vocational training
TRANSCRIPT
3. TELECOMMUNCATION
(i) Need of Intercom:
The limitation of dual phone is that only parties
can share their information and they have on connection to the
surroundings.
When conversation between many people are
required(but not more than 25people) only two people at a time
intercom can be used.
In Intercom connected telephone systems
there is no dialing systems but a rotary systems provided where
numbers are marked as the capacity of the intercom. Suppose we are
using 10 line intercom then there will be 10 numbers marked on the
rotary system and pointer which is initially holds at off position. The
party which wants to initialize conversation will rotate the pointer to
the number of the second party with whom he/she wants to talk then
a ring tone rights on the second party phone and conversation stars.
The intercom are basically provided in a
house or in a corporate office.
Switching System:
With the introduction of switching systems
the subscribers are not connected to the switching system.
When a subscriber wants to communicate
with another a connection is established between the two at the
switching system.
In switching system only one link per
subscriber is required between the subscriber and the switching
system and the total number of such links equal to the number of
subscribers connected to the system.
The function performed by a switching
system in established connections are known as control function .
Switching System
Manual automatic
Electromechanical electronic
Step by step crossbar space division time division switching switching
Digital Analog
Space switch time switch combination switch
Automatic switching system were manual and operator
oriented .Automatic switching system can be classified as
Electromechanical and Electronic.
Electromechanical switching system include step by step
and crossbar systems.
The control functions in a step by step systems are
performed by circuit associated with the switching
elements in the system.
Crossbar systems have hard wired control subsystems
which uses relays and latches.
Automatic Telephone systems are rapidly replacing
manual one due
to their outstanding merits over the latter types some of which are
enumerated below;
In Automatic telephony higher level of secrecy is maintained due
to absence of operators who can overhear the conversation if
they like in the manual telephone systems.
The working of an Automatic Telephone System does not depend
for its efficiencies of the operators.
There is no possibility of the calls being missed or wrong
metering being done due to fault of operators or due to phonetic
errors between the subscribers and operators.
As no operator is required the running cost of the exchange is
reduced.
BHEL manufacturers EPABX and RAX systems based on
C-dot technology and has plans to make other ranges of
telecommunication equipments also.
There is basically used for connecting links between
various modules like peripherals, exchange and its equipments .it is
necessary to run a number of internal cables of suitable conductors
between the following stages and frames:-
1. Handset to exchange's Cable chamber.
2. cable chamber to M.D.F.
3. M.D.F to I.D.F.
4. I.D.F to number block .
5. number block to exchange equipment.
6. Between two Exchanges.
7. Between two cities.
8. Between two Countries.
Prior to advent of Electronics Exchange inter-
connection of various circuits are made by mechanical contacts
that are operated by mechanical movements produced by the
attraction of an iron armature of an electromagnetic or by the
operation of an electric motor. there are some advantages of
such system for using mechanical contacts due to the following
reasons:
Contacts are subjected to wear and tear.
Require adjustments time to time .
Maintenance is highly precise.
Dependency on the Exchange Operator.
No Secrecy of Conversation.
Huge Exchange Operating Staff Requirements
4. NECESSITY OF AN EXCHANGE:-
If a person wants to talk a second person outside the
house or corporate office on a telephone then he have to abide the
rules and Regulations set by Department of telecommunication India
means that he/she have to make his/her call through the Exchange.
Exchange can be broadly divided into two as:-
1. Manual Exchange
2. Automatic Exchange
Communication Facility in BHEL:-
BHEL
INTERNAL INTERNAL/EXTERNAL(PABX)
Main Exchange sec.6 CFFP(C-Dot)
Main Hospital
(Max Exchange)
(C-Dot)
Description of MAX Exchange:
The main features of the MAX Exchange is given as
below:-
1. it is capable for 2000lines.
2. the technology is provided by Jewnontshinider France which
has its technical collaboration with Uptron India Limited
Lucknow.
3. the Uptron India Limited ,Lucknow has provided this MAX
Exchange to BHEL Haridwar and maintenance of this exchange is
under the hands of Uptron India Limited, Lucknow and BHEL
pays a sum of Rs 6lacs per annum for maintenance.
4. the technology used is PCM (pulse code modulation)and TDM
(time division multiplexing)
5. the exchange is known as TLC10 exchange.
