HARDWARE ARCHITECTURE OF CDOT MAX-XL SWITCHING

SYSTEM AND ANALYSIS OF DIAGNOSIS REPORTS

MAIN PROJECT REPORT

SUBMITTED IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

BACHELOR OF TECHNOLOGY
IN
ELECTRONICS AND COMMUNICATION ENGINEERING
BY

S.PRABHU (06261A0446)

K.SANDEEP KUMAR (06261A0424)

L.VICKRAM KUMAR (06261A0425)

Department of Electronics and Communication Engineering

MAHATMA GANDHI INSTITUTE OF TECHNOLOGY

(Affiliated to Jawaharlal Nehru Technological University, Hyderabad, A.P.)

Chaitanya Bharathi P.O., Gandipet, Hyderabad – 500 075

2010

CERTIFICATE

1
 This is to certify that the project work entitled “HARDWARE ARCHITECTURE OF
CDOT MAX-XL SWITCHING AND ANALYSIS OF DIAGNOSIS REPORTS” is a
bonafide work carried out by

K.SANDEEP KUMAR (06261A0424)

L.VICKRAM KUMAR (06261A0425)

S.PRABHU (06261A0446)

in partial fulfillment of the requirements for the degree of BACHELOR OF

TECHNOLOGY in ELECTRONICS & COMMUNICATION ENGINEERING by the
Jawaharlal Nehru Technological University, Hyderabad during the academic year
2009-10.
The results embodied in this report have not been submitted to any other University or
Institution for the award of any degree or diploma.

(Signature)
(Signature)
---------------------------
---------------------------
Internal guide external
examinar Mrs.J.snehalatha
Assnt.professor

(signature)

E.NAGABHUSHANAM
Professor and HOD(ECE)

2
 ACKNOWLEDGEMENT

We are privileged to have V.V.V.SATYANARAYANA garu as our project guide who is

one amongst the Sub divisional engineer at bharat sanchar nigham limited is
consistent encouragement and rational knowledge were like a boon to the completion of
this project.

Also, We are very much gratified to E.NAGABHUSHANAM garu, our

honorable Head of the Department of electronics and communication Engineering,
Mahatma Gandhi Institute of Technology, and our project guide,for providing us all
the resources needed in order to carry our work process,at our department.

We are soliciting our sincere thanks to Prof.G.CHANDRA MOHAN REDDY

garu, principal, Mahatma Gandhi Institute of Technology for his provocative
conceptions.

Finally, We would like to thank All the staff members of the Department of
Electronics and communication engineering who have immensely worked to mould us,
directly or indirectly, in successfully terminating our project.

With pleasure, I thank my parents for their encouragement and blessings to

complete this project work.

S.prabhu

k.sandeep kumar

L.vickram kumar

3
 Bharat Sanchar Nigam Limited
(A Govt. of India Enterprise)
Regional Telecom Training Centre
Gachibowli, Hyderabad - 500 032
Phone: 040-23000232 Fax : 040-23000229
Web site: www.rttchyd.bsnl.co.in  
An ISO 9001-2000 Certified Institute

CERTIFICATE

This is to certify that

SL.No Name of the Student Roll No.
1. K.SANDEEP KUMAR 06261A0424
2. L.VICKRAM KUMAR 06261A0425
3. S.PRABHU 06261A0446
Have undergone project training at Regional Telecom Training Centre, BSNL,
Gachibowli, Hyderabad. The Project “HARDWARE ARCHITECTURE OF CDOT
MAX-XL SWITCHING AND ANALYSIS OF DIAGNOSIS REPORTS” is record
of the bonafied work undertaken by them towards partial fulfilment of the academic
requirements for award of B. Tech in Electronics and Communication Engineering from
MAHATMA GANDHI INSTITUTE OF TECHNOLOGY.They have successfully
completed the project under the guidance of MR.V.V.V.SATYANARAYANA(SDE)
from Feb to Apr 2010.

Project Guide
(V.V.V.SATYANARAYANA) PRINCIPAL,
(SDE) RTTC, HYDERABAD

TABLE OF CONTENTS

4
Chapter 1. Introduction to switching 01

1.1 Switch 02

1.2 Circuit switching 02

1.3 Packet switching 04

1.4 TST switching 05

Chapter 2. Principles of electronic exchange 09

2.1 Main blocks 11

2.2 MDF 11

2.3 Evolution of telephone exchange 11

2.4 Terminal equipments 13

Chapter 3.Introduction to CDOT 14

3.1 General 15

3.2 Basic building modules 16

Chapter 4. Hardware architecture of CDOT DSS MAX XL 19

4.1 BM module 20

4.2 CM module 34

4.3 System capacity 37

4.4 CCS7 signaling 39

4.5 RSU status 40

Chapter 5.CDOT capacity 43

5
 5.1 Introduction 44

5.2 Termination capacitance 44

5.3 Exchange configuration 45

5.4 Traffic carring capacity 47

5.5 BHCA handling capacity 47

5.6 System realibility 48

Chapter 6. Subscriber features 50

6.1 Introduction 51

6.2 PSTN & ISDN SERVICES 51

6.3 Call offering supplementary service 52

6.4 Call completion service 53

6.5 Multiparty service 54

6.6 miscellaneous service 54

Chapter 7. Software architecture 58

7.1 Introduction 59

7.2 Overview 59

7.3 CDOT real time OS 60

7.4 CCS7 call processing 65

Chapter 8. Commands 68

Chapter 9. Diagnosis reports 70

6
ABSTRACT

7
The main Objective  of this project involves study of different
Hardware Architectures of CDOT Main Automatic Exchanges and
analysis of various diagnosis reports . The Inputs  Used for this
project are , CDOT Hardware Equipment and Terminals for
testing and analysis of different types of faults .this project
usually deals with  Practically observing  different Hardware
Architectures of CDOT Main Automatic Exchange-XL type
switching system and analyzing the various diagnosis reports by
testing of different hardware units through Man- Machine
Interface commands.  Practical observations of diagnosis reports
and analysis in CDOT exchange, repairing the final reports.

The hardware architecture of cdot max xl

exchange usually consists of thirty two BM and each BM consists of
six frames while each frame consists of twenty six slots and in each
slot any one of terminal cards or control cards are placed .This
project deals with testing of various cards and preparing diagnosis
reports on various cards which were under test

8
 Chapter 1

Introduction to switching

1 Introduction to switching

1.1switch

In electronics, a switch is an electrical component that can break an electrical

circuit, interrupting the current or diverting it from one conductor to another. The most
familiar form of switch is a manually operated electromechanical device with one or
more sets of electrical contacts. Each set of contacts can be in one of two states: either

9
‘closed’ meaning the contacts are touching and electricity can flow between them, or
‘open’, meaning the contacts are separated and nonconducting.

A switch may be directly manipulated by a human as a control signal to a system,

such as a computer keyboard button, or to control power flow in a circuit, such as a light
switch. Automatically-operated switches can be used to control the motions of machines,
for example, to indicate that a garage door has reached its full open position or that a
machine tool is in a position to accept another workpiece. Switches may be operated by
process variables such as pressure, temperature, flow, current, voltage, and force, acting
as sensors in a process and used to automatically control a system. For example, a
thermostat is an automatically-operated switch used to control a heating process. A
switch that is operated by another electrical circuit is called a relay. Large switches may
be remotely operated by a motor drive mechanism. Some switches are used to isolate
electric power from a system, providing a visible point of isolation that can be pad-locked
if necessary to prevent accidental operation of a machine during maintenance, or to
prevent electric shock.

1.2Circuit Switching

Circuit switching is the most familiar technique used to build a communications

network. It is used for ordinary telephone calls. It allows communications equipment and
circuits, to be shared among users. Each user has sole access to a circuit (functionally
equivalent to a pair of copper wires) during network use. Consider communication
between two points A and D in a network. The connection between A and D is provided
using (shared) links between two other pieces of equipment, B and C.

A connection between two systems A & D formed from 3 links

10
Network use is initiated by a connection phase, during which a circuit is set up between
source and destination, and terminated by a disconnect phase. These phases, with
associated timings, are illustrated in the figure below.

A circuit switched connection between A and D

(Information flows in two directions. Information sent from the calling end is shown in
pink and information returned from the remote end is shown in blue)

After a user requests a circuit, the desired destination address must be

communicated to the local switching node (B). In a telephone network, this is achieved
by dialing the number.

Node B receives the connection request and identifies a path to the destination (D)
via an intermediate node I. This is followed by a circuit connection phase handled by the
switching nodes and initiated by allocating a free circuit to C (link BC), followed by
transmission of a call request signal from node B to node C. In turn, node C allocates a
link (CD) and the request is then passed to node D after a similar delay.

11
 The circuit is then established and may be used. While it is available for use,
resources (i.e. in the intermediate equipment at B and C) and capacity on the links
between the equipment are dedicated to the use of the circuit.

After completion of the connection, a signal confirming circuit establishment (a

connect signal in the diagram) is returned; this flows directly back to node A with no
search delays since the circuit has been established. Transfer of the data in the message
then begins. After data transfer, the circuit is disconnected; a simple disconnect phase is
included after the end of the data transmission.

Delays for setting up a circuit connection can be high, especially if ordinary

telephone equipment is used. Call setup time with conventional equipment is typically on
the order of 5 to 25 seconds after completion of dialing. New fast circuit switching
techniques can reduce delays. Trade-offs between circuit switching and other types of
switching depend strongly on switching times.

1.3Packet Switching

What is packet switching? Like the development of hypertext, packet switching is

an idea that seems to want to have been discovered, found independently within a few
years by two different people separated by one of the earth’s largest oceans. The
revolutionary concept formed the foundation for the design of the Arpanet, and then the
Internet Protocol, providing the key enabling technology that has led to the success of the
Internet today.

The packet switching concept was a radical paradigm shift from the prevailing
model of communications networks using dedicated, analog circuits primarily built for
audio communications, and established a new model of discontinuous, digital systems
that break messages into individual packets that are transmitted independently and then
assembled back into the original message at the far end.

