CSMACD shortcut for Carrier Sense MultipleAccess/Collision Detect, it is the protocol for carrier transmission access inEthernet networks. Moreover, how network devicesrespond is defined by CSMACD, basically whentwo devices attempt to use a data channel at the same time and come across adata collision. After that, each device will wait for random time and will try againuntil it is transmission sent successfully.Furthermore, the CSMA/CD method is specified in IEEE 802.3 and ISO 8802.3 standard. The next figure shows theprocess of CSMACD method.
The best example for CSMA/CD is to assume that there are manypeople in a meeting having a conversation. Each one has a chance to speak whilethe others listen to the one whose speaking and waiting for their opportunityto speak. This resembles the Carrier Sense Multiple Access(CSMA) which is aprotocol of a network that senses or listens to the network signal over amedium before any data is transmitted. Once the speaker is over, a moment ofsilence takes place. After that, other or others will try to speak and if morethan one person speak at the same time, collision will occur. As a result, oneis allowed to speak while others are silenced, this is known as collisiondetection (CD).
However, CSMACD is not suitable for Wi-Fibecause Wi-Fi networks have hidden node problem which is basically as shown in figure2, assuming B is the Access Point, station A is able to transmit information tostation B(AP), and B (AP) can transmit information to A as well. However,stations A and C are hidden from each other so they cannot transmit any informationbetween them. As a result, Carrier Sense Multiple Access/Collision Detect CSMACDwill not be able to work in this case and collisions will happen. Therefore, thebest solution is to use Carrier Sense Access/Collision Avoidance CSMA/CA. While the bestexample to understand how Carrier Sense Access/Collision AvoidanceCSMA/CA works is to assume that there is a lecture. Once the lecturer is over,the lecturer will ask the student if there are any questions regarding thelecture. Where all the student getting prepared to ask some question and thisknown as Multiple Access (MA). Then one of the student will look right and leftto see if anyone is going to ask question and this is knowns as Carrier Sense.
Whenthere is one student wants to ask question, the rest are waiting for questionto be asked, this is known as Collision Avoidance (CA). CSMACA shortcut for Carrier Sense Multiple Access/CollisionAvoidance, it is the protocol for carrier transmission access in Wi-Finetworks. It checks or listen to the medium before a node transmits data. thenode send it’s signal when the medium is not busy. After that, it will back offand wait for a random amount of time and try again if it detects the medium isused. Furthermore, CSMA/CA tries to prevent collisions before they happenunlike CSMA/CD which deals with transmissions after a collision has occurred.