“Request to Send” (RTS) is a protocol mechanism used in wireless and wired networking, especially within the context of the IEEE 802.11 (Wi-Fi) standard, to manage access to a shared communication medium and mitigate the “hidden node problem.”
Here’s an overview of RTS:
Purpose:
- The primary purpose of the RTS/CTS (Clear to Send) mechanism is to reduce collisions that happen when multiple nodes transmit data simultaneously. It’s particularly useful in wireless networks where not all nodes might be able to detect each other due to range limitations (known as the “hidden node problem”).
Operation:
- Before a node starts transmitting a large frame of data, it sends a short RTS frame to the receiving station.
- The receiving station replies with a CTS frame, signaling that it is ready to receive the data and telling other nodes to wait.
- Other nodes in the vicinity, upon hearing the RTS or CTS, will defer their transmissions to avoid causing interference.
Hidden Node Problem:
- Imagine two nodes, A and C, both of which are in range of a central node B but not in range of each other. If A starts transmitting to B, C might not hear A’s transmission and might think it’s okay to also transmit to B, causing a collision at B. The RTS/CTS mechanism helps prevent this. When A sends an RTS to B, B replies with a CTS that C can hear, signaling C to wait.
Trade-off:
- While RTS/CTS can help reduce collisions, it introduces overhead due to the RTS and CTS frames. Therefore, it’s typically used in situations where the risk of collision is high, or the data frames being transmitted are large.
By using RTS and CTS frames, Wi-Fi networks can operate more efficiently, especially in environments with many active nodes or where the hidden node problem is prevalent.