When the CC options are to be inserted into the packet (code for determining if CC options are to be used can be seen in appendix A.2.8), checks must be made to determine which CC option to send. The decision is based on which of the SYN or ACK flags are set, and what the TAO cache values are. This check was incorporated in the tcp_calc_cc_options() function. See table 6.4 for the states and the corresponding CC value to send. Appendix A.1.1 contains the code for tcp_calc_cc_options().
Table 6.4: Selection of CC option