Behind the completion of any successful work there lies the contribution
of not one but many individuals who may have directly or indirectly
contributed to it.
I first of all want to thank BHARAT SANCHAR NIGAM LIMITED
(BSNL) for providing me this valuable opportunity to work and learn
with them. I owe my personal thanks to my trainer in charge –Mr.
R.P.Tiwari who extended full support and co-operation at every stage of
my training period.
I am also thankful to my parents and friends for their constant
encouragement and helping me in my endeavor.Last, but not the least, I
would like to thank everyone who has contributed for the successful
completion of my training.
Organizations are made up of people and function through people.
Without people, organizations cannot exist. The resources of men,
money, material, machinery, and mechanism are connected, coordinated
and utilized through people. Engineers need to concentrate more on
mechanism and the way in which things have been made. The need of
training arises for doing things yourself, understanding its way.
Practical exposure for doing things makes a person conversant to the
technicalities involved in any job. In view of such benefits, imparting of
vocational training has been made an integral part of any academic
In B.S.N.L., training is given to Engineering Aspirants to secure future in
the dynamic world of telecommunications. Today telecommunication
industry is one of the very fastest growing industries in the world.
In this order I have taken 28 days BSNL training. In my report I try to
introduce Basic communication system, optical fiber, GSM concepts and
India is the fourth largest telecom market in Asia after China, Japan and
South Korea. The Indian telecom network is the eighth largest in the
TYPE: COMMUNICATION SERVICE PROVIDER
AVAILABLITY: NATIONAL EXCEPT DELHI & MUMBAI
OWNER: THE GOVERNMENT OF INDIA
HOW BSNL CAME IN TELECOM MARKET:
The initial phase of telecom reforms began in 1984 with the creation of
Center for Department of Telematics (C-DOT) for developing indigenous
technologies and private manufacturing of customer premise equipment.
Soon after, the Mahanagar Telephone Nigam Limited (MTNL) and
Videsh Sanchar Nigam Limited (VSNL) were set up in 1986.The
Telecom Commission was established in 1989. A crucial aspect of the
institutional reform of the Indian telecom sector was setting up of an
independent regulatory body in 1997 – the Telecom Regulatory Authority
of India (TRAI), to assure investors that the sector would be regulated in
a balanced and fair manner. In 2000, DoT corporatized its services wing
and created Bharat Sanchar Nigam Limited.
BSNL CONTRIBUTION TO DEVELOPMENT OF TELECOM:
Bharat Sanchar Nigam Limited was formed in year 2000 and took over
providers role from DOT. BSNL’s roadmap for providing customer with
access to the latest telecommunications services without losing sight of
universal service access has been by way of utilizing optimally the
existing infrastructure and accelerating advances in technological
component by innovative absorption.
BASIC TELECOMMUNICATION NETWORK
This section includes brief introduction of how a call is processed when
we dial a call from basic telephone to another basic telephone or from
basic to mobile or vice versa.
· When a subscriber calls to another subscriber first its request goes to
the nearest switching centre that is PSTN (Public Switching
Telecommunication Network). Then it processes the caller and
subscriber’s number if it exists in the same BSC then call setup is
· If subscriber is not in the same BSC (Base Switching Centre) then call
transfer to MSC (Main Switching Centre) then it transfers the call to
prior BSC then call setup is completed.
· If Caller calls to a mobile subscriber then call transfer is done by
MTSO now call transfer is done on BTSs (Base Transceiver Station)
and call setup is completed.
FUNCTION OF EXCHANGE:
· Exchange of information with subscriber lines with other exchange.
This is done by two type of signaling:
1. Inchannel signaling
2. Common channel signaling
· Processing of signaling information and controlling the operation of
· Charging and billing.
· All control functions by series of instructions are stored in memory.
· Memories are modifiable and control program can always be
rewritten. For each call processing step decision is taken according to
class of service.
Leased line connectivity is provided in carrier room. This room has two
1. Conventional leased line system
CONVENTIONAL LEASED LINE SYSTEM:
· It consists of modems and routers that are provided by the company
requesting for that network.
· Connectivity of different ATM, banks etc. is provided by BSNL here.
· For this, we have 4 modems (2 in Exchange, 1 at sender and 1 at
· Modems are used for short distances i.e. trans and receive part are
received here and local lead connection is given to the subscriber.
