INTERNSHIP REPORT
PAKISTAN TELECOMMUNICATION COMPANY LIMITED
(Operation Transmission South, IGE Building Martson Road Karachi)
Submitted by: Hayat Wali
BE-Electronics Iqra University, Defence
View Phase 2 Karachi
Period of internship: July 4, 2011 to August 13, 2011
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Introduction
Pakistan Telecommunication Company Limited is one of the most prestigious
public sector companies of Pakistan, It operates throughout Pakistan. It is
functional in different parts of Karachi.
I was offered internship in Operation Transmission South, IGE Building Marston Road
Karachi. The duration of my internship was one and half months, which I have completed
successes fully. These days were some of the important days of my life, in which I could
achieve a practical knowledge of my theoretical learning. That was an environment fell
equipped with engineering applications
I was supposed to get training in six divisions named as
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International transmission and maintenance (ITMC)
SMW-3 (South East Asia Middle East West Europe)
SMW-4 (South East Asia Middle East West Europe)
New cable and network support ( NC & NS)
Multimedia and Broad Band (MM & BB)
Optical Fiber System (OFS)
These were the six divisions in which I have spent six weeks, with one week at each division.
ITMC
(International transmission and maintenance)
The main task of ITMC is to provide cooperation between local media and
international media. It establishes connectivity between the local haul or back haul
and the forward haul or international media. This connectivity consists of voice
and data. The transmission of voice and data is accomplished by using different
techniques. The signals to be transmitted need to be undergone techniques like
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sampling, quantization, encoding and transmission. To increase the capacity of the
transmission media techniques like multiplexing, modulation are also used.
MODULATION
 Original signal superimposed on carrier frequency.
 Signal transmitted at higher frequency in order to increase efficiency.
 Carrier frequency changes according to original signal. AM,FM etc
MULTIPLEXING
Different signals are combined together and transmitted along the channel in
order to save the bandwidth. (Many into one)
FOUR TYPES OF MULTIPLEXING ARE:
1.
2.
3.
4.
Space Division Multiplexing – space is divided.
Frequency Division Multiplexing – frequency is divided.
Time Division Multiplexing – time is divided.
Code Division Multiplexing – space, time and frequency is divided.
PCM (PULSE CODE MODULATION)
PCM is a modulation technique in which analog signals are converted into digital
signals it consists of 3 steps:
Sampling – An analog signal is divided into 8000 samples
Quantization – each sample is rounded up or down based on the algorithm.
Encoding – Finally the sample is encoded.
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PROCESS
 1 sample information = 8bit
 8000 samples processed in 1sec.
 Therefore 8000sample info = 8*8000 = 64000 bits = 64kb/sec.
 30 voice calls are transmitted together.
 30*8000 = 240000 samples
 30*64kbps = 1920kbps
 1frame = 32bits, therefore 32*64 = 2048kb/sec = 2Mb/sec= E1
PLESIOCHRONOUS DIGITAL HIERARCHY
PDH is obsolete in today’s world due to drawbacks. Following are the
disadvantages of PDH:
 No NMS (Network Management System). No interaction between man and
machine.
 No software control.
 No standard defined internationally.
 Vendor bounded.(different vendors could not communicate with each
other).
 Bit interleaving. (bitwise transmission)
 No add drop directly.
 Point to point.
SYNCHRONOUS DIGITAL HIERARCHY(SDH)
SDH is the upgraded version of PDH, fulfilling the drawbacks of PDH.
Characteristics of SDH are:
 NMS.
 Software control.
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 Multi vendor.
 Add drop directly.
 Byte interleaving.(Byte wise transmission)
 Point to point and multipoint.
 International standard.
SMW-3
 SWM-3 connects 35 countries to Pakistan by means of optical fiber.
 STM-64 is 1‫ גּ‬i.e. 55 nanometer.
 IPLC (LEASE CUSTOMER): Uses their own bus a single telephone line
dedicated to themselves.
 PFE (Power Feeding Equipment): Power cable travels along the optical fiber
cable to provide power to regenerators and repeaters in the sea.
