TCP checksum

[treiher]

The calculation of the TCP checksum requires access to fields of the IP packet:

The checksum also covers a 96 bit pseudo header conceptually prefixed to the TCP header. This pseudo header contains the Source Address, the Destination Address, the Protocol, and TCP length.

The current message specifications for IP packets and TCP segments are independent of each other, and thus it is not possible to reference fields of an IP packet from a TCP segment. One possible solution would be removing the independence between the message specifications, e.g., by merging the IP packet and the TCP segment specification into one combined TCP/IP message. Another solution could be the use of parameterized messages.