Question

A host sends five packets and receives three acknowledgments. The time is shown
as hour:minute:seconds.
a. Segment 1 was sent at 0:0:00.
b. Segment 2 was sent at 0:0:07.
c. ACK for segments 1 and 2 received at 0:0:08.
d. Segment 3 was sent at 0:0:20.
e. Segment 4 was sent at 0:0:25.
f. Segment 5 was sent at 0:0:29.
g. ACK for segments 3 received at 0:0:45.
h. ACK for segments 3 received at 0:0:47.
i. ACK for segments 3 received at 0:0:49.
j. ACK for segment 4 and 5 received at 0:0:65.

1. Calculate the values of RTTM, RTTS, RTTD, and RTO if the original RTO is 8 seconds.
2. Did the sender miss the retransmission of any segment? Show which segments
should have been retransmitted and when. Rewrite the events including the
retransmission time.

Answer 1

Explanation:

TCP timer is the timer and it implementation uses four timers. There are four timers are as follows:

1. Retransmission

2. Persistence

3. Keepalive

4. TIME_WAIT

Congestion Occurs:Retransmission can occur in one of two cases: when the RTO timer times out or when three duplicate ACKs are received. In both cases, the size of the threshold is dropped to half (multiplicative decrease). Most TCP implementations have two reactions:1. If a time-out occurs, there is a stronger possibility of congestion; a segment has probably been dropped in the network and there is no news about the following sent segments. In this case TCP reacts strongly:a. It sets the value of the threshold to half of the current window size.b. It reduces cwnd back to one segment.c. It starts the slow start phase again.2. If three duplicate ACKs are received, there is a weaker possibility of congestion; a segment may have been dropped but some segments after that have arrived safely since three duplicate ACKs are received. This is called fast transmission and fast recovery. In this case, TCP has a weaker reaction as shown below:a. It sets the value of the threshold to half of the current window size.