- What is FCS?
- The Frame Check Sequence (FCS) is an essential component in networking used to verify the accuracy of data transmission.
- It is primarily employed in data transmission protocols to ensure that frames (data packets) have been transmitted without errors.
- Purpose of FCS:
- FCS serves as an error detection mechanism.
- It detects errors in frames transmitted across a network, including the address field, control field, and information field.
- How FCS Works:
- When a message is divided into data frames for transmission, each frame has FCS bits appended to it.
- These FCS bits are calculated based on the entire frame (including the payload) and serve as a checksum.
- At the destination, the receiver computes the running sum of the entire frame (including the FCS bits).
- The calculated FCS is then compared with the FCS bits in the received frame.
- Error Detection Process:
- If the calculated FCS matches the received FCS, the transmission is considered successful.
- If the FCS does not match, it indicates that the frame has been corrupted during transmission.
- In such cases, the frame is discarded.
- FCS Size:
- The size of the FCS field varies:
- It can be either 2 bytes or 4 bytes.
- The specific size depends on the communication protocol being used.
- The size of the FCS field varies:
- Error Recovery:
- FCS is responsible only for error detection, not error recovery.
- The recovery process depends on the transmission protocol:
- Ethernet: Frames are discarded upon error detection, and no retransmission occurs.
- TCP: Corrupted frames are discarded, and TCP initiates error recovery by retransmitting the affected frames.
- Example Scenarios:
- Ethernet:
- If an Ethernet frame gets corrupted during transmission, its FCS bits will change.
- At the destination, the calculated FCS is compared with the received FCS.
- If they don’t match, the frame is discarded, resulting in data loss.
- TCP:
- TCP also discards corrupted frames but takes additional action:
- It initiates error recovery by retransmitting the affected frames.
- This ensures that data is not lost.
- TCP also discards corrupted frames but takes additional action:
- Ethernet:
What is FCS (frame check sequence)
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