$5.(14$pt$)$ Consider the figure below, which plots the evolution of TCP Reno's congestion window at the beginning of each time unit $($where the unit of time is equal to the RTT$).$ Answer the following questions.

$($The initial value of cwnd is $\backslash (\backslash$mathbf$\{1\}\backslash )$ and the initial ssthresh is $\backslash (\backslash$mathbf$\{8\}\backslash ).)$

$451$

IIme unit $($in K$$I$)$

a$)$ Give the intervals of time when TCP slow start is operating.

b$)$ Give the intervals of time when TCP congestion avoidance is operating.

c$)$ Give the times at which the first packet in the sent flight of packets is lost, and indicate whether that packet loss is detected via timeout, or by triple duplicated ACKs.

d$)$ Give the times at which the value of ssthresh changes, and give the new value of ssthresh.