Note that in both packets the real sequence number is some random value and those zeros are only Wireshark contribution to make our analysis easier. In the second packet the seq=0 as in the previous one and for the same reason. ![]() This packet is the first on this connection, so no ack as there is no previous data to be ACKed. In the first packet, the seq=0 indicates that this side didn't transmit anything before and this is the first byte to be transmitted.This is the 3-way handshaking procedure we saw before Wireshark also displays the ACk starting from 0 to make analysis easier but you can get the actual ACK value from the raw ACK field. The receiver sends the total number of bytes it got from the transmitter as an acknowledgement to tell the transmitter that everything is correct, so the transmitter can continue sending the remaining packets. ![]() The next sequence number field of each packet represents the sequence number that you should find in this side next packets if no drops or out of order packets happened. For each byte sent, the transmitting side will increase the sequence number by one.To make analysis easier, Wireshark will show this field starting from 0 but you can get the actual sequence number from the raw sequence number field on the Wireshark expert view. This number represents the number of the first byte this side will send to the other side. At the connection start, each side of the connection picks some random number called initial sequence number ISN.The procedure of TCP transmission is as follows TCP is using the cumulative acknowledgement approach, in which the TCP receiver is normally sending an ACK that represents the amount of contiguous data it got. ![]() ![]()
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