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RTS/CTS request to send / clear to send

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RTS/CTS (Request to Send/Clear to Send) is a mechanism used in wireless communication protocols, particularly in the field of computer networking, to manage the flow of data between devices. It is commonly employed in wireless local area networks (WLANs) that use the IEEE 802.11 standard, which is the basis for Wi-Fi networks.

The purpose of RTS/CTS is to prevent collisions between data packets transmitted by different devices on the same wireless channel. Collisions occur when two or more devices attempt to transmit data simultaneously, resulting in a garbled signal that cannot be properly received by any of the devices. By using the RTS/CTS mechanism, devices can coordinate their transmissions and avoid such collisions.

Here's how the RTS/CTS mechanism works:

  1. Request to Send (RTS): When a device, known as the sender, wants to transmit data, it first sends a small control packet called RTS. The RTS packet includes information about the length of the data packet the sender intends to transmit and reserves the wireless channel for a specified duration, known as the RTS duration.
  2. Clear to Send (CTS): Upon receiving the RTS packet, the receiving device, known as the receiver, checks if it is ready to receive data. If the channel is clear and the receiver is ready, it sends a CTS packet back to the sender. The CTS packet indicates that the receiver is prepared to accept the data packet from the sender. Similar to the RTS packet, the CTS packet reserves the channel for a specific duration, called the CTS duration.
  3. Data Transmission: After the sender receives the CTS packet, it can begin transmitting the actual data packet. Other devices within the range of the sender and receiver, known as the potential interferers, listen to the RTS and CTS packets and defer their own transmissions until the channel becomes free.
  4. Acknowledgment: Once the data packet is transmitted, the receiver sends an acknowledgment (ACK) packet to the sender, confirming successful reception of the data. This allows the sender to know that the data was successfully received and avoids the need for retransmission.

The RTS/CTS mechanism helps to mitigate the hidden terminal problem, which occurs when two devices are within range of a receiver but out of range of each other. Without RTS/CTS, these devices may simultaneously transmit to the receiver, leading to collisions. RTS/CTS ensures that the potential interferers listen to the RTS/CTS exchange and refrain from transmitting until the channel is clear.

It is important to note that the RTS/CTS mechanism introduces additional overhead in the wireless communication process, as it requires the transmission of control packets. In situations where the network is not congested and the data packets are small, the overhead of RTS/CTS may outweigh the benefits. Therefore, the use of RTS/CTS is typically optional and can be configured based on the specific requirements of the network.