BSNL Training Report Insights

2015
Ojas Maheshwari
R.No – 0915EC121050
Branch – Electronics &
Communication
IITM Gwalior
BSNL TRAINING REPORT
BSNL,Transport Nagar, Gwalior

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PREFACE
Practical training in an industry is an essential part of an engineering curriculum towards
making a successful engineer, as in an industry only a student can realize the theory thought in
classroom and it also gives an exposure to modern technology.
In the field of Electronics Computer engineering there has been rapid development to
support the ever increasing volume information, so Electronics students has an opportunity
during Training period to knowledge about the latest technologies.
The training period of 30 days is not much sufficient to take complete knowledge of
technology used but one is expected to identify components, the process flow in an industry for
high efficiency and about the knowledge of product technology.
Practical knowledge means the visualization of the knowledge, which we read in books.
For this we perform experiments and get observations. Practical knowledge is very important in
every field. One must be familiar with the problems related to that field so that we may solve
them and became successful person.
After achieving the proper goal of life an Engineer has to enter in professional life. According to
this life he has to serve an industry, may be public or private sector or self-own. For the efficient
work in the field he must be well aware of practical knowledge as well as theoretical knowledge.
To be a good Engineer, one must be aware of the industrial environment & must know about
management, working in industry, labor problems etc., so we can tackle them successfully.
Due to all the above reasons & to bridge the gap between theory and practical, our engineering
curriculum provides a practical training course of 30 days. During this period a student in
industry and gets all type of experience and knowledge about the working and maintenance of
various types of machinery.
Since time immemorial, a man has tried hard to bring the world as close to himself as
possible. His thirst for information is hard to quench so he has continuously tried to develop
new technologies, which have helped to reach the objective.

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The world we see today is a result of the continuous research in the field of
communication, which started with the invention of telephone by Graham Bell to the current
avatar as we see in the form INTERNET and mobile phones. All these technologies have come to
existence because man continued its endeavor towards the objective.
This project report of mine, STUDY OF TRENDS TECHNOLOGIES IN COMMUNICATION
AND NETWORKING has been a small effort in reviewing the trends technologies prevailing. For
this purpose, no organization other than BAHRAT SANCHAR NIGAM LIMITED could have been a
better choice.
I have undergone by 30days of training at BHARAT SANCHAR NIGAM LIMITED, Transport
Nagar, Gwalior (M.P.) This report has been prepared on the basis of the knowledge which I
acquired during my 30days (5-06-2015 to 5-07-2015) training at Company.

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Acknowledgement:-
Practical training has an important role in a shaping up an engineering student for
practical knowledge how a keeping him update with latest technology. First of all, I would like
to express my attitude towards Mr. Shashank Jain (Training , IITM,Gwalior) and towards Mr.
Ashish Garg (H.O.D., Electronics department,IITM,Gwalior) for providing me a great
opportunity to undertake training at BSNL, Gwalior.
I would also like to thanks to Mr.Devendra Gurjar and the co-operative management
helpful staff for giving me a knowledge of their services and helping me time to time.
Last but not least I would like to thanks to training incharge Mr. A.K. Gupta (SDE SDOP)
BSNL ,Gwalior for arranging the training programmer for my practical training.
With extreme regards and obligations.

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CONTENTS: -
1) INTRODUCTION
2) COMPANY PROFILE
3) PROFILE OF THE COMPANY’S BUSINESS
A. GLIMPES OF MAIN SERVICE OFFERED
i. BASIC AND LIMITED MOBILE TELEPHONE SERVICES
ii. CELLULAR MOBILE TELEPHONE SERVICES
iii. INTERNET SERVICES
iv. INTELLIGENT NETWORK
v. THIRD GENERATION 3G WIRELESS TECHNOLOGY
4) STRUCTURE AND ABOUT THE EXCHANGES
i. COMPUTER UNIT
ii. POWER PLANT
iii. AC Plant (CENTRAL AIR CONDITIONER)
iv. MDF (MAIN DISTRIBUTION FRAME)
5) CONNECTING SYSTEM
6) C-DOT EXCHANGE
1. GENERAL INTRODUCTION
2. SYSTEM ARCHITECTURE
3. BASIC MODULE
4. GENERAL FEATURES

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7) OCB 283 EXCHANGE
1. SYSTEM DESCRIPTION
2. SALIENT FEATURES
3. HARDWARE ARCHITECTURE
8) EWSD EXCHANGE
5. GENERAL OVERVIEW
6. INTRODUCTION OF EWSD
7. FUNCTIONAL BLOCK DIAGRAM OF EWSD
8. GENERAL FEATURES
9. SWITCHING NETWORK (B)
10. INTERCONECTIONS OF SWITHING MODULE
11. SWITCHING TECHNIQUES
9) INTERNET
10) CELLULAR MOBILE SERVICES
1. WLL (WIRE LESS IN LOCAL LOOP) MOBILE
2. CODE DIVISION MULTIPLE ACCESS (CDMA) MOBILE
3. GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM)
4. THIRD GENERATION (3G) TECHNOLOGY
11) CONCLUSION
12) GLOSSARY OF TERMS AND ABBREVIATIONS

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Introduction:-
Today, BSNL is the No. 1 telecommunication company and the largest public sector
undertaking of India and its responsibilities includes improvement of the already impeccable
quality of telecom services, expansion of telecom services in all villages and instilling confidence
among its customers.
Apart from vast network expansions, especial emphasis has given for introducing latest
technologies and new services like I-NET, INTERNET, ISDN (INTEGRATED SERVICES DIGITAL
NETWORK), IN (INTELLIGENT NETWORK), CDMA, GSM and WLL (WIRELESS IN LOCAL LOOP),
BROADBAND, 3G services etc. Now BSNL has also entered in mobile communication. BSNL has
all the new services send technological advantages, which are available with any well,
developed Telecom network anywhere else in the country.
Full credit for all above achievement goes to the officers and staff of the BSNL. The
administration is fully aware of the challenges lying ahead and quite committed to provide the
latest and best telecom services by their continued support and active co-operation.

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COMPANY PROFILE
BHARAT SANCHAR NIGAM LIMITED
Bharat Sanchar Nigam Limited (BSNL) is India's leading telecommunications provider and the
country's largest public-sector firm. BSNL provides local-exchange access and domestic long-distance
services through a network of more than 45 million access lines covering most of India. It also offers
wireless communications, data and Internet services, as well as business voice and data services. The
company is still controlled by the government, as is one of India's other large phone companies,
Mahanagar Telephone Nigam Limited (MTNL). Plans to merge the two companies have been discussed
but seem to be on hold.
HIGHLIGHTS
 Bharat Sanchar Nigam Limited has a vast reservoir of highly skilled and
Experienced work force of about 3,57,000 personnel.
 We believe that our staff, which is one of the best trained manpower in the
telecom sector, is our biggest asset.
 To meet the technological challenges, employees are trained for technology
up-gradation, modernization, computerization etc in BSNL's training Centers
spread across Country.
 To apex training centers of BSNL i.e. Advance level Telecom Training Center
(ALTTC) at Ghaziabad and Bharat Ratna Bhimrao Telecom Training Center
At Jabalpur are comparable to any world class Telecom Training Center.
Moreover, 43 zonal training centers and a National Academy of Telecom
Finance and Management have been running for several years now.

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 Different curriculum run in these centers to impart technology based training,
Training for Attitudinal change, basic educational and skill development
Program etc.
DOT: -
Till 31st December, 1984, the postal, telegraph and telephone services were
managed by the Posts and Telegraphs Department. In January 1985, two separate Departments
for the Posts and the Telecommunications were created. The accounts of the department,
initially, were maintained by the Accountant General of the P&T. However, by April 1972, the
telecommunications accounts were separated. Simultaneously the department also started
preparing the balance sheet annually. With the takeover of the accounts from the audit and
delegation of larger financial powers to the field units, internal Financial Advisers were posted to
all the circles and units.
DEPARTMENT OF TELECOMMUNICATIONS (DOT)
The Telecommunication Board consisted of the Secretary Telecommunications, who was the
Chairman with Member (Finance), Member (Operations), Member (Development), Member (Personnel)
and Member (Technology). The Telecom Commission was constituted in 1989. The Commission has the
DoT Secretary as its Chairman with Member (Services), Member (Technology) and Member (Finance) as
its full time members. The Secretary (Finance), Secretary (DoE), Secretary (Industries) and Secretary
(Planning Commission) are part time members of the Commission. The Department in 1986 reorganised
the Telecommunication Circles with the Secondary Switching Areas as basic units. This was
implemented in a phased manner. Bombay and Delhi Telephones were separated to create the new
entity called Mahanagar Telephone Nigam Ltd. (MTNL). On 1st October 2000, Department created BSNL,
a new entity to operate services in different parts of the country as a public sector unit.

