MLT-3 encoding (Multi-Level Transmit) is a

line code In telecommunication, a line code is a pattern of voltage, current, or photons used to represent digital data transmitted down a communication channel or written to a storage medium. This repertoire of signals is usually called a constrained c ...

(a signaling method used in a

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

system for transmission purposes) that uses three

voltage Voltage, also known as electric pressure, electric tension, or (electric) potential difference, is the difference in electric potential between two points. In a static electric field, it corresponds to the work needed per unit of charge to m ...

levels. An MLT-3 interface emits less

electromagnetic interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electros ...

and requires less

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

than most other

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that ta ...

ternary Ternary (from Latin ''ternarius'') or trinary is an adjective meaning "composed of three items". It can refer to: Mathematics and logic * Ternary numeral system, a base-3 counting system ** Balanced ternary, a positional numeral system, useful ...

interfaces that operate at the same

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction w ...

(see PCM for discussion on bandwidth / quantization tradeoffs), such as Manchester code or

Alternate Mark Inversion In telecommunication, bipolar encoding is a type of return-to-zero (RZ) line code, where two nonzero values are used, so that the three values are +, −, and zero. Such a signal is called a duobinary signal. Standard bipolar encodings are designed ...

. MLT-3 cycles sequentially through the voltage levels −1, 0, +1, 0. It moves to the next state to transmit a 1 bit, and stays in the same state to transmit a 0 bit. Similar to simple NRZ encoding, MLT-3 has a coding efficiency of 1 bit/baud, however it requires four transitions (

baud In telecommunication and electronics, baud (; symbol: Bd) is a common unit of measurement of symbol rate, which is one of the components that determine the speed of communication over a data channel. It is the unit for symbol rate or modulatio ...

) to complete a full cycle (from low-to-middle, middle-to-high, high-to-middle, middle-to-low). Thus, the maximum fundamental frequency is reduced to one fourth of the baud rate. This makes signal transmission more amenable to copper wires. The lack of transition on a 0 bit means that for practical use, the number of consecutive 0 bits in the transmitted data must be bounded; i.e. it must be pre-coded using a

run-length limited Run-length limited or RLL coding is a line coding technique that is used to send arbitrary data over a communications channel with bandwidth limits. RLL codes are defined by four main parameters: ''m'', ''n'', ''d'', ''k''. The first two, ''m'' ...

code. This results in an effective bitrate slightly lower than one bit per baud or four bits per cycle. MLT-3 was first introduced by Crescendo Communications
Network World, June 29, 1992, page 19 as a coding scheme for

FDDI Fiber Distributed Data Interface (FDDI) is a standard for data transmission in a local area network. It uses optical fiber as its standard underlying physical medium, although it was also later specified to use copper cable, in which case it m ...

copper interconnect (TP-PMD, - initial implementation; also see patent aka CDDI). Later, the same technology was used in the

100BASE-TX In computer networking, Fast Ethernet physical layers carry traffic at the nominal rate of 100 Mbit/s. The prior Ethernet speed was 10 Mbit/s. Of the Fast Ethernet physical layers, 100BASE-TX is by far the most common. Fast Ethern ...

physical medium dependent sublayer, given the considerable similarities between

and 100BASE- F physical media attachment layer (section 25.3 of IEEE802.3-2002 specifies that ANSI X3.263:1995 TP-PMD should be consulted, with minor exceptions). Signaling specified by 100BASE-T4 Ethernet, while it has three levels, is not compatible with MLT-3. It uses selective

base-2 A binary number is a number expressed in the base-2 numeral system or binary numeral system, a method of mathematical expression which uses only two symbols: typically "0" (zero) and "1" ( one). The base-2 numeral system is a positional notatio ...

to base-3 conversion with direct mapping of base-3 digits to line levels ( 8B6T code).

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References

Line codes {{telecomm-stub

See also

External links

References