Description of SECT -6 Exchange :-
The main features of exchange established in sector 6 has all
properties same as that of main exchange in Telecom department.
But it has only 335 lines working till date.
Description of PABX Exchange:
PABX exchange can support up to 500 lines. The 500 lines in
the exchange are divided as:-
PABX-500 lines
96 lines Digital 404
lines analog
the main features of this exchange it as :-
1. the technology has been provided by ALCATEL.
2. This exchange has been established in 2000 and is
under the guarantee period of maintenance.
3. The technology used in this exchange is PCM/TDM.
4. The exchange has been supplied to BHEL Haridwar by
Telecommunication consultant India limited and maintained by TELEX.
5. ELECTRONIC EXCHANGES :
In electronic exchange electronic devices effect the interconnection
between different transmission circuits and Electromechanical relays
and switches are dispensed with such electronic devices remove
difficulties associated with mechanical contacts . The greatest
advantage of using electronic devices in place of electromechanical
devices is that no time is loosed in making a connection and a very
high speed of operation is possible .
Electronic Exchanges are of two types :-
1. Tone Type
2. Pulse Type
1. Tone Type : In this type of exchange sine waves are used . There
speed of dialing for a given number is more than that of pulse type.
2. Pulse Type : In this type of exchange square wave is used due to
which the dialing speed is lesser. The telephone apparatus used for
both types are different in construction . But not a days both type of
apparatus are integrated in a single machine in which switch over can
be made via a selector switch .
6. TONES USED IN MODERN TELEPHONY :1.
Dial Tone : When handset is picked up from the cradle. Then
Dial Tone is heard if a free lines is available. This means that the
instrument is ready ,to send the signals to the exchanges, when
the subscriber takes up the receiver then signals are sent M.D.F.
then to I.D.F. line number blokes and to peripherals wherein
various line- cards are mounted in a shelf when corresponding
number on the line card is free then the ringer section of that
peripherals generates a signal called tone. This tone is a
continuous burble sound of HooHz modulated by 25 Hz, and is
sent to the calling subscriber as soon as his line seize the free
line. The subscriber must not dial before receiving this tone:
otherwise he is label to get wrong connection. If he does not get
this tone, he should try after some time.2.
Busy tone : When the called subscriber is engaged with other
call, tone is heard. It consists of sound of ; HooHz : which is
regularly interrupted at equal intervals. It is generally on for 0.75
Sec and off for also 0.75 Sec.3.
Ringing Tone : When a number is dialed then telephone of the
called subscriber start ringing. Calling subscriber should get this
information and this is indicated by sending ringing tone of
interrupted 400 Hz. Supply modulated by 25 Hz. And its
durations are generally equal to the duration of ringing current ,
which rigs the bell. It may be 0.4 Sec. ON, 0.2 Sec OFF,0.4 Sec.
ON and 0.2 Sec OFF and so on or it may be 0.75 Sec ON and 0.75
Sec OFF and so on. When this ringing tone is received, the calling
Subscriber knows that the connection is complete and that the bell of
the called subscriber is ringing.
4. Number Unobtainable Tone : This tone is sent when the number
dialed can be not be obtain. If any subscriber dials which is not actually
connected to the exchange. This indication is send, this is also a tone
of HooHz interruption of 200 microsecond every 3 Sec.
Now a days push button type telephone apparatus are used. This
apparatus can be exploded into following section.
1. Ringer Section
2. Speech Section (Transmitter and receiver section)
3. Voltage limiter Section
From telephone exchange two wires or connectors run for each number
, in which one is neutral and other is main or positive . For the
telephone circuit to work the necessary supply is provided by the
exchange . Like other circuit is established between calling and called
subscriber . When one dials a number then the corresponding relays at
the exchange established a circuit automatically . The telephone
exchange supplies 40-60 volt D.C and 110/20 Hz. To operate this
circuit .This is required because of voltage drop that may crept in long
transmission wires. As soon as the handset is picked up this 48- Volt
DC supply is available at voltage limiter section dialing pulse generator
and speech section.
7. FREQUENCIES USED IN TELEPHONY :
In Telephone dialing two types of frequencies are used:
High band tone (1215 Hz to 1645 Hz)
Low band tone (701 Hz to 936 Hz )
The numbers from 1 to 5 falls in low band and 6 to 9 falls in
high band . Till the handset is on hook ,the ringing section of the
apparatus is on through telephone line but on lifting the hand
set the ringing section becomes off, also the dialing and speech
section becomes ready . on lifting the handset first the dial tone
is receive which is amplified by the amplifier of speech section .