The conceptual breakthrough advantage of packet switching was “enabling more

with less” through packet-level multi-tasking – routing multiple communications over the

12
same wire at the same time — enabling the construction of data networks at much lower
cost with greater throughput, flexibility, and robustness. The following sections provide
more information.

1.4 Time space time switch

In these terminals This invention relates in general to time space time (TST)
telecommunication system switches, and, in particular, to time folded TST switches for
interconnecting digital Time Division Multiplex (TDM) communication lines, with both
path connections required for a completed communication link automatically established
in one operation, with a second path the mirror image of the first path.

Time Space Time (TST) switches are a particularly useful configuration of

switching elements providing both time and space translation between channels of Time
Division Multiplexed (TDM) telecommunications transmission lines. A TST switch
interconnects digital bi-directional TDM communication lines with TDM communication
involving the sharing of single transmission paths, individually, in time to provide
multiple channels in a single transmission medium. This is a fundamental system
improvement in telephone communications that should prove helpful in reducing cost of
ordinary telephone service, and in enhancing the ability to provide many new kinds of
service, in meeting expanded communications needs. Electromechanical crossbar and
relay switching systems, as generally used today in telecommunications switching, have,
for practical purposes, reached the limit of their capabilities. Extensive, continued
adherence to these older technologies severely restricts capability, and greatly increases
costs of telecommunication systems; and, particularly so with expansion to systems of
great size and complexity. While many advances have been made in capability and
efficiency in the transmission area, with microwave, satellite, and high-capacity cable,
and with both analog and digital repeaters and terminals being used, the exchange plant,
including switching equipment in central offices and branch exchanges, remain in
essence the same as in the very early days. Recent advances in solid state technology
make the use of all digital switching and transmission techniques more attractive today
than ever before.

13
 The advent of digital multiplex transmission systems gives rise to many
possibilities; particularly with TDM multiplex terminals beginning to look like switches.
Message signals appear in “time slots,” and transfer of signals between time slots is
accomplished by a “time slot interchange,” with time-division switches connected
directly to multiplex transmission lines. Another important saving is accomplished
through elimination of digital-to-analog, and analog-to-digital, conversions of every
switch. The existing local exchange area plant represents the major part of telephone
plant investment, and the least efficient portion of the system—with large quantities of
scarce materials required. Further, physical congestion problems are encountered with
entrance cables as they approach the central office, and, many times, there are difficult
growth problems in central office main distribution frames. Present central office
switching includes bulky electromechanical switching stages located in large, costly
building space. Costs for new construction and maintenance of such traditional exchange
area plants are constantly increasing, particularly with large cable networks employed
when cable pair utilization is inherently very low with a dedicated physical wire pair used
to connect each subscriber station to its central office. Thus, system improvements
attainable with time division transmission and switching techniques are very significant.
This has led to Time Space Time (TST) switching structures, and, with some TST
switches, an improved “folded” operation configuration. Folded operation TST switches
are provided not only with a single stage square switch as a single space switch stage, but
also as larger switches having multiple stage space switching sections. Connect and
disconnect procedures are simpler with folded operation TST switches since a second
path is automatically specified whenever the first path is selected. Thus, only one
pathfinding operation is required in a folded switch, and the disconnect procedure is
simpler since both paths can be released simultaneously. Blocking problems are reduced
by one half with a second path through the switch automatically available when an idle
first path is found. Further, control information for the two paths can be shared, thereby
providing some economy in the size of the control store.

It is therefore a principal object of this invention to provide a time folded time

space time (TST) switch system achieving great improvements in operation in selectively

14
interconnecting digital bi-directional Time Division Multiplexed (TDM) transmission
paths.

Another object is to minimize equipment costs, while achieving improved reliability and
lessened maintenance requirements through use of time folded TST switches.

A further object is to reduce signal path switch blocking problems through use of such
time folded TST switches.

Still another object is to simplify switch connect and disconnect procedures with a second
through switch path being automatically specified whenever the first path is selected.

Another object is to achieve a further reduction in equipment requirements through

control information sharing with time folded TST switches.

Features of this invention useful in accomplishing the above objects include, in a

time folded TST (time space time) switch, the selective controlled interconnection of
digital time division multiplex (TDM) communication paths, with both path connections
required for a completed communication link automatically established in one operation,
with a second path, the mirror image of the first path. The time folded operation involves
using separate time slots (usually adjacent time slots) for the two paths of each full
duplex connection. Thus, the time folded operation makes it possible to share path
elements for both directions of a full duplex connection. Time folded operation with the
use of separate time slots for each direction of a connection can also reduce the speed
requirements of the time stage memories. When two channels of the same TDM input are
being interchanged (switched), two accesses to the same inlet and two accesses to the
same outlet are required. If the interchange is made during one space switch time slot,
two accesses of each inlet memory and each outlet memory are required during the one
time slot. With applicant’s time folded TST switch units, however, only one access per
memory is required during each space switch time slot.

15
16
 Chapter 2

Principles of electronic exchange

2 PRINCIPLS OF ELECTRONIC EXCHANGE

switch

circuit Store forawrd

17
 Message Packet

datagrammm
virtual

Telephone exchange

Terminating equipment Switching equipment

Analog Digital

Space switch Time switch

2.1 Main blocks

 Power(battery)

 Power plant

 Engine alternator

 Mdf

 Switch

 OMC(operation & maintenance control)

18
 power required for telephone exchange is -48v to -52v DC .Not AC because harmonics
or repeals may damage our equipments and relays also use DC supply ,negative supply
inorder to trace earth faults easily

2.2 MDF (MAIN DISTRIBUTION FRAME):

Usally consists of two sides

 Exchange side

 Line side

Role of MDF is to connect line side and exchange side

2.3 EVOLUTION OF TELEPHONE EXECHANGE

 MANUAL TYPE OF EXCHANGE

 ELECTROMECHANICAL

 ELECTRONIC

DRAWBACKS OF ELECTROMECHINACAL EXECHANGE

 Large equipment

 Noice

 Adjustment

 Less facilities to subscribers

 Limited availability

ELECTRONIC EXECHANGE

 Its Program based exechange

 Uses stored program controller

19
 Block diagram:

Terminal equipment Switching network

Command control equipment

Input/output peripherals

2.4 TERMINAL EQUIPMENT

 Physical termination usually consists of the fallowing operations

 B-battery feed

 O-over voltage protection

 R-ringing

 S-super vision

 C-coding

20
 H-hybrid

 T-testing

21
 Chapter 3

CDOT MAX-XL

3 C-DOT MAX-XL

3.1 GENERAL

C-DOT DSS MAX is a universal digital switch which can be configured for
different applications as local, transit, or integrated local and transit switch. High
traffic/load handling capacity up to 8,00,000 BHCA with termination capacity of 40,000
Lines as Local Exchange or 15,000 trunks as Trunk Automatic Exchange, the C-DOT

22
DSS family is ideally placed to meet the different requirements of any integrated digital
network.

The design of C-DOT DSS MAX has envisaged a family concept. The advantages of
family concept are standardized components, commonality in hardware, documentation,
training, installation and field support for all products and minimization of inventory of
spares. In fact this modular design has been consciously achieved by employing
appropriate hardware, software, and equipment practices.

The equipment practices provide modular packaging. Common cards and

advanced components have been used in the system hardware in order to reduce the
number and type of cards. Standard cards, racks, frames, cabinets and distribution frames
are used which facilitate flexible system growth. Interconnection technology has been
standardized at all levels of equipment packaging. All these features, together with
ruggedised design, make C-DOT DSS MAX easy to maintain and highly reliable.

C-DOT DSS MAX –XL is a universal digital switch, which can be configured
for different application as local, transit or integrated local cum transit switch. The
hardware architecture of C-DOT DSS MAX – XL utilizes state of the art microcircuitry
& modular packaging. It utilizes advanced concept in hardware design such as duplicated
& distributed microprocessor based control, hybrid integrated circuit & single chip digital
signal processors for MF& DTMF receivers. The software has been written in high level
language(C) & the man machine interface language is a simple English like language.
Now CDOT DSS Exchange can upgrade to provide ISDN service by adding minimum
additional hardware units.

The system employs a T-S-T switching configuration and is based on a 32

channel PCM structure. It uses a basic rate of 64 Kbps & 2 mbps primary multiplexing
rate. Basic memory unit has been implemented as a 16MB dynamic RAM board with 256
KB as basic dynamic RAM chip. Single chip digital signal processors are used for
implementing DTMF & MF receivers.

Another important feature of the design is the provision of both local and
centralized operation and maintenance. Beginning with local operation and maintenance,

23
with the installation of similar digital switches in the network, centralized operation and
maintenance will provide maintenance and administration services very economically.
All these services are provided through a simple, interactive man-machine interface.

3.2 BASIC GROWTH/BUILDING MODULES

C-DOT DSS MAX exchanges can be configured using four basic modules

(Fig. 1.1)

 Base Module

 Central Module

 Administrative Module

 Input Output Module

i) BASE MODULE

The Base Module (BM) is the basic growth unit of the system. It interfaces the
external world to the switch. The interfaces may be subscriber lines, analog and digital
trunks, CCM and PBX lines. Each Base Module can interface upto 2024 terminations.
The number of Base Modules directly corresponds to the exchange size. It carries out
majority of call processing functions and, in a small-exchange application, it also carries
out operation and maintenance functions with the help of the Input Output Module.

In Single Base Module (SBM) exchange configuration, the Base Module acts as
an independent switching system and provides connections to 1500 lines and 128 trunks.
In such a configuration, the Base Module directly interfaces with the Input Output
Module for bulk data storage, operations and maintenance functions. Clock and
synchronization is provided by a source within the Base Module. It is a very useful
application for small urban and rural environments.

With minimum modifications in hardware through only one type of card, a Base
Module can be remotely located as a Remote Switch Unit (RSU), parented to the main
exchange using PCM links.

