RFC 1060                    Assigned Numbers                  March 1990


                             X.25 TYPE NUMBERS

   CCITT defines the high order two bits of the first octet of call user
   data as follows:

      00 - Used for other CCITT recomendations (such as X.29)
      01 - Reserved for use by "national" administrative
           authorities
      10 - Reserved for use by international administrative authoorities
      11 - Reserved for arbitrary use between consenting DTEs

      Call User Data (hex)     Protocol                      Reference
      -------------------      --------                      ---------

      01                       PAD                            [GS2]
      C5                       Blacker front-end descr dev    [AGM]
      CC                       IP                             [69,AGM]*
      CD                       ISO-IP                         [AGM]

      * NOTE: ISO SC6/WG2 approved assignment in ISO 9577 (January 1990).