Problem
Ethernet has been around for a long time, eliminating other wired technologies such as Token Ring.
Token Ring allows each device on a network to take turns transmitting. To use an analogy, Token Ring worked like a stoplight, giving each device a turn to go. Since everyone gets a turn (and all Token Ring devices follow the rules), there were virtually zero collisions on a Token Ring network.
Ethernet, on the other hand, is like a roundabout. Anyone can go ahead at any time when it appears to be clear. If there is a collision, we clean it up and resume traffic flow. Since the repercussions of a data collision are relatively low, it is less wasteful to just allow the collisions to happen and react to them. While this sounds careless, it is quite effective for low numbers of devices. As the number of devices scaled up, so did collisions and inefficiency.
Both systems with some situation where an otherwise uncontrolled medium can follow some basic rules to make sure the devices each take turns sending data. However, Ethernet 'won' the networking battle back in the 1980's. So much has changed! Data collisions are virtually eliminated due to switch technology.
CSMA/CD can seem like a strange system, but in reality we use very similar social norms to navigate similar problems. Think about a full classroom of 30 students. Each student has something to say at regular intervals. What rules would you put in place so each student would get a chance to speak as quickly as possible, without interrupting other students? Is it more like Ethernet or Token Ring?
Of the three examples (car traffic, classroom speaking, and CSMA/CD), which do you think is the most effective mechanism, and why?
Looking forward, is there an even better way to handle multiple devices that need to communicate at the same time? If we could replace Ethernet's CSMA/CD system going forward, what new rules would we replace it with?