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PARTICULARS OF THE ORGANISATION
Date of
incorporation
Incorporated on 15.9.2000, vide Registration No. 55-107739, dated the
15th
September, 2000 and became entitled to commence business with
effect from 19th
September, 2000.
The Company (BSNL) took over the .business of providing telecom
services and network management throughout the country except the
metro cities of Delhi and Mumbai of the erstwhile service providing
departments of the Govt. of India, i.e., the Departments of Telecom
Services and Telecom Operations i.e. 1.10.2000 pursuant to an MOU
signed between the BSNL and the Govt. of India.
Type of Company Government Company under Section 617 of the Companies Act, 1956.
Administrative
Ministry
Govt. of India, Ministry of Communication and Information Technology,
Department of Telecommunications.
Details of
Disinvestments
The entire share capital of the Company is held by the Govt. of India
Shareholding
pattern
Government of India is holding 100% of the share capital of the Company
Listing with Stock
Exchanges
Not applicable, as the BSNL is an unlisted company
Share Capital Authorized Capital – Rs.17,500 crores, divided into 1,000,00,00,000[One
Thousand Crores] Equity Shares of Rs.10/- each; and 750,00,00,000
[Seven Hundred and Fifty Crores] Preference Shares of Rs.10/- each
Paid Up Share Capital - Rs.5,000/- crores of Equity Shares and Rs.7,500/-
crores of Preference Share Capital

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PROFILE OF THE COMPANY’S BUSINESS
A. GLIMPSES OF MAIN SERVICES OFFERED
1. BASIC AND LIMITED MOBILE TELEPHONE SERVICES
BSNL is the leading service provider in the country in the Basic Telephone Services. As of now
more than 35 million Direct Exchange Lines & more than 2.2.Million telephones in the Limited Mobile
telephone Services are existing. BSNL has provides a number of attractive tariff packages & Plans which
shall further strengthen its subscriber base.
2. CELLULAR MOBILE TELEPHONE SERVICES
BSNL’s GSM Technology based Cellular Mobile Network has reached a long way, covering more
than 6400 towns, with a subscriber base of over 1.54 crore as on 31st
Jan. 2006 out of which 1.16 Crore
cellular telephones are in the prepaid segment.
3. INTERNET SERVICES
BSNL offers Dialup and Broad Band Internet services to the customers by Post-paid service with
the brand name ‘Net one’, and pre-paid service with the brand name ‘Sancharnet’. The post-paid service
is a CLI based access service, currently operational in 100 cities. Sancharnet is available on local call basis
throughout India to ISDN and PSTN subscribers. The Internet Dhaba scheme of the Company aims to
further promote Internet usage in rural and semi urban areas.
To keep pace with the latest and varied value added services to its customers, BSNL uses IP/MPLS
based core to offer world class IP VPN services. MPLS based VPNs is a very useful service for Corporate,
as it reduces the cost involved as well as the complexity in setting up VPNs for customers networking. As
on 31.03.2005, your Company’s total Internet customer base was 17,98,089 and total Internet Dhabas
were 4143. A total of 708594 dial up Internet connections have been given during 2004-2005, against a
target of 7 Lakhs. BSNL plans to give 1215980 more dial up connections during the year 2005-06. As on
31.1.2006, there were 2367404 internet subscribers working in BSNL net work.

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BSNL has launched its Broadband Services under the brand name ‘DataOne’ on 14/1/2005. This
offers services like High Speed Internet Access with speed ranging from 256 Kbps to 8 Mbps. Other services
like streaming video, Video on Demand, Bandwidth on demand etc., have also been planned. As on
31.12.2005, there were more than 356000 broad band connection provided by the BSNL. There are plans
to give 2 million and 3 million connections in 2006 and 2007 respectively.
4. INTELLIGENT NETWORK
Intelligent Network Services is a service that incorporates several value added facilities,
thoroughly designed to save time and money, and enhance productivity. At present, your company offers
Free Phone (FPH), Premium Rate Service (PRM), India Telephone Card (ITC), Account Card Calling (ACC),
Virtual Private Network (VPN), Universal Access Number (UAN) and Tele voting IN services. With the
commissioning of five numbers of new technology IN Platforms (Four General purpose and One Mass
Calling) at Kolkata, Bangalore, Ahmadabad and Hyderabad, the India Telephone Card facility and new
value added services are being provided throughout the country. Activation of these new IN platforms
had increased the sale of ITC Cards taking the figure to Rs.265 crores in 2004-05 alone.
5. Third Generation (3G) Wireless Technology
Capability to support circuit and packet data at high bit rates:
 144 kilobits/second or higher in high mobility (vehicular) traffic
 384 kilobits/second for pedestrian traffic
 2 Megabits/second or higher for indoor traffic
Support of multimedia services/capabilities:
 Fixed and variable rate bit traffic
 Bandwidth on demand
 Asymmetric data rates in the forward and reverse links
 Multimedia mail store and forward
 Broadband access up to 2 Megabits/second

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STRUCTURE AND ABOUT THE EXCHANGES
All telephone subscribers are served by automatic exchanges, which perform the
functions the human operator. The number being dialed is stored and then passed to
the exchange’s central computer, which in turns operates the switching to complete the
call or routes it a higher level switch for further processing. Today’s automatic
exchanges uses a pair of computers, one running the program that provides services and
the second monitoring the operation of the first, ready to take over in a few seconds in
the event of equipment failure.

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Various exchanges present in BSNL are:-
 C-DOT
 E-10B
 OCB283 (Exchange & TAX)
 EWSD (Exchange & TAX)
All exchange has some purposes and some basic structural units, which are:
1. subscriber’s connection unit
2. Switching network (CX)
3. Control unit
4. OMC (Operational & maintenance Control)
STRUCTURE OF THE EXCHANGE
For smooth working of an exchange following unit are very important: -
1. Computer Unit: - it deals with additional services of the exchange to the customers with the
help of computers.
2. Power Plant:- to feed proper power supply to exchange
3. AC Plant: - to maintain the continuous temperature + or – 2 degree Celsius to the digital
switch (exchange).
OMC
Room
Switch
Room
M.D.F.
(Main Distribution Frame)
ETM
(Translator and Interpreter)
Exploitation Room

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4. MDF: - to connect switch (exchange) with the external environment (subscriber) i.e. it is the
interface between subscribers and exchange.
1. Computer unit: -
as the name specified it is the main part of the exchange that deals with the all services
provided by the exchange to the customers with the help of computer. It also provides the updated data
to all other part of the exchange.
The customers are using the services of the exchange by using the internet also gets connected
to the main server present this room via an internet room.
It mainly consists of the servers that are providing the different services. The main servers of
this room are:-
IVRS is used for the change number services provided by the exchange.
CERS are provided by the exchange to avoid the problems that the users are facing the repairing
of telephone. In this system when the user enters its complained it gets directly entered to the server
and user is allotted with an id number.
LOCAL DIRECTORY ENQUIRY is another services provided by the exchange, by using this;
subscribers calls the particular number and gets the directory enquiry. The server present in the main
computer room provides this service.
INTERNET DIRECTORY ENQUIRY is the latest service by the exchange. In this type of service
makes it enquiry using the internet, which gets connected to the main server at the internet room in the
exchange and further to the main server in the computer room.
2. POWERPLANT: -
As we know that, the power is the main source or any organization. It is the case of E-10B
exchange. That is the first requirement of any organization is the input.
The main source of this exchange is AC supply. However, as soon as the power supply is gone off,
then what is source? No one think on this that the telephone is always plays its role in the human
life. Even if the power supply gone off. Thus there must be adjustment source of power.
The main parts of the power room are: -
i. Batteries: - these are the instant sources of the power as soon as power is gone off.

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ii. Charging- Discharging Unit: - the batteries we are using in the power room need
timely charging. As soon as the AC power supply is on, we make use of the charging
unit present in the power room. The slowly charging of the batteries is known as the
trickle charging. But sometimes we need the BOOSTER charging. In this type of
charging awe take of the batteries from the load and charge separately, until it gets
fully charged.
The main work of the discharging unit is to control the discharging of the batteries.
iii. Inverter and Converter Unit: - the main use of this system is to change AC mains to
DC and vice versa as required by the parts of exchange.
iv. Engine Room:-we know that the batteries are the instant source of supply but we
cannot use it for much larger time, thus for this, we have an engine to generate the
power supply. They are of 885 KVA. Thus, this room controls the supply of the
engine.
UPS OPERATING MODES:
UPS system has three operating mode which can be designated as
1. Normal mode
2. Emergency mode
3. Recovery mode
I. NORMAL MODE:
The rectifier charger draws power from the ac mains & convert it into DC. This DC power is
supplied to the inverter which converts it back into AC power to feed the critical load connected to the
output of the inverter. A small amount of DC owner is also supplied to the battery which is connected to
the output of the rectifier charger. The battery is thus kept in a fully charged condition by the rectifier
charge. In this condition the battery is said to be on float across the rectifier charger.

