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{{Short description|ISDN configuration}}
{{more footnotes|date=March 2013}}

[[File:ISDN telefono.jpg|thumb|right|An ISDN phone]]

'''Basic Rate Interface''' ('''BRI''', '''2B+D''', '''2B1D''') or '''Basic Rate Access''' is an [[Integrated Services Digital Network]] (ISDN) configuration intended primarily for use in [[subscriber line]]s similar to those that have long been used for [[Plain old telephone service|voice-grade telephone service]].
As such, an ISDN BRI connection can use the [[Plain old telephone service|existing telephone infrastructure]] at a business.

The BRI configuration provides 2 data (bearer) channels ([[B channel]]s) at 64 kbit/s each and 1 control (delta) channel ([[D channel]]) at 16 kbit/s. The B channels are used for [[Human voice|voice]] or user [[data]], and the D channel is used for any combination of data, [[Signaling (telecommunications)|control signaling]], and [[X.25]] packet networking.<ref>{{foldoc|Basic+Rate+Interface}}</ref> The 2 [[B channel]]s can be aggregated by [[channel bonding]] providing a total data rate of 128 kbit/s. The BRI ISDN service is commonly installed for [[residential]] or small business service (ISDN [[PABX]]) in many countries.

In contrast to the BRI, the [[Primary Rate Interface]] (PRI) configuration provides more [[B channel]]s and operates at a higher [[bit rate]].

==Physical interfaces==
The BRI is split in two sections:
a) in-house cabling (S/T reference point or S-bus) from the ISDN terminal up to the [[network termination 1]] (NT1) and
b) transmission from the NT1 to the central office (U reference point).

* The in-house part is defined in [[I.430]] produced by the [[International Telecommunication Union]] (ITU). The S/T-interface ([[S_interface|S0]]) uses four wires; one pair for the [[uplink]] and another pair for the [[downlink]]. It offers a full-duplex mode of operation. The I.430 protocol defines 48-bit [[data packet|packet]]s comprising 16 [[bit]]s from the B1 channel, 16 bits from B2 channel, 4 bits from the D channel, and 12 bits used for [[synchronization]] purposes. These packets are sent at a rate of {{val|4|ul=kHz}}, resulting in a gross [[bit rate]] of 192 kbit/s and{{dash}}giving the data rates listed above{{dash}}a maximum possible throughput of {{gaps|144|kbit/s}}. The S0 offers point-to-point or point-to-multipoint operation; Max length: {{convert|900|m}} (point-to-point), {{convert|300|m}} (point-to-multipoint).
* The [[U interface|Up Interface]] uses two wires. The gross bit rate is 160 kbit/s; 144 kbit/s throughput, 12 kbit/s sync and 4 kbit/s maintenance. The signals on the U reference point are encoded by two modulation techniques: 2B1Q in North America, Italy and Switzerland, and 4B3T elsewhere. Depending on the applicable cable length, two varieties are implemented, [[UPN interface|UpN]] and [[Up0-interface|Up0]]. The [[UK0-Interface|Uk0]] interface uses one wire pair with [[echo cancellation]] for the long [[Last mile (telecommunications)|last mile]] cable between the [[telephone exchange]] and the [[Network termination 1|network terminator]]. The maximum length of this BRI section is between {{convert|4 and 8|km}}.

==References==
{{Reflist}}

==External links==
*{{cite web|url=http://www.birds-eye.net/definition/b/bri-basic_rate_interface.shtml |title=BRI defined on birds-eye.net |access-date=2012-08-25 |url-status=dead |archive-url=https://web.archive.org/web/20120825163144/http://www.birds-eye.net/definition/b/bri-basic_rate_interface.shtml |archive-date=2012-08-25 }}

[[Category:Integrated Services Digital Network]]

Basic Rate Interface - Revision history

imported>Kvng: foldoc attribution, see Template_talk:FOLDOC#It_doesn't_matter_whether_readers_care