Ethernet - implementation of the IEEE 802.3 protocol.

Wikipedia topic : Ethernet

Developed ~ 1973-1980, and implemented by a coalition of companies as an alternative to Token Ring and other proprietary networks.

Protocol standard in early 1980's by the Institute of Electrical and Electronics Engineers (IEEE).

Uses a 48-bit Media Access Control (MAC) address to uniquely identify any interface.

On hopper/turing run :

/sbin/ifconfig

The MAC protocol is used by Ethernet, Bluetooth, Modern Token-ring, Wireless, etc. and most other devices following the IEEE 802 protocol.

Designed to be transmitted over copper-wire and fiber-optics.

Originally, 10 Mbits/s, now variations of 100 Mbits/s to 100 Gbits/s.

Information from the upper level of the protocol stack is packaged in a frame at the data-link layer.

See Wikipedia : Ethernet frame

Frame consists of :

Preamble - used to synchronize clock on receiving node.
Start of Frame (SFD) - marks the start of the actual frame.
Destination MAC address - address of another node on local network or the node address of the gateway router off of the local network.
Source MAC address - address of this communicating node.
Various flags for quality and type of transmission.
Updates to the IEEE 802 protocol allow the Ethernet2 frame to flag things about the payload that could help the gateway router better route the payload.
Example : Payload is using IPv4 or IPv6. The Internet layer handles each of these differently.
Payload - this is the information be transmitted. The source and destination IPs and ports are inside the payload and are processed by the Internet and Transport layers of TCP/IP stack protocol.
Minimum of 46 octets and maximum on 1500 octets.
Jumbogram - non-standard 9000 byte packet. Requires support on switches(hub) that packet passes through. More common on Gbit Ethernet.
Frame Check Sequence (FCS) - cyclic redundancy check (CRC).
CRC performs some type of modulo math and appends a value to the end of the data stream being sent.
The receiving end performs the same math and with the added value, the results should be zero.
If it is not, the receiver signals data corruption and the sender re-transmits.
End of Frame - specific bit pattern to flag end of frame.
Inter-packet gap - minimum idle of a certain length.

Additionally, the 8-bit bytes of data are encoded in a large byte (10-bit) which provides critical timing information.

What this means is that, between the frame information and the encoding,
100 Mbits/sec actually delivers closer to 70 Mbits of user data.

Connectivity Ethernet is broadcast and theoretically CSMA/CD Implemented over copper (twisted pair), Coaxial, and Fiber.

Most common is twisted pair using an RJ45 jack.

Lines are positionally important, so jack is asymmetrical.

Network arranged as a tree or star with root usually gateway out of local network.

Topology - tree, ring, star, bus.

10baseT - early version, 10 Mi-bit/sec, used a repeater hub. Signals coming from any node were broadcast to all nodes on hub and collisions possible.

Repeater hubs often had either a dedicated port out of the local cluster of nodes or a port that could be switched to be so.

10baseT and Gbit now use switching hubs. Each connection is isolated and buffered. The switch then selects optimal times to move frame along.

Repeaters - because electrical signals fade and distort over distance, a repeater acts to boost and clean the signal as it is passed along.

Switches, by their nature, act as repeaters.

Bridge - bridges are a combination switch/repeater used when 2 portions of a local network are far apart. Smart bridges will attempt to smartly not repeat if then target node is not on a particular portion of the network.