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TUCoPS :: Phreaking General Information :: unddms.txt

Understanding the Digital Multiplexing System (DMS)

             Understanding the Digital Multiplexing System (DMS)

  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.

DMS switches were first introduced in 1979.  Since then it has been modified
to interface with numerous types of switches.  DMS has the ability to
interface with SP-1, #5 XBar, 1ESS, 2ESS, 3ESS, 4ESS, NX1D, NX1E, TSD, SXS,
ETS4, NO. 1 EAC, NO. 2 EAX, NO. 3 EAX, TSPS, CAMA/3CL boards, Stromberg
Carlson Turret of ONI and Visual Indicators, Modified North Electric TSD for
ONI, Stomberg Carlson (CAMA operator Position - ONI/ANI), AE #31 Switchboard,
Co-located NT/AE switchboard I/C, O/G, UDC data poller of OM, DACS (Directory
Assistance Charging System), NT #144 LTD, WECO #14 LTD, WECO #16 LTD, CALRS
(Centralized Automated Loop Reporting System), Badger 612A, AE #1 and #21 LTD,
AE #30, SC #14 LTD, Lordel MITS70 line Test System, Porta System Line Test
Unit, Pulsar II IMTS, Teradyne loop test unit, and the WECO MLT 1 (Mechanized
Loop Testing System).

Common Channel Interoffice Signaling
Common Channel Interoffice Signaling (CCIS) is a way of signaling and a way of
implementing network level services.  CCIS provides reliable, crystal clear
data signaling links between the network and the switching offices.  The CCIS
signaling method uses transmission equipment that is separate from voice

Common Channel Interoffice Signaling No. 6
The basis for the CCIS system is the International Consultative Committee on
Telephone and Telegraph (CCITT) No. 6 international standard, which is brought
to its fullest capacity for use in the Stored Program Control (SPC) network of

The CCIS6 network contains a bunch of signaling regions, each having a pair of
interconnected Signal Transfer Points (STP).  The switching systems put into
CCIS6 that connect to STPs are called Serving Offices (SO).

Band Signaling (CCIS-BS) is used on trunk signaling for intertoll-type trunks
using the CCIS network.

Direct Signaling (CCIS-DS) is used for signaling between SPC switching
machines and a Network Control Point (NCP).  At the present time, CCIS6 can
handle Enhanced INWATS Originating Screening Office (OSO), Calling Card
Validation (CCV), Mechanized Calling Card Service (MCCS), and Billed Number
Screening (BNS).  CCIS6 is available with DMS-100/200, DMS-200, and
DMS-100/200 or DMS-200 with TOPS.

CCIS6 Diagram:
                                            NSB        ST
                      ------------         - - - - - - - - - - -
          DTC        |            |      |            -------    |
         - - -  DS30 |    IPML    | DS30 |  - - -    | ||    |   |
--------|     |------|- - - - - - |------|-|     |---| ||    |   |
Digital  - - -       |            |      |  - - -    | ||    |   |
Trunks               |            |      |           | ||    |   |
                     |            |      |            -------    |
                     |            |        - - - - - - -|- - - -
          DTC        |            |          TM         |
  DIG    - - -  DS30 |    NUC     |  DS30   - - -      -----
--------|     |------|- - - - - - |--------|     |----|     |
^        - - -       |Network     |         - - -      -----
CCIS         \        ------------                     Modem
Signaling     \            |
           - - -         -----
AN Links--|     |       | CCC |
           - - -         -----


        DIG - Digital
        AN - Analog
        DTC - Digital Trunk Controller
        MSB - Message Switch Buffer
        ST - Signaling Terminal
        TM - Trunk Module
        NUC - Nailed-Up Connection
        IPML - Inter-Peripheral Message Link

Common Channel Interoffice Signaling No. 7
Common Channel Signaling (CCS) No. 7 or CCIS7 is a CCS system based on CCITT
No. 7.  CCIS7/CCS7 on the DMS switch consists of two parts:  the Message
Transfer Part (MTP) and the Interim Telephone user Part.  They are compatible
with DMS-100, DMS-200, DMS-100/200, and DMS-100/DMS-100/200 with TOPS.

CCIS7 can't tell the difference between banded and direct signaling.  CCIS7
uses Destination/Origination Point Codes (DPC/OPC) to route back to the

CCIS7 can handle Automatic Calling Card Service (ACCS), Enhanced INWATS, Local
Area Signaling Services, and Direct Service Dialing Capabilities.

Equal Access
The DMS-200 Access Tandem (AT) gives a traffic concentration and distribution
function for interLATA traffic originating and a distribution function for
interLATA traffic origination or terminating inside a Local Access and
Transport Area (LATA).  This gives the interLATA Carrier (IC) access to more
that one end office inside the LATA.  It can handle InterLATA Carrier access
codes (10xxx), 10xxx and 950-yxxx dialing, Automatic Number Identification
(ANI) on all calls, answer supervision, equal access Automatic Message
Accounting (AMA) for both originating and terminating calls, and operator
service signaling.