24
ii) CENTRAL MODULE

Central Module (CM) consists of a message switch and a space switch to provide
inter-module communication and perform voice and data switching between Base
Modules. It provides control message communication between any two Base Modules,
and between Base Modules and Administrative Module for operation and maintenance
functions. It also provides clock and synchronization on a centralized basis.

iii) ADMINISTRATIVE MODULE

Administrative Module (AM) performs system-level resource allocation and

processing function on a centralized basis. It performs all the memory and time intensive
call processing support functions and also administration and maintenance functions. It
communicates with the Base Module via the Central Module. It supports the Input Output
Module for providing man- machine interface. It also supports the Alarm Display Panel
for the audio-visual indication of faults in the system.

iv) INPUT OUTPUT MODULE (I0M)

Input, Output Module (IOM) consists of duplicated Input Output Processor (IOP).
The Input Output Processor (IOP) is a general-purpose computer with UNIX Operating
System. It is used as the front-end processor in C-DOT DSS. It handles all the input and
output functions in C-DOT DSS. The IOP is connected to AP/BP via HDLC links.

During normal operation, two IOP’s interconnected by a HDLC link, operate in a

duplex configuration. Working as front-end processor, it provides initial code down load
to the subsystems, man machine interface and data storage for billing and other
administrative information.

IOP interfaces various secondary storage devices like' disk drives, cartridge tape
drive and floppy drive. It supports printers and upto 8 serial ports for video display units
which are used for man- machine communication interface. All the bulk data processing
and storage is done in this module

Thus, a C-DOT DSS exchange, depending upon its size and application, consists
of Base Modules (maximum 32), Central Module, Administrative Module, Input/Output

25
Module and Alarm Display Panel. The Base Modules can be remotely located or co-
located depending on the requirement.

26
 Chapter 4

HARDWARE ARCHITECTURE IN C-DOT DSS

MAX-XL.

4 HARDWARE ARCHITECTURE IN C-DOT DSS

MAX-XL.

4.1 BASE MODULE

27
 BM-XL is the basic growth unit of CDOT DSS. It interfaces the external world to
the switch. The interface may be subscriber lines, analog & digital trunks, CCM & PBX
lines & digital links from remote modules & line concentrators. Each Base Module can
interface up to 2024 terminations. The numbers of BM directly correspond to the
exchange size. COT MAX-L & CDOT MAX-XL can contain maximum 16 & 32 BM
respectively. One BM contains four TUs, one BPU & one TSU. Base Module can be
remotely located as a RSU, parented to the main exchange using PCM links.

Function of BM.

Basic function of BM are-

I. Analog to Digital conversion of all signals on analog subscriber, trunks lines and
interfacing digital trunks.

II. Switching calls between terminals connected to the same BM

III. Communication with the AM via CM for administrative & mtce. functions and
also for call processing functions.

IV. Provision of special circuits for calls processing support e.g. digital tones,
announcements, terminal tester, and MF/DTMF controller etc

V. Provision for local switching & metering in case of RSU application in standalone
mode.

In stand-alone application (i.e. SBM) the BM acts as an independent switching

system & can provide switching of up to 1500 lines & 100 trunks. In such application, it
directly interfaces with the IOM for bulk data storage and operation & maintenance
function. The BM itself carries out the function of the AM. Clock & synchronization is
provided by source within the base module.

BM can be act as a remote switching module & communicate with host exchange
via digital links. Speed of digital link is 2 Mbps. Even when digital links fail between

28
RSU and main exchange, local call processing function will not be affected within the
RSU.

The BM hardware is spread over following type of units.

1. Analogue Terminal Unit – Analogue TU is used for interfacing analogue lines &
trunks & providing special circuits.

2. Digital Terminal Unit - Digital TU is used for interfacing digital trunks.

3. #7 Signaling Unit Module – to support SS7 protocol handlers and some call
processing function for CCS7 calls.

4. ISDN Terminal Unit- To support termination of BRI/PRI interfaces and

implementation of lower layers of DSS1 signaling protocol.

5. Time Switch Unit - TSU used for voice and message switching and provision of
service circuits.

6. Base Processor Unit –BPU used for control message communication and call
processing functions.

Terminal Unit (TU 1)

Terminal Unit (TU 2)

Terminal Unit (TU 3)

Terminal Unit (TU 4)

Base Processor Unit (BPU)

Time Switch Unit (TSU)

29
 Terminal Unit - TU provides interface to ordinary subscribers, CCB subscribers,
PABX subscribers, interexchange analog& digital trunks & Digital links from remote
concentrator or remote BM. One TU can support a maximum of 128 terminals &
employs two TIC (one active & other standby) for managing the processing functions.
Each TU consists of 26 slots. TU frame is equipped with Line circuit cards, TWT cards,
power supply units, E & M four wire trunk cards, Announcement cards lines & trunk
cards & duplicated control cards namely Terminal unit interface cards, TIC cards &
signaling processor cards. Each line card contains eight-termination circuit. The lines &
trunk are offered BORSCHT functions on the Terminal card.

BORSCHT stands for B – battery feed, O – over voltage protection, R – ringing,

S – supervision, C – coding& decoding, H – hybrid & T - testing.

BM also defined the TEN number of subscriber. 2 nd, 3rd, 4th & 5th digit of Terminal
Equipment Number shows Rack No., Frame No., Slot No. & Terminal Circuit No. Of
particular BM respectively. While 1st digit of TEN shows particular BM No. Of
exchange.

BM No. Rack No. Frame No

(1-32) (1-3) (1-6)

Slot No. Termination circuit No.

(1-26) (1-8)

SS7 Signaling Unit Module (SUM)- Any one of the ATU or DTU in a BM can
be replaced by SUM frame to support CCS7 signaling.

ISDN Terminal Unit (ISTU)

One of the four ATUs/DTUs in a BM can be replaced by ISTU to provide

BRI/PRI interface in CDOT DSS. The only constraint is that ISTU has to be principal TU

30
i.e. directly connected to TSU on 8 Mbps PCM link . The ATU/DTU cannot be used in
concentration with ISTU.

BASE PROCESSOR UNIT – BPU is the master controller in the BM. It is used
for

I. Call processing function (call processing subsystem software)

II. Administration function. (Admn subsystem software).

III. Maintenance (mtce subsystem software).

a). Fault detection (Detect faulty unit).

b). Fault localization (locate particular faulty card).

IV. Database – All data available in memory card of BPU.

V. Operating System – Manage all schedules of program.

It is implemented as a duplicated controller with memory unit.

BM-XL is modified at Base Processor shelf to cater for increased BHCA

capacity. The conventional BIC & BID cards are eliminated & only Base Processor
Controller (BPC) card and Base Memory Extender (BME) card having 16 MB memory
are provided in MAX-XL exchange. The power supply card in BPU is KO5. BUT of
BM-XL is implemented as a duplicated 16-bit controller with memory units. These
duplicated sub units are realized in the form of the Base Processor Controller (BPC) &
Base Memory Extender (BME) cards. BPC controls time switching within the BM via the
Base Master Switch and the Time Switch Controller. It communicates with the
Administrative Processor via BMS for operations & maintenance functions. BMS is said
to consist of MSC & MSD card whereas in XL Hardware, BMS consist of HMS card. In
SBM configuration, BPC directly interfaces with the ADP & IOM. Figure 2 summarizes
the various units and sub units of the BM. Nowadays 32MB High Performance Processor
Cards (HPC) used instead of BPC to support 8,00,000 BHCA.
TIME SWITCH UNIT (Figure – 3)– Basic function of TSU are -

31
I. Time Switching within BM

II. Routing of control messages within the Base Module & across Base Modules.
III. Service unit for providing call processing supports services like MF/ DTMF
circuits, answering circuits & tones etc.

Service Unit - Service Unit is integrated around three different cards as Tone
Generator with answering circuit (TGA), Service circuit Interface Controller (SCIC)
&MF/DTMF Controller (MFC) card. MF/DTMF Circuit is implemented by using single
chip, 4- channel digital signal processors. Two MFC cards are grouped to form a terminal
group. Up to four MFC Cards can be equipped. The TGA & two groups of MFCs form
three terminal groups towards service circuit interface.

Base Message Switch - BMS routes the control messages within the BM, across
different BMs & also AM via the CM. It is implemented as a duplicated MSC (16-bit
microprocessor) with six direct HDLC links and the message Switch Device (MSD) card
implementing 16-switched HDLC links. As a unit 22 HDLC channels are implemented
for communication with the Base Processor. Time Switch Controller, SCIC, TIC within
the BM and the four CMS complexes in CM. It acts as a message transfer points between
the Base Processor and these controllers. It receives messages from the Base Processor
and transmits them towards the appropriate controllers.

Time Switch – The Time Switch receives the following PCM links & performs time
switching on them for switching within the BM.
- Four, 128 channel multiplexes from four different Terminal Units.
- One 128-channel multiplex from the service Circuits Interface Controllers.
- Three 128-channel links to support on board three party conference circuits.

It multiplexes these 128 channel links to from 512 channel, 4Mbps multiplexed
bus towards the CM. The individual buses are called Bus 0& Bus1. Besides this it also
provides network switched path for message communication between BMs between BM
& CM.

32
The basic functions of a Base Module:

 Analog to digital conversion of all signals on analog lines and trunks

 Interface to digital trunks and digital subscribers
 Switching the calls between terminals connected to the same Base Module
 Communication with the Administrative Module via the Central Module
for administrative and maintenance functions and also for majority of
inter-BM switching (i.e. call processing) functions
 Provision of special circuits for call processing support e.g. digital tones,
announcements, MF/DTMF senders/receivers

 Provision for local switching and metering in stand alone mode of Remote
Switch Unit as well as in case of Single Base Module Exchange (SBM-
RAX)
For these functions, the Base Module hardware is spread over different types of Units.

(Ref. fig. 3.1)

 Analog Terminal Unit - to interface analog lines/trunks, and providing

special circuits as conference, announcements and terminal tester.
 Digital Terminal Unit - for interfacing digital trunks i.e. 2Mbps E-1/PCM
Links

 #7 Signalling Unit Module - to support SS7 protocol handlers and some

call processing functions for CCS7 calls.
 ISDN Terminal Unit - to support termination of BRI/PRI interfaces and
implementation of lower layers of DSS1 signalling protocol.