 DCN (DATA Communications Network): consists of routers which define the
wavelength (‫)גּ‬. Mumbai is connected to fiber pair1 (‫=גּ‬4) and Fujairah is
connected to (‫=גּ‬6). Router recognizes which cable is of Mumbai and which is
of Fujairah. Cable from DCN connects to SLTE (Submarine Line Terminating
Equipment). Each country has its own SLTE.
ROUTERS  TRIBUTRY  COMMON  TWMA (Trans Wavelength Multiplex
Amplifier)
 TWMA(Trans Wavelength Multiplex Amplifier) is used to amplify the signals
while transmitting
 RWDA (Receive Wavelength Differential Amplifier) amplify the signals while
receiving.
 Data rate in tributaries is STM-64.
 FEC encoder (Forward Error Correction): Encodes the data in tributary to
enable error correction.
 Western side is connected by Djibouti at (‫=גּ‬4) and (‫=גּ‬6).
 1‫ =גּ‬STM-64 = 10gbps.
 De multiplexing occurs while receiving. STM-64  STM-16  STM-4  E1
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ADM
ODF
LOWER ORDER MUX
DIRECT CUSTOMER
 STM-4 to STM-64 = Higher Order.
 E1 to STM-1 = Lower Order.
SMW – 4
 2 Power Feeding Equipments installed.
o 1 for SMW-3.
o 1 for SMW-4.
 Connects Pakistan to 17 different countries.
 Process same as SMW-3.
 Marine cables come and connect to DCN (Data Communication Network).
 From DCN cables are connected to SLTE.
 SLTE transfers the cables to ADM.
o STM-64 gets de multiplexed to STM-16, STM-4, and STM-1.
 Then the cables are fed to ODF.
o This distributes the connection locally.
DCN
SLTE
ADM
ODF
We have rectifiers to prevent damage.
SMW-4 connects Pakistan to 17 countries. Few examples are:
East
West
Malaysia
SA
Singapore
UAE
India
Alexandria
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WDM (Wavelength Division Multiplexing):
 Different SDH come and connect to WDM.
 Based on the frequency WDM allots channels to different signals.
 Segment  grouping of signals (countries are divided into segments) so that
a problem occurs it can be rectified easily.
 Last station Marseille(France)
 Installing new project IMWE(Indian Middle East Western Europe)
Multimedia and Broad Band
.
Broadband
The word broadband is used for the minimum bandwidth which can support the
transmission of multimedia services.
Broadband access
Broadband access is the high speed connection between the end user and internet
through certain kind of network.
Broadband Access Technologies
XDSL
HSDL…….High speed digital subscriber
SDSL………symmetric DSL
ADSL……….Asymmetric DSL
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VDSL………Very high bit rate DSL
EDSL……..Ethernet DSL
ISDL………..ISDN DSL
UDSL………….Ultra high DSL
HFC…….Hybrid fiber coaxial
Home PNA………..Home phone line
Ethernet
Wireless Broadband
LMDS……..local multipoint Distribution
DBS…………Direct Broad service
Microwave Radio Access
Gprs………..General packet Radio service
Optical access network
Plc……….Power line cable
SDH………synchronous digital hierarchy
Frame relay.
Theses are some broadband access technologies, which are used to access
internet and other broadband services.
DSL Principles
SHDSL
It is Single pair high bit rate DSL, one pair, symmetric transmission, Variable data
rates
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Generally the variable data rate is 192 Kbps………..2.312Kbps
The range is valid up to a range of 5 Km.
VDSL
VDSL is very high data rate DSl, one wire pair, variable Data rates, Valid up to 5 Km.
The data rate is up to 13mbps to 52Mbps.
ADSL
One wire pair, Asymmetric transmission, data rates from 64 Kbps to 1.5 Mbps,
covering a distance of 5 Km.
Optical fiber system (OFS)
Optical fiber system consist a network of optical fibers which are used for the
transmission of optical signals.
Initially all the signals are analog signal which can’t be transmitted to long distance
because they undergo transmission impairments and path losses. To minimize
such problems optical fibers have been designed because in which signals are
although analog but they undergo a very low line problems.
