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.:: Understanding the Digital Multiplexing System (DMS) ::.

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Current issue : #12 | Release date : 1987-03-29 | Editor : Taran King
Index of Phrack 12Taran King
Pro-Phile IX on Agrajag The ProlongedTaran King
Preview to Phrack 13-The Life & Times of The ExecutionerThe Executioner
Understanding the Digital Multiplexing System (DMS)Control C
The Total Network Data SystemDoom Prophet
CSDC II - Hardware RequirementsThe Executioner
Hacking : OSL SystemsEvil Jay
Busy Line Verification Part IIPhantom Phreaker
Scan Man's Rebuttal to Phrack World NewsScan Man
Phrack World News XII Part IKnight Lightning
Phrack World News XII Part IIKnight Lightning
Title : Understanding the Digital Multiplexing System (DMS)
Author : Control C
                               ==Phrack Inc.==

                     Volume Two, Issue 12, Phile #4 of 11

          <S>    A Tribunal Communications Ltd. (c) 1987        <S>
          <h>                                                   <p>
          <a>Understanding the Digital Multiplexing System (DMS)<a>
          <d>                   Part 1                          <w>
          <o>                By Control C                       <n>

  The DMS switching system, is a lot smaller than normal systems. It takes up
less than 16% of the space for the same number of Step-By-Step (SXS) lines and
20% of cross bar.  This is done by taking the hardware out of the CO and
putting them closer to a group of subscribers. Then central office services
can be provided over shorter loops.

  DMS offers remote switching with a bunch of remote modules in a bunch of
sizes and capabilities. Some include SXS replacement or growth, Outside plant
cable relief, and Office feature's.  The use of remote modules give the CO
more floor space that would usually be used by the Line Concentrating Modules
(LCMs), Main Distribution Frame (MDF), and cable equipment.  The advantage of
these modules is that it extends the service radius of the CO, this means
outside plant savings. Remote modules can be located up to 150 miles away
without messing up transmissions.

  Other advantages of the DMS system are that it allows integration between
Transmission facilities and switching systems.  It's hardware & software is
designed to give a full range of switching applications for Private Branch
Exchange (PBX) business systems, local, toll, and local/toll requirements. The
same Central Control Complex (CCC) and switching networks are used throughout
the whole system.  The only difference between each system is the peripheral
units, and software packages. It has a Maintenance and Administration Position
(MAP) which is a integrated multifunction machine interface that switch
maintenance, line and trunk network management, and service order changes can
be carried out.

  The software for the central processor is written in PROTEL, a high level
pascal based language.  Peripheral processors use a XMS-Pascal software

  DMS has a high line and trunk capacity. It has up to 100,000 lines on a
DMS-100 or 60,000 trunks on a DMS-200.  It also gives up to 1.4 million
two-way CCS through the switching network.  The processor can accept up to
350,000 call attempts.

  Here's a list of the DMS systems in use today:

DMS-100 - is a class 5 local office with the ability to handle 1,000 to
100,000 lines.  It can give basic telephone service or expanded to handle IBN
custom calling features.  The DMS-100 MTX gives cellular radio services.  A
local office can also be adapted to Equal Access End Office (EAEO).

Remote Switching Center (RSC) - Ability to handle up to 5,760 lines.

Remote Line Concentrating Module (RLCM) - Ability to handle up to 640 lines.
It uses host Line Concentrator Module (LCM) that can be used by the RSC or
directly by the host DMS-100.

Outside Plant Module (OPM) - Ability to handle up to 640 lines. This also can
be used by the RSC or directly by the host DMS-100.

Subscriber Carrier Module (SCM-100) - There are three basic types of
   1- Subscriber Carrier Module Rural (SCM-100R) - This eliminates the central
      office Central Control Terminal (CCT) by integrating directly into the
      DMS-100 through the DMS-1 span lines.
   2- Subscriber Carrier Module SLC-96 (SCM-100S) - This gives a direct
      interface between DMS-100 and AT&T's SLC-96 digital loop carrier
   3- Subscriber Carrier Module Urban (SCM-100U) - It's used as an interface
      to the DMS-1 Urban.  The DMS-1 urban is a digital subscriber carrier
      system modified for use in Urban areas.  It gives Plan Ordinary
      Telephone Service (POTS) and special services between a central office
      and residential and business communities. It has the ability to handle
      576 lines of POTS and special services.

