07/15/82  Common access class ceiling

Facilities like the Inter-Multics File Transfer (IMFT) facility
translate Access Isolation Mechanism (AIM) attributes between two
systems.  For these facilities, the concept of a common access class
ceiling is used to control the data which may be transferred between
the systems.

The common access class ceiling between two systems is defined as all
sensitivity levels from level 0 (usually un-named) up to but not
including the first level which does not have the same long and short
name on both systems and all access categories that have the same long
and short names on both systems.

If the long and short names of sensitivity level 0 are not the same on
both systems, then the two systems have no common acccess ceiling and
are isolated from each other.


For example, if system A defines the following AIM attributes --

	level 0	     *-* UN-NAMED *-*
	level 1	     unclassified	     u
	level 2	     secret	     s
	level 3	     top secret	     ts

	category 1     SSTD		     sstd
	category 2     LISD		     lisd
	category 3     FSD		     (none)
	category 4     Marketing	     (none)


and system B defines the following attributes --

	level 0	     *-* UN-NAMED *-*
	level 1	     unclassified	     u
	level 2	     restricted	     (none)

	category 1     MPO		     (none)
	category 2     LISD		     lisd
	category 3     FSD		     fsd
	category 4     SSTD		     sstd


then the common access ceiling is --

	unclassified, LISD, SSTD


                                          -----------------------------------------------------------


Historical Background

This edition of the Multics software materials and documentation is provided and donated
to Massachusetts Institute of Technology by Group BULL including BULL HN Information Systems Inc. 
as a contribution to computer science knowledge.  
This donation is made also to give evidence of the common contributions of Massachusetts Institute of Technology,
Bell Laboratories, General Electric, Honeywell Information Systems Inc., Honeywell BULL Inc., Groupe BULL
and BULL HN Information Systems Inc. to the development of this operating system. 
Multics development was initiated by Massachusetts Institute of Technology Project MAC (1963-1970),
renamed the MIT Laboratory for Computer Science and Artificial Intelligence in the mid 1970s, under the leadership
of Professor Fernando Jose Corbato. Users consider that Multics provided the best software architecture 
for managing computer hardware properly and for executing programs. Many subsequent operating systems 
incorporated Multics principles.
Multics was distributed in 1975 to 2000 by Group Bull in Europe , and in the U.S. by Bull HN Information Systems Inc., 
as successor in interest by change in name only to Honeywell Bull Inc. and Honeywell Information Systems Inc. .

                                          -----------------------------------------------------------

Permission to use, copy, modify, and distribute these programs and their documentation for any purpose and without
fee is hereby granted,provided that the below copyright notice and historical background appear in all copies
and that both the copyright notice and historical background and this permission notice appear in supporting
documentation, and that the names of MIT, HIS, BULL or BULL HN not be used in advertising or publicity pertaining
to distribution of the programs without specific prior written permission.
    Copyright 1972 by Massachusetts Institute of Technology and Honeywell Information Systems Inc.
    Copyright 2006 by BULL HN Information Systems Inc.
    Copyright 2006 by Bull SAS
    All Rights Reserved