 Time Switch Unit - for voice and message switching and provision of
service circuits.
 Base Processor Unit - for control message communication and call
processing functions.

Analog Terminal Unit (ATU)

33
 The Analog Terminal Unit (ATU) is used for interfacing 128 analog terminations
which may be lines or trunks. It consists of terminal cards which may be a combination
of Line Circuit Cards (LCC), CCB with Metering (CCM) cards, Two Wire Trunk (TWT)
cards, E&M Two wire (EMT) Trunk cards and E&M Four wire (EMF) trunk cards,
depending upon the module configuration. Also, provision has been made to equip
Conference (CNF) card to support “six party” conference, Announcement (ANN) to
support 15 user-friendly announcement messages, and Terminal Test Controller (TTC)
for testing of analog terminations. Power Supply Unit (PSU-I) provides logical voltages
and ringing current in the ATU.

Analog Subscriber Line Cards

Two variants of subscriber line cards as LCC or CCM with interfaces upto 8
subscribers, provide basic BORSCHT functions for each line. Analog to digital
conversion is done by per-channel CODEC according to A-law of Pulse Code
Modulation. Each CCM card has the provision of battery reversal for all the 8 lines with
the last two lines having provision to generate 16 KHz metering pulses to be sent to
subscriber's metering equipment.

The 8-bit digital (voice) output of four LCCs is multiplexed to form a 32-channel, 2
Mbps PCM link - also called a terminal group (TG). Since a Terminal Unit has a
maximum of 16 terminal cards, there are four such terminal groups. The signalling
information is separated by a scan/drive logic circuit and is sent to the signalling
processor on four different scan/drive signals. The LCC/CCM also provides test access
relay to isolate the exchange side and line side to test it separately by using the Terminal
Test Controller (TTC).

Analog Trunk Cards

Analog trunk cards interface analog inter-exchange trunks which may be of three
types as TWT, EMT and EMF. These interfaces are similar to Subscriber Line Card, with
only difference that the interfaces are designed to can/drive events on the trunks as per
predefined signalling requirement.

34
Signalling Processor (SP) Card

Signalling Processor (SP) processes the signalling information received from he

terminal cards. This signalling information consists of scan/drive functions like
origination detection, answer detection, digit reception, reversal detection, etc. The
validated events are reported to Terminal Interface Controller for further processing to
relieve itself from real-time intensive functions. Based on the information received from
the Terminal Interface Controller, it also drives the event on the selected terminal through
scan/drive signals.

Terminal Interface Controller (TIC) Card

Terminal Interface Controller (TIC) controls the four terminal groups (TG) of 32
channels, and multiplex them to form a duplicated 128-channel, 8 Mbps link towards the
Time Switch (TS). For signalling information of 128- channels, it communicates with
Signalling Processor (SP) to receive/send the signalling event on analog terminations. It
also uses one of the 64 kbps channel out of 128 channels towards Time Switch, to
communicate with Base Processor Unit (BPU). In concentration mode, three other
Terminal Units share this 128-channel link towards the Time Switch to have 4:1
concentration.

Terminal Interface Controller is built around 8-bit microprocessor with associated

memory and interface and it is duplicated for redundancy.

Special Service Cards

A Terminal Unit has some special service cards such as Conference (CNF) Card
to provide six party conference. Speech samples from five parties are added by inbuilt
logic and sent to the sixth party to achieve conferencing. Terminal Test Controller (TTC)
Card is used to test analog terminal interfaces via the test access relays on the terminal
cards.

35
 Announcement Controller (ANN) Card provides 15 announcements on broadcast
basis. Only one service card of each type is equipped in a Base Module with provision of
fixed slot for TTC and variable slots for CNF/ANNC.

Announcement and Conference Cards are equipped in Terminal Unit through S/W
MMC command. Two slots are occupied by each card i.e. 16 channels for each card is
used out of 128 channels available on a Bus between a TU &TS.

Digital Terminal Unit (DTU)

Digital Terminal Unit (DTU) is used exclusively to interface digital trunks. One
set of Digital Trunk Synchronization (DTS) card along with the Digital Trunk Controller
(DTC) card is used to provide one E-1 interface.
Each interface occupies one TG of 32 channels and four such interfaces share 4
TGs in a Digital Terminal Unit. The functions performed by TIC and SP in Analog
Terminal Unit, are collectively performed by the Terminal Unit Controller (TUC) in the
Digital Terminal Unit. The scan functions are - HDB3 to NRZ code conversion, frame
alignment and reconstitution of the received frame. The drive functions include insertion
of frame alignment pattern and alignment information. Each interface can be configured
as CAS or CCS interface.

36
ISDN - Terminal Unit (ISTU)

One of the four ATUs/ DTUs in a BM can be replaced by ISTU to provide

BRI/PRI interfaces in C-DOT DSS. The only constraint is that ISTU has to be principal
TU i.e. directly connected to TSU on 8 Mbps PCM link. The ATU/DTU cannot be used
in concentration with ISTU. By equipping one ISTU in the exchange, a max. of 256 B
channels are available to the administrator which can be configured as BRI, PRI or any
mix as per site requirement. Depending on the requirement of number of ISDN-
Interfaces, one or more ISTUs can be integrated in C-DOT DSS, either in one BM or
distributed across different BMs.

Time Switch Unit (TSU)

Time Switch Unit (TSU) implements three basic functions as time switching
within the Base Module, routing of control-messages within the Base Module and across
Base Modules and support services like MF/DTMF circuits, answering circuits, tones,
etc. These functions are performed by three different functional units, integrated as time
switch unit in a single frame
Base Processor Unit (BPU)

Base Processor Unit (BPU) is the master controller in the Base Module. It is
implemented as a duplicated controller with memory units. These duplicated sub-units
are realised in the form of the following cards:

 Base Processor Controller (BPC) Card

 Base Memory Extender (BME) Card
BPC controls time switching within the Base Module via the Base Message
Switch and the Time Switch Controller. It communicates with the Administrative
Processor via Base Message Switch for operations and maintenance functions. In a SBM
configuration, BPC directly interfaces with the Alarm Display Panel and the Input Output
Module.

37
 To support 8,00,000 BHCA, the BPC card is replaced by High performance
Processor Card (HPC). It is pin to pin compatible for hardware and also for software so
that they are interchangeable at any site to meet specific traffic requirement.
NOTE: TU CAN BE ATU, DTU, ISTU or #7SU WITH ONLY EXCEPTION THAT
TU-4 SHOULD BE ATU IN CASE OF LINE BM AND ANALOG TRUNK BM

SS7 Signalling Unit Module (SUM)

Any one of the ATU or DTU in a BM can be replaced by SUM frame to support CCS7
signalling. Only one such unit is equipped in the exchange irrespective of its
configuration or capacity. For details of SUM architecture

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
0 1 2
S 3 4 5 6
S 7 8 9 0 1 2 3 4 5 6

P P
P P
T C T T T C
S T T T T T T T T T T T T T T T T S
I / U U I /
U C C C C C C C C C C C C C C C C U
C I I I C I
I I
S S

P P

FIG: 3.1 BASE MODULE (BM) CONFIGURATION

NOTE: 1) TC MAY BE LCC, CCM, TWT or EMF

2) IN CASE OF TU4 AS ATU IN BM, SLOT 24 WILL BE TTC

38
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
0 1 2 3 4 5 6 7 8 9 0 1 2
D 3 4 5 6
P D D D D D D D P
T T T T T
S T T T T T T T S
U U U U S
U S C S C S C C U
C I I C 3
I 0 0 1 1 2 2 3 I

FIG: 3.2A ANALOG TERMINAL UNIT (ATU) CONFIGURATION

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P P 0 1 2 I3 I4 I5 I6 I7 I8 9 0L 1L 2L 3L 4L 5L 6L
L L L L L L L L L
S S T C I I C T C C C C C C C
C C C C C C C C C
U U C C C C C C 1 1 1 1 1 1 1
1 2 3 4 5 6 7 8 9
1 2 0 0 0 1 1 1 0 1 2 3 4 5 6

FIG: 3.2B DIGITAL TERMINAL UNIT (DTU) CONFIGURATION

NOTE: LC MAY BE BRL or PRL CARDS

39
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
0 1
H 2 3 4 5 6
H 7 8 9 0 1 2 3 4 5 6

P P
P P S S S S T T S S S S P P
B C T T C B
S S H H H H U U H H H H S S
M / U U / M
U U M M M M I I M M M M U U
E B C C B E
1 2 1 2 3 4 5 6 7 8 4 3
P P

C C

FIG: 3.2C Istu configuration

NOTE: 1) SHM IS #7 PROTOCOL HANDLER CARD

2) WITH BPC, ONLY SHM 1-4 CAN BE EQUIPPED

3) HPC IS USED TO SUPPORT SHM1-8 CARDS AND HIGHER MESSAGE

PROCESSING CAPABILITY

40
 Fig:3.2d #7su configuration
NOTE: HPC USED TO SUPPORT 800K BHCA

1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P S 0 1 2 3 4 5 6 7 8 9 0 1
S 2 3 4 5
P 6
T M M A M M T T T T T T T T M M A M M T
S C C S
G F F F S S S S S S S S S S S S F F F G
U I I U
A C C B D C I M C S S C M I C D B C C A
II C C II

FIG: 3.2E BASE PROCESSOR UNIT (BPU) CONFIGURATION

NOTE: 1) REPLACE TSS CARDS BY ETS CARDS IN CASE OF REMOTE
BASE MODULES (RSU)

2) MSC AND MSD CARDS ARE REPLACED BY HMS FOR 800K BHCA

4.2 CENTRAL MODULE

The basic function of CM is

I. Bus Termination.

II. Space Switching.

III. Space switching control

IV. Administration

CM is responsible for space –switching have inter modules calls &

communication between BMs & AM. For this function, CM has a space switch, space
switch controller and a central message switch. CM-XL provides connectivity to up to 32

41
BM-XL. Each BM-XL interface with CM-XL via two 512 channel parallel buses each
operating at 4Mbps. It provides control message communication between any BMs for
operation & mtce. Function. It also provides clock & synchronization on a centralized
basis.

