rfc793 - *Postel original
rfc1072 - extensions for long delay paths
rfc1122 - *Corrections to 793
rfc1185 - extensions for high speed paths (MSL Appendix)
rfc1323 - supersedes 1072 + 1185 (Window Scale, RTTM, PAWS)
rfc1337 - TW Assassination (ignore RST fix)