Question

Host A and B are communicating over a TCP connection. The initial sequence number at Host A is 2171. Host A opens the connection, sends three segments, the second of which carries 400 bytes of data, and closes the connection. In the segment sent by Host A, source port number is 303, and the destination port number is 80. ) What is the value of the sequence number of the SYN segment? (1.5 marks) ) What is the value of the sequence number of the data segment? in the acknowledgment of the second segment,what is the acknowledgment number, the source port number, and the destination port number? ) What is the value of the sequence number of the FIN segment? (1.5 marks)

Answer 1

Given : -

Looking from the prospective of Host A the following things are given.

Initial sequence number = 2171.

size of 2nd segments = 400 bytes.

source port no = 303.

destination port no = 80.

As per understanding Host A is client and Host B is server.

a) The value of the sequence number of the SYN send by host A = seq no of 1st segments ie 2171.

b) The value seq no of the data segments are following : -

The value of 1st data segment sequence no = 2171 ie (intial seq no).

The value of 2nd data segment sequence no = 1st segment sequence no + destination port no ie 2171 + 80 = 2251.

The value of 3rd data segment sequence no = 2nd segment sequence no + size of 2nd segments ie 2251 + 400 = 2651.

c) The acknowledgment number of 2nd segments, the source port number, and the destination port number is following: -

As the acknowledgment is send by Host B (server).So,now the source is Host B .therefore the source port no is 80,destination port no will be 303 and ACK No = sequence no of 2nd data segment send by Host A + size of 2nd segment ie 2251 + 400 = 2651.

d) The value of the sequence number of the FIN segment is following: -

FIN segment is requested by the client ie Host A.To initiates the closing procedure.FIN is basically a Bit flag has value 0 or 1.

Here in the question it is written that after sending of 3 data segments the connection closes.So the Value of FIN flag is set to 1.