TCP - role of checksum field

In a TCP communication, the checksum field within the TCP header is used  to ensure data integrity for end-to-end communications. The checksum provides end-to-end error detection between the source and destination application and is tested when received by the intended application. This means that it checks for errors across the entire path of the communication. If the checksum fails, the receiver will not accept the segment but will inform the sender to resend the segment that was not received correctly. TCP does not simply drop the segment. This is part of why TCP is considered a “reliable” protocol because it has mechanisms to correct faults rather than simply discarding the segment.

In contrast, similar mechanisms on other layers, such as the FCS in the Ethernet trailer, operate on a hop by hop basis rather than in an end to end manner.