· Local lead faults can be handled here but the trans and receive faults
can be handled by the department meant for it.
· Accept 64Kbps or 2 Mbps.
· For long distance communication we have MUXS and data is sent
through optical fibers. MUXS are present at both the ends.
MDF(MAIN DISTRIBUTION FRAME):
M.D.F. is a media between switching network and subscriber’s line. It is
a termination point within the local telephone exchange where exchange
equipment and terminations of local loops are connected by jumper wires.
MANAGED LEASED LINE NETWORK:
The MLLN service is specially designed mainly for having effective
control and monitoring on the leased line so that the down time is
minimized and the circuit efficiency is increased. This mainly deals with
data circuits ranging from 64 Kbps to 2048 Kbps
FUNCTIONS OF MDF:
· All cable copper wires supplying services through user telephone lines
are terminated and distributed through MDF.
· The most common kind of large MDF is a long steel rack accessible
from both sides. Each jumper is a twisted wire.
· It consists of local connection and broadband connection frames for
the main Exchange area.
· The MDF usually holds central office protective devices including
heat coils and functions as a test point between a line and the office.
· It provides testing of calls.
· It checks whether fault is indoor or external.
· All lines terminate individually.
1. 24 hrs Performance Monitoring of the circuit.
2. Circuit fault reports generated proactively.
3. On Demand the Bandwidth can be increased.
4. Low lead time for new circuit provisioning.
· It provides -48V to the switch rooms and 48V to the connections.
· Batteries are artificially discharged once in a year for their
· Cooling is provided through fans & AC.
· There is earth region too for protection.
APPLICATION OF MLLN:
1. Corporate high speed internet access through Broadband.
2. LAN interconnection.
3. Hotline connectivity for voice.
4. Point to point connection for data circuit.
5. Point to multipoint connection.
Traditional mobile service was structured similar to television
broadcasting: One very powerful transmitter located at the highest spot in
an area would broadcast in a radius of up to fifty kilometers. The Cellular
concept structured the mobile telephone network in a different way.
Instead of using one powerful transmitter many low-powered transmitter
were placed throughout a coverage area. For example, by dividing
metropolitan region into one hundred different areas (cells) with low
power transmitters using twelve conversations (channels) each, the
system capacity could theoretically be increased from twelve
conversations using one hundred low power transmitters.
A cell is the basic geographic unit of cellular system. The term cellular
comes from the honeycomb areas into which a coverage region is
divided. Cells are base stations transmitting over small geographic areas
that are represented as hexagons. Each cell size varies depending upon
landscape. Because of constraint imposed by natural terrain and man-made
structures, the true shape of cell is not a perfect hexagon.
A group of cells is called a cluster. No frequencies are reused in a cluster.
Features of Digital Cellular Systems:
· Small cells
· Frequency reuse
· Small, battery-powered handsets
· Performance of handovers
The spectrum allocated for a cellular network is limited. As a result
there is a limit to the number of frequencies or channels that can be used.
A cellular network can only provide service to a large number of
subscribers, if the channels allocated to it can be reused. Channel reuse is
implemented by using the same channels within cells located at different
positions in the cellular network service area.
Radio channels can be reused provided the separation between cells
containing the same channel set is far enough apart so that co-channel
interference can be kept below acceptable levels most of the time
GLOBAL SYSTEM FOR MOBILE COMMUNICATION
In wireless communication every region is divided into cells. Cell size is
constant for whole system. GSM is a form of multiplexing, which
divides the available bandwidth among the different channels. Most
of the times the multiplexing used is either TDM (Time division
multiplexing) or FDM (Frequency Division Multiplexing). SM
differs from its predecessor technologies in that both signaling and
speech channels are digital, and thus GSM is considered a second
generation (2G) mobile phone system.
A GSM system is basically designed as a combination of three major
subsystems: the network subsystem, the radio subsystem, and the
operation support subsystem. In order to ensure that network operators
will have several sources of cellular infrastructure equipment, GSM
decided to specify not only the air interface, but also the main interfaces
that identify different parts. There are three dominant interfaces, namely,
an interface between MSC and the base Transceiver Station (BTS), and
an Um interface between the BTS and MS.
