$3.($a$)$ A TCP sender$,$ called Ois$$n$,$ and a TCP receiver, called Niamh, communicate over a

connection, in which segment loss is possible. Ois$$n$$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.

Ois$$n Niamh

Ois$$n segment

Ois$$n segment

Ois$$n segment

Ois$$n segment

Ois$$n segment

X

X

X

Ack seg.

t $=1$

t $=2$

t $=3$

t $=4$

t $=5$

t $=8$

t $=9$

t $=10$

t $=11$

t $=12$

t $=15$

t $=16$

t $=17$

t $=18$

t $=19$

Ack seg.

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$)$