Physical Layer Operations

No matter which PHY layer implementation is being used by the wireless station to transmit or receive data, there is a functional commonality between them all. Each STA must wait and listen to see whether there is data being sent that it must receive and process, or it must wait and listen to see whether the channel is clear so that it can transmit. The details of how these tasks are performed vary between the different PHY layer implementations and are beyond the scope of what is covered in this book. The following paragraphs describe these three modes or states that an STA will transition between:

Carrier Sense/Clear Channel Assessment (CS/CCA)

If the station is not currently transmitting or receiving, it listens and senses the channel either to detect the beginning of a network signal that can be received (carrier sense) or to identify whether the channel is unused and available prior to transmitting a packet (clear channel assessment).