A proposed NAK-based (negative ACK-based) sliding window, automatic-repeat-request (ARQ) protocol for point-to-point connections operates as follows.

i. The sender sends frames with increasing sequence numbers to the receiver. Only frames received in correct order are accepted by the receiver.

ii. The receiver sends a NAK back to the sender when it receives an out-of-sequence frame. The NAK contains the sequence number of the frame the receiver is expecting next.

iii. When the sender receives a NAK, the sender begins retransmitting frames, with increasing sequence numbers, starting from frame that the NAK indicated the receiver is expecting next.

Assume that the sender's transmit window is large enough that the sequence numbers do not warp around before the transfer is complete.

(a) Sketch a time diagram similar illustrating what happens when a frame gets lost between the sender and the receiver. It should be clear from your diagram how the protocol handles this situation.

(b) Sketch a time diagram illustrating what happens when a NAK gets lost between the receiver and the sender. It should be clear from your diagram how the protocol handles this situation.

(c) There exists an error scenario, where frames are lost, that this protocol can not handle. Describe and diagram this error scenario and explain how the protocol could be modified