All You Need To Know About CSMA/CD

All You Need To Know About CSMA/CD

What is CSMA/CD?


There are many protocols that are used for communication within Ethernet networks, but one if the most significant protocols is the Carrier Sense  Multiple Access With Collision Detection (CSMA/CD) protocol. Which is responsible for reliable, collision-free communication.

Think about a situation where there are 'n' numbers of station on a link and all are waiting to transfer information via that channels. In this event, all 'n' station would want to get the link/channel to transport their particular data. The problem appears when more than 1 station transfers the information at the same time. In cases like this, there'll be a collision in the data from various channels.

CSMA/CD is just one such procedure where the different station that follows this protocol agree on certain conditions and collision detection steps for successful transmission. This protocol determines which station will transmit when so that the information reaches the destination without any corruption.

What CSMA/CD Protocol Stands For?


Step 1: Carrier Sense (CS) – It is a scheme developed to provide a device on an Ethernet network with the ability to sense whether the line for communication is idle or not.

Step 2: Multiple Access (MA)- It allows all machines on an Ethernet network to communicate freely as long as the line is idle.

Step 3: Collision Detection (CD)- It makes sure that if two devices start to transmit data at the same time, the communication is cancelled and the data re-transmitted after a certain period of time.



Carrier sense Multiple Access with Collision Detection
CSMA/CD




How CSMA/CD is work?


To visualize how each of these three steps works in an actual network, imagine an Ethernet network with four devices, A, B, C, and D. If device A intends to send a data package to device D, It First need to “sense” that no other device is already using the network if the line is idle, the device will start transmitting the data. Each packet of data transmitted over an Ethernet network contains within itself the destination address and the sender address. The data is transmitted to all the devices connected to the network; however, a network which has a different destination address (B or C in this example) discards the data. Device D received the data and issues a receipt signal to device A.


However, it can often happen that another device on the network starts to transmit another set of data at the same time. This is a ”collision” scenario where each of the machines cancels transmission for a specific period of time, after which both of the transmission are attempted again. The whole process can be seen in the below diagram.


Carrier Sense Multiple Access With Collision Detection
CSMA/CD Flow Chart

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