ETHERNET:
Networks have certain rules, called "Protocols," to send and receive data, one of them is "Ethernet." Currently, this is the most common used protocol. It uses a high-speed network and bus topology, so it is relatively simple and cheaper. Since all the nodes use the same cable to send and receive data, they must follow a set of rules about when to communicate, otherwise, two or more computers could transmit at the same time, causing lost messages. Before transmitting the data, a node listens to find out if the cable is in use. If so, the node must wait. When the cable is free from other transmission, the node must wait. When the cable is free from other transmission, the node can begin transmission immediately. This process is also known as "Carrier sense Multiple Access with Collision Detection."
If by chance, two nodes transmit data at the same time, the messages collide. When a collision occurs, a special messages, lasting a fraction of a second, is sent out over the network to indicate that it is jammed. Each node stops transmitting, waits a random period of time, and then transmits again. Since the wait period for each node is random, it is unlikely that they will begin transmitting at the same time again.
Ethernet bus topologies are easy to install and don't require much cabling compared to the alternatives. 10Base-2 and 10Base-5 both were popular Ethernet cabling options years ago. However, bus networks work best with a limited number of devices. If more than a few dozen computers are added to a bus, performance problems will likely result. In addition, if the backbone cable fails, the entire network effectively becomes unusable.
"Collision Detection" is a local area network access method in which contention between two or more stations is resolved by collision detection. When two stations transmit at the same time, they both stop and signal a collision has occurred. Each then tries again after a waiting predetermined time period. To avoid another collision, the stations involved each choose a random time interval to schedule the retransmission of the collided frame. On the other hand, in "Carrier Sense" a node listens to the bus for a predetermined amount of time before transmitting and waits until the talking node has completed transmission. And "Collision Resolution" allows multiple devices to talk at once a protocol determines that which device receives priority.
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