Documentation

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 ENGINEERINGBY

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.snehalathaAssnt.professor

(signature)

E.NAGABHUSHANAMProfessor 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

4

TABLE OF CONTENTS

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

5

Chapter 5.CDOT capacity 43

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

6

Chapter 9. Diagnosis reports 70

7

ABSTRACT

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

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Chapter 1

Introduction to switching

1 Introduction to switching

1.1switch

9

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

‘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.

10

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

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.

11

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.

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

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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

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

13

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.

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

14

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

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

15

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.

16

Chapter 2

Principles of electronic exchange

2 PRINCIPLS OF ELECTRONIC EXCHANGE

17

Telephone exchange

Terminating equipment Switching equipment

Analog Digital

Space switch Time switch

2.1 Main blocks

Power(battery)

18

switch

Store forawrdcircuit

Message Packet

datagravirtual

Power plant

Engine alternator

Mdf

Switch

OMC(operation & maintenance control)

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

19

Limited availability

ELECTRONIC EXECHANGE

Its Program based exechange

Uses stored program controller

Block diagram:

2.4 TERMINAL EQUIPMENT

Physical termination usually consists of the fallowing operations

B-battery feed

20

Switching networkTerminal equipment

Command control equipment

Input/output peripherals

O-over voltage protection

R-ringing

S-super vision

C-coding

H-hybrid

T-testing

21

Chapter 3

CDOT MAX-XL

3 C-DOT MAX-XL

3.1 GENERAL

22

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

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

23

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,

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.

24

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.

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

25

Thus, a C-DOT DSS exchange, depending upon its size and application, consists

of Base Modules (maximum 32), Central Module, Administrative Module, Input/Output

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. 2nd, 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.

33

Analog Terminal Unit (ATU)

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

34

only difference that the interfaces are designed to can/drive events on the trunks as per

predefined signalling requirement.

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

0

1

1

12 1

3

14 1

5

16 1

7

1

8

1

9

2

0

21 2

2

2

3

2

4

2

5

2

6

P

S

U

I

T

C

T

C

T

C

T

C

T

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T

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T

C

T

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T

I

C

S

P

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/

I

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P

T

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T

U

I

T

I

C

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/

I

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P

T

C

T

C

T

C

T

C

T

C

T

C

T

C

T

C

P

S

U

I

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

0

1

1

1

2

1

3

14 1

5

1

6

1

7

1

8

1

9

2

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2

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23 2

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T

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0

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T

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1

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T

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1

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I

T

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I

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U

C

D

T

S

2

D

T

C

2

D

T

S

3

D

T

C

3

P

S

U

I

FIG: 3.2A ANALOG TERMINAL UNIT (ATU) CONFIGURATION

1 2 3 4 5 6 7 8 9 1

0

1

1

12 1

3

14 1

5

16 1

7

1

8

19 2

0

21 2

2

23 2

4

2

5

2

6P

S

U

1

P

S

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2

L

C

1

L

C

2

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C

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L

C

4

L

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5

L

C

6

L

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7

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I

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1

L

C

9

L

C

1

0

L

C

11

L

C

1

2

L

C

13

L

C

1

4

L

C

1

5

L

C

1

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 10 1

1

1

2

1

3

14 1

5

1

6

1

7

1

8

19 2

0

2

1

2

2

23 2

4

2

5

2

6

P

S

U

1

P

S

U

2

B

M

E

S

H

M

1

S

H

M

2

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H

M

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H

M

4

H

P

C

/

B

P

C

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C

T

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I

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U

I

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C

H

P

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/

B

P

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H

M

5

S

H

M

6

S

H

M

7

S

H

M

8

B

M

E

P

S

U

4

P

S

U

3

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

1 2 3 4 5 6 7 8 9 1

0

1

1

1

2

1

3

1

4

1

5

16 1

7

1

8

1

9

2

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1

2

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3

24 2

5

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II

B

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H

P

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/

B

P

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H

P

C

/

B

P

C

B

M

E

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U

II

Fig:3.2d #7su configuration

NOTE: HPC USED TO SUPPORT 800K BHCA

1 2 3 4 5 6 7 8 9 10 1

1

12 1

3

1

4

1

5

1

6

1

7

18 1

9

2

0

21 2

2

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4

2

5

2

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A

M

F

C

M

F

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T

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A

F

B

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F

C

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F

C

T

G

A

P

S

U

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

41

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

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

42

& 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)

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

e

Configuration Termination capacity BHCA Application

1. SBM-L 1BM+2LMs 1500 Lines + 128

Trunks or 450 Trunks

only

8500 Medium size rural

switch.

2. MAX-L 16 BMs-L 20,000 Lines + 3,000

Trunks or 7200

Trunks only

1,30,000 Large size

urban/Metropolitan

switch

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

switch.

4. MAX-

XL

32BMs-L 40000 Lines + 6000

Trunks or 14500

Trunks only

3,00,000 Very Large

capacity switch for

Metropolitan area

5. RSU 1BM-

XL+2LMs

2000 Lines 12,500 Remotely located

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

SYSTEM

ARCHITECTURE

FIG 1.1

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):

A Analog Line CardLCC – 8 Analog Subscribers

CCM – 8 CCB subscribers with last two ports

supporting 16-kHz metering pulsesB Analog Trunk Card TWT/ EMF – 8 Trunks

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):

A Analog TU (ATU)16 Analog Terminal Cards (LCC/ CCM/ TWT/

EMF) to support any combination of Lines &

Trunks in multiple of 8 terminationsB Digital TU (DTU) Four 2-Mbps E-1 links as CAS/ CCS7

C #7 Signalling Unit Module

(SUM)

64 Nos., #7 Protocol Handlers/signalling links

D ISDN Terminal Unit (ISTU) 256 Bearer Channels to be configured as BRI,

PRI or any combination3 Base Module (BM):

45

A Base Module (Line)480 Analog Subscribers. A maximum of 256

B-Channels for ISDN interface can be

provided at the cost of 128 subscriber lines.

B Line Module (LM)768 Analog subscriber lines. A maximum of

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 Single Base Module (SBM) 1,500 Lines & 128 Trunks. The trunks can be

analog and/or digital. The number of trunks can be

increased at the cost of subscribers.

2

Multi-Base Module (MBM) (DSS MAX)

i) MAX-XL

Ideal configuration to support 40,000 lines and

5,500 trunks with 20 Line BMs and 12 Trunk

BMs. The trunk capacity can be increased by 450

at the cost of 2,000 subscribers or vice versa.

ii) MAX-L

Ideal configuration to support 20,000 lines and

2,700 trunks with 10 Line BMs and 6 Trunk BMs.

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

(RSU)

250 Erlangs. The BHCA capacity depends on

the type of processor used. It may be 12,600 or

30,000.

3. DSS-MAX/TAX

i) MAX-XL

Not less than 7,500 Erlangs. The BHCA

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

48

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

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

50

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.

51

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

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.

53

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.

ii. Hot Line (Without Time-out)

54

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

55

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

56

- 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.

57

Chapter 7

Software Architecture

7 Software Architecture

58

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.

64

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.

67

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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