In an ISDN system, there are two types of services: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). While the former is installed in home or small business organizations, the latter is for large organizations that have their own PBX systems. There are a number of B-channels and D-channels in the system that carry data, video, voice with various signaling and control information. But what is the Primary Rate Interface and how does it work?

What is PRI Line?

The primary rate interface is made up of 64 Kbps D-channels and 23 Kbps B-channels. Here, it uses the T-1 line. It also consists of a 30 Kbps D channel and a 30 Kbps B channel, which use an E1 line. If a user accesses the Primary Rate Interface on a T-1 line, he can get an Internet speed of up to 1,544 Mbps. On the other hand, a user on the E1 line can get services up to Mbps. PRI uses the Q protocol .931 over the D channel.

There are some countries where this system is carried on a T-carrier system line, while the E-carrier line is available all over the world. The users of the system are directly connected to the central office of the telephone company.

Benefits of PRI Circuits

1. The service provider gives almost 500 numbers for each line. Therefore, it becomes easier for strangers to call the extension directly without going through the PBX auto attendant.

2. Through a PRI line, it is possible to have access to voice and data. There are also some service providers that offer free data transmission for a certain period of time.

3. Call hunting is also easy with a primary rate system. But for analog trunks, the service provider needs to extend the installation and also include an additional cost.

4. What are the other benefits of this system? It can be used for voice connectivity, video conferencing, data connectivity, fax, etc. And all this can be done simultaneously.

5. This circuit is always better than analog trunks as it is an end-to-end digital system.

6. Due to fiber optic materials, the cable is much more redundant than analog trunks. Also, you will face less troubleshooting here than on other systems.

7. It’s almost impossible to touch your digital phone lines and listen to your conversation now.

8. You don’t have to wait long to initiate a call here.

9. As there are several service providers that come with flexible plans, this system also becomes affordable for small businesses.

PRI Circuit Limitations

1. If the minimum rent is less than the average value of calls in an analog system, then installing a PRI circuit is not very economical.

2. If you have to make international calls, this system is not profitable. You can choose SIP or ITSP services at a lower rate to make these types of calls.

3. You need to pay for inter-branch communication if you install this line. By installing VOIP systems, you can communicate between branches over the Internet at a much lower cost.

4. You can buy primary rate lines only if you buy them from your EPABX provider.