PRI (Primary Rate Interface) circuits are a type of telecommunications service used for connecting private branch exchange (PBX) systems to the public switched telephone network (PSTN). PRI circuits are a type of ISDN (Integrated Services Digital Network) service that provides high-capacity voice and data transmission over a single line.

A PRI circuit typically consists of 23 channels, each of which can carry voice or data traffic at a rate of 64 kilobits per second (kbps). One channel is used for signaling, leaving 22 channels for voice or data traffic. The total capacity of a PRI circuit is therefore 1.544 megabits per second (Mbps).

PRI circuits are commonly used in business environments where high volumes of voice traffic are expected. They are typically installed between a PBX system and the PSTN to provide direct inward dialing (DID) and other advanced calling features. PRI circuits can also be used for data transfer, such as connecting to the internet or other private networks.

One of the key benefits of PRI circuits is their reliability. Since they are a dedicated service, there is no risk of network congestion or performance degradation due to other users on the same network. Additionally, PRI circuits can be configured with automatic failover to ensure that the connection remains up and running even in the event of a network outage.

Another benefit of PRI circuits is their flexibility. They can support a wide range of advanced calling features, such as caller ID, call waiting, call forwarding, and conference calling. They can also be configured to support both voice and data traffic, allowing businesses to use a single circuit for all their telecommunications needs.

In summary, PRI circuits are a high-capacity telecommunications service used for connecting PBX systems to the PSTN. They provide reliable, flexible, and feature-rich voice and data transfer capabilities for businesses that require high volumes of voice traffic.