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Tele-Communication (Telecom) Terms Glossary and Dictionary
4B/3T
4B/3T, also known as MMS43 code, is a type of line encoding method for ternary block encoding of binary signals, where four binary elements (binary block 4B) are represented as three ternary elements (ternary block 3T). 4B/3T encoding uses a matrix that maps each of the 16 bit patterns to 4 bits of the ternary signals. Four different ternary sequences are mapped to each 4 bit word. This encoding method is used by the ISDN Basic Rate Interface as a transmission method. 4B/3T encoding is also used in the exchange area between the ISDN exchange and the network terminator. The ternary representation of the data stream supports data rates of 160 kbit/s at a clock speed of 120 kbit/s. This allows for a maximum distance of 8 km between the network terminator and the ISDN exchange.
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