Space Switch And Space Switch Controller

MUX cards extract time slots 0& 1 from Bus 0& Bus 1 from the BMs. These
Time Slots carrying control information are simultaneously extracted by the two MUX
Cards for higher reliability. Since each MUX cards receives both Bus 0& Bus 1, it
extracts total 4 time slots. These time slots from each BM are sent to the CMS. The CMS
sends these time slots to the Space Switch Controller on a 128-channel link. The SSC
controls the space switching based upon this information. Space Switch is implemented
on three cards – two MUX Cards & a space Switch card.

Central Message switch

CMS is the central message transfer point of switch. It is implemented as four

different message switches, working in load sharing mode. All CMSs are used for routing
of messages across the Base Modules. On the other hand only CMS1 & CMS2 interface
with the Administrative Processor for routing control message between Base Processors
& Administrative Processor. This communication is used to access office data for routing
inter-module calls and administration and maintenance function.

Bus Termination Unit (BTU)

Space Switching Unit (SSU)

Space Switching Unit (SSU

Bus Termination Unit (BTU

Space Switching Controller Unit (SSCU)

Administration Processor Unit (APU)

42
ADMINISTRATIVE MODULE
AM performs system level resources allocation and processing function on a
centralized basis. It performs all the memory and time intensive call processing support
functions and also administration & maintenance function. AM-XL consists of a
duplicated 16/32-bit controller called the Administrative Processor Controller. It
communicates with Base Processors via the Central Message Switch for control messages
and with the duplicated Input Output Processors in the Input Output Module for
interfacing peripheral devices.

ALARM DISPLAY PANEL

Alarm Display Panel (ADP) is a microprocessor based hardware unit, which is
attached to the BP (in SBM configuration) or AP (in MBM configuration) via HDLC
links for providing audio-visual indication of system faults. It is a three-card
implementation. A matrix of LEDs is provided to indicate the maintenance status of the
switch units and their level of initialization. A seven-segment display shows the count of
links and trunks currently faulty. Keys are provides for manual acknowledgment,
initiating self-test and selective audio disable

43
FIG: 3.2F TIME SWITCH UNIT (TSU) CONFIGURATION

44
4.3 SYSTEM CAPACITY

The capacity of CDOT MAX-XL is defined in terms of the following parameters.

I. The termination capacity as lines & trunks – The CDOT MAX-XL can
support up to 40,000 lines & 5500 trunks or up to 14,500 trunks depending
upon its configuration as local exchange or TAX exchange.
II. The amount of traffic that can be switched – The traffic capacity of CDOT
MAX-XL is up to 8000 erlangs. This figure is based on the ideal traffic of
one erlang / switched circuit. Normally a figure of 0.8E traffic per circuit is
considered to be practical & the above capacities may be reduced
accordingly. Capacities are reduced to not less than 7,500 Erlangs.
III. The number of Busy Hour Call Attempts (BHCA) that can be processed –
Base processor has the capability of handling 12,500 BHCA, which can be
increased to 30,000 using upgraded processor card. The CDOT MAX – XL
exchange with 32 BM handle up to 3,00,000 BHCA. By upgrading the
processor card, it is increased to 8,00,000 BHCA.

45
 Various exchange configuration & their traffic capacities are given in below table.

SN Exchang Configuration Termination capacity BHCA Application

e

1. SBM-L 1BM+2LMs 1500 Lines + 128 8500 Medium size rural

Trunks or 450 Trunks switch.
only

2. MAX-L 16 BMs-L 20,000 Lines + 3,000 1,30,000 Large size

Trunks or 7200 urban/Metropolitan
Trunks only switch

3. SBM-XL 1BM+2LMs 1500 Lines + 128 12,500 Medium size rural

switch.

4. MAX- 32BMs-L 40000 Lines + 6000 3,00,000 Very Large

XL Trunks or 14500 capacity switch for
Trunks only Metropolitan area

5. RSU 1BM- 2000 Lines 12,500 Remotely located

XL+2LMs switch.

46
 4.4 CCS-7 Signaling Feature
Apart from handling CAS schemes, CDOT MAX-XL also supports CCITT (ITU-T)
Signaling System No. (CCS –7). The implementation of Message Transfer Part (MTP) is such
that the C-DOT MAX-XL can function both as a Signaling Point & a Signal Transfer Point. The
STP function does not affect the call handling performance of the switch. Presently, among the
level 4 user parts, the Telephone User Part (TUP) & plain telephony services of ISDN User Part
(ISUP) have been implemented. Later software releases will also incorporate the other features
of ISDN user Part (ISUP), signaling connection Control Part (SCCP), Transaction Capabilities
Application Part (TCAP) etc. as per CCITT (ITU-T) recommendations.

ISDN – FEATURES

The ISDN traffic is of two distinct types

I – Circuit switched voice & data.
II – Packet switched data.
In case of circuit switched voice & data, the traffic is routed through ISDN/PSTN
network. In case of packet switched data, the packet traffic is routed /circuit switched to PSPDN
where packet processing takes place.
In CDOT MAX-XL architecture the ISDN interfaces are terminated on a new add – on
terminal unit as ISTU. A max. of 256 bearer channels are provided by integrating one ISTU,
which can be configured to support any combination of BRI or PRI interfaces. If the requirement
of BRI / PRI interfaces are more than 256 bearer channels one or more ISTUs can be integrated
in CDOT MAX – XL with the option of equipping them in the same BM or distributed across
different BMs in the exchange. One of the ATUs/DTUs in a BM can be replaced by ISTU. The
only constraint is that ISTU has to be principal TU i.e. directly connected to TSU on 8 Mbps
PCM link. The ATU/DTU cannot be used in concentration with ISTU.

In CDOT MAX-XL, the entire PSTN feature available for analog subscriber is also
available to ISDN subscribers.

4.5 RSU Status

39
 Remote Switch Unit is an integral part of CDOT MAX-XL. For connectivity of RSU, the
normal switch can be modified for remote location & communication with the host exchange via
2 mbps digital links.

If ESL card is provided in CM-L one local BM & one RSU can be connected. ESM card
is required for in CM-XL Exchange for connecting remote switch unit. Total 16 numbers of
PSM/ESM cards are provided in copy-1 Base Termination Unit. Hence the number of RSUs is
limited to 16 nos. only in case of remotely located BM. For RSU working a minimum of 4 PCM
s and a max. Of 16 PCMs (2 MB streams) are required. As per the traffic condition and the
number of terminations at RSU the PCM links between the MAX-XL and RSU can be added by
software commands.

REMOTE SWITCH UNIT

Remote Switch Unit (RSU) is an integral part of C-DOT DSS architecture. In order to
realise a RSU, the normal BM can be modified for remoting with the host exchange via 2 Mbps
digital links. The number of 2 Mbps links between the Main Exchange and RSU is primarily
determined by the traffic. A maximum 16 PCMs can be provided between a RSU & Main
exchange. Analog and Digital trunk interfaces are also implemented in RSU to support direct
parenting of small exchanges from RSU itself instead of parenting it to the main exchange which
will ultimately save the media required from main exchange. As far as call processing is
concerned, RSU is an autonomous exchange capable of local-call completion. Operation and
maintenance functions are handled by the host exchange. In the event of failure of PCM links,
RSU goes into standalone mode of operation. In case it is not possible to process a call request
due to unavailability of links to the host, the subscriber is connected to appropriate tone or
announcement.

During standalone mode of operation, the local and incoming terminating calls in RSU
are switched and the metering information of all the RSU subscribers is stored in the RSU. It is
sent to the host whenever the PCM links are available again.

Only the even numbered BMs can be configured as RSU i.e. a maximum 16 RSUs are possible
in C-DOT DSS MAX-XL and 8 RSUs in MAX-L.

TYPES OF APPLICATION

40
The system can be put to the following applications:Replacements

The exchange can serve as replacement of an existing switching system due to be phased
out from the network.

Line service feature

This section relates to various types of lines that the exchange can cater to, and briefly, services
offered to such lines.

ORDINARY LINE

A subscriber may have an ordinary telephone instrument connected to his/her line.

COIN TELEPHONE (CCB LINE)

The system provides a service by means of a special telephone permitting outgoing calls
after insertion of adequate coin(s) or token(s) and incoming calls without payment. The two
classes of service are:
Local-calls within Unit Fee Zone (UFZ) can be made from coin collection box telephone. STD –
from STD coin box telephones, the STD calls and calls to some special services are permitted
(Not available presently).

41
 FIG 1.1
SYSTEM

ARCHITECTURE

42
 Chapter 5
CDOT SYSTEM CAPACITY

43
 5 CDOT SYSTEM CAPACITY

5.1 INTRODUCTION

The capacity of C-DOT DSS is defined in terms of the following parameters:

• .The termination capacity expressed as the number of lines and trunks

• The amount of traffic (in Erlangs) that can be switched

• The number of Busy Hour Call Attempts (BHCA) that can be processed with a given call-mix
while meeting the overall service quality requirements

This section indicates the maximum capacity of different system elements as well as that
of complete exchange, equipped to its ultimate termination capacity. It has been ensured that the
specified parameters are valid to meet overall reliability objectives for the C-DOT DSS as
specified in ITU-T recommendations.

5.2 TERMINATION CAPACITY

A Terminal Card is the basic system element. It interfaces/ terminates the lines and
trunks. The next higher element is a Terminal Unit. The types of terminal cards and terminal
units used in C-DOT DSS along with its functions are explained in H/W description.
Termination capacity of a BM is 488 analog terminals and that of LM is 768 analog terminals. A
BM can be concentrated with 2 LMs to provide maximum termination capacity of 2024 analog
lines. In case of a BM, a maximum of 256 B- channels can be provided for ISDN terminations at
the cost of 128 analog lines. In its maximum configuration of one BM and 2 LMs with
termination capacity of 2024 analog lines, 256 B-channels are provided at the cost of 512 analog
lines. One to one replacement of B-channels is planned in immediate future.

