PRI T1 Lines Of Service

Primary rate interface (PRI) is a telecommunications service provided to businesses and large enterprises. PRI is considered the standard amongst telecommunication services and provides services to offices. PRI is based on the T1 carrier line in the US and Canada (E1 in Europe). T1 carrier lines are generic designators for any telecommunications carrier system which has been digitally multiplexed. T1 means any data circuit that runs at 1.544-Mbits line rate. The specification of PRI T1 lines is to data and voice transmission between the network and the user.

PRI provides a varying number of channels. These channels are also dependent on the country with which the PRI service is being implemented. PRI is available to serve the US, Canada, and Europe. T1 lines in the US and Canada consist of 24 channels, in Europe the E1 consists of 31.

The Integrated Services Digital Network (ISDN) is a set of communications standards for digital transmission voice, video, data, and other network services over the traditional circuits of the telephone network. PRI is one of the two levels of service provided by the ISDN; the other is Basic Rate Interface (BRI). BRI is used for smaller businesses and homes while PRI is for larger enterprises.

What are PRI and BRI?

Both PRI and BRI have a number of B-channels and D-channels. These channels carry different types of information. A B-channel (bearer) is an ISDN channel which carries primary data. B-channel carries voice, data, and other services. A D-channel (data) is another ISDN channel which carries data. D-channel carries control and signaling information.

Primary Rate Interface is considerably larger than Basic Rate Interface. Primary Rate Interface (PRI) has lettered channels, 23 B-channels and one D channel for T1 line. For E1 line, PRI consists of 30 B-channels on one D-channel.

If PRI is paired, a larger connection could be possible. For example, a PRI could have 47 B-channels (23+24) and one D-channel. These types of pairing are often called 47B+D, although 46 B-channels and 2 D-channels are more common. This same principle can also be applied to E1s as well. Both T1 and E1 can have more than 2 PRIs, however, no more than 2 D-channels are permitted. If more than 2 D-channels are required and/or needed, additional PRIS are added to the group.

Application of Primary Rate Interface

A Primary Rate Interface (PRI) T1 user will have access to a 1.472-Mbits data service. A PRI E1 user would have access to a 1.920-Mbits data service.

Medium-large enterprises with digital Private Branch Exchanges (PBXs), typically use the primary rate interface. PBXs are telephone exchanges that operate for a particular enterprise, as opposed to one that a telephone company operates for many businesses or for the general public. These PBXs provide these enterprises with digital access to the Public Switched Telephone Network (PSTN). PSTN is a network of the worlds public telephone networks. PSTN consists of phone lines, fiber optics, cables, cellular networks, microwaves, communication satellites, and underwater telephone cables.

The 23 B-channel (30 in Europe) can be used and reassigned according to the users needs. It can do specific tasks such as video conferences.