MadeEasy Test Series 2017: Computer Networks - Sliding Window

Question

Consider the sliding window protocol used at transport layer to transfer the segments, the receiver sends “ACK K + 1” when it receives a packet with sequence number “K” and window size is denoted by “W”. Assume the sender’s packets start with sequence number 1. Which of the following is correct about sliding window protocol?

(A) Between two ACK packets, the sender will never send more than one packet

(B) The sender must retransmit any packets for every single duplicate ACK it receives.

(C) Any new (previously unsent) packet with sequence number greater than “W” is sent by sender iff a new (previously unseen) ACK arrives.

(D) None of the above

Answer 1

option D seems correct

for option (A)-sender can send more than one packet in case of the cumulative acknowledgement.

For option (B)-its false,in case of packet lost ..three duplicate acknowledgements are there and sender retransmit only one packet

for option (c)-its false,due to packet loss (it was unsent )if previous (not new) acknowledgement arrives then that packet can be sent.

Comments

Can you explain the answer a bit

Answer 2

B , Because , when First pkd sent  with ACK no. 1, receiver received value= 1+1=2, and then Sender Send the next pkt  with ACK 2 ,but , if the time period was over before reaching the pks of Ack 2, receiver the the previous Ack 1 +1 to Sender, and the sender again send the pkt of ACK 2, And this process repeat ...