IEEE 802.11 RTS/CTS

RTS/CTS = Request to Send / Clear To Send

A sending node wishing to send data sends a Request to Send frame. The destination node replies with a Clear To Send frame. Any other node receiving either the RTS or the CTS frame should refrain from sending data for a given time. The amount of time any other node should wait before trying to get access to the medium is included in both the RTS and the CTS frame.

The RTS/CTS mechanism is a way to solve the so called Hidden Terminal Problem.