Control frames are used to manage the information exchange between a wireless client and an AP. They help prevent collisions from occurring on the wireless medium.
The figure displays the field value of common control frames including:
- Request to Send (RTS) frame - The RTS and CTS frames provide an optional collision reduction scheme for APs with hidden wireless clients. A wireless client sends an RTS frame as the first step in the two-way handshake, which is required before sending data frames.
- Clear to Send (CTS) frame - A wireless AP responds to an RTS frame with a CTS frame. It provides clearance for the requesting wireless client to send a data frame. The CTS contributes to collision control management by including a time value. This time delay minimizes the chance that other wireless clients will transmit while the requesting client transmits.
- Acknowledgment (ACK) frame - After receiving a data frame, the receiving wireless client sends an ACK frame to the sending client if no errors are found. If the sending client does not receive an ACK frame within a predetermined period of time, the sending client resends the frame.
Control frames are integral to wireless transmission and play a significant role in the media contention method used by wireless, known as Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).