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Hidden Terminal Problem

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The Hidden Terminal Problem describes the situation in a WLAN environment with at least three nodes, where at least two nodes can't communicate with each other because they are out of each other's range.

Imagine three nodes called A, B and C arranged in a line with a distance of n meters between each other. Let the communication range of each node be a circle around its position with a radius r>n but r<2*n. Now node B can "see" both nodes A and C, but node A as well as node C can only "see" node B.

The Hidden Terminal Problem can lead to data collision, because node A can't see when node C is sending data to node B and therefore try to also send data to node B. A possible solution for this problem used in the 802.11 specification is the 802.11 RTS/CTS.