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Calculation of Port Numbers in TCP Connection

1. Hosts A and B are communicating over a TCP connection, and Host B has already received from Host A all bytes up through (and including) byte 248. Suppose Host A then sends two segments to Host B back-to-back. The first and second segments contain 40 and 60 bytes of data, respectively. In the first segment, the sequence number is 249, the source port number is 503, and the destination port number is 80. Host B sends an acknowledgment (ACK) whenever it receives a segment from Host A.

a) In the second segment sent from Host A to Host 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 acknowledgement of the first arriving segment what are the acknowledgement sequence number, the source port number, and the destination port number?
c) If the second segment arrives before the first segment, in the acknowledgement of the first arriving segment what is the acknowledgement sequence number?

Solution Preview

a)
sequence number is 289 (guide: sequence number will be first byte of the next sequence of bytes transmitted. as the first segment sent had
40 bytes, the next sequence number will ...

Solution Summary

The guide gives detailed solutions for calculations of sequence number, source port number, and destination port number by three sending orders: host A to host B, host A before host B and host A after host B.

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