The problem(s) in piggybacking acknowledgement frames is:
A. There is no need to send separate acknowledgement frames
B. It requires more bandwidth
C. To ascertain, how long the data link layer must wait for a packet onto which the acknowledgement is attached
D. Numbers of acknowledgement frames decrease
Choose the correct answer from the options given below:

Correct option is D

Piggybacking is a technique used in the Data Link Layer in which an acknowledgment (ACK) is attached to an outgoing data frame instead of sending a separate acknowledgment frame.
Let us examine each statement.
A. There is no need to send separate acknowledgement frames — Not a problem
This is actually an advantage of piggybacking. Instead of:
Data Frame + Separate ACK
the ACK is included with a data frame:
Data + ACK
Thus, the number of separate ACK frames is reduced. So, A is not a problem.
B. It requires more bandwidth — False
Piggybacking generally saves bandwidth because a separate ACK frame does not need to be transmitted. Therefore, it does not require more bandwidth. So, B is not a problem.
C. Determining how long the Data Link Layer should wait for a packet onto which the ACK can be attached — True
This is the main disadvantage of piggybacking. When a data frame is received, the receiver may wait for some time to see whether it has its own data frame to send. If such a frame becomes available, the ACK can be attached to it.
However, if the receiver waits too long, the sender may assume that the frame or ACK has been lost and retransmit the data.
Therefore, the Data Link Layer must carefully determine the maximum waiting time for piggybacking. C is a problem.
D. Number of acknowledgement frames decrease — Not a problem
Reducing the number of separate ACK frames is an advantage, not a problem. It reduces:
· Control-frame overhead
· Bandwidth consumption
· Number of transmitted frames
Therefore, D is not a problem.
Information Booster
1. Piggybacking attaches an ACK to an outgoing data frame.
2. It is commonly used in bidirectional communication.
3. Its major advantage is reduced control-frame overhead.
4. Its major disadvantage is the need to decide how long to wait before sending a standalone ACK.
5. If the waiting period is too long, unnecessary retransmissions and delays may occur.
Additional Knowledge
Without piggybacking:
Data Frame → ACK Frame
With piggybacking:
Data Frame + ACK
Hence, Piggybacking saves bandwidth but introduces an ACK-waiting-time issue.