Question $3$

$($a$)$ Network congestion management requires for the TCP to evaluate the Retransmission

Time$-$Out $(RTO)$ interval using the Jacobson's algorithm. The algorithm dynamically

calculates the round trip time $(RTT$ and its mean deviation $D,$ which are then used to

update the current RTO. The current estimates of the $RTT$ and $D$ are: $RT{T}_0=100ms,$

$D_0=10ms,$ and the three subsequent measured $RTTs$ are: $M_1=90ms,M_2=110ms,$

and $M_3=100ms.$

$($i$)$ Apply Jacobson's algorithm and calculate the new updated RTOs. Compare the

final updated RTO with its initial value $RT{O}_0$ and explain these results. Assume

the smoothing factor $=0\mathrm{.}875.$

$($ii$)$ What does the value of the smoothing factor $$ represent?

$($iii$)$ Discuss what will happen if TCP will set up its retransmission timer with the time$-$

out interval considerably smaller or considerably larger than the evaluated RTO.

$($b$)$ In a TCP the sliding window $W_s$ is fixed at $30$ kilobytes, the maximum segment size

$(MSS)$ is $2$ kilobytes. Assuming that the congestion window $W_c$ is evaluated using the slow$-$

start algorithm, calculate how long it takes before the first full size window is sent. The

round$-$trip time $RTT$ is $10ms.$

$($c$)$ Routing of packets in the global Internet relies on a hierarchical approach.

$($i$)$ Explain what is meant by hierarchical routing.

$($ii$)$ List the four classes of routers used in the global Internet and explain the purpose

of each of them

$($iii$)$ Explain why the Routing Information Protocol $($RIP$)$ and the Open Shortest Path

First $($OSPF$)$ protocol could not be used over the entire Internet.

$($iv$)$ List the main control $($adjunct$)$ protocols and explain briefly their functions.

Question $4$