The Primary Rate Interface (PRI) is a

telecommunications Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

interface standard used on an

Integrated Services Digital Network Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. ...

(ISDN) for carrying multiple DS0 voice and data transmissions between the network and a user. PRI is the standard for providing telecommunication services to enterprises and offices. It is based on T-carrier (T1) transmission in the US, Canada, and Japan, while the E-carrier (E1) is common in Europe and Australia. The T1 line consists of 23 bearer (B) channels and one data (D) channel for control purposes, for a total bandwidth of 24x64-kbit/s or 1.544 Mbit/s. The E1 carrier provides 30 B- and one D-channel for a bandwidth of 2.048 Mbit/s. The first timeslot on the E1 is used for

synchronization Synchronization is the coordination of events to operate a system in unison. For example, the Conductor (music), conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are sa ...

purposes and is not considered to be a B- or D-channel. The D-channel typically uses timeslot 16 on an E1, while it is timeslot 24 for a T1. Fewer active bearer channels, sometimes called user channels, may be used in fractional T1 or E1 services.

ISDN service types

The

(ISDN) prescribes two levels of service: * Basic Rate Interface (BRI): one 16-kbit/s D channel with two 64-kbit/s B channels, intended for small enterprises and residential service. * Primary Rate Interface (PRI): one 64-kbit/s D channel with 23 (1.544 Mbit/s T1, a.k.a. "23B + D") or 30 (2.048 Mbit/s E1, a.k.a. "30B + D") 64-kbit/s B channels, intended for large organizations. Each B-channel carries data, voice, and other services. The D-channel carries control and signaling information. Larger connections are possible using PRI pairing. A dual T1-PRI could have 24 + 23 = 47 B-channels and 1 D-channel (often called "47B + D"), but more commonly has 46 B-channels and 2 D-channels thus providing a backup signaling channel. The concept applies to E1s as well and both can include more than 2 PRIs. When configuring multiple T1's as ISDN-PRI's, it's possible to use NFAS (non-facility associated signaling) to enable one or two D-channels to support additional B-channels on separate T1 circuits.

Application

The Primary Rate Interface channels are typically used by medium to large enterprises with digital

private branch exchange A business telephone system is a telephone system typically used in business environments, encompassing the range of technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone system differs from ...

(PBX) telephone systems to provide digital access to the

public switched telephone network The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists o ...

(PSTN). The B-channels may be used flexibly and reassigned when necessary to meet special needs such as video conferences. PRI channels and

direct inward dialing Direct inward dialing (DID), also called direct dial-in (DDI) in Europe and Oceania, is a telecommunication service offered by telephone companies to subscribers who operate private branch exchange (PBX) systems. The feature provides service for m ...

are also common as a means of delivering inbound calls to

voice over IP Voice over Internet Protocol (VoIP), also known as IP telephony, is a set of technologies used primarily for voice communication sessions over Internet Protocol (IP) networks, such as the Internet. VoIP enables voice calls to be transmitted as ...

gateways from the PSTN.

References

*{{FS1037C Integrated Services Digital Network

ISDN service types

Application

See also

References