Can SIP Trunking Supplant ISDN PRI?

Companies large enough to use multiple business telephone lines are good candidates for digital trunk lines. It used to be that you needed a dozen or two outside lines before digital trunks made sense. Now just a few lines plus broadband Internet can make telephone trunks attractive.

Just what is a telephone trunk? It’s a collection of telephone lines, all bundled together. We tend to think of landlines as individual connections. One analog landline is a single pair of small plastic coated copper wires twisted together in a spiral. This isn’t just to keep related wires in pairs to form a complete circuit. The twisted form causes induced magnetic fields to cancel out over distance. This reduces the amount of hum, noise and crosstalk from other telephone lines.

Companies that have a few outside lines often have what’s called a key telephone system. The “key” refers to the line select buttons on the phones themselves. It’s up to the user to note which lines are being used by observing an indicator light for that line button. Unlit line button are free lines that you can use to call out. Each line is an individual analog phone line. They generally come-in through cables of 25 pairs or more called binder groups. You might think of this large cable as an analog trunk line.

The impetus for digital trunk lines is the opportunity to use less copper wiring to transport the same number of phone calls. Stretching miles of binder cable from your location to the telephone company central office (CO) costs a goodly sum. That’s nothing compared to the cost of running long distance lines dozens or hundreds of miles. The first digital trunk was the T1 line. It uses multiplexing to create a stream of 24 channels in 24 serial timeslots. Each channel represents one telephone line. The T1 trunk itself uses 1 or 2 pair of wires versus 24 pair for an equivalent analog trunk.

A T1 telephone trunk can be connected to a channel bank that converts between the digital line and analog telephones. This allows companies with key telephone systems to lease a T1 line at lower cost than 24 separate analog phone lines. A more popular use for this many lines is to connect to an in-house PBX or Private Branch Exchange. The PBX system automatically manages all the outside lines and offers 3 or 4 digit dialing for in-house calls.

An upgrade to the T1 telephone line is the ISDN PRI trunk. The two standards are very similar. ISDN PRI stands for Integrated Services Digital Network Primary Rate Interface. This is quite a mouthful, but is part of an industry standard that has become very popular for business telephony. The difference between T1 telephone and ISDN PRI trunks is that ISDN reserves one of the channels for switching and data. ISDN PRI offers 23 phone lines plus Caller ID, ANI, and much faster switching. Both T1 and PRI interfaces are common on modern PBX phone system designs. They are either a standard features or can be added with a plug-in card.

What’s the advantage of T1 telephone or ISDN PRI to the business user? They cost less than ordering 23 or 24 separate analog phone lines. The person in the office taking a call on their desk phone can’t tell how the phone lines come into the back room. The manager paying the monthly phone bill sure can.

There’s an even newer form of digital telephone trunk available now called the SIP Trunk. SIP refers to the signaling system used by VoIP telephones. It is computer network based rather than telephone industry based. This allows voice and data to be combined or “converged.” Once you have a converged network, you no longer need separate LAN and telephone wiring. Everything in on the LAN.

What the SIP Trunk does is connect your LAN to your phone service provider. This is a long haul private point to point connection so your “phone company” can be located anywhere. It doesn’t matter where those twisted pairs in the ground go. On the network, one location is as close as another.

The other advantage of SIP Trunking is that it can transport both telephone calls and broadband Internet service at the same time without one interfering with the other. Telephone calls have priority in this system so that voice quality is preserved regardless of what is happening on the Internet. Your calls never actually go on the Internet. The simply share a trunk that transports both.

This offers a terrific advantage for smaller companies. Most every business now uses both telephone and Internet service, so why not have them both provided on a single line instead of two? This maximizes the efficiently of the trunk line and saves money for the business user.

ISDN PRI is still wildly popular as a trunk line for PBX systems. Newer IP PBX systems will support both ISDN PRI and SIP Trunking. Why make the change? Compare prices and features to see if SIP Trunks can save you significant money. Smaller companies that can’t possibly imagine using 23 outside phone lines will likely find that SIP Trunking can be scaled down to the number of lines they really need and that’s all they have to pay for. The option of having broadband delivered on your SIP Trunk is also a plus for smaller companies that don’t need the whole trunk for telephone lines.

A potential game changer is the rise of hosted PBX systems or PBX in the cloud. Hosted services connect via SIP Trunk and there is no PBX equipment or phone lines at your location. You pay per user by the month. This offers tremendous flexibility, as you can always order up more “seats” when business increases and you need them.

Are you interested in new business telephone service or are at the point where your current phone system is out of capacity or too costly to maintain? Don’t lock in your decision on how to proceed until you check the latest prices and features of ISDN PRI, SIP Trunking and Hosted PBX services.

