What is RTS and CTS in WLAN?

RTS/CTS (Request To Send / Clear To Send):

 This is the optional mechanism used by the 802.11 wireless networking.

This protocol is using to reduce collisions introduced by hidden nodes problem.

It means Request-to-send and Clear-to-send . when stations are communicating each other it will be used inorder to avoid collision

REQUEST SEND AND CLEAR SEND ITS STANDS FOR RTS AND CTS ACTUALLY ITS FLOW CONTROL MACHANISM OF NETWORK FIELD.

RTS (Request to Send) & CTS (Clear to Send) . Sender request to reciver with RTS packets and Reciver response with CTS packets.

RTS (Request to Send) & CTS (Clear to Send) was used to avoid frame collisions in the hidden node problem and was used by the 802.11 networking protocol as an optional mechanisam. Modern RTS & CTS includes acknowledgments and does not solves exposed node problem which was solved earlier.

RTS and CTS work with data transmition medium. Sender request to reciver with RTS packets and Reciver response with CTS packets.

RTS (Request to Send) & CTS (Clear to Send) was used to avoid frame collisions in the hidden node problem and was used by the 802.11 networking protocol as an optional mechanisam. Modern RTS & CTS includes acknowledgments and does not solves exposed node problem which was solved earlier.

The RTS frame contains five fields, which are:

1. Frame Control
2. Duration
3. RA (Receiver Address)
4. TA (Transmitter Address)
5. FCS

The CTS frame contains four fields, which are:

1. Frame Control
2. Duration
3. RA (Receiver Address)
4. FCS

The ACK frame contains four fields, which are:

1. Frame Control
2. Duration
3. RA (Receiver Address)
4. FCS

Request to Send (RTS) and (CTS) clear to send is optional mechanism by 802.11 wireless networking protocol to reduce frame collision .or

RTS/CTS is an additional method to implement virtual carrier sensing in (CSMA/CA). By default, 802.11 relies on physical carrier sensing only which is known to suffer from the hidden node problem.

RTS/CTS packet size threshold is 0–2347 octets. Typically, sending RTS/CTS frames does not occur unless the packet size exceeds this threshold. If the packet size that the node wants to transmit is larger than the threshold, the RTS/CTS handshake gets triggered. Otherwise, the data frame gets sent immediately.

The RTS frame contains five fields, which are:

1.      Frame Control

2.      Duration

3.      RA (Receiver Address)

4.      TA (Transmitter Address)

5.      FCS

The CTS frame contains four fields, which are:

1.      Frame Control

2.      Duration

3.      RA (Receiver Address)

4.      FCS

The ACK frame contains four fields, which are:

1.      Frame Control

2.      Duration

3.      RA (Receiver Address)

4.      FCS

Legacy devices  will not be able to read data transmission is being done by advanced 802.11bands due to the difference in the modulation technology. For example 802.11b clients will not be able to understand 802.11g transmission. These devices may try to communicate with the AP, which would eventually cause for a collision. Hence, RTS/CTS will be sent by 802.11g clients and the AP with lower data rates, which would be readable to 802.11b clients. So they can update their NAV with the duration for the current transmission before it tries to gain the medium.

The 802.11AC also sends beacon/RTS/CTS with lower data-rates so that 802.11a/n can read them.

RTS/CTS in action

If you enable RTS/CTS on a particular station, it will refrain from sending a data frame until the station completes a RTS/CTS handshake with another station, such as an access point. A station initiates the process by sending a RTS frame. The access point receives the RTS and responds with a CTS frame. The station must receive a CTS frame before sending the data frame. The CTS also contains a time value that alerts other stations to hold off from accessing the medium while the station initiating the RTS transmits its data.

The protocalls called as Request To Send and Clear To Send Which Avoides any collition between the data packets in any netwark.