Notes:
10BASE5 is the original Ethernet backbone, and is occasionally referred to as thicknet or thick Ethernet because of the thick 50 ohm coax that was used as the physical medium. 10BASE5 is a bus topology that uses transceiver cables to attach stations to the central 10BASE5 cable. Maximum segment length: 500 meters Maximum number of segments connected with repeaters: 5 (2500 meters) Maximum attachments per segment: 100 Minimum separation between attachments: 2.5 meters
AUI signaling was 1.4 V P-P +0.7VDC to –0.7VDC differential, manchester encoded on the wire at 20 MHz, 0 to plus and minus 2.5 VDC differential. Manchester encoding was used for all 10Base standards.
Then there are limitations on the number of repeaters and cable segments allowed between any two stations on the network. There are two different ways of looking at the same rules: 1. The Ethernet way: A remote repeater pair (with an intermediate point-to-point link) is counted as a single repeater (IEEE calls it two repeaters). You cannot put any stations on the point to point link (by definition!), and there can be two repeaters in the path between any pair of stations. This seems simpler to me than the IEEE terminology, and is equivalent. 2. The IEEE way: There may be no more than five (5) repeated segments, nor more than four (4) repeaters between any two Ethernet stations; and of the five cable segments, only three (3) may be populated. This is referred to as the "5-4-3" rule (5 segments, 4 repeaters, 3 populated segments).