Question

Consider a simplified actual TCP senderreceiver, described as follows: .Upon a loss (timeout or triple-duplicate ACKs), the sender o transmits the oldest unACKed packet (whose sequence number Base) o restarts the timer Upon receiving an ACK with a Sequence #y > Base. o it considers all packets with sequence numbers s y as ACKed (cumulative ACK) o Sets Base to the sequence number of the packet immediately after the packet whose sequence number is y o Restarts the timer . When the receiver receives o an in-order packet, t ACKs it immediately (delayed ACKing is not enabled), and delivers it to the application o an out-of-order packet, it ACKs the previously-ACKed packet, and buffers the received packet a packet that fills a gap, it ACKs the packet with largest sequence # in the contiguous list of ACKed packets, starting at Base .If the Sender needs to transmit in response to receiving an ACK, it retransmits immediately in the same time slot . Sender transmts only .When timeout occurs, sender retransmits immediately in the same time slot . Timeout of the sender is set to 15 milliseconds Window size is fixed to 4 segments (i.e., TCP congestion control is not invoked) Trip time from sender to receiver is 3ms, and the same is from the receiver to sender MSS-1.5KB The sender wants to transmit a small file whose size is 12KB Consider the scenario on the last page of this exam booklet o The only loss in the whole scenario is the one shown in the diagram When will the sender transmit the last packet? a) Before 15 ms c) Between 18 and 21 ms, inclusive e) After 25 ms b) Between 15 and 17 ms, inclusive d) Between 22 and 25 ms, inclusive bi When will the application at the receiver get the entire file? a) Before 15 ms c) Between 18 and 21 ms, inclusive e) After 25 ms b) Between 15 and 17 ms, inclusive d) Between 22 and 25 ms, inclusive c When will the sender know that the receiver received all packets? a) Before 15 ms c) Between 18 and 21 ms, inclusive e) After 25 ms b) Between 15 and 17 ms, inclusive d) Between 22 and 25 ms, inclusive

Answer 1

Your marked answers are all correct i.e. :

a.) c) between 18 and 21ms

b.) d) between 22 and 25ms

c.) e) After 25ms as the pack