$($a$)$ In a communications network, nodes A and B are connected via a data link with a

capacity of $10$ Gigabits$/$s$.$ The link transmits packets of $1500$ bytes, and each packet is

acknowledged by a $150-$byte frame. The propagation speed of the transmission medium

is $200,000k\frac{m}{s}.$ It is assumed that there is negligible buffering and processing time in

the nodes. The distance between nodes A and B is $8km.$

$($i$)$ What is the duration of the Round Trip Time for this connection, which is mea$-$

sured from the initiation of the message transmission from the source until the

reception of the acknowledgement by the source?

$($ii$)$ Calculate the Window Size that enables uninterrupted utilization of the link, as$-$

suming that no errors occur, using Sliding Window flow control.

$($iii$)$ Evaluate the flow control system when it uses the following algorithms and pa$-$

rameters:

A$.$ Go Back $N$ and $3-$bit sequence numbers;

B$.$ Go Back $N$ and $7-$bit sequence numbers;

C$.$ Selective Repeat and $3-$bit sequence numbers;

D$.$ Selective Repeat and $7-$bit sequence numbers.

$($iv$)$ Which algorithm and sequence number bit$-$size allows for uninterrupted utilization

of the link.

$[10$ Marks$]$