3.  MAINTENANCE CONCEPT


3.01   The  basic concept of the  DMS Maintenance System  is that
each maintenance SS has the responsibility to locate and diagnose
an error condition which is presented to it.   The maintenance SS
must determine  first if the  error lies  within its own  area of
responsibility.   If  the error is  within the  responsibility of
the maintenance SS, the error is diagnosed to determine what item
is causing the  error, and a message  is sent to the  routing and
reporting SS.    If the  error is not  within the  maintenance SS
tself, the  error message is passed  to the next  appropriate SS
which takes similar action until the error is finally located.


3.02   MAN-MACHINE INTERFACE (MMI)


3.03   Maintenance personnel  can access each of  the maintenance
SS  via the  VDU  keyboard and  obtain  status  information as  a
display on the  VDU screen. An additional or  alternative MMI can




               (c)  NORTHERN TELECOM LIMITED, 1978
                 MAINTENANCE SYSTEM DMS-100/200








                        NTP 297-1001-106                   PAGE 6
                       PREL., ISSUE 01D01
                          May 25, 1978



also be provided by TTY.


3.04   TELESCOPING


3.05    The  MAP  maintenance  function  uses  the  technique  of
'telescoping' to examine the operation  of the DMS.   Telescoping
permits ever-increasing  details about system status  or troubles
to be obtained, starting at  the maintenance sub-system level and
descending to lower  levels until the fault  is eventually traced
to a replaceable component level.


3.06    Refer to  Figure 2-2.   The  screen of  the VDU  displays
various levels  of status  information in  the System  Status and
Command Interpreter  areas.   The  Command Menu  Area displays  a
list  of possible  functions or  commands  which the  maintenance
personnel can perform  at each level of  interrogation.   The use
of menus minimizes  the necessity for memorizing  the commands or
refering to documentation.   Commands entered are repeated in the
Input Echo area.