GSM NETWORK STRUCTURE
Every telephone network needs a well-designed structure in order to route
incoming called to the correct exchange and finally to the called
subscriber. In a mobile network, this structure is of great importance
because of the mobility of all its subscribers [1-4]. In the GSM system,
the network is divided into the following partitioned areas.
· GSM service area;
· PLMN service area;
· MSC service area;
· Location area;
MAIN FEATURES OF GSM:
· Support for voice and data services
· Better frequency efficiency, smaller cells and more customers per cell
· High audio quality and reliability for wireless, uninterrupted phone
calls at higher speeds (e.g. from cars, trains) i.e. high transmission
· Authentication via chip-card and PIN.
· Worldwide connectivity.
· BASE STATION SYSTEM (BSS)
· NETWORK SWITCHING SUBSYSTEM (NSS)
MOBILE STATION (MS):
A mobile unit is a transmitter as well as receiver too. It has a SIM
(Subscriber Identity Module) which gives a unique identity of a
subscriber. Every mobile unit has a unique IMEI (International Mobile
Equipment Identity) number.
BASE TRANSCEIVER STATION (BTS):
· A base transceiver station or cell site (BTS) is a piece of equipment
that facilitates wireless communication between user equipment (UE)
and a network.
· It encodes, encrypts, modulates and feeds the RF signal to antenna.
· It produces time and frequency synchronization signals.
· It does power control and frequency hopping too.
BASE STATION CONTROLLER (BSC):
· Its main work is to control several transceivers.
· Switching between BTSs
· Managing of network resources
· Mapping of radio channels
NETWORK AND SWITCHING SUBSYSTEM:
This subsystem does mainly switching, mobility management,
interconnection to other networks, system control.
1. MOBILE SERVICES SWITCHING CENTRE (MSC):
It controls all connections via a separated network to/from a mobile
terminal within the domain of the MSC – several BSC can belong to a
MSC. The basic switching function of performed by the MSC, whose
main function is to coordinate setting up calls to and from GSM users.
FUNCTION OF MAIN SWITCHING CENTER (MSC):
· Manages communication between GSM and other network (PSTN,
Data Network and GPRS).
· Call setup basic switching, call handling.
· Location register
· Billing for subscriber
Home Location Register (HLR):
The HLR is a database that permanently stores data related to a given set
of subscribers. Various identification numbers and addresses as well as
authentication parameters, services subscribed, and special routing
information are stored.
The HLR is responsible for storage and provision of SIM authentication
and encryption parameters needed by the MSC where the MS-SIM is
operating. It obtains these parameters from the AUC.
The HLR maintains record of which supplementary service each user has
subscribed to and provides permission control in granting services. Some
data are mandatory, other data are optional. Both the HLR and the VLR
can be implemented in the same equipment in an MSC (collocated). A
PLMN may contain one or several HLRs.
Visitor Location Register (VLR):
The VLR is collocated with an MSC. A MS roaming in an MSC area is
controlled by the VLR responsible for that area. When a MS appears in a
LA, it starts a registration procedure. The MSC for that area notices this
registration and transfers to the VLR the identity of the LA where the MS
is situated. A VLR may be in charge of one or several MSC LA’s. The
VLR constitutes the databases that support the MSC in the storage and
retrieval of the data of subscribers present in its area. When an MS enters
the MSC area borders, it signals its arrival to the MSC that stores its
identify in the VLR. The information necessary to manage the MS is
contained in the HLR and is transferred to the VLR so that they can be
easily retrieved if so required. the data are present in the VLR only as
long as the MS is registered in the area related to that VLR.
EQUIPMENT IDENTIFY REGISTER
EIR is a database that stores the IMEI numbers for all registered ME
units. The IMEI uniquely identifies all registered ME. There is generally
one EIR per PLMN. The EIR keeps track of all ME units in the PLMN. It
maintains various lists of message. There are three classes of ME that are
stored in the database, and each group has different characteristics.
· White List: contains those IMEIs that are known to have been
assigned to valid MS’s. This is the category of genuine
· Black List: contains IMEIs of mobiles that have been reported
· Gray List: contains IMEIs of mobiles that have problems (for
example, faulty software, wrong make of the equipment). This
list contains all MEs with faults not important enough for
The AUC stores information that is necessary to protect communication
through the air interface against intrusions, to which the mobile is
vulnerable. The legitimacy of the subscriber is established through
authentication and ciphering, which protects the user information against
unwanted disclosure. Authentication information and ciphering keys are
stored in a database within the AUC, which protects the user information
against unwanted disclosure and access.