When a number is pressed on the keyboard the dialing
pulses are made on and off according to the number dialed . For
example if 5 is pressed then dialing pulses are made on and off 5
times . This process can be heard . On the receiver . There is a
gap of 1 Sec. Between consecutively pressed numbers.
When the handset is placed on or is lifted from the
instrument a switch is operated called the hook switch.
The main function of this switch is to toggle between
telephone line ringer, dialing & speech sections of the telephone
when the handset is on the telephone then ringer section of the
telephone is on while on lifting it ringer section is disconnected
and dialing section is connected.
8. HOW THE TELEPHONE CALL IS MADE :
Telephone call is characterized in to two sections:
1. Outgoing calls
2. Incoming calls
1. outgoing calls : Generally a voltage of 48v D.C. always
remains on the telephone line but as the handset is picked up the
voltage limiter drops this voltage to 9-12v on hearing the dial tone it is
confirmed that the apparatus it ready to works and after dialing the
number a ringing pulse is send to the called party. When the calling
party picks up the handset the billing meter of the exchange becomes
activated. There is a counter in the exchange, which counts the pulse
and converts them in to cells.
2. Incoming calls : There are just opposite of outgoing calls.
In the incoming calls the telephone detects the ringing signals from the
exchange and provides the ring at the instance of ringing signal there
remains a voltage of 75-110/20Hz on the telephone. A high voltage
(A.C.) is sent from the ringer section of the exchange to start the ringer
circuit of the telephone, when the ringing signal is received it should be
properly isolated as it may give a shock. The ringing circuit is on until
the handset is not picked up at called party. The duration of this tone, if
unattended, is /minute after which an engage tone is hear. After lifting
the handset a circuit is established and a call is made.
9 .POWER SUPPLY FOR EXCHANGE :
There are various power providing circuits available in
the exchange to run the circuitry. These are broadly categorized in two
categories:
1. Outside the exchange.
2. Inside the exchange.
Outside the exchange:
Since the voltage supplied in Indian subcontinent is
220 volts/50Hz. AC but for the normal working of the exchange 48
volts of DC is required.
Hence a rectifier circuit ,backed with battery array
for power failure ,it used. Battery backup is utilized for smooth
operation of the exchange during power failures. For battery back
up lead acid battery from the rectifier block, so that during power
failures the exchange supplies are not terminated.
Inside the exchange :
Inside the telephone exchange various type of
power supplies are used for powering various modules of them are :
1. -5V.12A 2. +5V.12A 3. +12V.6A
Faults Due to Power Supply:
1. Telephone dead . 5. Distorted Speech-
Noising
2. One way due to earthling . 6. False Ring
3. Wrong dialing.
4. Cross connection.
10. FRAMES USED IN TELECMMUNICATION:
1. M.D.F(Main Distribution Frame)
2. I.D.F(Intermediate Distribution Frame)
M.D.F :-
This frame serves the following purposes.
It is place where both external and internal cables are
terminated. The external individuals cables conductors from
subscribers who are necessarily from the same locality and as
such their numbers cannot be in numerical order. On the other
hand, the internal cable conductors come from apparatus side in
numerical order. The cross-section between the two cables is
done in the MDF through jumper wires.
It carries all the protectors used in the exchange. The
different protectors that are used are-
a) Fuses
b) Heat coils
c) Lighting protectors
This MDF is an ideal place for testing purpose. Both the
internal and the external cables are available at this frame and,
therefore, both external and internal wiring and lines can be
tested for this purpose.
I.D.F :-
These frames like M.D.F consists of a large
number of vertical with horizontal cross arms fitted with tag
blocks at both the ends. The cable from M.D.F. is terminated
on the multiple side from where connection are extended to
metering and from the exchange side cables are run to the
respected line-cards. The two tag blocks are joined by means
of jumper wires as in the M.D.F. so that any subscriber can be
given connection to any unselected on the line- cards. The
subscriber and, therefore their unselected are divided in to
different groups and it is necessary for these groups to
originate more or less the same amount os traffic for smooth
distribution among different trunks.
11. TLEPHONE LINES :
In BHEL – Haridwar three types of telephone lines are used.
