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Basic Rate Interface (BRI,2B+D,2B1D) orBasic Rate Access is anIntegrated Services Digital Network (ISDN) configuration intended primarily for use insubscriber lines similar to those that have long been used forvoice-grade telephone service.As such, an ISDN BRI connection can use theexisting telephone infrastructure at a business.

The BRI configuration provides 2 data (bearer) channels (B channels) at 64 kbit/s each and 1 control (delta) channel (D channel) at 16 kbit/s. The B channels are used forvoice or userdata, and the D channel is used for any combination of data,control signaling, andX.25 packet networking.^[1] The 2B channels can be aggregated bychannel bonding providing a total data rate of 128 kbit/s. The BRI ISDN service is commonly installed forresidential or small business service (ISDNPABX) in many countries.

In contrast to the BRI, thePrimary Rate Interface (PRI) configuration provides moreB channels and operates at a higherbit rate.

The BRI is split in two sections:a) in-house cabling (S/T reference point or S-bus) from the ISDN terminal up to thenetwork termination 1 (NT1) andb) transmission from the NT1 to the central office (U reference point).

• The in-house part is defined inI.430 produced by theInternational Telecommunication Union (ITU). The S/T-interface (S₀) uses four wires; one pair for theuplink and another pair for thedownlink. It offers a full-duplex mode of operation. The I.430 protocol defines 48-bitpackets comprising 16bits from the B1 channel, 16 bits from B2 channel, 4 bits from the D channel, and 12 bits used forsynchronization purposes. These packets are sent at a rate of4 kHz, resulting in a grossbit rate of 192 kbit/s and – giving the data rates listed above – a maximum possible throughput of144kbit/s. The S₀ offers point-to-point or point-to-multipoint operation; Max length: 900 metres (3,000 ft) (point-to-point), 300 metres (980 ft) (point-to-multipoint).
• TheU_p 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,U_pN andU_p0. TheU_k0 interface uses one wire pair withecho cancellation for the longlast mile cable between thetelephone exchange and thenetwork terminator. The maximum length of this BRI section is between 4 and 8 kilometres (2.5 and 5.0 mi).

• "BRI defined on birds-eye.net". Archived fromthe original on 2012-08-25. Retrieved2012-08-25.

• Integrated Services Digital Network

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