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Hidden/Exposed Station

Wireless LANs have somewhat different properties than wired LANs and require special MAC sublayer protocols. In some wireless LANs, not all stations are within range of one another, which leads to some complications.

In order to illustrate the hidden and exposed station problem, consider a scenario with four wireless stations. The radio range is such that only direct neighbors are within each other's range and can potentially interfere with one another. All stations use CSMA (Carrier Sense Multiple Access) that means before starting a transmission they just listen for other transmissions. The problem is that a station really wants to know whether there is activity around the receiver, but CSMA merely tells if there is activity around the station sensing the medium.