How Does a T1 PRI Really Work?

Here’s a brief description of the difference between T1 voice vs PRI…

PRI or Primary Rate Interface is a switched service delivered OVER a T1 connection . If someone were to say “I want to order a PRI to location X.” What is being requested is a connection to a trunk side module capable of ISDN protocol to a Telco switch delivered to location X via a DS1 rate (T1) circuit.

Now if someone were to say “I want to order a T1 to that SAME location X.” … well… That wouldn’t be enough info… A T1 from where to where? A T1 for what? By just asking for a T1, nothing is understood or implied about where or what the circuit would be used for. A T1 can be used to truck data at the rate of 1.544 Mbps from one location to another… With channel banks and appropriate DS0 level cards, a T1 can be used to truck up to 24 separate and distinct DS0 signals (analog data, analog voice, or Digital Data Service) from one location to another… A T1 can be used to connect one location to an ISP Internet Edge device to connect a customer to the World Wide Web… In other words, a T1 is a multi use pipe….

With a point to point T1 you can use it for voice and/or data depending on the equipment you have at each end. They are basically just providing the “Pipe” and it is up to you what it is used for.

The thing with T1′s and PRI’s is it all depends on what equipment is connected to it on each end.

As quoted above, a T1 is just a 24 channel circuit that can be used for multiple things. A PRI is a protocol that uses the 24th channel to control what the other 23 channels are used for.

In a nutshell – a T1 has 24 channels using 56K for data and 8K for signalling. A PRI has 24 channels and uses 23 for data and the 24th for signalling. Also you can break down the channels on a T1 for different type of service. On the PRI all 23 channels have to be the same.

The features…. or lack of…. totally depend on where the circuit is going and what it is connected to on the other end.

Keeping it on simple terms….

PRI is a different protocol to be used with voice services over the T1 line. Where as a t1 line can also be used for voice but without using the PRI protocol and probably using different equipment at the other end to get the dial tone….

Of course….there are a lot more technical details dealing with ISDN lines (PRI’s/BRI’s) but you’ve got the basic idea.

The simplest approach to finding the best solution is to request infrastructure design and rate quotes for PRI and/or T1 voice service…. comparing providers available in your area….using the free consultative support of: FreedomFire Communications. Getting expert consultation in this manner will save you time, effort, frustration….and money.