Editing Basic Rate Interface (section)

==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|S<sub>0</sub>]]) 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 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 interface|U<sub>p</sub> 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 in North America, Italy and Switzerland, and 4B3T elsewhere. Depending on the applicable cable length, two varieties are implemented, [[UPN interface|U<sub>pN</sub>]] and [[Up0-interface|U<sub>p0</sub>]]. The [[UK0-Interface|U<sub>k0</sub>]] 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}}.