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In this mode the battery does not supply any power to the inverter.
II. EMERGENCY MODE: -
Emergency mode occurs when there is an interruption in the AC input to the rectifier charger.
Interruption like voltage dips below the limit acceptable to the rectifier charger to fall. But the input of
the inverter cannot fall because the battery is across inverter input & it maintains the voltage. AC mains
is interrupted, the source of the inverter input current gets instantaneously transferred from the
rectifier charger to the battery when the output voltage generated by the rectifier charger falls below
the battery voltage. The battery which was earlier on float (charged) instantaneously goes into discharge
& then supplies power to the inverter till the AC mains resumes or the battery gets fully discharged.
During this mode current cannot flow back from the battery into the AC mains because the voltage
reverse biases the diodes or THYRISTORS in the rectifier charger.
III. RECOVERY MODE:

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The recovery mode commences when the AC mains resumes after the interruption. When the
generated voltage of the rectifier exceed the battery voltage. The input current of the inverter gets
instantaneously transferred from the battery to the rectifier charger. During this mode the rectifier
charger not only supplies power to the inverter but also supplies charging current to the battery to
restore the charge lost by the battery during the emergency mode. When the battery gets fully charged,
the charging current decreases progressively and the battery reverts to the float mode and the UPS to
the normal mode.
The duration of the recovery mode depends on the extent of battery discharged, approximately
10 to 20 hours depending on the battery specifications and the design of the rectifier charger.
3. AC PLANT (CENTRAL AIR CONDITIONER)
for the function of electrical equipment, cooling system is basic requirement. The basic
advantages of cooling systems are following-
It provides the thermal stability so that the temperature does not reach the tolerance limit of
electronic equipment.
It saves equipment from dust so to avoid malfunction of equipment’s.
It protects equipment from excess humidity which can caused rusting of equipment.
The basic unit of measurement used in the industry is known as “ton of refrigeration” (TR) which

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is equivalent to the heat extracted in 24 hours for converting thousands kg of liquid to ice at zero
degree.
The compressor is the heart of the AC system and the costliest. It increases the pressure and
temperature of the refrigerant gas coming from the evaporator coils by compressing it.
Compressor comes in various types. The most widely used is simple reciprocal type a cylinder and
piston arrangement. For capacity more than 120 TR, centrifugal compressors are used. The
condenser liquefies the refrigerant gas by a heat exchange process. The capillary tube or the
expansion valve pressurizes liquid refrigerant and meters it flows to the evaporator.
The refrigerant then passes through the evaporator coils, which extract heat out of the ambience.
4. MAIN DISTRIBUTION FRAME
The primary function of MDF is: -
The fault of telephone number is removed in the MDF; it is called as Fault Remove Section.
For removing the fault of telephone number, we use the testing
these testing are T.T.Y. testing, Group testing, etc.
For any type of testing firstly we need the vertical no. or the live tester, printer and computer
test N.E. number of that particular telephone number.
The telephone numbers are also disconnected in the MDF because of some specific reason.
 ORGANISATION OF THE MDF
PARTS OF THE MDF
1. V.F. (Vertical frame)
2. N.E. (number of equipments)
3. Module.
4. Selector.
5. Wire and Cable.
V.F. (Vertical frame):-
V.F. has distribution of wire in 10-10 horizontal sequence, left side connectwith switching room
and back side connect subscribers color wire. One V.F.has 100 pair of wire. Color wires connect
with subscribers by groundingpath. This color wire connects with pillar.
Pillar has different no. of pair. It depend on phone connection in particularareas and after then
pillar connect with D.P. (distribution point). Distributionpoint has 5-10 pair of wire. By the cable
this one-one pair goes in thesubscriber’s phone and 10 connections can connected with one D.P..

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Figure: - Vertical Frame in M.D.F.
N.E. (Number of Equipment): -
N.E. frame is directly connected with switch room by this no. Find out thefault card of subscriber. Many
time no. any fault in pillar pole and M.D.F.then find out the N.E. no of particular subscriber and check
the fault. Card ofswitch room connection depends only on N.E. no means that with the N.E.no. check the
reconnection between subscriber and M.D.F.
Module: -
Module is a medium, which connects M.D.F. CONNECTION OF N.E.fromsubscriber. It is a small hall. This
module is present in V.F. is present in V.F.connect 100 module. No of module is directly proportional to
no of pair.
Selector: -
In the M.D.F. department an important work is long distancecommunication. Many frames have many
branches in different cities. Forcommunication in modern banks, hotels, companies and their branches
thehelp of modem is required. Selector is old manner but advance selector is amodem.. Selector of old
manner work by help of a worker. Main form call inmain exchange and branch for communication.
Old manner selector have many disadvantage:-
1. This takes much of time.
2. Need a worker for connection for between two branches.
3. Indirect communication

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Wire and Cable: -
Wire and cable are the medium for any connection. The different type of
cables use for connection: -
1. Terminal cables
2. Inter frame cables
3. Power cables
4. Maintenance panel cable
5. Ground wires
FUNCTION OF MDF: -
• A fixed means of terminating the external cables.
• A means for mounting the protective devices for incoming circuits.
• A convenient point of interception for locating of faults.
• A means for cross connecting the external circuits to the appropriate
Internal circuits.
The MDF is properly earthed for the protection of the equipment. The external
pairs are area wise terminated on the line side of the frame, while connection from
the equipment is done on the exchange side in a numerical order. By
interconnections at this frame with the help of jumper wires, any subscriber in any
area can be given any exchange number. This MDF mounts Delay Fuses only.
PROTECTIVE DEVICES : -
Comprehensive protection against effects of lightning
and power line contacts, is achieved in practice by fuses, arresters and heat coils.
They are not affected by normal speech and signaling voltage and current but
operates when the foreign voltage or current on the line is excessive. The line is
then disconnected automatically from the equipment or a connection to earth is
For safety precautions fuses are used. Every subscriber line has individual fuse.
These fuses are made of GD (gas discharge) tube, which are connected in parallel.
These fuses have two sides, one is exchange side and other is subscriber side.
Connections between the different tag blocks are made using the jumper wires of
red and white colors.
GD tubes are connected in parallel while electrical fuses are connected in series.
In electrical fuse, when high voltage appears across it, then it will break up the
Connection and thus safeguard the system. If GD tube is connected in series, then
due to high voltage across any line, the whole exchange will be disconnected.
Thus when GD tubes are connected in parallel, it will provide the required
facility.

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CONNECTING SYSTEM
Exchange Side Line Side
 Cables from all the Exchanges reach the MDF
 From the MDF Underground Jumper Cables go to the Cabinets
* The Capacity of the Cabinets is large around 2000 pairs
* If the number of subscribers is small then there is no need for
the Cabinets
 From the Cabinets the cables go to the Pillars
*the position of the pillars is chosen such that the length of the wires going to the DPs is equal
in all directions
 From the Pillars the wires go to the DPs
* the capacity of each of the Pillars is about 10 or 15
 From the DPs the wires go to the subscribers’ homes
When a fault like Phone dead is reported then first check is made at the MDF
EXCHANGE MDF CABINETS PILLARS
DISTRIBUTION
POLES
SUBSCRIBERS

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(i) a Phone Set is inserted on the Line Side, some number is dialed and it is checked
if the conversation takes place properly
(ii) if the conversation takes place properly then the fault is said to be on the Line
Side (Outdoors)
(iii) But if there is no Dial Tone then the fault is said to be on the Exchange side
(Indoors)
 The fault in the Outdoors is checked first of all at the DP
If there is dial tone at the Pillar but not in the subscribers home then the fault is in
between the DP and the subscribers phone set.
 Otherwise at the Pillar If there is dial tone at the Pillar but not at the DP then
the fault is in between the DP and the Pillar
 Otherwise the phone is checked at the Cabinet If there is dial tone at the
Cabinet but not at the Pillar then the fault is in between the Cabinet and the Pillar
 Otherwise the only option left is that the fault is in between the MDF and the
Cabinet

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C-DOT EXCHANGE
INTRODUCTION
Center development of telematics was formed in year 1985 by an act of parliament under
Ministry of telecommunication with prime objective to develop indigenous state of art
Electronics switch suitable for indian network condition. Various products proposed to
Be developed by C-DOT include small RAX exchange of 128 ports for rural network to
Big C-DOT MAX-XL exchange for metropolitan applications.
C-DOT DSS MAX is a universal switch and can be used as local, transmit or integrated
Local and transmit switch. It can have minimum capacity of 512 ports. And can grow upto
16000 ports without concentration. It has digital switching based on basic 64kpbs basic
Rate and 2mbps primary rate multiplexing structure.
The development of C-DOT DSS MAX has taken place in family concept. It is fully
Integrated switch starting from smaller switches, bigger switches and can be built in a
Modular fashion by configuring hardware and software modules in variety of ways.
The C-DOT DSS system can be used in telecommunication network at the various
Switching nodes for different type of services. Some of them are
C-DOT DSS as MAX
This can be used as main automatic exchange which is expandable to large capacity of
Order of 2000 lines or beyond. The MAX may be here remote module (RM) and remote
Line concentrators (RLC) connected to it.
C-DOT DSS as RAX
This can be used as rural automatic exchange and is expandable upto 2000 lines capacity.
Single base module configuration comes under the RAX category. Thus it is universal
Switch which can be configured as local, transit and integrated local and transit switch. It
Provides both local and centralized operation and maintenance.
SYSTEM ARCHITECTURE
It can serve metropolitan, urban, rural environments. Its architecture is such that it is
possible to upgrade a working C-DOT SBM( single base module) or MBM ( multi base
module) exchange to provide ISDN service through RSU ( remote switching unit). RSU
can provide switching facility locally even in case of failure of communication path to
parent exchange. In uses TST (time space switching).

