$($a$)$ A TCP sender$,$ called Ois$$n$,$ and a TCP receiver, called Niamh, communicate over a connection, in which segment loss is possible. Ois$$n$\text{'}$s goal is to send ten segments to Niamh. Ois$$n sends an initial window of five segments at times $t=1,2,3,4$ and $5$ respectively.

The initial value of the sequence number used by Ois$$n is $69.$ Every segment sent to the Niamh contains $975$ bytes.

The delay between Ois$$n and Niamh is $7$ time units. For example, the first segment arrives at Niamh's TCP at time $t=8$ units. The ACK corresponding to this segment arrives at time $t=15.$

Three of the five segments are lost between Ois$$n and Niamh. None of the ACKs are lost. No timeouts occur, and any out of order segments received are thrown out.

Figure $6$: TCP Sender and Receiver.

$($i$)$ What are the sequence numbers of the segments sent at times $t=1,2,3,4$ and $t=5?$

$($ii$)$ What are the values of the ACK numbers sent at times $t=8,9,10,11$ and $t=12?($If the corresponding segment is lost, respond by writing $"x")$

$($iii$)$ What are the sequence numbers of the segments sent at times $t=15,16,17,18$ and $t=19?($If and ACK never arrives, give $"x"$ as your answer$)$

$[10$ Marks$]$