6. In protocol rdt3.0, the ACK packets flowing from the receiver to the sender d

Question

6. In protocol rdt3.0, the ACK packets flowing from the receiver to the sender do not have sequence numbers (although they do have an ACK field that contains the sequence number of the packet they are acknowledging). Why is it that our ACK packets do not require sequence numbers? (5 points)

7. Host 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 100 and 200 bytes of data, respectively. In the first segment, the sequence number is 127, the source port number is 340, and the destination port number is 120. Host B sends an acknowledgment whenever it receives a segment from Host A. (15 points)

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 segment, what is the acknowledgment number, the source port number, and the destination port number?

c. If the second segment arrives before the first segment, in the acknowledgment of the first arriving segment, what is the acknowledgment number?

Explanation / Answer

6. When receiver receive the packets it sends the acknowledgment(ACK) to the sender to inform the sender that transmit data packet was received sucessfully. Because ACK is using for confirmation of every data packets therfore sender does not need the sequence no to detect the duplicate data packet. In ACK data packets sender check that acknowledgment is not duplicate.

If sender find that acknowledgment recived from receiver is duplicate then it ignore the data flowing otherwise send next data packet.

Answer 7 :

a) In the second segment sequence number is 227 , source port is 340 and destination port is 120

b) If the first segment arrives before the second segment, then the acknowledgment of the first arriving segment is 227 , source port(340) and destination port(120) will remain same.

Acknowledgment no send from Host B to host A (227) = Sequence no (100) + data packet size (100)

c) If the second segment arrives before the first segment then acknowledgment of the first arriving segment is 127 because 127 byte of first segment has not received yet.

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