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C-DOT DSS MAX exchange can be configured from the following basic modules:
1. Base Module (BM)
2. Central Module (CM)
3. Administrative Module (AM)
4. Input Output Processor (IOP)
5. Alarm Display Panel (ADP)
BASE MODULE (BM)
Depending upon the capacity of the exchange either single BM or more BMs are used. In
case of 512 ports, only one BM is used. However under low traffic condition, the
capacity of the ports can be increased up to 2048 ports by using two line modules and
adopting concentration mode. In multi module working of BMs will range from 2 to 32.
Frames of BM
One BM consists of 6frames inside it. The top four frames are called terminal units (TU).
TU houses various types of cards in them e.g. Power Supply Card (PSU), Subscriber Line
Card (SLC), Trunk Cards (TWT), Announcement Card (ANNC), Conference Card
(CONF), Terminal Test Controller Card (TTC).The fifth frame of BM is called Base
Processor Unit (BPU) which is the heart of the system. It consists controller and memory
cards. The sixth frame of the BM is called Time Switch Unit (TSU).
Power Supply
To energize various cards in the BM, different DC Voltages are required. They are –48V,
+5V, +12V, -12V and –9V.for this purpose two types of power supply cards are
employed:
a) PSU-1: It caters various supplies to the four terminal units of the BM.In each TU, two
PSU-1cards are there which work in load sharing mode i.e. in case of PSU-1card goes
faulty, the other is capable of taking the full load of the terminal unit.
b) PSU-2: Two cards are used each in BPU and TSU.
PSU-1differs from PSU-2 in one respect i.e. PSU-1besides supplying various D.C.
supplies, generates 75V AC ringing current.
CENTRAL MODULE (CM)
When in the system the number of BMs exceeds one ,the CM is used. The purpose of CM
is to provide setting up of calls between a subscriber of one BM and a subscriber of the
other BM. For this purpose one CM is sufficient up to 32 BMs.
ADMINISTRATIVE MOFULE (AM)
Like CM, AM also used when the number of BMs in the system exceeds one. The AM is
housed along with CM in one cabinet called CM.AM performs administrative and
maintenance function.

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INPUT OUTPUT PROCESSOR (IOP)
The IOP performs following function:
1) Serves as a media for man machine communication.
2) Keeps the data concerning system.
3) Does system initialization.
IOP is connected to the following peripheral units for the purpose noted against each,
⇒ Visual Display Unit: This is used for giving command to establish
communication with the system. VDU gives the display of the reports as a result
of the command execution.
⇒ Printer: For the printed reports.
ALARM DISPLAY UNIT (ADP)
This is basically used for displaying the alarms raised in the system. The alarm gives both
audio and visual indication. However, the audio alarm can be stopped by pressing
acknowledge button on the ADP. The alarms raised are of three types,
⇒ Critical: indicated by red LED.
⇒ Urgent: indicated by orange LED.
⇒ Non-urgent: indicated by green LED.
SYSTEM FEATURES
• The C-DOT is a fully digital system with stored program control.
• In non-concentration mode of working, the switch is non-blocking i.e. calling party
gets the called party if it is free.
• System environment
• a) Temperature = 17C to 27C
• Relative Humidity = 45% to 65%
• The application of C-DOT can be either new exchange or a replacement of the
existing exchange.
• The C-DOT can be used as a local or transmit exchange.
• The system has a modular growth i.e. for expanding the capacity of the exchange
additional modules are to be installed.
• The system provides for detailed billing in case of STD and ISD calls. However
billing for local calls can also be arranged.
• The C-DOT employs distributed control system.
SUBSCRIBER FEATURES
• The subscriber can make local, national and international calls.
• The system provides for automatic selection of a free line from a group of lines
serving a subscriber i.e. PBX hunting.
• The system enables the subscriber to make a call to a fixed destination just by lifting

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his hand set.
• When a subscriber is busy, there is a possibility of losing incoming calls. With the
queue service system such call are not lost and on the contrary these calls are placed
in the queue with appropriate announcement to the caller.
• The subscriber can lock his outgoing calls.
• The subscriber can divert his calls.
• The trunk offer service enables the operator to interrupt a call in progress so that
another incoming call could be offered to the concerned subscriber if he agrees to
accept the call.
• The Coin Collection Box (CCB) allows installation of a special telephone permitting
outgoing calls after insertion of adequate coins.
BASIC SERVICES
• SUBSCRIBER DIALED CALLS
A subscriber can make local, national and international calls. These calls can be made
using push button telephone sets employing dual-tone multi-frequency ( DTMF ) signals
or dial pulses.
PBX facilities :
⇒ Facilities available on PBX lines include
⇒ Direct inward dialing (DID) :
⇒ Calls can be dialed from a telephone line connected to the public network directly
to extensions of a PBX using the CDOT exchange
Line hunting
The CDOT exchange provides for automatic selection of a free line from a group of line
serving a subscriber on receipt of a call to that subscribers general directory number.
• RAPID CALL SET-SERVICES
Hot line
The system provides the possibility for a subscriber to make a call to a fixed destination
by just lifting his handset.
CALL BOOKING SERVICES
Alarm call
The possibility for a subscriber to cause an alarm call or calls to be made to his line at a
Time or times specified in advance by him and to hear APPROPRIATRE announcement
When the call answered.
The alarm call service may be offered on a manual, semi-automatic or automatic basis.
CALL RESTRICTION SERVICE

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A subscriber can have his incoming/outgoing calls barred. These includes denying all
calls to a line, While allowing it to originate call denying various category of originations
from a line while allowing incoming calls to terminate normally on it.
CALL COMPLETION SERVICES
AUTOMATIC CALL BACK
It provides the the subscriber to be rung and get connected to the wanted subscriber if an
Earlier attempt was not successful on account of called subscriber being busy. Automatic
call back is possible for
⇒ An intra-exchange call and
⇒ An inter-exchange call
DIVERSION ON BUSY
It provides the po0ssibility for a subscriber, who cannot receive a call because he is busy,
to have the call diverted to another subscribers’ number.
CALL WAITING
A subscriber engaged on an existing call is given an indication that a caller is that a
caller is attempting to obtain connection to his number. When the warning tone is fed to
the engaged subscriber, he must respond either by flashing the hook switch or by
terminating the call within t seconds. Otherwise the calling party is fed busy tone.
PRIORITY LINES
It provides the possibility of having some line in the exchange which get preference in
being served in case abnormal condition like, overload or route congestion developed in
the exchange.
TRUNK OFFER
It makes it possible for the operator to interrupt a call in progress, in order to allow
another incoming call to be offered.
CALL CHARGE SERVICES
These facilities can be grouped into two charging information services
⇒ charging debiting services
⇒ charging information services
⇒ Subscriber’s home meter or check meter
⇒ Printed record on duration
⇒ Coin collection boxes non metered lines

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OCB-283- System Description
All new technology switching system are based on stored programmecontrol concept. The all-processing
programs are distributed over differentcontrol organs of the system and are stored in ROM/RAM of the
units. Datarequired to handle the calls are also managed in the RAMs of differentcontrol units.
Processor in the control units by using the programme and datastored in unit ROM/RAM process and
handle calls. Handling or processing acall ultimately establish a connection in a switch between I/C and
O/G ends.Depending on the system the name and architecture of control units switchmay change but
basic criterion for switching remains or less the same.
OVERVIEW OF OCB 283 DIGITAL ELECTRONIC SYSTEM: -
OCB 283 is digital switching system which supports a variety of communication needs like basic
telephony, ISDN, interface to mobile communication, data communication etc. This system has been
developed byCITALCATEL of France and therefore has many similarities to its predecessorE-10B (also
known as OCB 181 in France).
The first OCB 283 exchanges of R11 version were commissioned in Brest and Beijing(China) in 1991. The
first OCB-283 exchange came to India in1993. Subsequently, the system has been upgraded and current
version R-20was fully validated in January 1994. The exchanges, which are being supplied. The basic
architecture remaining same, facilities both to subscribers and administration are supported by later
versions.
Salient Features of the system: -
i. It supports both analogue and digital subscribers
ii.It provides telephony ,I.S.D.N., Data communication, cellular radio and other valuable services.
iii.The system has Automatic Recovery feature. When a serious fault occurs in control unit , it
gives message to SMM(O&M unit). The SMM unit puts this unit out of service , load the software of this
unitin a back up unit and brings it into the service. Diagnostic programmmes are run on the faulty unit
and printed on the terminal.
Iv . Every system in OCB-283 works in duplex. One system remains in
working condition and other remains in stand by mode.
v. The charge accounts of the subscriber are automatically save on thedisk once in a day. This avoids the
loss of revenue in case of totalpower supply failure.
vi. This system requires very less space .there is no fix rack and suite
configuration in the system. It provides great flexibility
SUBSCRIBER FECILITIES PROVIDED BY OCB TAX

