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 (
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
packets comprising 16
bits 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 , resulting in a gross
bit rate of 192 kbit/s andgiving the data rates listed abovea maximum possible throughput of . The S0 offers point-to-point or point-to-multipoint operation; Max length: (point-to-point), (point-to-multipoint). • The
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 and
Up0. The
Uk0 interface uses one wire pair with
echo cancellation for the long
last mile cable between the
telephone exchange and the
network terminator. The maximum length of this BRI section is between . ==References==