QUESTION #3:

4-bit sequence number for the open window

having 4 bits -> how many different numbers can be represented?

                 16 different numbers: [0, 1, 2, 3, 4, ...... 15]

AT THE BEGINNING:

                 Sender Open window: LHS: 0  ---  RHS: 15

                 Receiver Open window: LHS: 0  ---  RHS: 15

AAFTER (a): 

               (i) A (SENDER) sent frames, 0, 1, 2, 3, and 4 to B.

                   SENDER LHS: 0 -> [5]
 
                   SENDER RHS: [15] (no change)

                   RECEIVER LHS: [0] (no change)  
 
                   RECEIVER RHS: [15] (no change)


               (ii) B received 0, 1, 2, and 3 from A.

                   SENDER LHS: [5] (no change)
 
                   SENDER RHS: [15] (no change)

                   RECEIVER LHS: 0 -> [4]
 
                   RECEIVER RHS: [15] (no change)


               (iii) B sent ACK frames for frames 0, 1, 2, and 3.

               (iv) A received ACK 0 and 1.

AAFTER (b): suggest to apply the same procedure (one at a time)