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OCR-283 provides a large no of facilities. Some facilities are available toonly digital subscriber and as
such they can not be availed by analoguesubscriber. To avail these facilities subscriber number are given
specialcategories by man machine commands.
FACILITIES TO THE SUBSCRIBERS
1. A line can be made only outgoing on incoming.
2. Hotline Facility. It is of two types: -
1. Immediate Hotline Facility.
2. Delay Hotline Facility.
3. Abbreviated dialing.
4. Conference between four subscribers.
5. Automatic cal back on busy.
6. Priority line.
7. Malicious call identification.
8. Detailed Billing.
FACILITES TO DIGITAL SUBSCRIBERS
Digital subscribers are provided all the facilities available to all analogue
subscribers . in addition ,they are provide following facilities which is called
ISDN service . An ISDN subscriber can use many electronic devices on its
telephone line and can utilize them for two or more simultaneous calls for
either –
• VOICE
• DATA
• VIDEO
The following is the list of some of the services to digital subscribers: -
1. the system can provide 2,3,4 facimile services.
2. it provides videotext services.
3. it also provides call trnsfer facility
Brief description of the functional components
BT (Time base) : Time pulses are generated in triplicate and distributed to
LRs at Switching unit. The time base is usually synchronised with the network by a synch. interface.
Synchronisation interface gets the clock from PCMs which carry traffic also and synchronises the local
clock with the PCM clock and thus network synchronisation is achieved.
Host switching Matrix (MCX)/Switch Control Function “COM”

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This is a pure time switch of maximum 2048 LRs connectivity capability.The switching of LR time shots
are controlled by the function COM whichin turn obtains the connection particulars from call handler
known as Multiregister.
CCS # 7 Protocol Manager (PU/PE)
64 kbps signalling channels are connected to this by semipermanent link and
carries out level 2 and level 3 of the signalling message transfer.
The defence and signalling link resource allocation is done by a control
function PC.
Protocol Handler : The signalling protocol between an access network an
d local exchange is processed and managed by this function.
Call Handler “MR”:
This obtains necessary data from subs and circuits and process for connection and disconnection of call
with the help of a database manager TR. In addition this helps in carrying out circuit tests and some
obser vations. Besides MR function there is one CC (Call Contorl) function which again contains register
to handle CCS # 7 calls in conjunction with MR registers.
Data Manager TR:
This function is responsible for managing and storing various subscriberand trunks related data base.
The data is returned by the call handler “MR”as and when required during call processing.
Charging function (TX):
This function is responsible for charge computation on the basis of certain charging parameters supplied
by the translator during analysis of digits received from a source (Subs or Circuit). This also prepares
detailed billing messages and forwarding the same to the operation & maintenance function for further
processing. Besides the charge related function the TX also is responsible for carrying out some traffic
observation on subscriber and trunks.
Matrix handler (GX)
This function is responsible for processing and for defence of connections on
receipt of :- request for connection and disconnection from MR or MQ

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(marker).fault in connection signalled by the switching controller function(COM).GX also carrier out
monitoring of connections and checks data link speriodically..
Message Distribution function (MQ) marker:
Its function is to format if required and distribute messages
It also supervises semipermanent links .
Interchange of messages between different communication multiplexes.
PCM controller (URM) :
PCM interface receives PCM from other exchanges remote subs accessunits, access networks and digital
recorded announcement systems and theURM function carrier out the following:
-
HDB3/Binary code conversion
-
Injection / extraction of TS 16 for CAS.
OM Function:
This function enables to create all data required for subs/circuits and their testing. This also enables
spontaneously issuing fault and alarm messages incase of indications coming from OCB units.OM
function further provides features for saving detail billing/ bulk billing messages on mag tape(cartridge)
.The OM function possess a two way communication path with the exchange system.

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Subscriber access function :
This functional component is implemented in CSNL/CSND or CSED and is responsible to forward new call
connection & disconnection requests to control functions
RACKS OF SUBSCRIBER CARDS IN OCB-283
Hardware architecture of OCB-283 Switching
Systems
1. Various functional components discussed in the previous chapter are
required to be implemented in some hardware unit.
For this purpose functions are classified as under:-
Subs access functions
PCM connection interface
Auxiliary functions interface
Control functions
OM function
OCB – 283 system does not include the subs access systems but can support
different type of subs access systems.
2. There are different type of subs access units like CSNL/CSND i.e. local
and distant digital (Numerique) subs connection unit and CSED i.e. (Distant
analogue subs connection unit).A detail description of subs interface
provided in OCB shall be discussed in yet another chapter.

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3. Control functions – Concept of station
For all control function or functions OCB-283 uses concept of a station.
Following type of stations are available:
3.1 SMT: Trunk multiprocessor station – This implements the URM
function for PCMs i.e. responsible to handle CAS and be transparent to
CCS# 7 signalling
RACKS OF SUBSCRIBER CARDS
3.2 SMA : Auxiliary multiprocessor station. These stations implement one
or more auxiliary functions like ETA, PU/PE or V 5.2 functions.
However, while ETA & PU/PE functions can be implemented in one
station, V 5.2 function is implemented in SMA without any other
auxiliary function.
SMA RACK
SMX: Switch multiprocessor station This implements the switching function
(COM) and contains the switch matrix system also.
3.4SMC : Command or control multiprocessor station.
This type of station implements one or more control functions like MQ, TR,
TX, MR, GX, PC etc.
3.5 SMM:
Maintenance multiprocessor station implementing all
OM functions. This supports process for, dialogue with OCB, data base
management and handling spontaneous message generated by OCB units.
3.6 STS : Synchronization and time base station. This station is
responsible for generating exchange clock and synchronize the same
with the network.
SUBSCRIBER CARDS: -
The main and important thing of OCB-283 is subscriber cards. The view of
subscriber cards is shown below in figure. One subscriber card can support 8
or 16 subscribers. Old versions of OCB-283 were supporting 8 subscriber
per card . now the latest version of OCB-283 is supporting 16 subscribers per card. One rack consist of
128 cards and each card have 16 subs cribers.
No of racks are decided on the bais of no of subscriber in that particular
exchange. subscriber cars is shown in figure
exchange. subscriber cars is shown in figure:-

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EWSD
EWSD and Office Switch
1. General Overview
EWSD (Elektronisches Wählsystem Digital in German, Electronic Digital Switching
System/Electronic World Switch Digital in English) is one of the most widely installed telephone
exchange systems in the world. EWSD can work as a local or tandem switch or combined local/tandem,
and for landline or mobile phones. It is manufactured by Siemens AG, who claims that EWSD switches
perform switching for over 160 million subscriber lines in more than 100 countries.
DeTeWe bought its first EWSD under license in 1985 for remote switching. Bosch built its first
EWSD as a local exchange in 1986. Deutsche Telekom, formerly Deutsche Bundespost, the largest
German telephone company, uses EWSD and System 12 (Alcatel), the former more than the latter.
In 2007, Nokia Corporation and Siemens AG formed the new company Nokia Siemens Networks,
and responsibility of further development and shipments of the EWSD system is dependent on this new
company.

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Contents
 1 Hardware
 2 Software
 3 Technical data
Hardware
Main subsystems are:
 CP (Central Processor)
 MB (Message Buffer)
 CCNC (Common Channel Network Control)
 LINE (Analog Line Group)
 LTG (Line Trunk Group)
 DLU (Digital Line Unit)
 SN (Switching Network)
All system units are redundant so the inactive side can take over immediately in case of an error.
DLU handles analog and ISDN lines and includes codec’s for analog lines, one of the BORSCHT
functions for subscriber lines. Digital signals are assigned a time slot. DLU concentrates traffic onto a
Line B unit, as well as Primary ISDN and V5.2 connections. Supervision and address signaling (dial pulse,
DTMF) are also integrated in the DLU. For PCM-30 (E-1) connections to other exchanges, Line C Units are
used, which also handle signaling including SS7, MFC R2 signaling, IKZ (dial pulse), and E&M.
he Switching Network consists of 4 space division stages of 16x16 switches, and a time division
section with 16 stages of 4x4 switches. Control is provided by the CP Co-ordination Processor.
Software
The software of EWSD is called APS (Automatic Program System). The APS is on a hard drive and
includes the operating system, developed by Siemens in cooperation with Bosch. It is predominantly
written in the CHILL language. Application software is switch specific and serves among other things
traffic management, path search, and call charging. Support software serves translating programs,
binding modules as well as administration of libraries for generating data. Operating and data
communication software serve for co-operation of maintenance centers and switching centers.

