Answer the following questions related to the FSMs for the Selective-Repeat protocol with m = 7 bits. Assume the window size is 64. (Figure 23.34):

a. The sending machine is in the ready state with S_f = 10 and S_n = 15. What is the sequence number of the next packet to send?
b. The sending machine is in the ready state with S_f = 10 and S_n = 15. The timer for packet 10 times out. How many packets are to be resent? What are their sequence numbers?
c. The sending machine is in the ready state with S_f = 10 and S_n = 15. An ACK with ackNo = 13 arrives. What are the next values of S_f and S_n? What is the action in response to this event?
d. The sending machine is in the blocking state with S_f = 14 and S_n = 21. What is the size of the window?
e. The sending machine is in the blocking state with S_f = 14 and S_n = 21. A_n ACK with ackNo = 14 arrives. Packets 15 and 16 have already been acknowledged. What are the next values of S_f and S_n? What is the state of the sending machine?
f. The receiving machine is in the ready state with R_n = 16. The size of the window is 8. A packet with sequence number 16 arrives. What is the next value of R_n? What is the response of the machine to this event?

Transcribed Image Text:

Figure 23.34 FSMS for SR protocol Sender Time-out. Resend all outstanding packets in window. Reset the timer. Request came from process. Make a packet (seqNo = S). Store a copy and send the packet. Start the timer for this packet. Set S, = S, + 1. Window full (Sa = Sp+ Ssize? Time-out. Resend all outstanding packets in window. Reset the timer. [true] [false] Start Ready [true] Blocking A corrupted ACK or an ACK about a non- outstanding packet arrived. [false] Window slides? A corrupted ACK or an ACK about a non- outstanding packet arrived. Discard it. An error-free ACK arived that acknowledges one of the outstanding packets. Discard it. Mark the corresponding packet. If ackNo = Sf. slide the window over all consecutive acknowledged packets. If there are outstanding packets, restart the timer. Otherwise, stop the timer. Note: All arithmetic equations are in modulo 2". Receiver Error-free pucket with seq No inside window arrived. Note: All arithmetic equations are in modulo 2". If duplicate, discard; otherwise, store the packet. Send an ACK with ackNo = seqNo. If seqNo = Ry, deliver the packet and all consecutive previously arrived and stored packets to application, and slide window. Ready Corrupted packet arrived. Discard the packet. Error-free packet with segNo outside window boundaries arived. Start Discard the packet. Send an ACK with ackNo = Rr