NTP
                           NTP 297-1001-100                   PAGE 3
                          PREL., ISSUE 01D03
                               79 09 21



  2.  OVERVIEW (Figure 1)

  SPEECH AND MESSAGE LINKS

  2.01   The  four functional areas  of the DMS-100  Family switches
  are interconnected by links carrying speech samples and/or control
  messages in the form of serial digital data.

  2.02   Each link  provides a 2-way (4-wire)  transmission path for
  32 channels of  time division multiplexed data.   The speech links
  have 30 channels allotted for transmission of Pulse Code Modulated
  (PCM) speech samples, and two  channels for control mesages, while
  all the 32 channels of the  message links are allotted exclusively
  to control messages.


³ CCC DUPLICATION

³ 2.03   The  components  of  the  CCC   area  are  duplicated,  for
³ reliability, and  operate as synchronized  pairs, with one  CCC in
  service (active), performing call-processing and other operations,
  while the other  CCC (inactive) performs the  same operations, but
  checks for  asynchronism between itself  and the active  CCC.  Any
  discrepancy  between  the   two  CCC  results  in   a  maintenance
  interrupt, leading to recovery action.


³ NETWORK DUPLICATION

³ 2.04  The  components of the NET  are also duplicated  as separate
³ identical entities, providing  two parallel sets (or  "planes") of
  2-way  transmission  paths  for  each  connected  channel  between
  peripheral modules.  The duplicated parallel  paths ensure that if
  one channel in a transmission  path fails, the alternative channel
  is immediately available while recovery action is taken to restore
  the failed  channel.  The duplicated  networks are referred  to as
  Plane-0 and Plane-1.



















                  DMS-100 FAMILY SYSTEM DESCRIPTION
                  (c) NORTHERN TELECOM LIMITED, 1978


                           NTP 297-1001-100                   PAGE 4
                          PREL., ISSUE 01D03
                               79 09 21



  PERIPHERAL MODULES AREA

  2.05   The  peripheral modules  area comprises any  one or  all of
  three types  of PM; the Line  Module (LM), the Trunk  Module (TM),
  and  the Digital  Carrier  Module (DCM).   The  PM interface  with
  subscriber lines (LM), analog trunks  (TM), and digital DS1 Trunks
  (DCM),  respectively.  Each  PM has  a  Peripheral Processor  (PP)
  function which performs local processing action within its PM, and
  controls the  flow of messages between  itself and the  CCC.  This
  autonomous action  by the  PP relieves  the CCC  of routine  local
  processing,  enabling  the  CCC to  concentrate  on  higher  level
  activities.


  MAINTENANCE AND ADMINISTRATION AREA

  2.06    The  Maintenance  and Administration  area  comprises  the
  Input/Output Controllers (IOC), which provide an interface between
  the various I/O  devices, used for maintenance  and administrative
³ purposes, and the CCC.  The IOC  also contain PP, to perform local
³ processing actions, and Device Controllers (DC), which communicate
  with   the   I/O   device   itself.    Typical   maintenance   and
  administrative   I/O    devices   are:   magnetic    tape   units,
  Teletyprinters (TTY), and the Visual Display Unit (VDU).

  2.07   The IOC  collect data from the various  DC, and communicate
  to and from  the CCC area via message links.   These message links
³ are not  duplicated as  are those  to the  Network, but  share the
³ message traffic, since each IOC has access to either CCC area.



























                  DMS-100 FAMILY SYSTEM DESCRIPTION
                  (c) NORTHERN TELECOM LIMITED, 1978