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EWSD EXCHANGE
2. INTROCDUCTION OF EWSD
Switching network (SN) performs the switching function for speech as well as for messages in an
EWSD exchange. For this purpose it is connected to LTGs and CCNC for speech/data and to CP (through
MB) for exchange of control information. Switching network with ultimate capacity up to 63 LTGs is called
SN DE4. For larger exchanges SN DE5.1 is used which can connect up to 126 LTGs. Similarly SN DE5.2 can
connect up to 252 and SN DE5.4 up to 504 LTGs.
DLU LTG(B)
LTG(C)
CCNC
MB
CCG
SYP
OMT PRINTER
CP
MTU
MDD
SN
Figure 1. Position of Switching Network in EWSD

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3. BLOCK DIAGRAM OF EWSD
EWSD switching system structure chart
DLU
Digital line unit
 SLM(A,D,X,I) - subscriber
line modules
 DLUC - Digital line unit
controller
LTG
Line trunk group
SN
Switching network
SSNC
Signaling system network control
CCNC
Common channel network control
MB
Message buffer
CP
Coordinating processor
 BAP - base processor
 CAP - call processor
 CMY - common memory
 IOC- I/O controller
 AMP - ATM bridge
processor
 B:CMY0(1) - common
memory access bus
CCG
Central clock generator
Net
Manager
Network management system

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4. GENERAL FEATURES
Switching network is provided in capacity stages SN: 63LTG to SN: 504LTG, i.e. up to 63 LTGs can
be connected or, via other intermediate capacity stages, up to 504 LTGs can be connected. The modularly
expandable SN has negligibly small internal blocking and can be used in EWSD exchanges of all types and
sizes.
The self monitoring switching network uses a uniform through connection format. Octets (8 bit
speech samples) from the incoming time slots are switched to the outgoing time slots leading to the
desired destination fully transparently. This means that each bit of all octets is transmitted to the output
of the switching network in the way that it appears at the input (bit integrity). For each connection made
via the switching network, the octets have the same sequence at the output as at the input (digit sequence
integrity). The switching network’s full availability makes it possible for each incoming octet to be switched
at any time to any outgoing highway at the output of the switching network. The time slots used in
switching network for making through-connections make up a 64 Kbit/s connection path.
All of the switching network’s internal highways have a bit rate of 8192 bits/s (Secondary Digital
Carriers, SDCs). 128 time slots with a transmission capacity of 64 Kbits/s each (128x64 = 8192 Kbits/s) are
available on each 8192 Kbits/s highway. Separate cables each containing several (eight or sixteen) such
internal highways, are used for each transmission direction. All externally connected highways also have
the same uniform bit rate.
The switching network combines the numerous switching network functions in a few module
types. These modules work at very high through-connection bit rates; 8192 Kbits/s and some even at
32768 Kbit/s. For example 1024 connections can be switched simultaneously through a space stage with
16 inputs and 16 outputs. Although these highly integrated switching network modules switch a large
number of connections with a high degree of reliability, the EWSD switching networks are always
duplicated. The amount of space needed for the switching network in the EWSD exchange is still very low
despite this duplication.
Two different switching network versions have been supplied in India:
* Switching network [SN] supplied with first 110K order.
* Switching network B [SN (B)] supplied with subsequent orders.

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5. Position and Functional Structure
Switching network is connected to LTGs and CCNC for speech/data and to CP (through MB) for
exchange of control information. Figure 1 shows the position of switching network in EWSD exchange
with reference to other equipments.
For security reasons, entire SN is duplicated. The two sides of SN (SN0 and SN1) are called planes.
The external highways for both transmission directions i.e. between the switching network and one LTG
or between the switching network and one Message Buffer Unit (MBU) are identified as follows as shown
in figure 2.
* SDC: LTG interface between SN and LTG: time slot 0 for message exchange between the LTG
and coordination processor (CP) as well as between two LTGs, time slot 1 to 127 for subscriber
connections.
* SDC: CCNC interface between the SN and the common channel signaling network (CCNC): for
common channel signaling.
* SDC: TSG interface between SN and a message buffer unit assigned to CP (MBU: LTG) for
message exchange between the CP and the LTGs as well as between the LTGs.
* SDC: SGC between the SN and an MBU: SGC of the CP for setting up and clearing connections.
Switching network in EWSD exchanges uses time and space switching and therefore it is
functionally divided into Time Stage Group (TSG) and Space Stage Group (SSG). SN DE4 with capacity stage
SN: 63LTG has a TST structure and TSG/SSG division is not applicable in this case
TSGs and SSGs are interconnected through internal 8 Mb/s interfaces called SDC:SSG. TSGs of
both planes are connected to SSGs of both planes, and thus these provide further security.
Each TSG and SSG have its own Switch Group Control(SGC) that is connected to CP via MB through
interfaces SDC:SGC.

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6.1 Switching path
The switching network is subdivided into time stage groups (TSG) and space stage groups (SSG).
Due to its modular structure, the EWSD switching network can be partially equipped as needed and
expanded step by step. The switching network uses the following switching stages:
 one time stage incoming (TSI)
 three space stages (SS) and
 One time stage outgoing (TSO).
These time and space stages (functional units), shown in figure 3, are located in the following
module types:
 Link interface module between TSM and LTG (LIL)
 time stage module (TSM)
 link interface module between TSG and SSG (LIS)
 space stage module 8|15 (SSM8|15)
 space stage module 16|16 (SSM16|16)
The switching network capacity stage SN:63LTG, however has a TST structure with only one space
stage as shown in figure 4. Module types LIS and SSM 8|15 are not there in SN:63 LTG. Further, the
modules and the TSGs/SSGs are interconnected
6.1.1 LIL & LIS:
The receiver components of the LIL and LIS compensate for differences in propagation
times via connected highways. Thus, they produce phase synchronization between the incoming
information on the highways. These differences in propagation times occur because an exchange’s racks
are set up at varying distances to each other. Module LIL is connected on the interface to LTGs and has 4
inputs and 4 outputs while module LIS is connected on the interface to SSG and has 8 inputs and 8 outputs.

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TSM:
The number of TSMs in a switching network is always equal to the number of LILs. Each TSM
contains one time stage incoming (TSI) and one time stage outgoing (TSO) (Figure 5). The TSI and the TSO
handle the incoming or outgoing information in the switching network. Between input and output, octets
can change their time slot and highway via time
Stages. Octets on four incoming highways
are cyclically written into the speech memory of a
TSI or TSO (4x128 = 512 locations corresponding to
512 different time slots). The speech memory areas
0 and 1 are used alternately in consecutive 125-
microseconds periods for writing the octets. The
connections to be made determine the octet
sequence during read-out. The stored octets are
read-out to any one of 512 time slots and then
transferred via four outgoing highways.
5.1.2. SSM8|15 and SSM 16|16:
The SSM 8|15 contains two space stages as shown in figure 6. One space stage is used for
transmission direction LIS  SSM 8|15  SSM 16|16 and has 8 inlets and 15 outlets while a second space
stage is used for transmission direction SSM 16|16  SSM 8|15  LIS and has 15 inlets and 8 outlets. Via
space stages, octets can change their highways between input and output, but they retain the same time
slot. Space stages 8|15, 16|16 and 15|8 switch the received octets synchronously with the time slots and
the 125-microsecond periods. The connections to be switched change in consecutive time slots. In this
process, the octets arriving on incoming highways are “spatially” distributed to outgoing highways . In
capacity stages with a TST structure, the SSM 16|16 Switches the octets received from the TSIs directly
to the TSOs.
LIL
0
 SSM16|16
 or LIS

3
0



3
TSM
Figure 5 : Time stage
module (TSM)
LIL
0



3
TSO
TSI
0
 SSM16|16
 or LIS

3

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0

 SSM16|16

14
0
 SSM16|16


14
SSM16|16
TSM
or
0
0
TSM
or
SSM8|15
0



7
0



7
SSM8|15
SS 8|15
LIS
LIS
Figure 6 : Space stage modules (SSM16|16 and SSM8|15)
7.1 Control section:
Each TSG, each SSG, and with SN: 63LTG, each switching network side has its own control. These
controls each consist of two modules viz. switch group control (SGC) and link interface module between
SGC and MBU: SGC (LIM)
An SGC consists of a microprocessor with accompanying memory and peripheral components.
The main tasks of an SGC are to handle CP commands (such as connection setup and clear down), message
generation and routine test execution. Apart from the interface to the message buffer unit (MBU: SGC),
an LIM has a hardware controller (HWC) and a clock generator for clock distribution.
7.2Firmware
The firmware for the switching network is permanently stored in the program memory of each
SGC. For this reason, it does not have to be loaded or initialized by the coordination processor (CP). SN
firmware is organized in the following manner:
 executive control programs
 call processing programs
 maintenance programs
 startup and safeguarding programs

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6. Switching network (B)
Switching network (B) is a special compact version of switching network wherein a number of
functional units are integrated over a single module. This arrangement has the following advantages:
* Reduction in shelf space
* Reduction in number of PCB types
* Utilization of available space in SN rack for accommodating LTGs
Functionally SN(B) is entirely similar to SN. However, only the following five types of modules are
used in SN(B) as shown in table 3.
TSMB: Two LILs and two time stage modules TSMs are combined to form one TSMB.
LISB: This is formed by combining two LIS functional units in a TSG.
SSM8B: Two LIS and two SSM8|15 functional units in a SSG are combined
to form one SSM8B.
SSM16B: This is formed by combining eight SSM16|16 functional units.
SGCB: Functional units LIM and SGC are combined to form one SGCB.
TABLE 3: SN(B) Module
PCB
No. of
cards in
SN(B)
:63LTG
No. of cards
in TSG of
SN(B):DE5
No. of cards
in SSG of
SN(B):DE5
Equivalent modules in SN
TSMB 8 8 - 2 X TSM +
2 X LIL
LIS - 4 - 2 X LIS of TSG
SSM8B - - 8 2 X LIS of SSG +
2 X SSM8|15

