Question

Explain what is RTS/CTS scheme. How can they mitigate the exposed node and hidden node problems?

Answer 1

RTS is Request to Send. CTS is Clear to Send. RTS/CTS is the optional mechanism used by wireless networking protocol to reduce frame collisions introduced by hidden node problem.The protocol fixed exposed node problem too.

RTS/CTS Mechanism:

In wireless networking the hidden node problem occurs when node communicate with wireless access point but cannot directly communicate with access point.

To overcome the hidden node problem Request to Send / Clear to Send is implemented at Access point in conjuction with Carrier Sense Multiple Access with collision avoidance.

When a node wants to transmit data to another node it sends out Request to Send.The receiver node replies with Clear to Send.After the transmitter node receives Clear to Send it transmits data.

Exposed Node Problem:

In wireless networks when a node is prevented from sending data to other nodes because of neighbouring transmitter is known as exposed node problem.

RTS/CTS mechanism helps to solve the exposed node problem if nodes are synchronised and packet size and data rate are same for transmitting nodes.When a node hears an Request to Send from neighbouring node but not corresponding Clear to Send node can deduce that it is an exposed node and is permitted to transmit to other neighbouring nodes.