In Computer Networking: A Top-down Approach (6th)the solution to problem 11 is m
ID: 3528874 • Letter: I
Question
In Computer Networking: A Top-down Approach (6th)the solution to problem 11 is missing. Here is the question... Consider the rdt2.2 receiver in Figure 3.14, and the creation of a new packet in the self-transition (i.e., the transition from the state back to itself) in the Wait-for-0-from-below and the Wait-for-1-from-below states: sndpkt=make_pkt(ACK,1,checksum) and sndpkt=make_pkt(ACK,0,checksum). Would the protocol work correctly if this action were removed from the self-transition in the Wait-for-1-from-below state? Justify your answer.Explanation / Answer
No,The protocol would not work correctly.
The receiver in rdt2.2 sends an acknowledge with a sequence number to the sender to acknowledge that the received packet is not corrupted. If the action was removed, there will be two main difficulties.
1.Sender will have no receiver feedback.The sender will never know whether the last packet sent was correctly received or not.
2.The receiver will have no means of detecting a garbled reception of ACK on the sender side.You see,the receiver sends the ACK packet with a sequecnce number(0 and 1).The receiver doesn't know whether the ACK was received at sender side correctly or not.Only the sequence number of the received packet tells the receiver whether the sender is resending the previously transmitted packet(will have same sequence number of the recently received packet). So the receiver feedback of sequence number will also be lost if actionsndpkt=make_pkt(ACK,1,checksum) is removed.