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11.Interconnection of Switching Modules
Switching modules in EWSD switching network are connected in a manner so as to ensure
nearly full availability. One module LIL, which can handle highways coming from 4 LTGs is
connected to 4 inlets of a module TSM on one-to-one basis. Thus these 4 highways coming from
4 LTGs undergo a T-switching function and are then connected to inlets of 4 different LIS modules.
The 8 inlets of a LIS module are connected to outlets of 8 different TSMs. Two such groups form
a Time Stage Group wherein 63 LTGs can be connected. The TSG has 64 outlets coming out of 8
LIS modules. The interconnection arrangement is shown in figure 13.
Eight outlets of LIS modules in TSG are connected to 8 inlets of LIS modules in SSG on one-
to-one basis. One SSG consists of 16 LIS modules and therefore two TSGs can be connected to
one SSG. There is again one-to-one connection between 8 outlets of LIS modules and 8 inlets of
SSM8|15 modules. Fifteen outlets of SSM8|15 and 16 inlets of SSM16|16 are cross connected.
Similarly 16 outlets of SSM16|16 and 15 inlets of SSM15|8 are cross connected. The
interconnection arrangement within SSG is shown in figure 14.
All the TSGs of SN are connected to all the SSGs in such a manner as to ensure nearly full
availability. The interconnection of TSGs with SSGs in case of SN:504 LTG is shown in figure 15,
and that for SN:252 LTG and SN:126 LTG are shown in figure 16.
Interconnection of the modules in SN DE4 is simpler as there are no TSG or SSG. The TSMs
are directly connected to SSM16|16 as shown in figure 17.

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LIS
0
0
8 15
SSM
0
To inputs 0
of SSM1-13
1
0
16 16
SSM
0
0
LIS
0
8 15
15 15
To inputs 15
of SSM1-13
1
0
16 16
14
0 0
SN1
SN0
MBU:SGC
LIM SGC
Figure 14: Space Stage Group Internal connections

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SWITCHING TECHNIQUE
 SPACE DIVISION SWITCHING
 MULTIPLE STAGE SWITCHING
 TIME DIVISION SWITCHING
 TWO-DIMENSIONAL SWITCHING
 MULTI STAGE TIME AND SPACE SWITCHING
INTERNET
Introduction:
The Internet is not a program, not software, not hardware or a big system. It is a group of various co-
operating computers worldwide interconnected by computer based on TCPIP communication
protocols. People use it to get information over a standard communication link. The hundreds or
thousands or millions of computer network are connected to each other for exchanging the information
which is based on the unique identity and set of procedures. Internet is a series of interconnected
networks providing global link to information.
GIAS: BSNL launched the Gateway Internet Access Service (GAIS) through dial up/leased/ISDN network.
Users can access GAIS from 99 cities in India by this means.
COMMON TERMINOLOGY USED IN INTERNET:

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WWW:
World Wide Web (WWW) is a wide area hypermedia information retrieval aiming to give
universal access to a large universe of documents.
HTTP:
Hyper text transmission Protocol (HTTP) is the communication protocol used to transfer
documents from the server to client over the WWW (http:// www).
HTML:
Hyper Text Markup Language (HTML) is a system of marking or tagging the various parts of web
documents to tell the browser software how to display the document text, link graphics and
link media.
ISDN:
Integrated Service Digital Network (ISDN) is a digital phone connection technology that provides
both voice and data services over the same connection.
ISP:
Internet Service Provider (ISP) is an agency that provides Internet access and other net related
services.
NATIONAL INTERNET BACKBONE (NIB)
Networking is a key component of any Internet Services Provider (ISP) operations. The networking
equipments like access servers, routers and modems are critical to the successful functioning of ISP.
An ISP node where subscribers enter internet, consists of a set of equipments as given below.
Access server
Router
Modem bank
LAN (Local Area Network) components
Security server
Rack, console & power supply
Network management agent.

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CELLULAR MOBILE SERVICES: -
Cellular is one of the fastest growing and most demanding telecommunication applications. Today, it
represents a continuously increasing percentage of all new telephone subscriptions around the world.
Currently there are more than 45 million subscribers in worldwide and nearly 50% of those subscribers
are located in USA. It is forecasted that cellular system using a digital technology will become the
universal method of telecommunications. By the year 2005, forecasters predict that there will be more
than 100 million cellular subscribers worldwide.
1. WIRELESS IN LOCAL LOOP (WLL) MOBILE
WLL is a communication system that connects customers to the Public Switch Telephone
Network (PSTN) using radio frequency signals as substitutes of conventional wires for all part of
connection between the subscribers and the telephone exchange. It works on CDMA technique.
The local loop is access part of telecommunication network i.e. the part between PSTN switch
and subscribers. WLL network application involves uses of radio to replace of the wire link
between PSTN switch and subscriber. The radio technology is able to provide same quality of
services as that provided by the wires line. Application of wireless loop technology has just been
started in the worldwide. There is no standard for this so far. However, a number of national
and international air interface standards for digital cellular mobile telephone system are
available.
TECHNICAL ASPECTS:
WLL is based on CDMA technique and is entirely different from GSM. The system for
WLL services can be divided in two following parts:-
BSC (Base Switching Centre):- It provides links between BTS & BSM; it consists of
different processors, in BSNL it is of SUN Polaris of LG Company. In LG 1 BSC can have 48 BTS? In
BSNL we have two types of BSC:-

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I. V-5.2:- This type of BSC cannot switch by itself so it is dependent on local exchange /
PSTN for switching and keeping records of billing etc. BSNL uses this type of BSC for rural areas.
ii. CCS-7 / R2:- These types of BSC are totally automatic it doesn’t depend on local
exchange for its functions, it is complete in itself. BSNL uses this type of BSC for urban areas.
BTS (Base Transreceiver System):- As it is clear from its name it transmits as well as receive
signal, it works as an amplifier (router) to overcome the loss in signal in transmission.
BSM (Base Station Management):- It controls and manages the WLL services. It can
troubleshoot the problem; add new users as well as capable to block service given to user. It is
basically a computer system, which manages the whole process of WLL service. In BSNL BSM are
two UNIX based computer system.
ADVANTAGES OF WLL:
Country wide induction of WLL underway of areas than are non-feasible for the normal
network
Helping relieves congestion of connections in the normal cable / wire based network in urban
areas
Limited the mobility without any airtime charges
It has improved signal and reducing the interference
Greater capacity than mobile
Provides ease of operation, administration & maintenance at lower cost.
The telecommunication is the biggest factor in influencing the speed of life in the modern age.
Today we can get connection with any corner of world through the push button of computer;
with the small mobile phone we can send not only the messages but also the secret document.
As we know that there is positive view behind any mention that it should be helpful in the
development of society. But humans have diverted mentality some of them of positive view and
some of them of negative view. Where use any invention for the welfare of society but some
uses for the satisfaction their disturbed mentality and to earn more and more money whether it

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may be harmful for the society. They infringe the norms of society and their behavior is
condemned as antisocial, immoral and sinful.
2. CODE DIVISION MULTIPLE ACCESS (CDMA):
CONCEPT OF MULTIPLE ACCESSES: -
Multiple access system allows a large number of users to share a common pool of radio
telephone circuits, like sharing of trunked radio facility. Multiple access radio has similarity to
the LAN in which the common channel is available to all users. The circuits are demands
assigned i.e. assigned on demand first-cum-first-served basis. The provision of access to the
radio circuits methods of multiple accesses are:
CDMA: - Where large number of transmission are combined on the same channel at the same
time and separated by the codes.
WHAT IS CDMA?
CDMA, a cellular technology originally known as IS-95, competes with GSM technology for
dominance in the cellular world.
There are now different variations, but the original CDMA is known as CdmaOne.
Latest CDMA global subscriber & operator’s numbers
As of December 2002, there were 120 million users worldwide, with 55 million of these in the
USA.
See other cellular technology in the world.
We now have CDMA2000 and its variant like 1X EV, 1XEV-DO and MC 3X. The refer of variant of
usage of a 1.25 MHz channel. 3X uses a 5 MHz channel. Wide band CDMA forms that the basis of
UMTS 3G networks, developed originally by Qualcomm, high capacity and small cell radius,
employing spread-spectrum technology and special coding scheme characterized by CDMA.
The Telecommunication Industry Association (TIA) in 1993 adopted CDMA. May 2001 there
were 35 million subscribers on cdmaOne system worldwide. Over 35 countries have either

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commercial or trial activity ongoing. There were already 43 WLL systems in 22 countries using
cdmaOne technology.
Enhancing today’s data capabilities is the 1XRTT CDMA standard this next evolutionary step for
cdmaOne operators will provide data rates up to 300 kbps, significant capacity increases as well
as extended batteries life for handsets.
Worldwide resources are being devoted to roll out third generation CDMA technology, including
multi-carrier (cdmaOne2000 1xMC and HDR in 1.25 MHz bandwidth and 3xMC in 5 MHz
bandwidth) and direct spread (WCDMA in 5 MHz bandwidth).
This first phase of cdmaOne2000 variously called 1XRTT, 3G1X or just plain 1X is designed to
double current voce capacity and support always on data transmission speed 10 times faster
than typically available today, some 153.6 kbps on both the forward and reverse links.
3. GLOBAL SYSTEM FOR MOBILE COMMUNICATION (GSM): -
The GSM Association is a unique organization, with a truly global reach, offering a full
range of business and technical services to its members. Now as the wireless family unfolds the
association is deriving forward its vision of seamless, limitless, world of wireless communication.
Throughout the evolution of cellular telecommunications, various systems have been developed
without the benefit of standardized specifications. This presented many problems directly
related to compatibility, especially with the development of digital radio technology. The GSM
standard is intended to address these problems.
Global system for mobile communication (GSM) is a globally accepted standard for digital
cellular communication. GSM is the name of a standardization group established in 1982 to
create a common European mobile telephone standard that would formulae the specifications
for a pan-European mobile cellular radio system operating at 900 MHz it is estimated that many
countries outside of Europe will join the GSM partnership.

