Hosts A and B are communicating over a TCP

connection, and Host B has already received from A all bytes up through byte 126. Suppose

Host A then sends two segments to Host B back-to-back. The first and second segments

contain 80 and 40 bytes of data respectively. In the first segment, the sequence number is 127,

the source port number is 302, and the destination port number is 80. Host B sends an

acknowledgment whenever it receives a segment from Host A.

a - In the second segment sent from Host A to B, what are the sequence number, source port

number, and destination port number?

b - If the first segment arrives before the second segment, in the acknowledgment of the first

arriving segments, what is the ACK number, the source port number. and the destination port

number?

c - If the second segment arrives before the first segment, in the ACK of the first arriving

segment, what is the ACK number?

Answers explained below

Explanation:

In the second segment sent from Host A to B, what are the sequence number, source port number, and destination port number?

Answer:

The sequence number is 127 + 80 = 207

, the source port number is 302, and the destination port number is 80.

(b)

If the rst segment arrives before the second segment, in the acknowledge-ment of the rst arriving segment, what is the acknowledgement number, the source port number, and the destination port number?

Answer:

The acknowledgement number is 207, source port number is 80 and the destination port number is 302

If the second segment arrives before the rst segment, in the acknowledge-

ment of the rst arriving segment, what is the acknowledgement number?

Answer:

The acknowledgement number is 127, indicating that it is still

waiting for bytes 127 and onwards.

(d)

Suppose the two segments sent by A arrive in order at B. The rst ac-

knowledgement is lost and the second acknowledgement arrives after the

rst timeout interval. Draw a timing diagram, showing these segments

and all other segments and acknowledgements sent. (Assume that there

is no additional packet loss.) For each segment in your gure, provide the

sequence number and the number of bytes of data; for each acknowledge-

ment that you add, provide the acknowledgement number.

Answer:

(c)

If the second segment arrives before the first segment, in the acknowledgement of the first arriving segment, what is the acknowledgement number?

Answer:

The acknowledgement number is 127, indicating that it is still waiting for bytes 127 and onwards.