Multiple access protocols that enable networked computing devices to share a medium, such as Ethernet, are well developed and understood. Yet the nature of the wireless medium makes traditional methods of sharing a common connection more difficult. Collision detection has caused many problems in networking and this is particularly the case with wireless networks. Collisions occur when two or more nodes sharing a communication medium transmit data together, the two signals corrupt each other, and the result is garbage. This has always been a problem for computer networks and the most simple protocols often do not overcome this problem.
More complex protocols check the channel before transmitting data.
This is very simple with Ethernet as it merely involves checking the voltage on the wire before transmitting. Coupled with this, the hidden terminal problem has been identified in wireless systems and is caused by problems in collision detection. In a wireless environment this is not a safe assumption. Obstructions and distance between A and C may cause C to be hidden from A with neither one detecting a collision when transmitting to B, causing the network to become unreliable. This process informs any near by stations that data is about to be sent, helping them to avoid transmitting and causing a collision.