A media access control method used in ethernet technology.
Carrier refers to the medium of transmission like the electronic bus in Ethernet network or electromagnetic spectrum in WI-Fi networks. These media carry data with them that’s why they are called ‘carriers’.
A node (NIC) on a network can listen or sense the transmission medium for the packets.
Multiple Access means that every node on the network has the equal right to access the transmission medium but take turns to access and use it.
What does all this mean?
Before data is transmitted to the medium by a node, the node checks or listens to the transmission medium → If the medium is not busy, the node transmits the data, else the node will wait and try again after some random amount of time.
CSMA is just like a 4-way junction of roads.
Collision Detection
A node can hear a collision happening. For example:
Suppose A and C send the data at the same time and find that the medium is not busy, and so they do it. At the destination, a collision occurs. The two nodes are able to detect the collision and will back off and wait and decide using some randomization, who will transmit data first. Hence, avoiding collision again.
CSMA/CD is an old technology used in early ethernet devices like the hub. Understanding this would allow us to grasp quickly the working of the WI-FI access method CSMA/CA.