In an ISDN system, there are two types of services: Basic Rate Interface (BRI) and Primary Rate Interface (PRI). While the first one is installed at home or small business organizations, the later one is for large organizations which have their own telephone exchange systems. There are number of B-channels and D-channels in the system which carries data, video, voice with several control and signaling information. But, what is Primary Rate Interface and how does it work?
What is PRI Line?
The Primary Rate Interface comprises of a 64 Kbps D-channels and 23 Kbps B-channels. Here, it uses T-1 line. It also consists of one D-channel and 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 internet speed up to 1.544 Mbps. On the other hand, an E1 line user can get services up to Mbps. PRI utilizes Q.931 protocol over D-channel.
There are some countries where this system is carried on a T-carrier system line while E-carrier line is available worldwide. The users of the system are directly connected with the telephone company's central office.
Advantages of PRI Circuits
1. The service provider gives almost 500 numbers for each line. Therefore, it becomes easier for the outsiders to call the extension straight without going through the PBX Auto-attendant.
2. Through a PRI line, it is possible to have voice and data access. There are also some service providers which offer free data transmission for certain period of time.
3. Call hunting is also easy with a Primary Rate system. But for the analog trunks, the service provider needs to extend the facility and also include additional cost.
4. What are the other benefits of this system? It can be utilized for voice connectivity, video conferencing, data connectivity, faxing, etc. And all these can be done simultaneously.
5. This circuit is anytime better than the analog trunks as it is an end-to-end digital system.
6. Due to the fiber optic materials, the wire is far more redundant than analog trunks. Also, you will face less troubleshooting here than other systems.
7. Tapping your digital phone lines and listening to your conversation is almost impossible now.
8. You don't have to wait long to start a call here.
9. As there are several service providers who comes with flexible plans, this system also become economical for small companies.
Limitations of PRI Circuits
1. If the minimum rental is less than the average value of calls in an analog system, then installing PRI circuit is not that much economical.
2. If you have to make international calls, this system is not cost-effective. You can choose SIP or ITSP services at lesser rate to make such calls.
3. You have to pay for Inter branch communication if you install this line. If you install VOIP systems, you can make inter branch communication over internet at much lower cost.
4. You can buy Primary Rate lines only if you buy those from your EPABX vendor.
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