PER MESSAGE:
7 bits - NetMessageType
1 bit - Is a message fragment?

[8 bits NetMessageLibraryType, if NetMessageType == Library]

[16 bits sequence number, if NetMessageType >= UserSequenced]

8/16 bits - Payload length in bits (variable size ushort)

[16 bits fragments group id, if fragmented]
[16 bits fragments total count, if fragmented]
[16 bits fragment number, if fragmented]

[x - Payload] if length > 0