CompTIA Network+ Practice Test

What is the purpose of the Frame Check Sequence (FCS) in an Ethernet frame?

1. To organize the data payload

2. To encrypt the data

3. To calculate checksums for error detection

4. To determine frame type

The correct answer is: To calculate checksums for error detection

The Frame Check Sequence (FCS) is a crucial component in an Ethernet frame, primarily serving the purpose of error detection. When data is transmitted over a network, there is always a possibility that it may become corrupted due to interference, hardware faults, or other transmission issues. The FCS is a type of checksum that is calculated based on the contents of the frame prior to transmission. Upon receiving the frame, the destination device recalculates the FCS based on the received data and compares it against the FCS value included in the frame. If both values match, it indicates that the frame was likely received without errors. If there is a discrepancy, it suggests that the frame may have been altered, prompting the receiver to discard it or request a retransmission. This process is essential for maintaining data integrity across the network. While some choices might touch on relevant concepts, they do not align with the specific function of the FCS. Organizing the data payload and determining the frame type address other aspects of frame structure but do not directly pertain to error detection. Encrypting the data involves securing the information being transmitted, which the FCS does not accomplish. Thus, the primary purpose of the FCS is indeed to calculate checksums for error