(16 . 6)(16 . 17)
  -- all messages and packets are simply arrays of octets at low level/raw
  type Octets is array( Natural range <> ) of Interfaces.Unsigned_8;

  -- length of a text field (i.e. 16 bits, strictly > 0)
  subtype Text_Len is Positive range 1..2**16-1;

  -- "text" type has a 2-byte header with total length
  -- Len here is length of actual content ONLY (i.e. it needs + 2 for total)
  type Text_Octets( Len: Text_Len := 1 ) is
    record
      -- actual octets making up the "text"
      Content: Octets( 1..Len ) := (others => 0);
    end record;

  -- constants from SMG.COMMS standard specification

    -- RSA key size in octets