The third field in an INSTEON message, the Message Flags byte, not only signifies the Message Type but it also contains other information about the message.  The three most-significant bits, the Broadcast/NAK Flag (bit 7), the ALL-Link Flag (bit 6), and the ACK Flag (bit 5) together indicate the Message Type.  Message Types will be explained in more detail on their subpage.  Bit 4, the Extended Message Flag, is set to one if the message is an Extended-length message, i.e. contains 14 User Data bytes, or else it is set to zero if the message is a Standard-length message.  The low nibble contains two two-bit fields, Hops Left (bits 3 and 2) and Max Hops (bits 1 and 0).  These two fields control message retransmission as explained below (see Message Retransmission Flags43).  The table below enumerates the meaning of the bit fields in the Message Flags byte.  The Broadcast/NAK Flag (bit 7, the most-significant byte), the ALL-Link Flag (bit 6), and the ACK Flag (bit 5) together denote the eight possible Message Types.