primary Rate Interface

ISDN, the Integrated Services Digital Network, is a digital telephone standard that made voice and data services widely available long before the more recent deployment of Enterprise VoIP and MPLS networks. ISDN's Primary Rate Interface is more in demand today than ever. That's because it is tightly integrated with the installed base of telephone trunk lines that are almost universally available.

ISDN was the telcos' response to a change in technology that saw modems being installed on analog telephone lines to transfer data over long distances. The toll network was only designed for a limited voice bandwidth and tops out at about 56 Kbps when used as data bandwidth. In addition, analog modems use the same frequencies as telephone audio. You can use the line for data or voice, but only not both at the same time.

ISDN drew on existing digital carrier technology based on 64 Kbps channels. One channel can carry one telephone conversation, once the call is digitized using a CODEC or Coder / Decoder. These channels are the building blocks of T1, DS3, SONET and other digital carriers. The smallest unit is the DS0 which is a single 64 Kbps channel.

What ISDN did was to create two services for digitized voice and data. Note that once voice is digitized it actually is a data stream and can be carried by a digital trunk line side by side with computer data. Unlike VoIP, which consists of voice packets that all flow down the same line with data packets, ISDN keeps the voice and data channels separate.

The BRI or Basic Rate Interface consists of two 64 Kbps B or bearer channels plus one 16 Kbps D or delta channel. Each of the bearer channels can carry one telephone conversation or a 64 Kbps data link. The delta channel is used for signaling and other services such as Caller ID.

BRI was originally intended for residential and small business use. With a ISDN BRI connection you could have a telephone line and a 64 Kbps Internet connection, 2 telephone lines, or combined data of 128 Kbps. BRI was never widely adopted because other services such as DSL and Cable Internet became available with far greater bandwidths.

While BRI came too late to be a dominant digital line service, PRI or Primary Rate Interface has flourished. PRI consists of 23 bearer channels and 1 delta channel. Shorthand for this is 23 B + D. In this case all channels are 64 Kbps. The larger D channel can handle signaling for all 23 of the other channels. The total of 24 channels is exactly the right size for a T1 line, which is widely available. Thus, T1 lines are used to carry ISDN PRI. In this case, they are often called T1 PRI lines or T1 PRI service.

What has made T1 PRI such a popular service is that it is the perfect digital trunk to support PBX or Private Branch eXchange telephone systems used by businesses and call centers. Each T1 PRI line can replace up to 23 analog telephone lines. It's usually much more cost effective to order T1 PRI service than to bring in a dozen or more separate analog lines. Using the D channel to send signaling to the telephone company and receive Caller ID information results in faster call set-ups and disconnects, which can be important in busy call center operations.

Another popular use for T1 PRI has been to support modem banks. A dozen or more dial-up modems can be deployed by an Internet Service Provider at a single location and will communicate with the ISP via the T1 PRI connection. Each modem is supported by a single bearer channel.

Is ISDN PRI service priced right for your company? You can find out with a quick online price and availability search right now. Our friendly consultants will also be happy to review your needs and recommend the most cost effective solutions from a variety of competing carriers.