CompTIA Network+ Practice Test

What is added to an Ethernet frame as part of error detection?

1. Frame Sequence Number

2. Frame Check Sequence (FCS)

3. Ethernet Address

4. Header Check Sum

The correct answer is: Frame Check Sequence (FCS)

The Frame Check Sequence (FCS) is a crucial component added to an Ethernet frame for error detection purposes. It is a form of a checksum that is used to ensure data integrity as the frame travels over the network. When the sender transmits the Ethernet frame, the FCS is calculated based on the data contained within the frame. This involves applying a mathematical algorithm (typically CRC, or Cyclic Redundancy Check) to generate a unique value that reflects the contents of the frame. Upon receiving the frame, the receiving device recalculates the FCS from the data it has received and compares this value with the FCS value that was sent within the frame. If the two values match, it indicates that the frame has not been corrupted during transmission. If there is a mismatch, it signals that an error has occurred, and the frame will typically be discarded or a request for retransmission will be initiated, depending on the protocol in use. While other components such as Ethernet addresses are crucial for identifying devices on the network and ensuring proper routing of frames, they do not serve the purpose of error detection. Similarly, headers and sequence numbers play different roles in data transmission but are not involved in the actual error-checking process like the FCS is