Base Module and Line Module are the highest level of system elements Each Base
Module has four Terminal Units whereas a Line Module has six Terminal Units.

A maximum of 16 BMs can be connected in MAX-L and 32 BMs can be connected in MAX-XL
configurations.

44
Table2.1 summaries the termination capacities of the various system elements of CDOT DSS
MAX.

5.3 EXCHANGE CONFIGURATIONS

C-DOT DSS MAX can be configured to support any combination of lines and trunks. For
different applications in the network as Local Exchange, Local cum Tandem Exchange. Trunk
Automatic Exchange (TAX) or Integrated Local cum Transit (ILT) Exchange.

In its maximum configuration, upto 40,000 lines and 5.500 trunks are supported when
configured as Local/Local cum Tandem. When configured as TAX, 14,500 trunks are supported.

Table 2.1

Termination Capacity of System Elements

Sl System Element Termination Capacity

1 Termination Cards (TC):
LCC – 8 Analog Subscribers
A Analog Line Card
CCM – 8 CCB subscribers with last two ports
B Analog Trunk Card TWT/ EMF16-kHz
supporting – 8 Trunks
metering pulses
C A set of DTS/DTC Cards One 2-Mbps E-1 link as CAS/CCS trunks
D #7 PHC Card (SHM) 8 Protocol Handlers/ Signalling Links
E ISDN-BRI Card 8 BRI (2B+D) Interface i.e. 16 B-channels
F ISDN-PRI Card One PRI (30B+D) Interface i.e. 30 B-channels
2 Terminal Unit (TU):
16 Analog Terminal Cards (LCC/ CCM/ TWT/
A Analog TU (ATU)
EMF) to support any combination of Lines &
Trunks in multiple of 8 terminations
B Digital TU (DTU) Four 2-Mbps E-1 links as CAS/ CCS7
C #7 Signalling Unit Module 64 Nos., #7 Protocol Handlers/signalling links

D (SUM)
ISDN Terminal Unit (ISTU) 256 Bearer Channels to be configured as BRI,
PRI or any combination
3 Base Module (BM):

45
 480 Analog Subscribers. A maximum of 256
A Base Module (Line)
B-Channels for ISDN interface can be
provided at the cost of 128 subscriber lines.
768 Analog subscriber lines. A maximum of
B Line Module (LM)
two LMs connected with BM supports 2024
lines.
C BM (Analog Trunks) 488 Analog Trunks
D BM (Digital Trunks) Fifteen 2-Mbps E-1 links as CAS/ CCS7

E BM (Analog + Digital) Three possible configurations as 360 AT+ 4

PCMs/ 232 AT+ 8 PCMs/ 104 AT+ 12 PCMs

Table-2.2

Termination Capacity of Exchange Configurations

Sl Exchange Configuration Termination Capacity

1,500 Lines & 128 Trunks. The trunks can be
1 Single Base Module (SBM)
analog and/or digital. The number of trunks can be
Multi-Base Module (MBM) (DSSincreased
MAX) at the cost of subscribers.
Ideal configuration to support 40,000 lines and
2
5,500 trunks with 20 Line BMs and 12 Trunk
i) MAX-XL
BMs. The trunk capacity can be increased by 450
at the cost of 2,000 subscribers or vice versa.

Ideal configuration to support 20,000 lines and

2,700 trunks with 10 Line BMs and 6 Trunk BMs.
ii) MAX-L
The trunk capacity can be increased by 450 at the
cost of 2,000 subscribers or vice versa.

3 Remote Switching Unit (RSU) 2,000 subscriber lines. Trunk interface at the cost
of subscriber lines.
4 Multi-Base Module TAX 14,500 Trunks

46
Note: out of the total equipped capacity, a maximum of 30,000 lines may be remote subscribers
through RSUs in MAX-XL whereas 14000 lines may be Remote Subscriber through RSUs in
MAX-L.

5.4 TRAFFIC CARRYING CAPACITY

The traffic carrying capacity of C-DOT DSS MAX is ideally 8000 Erlangs in case of MAX-XL
and 4000 Erlangs in case of MAX-L exchanges.

This figure is based on the ideal traffic of one Erlang per switched circuit. But the actual
traffic carrying capacity of one switched path is always less than one in practical application.
Accordingly capacities are reduced to not less than 7,500Erlangs incase of MAX-XL and to 3800
in case of MAX-L exchanges.

5.5 BHCA HANDLING CAPABILITY

The basic processing elements of the exchange are the Base Processor (in the Base
Module). Base processor has the capability of handling 12,500 Busy Hour Call Attempts which
can be increased to 30,000 using upgraded processor card. The C-DOT DSS MAX (MAX-XL)
exchange with 32 Base Modules can handle upto 3,00,000 BHCA. By upgrading the processor
card in BM/CM/AM/SUM and message switch in all the BMs, it is increased to 8,00,000 BHCA.

In case of MAX-L exchanges with 16 BMs connectivity, the BHCA handling capability is
1,50,000.

Various exchange configurations and their traffic capacities are summarised in Table2.3.

47
 Traffic Capacity of Exchange Configurations

Sl.No. Exchange Configuration Traffic Capacity Description

I. SBM-RAX 250 Erlangs. The BHCA capacity depends on

the type of processor used and it may be 12,500 or

30,000.

2. Remote Switching Unit 250 Erlangs. The BHCA capacity depends on

(RSU) the type of processor used. It may be 12,600 or
30,000.

3. DSS-MAX/TAX Not less than 7,500 Erlangs. The BHCA

i) MAX-XL capacity is more than 3,00,000 and upgradable to

8,00,000 by upgrading only processor cards.

ii) MAX-L Not less than 3800 Erlangs. The BHCA capacityis
1,50,000.

Note: For some of the sites already commissioned with one of the first three configurations,
overall BHCA handling capacity may be lower due to use of old processor cards.

5.6 SYSTEM RELIABILITY

The C-DOT DSS MAX is designed to meet the reliability standards as defined in the
specifications. The system uses fully digital techniques for switching including the subscriber
stage. The system is built using a minimal number of standard units/modules which allow
flexible growth of the exchange and easy upgradation in technology and new features.

A very important feature of C-DOT DSS MAX architecture is the extensive duplication
of units. All controller units are duplicated or have n+1 redundancy. Software design matches the
high degree of redundancy provided by hardware to minimize the system down time.

To minimize failures caused by human and/or software errors the C-DOT DSS MAX has
extensive software maintenance functions. The design of software is such that propagation of
software faults is contained and it provides sufficient checks to monitor the correct functioning
of the system. The facilities are in-built to ensure automatic software recovery on detection of

48
software faults. Whenever a faulty condition occurs the software provides for the isolation of the
faulty subsystem and automatically initiates diagnostic programs for diagnostic purposes. The
diagnostic programs have a design objective of localizing 95 of the faults to a single PCB level
and the rest to a two PCB level. Provision is also made for safety of charge-records. The
charging information is dumped at regular intervals to non-volatile duplicated back-up memories
automatically. The software maintenance functions include data audits as well; as system
integrity monitors and controls.

Alarm Display Panel is provided for a continuous indication of the system status. Audio-visual
alarms are provided.

49
 Chapter 6

SUBSCRIBER FEATURES

6 SUBSCRIBER FEATURES
6.1 INTRODUCTION

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 The C-DOT Digital Switching Systems offer a wide range of telephony features and
supplementary services. Further capabilities can be developed to meet specific customer needs.
Due to mandatory requirement of exchange of messages between the switching systems and
user's equipment, some of the services are exclusively offered to ISDN-subscribers. In case of
few of the services offered to PSTN and ISDN subscribers, the implementation of services to
PSTN subscribers may be partial and invocation procedure may also differ.

6.2 PSTN (ANALOG) AND ISDN SUBSCRIBER SERVICES

The subscriber services provided by C-DOT DSS MAX exchanges for PSTN (Analog) as
well as ISDN subscribers are-explained as per their logical grouping:

Number Identification Services

i) Calling Line Identification Presentation (CLIP)

When this service is subscribed by a user as terminating facility, all the incoming calls are
offered to the user along with the details of calling party's identity.

In exceptional cases as the calling party has subscribed CLIR or interworking constraints in the
network, it will not be possible to provide caller's identity.

ii) Calling Line Identification Restriction (CLIR)

This service is offered to the calling party to restrict presentation of it's number to the
called party. When CLIR is subscribed, the originating exchange notifies the destination
exchange that the calling party's number is not allowed to be presented to the called party. The
terminating local exchange may indicate to the called user that the calling user identity is
unavailable due to restriction.

iii) Calling Line Identification Restriction Override (CLIRO)

Subscriber with CLIRO as terminating facility instead of CLIP, receives the call with the
calling line identification even if the calling party has requested that his (the calling party's)
identification should not b« presented to the called user.

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The CLIRO facility is offered at the discretion of the administration to special category
subscribers like the police, hospitals, operator positions and other emergency centres.

iv) Malicious Call Identification (MCID)

This facility is used for ascertaining the origin of malicious calls. During conversation the
subscriber has to use suitable procedure to notify the exchange about the malicious call. The detail
of the call is recorded in the exchange which can be retrieved later on. If the caller is from an
exchange which does not support identification of calling line, "junction identity" is found and an
"identification request" may be sent to the originating exchange by tee exchange personnel.

6.3 Call Offering Supplementary Services

Call offering services permit the served user to request the network to divert the incoming
calls to a specific number. In call forwarding, the network forwards the call to a pre-registered
number which can be specified by the user or exchange administrator.

i) Call forwarding unconditional (CFU)

This service permits the served user to request the exchange to forward all incoming calls
to other Number. The served user's originating service remains unaffected. The other number
could be a fixed pre-determined number or a number specified by the subscriber in the activation
request.

52
Call Forwarding Busy (CFB)
This service permits the served user to request the exchange to forward all incoming calls to
other number if the served users number is not free. The served user's originating service remains
unaffected.
iii) Call forwarding no reply (CFNR)
This service permits the served user to request the exchange to forward all incoming calls which
are not replied with in ring timeout period. The served user's originating service remains
unaffected.

