RTS-CTS
RTS-CTS (Request To Send - Clear To Send) is a common handshaking mechanism used on MAC protocols. Nodes, after sensing a chanel and detecting it is free, send a RTS packet to the receiver. The receiver will only reply with a corresponding CTS if it also senses that the channel is free, avoiding the hidden terminal problem. Nodes that receive any CTS packet, should assume the channel will be busy next (except for the node that sent the corresponding RTS).