The contention mode is used in the access procedures of local networks and satellite connections. In this access method, the connected stations compete for the transmission rights on the transmission medium.
For local networks in bus topology, decentralized control is required to allow all connected stations equal access to the transmission medium. In this access method, the stations compete with each other for access to the transmission medium. Hence the term competitive mode or contention mode. The station that claims the transmission medium first can use it and transmit its data. However, if two or more stations access the medium at the same time, collisions occur between the signals of the different stations. Therefore, contention mode is also referred to as collision-affected access methods.
One of the best-known stochastic access methods is Ethernet's CSMA/ CD, in which the transmission medium is first listened to - carrier sense( CS) - to see whether it is free or being used for other transmissions, and only then is media access initiated - medium access ( MA). Collision detection (CD) is then used to detect collisions.