RTS/CTS stands for “Request to Send/Clear to Send” and is a handshake mechanism used in wireless networks, particularly in the IEEE 802.11 (Wi-Fi) protocol, to mitigate the “hidden node problem” and manage access to the shared communication medium.

Here’s a breakdown of RTS/CTS:

Purpose:

  • The primary objective of the RTS/CTS mechanism is to reduce collisions on the network caused by multiple nodes attempting to transmit data simultaneously. This protocol is especially useful in wireless environments where certain nodes might not be able to detect each other due to range or other physical obstructions.

Process:

  • RTS (Request to Send): Before a node (say, Node A) begins transmitting a data packet, it sends an RTS frame to the destination node (Node B) to request permission to send its data.
  • CTS (Clear to Send): Upon receiving the RTS, Node B responds with a CTS frame, signaling that it is ready to receive the data. The CTS also informs other nodes in the vicinity to refrain from transmitting data for a specified duration, thus preventing potential collisions.

Hidden Node Problem:

  • Consider three nodes: A, B, and C. Node A and Node C are both within range of Node B but not each other. If Node A starts transmitting to Node B, Node C might not detect A’s transmission and might believe it’s okay to transmit to Node B simultaneously. This scenario would result in a collision at Node B. By using RTS/CTS, Node A can inform Node B (and indirectly Node C) to wait, avoiding the collision.

Overhead:

  • While the RTS/CTS mechanism can significantly decrease collisions, it introduces some overhead due to the additional RTS and CTS frames. As a result, its use is typically adaptive, being employed in situations where the network determines the risk of collision is high or when transmitting large data frames.

Configuration:

  • Most modern Wi-Fi equipment and software allow network administrators to enable or disable RTS/CTS. When enabled, there’s often a configurable threshold determining the frame size at which the RTS/CTS mechanism is triggered.

In summary, the RTS/CTS mechanism in wireless networks, like Wi-Fi, helps ensure smoother and more efficient communication, especially in environments with potential signal interference or multiple active nodes.