PUBLIC SWITCH TELEPHONE NETWORK
The public switched telephone network (PSTN) is the aggregate of the
world's circuit-switched telephone networks that are operated by national,
regional, or local telephone operators, providing infrastructure and
services for public telecommunication. The PSTN consists of telephone
lines, fiber optic cables, microwave transmission links, cellular
networks, communications satellites, and undersea telephone cables, all
interconnected by switching centers, thus allowing any telephone in the
world to communicate with any other.
OPERATION AND MAINTENANCE CENTER
The operations and maintenance center (OMC) is connected to all
equipment in the switching system and to the BSC. The implementation
of OMC is called the operation and support system (OSS). The OSS is
the functional entity from which the network operator monitors and
controls the system. The purpose of OSS is to offer the customer cost-effective
support for centralized, regional, and local operational and
maintenance activities that are required for a GSM network..
FEATURES OF GSM:
· GSM is already used worldwide with over 450 million subscribers.
· International roaming permits subscribers to use one phone
throughout Western Europe. CDMA will work in Asia, but not
France, Germany, the U.K. and other popular European destinations.
· GSM is mature, having started in the mid-80s. This maturity means a
more stable network with robust features. CDMA is still building its
· The availability of Subscriber Identity Modules, which are smart
cards that provide secure data encryption give GSM m-commerce
GENERAL PACKET RADIO SERVICE (GPRS)
General packet radio service (GPRS) is a packet oriented mobile data
service available to users of the 2G cellular communication systems,
global system for mobile communications (GSM), as well as in the 3G
systems. In 2G systems, GPRS provides data rates of 56-114 kbps. It
provides moderate speed data transfer, by using unused time division
multiple access (TDMA) channels.
Its supported protocols are Internet Protocol (IP), Point to Point Protocol
(PPP) and X.25.
GPRS data transfer is typically charged per megabyte of traffic
transferred, while data communication via traditional circuit switching is
billed per minute of connection time, independent of whether the user
actually is using the capacity or is in an idle state. GPRS is a best effort
packet switched service, as opposed to circuit switching, where a certain
Quality of service (QoS) is guaranteed during the connection for non-mobile
GPRS extends the GSM circuit switched data capabilities and makes the
following services possible:
· “ Always on” Internet access
· Multimedia messaging service (MMS)
· Push to talk over cellular (PoC/PTT)
· Instant messaging and presence – wireless village
· Internet applications for smart devices through wireless application
· Point to Point (P2P) service: inter-networking with the internet
· Increase message sending speed 30 messages per minute
CODE DIVISION MULTIPLE ACCESS (CDMA)
Code Division Multiple Access (CDMA) consistently provides better
capacity for voice and data communications that other commercial
mobile technologies, allowing more subscribers to connect at any given
time, and it is the common platform on which 3G technologies are built.
CDMA is a spread spectrum technology, allowing many users to occupy
the same time and frequency allocations in a given band/space. As it
name implies, CDMA assigns unique codes to each communication to
differentiate it from others in the same spectrum resources, CDMA
enables many more people to share the airwaves at the same time than do
ADVANTAGES OF CDMA:
· Increased cellular communications security.
· Simultaneous conversations
· Increased efficiency, meaning that the carrier can serve more
· Smaller phones
· Low power requirements and little cell-to-cell coordination needed
· Extended reach-beneficial to rural users situated far from cells.
DISADVANTAGES OF CDMA:
· Due to its proprietary nature, all of CDMA’s flaws are not known
to the engineering community.
· CDMA is relatively new, and the network is not as mature as
· CDMA cannot offer international roaming, a large GSM
DIFFERENCE BETWEEN CDMA AND GSM:
· The GSM stands for global system for mobile communication and
CDMA for code division multiple accesses.
