Ethernet speed limit: 3Mbps, 100Gbps (on)
In the 1970s, although the backward and rudimentary media, such as television, prevailed, it was not so pale that there was no color in modern communication systems. Indeed, the state-of-the-art Advanced Research Projects Agency Network developed by the US Department of Defense's Advanced Research Projects Agency (the world's first operating packet-switching network, the ancestor of the global Internet) had a modem speed of only 50. Kbps, and the size of the refrigerator is huge; as for the widely spread Bell 103 modem, its transmission speed is only 300 bits per second. Fortunately, with the increase in the total number of computers, long-distance digital communication has become quite popular. Terminals can also be connected to mainframe computers or microcomputers via relatively short simple lines or more complex multipoint systems.
These are the sesame seeds and rotten millet. The real new thing in the 1970s was the local area network (LAN). How does it connect all the computers?
The highlight of the LAN is that it can connect to more than two computer systems. Therefore, a simple single-wire bidirectional transmission line is not enough. In theory, the star, ring, and bus topologies can connect thousands of computers into a local area network. The star bus topology connects each computer to several central nodes, which is clearly sufficient for this requirement. The bus topology consists of a single long cable that is routed along the cable. In the ring topology, a cable is used to string together a computer and finally end to end to form a complete ring structure.
Pic: Topology
In practice, things are far from theoretically simple. Token Ring is a LAN technology that uses a star topology. But this is not visible from the way the cable is connected, because all computers are connected to the central monitoring system (similar to today's Ethernet switches). But these lines do form a ring structure. Token Ring uses a sophisticated token delivery system to determine which computer and when to send data packets. A token is circulated in the ring structure, and the computer holding the token is responsible for sending out the message. The token bus uses a physical bus topology, but there is also a token passing scheme that is used to determine the access rights of each computer to the bus. Due to its complexity, the token network appears to be weak in the face of many types of failures. However, this kind of network form does have the advantage of “the operation effect can be predictedâ€. The operation effect of the network can be accurately calculated in advance, which is of great significance at some application levels.
Pic: Token Ring
But in the LAN standardization war, the last laugh is Ethernet. It is the killer of Ethernet to lobby officials in the standardization organization and advocate their own smart, concise, low-implementation design. Ethernet is constantly striving to discover and absorb higher-speed network transmission protocols, and to use their technological advantages as their own, making this network standardization dispute increasingly lost. A few decades later, Ethernet finally dominated the rivers and lakes.
If you have ever noticed the network cable behind your computer's buttocks, you are curious about where Ethernet starts, how far it runs, how it works, and you don't have to scratch your head. And listen to me slowly.
Xerox PARC presents you
Ethernet was invented by Bob Metcalfe and other Xerox Palo Alto Research Center (PARC) employees in the mid-1970s. PARC's experimental Ethernet network speed is up to 3Mbps. "This data transfer speed is slower than the computer access to the main memory, but it is enough." Due to the considerable network speed, data packets are not delayed on the Ethernet interface. The name "Ethernet" comes from "Light Ethernet", a fictional concept that was once thought to be the medium of electromagnetic wave transmission (just as the transmission medium of sound waves is air).
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