What Is The Function Of The Crc Value That Is Found In The Fcs Field Of A Frame?
What Is The Function Of The Crc Value That Is Found In The Fcs Field Of A Frame?
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What Is The Function Of The Crc Value That Is Found In The FCS Field Of A-Frame?
The CRC value that is found in the FCS Filed of an A-Frame function for the integrity of the received frame. Before we discuss the function of the CRC value that is found in the FCS field of a frame, let us actually know what is FCS.
When a frame sends data from one device to another, it has a possibility that the data might have some errors or corruption in it. The FCS can be generated at layer 2 of the OSI model, i.e data link layer.
The FCS stands for frame check sequence, which is present at layer 2 of the data link layer. The frame check sequence is like an error detection code that is present in a frame. These frames are used to send the data at the upper layers of the OSI model and at last to reach the application layer of the OSI model. Let us take an example to understand what is error checking means.
The error detection is nothing but the frame which is got damaged must be discarded, but it does not take any action to resend or retransmit the data that is damaged. Unlike the data link layer, the other protocols will execute the error recovery.
The FCS field of a frame contains a number in it. This number is calculated by the source of the code based on the data that is present in it. The calculated number is then added to the end of the frame sent to the destination address.
After the destination device receives the frame, the FCS number got recalculated, and then it compares with the number that is present in the frame. If the compared numbers are different then it is considered as the error and that frame is get discarded. The sender will perform the cyclic redundancy check and add it as a trailer in the frame.
Now, at the receiving end, it recomputes the CRC, and then it compares it with the received FCS. In this way, we can identify if any data loss has occurred, if there are any changes that we find, then we can consider it as the data loss or error and we just discard it.
The Frame Check sequence is often transmitted in a way that the receiver can compute the sum of the entire frame along with the trailer of the frame check sequence. The FCS can be found immediately after the frame ending of the delimiter. This FCS is mostly found in Ethernet and other IEEE protocols with the size of the 32 bits, in the X.25 with the size of the 16 bits and can be 32 bits. In the HDLC it can be found with the size of the 16 bits or it can be the size of the 32 bits. And in the frame relay with the size of the 16 bits, in point to point protocol with the size of the 16 bit or it can be a size of the 32 bit.