· GSM is a form of multiplexing, which divides the available
bandwidth among the different channels. Most of the times the
multiplexing used are either TDM (Time Division Multiplexing) or
FDM (Frequency Division Multiplexing). On the other hand
CDMA is a type of multiple access scheme (which means allotting
the given bandwidth to multiple users) and makes use of spread
spectrum technique which is essentially increasing the size of
· In CDMA each user is provided a unique code and all the
conversations between 2 users are coded. This provides a greater
level of security to CDMA users than the GSM ones.
Optical Fiber is new medium, in which information (voice, Data or
Video) is transmitted through a glass or plastic fiber, in the form of light,
following the transmission sequence give below :
(1) Information is encoded into Electrical Signals.
(2) Electrical Signals are converted into light Signals.
(3) Light Travels down the Fiber.
(4) A Detector Changes the Light Signals into Electrical Signals.
(5) Electrical Signals are decoded into Information.
OPTICAL FIBER TRANSMISSION
ARCHITECTURE OF FIBER:
The optical fiber has two concentric layers called the core and the
cladding. The inner core is the light carrying part. The surrounding
cladding provides the difference refractive index that allows total internal
reflection of light through the core. The index of the cladding is less than
1%, lower than that of the core. Most fibers have an additional coating
around the cladding. This buffer coating is a shock absorber and has no
optical properties affecting the propagation of light within the fiber.
In an optical fiber, a refracted ray is one that is refracted from the core
into the cladding. Specifically a ray having direction such that where r is
the radial distance from the fiber axis, φ(r) is the azimuthal angle of
projection of the ray at r on the transverse plane, θ(r) is the angle the ray
makes with the fiber axis, n (r) is the refractive index at r, n (a) is the
refractive index at the core radius, a. Refracted rays correspond to
radiation modes in the terminology of mode descriptors.
For the fiber to guide the optical signal, the refractive index of the core
must be slightly higher than that of the cladding. In different types of
fibers, the core and core-cladding boundary function slightly differently
in guiding the signal. Especially in single-mode fibers, a significant
fraction of the energy in the bound mode travels in the cladding.
The light in a fiber-optic cable travels through the core (hallway) by
constantly bouncing from the cladding (mirror-lined walls), a principle
called total internal reflection. Because the cladding does not absorb any
light from the core, the light wave can travel great distances. However,
some of the light signal degrades within the fiber, mostly due to
impurities in the glass. The extent that the signal degrades depends on the
purity of the glass and the wavelength of the transmitted light.
Phenomena of Total internal reflection.
Light at less than
critical angle is
absorbed in jacket
Light is propagated by
total internal reflection
Fig. Total Internal Reflection in an optical Fibre PROPAGATION OF LIGHT THROUGH FIBRE
There are two types of fibers:
(I) Step Index fiber (Step Index fiber)
(II) Graded Index fiber (Graded Index fiber)
(I) STEP-INDEX FIBER: It has a large core, up to 100 microns in
diameter. There is a step change between the core-cladding interface. As
a result, some of the light rays that make up the digital pulse may travel a
direct route, whereas others zigzag as they bounce off the cladding. This
type of fiber is best suited for transmission over short distances, in an
endoscope, for instance.
(II) GRADED-INDEX FIBER: It contains a core in which the refractive
index diminishes gradually from the center axis out toward the cladding.
There is gradual change between the core-cladding interface. The higher
refractive index at the center makes the light rays moving down the axis
advance more slowly than those near the cladding. A digital pulse suffers
11.4 ADVANTAGES OF FIBRE OPTICS:
• SPEED: Fiber optic networks operate at high speeds - up into the
• BANDWIDTH: large carrying capacity.
• DISTANCE: Signals can be transmitted further without needing to be
refreshed or strengthened.
• RESISTANCE: Greater resistance to electromagnetic noise such as
radios, motors or other nearby cables.
• MAINTENANCE: Fiber optic cables costs much less to maintain
Engineering student will have to serve in the public and private sector
industries and workshop based training and teaching in classroom has
advantage but has its own limitation. Practical training is one of the major
steps in this direction. I did my training from RTTC BSNL, Lucknow
which is one of the best known communication service provider
companies of India. The training helps me in gaining in depth knowledge
of the working of telephone exchange, various technologies of BSNL
GSM, GPRS, MLLN and optical fiber transmission etc.
In the end, I hereby conclude that I have successfully completed my
industrial training Mobile Communication System.