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OBJECTIVES OF GSM SYSTEM:
One of the important objectives of GSM group is to evolve a unified standard to provide
seamless roaming across Europe. Another landmark decision taken by the group is to standardize
a digital radio interface for the communication between the mobile handset and the radio
transmitter / receiver. The design objectives of the GSM system can be briefly states as below:
 Excellent speech quality
 High security and privacy
 Low module terminal cost
 Low service and facilities cost
 Design of sleek and handled mobile terminals
 International roaming
 Wide range of services and facilities
 Ability to adopt to new and innovative features
 Narrowband ISDN compatibility
 Digital Radio
 High Spectral efficiency
GSM NETWORK ELEMENTS AND ARCHITECTURE:
1. Mobile Station (MS)
i. Mobile Terminal or Equipment (MT)
ii. Subscriber Identity Module (SIM) Card
2. Base Station Subsystem (BSS)
i. Base transceiver Station (BTS)
ii. Base Station Controller (BSC)
iii. Main Station Controller (MSC)
iv. Transcoding and Rate Adoption Unit (XCDR/TRAU)
3. Network Switching Subsystem (NSS)
i. Registration
ii. Authentication and security
iii. Location updating
iv. Handovers and
v. Routing to roaming subscribers
4. Operation and Maintenance Subsystem (OMS)

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i. Operation and Maintenance Centre – Switch
ii. Operation and Maintenance Centre – Radio
5. Enhanced Services Subsystem (ESS)
6. Billing and Customer Care System (B&CCS)

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4. THIRD GENERATION 3G TECHNOLOGY : -
Introduction: -
Third generation (3G) networks were conceived from the Universal Mobile
Telecommunications Service (UMTS) concept for high speed networks for enabling a variety of
data intensive applications. 3G systems consist of the two main standards, CDMA2000 and W-
CDMA, as well as other 3G variants such as NTT DoCoMo's Freedom of Mobile Multimedia
Access (FOMA) and Time Division Synchronous Code Division Multiple Access (TD-SCDMA) used
primarily in China.
Data Speed
The data speed of 3G is determined based on a combination of factors including the chip
rate, channel structure, power control, and synchronization.
An example of calculating the theoretical 3G data speed is as follows:
 W-CDMA assigned code 400-500 Kbps/code. 6 codes X 400 > 2Mbps (UMTS target for 3G
data speed in fixed location)
Actual data speeds will vary in accordance with several factors including:
 Number of users in cell/sector
 Distance of user from cell
 User is moving or stationary
 Network operator capacity and network optimization requirements
1xEV-DO is a data-only solution, supporting a theoretical data speed of up to 2.457
Mbps
1xEV-DV is a data and voice solution, supporting a theoretical data speed of up to 3.072
Mbps
FOMA has two operational modes, supporting a dedicated 64 Kbps connection or a 384
Kbps downlink/64 Kbps uplink best-effort connection.
TD-SCDMA can operate in 1.6 MHz or 5 MHz mode for 2 Mbps or 6 Mbps respectively

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3G is the short form for third-generation technology. It is one of the popular mobile phone
standards. The services utilizing 3G provide the ability to transmit both voice data such as calls and non-
voice data such as instant messaging, email and video telephony at the same time. Japan was the first
country to introduce 3G on a wide scale commercially. In 2005, almost 40 per cent of the subscribers in
Japan used 3G services. On the technical front, 3G services are wide area cellular telephone networks
unlike IEEE 802.11 networks, which are short range networks meant for Internet access. Now, 3G is
being used to provide various services.
You have to plug in 3G Data Card into your laptop and can get the fastest available connection,
with mobile broadband speeds of up to 1.8 Mbps. It’s neat, compact design makes it easy to use; you
can easily swap it between laptops for use at work, home or on the move. Laptops have a PC Card slot
(also known as a PCMCIA slot), or an Express Card slot. There is PCMCIA to Express Card Converter for
using 3G broadband; you need 3G Data card, network SIM card, software, user guide.
CONCLUSION: -
Hence in the last I can say that taking training in such an organization proved to be very
beneficial for me. I learnt quite a lot about electronic exchange, Internet, Land line, WLL,
Mobile GSM & 3G, and the basis of processing Exchange. I also got firsthand knowledge of how
a Telephone Exchange works.
The first phase of training has proved to be quite fruitful. It provides an opportunity to
encounter with such huge machines.
The architecture of company has various units. They are linked and working of whole
plant is controlled make the student realized that engineering is not just learning the structure
description and working of various machines. But the greater part is planning proper
management.
-------×-------

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GLOSSARY OF TERMS AND ABBREVIATIONS
ADM Add/Drop Multiplexers
ANALOGUE An electrical signal which is analogous to
changing physical quantity measured
BSC Base Station Controller
BTS Base Tran receiver Station
C-DOT Centre for Development of Telemetric
CD Cabinet Cable Distribution Cabinet
CDMA Code Division Multiple Access
CKM Cable conductor kilometer – cable
sheath kilometers multiplied by the
number of conductor pairs in each cable
CLIP Calling Line Identification Processing
COAXIAL CABLE A cable with a single wire in the centre of
cylindrical conductor forming a pair of
carrying electrical signals
CT BOXES Cable Termination Boxes
DECT Digital Enhanced Cordless
Telecommunications
DEL Direct exchange lines, one each for every
telephone connection
DIGITAL EXCHANGE The exchange having signals coded into
binary pulses and having little or no
moving parts
DIU DECT interface unit
DLC Digital Loop Carrier
DWDM Dense Wavelength Multiplexing
Terminal
EDX Electronic Data Exchange
EPABX Electronic Private Automatic Branch
Exchange
ETRP Electronic Trunk Relay Plates
EWSD TAX Electronic Wheeler System of Digital
Trunk Automatic Exchange
GHz Giga Hertz

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GSM Global System for Mobile
Communications
HDPE High density polyethylene
HDSL High bit rate Digital Subscriber Line
Hertz or Hz Frequency (cycles per second), named
after Heinrich Hertz - usually in ranges of
kilo 1000 - KHz, mega 1,000,000 - MHz or
giga 1,000,000,000 - GHz
IDR Intermediate Data Rate
ISDN Integrated Services Digital Network
LDST Long Distance Satellite Telephone
LOI Letter of Intent
MARR Multi Access Rural Radio
MBM Multi Base Module
Mbps Mega bits per second denoting digital
frequency
MCPC Multi Channel Per Carrier
MDF Main Distribution Frame
MUX Multiplex
NIT Notice Inviting Tender
NE Lines Non Exchange Lines
OFC Optical Fiber Cable
Optical Fiber (OF) Glass fibers using light waves for
transmission of signals
OLA Optical Line Amplifiers
OYT Own your telephone
PABX Private Automatic Branch exchange
PBX Private branch exchange
PCM Pulse Code Modulation
PCO Public Call Offices
PDH Plesiochronous Digital Hierarchy
PERT Chart Programmed Evaluation Review
Technique Chart
PI JF Cable Polyethylene Insulated Jelly Filled Cable
PSPDN Packet Switch Public Data Network

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PST Progressive Stock Taking
PSTN Public Switched Telephone Network
PVC Polyvinyl chloride
PW Private Wires
RLU Remote Line Unit
RSU Remote Switching Unit
SACFA Standing Advisory Committee on Radio
Frequency Allocation
SDH Synchronous Digital Hierarchy
SMPS Switch Mode Power Supply
SRCs Subscriber Record Cards
SSAs Secondary Switching Areas
STD Subscriber trunk dialing
STM Synchronous Transport Module
TAX Trunk automatic exchange
TDMA Time Division Multiple Access – A
transmission technique used in digital
radio transmission in which the use of a
frequency is divided into time slots that
are shared amongst several users.
TELEX TelePrompTer exchange
TTH Triangular Tubular Hybrid
UHF Ultra high frequency (300 to 3000 MHz)
VHF Very high frequency
VPT Village Public Telephones
VSAT Very small aperture terminal
WLL Wireless-in-Local Loop
-----×-----

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