FCS (4 bytes) (Ethernet)
Protocol: Ethernet Ethernet PCI
Field: frame check sequence (FCS)
Length: 4 bytes
Contents: checksum.
Frames with invalid checksums are discarded by the adapter. There is no error message sent to the source station.
If the collision detection function of an adapter detects a collision while sending a frame, transmission is stopped and an additional 'jam sequence' of 32 bits in length is sent. The jam sequence is a dummy checksum needed by other station's collision detection function: If a collision passes a repeater, the frame's electrical characteristics are valid again, and the frame's corruption can only be detected as caused by a collision by the combination of 'frame short error' (less than 64 bytes) and 'checksum error' (invalid FCS value).