Hidden node problem
In computer networking, the hidden node problem occurs when a node is visible from a wireless hub, but not from other nodes communicating with said hub. This leads to difficulties in media access control. Hidden nodes in a wireless network refer to nodes which are out
of range of other nodes or a collection for nodes. Take a physical
star topology with an Access Point with many nodes surrounding it
in a circular fashion; each node is within communication range of the Access Point,
however, not each node can communicate with each other. For example,
it is likely that the node at the far edge of the circle can see the access
point, which is known as r, but it is unlikely that the same
node can see a node on the opposite end of the circle, 2r (or simply the diameter). These nodes are known as hidden. The problem is when node r and r2 start to send packets simultaneously to the Access Point. Since node r and r2 can not hear each other Carrier sense multiple access with collision detection (CSMA/CD) does not work. The same problem exists in a MANET. IEEE 802.11 uses 802.11 RTS/CTS to partly overcome the hidden node problem.
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