4 binary, 3 ternary (4B3T)
The 4B3T coding is a line coding for blockwise ternary coding of binary signals. With 4B3T, four bits each (binary block 4B) are represented with three ternary signal levels (ternary block 3T). This means that a total of 16 binary values are mapped to 27 signal values. This coding method is also called MMS43 code, which stands for Modified Monitored Sum( MMS).
4B3T coding uses a table to assign the 16 bit patterns of 4 bits each to the ternary signals. Four different ternary sequences are assigned to each 4-bit word. The coding is used as a transmission method for ISDN at the UK0 interface. The 4B3T coding is used in the connection area between the ISDN exchange and the network termination. The ternary representation of the data stream reduces the data rate from 160 kbit/s to a step rate of 120 kBaud. This allows the maximum distance of 8 km between the network termination and the ISDN exchange to be achieved.