# Basic Rate Interface

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

thumb|right|An ISDN phone

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

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

In contrast to the BRI, the [Primary Rate Interface](/source/Primary_Rate_Interface) (PRI) configuration provides more [B channel](/source/B_channel)s and operates at a higher [bit rate](/source/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](/source/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](/source/I.430) produced by the [International Telecommunication Union](/source/International_Telecommunication_Union) (ITU). The S/T-interface ([S<sub>0</sub>](/source/S_interface)) uses four wires; one pair for the [uplink](/source/uplink) and another pair for the [downlink](/source/downlink). It offers a full-duplex mode of operation. The I.430 protocol defines 48-bit [packet](/source/data_packet)s comprising 16 [bit](/source/bit)s from the B1 channel, 16 bits from B2 channel, 4 bits from the D channel, and 12 bits used for [synchronization](/source/synchronization) purposes. These packets are sent at a rate of {{val|4|ul=kHz}}, resulting in a gross [bit rate](/source/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 S<sub>0</sub> 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<sub>p</sub> Interface](/source/U_interface) uses two wires. The gross bit rate is 160&nbsp;kbit/s; 144&nbsp;kbit/s throughput, 12&nbsp;kbit/s sync and 4&nbsp;kbit/s maintenance. The signals on the U reference point are encoded by two modulation techniques: [2B1Q](/source/2B1Q) in North America, Italy and Switzerland, and [4B3T](/source/4B3T) elsewhere. Depending on the applicable cable length, two varieties are implemented, [U<sub>pN</sub>](/source/UPN_interface) and [U<sub>p0</sub>](/source/Up0-interface). The [U<sub>k0</sub>](/source/UK0-Interface) interface uses one wire pair with [echo cancellation](/source/echo_cancellation) for the long [last mile](/source/Last_mile_(telecommunications)) cable between the [telephone exchange](/source/telephone_exchange) and the [network terminator](/source/Network_termination_1). 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

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Adapted from the Wikipedia article [Basic Rate Interface](https://en.wikipedia.org/wiki/Basic_Rate_Interface) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Basic_Rate_Interface?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.