Usually in transmission of signal at a certain distance repeaters are used which
regenerate the signal again; in case of optical fibers these repeaters are installed at
a large distance usually 25 km.
Because of there light weight optical fibers are very easy to install even under
water. Use of Optical fibers has increased the capacity of data transmission
through a media. It is said that the bandwidth of a single optical fiber can be
increased to infinity by using modern multiplexing techniques.
A single optical fiber can support a data of 10 GB. This is used commonly in long
distance transmission.
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STRUCTURE OF OPTICAL FIBER
Optical fiber generally consists of three parts
 Core
 Cladding
 Jacket
CORE
Core is the inner most section and consists of one or more strands, made up of
glass or plastic, the core has a diameter of 50 micrometer.
CLADDING
A glass or plastic coating having optical properties different from those of the core,
and has diameter of 125 micrometer. The interface between core and cladding act
as a reflector to confine light that would otherwise escape the fiber.
JACKET
The jacket is composed of plastic and other materials layered to protect against
moisture, abrasion, crushing and other environmental dangers.
MODES OF TRANSMISSION
The transmission of light signals through an optical fiber is accomplished by using
different transmission modes like Single mode, graded index Multimode, step
index mode.
SINGLE MODE
In single mode, the light rays travel in a straight line. Some Spacing is kept
between the rays to avoid interference. This mode is used for large distance
communication
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GRADED INDEX MULTIMODE
This mode of transmission is done by varying the index of refraction of the core.
Refractive index is higher at centre whereas it decreases towards the corners.
This transmission mode is used for shorter distances.
STEP INDEX MULTIMODE
Rays at shallow angle are reflected and propagated through along the fiber other
rays are absorbed by the surrounding material. With this mode multi paths exist
due to which signals undergo dispersion and data can’t be accurately achieved.
NEW CABLES AND NETWORK SUPPORT
This division of PTCL is associated with the repairing and maintenance of cables
and optical fibers. New cables are put by this division by replacing the existing
worn out cables. This division usually works outside of the terminal. Different
devices are used to repair cable. If somehow a fault occurs in a cable a device
named as megger is used which measures the distance of fault from the terminal.
Megger is also used to check the condition of a cable whether it is proper
condition or not.
The device used to repair cable is OTDR or Optical time domain reflect meter.
OPTICAL TIME DOMAIN REFLECTOMETER
It is an optoelectronic device used for estimating the fibers length and overall
attenuation, including splice and mated connectors losses. It may be used to locate
faults, such as breaks and to measure optical return loss. Testing is done for one
end only.
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STEPS INVOLVED IN REPAIRING AN OPTICAL FIBER
An optical fiber is repaired in three steps
 Cladding
 Cleaving
 Cleaning
Cladding
The first step of repairing an optical fiber is cladding, in which the jacket is
removed. As an optical fiber consists of many pairs so color coding is used to
differentiate between the damaged and sound pairs.
Cleaving
Cleaving is the process of cutting the damaged part. Cleaving is a done by an
instrument which consists of diamond. As the jacket of optical fiber is very strong,
therefore it is necessary to get the job done by some sort of sharp instrument.
Cleaning
Dust particles are removed through an alcoholic gauss. Then splicing machine is
used to join the broken ends.
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CONTENTS
Introduction…………………………………………………………………………………………………………02
ITMC……………………………………………………………………………………………………………………02
 Modulation…………………………………………………………………………………………………02
 Types of Multiplexing………………………………………………………………………………….02
 Synchronous Digital hierarchy…………………………………………………………………….04
SMW-3………………………………………………………………………………………………………………..05
SMW-4………………………………………………………………………………………………………………..06
 WDM…………………………………………………………………………………………………………..07
Multimedia and Broadband…………………………………………………………………………………07
 Broadband Access Technologies……………………………………………………….………..07
 DSL Principles………………………………………………………………………………….………….08
Optical Fiber Systems………………………………………………………………….……….………………09
 Structures of optical fiber………………………………………………………….………………..10
 Modes of transmission………………………………………………………………………….…….10
New cables and Network Support……………………………………………………………………….11
 OTDR…………………………………………………………………………………………..………………11
 Steps of repairing Cable………………………………………………………………………………12
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