9.1 TCP Segments
The structure of a TCP segment is illustrated in the following figure:
Figure 9.4: TCP segment
The source port is the port of the TCP segment source while the destination port is the port of the TCP segment destination. The five entries, source port, destination port, source IP address, destination IP address, and TCP protocol, unambiguously identify the particular connection on the Internet at any given time.
A TCP segment is part of the data flow between the source and the destination. The sequence number is the sequence number of the first byte of a TCP segment in the data flow from the source to the destination (TCP transfers bytes from the sequence number of the transferred byte to the length of the segment). The data flow in the opposite direction has an independent (different) numbering of its data. Since the transferred byte sequence number is 32 bits long, after reaching a value of 232-1, it cyclically attains a value of 0 again. Numbering usually does not start...