They are :-
1. MAX lines
2. PABX lines
3. DOT lines
MAX lines
MAX lines are used for internal communication links BHEL.
PABX
PABX lines are used for both internal and external
communions links in BHEL. If the user wants to dial outside the
periphery of BHEL, he can use these lines. There are about 500
lines available here. These lines are distributed in 17 lines – card
with 24 line members in each. Its I.D.F. section has 40 tag block.
96 numbers available here are there connected via digital lines in
which a host of facilities are provides that can be accessed using
code 69.
DOT lines :
There lines are the direct telephone lines from D.O.T. the
facility they provide is called DID (Direct Inwards Dialing). It has 24
lines and any BHEL number starting with digit 5 can be accessed using
code 48.
12. CONNECTION TYPES :
Type of connections
With wires i.e. cables
Wireless Microwave links through satellite.
Cables : Two types of cables are used in telephony.
1. Underground Cables:-These type of cables run under the earth
and are basically used to connect the exchange to the subscriber’s
Distribution Box. They are further of two types based upon their
construction and the insulating material used.
(a) Paper Care A.T.C (Armored Tin Cables)
(b) Jelly filled A.T.C (Armored Tin Cables)
2. Over head Cables:- These type of cables are used to connect
the equipments inside the exchange and connect the peripheral
divides to the subscriber’s distribution Box (D.B.) they are generally of
PVC type.
In an exchange based upon the number of conductor pair
following types of cables are used :
1. Single pair cables.
2. 2 pair cables
3. 5 pair cables.
4. 10 pairs cables.
5. 20 pairs cable.
6. 50 pairs cables.
13. COLOR CODING:-
Type of cable color of wires
Single Pair : Blue wire
2 Pair Cable: Blue , White , Red ,orange/white, red.
5 Pair Cable: Blue , White , orange, white/green, white /brown white
slate /grey white.
100 Pair Cable: The color coding is same as that of the above 20
pairs cable except that the mate color is changed after
each bunch of 20 pairs.
Pair mate Color:-
1. 20 Pairs white
2. 20 Pairs Yellow
3. 20 Pairs Black
4. 20 Pairs Violet
5. 20 Pairs Red
14.AN OVERVIEW OF C-DOT EXCHANGE :
C-DOT exchange are 2 in numbers which are established in main
hospital of 256 points and second in CFFP have 128 points.
64-point ,C-DOT Exchange :
It is the minimum possible points in the C-DOT exchange . It
can use only 148 lines for the subscriber and the rest 16 points are
kept by the exchange itself.
128-Point,C-DOT Exchange :
In 128 points C-DOT Exchange 88 points are used for the
subscribers and 46 points are used by the exchange and remaining 4
points are used for conferencing facility in the exchange . thus this
exchange have only one conferencing facility for the 4 parties.
256 Points, C-DOT Exchange :
In 256 points C-DOT exchange 204 lines in which 8 lines are used
for conferencing , thus remaining 196 lines are used for the
subscriber . The remaining 52 lines are used by the exchange itself .
The 256 points C-DOT exchange can provide 2, four party
conferencing.
NOTE :-
The cords used in 128 points C-DOT exchange are as-
PSU- Power supply unit
TGD – Tone generator diagnostic
JUN- Junction card connecter between two exchange.
SPC – signal processor card.
XSC- Extended Switching Cubical .
LCC-Line Connector Card.
CNF- Conferencing card
DTA- Data Transmission Access.
Out of the above mentioned cards. The power supply unit (PSU).
Tone generator diagnostic (TGD), junction card connector (JUN) Signal
processor card (SPC)and extended switching cubical (XSC)are used two
in numbers to rescue the exchange from any damage .
Configuration of Exchange :-
Max Parts 64 parts 128 Parts
256 Parts
Max Junctions 8 16
32
Max extension without CNF 48 96
208
Max Extension with CNF 40 80
200
Conferencing part Tone parts 8 8
8
Tone parts 8 16
16
Max operator Console 1 2
4
Control Simple duplex
Duplex
Technology PCM/TDM PCM/TDM
PCM/TDM
Features of C-DOT –
1. No A/c required
2. Redundancy of Control modules
3. Expandiability
4. PFC:Power Failure Cut
5. Emergency Services –Fire , Police , Hospital, Electric
Substation, Head of Org.
