CSC $430$ Data Communications Exercise $3\mathrm{.}4$

SLOW START, CONGESTION AVOIDANCE, AND FAST RETRANSMI T

Consider the figure below, which plots the evolution of TCP$\text{'}$s congestion window at the beginning of each time unit $($where the unit of time is equal to the RTT$)$; TCP sends a "flight" of packets of size cwnd at the beginning of each time unit. The result of sending that flight of packets is that either

$($i$)$ all packets are ACKed at the end of the time unit,

$($ii$)$ there is a timeout for the first packet, or

$($iii$)$ there is a triple duplicate ACK for the first packet.

In this problem, you are asked to reconstruct the sequence of events $($ACKs$,$ losses$)$ that resulted in the evolution of TCP$\text{'}$s cwnd shown below.

following questions. The initial value of cwnd is $1$ and the initial value of ssthresh $($shown as a red $+)$ is $8.$ Format your answer like: $1,3,5,9$

$1)$ Give the times at which TCP is in slow start.

$2)$ Give the times at which TCP is in congestion avoidance.

$3)$ Give the times at which TCP is in fast recovery.

$4)$ Give the times at which packets are lost via timeout.

$5)$ Give the times at which packets are lost via triple ACK.

$6)$ Give the times at which the value of ssthresh changes.