is a system for connecting a number of computer systems to form a local area network, with protocols to control the passing of information and to avoid simultaneous transmission by two or more systems
is both a Layer 1 & Layer 2 protocol
uses CSMA/CD, however Ethernet links are largely point-to-point now (one host to an ethernet switch and/or interconnected switches). Therefore, CSMA/CD is largely obsolete because of separate collision domains

Physical Properties

using coaxial cable, twisted copper pairs, or optical fibers - cable types
transceiver - device able to transmit and receive signals
ethernet adaptor mediator between transceiver and host
repeater - device that forward signals
hub - a multiway repeater - repeats what it hears on one port and outputs to all other ports
4b/5b encoding is used in original specifications
8b/10b encoding is used on higher speed ethernet

Media Access Control (MAC)

if the link is idle, send the frame immediately
if the link is busy, wait until idle then send immediately. this is called 1-persistent protocol
if a collision is detected, send 96-bits: 64-bit preamble + 32-bit jamming sequence
each time transmit fails, the adaptor waits exponential backoff and then tries again
- fail 1: randomly wait for either 0, 51.2μs
- fail 2: randomly wait for either 0, 51.2μs, 102.4μs
- fail 3: randomly wait for either 0, 51.2μs, 102.4μs, 153.6μs
- etc, typically up to 16 times
- wait-time = rand(0, 2ᵏ-1) * unit-wait-time