PABX EXCHANGE:-
Private automatic branch exchange
This is the only exchange which can and directly on BSNL.
Manufacturer- ALCATEL
Supplier- TCIL
Card use in PABX:
1. Z-24 analog circuits
2. LDTL-8 tie line card 9.8 junction
3. INTF for communication between shell fs
4. NDPI for lines from control office BSNL
5. ATR-2
6. CPU
7. MMSFB
8. U8-3
9. SUVG
CODE FOR PABX:
1. NIGHT ALARM Activation code – 852
Cancellation code -853
2. RE-CALL 854
3. LAST CALLER CALL call back-851
15. GENREAL FAULTS OCCURING IN AN EXCHANGE :-
There is mainly two types of faults
. Faults that occur from line.
. occur due to Instrument.
Faults that occur from line:
These faults are categorized s under :
1. Break faults:- occur in the connector at home.
2. Loop faults:- line shorting fault.
3. Earth faults :- occur due to
Wetting of connector
Water in rod get-box
Weak insulation
Oxidation of copper wire
Faults that occur due to Instrument:
1. The number is not dialed.
2. One way speech. receiver coil is fault.
3. Plunger switch is faulty
16. USER FEATURES ON VARIOUS EXCHANGE:
A) MAX(UPTRON TLC-10)
Manufacturer- Jeumont Schneider, France capacity-2000 lines.
1. CALL PICK UP: 29-xxxx to pick up a call
ringing at another location xxx.
2. CALL TRANSFER: 2 parties conversing , any
party can dial 3
rd
party , then conversing among
them hang up.
3. PARTY CONFERENCE:
4. MALICIOUS CALL TRACE: dial 9 during
conversation, to trace a malicious call from a max
ex-tension.
5. APPOINTMENT REMINDER: Dial 7-xx-yy
B) SECTOR 6 EXCHANGE :
Manufacturer- Electronic division, Bangalore
Capacity-256 lines
Auto cal back:
Flash-71, call back only obtainable from local SN no’s
C) PABX=ALCATEL 4400
Manufacturer- ALCATEL, FRANCE
Capacity –500 lines
Technology used: PCM/TDM
1. TONE MUDE DIAL
Dial before no.
2. CALL TRANFER
On hearing promt “Please dial”
3. ENQUIRY CALL:
Put the party on hold
4. BROKER CALL :
between two party
5. CONFERENCE- 3 PARTY:
6. AUTO CALL BACK:
7. PASSWORD MODIFICATION
8. LAST CALLER CALL BACK
9. APPOINTMENT REMINER:
10. LAST NO. REDIAL
11. CALL PICK UP12.
CALL-PARK/ RETRIEVE:
D) BSNL
DYNAMIC LOCK
WAKE UP CALL
CALL WAITING
CALL TRANSFEROR FORWARDING
ABBREVIATED DIALING
17. OPTICAL FIBER SYSTEMS:
Fiber optic transmission medium is fast emerging s an alternating
and strong competitor to coaxial in tele communication networks.
Long distance data transmission in electrical cables suffer from
ground loop problems. The merits of the optical fibres system
from the fact that the basic material used in their used in their
construction is non metallic and electrically non conductive.
In contrast, the nonmetallic and totally dielectric fiber optical
cable are immune to radio frequency an other electromagnetic
interference ground loop and common mode and data can be
transmitted b/t points of vastly differ potential.
In optical cables the information is transmitted by packets of
photons which have no charge .
Fiber cable are about the thickness of a human hair any dirt
obstructing the optical port causes poor transmission The thin
dimension result in allow weight for a give n length when
compared to electrical cables
18. MAINTENANCE OF EXCHANGE :
The subject of maintenance of automatic telephone
exchange can be broadly divided under two categories :-
1. Prevention of service failures .
2. Location of faults and their removal.
Prevention of services failure can be done in following
ways :-
1. Suitable design and adoption of suitable adjustment
standards of the equipment part of the exchange can
minimize failure in service.
2. Some preventive measures may also reduce service failure
viz .Keeping the room and dust free ,maintaining
temperature and humidity under tolerable limits using air
conditioners etc.
3. Routine inspection ,routine test and routine adjustments
also help in preventing service failures.
When faults occur in some parts of the exchange , they should be
detected and removed s quickly s possible .
Various tools are also used to check the faults in the telephone
lines.
For checking fault inside the exchange