Answer

Piggybacking is a technique in bidirectional data communication where an acknowledgement (ACK) is attached to an outgoing data frame instead of sending a separate ACK frame.

Example

If A sends a data frame to B and B also has data to send to A, B can include the acknowledgement for A's frame in B's outgoing data frame.

Advantage

Piggybacking reduces the number of separate control frames and therefore improves bandwidth efficiency.

Limitation

The receiver may need to wait briefly for outgoing data before sending the ACK, so a maximum waiting/delay limit is normally used.

Exam-ready: Piggybacking means combining an ACK with an outgoing data frame to reduce overhead.