At this point the standard wiring model shifted from one long cable, snaking from host to host, to a “star” network, where each host connected directly to a central multipoint repeater. Repeaters soon evolved into multiport devices, allowing the creation of arbitrary tree (that is, loop-free) topologies. The only active components besides the stations were repeaters, originally intended simply to make end-to-end joins between cable segments. If two stations happened to transmit at the same time – most likely because they were both waiting for a third station to finish – their signals were lost to the resultant collision. In its most basic form, the Ethernet medium was one long piece of coaxial cable, onto which stations could be connected via taps. We choose to make the shared communication facility passive so that the failure of an active element will tend to affect the communications of only a single station.Ĭlassic Ethernet was indeed simple, and – mostly – passive. We cannot afford the redundant connections and dynamic routing of store-and-forward packet switching to assure reliable communication, so we choose to achieve reliability through simplicity. The authors described their passive architecture as follows: The data rate was 10 megabits per second, and all connections were made with coaxial cable instead of today’s twisted pair.
The original Ethernet specification was the 1976 paper of Metcalfe and Boggs. While the 10 Mbps speed is obsolete, and while even the Ethernet collision mechanism is largely obsolete, collision management itself continues to play a significant role in wireless networks. However, because the potential for packet collisions makes Ethernet speeds scale in odd ways, we will start with the 10 Mbps formulation. The following chapter covers more advanced features, such as the spanning-tree algorithm, virtual LANs, Ethernet hardware, TRILL/SPB and software-defined networking.Ĭurrent user-level Ethernet today (2020) is usually 100 Mbps or Gigabit, with Gigabit and 10 Gigabit Ethernet standard in server rooms and backbones.
In this chapter we cover the more universal Ethernet concepts, such as would be encountered in any residential or small-office Ethernet setting and including switching and learning. We now turn to a deeper analysis of the ubiquitous Ethernet LAN protocol.
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