DMS-200 - Has the ability to handle from a few hundred to 60,000 trunks.  This
switch can also serve a Access Tandem (AT) function. The Traffic Operator
Position System (TOPS) puts operator services into the DMS-200.  Operator
Centralization (OC) allows a single operator location by using the TOPS
positions to transfer operator services from other DMS-200 toll centers.  The
Auxiliary Operator Services System (AOSS) let operator services on calls that
need outside information (Such as Directory assistance).

DMS-100/200 - Allows local and toll features described above but also includes
a Equal Access End Office (EAEO)/Access Tandem (AT) combination.  It has the
ability to handle up to 100,000 lines or 60,000 trunks.

DMS-250 - This is a high capacity toll system for specialized common carriers
needing tandem switching operations.

DMS-300 - This is a toll system designed for international use. To my
knowledge there are only two DMS-300 switches in use at this time.

  DMS switches are divided into four "Functional" areas designed to do certain
operations. These areas are:

  1- Central Control Complex (CCC)
  2- Network (NET)
  3- Peripheral Modules (PM)
  4- Maintenance and Administration (MAP)

Here's a description of those areas.

Central Control Complex

Within the Central Control Complex (CCC), the main program in the switch
controls the processing of calls, maintenance and administrative routines, and
changes the activity for these routines to other areas of the switch. The CCC
sends messages to the network, the maintenance and administrative areas trough
message links and directs the functions to be run in those areas.


The Network Modules (NMs) handle the routing of speech paths between the
Peripheral Modules (PMs) and keep these speech connections for the rest of the
call.  The network handles message and speech links between the PMs and the

Maintenance and Administration

Within the Maintenance and Administration includes Input/Output Controllers
(IOCs) - IOCs interface local or remote input/output devices.  The I/O devices
are used to do testing, maintenance, or administrative functions for the

Peripheral Modules

Peripheral Modules (PMs) are used as interfaces between digital carrier spans
(DS-1), analog trunks, and subscriber lines.  The PMs are used for scanning
lines for changes of circuit state, doing timing functions used for call
processing, creating dial tones, sending, receiving signaling, and controlling
information to and from the CCC, and checking the network.

   Before 1984 only four types of PMs gave trunk interfaces to the DMS system;
these include Trunk Modules (TMs), Digital Carrier Modules (DCMs), Line
Modules (LMs), and Remote Line Modules (RLMs).  Since then ten more have been
added, these include Digital Trunk Controller (DTC), Line Group Controller
(LGC), Line Trunk Controller (LTC), Line Concentrating Module (LCM), Remote
Switching Center (RSC), Remote Line Concentrating Module (RLCM), Outside Plant
Module (OPM), Subscriber Carrier Module Rural (SCM-100R), Subscriber Carrier
Module SLC-96 (SCM-100S), and Subscriber Carrier Module Urban (SCM-100U).

Here's and explanation of those modules:

Trunk Module

The Trunk Module (TM) changes incoming speech into digital format, it has the
ability to handle 30 analog trunks. The Pulse Code Modulation (PCM)
information is combined with the trunks supervisory and control signals then
transmitted at 2.56 Mb/s over speech links to the network.

The TM also uses service circuits such as Multifrequency (MF) receivers,
announcement trunks, and test circuits.  Each TM has the ability to interface
30 analog trunks or service circuits to the network over one 32-channel speech
link.  The TM is not traffic sensitive so each trunk can carry 36 CCS.

Digital Carrier Module

The Digital Carrier Module (DCM) gives a digital interface between the DMS
switch and the DS-1 digital carrier.  The DS-1 signal consists of 24 voice
channels.  The DCM takes out and puts in signaling and control information on
the DS-1 bit streams which then makes them DS-30 32-channel speech links.  The
DCM can interface five DS-1 lines; 5*24=120 voice channels; into four 32-
channel speech links.  The DCM can carry a maximum of 36 CCS of traffic on
each trunk.

Line Module

The Line Module (LM) gives an interface for a maximum of 640 analog lines and
condenses the voice and signaling into two, three, or four DS-30, 32-channel
speech links.  Four speech links have the ability to handle 3,700 Average Busy
Season Busy Hour (ABSBH) CCS per LM.

