Ethernet was named after the luminiferous ether, through which electromagnetic radiation was once thought to propogate.

After the Xerox Ethernet became successful, Xerox, DEC, and Intel joined forces (Wonder Twin Powers activate!) and drew up a standard for a 10Mbps Ethernet, which formed the basis for 802.3. The term Ethernet refers to a specific product, not to all CSMA/CD protocols. It actually refers to the cable (see above write-up).
Ethernet is a networking technology. It is CSMA/CD, or Carrier Sense, Multiple Access, Collision Detect. All hosts on an ethernet segment can hear all communication going on. When a host wants to transmit, it checks to see if other transmissions are going on. Hence, the carrier sense part. If none are going on, it transmits. If all goes well, the transmission will be heard by all hosts on the segment, including the host the transmission was intended for. This is the Multiple Access part. If two hosts happen to transmit at the same time, a collision will ocurr, and both hosts will wait a random amount of time before transmitting again. This is the collision detect part.

Ethernet hardware addresses are 48 bits long, or six bytes. They are usually written in hex as follows: 2A:3F:00:11:55:2F. All ethernet interface manufacturers turn to a central registry to get addresses, to ensure that no two devices ever have the same hardware address. It is the ethernet controller's job to only pass along two types of frames to the host: Those with its destination address, and broadcast frames. All others should be ignored. This job can be extended to pass all frames along to the host, which is known as promiscuous mode, and is used to debug network problems and spy on people.

Ethernet can travel over many different media, at different signalling rates. The most common ethernet signalling rate is 10 megabits per second, which can travel over 10base-2, 10base-5, 10base-T, and so on. Then you have fast ethernet and gigabit ethernet, which have higher signalling rates, and hence, different media.

Ethernet is a layer 2 protocol in the OSI network model.

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