Etherloop is a hybrid technology combining aspects ofEthernet with other technologies to achieve a result not possible with either technology alone. EtherLoop was originally developed in the 1990s to allow high-speed data communication access to residential customers over standardtwisted-pair telephone lines, also known asplain old telephone service or POTS. The technology development effort was begun atNorthern Telecom in order to allowtelephone companies to compete with the high-speed local data access then beginning to be offered bycable TV providers.[1]: 5
Etherloop is also a communications architecture with much broader applications. Technically, the initial EtherLoop adopted the protocol concepts of an Ethernet short-distance physical network withdigital subscriber line (DSL) technology to facilitate the combination of voice anddata transmission on legacy physical infrastructure of standard phone lines over distances of several kilometers. The project goal was to overcome the limitations ofADSL andHDSL while maintaining high-quality and high-speed data transmission. By combining features ofEthernet and DSL, and usingdigital signal processors (DSP) to enable the "maximum possible bandwidth out of any twisted pair copper pipe," EtherLoop became an architecture able to address a much wider variety of data networking requirements than the original 1990s-2000s application of data over POTS lines.[1]: 5, 28
Other technologies termed "etherloop" have been developed, including use for automotive intra-vehicle communication in the 2020s, where agigabit Ethernet physical network has been used with a proprietarytime-sliced,network protocol fornear real-time, redundant control andfeedback of motor vehicle subsystems.[2][3]
EtherLoop was initially developed by Elastic Networks in the 1990s, to allow high-speed data communication access to residential customers over standardtwisted-pair telephone lines. The technology development effort had been started by Jack Terry ofNorthern Telecom in order to allowtelephone companies to compete with the high-speed local data access then beginning to be offered bycable TV providers.[1]: 5
In 1999, EtherLoop technology could, under the right conditions, facilitate speeds of up to 6 megabits per second over a distance of up to 6.4 km (21,000 feet).[1]
Thetelco EtherLoop design adopted the basic concepts ofdigital subscriber line (DSL) communications technology plusEthernet local area network technology to facilitate the combination of voice anddata transmission on legacy physical infrastructure of standardtwisted-pair telephone lines, orplain old telephone service (POTS).[1]: 5
Prior DSL implementations—Asymmetric DSL (ADSL) andHigh-bit-rate DSL (HDSL)—had technical issues that limited adoption in telephone networks. Sending high-speed data requires substantial power to drive the signal levels across copper lines. More signal delivered results incrosstalk with other copper lines in the typical 25 or 50 tightly-bundled pairs used in telephone wiring.
For DSL services to reach their theoretical performance maximums, a near-idealsubscriber loop is required. In the real world, however, most subscriber loops are far from ideal. The wire may change gauge [ranging from22 gauge to 26 gauge in POTS services]. This causes distortions and interference in a passing signal. It is also possible to havebridge taps on the loop, where a wire is attached to the main loop, but not connected to anything at the far end. Unconnected bridge taps causereflections in the signal – some of the incoming signal will bounce backwards, and this reflection willinterfere with the original signal.[1]: 7
The continuous power level required to operate DSL in the telco environment also increased the heat that needed to be dissipated over traditional phone service and increased the cost of the components.[1]: 7–10
Telco EtherLoop overcame some of the limitations while maintaining high-quality and high-speed data transmission by combining features of Ethernet and DSL, and usingdigital signal processors (DSP) to enable the "maximum possible bandwidth out of any twisted pair copper pipe," EtherLoop became an architecture able to address a much wider variety of data networking requirements than the original 1990s-2000s application of data over POTS lines.[1]: 5, 28 The initial EtherLoop implementation in 1999 used ahalf-duplex/bi-directional communication approach—but in only a single direction at a time, not simultaneously—plusburst packet delivery to mitigate several of the serious side effects of the legacy high-speed DSL offerings of the late 1990s. As such, EtherLoop transmission is less susceptible to interference caused by poor line quality,bridge taps, etc. in telephone company applications.[1]: 8–12
Later applications of EtherLoop in automotive systems overcame a different set of problems with EtherLoop-design solutions, as described in the Applications section below.
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