Exposed node problem

Here, if a transmission between S1 and R1 is taking place, node S2 is prevented from transmitting to R2 as it concludes after carrier sense that it will interfere with the transmission by its neighbor S1.

However note that R2 could still receive the transmission of S2 without interference because it is out of range of S1.

[1] IEEE 802.11 RTS/CTS mechanism helps to solve this problem only if the nodes are synchronized and packet sizes and data rates are the same for both the transmitting nodes.

[1] If the nodes are not synchronised (or if the packet sizes are different or the data rates are different) the problem may occur that the sender will not hear the CTS or the ACK during the transmission of data of the second sender.

The exposed node problem is not an issue in cellular networks as the power and distance between cells is controlled to avoid it.