6.4 Call Completion Services

i) Call Waiting

A subscriber engaged in an existing call, is given an indication (Call Waiting tone or ZIP
tone) that another caller is attempting to connect to his number. The caller will hear ring back
tone. By flashing the hook-switch the called subscriber can talk with either party while keeping
the other on hold (acceptance without clearing). If the called subscriber replaces his handset in
response to the tone (acceptance by clearing), the exchange will automatically extend ring to the
subscriber and re-establish the connection on answer with the party waiting.

ii) Call Hold

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 This facility is used by the user to put the existing conversation on hold for the time being
and initiate a new call or receive a call in waiting. The call, which has been put on hold, is
retrieved by the user as and when it is required. The procedure of invocation to put the
conversation on hold and its subsequent retrieval is different for ISDN and PSTN subscribers.

6.5 Multi-Party Services

i) Three party conference
The three party call service enables the served user to establish, participate in, and control a
simultaneous communication involving the served user and two other parties. The served user
can request to convert two party conversation into a three party conference. During the three
party conversation, the served user can disconnect one party, disconnect the 3-way conversation
or choose to communicate privately with one of the parties, in which case the call to the other
party is held.
ii) Multi party conference (Add-on conference)
The CONF (Add-on conference) service enables the served user to establish and control a
conference i.e. a simultaneous communication, involving of users (max. up to 6).

When the CONF service is invoked, the serving local exchange allocates conference
resources to the served user and add any existing call indicated by the served user to the
conference. On successful invocation of conference the served user becomes the 'conference
controller'. The conference Controller may then add, drop, isolate, and reattach parties from the
conference. The conference controller can also hold and retrieve the conference (e.g. to add
parties) and finally end the conference.

6.6 Miscellaneous Services

i. Hot Line (Timed)

This service is also referred as a Fixed Destination Call with Time-out. This allows a
subscriber to establish calls to a pre-registered number. After getting dial tone, if the subscriber
does not dial any digit for a specified minimum time, he is automatically connected to the
number already registered in the system. If subscriber dials digits before the time-out, a normal
connection is established in accordance with the dialled digits. Incoming calls are not affected by
this service.

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ii. Hot Line (Without Time-out)
This service is also referred a Fixed Destination Call - Immediate. This allows a
subscriber to establish calls to a pre-registered number by just lifting the handset. In this service
such a connection is set up immediately upon lifting the handset, hence the subscriber cannot dial
normal outgoing calls. Incoming calls are not affected by this service.
iii. Reminder Call/ Alarm Services
When this service is activated, the subscriber is offered a call initiated by the exchange at
a specified time/s. When the alarm call matures and is answered an announcement follows to
notify the alarm call.
This service is available in two forms:

(i) In semiautomatic form, the booking is manual through exchange operator and the
execution is automatic. In this case, the operator needs to be 'local' operator,
connected to the system via a VDU
(ii) (ii) In automatic form, the booking is done automatically by the subscriber through a
control procedure and its execution is also automatic.
iv. Subscriber Controlled Call Restriction Services
Denying all calls to a line, while allowing it to originate calls as per current access level,
Denying various level of originations from a line (no ISD calls, no STD and ISD calls, only local
calls and selected Level I services, etc.) while allowing incoming calls to terminate normally on
it.

Subscriber controlled barring offers flexibility to a subscriber to change outgoing restriction by

selecting one access level, using predefined procedure through secret password. To maintain the
secrecy of the password, the user can modify the password by using predefined procedure.

v. Intrusion Barring Service

For reasons of call security in terms of fully undisturbed call, subscriber can avail of
intrusion barring facility. This can be useful, for example, when data transmission is being
effected on the line.
vi. Dialling by Terminal Equipment Number
Sometimes, a specific line/trunk, tone or announcement is to be accessed by its Terminal
Equipment Number (TEN) in the exchange. This is specifically required for dialling to lines

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 which do not have a directory number w in case of "directed calls" via outgoing trunks. This
facility is used by the maintenance personnel as part of routine maintenance activities.
vii. Trunk Offer
This service makes it possible for the operator to interrupt a call in progress, in order to
allow another incoming call to be offered. The choice of accepting or rejecting the new call rests
with the subscriber.

viii. Queuing Service

This enables the subscriber to have one or more calls placed in a queue when his
line/group of lines are busy. When the subscriber line becomes free, the first caller in the queue
is connected and the other callers in the queue move one place ahead.
ix. Priority Subscriber
During overload and network congestion, priority service assures an improved service
level for priority subscribers such as those responsible for maintenance of law and order or
essential services. The priority subscribers are served even during overload due to heavy traffic
in the exchange via alternate group of trunks. A few trunks may be identified for this purpose
which are exclusively used by priority subscribers while normal subscribers are denied access to
them. The eligibility of priority subscribers for an alternate group of trunks is programmed by the
exchange administrator.
x. Distinctive Ringing for Long Distance Calls
The PSTN subscribers are connected different ringing cadence to inform them that this
call is a long distance STD/ISD call.

XI Basic Services

- Subscriber can dial local, national, international calls.

- Push button dialing services provided to subscribers to use push button telephone sets
employing DTMF signals.
- Coin collecting Box lines are provided.
- Number Identification service (Calling line identification presentation, Calling line
identification restriction & Calling line identification restriction override)
- Call forwarding facilities.
- Multi- Party (conference) services

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- ISDN Supplementary services.
XII OTHER SERVICES.

- Hot line Timed & without timed out services.

- Morning alarm facility.
- Call restriction services.
- Call forwarding facility.
- Conference facility.
- Malicious call identification facility.

interactive man-machine interface.

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 Chapter 7
Software Architecture

7 Software Architecture

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7.1 INTRODUCTION
The software architecture of C-DOT DSS MAX is distributed in nature and has
been designed to map onto the distributed control architecture of the system. The
switch hardware is surrounded by a number of software layers, each of which
presents higher levels of abstractions for the successive upper layers of software.
The major design objectives of the C-DOT DSS MAX software and the strategies
employed to achieve them are :
Simplicity : Layered architecture, loosely coupled modules, and well defined
message interfaces between modules.
Maintainability : Use of high-level programming language, proper
documentation, and modular design. Increased reliability due to fault-tolerant
software with automatic audits and recovery.
Efficiency : Time-critical processes coded in assembly-level language and very
strict checks on execution-times of all software modules.

7.2 SOFTWARE ARCHITECTURE OVERVIEW

C-DOT DSS MAX software is divided into a number of subsystems. Each subsystem
consists of a number of modules which are called 'processes'. A process consists of a
number of functions which are the smallest units in the software hierarchy.
Processes
There are two types of processes in the system. Eternal processes are created
at the time of system initialization and remain alive throughout the life of
the system. Dynamic processes, on the other hand, are created whenever an
event requiring the services of that particular type of process occurs. After
processing the input, the process dies whenever the logical chain of events
come to an end. While only one instance of an eternal process can be active
within a processor at one time, multiple instances of a dynamic process may
exist at a given time in a processor.
For example, the Status Control Process (SCP) gets a seizure on a particular
terminal and does subsequent processing. After validating the ori originating calls are allowed
from the terminal, SCP creates an Originating

59
Terminal Process (OTP) which manages the terminal till the termination of
the call and then kills itself. While there will be only one SCP in the
processor, the number of OTPs will be equal to the number of terminals in
the call set-up phase at any moment.
Software Subsystems
The main subsystems of C-DOT DSS MAX software are (Figure 5.1):
1. C-DOT Real-Time Operating System (CDOS)
2. Peripheral Processors Subsystem
3. Call Processing Subsystem
4. Maintenance Subsystem
5. Administration Subsystem
6. Database Subsystem
7. Input Output Processor (IOP) Subsystem

7.3 C-DOT REAL TIME OPERATING SYSTEM (CDOS)

The operating system is primarily responsible for the following functions and
services (Figure 5.2) :
Management of Processes
Synchronisation and Communication between Process
Time Management
Interrupt Handling
Resource Management
Memory Management
Online and Offline Debugging Facility
The operating system has been designed to minimise the overheads in terms of realtime. Each set
of primitives has a number of options through which additional
information can be passed on for synchronization and mutual exclusion.
In the distributed architecture of C-DOT DSS MAX, one of the important roles
played by the CDOS is to provide an effective interprocess communication between
processes residing in the same or different processors. A sender process is
transparent to the fact whether the destination process resides in the same or

60
different processor. For communication between processors, CDOS makes use of
C.85 protocol which utilises the HDLC based message network between processors played by
the CDOS is to provide an effective interprocess communication between
processes residing in the same or different processors. A sender process is
transparent to the fact whether the destination process resides in the same or
different processor. For communication between processors, CDOS makes use of
C.85 protocol which utilises the HDLC based message network between processors
Peripheral Processor Subsystem
The telephony software for handling lines, trunks, and service circuits is
controlled by the Peripheral Processors. These are 8-bit microprocessors
programmed in assembly-level language. The main activity of the telephony
software is to detect events and communicate them to the Base Processor
where logical call handling is done. The Peripheral Processors also carry out
the commands given by the Base Processor for generating suitable telephony
events on the outgoing lines and trunks.
Events like line seizure, answer, disconnection, and signalling information
between exchanges, etc., are examples of telephony events which are
processed by the Peripheral Processors. These events are converted into a set
of pre-defined messages which are sent to the Base Processor for subsequent
processing. Transmission of ringing current, outpulsing of decadic digits on a
junction and sending MF signals on junctions are some of the examples of the
events which are created by the Peripheral Processors under the control of
the Base Processor and sent on the outgoing external lines and trunks.
Another important function of Peripheral Processors is to carry out all the
maintenance related test functions on hardware. Peripheral Processors
operate test functions to be used by the maintenance software resident in the
Base Processor.
Since the firmware of the peripheral processors must be real-time sensitive,
it is programmed in assembly-level language and fused into EPROMs. The
firmware along with the hardware provides a higher logical view to the other
software subsystems and effectively insulates the hardware details from the

61
application programs.
Call Processing Subsystem
The Call Processing software subsystem receives the information about
of the cases). After fault repair, validation of the newly replaced card is
carried out before it is brought back in service. High degree of redundancy
provided by the architecture is fully exploited to keep the down-time to a
minimum. Reconfiguration is done with minimal disturbance to the
subscriber. Switch maintenance also ensures periodic automatic tests on all
the switch units.
Terminal Maintenance
Terminal Maintenance involves fault detection, fault reporting, and testing of
all the subscriber lines and trunks. Terminal Test Controller (TTC) performs
tests on the external lines and trunks as well as on the line and trunk
interface circuits within the exchange. Service circuits are also routined
periodically and faults are isolated through minimal human interface.
Human Interface
Human Interface provides man-machines communication between the
operator and the system. It supports the maintenance commands that are
given by the operator. Human interface also displays alarms via Output
Outside Dialogue (OOD) terminal and the Alarm Display Panel (ADP), and
prints maintenance reports that are generated as a result of tests, audits,
and diagnostics.
Administration Subsystem
Administration subsystem consists of traffic, billing, exchange performance
measurement, and human interface functions. It also provides online
software patching capability.
Administration subsystem is responsible for maintaining a large number of
traffic records on the basis of the information received it through Call Event
Records and a large number of traffic-related commands. Similarly, the
Traffic and Exchange Measurement Process correlates a number of these
traffic records and generates reports on the overall exchange performance.