The DMS-100 EA gives direct and tandem switched access service inside the LATA
for originating and terminating to interLATA Carriers.  It is available in the
following three ways:

Equal Access End Office (EAEO)
DMS-100 Equal Access End Office (EAEO) gives a direct interconnection to
interLATA Carriers' (IC) and international Carriers' (INC) Points of Presence
(POP) inside the LATA.

Access Tandem with Equal Access End Office
The DMS-200 Access Tandem (AT) when used with equal access end office (EAEO)
lets trunk tandem interconnect to ICs/INCs POP inside the LATA.

The connection of the Equal Access End Office (EAEO) to an IC/INC through the
DMS-200 Access Tandem (AT) uses what is called two-stage overlap output
pulsing which makes the time it takes to set up a call quicker.  The AT uses
the digits OZZ + XXX out pulsed  in the first stage to identify the IC/INC
dialed and to pick out outgoing trunk.  Then a connection is established from
the IC/INC to the EAEO through the AT.  The second stage digits consist of ANI
and the called numbers are passed through the DMS-200 AT at the IC/INC.

An AMA terminating record in AT&T format is produced by the DMS-200 for all
the EAEOs.  A per call terminating AMA record is made for calls that get to
the stage where the trunk from the IC/INC has been seized and a "wink" has
been returned by the DMS-200 AT.

Access Tandem with a Non-Equal Access End Office
DMS-200 AT using a non-equal access end office gives trunk tandem connection
to an IC/INC POP within the LATA.  To set up a call, connection of Feature
Group B (FGB) or Feature Group C (FGC) End Office to an IC/INC through the
DMS-200 AT uses the standard Bell Central Automatic Message Accounting (CAMA)
signaling.  The Access Tandem uses the XXX digits of the access code 950-YXXX
out pulsed from the FGB end office to identify the IC/INC and to connect to an
outgoing trunk.

Mechanized Calling Card Service (MCCS)
The fraudulent use of calling cards, third number and collect calls and the
increasing movement to automate current operator services has directly led to
the implantation of the Mechanized Calling Card Service (MCCS) to DMS-200/TOPS
and to the remote and host Operator Centralization (OC).

MCCS uses CCIS to relay queries and responses to and from the DMS-200/TOPS.
Operator handled calling card calls and the direct entry by subscribers of
Calling Cards by DTMF (Touch-Tone) telephones are given special provisions by
the MCCS.  Both the operator handling and the direct entry of calling card
calls are decreasing the size of the operators.

Billed Number Screening (BNS) gives an enhancement to the operator-handled
collect and third-number billing by using CCIS to screen a number at the
billing validation data base for billing restrictions (i.e. the third number
is a fortress).  This feature naturally will reduce fraudulent use of the
collect call feature.

Common Channel Interoffice Signaling-Direct Signaling (CCIS-DS), which is
the feature that the MCCS is designed around, is used to transmit messages to
and from many possible Billing Validation Centers (BVCs).  Messages
transmitted to the BVC about MCCS include the billing number and the Personal
Identification Number (PIN).  In BNS the messages have the special billing
number (collect or third number).  The return messages from the BVC include
validity (of the number), billing restrictions (if any), and the Revenue
Accounting Office (RAO) code.

Auxiliary Operator Services System
The DMS-200 Auxiliary Operator Services System (AOSS) is used primarily for
Directory Assistance and the intercept needs that are not included in the TOPS
package.  The AOSS is similar to TOPS and co-exists with TOPS on the DMS-200
Toll system.

Major benefits of the AOSS include:  Directory Assistance is provided with a
modern environment, AOSS position administrative activities are performed by
the DMS-200 toll maintenance system, trunking savings are achieved by
combining trunking for 1+, 0+, and Directory Assistance traffic, DA services
are managed by using TOPS methods, creation of a built-in training system
which does not require additional training equipment and reduces training

Integrated Business Network
The Integrated Business Network (IBN) is a revenue-producing concept designed
for small and big businesses to offer modernized PBX and Centrex features.
The Operating Company can use the IBN to maintain and enhance its competitive
position on a operational DMS-100 and DMS 100/200 switches.   While using the
DMS-100 switch, the Operating Company can support varying business features
along with existing local/toll traffic.

IBN services can be introduced to a Centrex-Central Office (CO) or a
Centrex-Customer Unit (CU) by additional software modules and minor hardware

Current IBN features include:  A growing system that can handle 30,000 lines,
networking capabilities, city wide service for DMS-100 switch and remotes for
any one customer Station Message Detail Recording (SMDR), which gives IBN
customers call records.  The records can be used for system analysis and
control and station charge-back.  SMDR can use LAMA records (if the IBN host
has LAMA equipment), centralized attendant maintenance, and administration
functions and Direct Inward Dialing (DID).

