3. Textbook problem 22(a)(b) (20 points, 10 points for a, 10 points for b)

P22. Consider the GBN protocol with a sender window size of 4 and a sequence

number range of 1,024. Suppose that at time 1, the next in-order packet

that the receiver is expecting has a sequence number of k. Assume that the

medium does not reorder messages. Answer the following questions:

a. What are the possible sets of sequence numbers inside the sender's

window at time 1? Justify your answer.

b. What are all possible values of the ACK field in all possible messages

currently propagating back to the sender at time t? Justify your answer.