Remote Line Module

The Remote Line Module (RLM) is a LM operating in a remote location from the
DMS host.  The RLMs can be located up to 150 miles from the host office,
depending on the transmission facilities.

Digital Trunk Controller

The Digital Trunk Controller (DTC) has the ability to interface 20 DS-1 lines.
Then the DS-1 lines are linked to the network by a maximum of 16 DS-30 speech
links; each trunk is able to handle 36 CCS.

Line Group Controller

The Line Group Controller (LGC) dose medium level processing tasks, with the
ability to use host and remote subscriber line interfaces.  The LGC has the
ability to use Line Concentrating Modules (LCMs), Remote Switching Centers
(RSCs), Remote Line Concentrating Modules (RLCMs), and Outside Plant Modules

The LGC can interface up to 20 DS-30 speech links from the LCMs or up to 20
DS-1 links with the ability to serve RSCs, RLCMs, or OPMs.

Line Trunk Controller

The Line Trunk Controller (LTC) combines the DTC and LGC functions and gives a
way to use all the equipment inside the office.  The LTC has the ability to
handle the LCM, RSC, RLCM, OPM, and digital trunk interfaces.

The LTC has the ability to give interfaces to a maximum of 20 outside ports
from DS-30A speech links or DS-1 links to 16 network side DS-30 speech links.

Line Concentrating Module

The Line Concentration Module (LCM) when used with the LGC or LTC is just an
expanded version of the line Module.  It can serve up to 640 subscriber lines
interfaced with two to six DS-30A  speech links.  Using six speech links 5,390
CCS can be handled per LCM.

Remote Switching Center

The Remote Switching Center (RSC) interfaces subscriber lines at a remote
location to a DMS-100 host.  It has the ability to handle interface for 5,760
lines and is used a replacements for dial offices or Private Branch Exchanges
(PBXs).  It can handle 16,200 CCS with the use of 16 DS-1 links.

The RSC consists of the following:

Line Concentrator Module (LCM) - These modules do line interface function.
They are the same as the LCMs that are used in the DMS-100 host.

Remote Cluster Controller (RCC) - This controller gives DS-1/LCM interface,
Local switching inside the remote, and Local intelligence and signaling when
in ESA.

Remote Trunking - Handles the use of RSC originating or terminating traffic
for digital trunking off the RSC.  It can give trunking to a CDO co-located
with the RSC or within the service range of the RSC, Private Automatic Branch
Exchanges (PABXs), or Direct Inward Dialing (DID) trunks.

Remote-off-Remote - Lets the RLCMs and OPMs connect to the RCC through DS-1
interfaces. It lets RLCM and OPM subscribers to use the same lines to the host
as the RSC subscribers.

Emergency Stand-Alone (ESA) - If communication with the DMS-100 is lost this
will allow you to call internal to the RSC.  It will give station-to-station
and station-to-trunk calls for POTS, IBN, and electronic business sets.

Remote Line Concentrating Module

The Remote Line Concentrating Module (RLCM)  is just a LCM used is a remote
location from the DMS-100 host.  The RLCM can handle 640 lines; this can is
sometimes used as a replacement for CDOs or PBXs.

Outside Plant Module

The Outside Plant Module (OPM) is an outside plant remote unit. The OPM can
handle 640 lines over six DS-1 links.

Subscriber Carrier Module

The Subscriber Carrier Module (SCM) gives a direct interface for remote

SCM-100R - It can interface up to five Northern Telecom DMS-1 Rural Remote
Terminals (RTs).  A DMS-1 rural remote terminal can interface up to 256 lines.
Communication between the RT and SCM- 100R is done through one or two span
lines for voice and one protection line.

SCM-100U - It can interface up to three DMS-1 Urban RTs.  A DMS-1 Urban can
interface up to 576 POTS or special service lines.  Communication from the RT
to the SCM-100U us done through a maximum of eight DS-1 links.

SCM-100S - It can interface up to four Mode I (non-concentrated) SLC-96
systems or up to six Mode II (concentrated) systems.  A SLC-96 can give
interface for up to 96 lines.

The SCM-100 takes away the need for central concentrating terminals and analog
line circuits at the host.

