StarLAN was the first implementation of 1 megabit per second (1Mbit/s) Ethernet over twisted pair wiring. It was standardized by the standards association of the Institute of Electrical and Electronics Engineers (IEEE) as 802.3e in 1986, as the 1BASE5 version of Ethernet.
StarLAN was developed by AT&T Corporation around 1984, with a name based on the fact that it used a star topology from a central hub in contrast to the bus network of the existing 10Base5 and 10Base2 networks.
The standard known as 1BASE5 was adopted as 802.3e in 1986 by members of the IEEE 802.3 standards committee as the Twisted Pair Medium Specification in section 12. StarLAN ran at a speed of 1 Mbit/s.
A major design goal in StarLAN was the reuse of existing telephony on-premises wiring and compatibility with analog telephone signals in the same cable bundle. The signal modulation and wire pairing used by StarLAN were carefully chosen so that they would not affect or be affected by either the analog signal of a normal call, on hook and off hook transients, or the 20 Hz high-voltage analog ring signal. Reuse of existing wires was critical in many buildings where rewiring was cost prohibitive, or where running new wire would disturb asbestos within the building infrastructure.
The wire positioning called T568B in the standard TIA/EIA-568 was originally devised for StarLAN, and pair 1 (blue) was left unused to accommodate an analog phone pair. Pairs 2 and 3 (orange and green) carry the StarLAN signals. This greatly simplified the installation of combined voice and data wiring in countries that used registered jack connectors and American wiring practices for their phone service (connecting both to the same cable was a simple matter of using a pin-pin RJ45 splitter or punching down the same wires to two ports). This arrangement prevented harm to private branch exchange (PBX) equipment in the event that a StarLAN cable was plugged into the wrong device.
The technology was patented by AT&T, and initially was part of a wider vision from AT&T, where it would link their UNIX-based AT&T 3B2 minicomputers to a network of MS-DOS PCs. It was adopted by other networking vendors such as Hewlett-Packard and Ungermann-Bass. Integrated circuits were introduced starting in 1986 that reduced the cost of the interfaces. StarLAN never became popular by itself, but provided the basis for the later 10 megabit per second standard 10BASE-T.
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