MLT-3 encoding

Example of MLT-3 Encoding. Light-colored lines indicate two previous states.

MLT-3 encoding (Multi-Level Transmit) is a line code (a signaling method used in a telecommunication system for transmission purposes) that uses three voltage levels. An MLT-3 interface emits less electromagnetic interference and requires less bandwidth than most other binary or ternary interfaces that operate at the same bit rate (see PCM for discussion on bandwidth / quantization tradeoffs), such as Manchester 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 1 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 for FDDI copper interconnect (TP-PMD,^[1] aka CDDI). Later, the same technology was used in the 100BASE-TX physical medium dependent sublayer, given the considerable similarities between FDDI and 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

• U.S. Patent 5,280,500

References

1. ^ American National Standards Institute (1994). "FDDI twisted pair physical layer medium dependent (TP-PMD)". American National Standard X3T12 (incorporates X3.263).  - initial implementation; also see patent

v • d • e Pulse-code modulation (PCM) digital encoding Main articles Unipolar encoding · Bipolar encoding · On-off keying Basic line codes Return to zero (RZ) · Non-return-to-zero, level (NRZ/NRZ-L) · Non-return-to-zero, inverted (NRZ-I) · Non-Return-to-Zero, space (NRZ-S) · Biphase (Bi-φ) · Manchester · Differential Manchester Extended line codes Conditioned Diphase · 4B3T · 4B5B · AMI code · Modified AMI code · Coded mark inversion · MLT-3 encoding · Hybrid ternary code · 6b/8b encoding · 8b/10b encoding · 64b/66b encoding · Eight-to-fourteen modulation · Delay/Miller encoding · TC-PAM Optical line codes Carrier-Suppressed Return-to-Zero · Alternate-Phase Return-to-Zero See also: Quantization · Sampling · Category:Line codes

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