Essay Example on CSMA CD shortcut for Carrier Sense Multiple Access Collision

CSMA CA to solve the hidden node problem It minimises the frame collisions in hidden stations figure 3 will be used again to explain the methodology of how RTS STC in CSMA CA solves the hidden node problem Whenever a node wants to send any data to another node it takes the permission from the receiver instead of acting as a sensor After that to have the permission there is a particular data known as RTS Request to Send that has to be sent For example in the scenario where node A wants to send data to node B in figure 3 it would start by sending an RTS packet to node B Node B will receive the packet and in the meantime no one is transferring any data to node B Next node B will give the permission for transmitting by sending a special packet known as CTS Clear to Send which contains the duration of this transmission The previously mentioned packet will be sent as a broadcast to both nodes A and C When node A receives it it will find out that the permission is granted and it will start transmission directly However when node C receive the broadcast it would know that a permission has been granted and there is a transmission taking place right now Node C will check the duration of that transmission between nodes B and A Consequently node C will not transmit any data Therefore instead of collision detection collision avoidance is used here and this is how this hidden terminal problem is solved Finally if there are a lot of collisions as a result of high utilisation and large frames the same principle can be applied Figure 5 gives data on the process of RTS CTS in CSMA CD 802 11 uses two of Carrier Sense CS mechanisms to estimate a clean channel One of them is Virtual Carrier Sense Mechanism it is referring to Network Allocation Vector NAV It used for maintaining the prediction of the future of traffic on the medium based on duration information that is revealed in RTS CTS frames from the duration field presented in the frames or prior to the actual exchange of data that are transmitted by STAs Figure 7 shows the Virtual carrier sense mechanism