Alternate Mark Inversion (AMI) is a line encoding technique (line code) for T1s which uses bipolar pulses to represent logical 1 values. It is therefore a three-level system. A logical 0 is represented by no symbol, and a logical 1 by pulses of alternating polarity. The alternating coding prevents the build-up of a DC voltage in the cable. This is considered an advantage since the cable may be used to carry a small DC current to power intermediate equipment such as line repeaters. In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes. ... T1 or T-1 is used for various purposes as a designation, abbreviation or identifier: In telecommunications see DS1 and T-carrier. ... Bipolar can refer to: Bipolar (biology) Bipolar disorder Bipolar junction transistor (electronics) This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Logic (from Classical Greek λόγος (logos), originally meaning the word, or what is spoken, but coming to mean thought or reason) is most often said to be the study of arguments, although the exact definition of logic is a matter of controversy amongst philosophers (see below). ... Direct current (DC or continuous current) is the continuous flow of electricity through a conductor such as a wire from high to low potential. ... In the physical sciences, potential difference is the difference in potential between two points in a conservative vector field. ... In electricity, current refers to electric current, which is the flow of electric charge. ...

AMI coding was used extensively in first-generation PCM networks, but suffers the drawback that a long run of 0's produces no transitions in the data stream (and therefore does not contain sufficient transitions to guarantee lock of a DPLL). Successful transmission therefore relies on the user not wishing to send long runs of 0's and this type of encoding is not therefore transparent to the sequence of bits being sent. For voice traffic the least significant bit of each frame (every eighth bit) is always set to '1', thereby generating enough transitions on the line. This is acceptable for voice, but not for data. PCM is an initialism which can have different meanings: Phase Change Material Pulse-code modulation Potential Cancer Marker This page concerning a three-letter acronym or abbreviation is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Many electronic systems use internal clocks which are required to be phase-aligned to and/or frequency multiples of some external reference clock. ...

There are other encoding schemes are two of many which have been developed to provide regular transitions irrespective of the data being carried. B8ZS is a newer format for North America, where HDB3 is the original line coding type used in Europe and Japan. B8ZS is an abbreviation for bipolar with eight-zero substitution. ... World map showing location of North America A satellite composite image of North America North America is a continent in the northern hemisphere, bounded on the north by the Arctic Ocean, on the east by the North Atlantic Ocean, on the south by the Caribbean Sea, and on the west... HDB3 (High-density bipolar-3 zeros) is a telecommunications line code mainly used in Japan and Europe (for example, in E-1 lines) and is based on AMI. It is also very similar to the B8ZS encoding used in T-1 lines. ... World map showing location of Europe Europe is geologically and geographically a peninsula, forming the westernmost part of Eurasia. ...

Example of AMI encoding: The pattern of bits " 1 0 0 0 0 1 1 0 " encodes to " + 0 0 0 0 - + 0 ".