E911 For Enterprise VoIP

The move from switched circuit to packet switched telephony has created some unintended consequences. One of these is emergency calling to 911. We take the 911 system for granted. When disaster strikes, just punch in those three little numbers and help will be on the way. Well, that’s the way it’s supposed to work.

Now consider this. There’s a fire in the maintenance closet down the hall and it’s getting out of control. You pick up your handset and dial 911. You reach the emergency operator and report the fire, then run out of the building and across the street. An hour later, the facility has burned to the ground and no fire trucks have shown up. How could this happen?

The fire trucks did show up within 5 minutes of your call. Unfortunately, they went to your main office in Phoenix. You just called from the satellite office in Indianapolis. Oops! Something is not set up properly on your VoIP phone system.

Such a problem would never arise on an analog landline phone. Why? Because the phone wire is in the ground at it always goes the same place. That’s why they call it a landline. VoIP, however, is a network service. As long as a SIP phone can connect to the network, it can make a call. It makes no difference where that connection takes place. Networks that encompass multiple locations need special consideration when they are converged for voice and data. The same technology that makes it easy to move phones around also makes it easy to lose track of just where they are plugged-in. This is especially true if any of your phones connect via the Internet.

XO Communications, a leader in enterprise VoIP deployments, has an instructional video called “9 Ways to Ensure E911 VoIP Service for Enterprise VoIP Deployments.” Have a look now and see if there is something needing your attention...



Make no mistake about it. VoIP technologies, including Hosted PBX and Unified Communications, offer enormous benefits in cost reduction and employee productivity improvement. Like all new technology, the more cutting edge the solution, the trickier it is to get it right. You want to be working with a top-tier service provider who understands the legal requirements for issues such as E911 and has processes in-place to ensure that your system is set up accurately.

If you are considering an upgrade to your business phone system, get recommendations, options and pricing on competing telephony solutions. Be sure you understand how they ensure accurate E911 call routing.

The Surprising Low Cost Phone Option

With all the hype over bundled services and broadband phone, you're probably thinking that only a chump would keep one of those old analog landlines. Not so fast. Despite all the heavy promotion, your cheapest telephone solution may well be that century-old technology combined with a competitive long distance service.

Perhaps that sounds outrageous, but have you actually priced out your options? To do this properly, you need two things. The first is the lowest cost local service that meets your needs. You're more likely than not to get that from your local telephone company. Depending on how many local calls you make and how long you talk, you can easily overpay by buying too much service. The minimum you need is line access, also called dial tone. It's just what it says. You pick up the phone, you hear a dial tone, and you make your call.

Next you likely need some way to make local calls. You can get unlimited service. But you may also be able to get metered service that charges so much per call or so much per minute. Sit down and figure out how much you really call in a month. It will be worth the exercise. If you make only a few calls or primarily talk long distance, you don't need deluxe local service.

You may also want Caller ID. That typically adds about $5 a month. I'd never give it up, because it helps me avoid talking to political campaigns, surveys, scams scheming for donations, and banks looking to promote yet another credit card.

Next, you'll want to have a low per minute rate long distance service. Ten years ago, switching your long distance service to save money was all the rage. Now it's something of a lost art due to the emphasis on cell phones, bundles and VoIP. Once again, before you buy too much, use a long distance rate calculator to see how much your long distance calling is really worth. Competition has driven rates down to a few pennies a minute for most calls. Even overseas calling is dirt cheap these days.

Why not just use the long distance service that comes with your local line by default? Because it's the default service, chances are pretty high that it is NOT the low cost option. It's just convenient for people who just want to call the phone company, ask to have a line installed, and dutifully pay the bills when they come in.

Hey, why not just buy one of those bundled services and get everything for one price? Once again, it sounds good, but a bundle may not be your lowest cost option. Competitive bundles give you local dial tone, a package of local minutes or unlimited service, and a package of domestic long distance minutes or unlimited service. It's really convenient because you get one bill and you know what the price is going to be every month. What you don't know is how much you could save by paying separate bills for local and long distance service.

You should also know that competitive bundles have to buy their local lines from the local telephone company. That's because by law all the analog copper phone lines belong to your incumbent local telco. So you won't be getting a break on local service. You may or may not get a decent deal on long distance service and calling features, depending on your usage pattern.

OK, then, why not avoid the copper phone line issue completely and go with a VoIP telephone service? The same discussion of paying a bundled rate for service you may not ever use versus paying by the minute applies. Also, unless you have very, very good broadband service, you'll find that voice quality suffers and you may not be able to talk on the phone and use your computer at the same time.

Certainly, this discussion makes the most sense for someone with a home office, or a small office with a couple of phones and one or two lines. Once your business gets larger than this, you should consider T1 digital phone trunks or SIP trunks to get the best value for your telephone expense dollar.