Operator Features

With the use of DMS-200 or DMS 100/200 switch, operator features are available
by the following:

Traffic Operator Position System (TOPS)
Operator Centralization (OC)
Auxiliary Operator Service System (AOSS)

Traffic Operator Position System (TOPS) gives many operator function on inward
and outward calls.  The TOPS integrates the operator system with the DMS-200
or DMS-100/200 toll switch.

One voice and one data circuit are needed for each operator position.  The
voice circuit is connected to a port of a three-port conference circuit.  The
other two ports are connected to the calling and called parties.  The data
circuit is used for a digital modem and is used to transmit data punched in by
the operator to the CCC for processing.

Operator Centralization

Operator Centralization (OC) lets the operator use the services given by the
DMS-200 or DMS-100/200 with TOPS.  With OC operator traffic from surrounding
DMS sites can be routed to a central host site.

                       Operator Centralization Diagram

          Routing                   - - -
         <-----\     DMS-200       | AMA |
                \   Remote TC     / - - -
                 = = = = = = =   /
                | \  ----- ___|_/
                |  \: DMS :   |
                |   : 200 :   |                    Host TC           -----
                |   :     :   |                = = = = = = = =     /| POS |
                |   :  (OC:___|               |   ---------   |   / |- - -|
                |   :     :   |\              |  : DMS-200 :  |  /  |Oper.|
                |    -----\   | \             |  :  (TOPS) :__|_/    -----
                 = = = = = = =   \____________|__:         :  |
          Trib Ope Traffic->\     ____________|__:OC)      :  |
                             \   /            |  :         :  |
          Non-DMS Remote TC     /             |   ---------   |
          = = = = = = = = = = =                = = = = = = = =
         |   --------   -----  |
         |  :  TDM   : :  (OC: |
         |  : Switch : :     : |      -----
         |  :        : : DMS :_|_____: AMA :
         |  :        : : 200 : |      -----
         |  /--------   -----\ |
          = = = = = = = = = = =
          /Routing             \ <-Trib Opr Traffic
          \------->             \

Auxiliary Operator Services System

The Auxiliary Operator Services System (AOSS) is made to handle directory
assistance, intercept, and that type of operator services, automatic call
distribution, call processing, call detail recording, and operator
administration functions for other operator services that do not need call
completion to a called party.  AOSS position uses the same hardware as the
TOPS links to the switch.

Equal Access

Equal Access (EA) is accessible through DMS switches with the addition of
software packages.  Both Equal Access End Office (EAEO) for the DMS-100 and
Access Tandem (AT) for the DMS-200 provide equal access features.

                Equal Access Network Application

                --------- __________________________________
(Phone)--------| DMS-100 |___________                       |
                ---------            |                      |
           NON-EAEO                  |                      |IC/INC
           --------               --------             /---------\   TO
(Phone)---|        |------------| DMS-200 |------------           ---- IC/INC
           --------              ---------             \---------/   /----->
                                     |                      |
                --------- ___________|                      |
(Phone)--------| DMS-100 |__________________________________|


The DMS-100 EAEO gives direct access to interLATA (Local Access and Transport
Area) carriers Point of Presence (POP) inside the LATA.  The DMS-200 AT gives
a traffic concentration and distribution function for interLATA traffic
originating  or terminating inside a LATA. It allows the following:

10XXX and 950-1XXX dialing
presubscription dialing
equal access and normal network control signaling
Automatic Number Identification (ANI) on all calls
custom calling services

Common Channel Interoffice Signaling

Common Channel Interoffice Signaling (CCIS) uses a separate data link to
transmit signaling messages between offices for many trunks and trunk groups.
There are two types of CCIS available in the DMS-200 or DMS-100/200, Banded
Signaling (CCIS-BS) and Direct Signaling (CCIS-DS).

CCIS-BS is for interoffice trunk signaling to give information on digits
dialed, trunk identity, and other class and routing information.  This kind of
trunk signaling takes less time to setup calls and put's an end to Blue

CCIS-DS is used to transfer call handling information past what is required
for trunk setup.  This type of signaling lets calling card validation,
mechanized calling card services and billed number screening to be used.

Cellular Mobile Radio Service

Cellular Mobile Radio Service is possible with the DMS-100 Mobile Telephone
Exchange (MTX).  The MTX has the ability to serve from a few hundred to over
50,000 people in up to 50 cells.

Thanks to Northern Telecom and my local CO.

   Control C

  March 1987
 End of Part 1

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