- MLT-3 encoding
MLT-3 encoding (Multi-Level Transmit) is a
line code (a signaling method used in atelecommunication system for transmission purposes) that uses threevoltage levels. An MLT-3 interface emits lesselectromagnetic interference and requires less bandwidth than most other binary or ternary interfaces that operate at the samebit rate (seePCM for discussion on bandwidth / quantization tradeoffs), such asManchester code or Alternate Mark Inversion.MLT-3 cycles through the voltage levels -1, 0, +1, and 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 2 bit/baud, however it requires four transitions (baud) 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.
MLT-3 was first introduced by
Cisco Systems as a coding scheme forFDDI copper interconnect (TP-PMD,cite journal
author = American National Standards Institute
year = 1994
title = FDDI twisted pair physical layer medium dependent (TP-PMD)
journal = American National Standard X3T12 (incorporates X3.263) - initial implementation; also see patent] akaCDDI ). Later, the same technology was used in the 100BASE-TX physical medium dependent sublayer, given the considerable similarities betweenFDDI and [Fast Ethernet|100BASE- [TF] X] 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 to base-3 conversion with direct mapping of base-3 digits to line levels (
8B6T code).External links
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References
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