Hidden Node and RTS/CTS
Why two clients that can't hear each other keep colliding at the access point, and how RTS/CTS and the NAV fix it. Drag the clients on a floor plan and step through what happens on the air.
How to use this tool controls and what to look for
Step through what happens on the air when two clients can't hear each other, then turn RTS/CTS on and compare.
Controls to change
- Layout: choose Hidden (far apart) or Not hidden (close together), or drag the clients on the floor plan.
- RTS/CTS: turn it Off or On.
- Next: step forward one event at a time. Back goes one step back, and Play runs it on its own.
- Speed: slow the playback down.
What to look for
- Hidden clients both think the channel is free and collide at the AP. Neither gets an ACK, so both retry.
- With RTS/CTS, the AP's CTS reaches both clients and sets a NAV, so the hidden client stays quiet.
- RTS/CTS adds two extra frames to every exchange, so it costs airtime even when there is no hidden node.
About this tool
Two clients that can't hear each other both think the channel is free, so they keep colliding at the access point. This explainer lets you drag the clients to change who can hear whom and step through what happens on the air, with and without an RTS/CTS exchange.
What you'll learn
- Why carrier sense fails when clients can't hear each other
- How RTS/CTS makes the AP warn every station around it
- How the NAV keeps hidden clients quiet
- What RTS/CTS costs in airtime, and its limits
Common questions
What is the hidden node problem?
Two stations that can't hear each other both transmit to the same access point at once. Neither senses the other, so their frames collide at the AP.
Does RTS/CTS fix hidden nodes?
It helps: the AP's CTS is heard by every station near it, so they hold off. It adds overhead to every exchange, so it's usually only used for larger frames or when collisions are high.
How else can hidden nodes be avoided?
Better AP placement, more APs at lower power so clients are closer, and avoiding long, narrow cells where clients sit on opposite sides of the AP.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.