When operating with a duplex setting of half-duplex, some data link errors, such as FCS, alignment, runts, and collisions are normal. Generally, a one percent ratio of errors to total traffic is acceptable for half-duplex connections. If the ratio of errors to input packets is greater than two or three percent, performance degradation may be noticeable.
In half-duplex environments, it is possible for both the switch and the connected device to sense the wire and transmit exactly at the same time, resulting in a collision. Collisions can cause runts, FCS, and alignment errors, which are caused when the frame is not completely copied to the wire, resulting in fragmented frames.