It is assumed that there are at least 40 packets buffered in the queue to be sent out by the sender, the network is stable (i. e., the propagation time between the sender and the server is roughly the same for every data packet and ack if it is not lost), the total transmission delay of 3 data packets are much smaller than RTT, 8-bit sequence numbers are used, window size N = 3, and initial send_base = 15.

Draw a diagram similar to PPT slide 21 titled "GBN in action" of Chapter 3 for the Go-Back-N approach to illustrate the interaction between the sender and the receiver between the moment when pkt15 is sent the first time by the sender and the moment when pkt21 is sent out the first time by the sender. During the interaction, only three abnormal events occur: pkt16 is lost on the way when it is sent to the receiver the FIRST time, the timer for pkt16 expires after ack#15 is received by the sender the SECOND time, and ack17 is lost on the way when it is sent to the sender the FIRST time. Please include all the details as given in PPT slide 21 in your diagram.

What are the values of send_base, nextseqnum, and N in this particular case?