RFC 1340 (rfc1340) - Page 3 of 139

Assigned Numbers

RFC 1340                  Assigned Numbers                   July 1992


Data Notations

   The convention in the documentation of Internet Protocols is to
   express numbers in decimal and to picture data in "big-endian" order
   [21].  That is, fields are described left to right, with the most
   significant octet on the left and the least significant octet on the
   right.

   The order of transmission of the header and data described in this
   document is resolved to the octet level.  Whenever a diagram shows a
   group of octets, the order of transmission of those octets is the
   normal order in which they are read in English.  For example, in the
   following diagram the octets are transmitted in the order they are
   numbered.


       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       1       |       2       |       3       |       4       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       5       |       6       |       7       |       8       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       9       |      10       |      11       |      12       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Transmission Order of Bytes

   Whenever an octet represents a numeric quantity the left most bit in
   the diagram is the high order or most significant bit.  That is, the
   bit labeled 0 is the most significant bit.  For example, the
   following diagram represents the value 170 (decimal).


                             0 1 2 3 4 5 6 7
                            +-+-+-+-+-+-+-+-+
                            |1 0 1 0 1 0 1 0|
                            +-+-+-+-+-+-+-+-+

                           Significance of Bits

   Similarly, whenever a multi-octet field represents a numeric quantity
   the left most bit of the whole field is the most significant bit.
   When a multi-octet quantity is transmitted the most significant octet
   is transmitted first.






Reynolds & Postel