5.   MESSAGE TYPES


INTER-MAINTENANCE SUB-SYSTEM MESSAGES


5.01    See Figure  2-1.   Transient errors  always  stay in  the
maintenance sub-system where they occured.  It is ONLY when these
errors persist that,  if not resolved, they  will be communicated
to   another   maintenance   sub-system   via   inter-maintenance
sub-system messages.


5.02    There are  two reasons  for communication  to take  place
between two maintenance sub-systems:


     (a) A  sub-system is giving  an error indication  to another
         sub-system. These are termed fault messages.

     (b)  A sub-system  is notifying  another  sub-system that  a
         component is no longer available for service.  These are
         termed status messages.


5.03   The  receiving sub-system  is responsible  for taking  the
appropriate   action  on   the  message.    Furthermore,  it   is




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responsible for communicating information concerning its activity
to  the routing  and  reporting SS.  Note  that the  transmitting
sub-system's  responsibilities  concerning  problems  related  to
other sub-systems  terminate as  soon as it  has disposed  of the
information.


MESSAGES  FROM THE  MAINTENANCE SUB-SYSTEMS  TO  THE ROUTING  AND
REPORTING SUB-SYSTEM


5.04   Refer to Figure 4-1.   Any maintenance sub-system can find
it necessary to send one of four types of messages to the routing
and reporting sub-system.  In the  usual order of occurrence, the
four types of messages are:


     (a)  Error  -   an  abnormal  event  has   occurred  in  the
         sub-system.

     (b) Diagnostic -  results from an attempt  by the sub-system
         to test a given aspect.

     (c) Action  - an  alteration has occurred  in the  status or
         organization of the sub-system's resources.

     (d) Exception - a report that a threshold has been exceeded.

     (e) Information - a report on  the instantaneous status of a
         sub-system.


5.05   These  messages are  passed to  the routing  and reporting
ub-system in packed (i.e. internal) format.  There are two kinds
of messages involved:


     (a)  Specific   responses  to  requests  from   the  command
         interpreter.

     (b) Unsolicited messages which are  submitted to the routing
         and   reporting   sub-system    without   any   specific
         destination from the sub-system's point of view.







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MESSAGES BETWEEN THE VDU AND THE ROUTING MECHANISM


5.06   Input from  the VDU moves through  the command interpreter
(CI). This  process is  responsible for  interpreting the  common
language  definitions of  system components  into internal  form.
This translated result and the request  or command is then passed
on to:


     (a) The relevant maintenance sub-system, or:

     (b) the routing mechanism, or:

     (c) the logging mechanism.


.07   In case  (b) above, the input either  performs routing and
eporting functions such  as setting thresholds, or  is passed on
to the logging  mechanism or the software-hardware  alarm system.
In  (c) the  input is  used  to retrieve  stored information  for
display.


5.08   Output  to the  VDU always  emerges from  the routing  and
reporting  sub-system.  This  includes responses  to requests  or
ommands  from   the  command  interpreter  to   the  maintenance
sub-system.


5.09   Output and inputs to any  other devices (i.e. printer) are
organized in the same way as the VDU.


MESSAGES   BETWEEN   REMOTE  MAINTENANCE   CENTERS   AND   TRUNKS
MAINTENANCE SS.


5.10    An external  interface  to the  trunk  maintenance SS  is
provided.  It is through such a  facility that messages will pass
between DMS and remote maintenance and administration centers.









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MESSAGES  BETWEEN  THE  I/O MESSAGE  SYSTEM  OR  ALARM  DETECTION
SUB-SYSTEM AND THE MAINTENANCE SUB-SYSTEMS


5.11   Major sources of indications to the maintenance sub-system
are  the  messages from  the  I/O  message  system or  the  alarm
detection sub-system.  Problems detected by these two systems are
routed to the relevant maintenance SS.


MESSAGES FROM THE CC MAINTENANCE SS TO SOFTWARE MAINTENANCE SS


5.12   When anomalies  in the CC Maintenance SS,  relating to the
software environment itself, occur the CC passes a message to the
SW  maintenance  SS.  This  is  the  only type  of  communication
between the SW maintenance SS and any other sub-system.