Bit,Code,Description,Reference
0,R,Request,[RFC5191]
1,S,Start,[RFC5191]
2,C,Complete,[RFC5191]
3,A,re-Authentication,[RFC5191]
4,P,Ping,[RFC5191]
5,I,IP Reconfiguration,[RFC5191]
6,E,prE-authentication,[RFC5873]
7-15,,Unassigned,