62
These reports are extremely useful in monitoring the health of the exchange
and for network planning.
Billing processes provide billing records and itemised/detailed billing
information for local and trunk calls. Detailed Billing Records are made by
default for all Regional (level '90’), STD and ISD calls. Detailed billing
records for local calls are provided for subscribers under local billing
observation. If the exchange is used as a leading TAX, Centralised Automatic
Message Accounting (CAMA) can be easily incorporated, provided the
signalling supports the required information flow from the originating
exchanges.
The exchange is connected with a number of VDUs for providing the human
interface. Man-machine communication is extremely user- friendly and
provides a large number of forms and menus for carrying out exchange
management functions. Over 200 man-machine commands are provided for
exchange operation, administration, and maintenance functions.
Database Subsystem
The management of global data, i.e., the data shared between various
applications and processes, is done by the Database subsystem. The
objectives of this subsystems are :
♦Easy Access : Database software provides uniform and easy access to the
database. This access is independent of the data as well as the application
to be accessed.
♦Quick Access : Quick access to data is ensured by structuring the data as
arrays and using indexing for accessing them. This is specially required
for real time sensitive application programs such as call processing
processes.
♦Transparency : Database software subsystem makes the application
programmer transparent to the actual data structures and data
organization. Thus, a change in data structures or data organisation does
not force a change in the application program.
♦Consistency : In order to satisfy real time applications, the database

63
cannot be totally non-redundant. Thus, in order to provide quick access to
duplicated data items, the database software maintains consistency
between these duplicated data items.
♦Security : Database subsystem keeps the database "locked" to protect it
against possible corruption.
♦Synchronization : In a multi-process environment, special care needs to
be taken to maintain data consistency at the end of multiple updations of
processes. This synchronization is provided by the database software
subsystem.
Keeping these objectives in mind, physical data is organized as global data
structures and resou Access Routines (DBARs). Global data structures are maintained on
terminal-related data (fixed office data and extended office data) and
centralised routing and translation tables. In addition, linked lists on free
global and local resources and a reference memory for unprotected terminal
status data are maintained.
Input Output Processor Subsystem
Input Output Processor (IOP) subsystem uses UNIX as the basic operating
system. IOP software subsystem is structured as a layer above UNIX and
comprises of the following parts as shown in fig. 5.5.
♦Command Interpretation Layer : A topmost layer, like a shell, to
receive, validate, and execute operator commands
♦Administration Software : A layer above UNIX which provides the
man-machine interface.
♦Maintenance Software : Used for initializing communication protocol
with C-DOT DSS MAX. It also provides software for synchronization of
duplex Input Output Processor.
The functions of IOP software subsystem in C-DOT DSS MAX are -
downloading and initialization, performance measurement of processes,
provision of man-machine interface and handling billing, traffic and
maintenance reports, etc.

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 7.4 CCS7 CALL PROCESSING
Building upon the discussion on the SUM architecture in the last chapter, the
hardware - software interactions are illustrated with the help of ISUP handling
procedure.
In C-DOT DSS MAX, ISUP call processing is different from that of PSTN calls
because the SUM hardware and software have to participate in call handling. Apart
from this, the general philosophy of call processing remains the same.
The Message Handler MH incorporates certain terminal handling functions for this
purpose. Outgoing CCS7 messages received from any Base Module are routed on
appropriate external signalling links as per the Destination Point Code (DPC) and
Signalling Link Selection (SLS) fields. Transfer messages are routed from any
incoming CCS7 signalling link to an appropriate outgoing CCS7 signalling link as
per DPC and SLS fields. The MH does the necessary protocol conversion and format
translation while routing incoming and outgoing CCS7 messages between Base
Modules and external signalling links. The message discrimination and routing
functions of MH is implemented on the 68302 processors in PHC. MH also acts as a
router for internal messages between 7CPU and other modules in the switch over
the C.85 channels.
The Signalling Network Management (SNM) function, consists of signalling link
management (link activation, deactivation, inhibition, blocking, etc.), signalling
traffic management (changeover, changeback, rerouting, etc.) and signalling route
management (transfer allowed, transfer prohibited, etc.). For connecting a protocol
handler or a signaling terminal in SUM to an external signaling data link towards
the network, the SNM takes help of maintenance software in the home BP for
getting the required paths nailed up. The maintenance software is also involved in
nailing up of internal message channels (C.85) in case of power on or any other level
of initialisation.
Application software (including protocol software, maintenance software and
administration software) resident in the SUM, runs on CDOS operating system In the following
sections, the process of handling an ISUP incoming- terminating
call and an ISUP transit call is described. Originating - outgoing call flow is

65
Essentially similar to the incoming - terminating call flow.
The discussion in subsequent sections is based upon the signalling message
sequence depicted in Fig. 5.6 and 5.7 and exchanged during the handling of a
successful and unsuccessful ISUP call.rce tables and the global data is accessed via Data Base
telephony events that occur outside the exchange. It processes this incoming
information and gives commands to the Peripheral Processors for
interconnecting subscribers through the switching network.
The Call Processing subsystem is divided into a number of eternal and
dynamic processes. The processing of a call is done on a 'half-call basis', i.e.,
corresponding to an originating terminal, an Originating Terminal Process
(OTP) is created. Similarly, corresponding to a terminating terminal, a
Terminating Terminal Process (TTP) is created. To supervise these two
processes, a Call Manager (CMR) is created on a per-call basis. Different
combinations of originating and terminating terminal processes enable the
system to handle local, outgoing, incoming, and transit calls. Figure 5.4
shows the processes involved in handling a call in a Multi Base Module
(MBM) configuration. Feature handling is done at the Call Manager level. Routing is handled by
Global Routing and Resource Allocation Process
(GRRA) and path allocation is done by Global Path Control (GPC) process. In
Single Base Module (SBM) configuration, GPC is not present. All access to
the data are made through Data Base Access Routines (DBARs). A special
feature of the Call Processing software subsystem is generation of an
exhaustive Call Event Record (CER) on every call. This Call Event Record
contains the complete detail of a call and is sent to the Administration
Software subsystem, at the termination of the call. The Administration
subsystem, in turn, processes the Call Event Records for extracting billing
and traffic related information in the form of reports. In case the call involves
a terminal under observation, a Call Detail Record (CDR) is also generated.
Maintenance Subsystem
The Maintenance software subsystem is responsible for the following major
functions:

66
♦Initialisation
♦System integrity
♦Switch maintenance
♦Terminal maintenance
♦Human interface
Initialisation
Initialisation consists of loading code and data from the IOP onto the System.
During initialisation, the Administrative Processor (AP) (under the control of
EPROM-based routines) establishes communication with the Initialisation
Process (IOPI) in the IOP. IOPI reads code files from the disk and transmits
them to AP. Base Processor code is broadcast to all the Base Processors in the
system through the Central Message Switch. However, since data files differ
from one Base Processor to another, they are loaded sequentially. Five levels
of initialisation are offered ranging from initialisation without the dislocation
of the single call stable upto higher and higher levels till the entire system is
cleared-up and reloaded.
System Integrity
When all the subsystems are performing normally, they keep sending
periodic sanity messages to the Base Processors. All Base Processors in turn
Keep sending messages to the Administrative Processor. Loss of sanity of a
processor is detected within a very short period of time and corrective action
(e.g., reconfiguration) is taken immediately. The most important activity
under System Integrity is to keep a check on the general integrity of the
system and to keep the system sane by resorting to the appropriate level of
initialisation. The integrity is checked by periodic and idle-time audits and also by the numerous
defensive checks built into the application processes
themselves.

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 Chapter 8

IMPORTANT COMMANDS

8 IMPORTANT COMMANDS
DISPL-SUB to display subscriber details

68
CRE-SUB to creating subscribers

DEL-SUB to deleting subscribers

DISPL-SUB-LIST to display subscriber list

DISPL-DIRNO-RSRV to display the reserved directory numbers

DISPL-DIRNO to display directory number for given status

MOD-LIN-CHAR to modify characteristics of line

MOD-LIN-STA to modify line status of a line

MOD–SUB- TEN to modify subscriber terminal equipment number

MOD-SUB-FAC to modify subscriber facility

FRC-SWU-OOS force switch unit out of service

FRC-SWU-INS force switch unit in service

DGN-SWU to diagnosis switch unit

MOD-SUB-CHAR to modify subscriber characteristics

FRC-TRM-INS to force terminal inservice

FRC-TRM-OOS to force terminal out of service

DISPL-MOD-STATUS to display module status

DISPL-MOD-INFO to display module information

DISPL-SWU-STATUS to display switching unit status

CHG-OUT-DEV to change out device

Chapter 9
Diagnosis reports

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