Chapter · Ethernet
The radio room
Why a cable, one shared channel and its collisions, what is inside a frame, who a frame is for, and how a hub became a switch.
- 01Why plug in a cable?4 minWi-Fi shares the air with every device in range and needs a password to join. An Ethernet cable to a switch gives a board a link of its own. This course pictures how that came about as a radio room, and says where the picture stops.
- 02One shared channel5 minThe first Ethernet was one coaxial cable that every station heard. Each listened before sending, stopped when two collided, and waited a random number of time slots, from a range that doubled after every repeat.
- 03What is inside a frame?5 minA frame opens with who it is for and who it is from, then names what it carries, carries it, and ends with a CRC. Counted from the destination address to the check, it runs from 64 to 1518 bytes.
- 04Who is this frame for?4 minEvery Ethernet interface has a 48-bit MAC address, and a filter that keeps frames for that address, for broadcast and for the groups it accepts. One bit of the first byte decides one or many.
- 05From hubs to switches5 minA hub repeats every bit to every port, so its stations still collide. A switch learns each source address and the port it came in on, sends by the destination, and floods what it has not learned.
Start at 01 and read down — the order is the order things get easier in. Or take the one with your part in it; every article stands on its own, and links back to whatever it needs.