Electronic Switched Network (ESN)
The Electronic Switched Network is designed to meet the telecommunication
needs of large multi-location corporations.  The ESN is made up of a SL-1 or
SL-100 Digital Business Communications System with networking features or a
DMS-100 IBN host.  The SL-1 can handle from 30-5000 lines.  The SL-100 and the
DMS-100 IBN hosts can hold from a few thousands to 30,000 lines.

A DMS-100 IBN or SL-100 can remotely serve many locations from the host site.
This is done by a connection through digital transmission facilities which are
set up at remote modules at the subscriber's premises.

Here are some diagrams showing the differences between normal private
telecommunications networks and ESN networks.

                      Normal telecommunications network

           -----               ------
 [Phone]--| SnS |             | SL-1 |-[Phone]
          | PBX |             | PBX  |
           -----               ------
           |  |DOD/DID   DOD/DID|  |
           |   -------   -------   |
           |Tie       | |       Tie|
           |Trunk  ---------  Trunk|
            ------| Class-5 |------
              ----| Centrex |----
             |     ---------     |
             |                   |
             |                   |
             |                   |
           -----  Tie Trunk  ---------
          | SnS | ----------| Class-5 |
          | PBX |           | Centrex |
           -----             ---------
             |                   |
             |                   |
             |                   |
             |                   |
          -------             ------
 [Phone]-| Small |           | SL-1 |-[Phone]
         |  PBX  |           |      |
          -------             ------

                                  ESN Network
          --------                               ----------
[phone]--| Remote |                             | SL-1 PBX |--[phone]
         | Module |                             | ESN Main |
          --------                               ----------
              |                                       |
              |  DS-1 Facility                        |  DS-1 Facility
              |            --------------             |
               -------->  | Local Class 5|  <---------
          [phone]---------|    DMS-100   |
                      ----|    IBN/ESN   |-------------
        2W Loop MFIDP |    --------------             | ESN Trunk Group
           or DS-1    |           |                   |     or DS-1
                      |         -----         ---------------
                      |        | CSC |       | Local Class 5 |
                   --------     -----        |    DMS-100    |
                  | SL-100 | <--- DS-1 ----> |    IBN/ESN    |
                   --------     Facility      ---------------
                      |                              |
                      |                              |
                      | DS-1 Facility                | DS-1 Facility
                      |                              |
                   --------                      ----------
         [phone]--| Remote |                    | SL-1 PBX |--[phone]
                  | Module |                    | ESN Main |
                   --------                      ----------

Specialized Common Carrier Service (SCCS)
The DMS-250 Specialized Common Carrier Service (SCCS) provides the capability
of Analog to Digital (A/D) and Digital to Analog (D/A) conversions which are
necessary with analog circuits.  The DMS-250 can also switch voice and data

The DMS-250 takes either analog or digitally encoded info and by using time
slot interchange, switches it from any input port to a temporary addressed and
connected exit port.  The info may or may not be converted back to analog.

Cellular Mobile Radio Service
A cellular system consists of two main parts:  a cellular switch and cell site

Cellular Switching Systems
A cellular switch performs three main functions:  audio switching, cell site
control, and system administration.

The DMS switches provide three basic implementations for cellular switching:
Stand-alone, Combined, and Remote.

Stand-alone switching is done by a Mobile Telephone Exchange (MTX) which is
interfaced with one or more class 5 end offices.  The connection is made by
DID/DOD trunks.  Depending on the needs of the area, the MTX can be divided as
follows:  MTX which serves urban areas, MTXC which handles suburban areas, and
MTXM which is used for rural areas.

Combined switching is incorporated into a DMS-100 by some hardware additions
and cellular software.  Combined switching is designed to give an easy,
cost-effective way to install cellular services to an existing host.

Remote Switching is done by combining Remote Switching Center (RSC) with a
Cell Site Controller (CSC).  This combination is hosted by either a
stand-alone or a combined switch.  Remote Switching is designed for serving
suburban centers, remote areas, or a small community and it gives extra
flexibility for a growing system.

All of these cellular switches have the ability to balance the workload among
various cell sites.  For example, if one site's workload reaches the
programmable level of congestion, calls would be routed to nearby sites that
can handle the extra calls.

Cell Site Equipment
Cell site equipment consists of a CSC and radio equipment.  The CSC is
controlled by the cellular switch and it controls radio equipment and
maintenance tasks.  The CSC will work on any MTX cellular switch because of
the Remote Cluster Controller (RCC).

The radio equipment consists of self-contained Radio Channel Units (RCU),
antennas, transmitter multi-couplers, and receiver combiners.

By different program software, an RCU can perform voice, control locating, and
test functions.  The self contained nature allows the RCU be remotely located
to the CSC.  A RCU has built-in circuitry for extended testing of the radio
part of the system.

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