1 A INDUSTRIAL TRAINING REPORT UNDERTAKEN AT BSNL EXCHANGE, KATHUA ON BASIC TELECOM SESSION 2012-2016 Submitted in partial fulfillment of the requirement for the award of the degree of Bachelor of Engineering In Electronics and Communication SUBMITTED BY: KANAV MANSOTRA 27-GCET-2012 VII SEM (ECE) ----------------------------------------------------------------------------- SUBMITTED TO: Department of Electronics & Communication Engineering Government College of Engineering & Technology Jammu ----------------------------------------------------------------------------
Transcript
1
A
INDUSTRIAL TRAINING REPORT UNDERTAKEN AT
BSNL EXCHANGE, KATHUA
ON
BASIC TELECOM
SESSION 2012-2016
Submitted in partial fulfillment of the requirement for the award of the degree of
Bachelor of Engineering In
Electronics and Communication
SUBMITTED BY: KANAV MANSOTRA
27-GCET-2012 VII SEM (ECE)
----------------------------------------------------------------------------- SUBMITTED TO:
Department of Electronics & Communication Engineering
Government College of Engineering & Technology Jammu
OFC, 50,430 RKm. of microwave network connecting 623 districts, 7330
cities/towns & 5.8 lakhs villages .
BSNL is the only service provider, making focused efforts & planned initiatives
to bridge the rural-urban digital divide in ICT sector. In fact there is no telecom
operator in the country to beat its reach with its wide network giving services
in every nook & corner of the country & operates across India except New
Delhi & Mumbai. Whether it is inaccessible areas of Siachen glacier or North-
Eastern regions of the country, BSNL serves its customers with a wide
bouquet of telecom services namely Wireline, CDMA mobile, GSM mobile,
Internet, Broadband, Carrier service, MPLS-VPN, VSAT, VoIP, IN Services,
FTTH, etc.
BSNL is numero uno of India in all services in its license area. The company
offers wide ranging & most transparent tariff schemes designed to suit every
customer. BSNL has 90.09 million cellular & 5.06 million WLL customers as
on 31.07.2011. 3G Facility has been given to all 2G connections of BSNL. In
basic services, BSNL is miles ahead of its rivals, with 24.58 million wireline
phone subscribers i.e. 71.93% share of the wireline subscriber base.
BSNL has set up a world class multi-gigabit, multi-protocol convergent IP
infrastructure that provides convergent services like voice, data & video
through the same Backbone & Broadband Access Network. At present there
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are 8.09 million broadband customers.
The company has vast experience in planning, installation, network
integration & maintenance of switching & transmission networks & also has a
world class ISO 9000 certified Telecom Training Institute.
During the 2010-11, turnover of BSNL is around Rs. 29,700 Crores.
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1. TELECOM 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.
1.1 CALL SETUP:
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 completed.
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.
FIG 1.1 HOW LINE REACHES FROM SUBSCRIBER TO EXCHANGE
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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 signaling network.
Charging and billing.
1.2: ELECTRONIC EXCHANGE:
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.
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Let us discuss a bit more about exchange:
ABOUT THE EXCHANGE
In the field of, a telephone exchange or telephone switch is a system of
electronic components that connects telephone calls. A central office is
the physical building used to house equipment including telephone
switches, which make "work" in the sense of making connections and
relaying the speech information.
TYPE’S OF EXCHANGE
Manual exchange
Strowger exchange
Cross bar exchange
Electronics exchange (analog and digital exchange)
MANUAL EXCAHNGE
With manual service, the customer lifts the receiver off-hook and asks
the operator to connect the call to a requested number. Provided that the
number is in the same central office, the operator connects the call by
plugging into the jack on the switchboard corresponding to the called
customer's line. If the call is to another central office, the operator plugs
into the trunk for the other office and asks the operator answering
(known as the "inward" operator) to connect the call.
STROWGER EXCHANGE
Strowger developed a system of automatic switching using an
electromechanical switch based around electromagnets and pawls. With
the help of his nephew (Walter S. Strowger) he produced a working
model in 1888 .selector starts in the 'home' position and with each
'impulse' the wiper contacts would progress round the output bank to the
next position. Each output would be connected to a different subscriber,
thus the caller could connect to any other subscriber who was connected
to that bank, without any manual assistance from an operator.
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Diagram of a simple Selector
In Figure 2 (above), the selector has 10 outputs, so a caller can choose
to connect to any of 10 different subscribers by dialing any digit from 1 to
0 (0=10). This sort of automatic selector is known as a Uni-selector, as it
moves in just one plane (rotary).
By mounting several arcs of outlets on top of each other, the number of
outlets can be increased significantly but the wipers are then required to
move both horizontally to select a bank and then vertically to move
around that bank to the required outlet. Such a selector is known as
a Two-Motion Selector. Two-motion selectors typically have 10 rows of
10 outlets, thus 100 possible outlets altogether. A two-motion selector
can therefore accept two dialed digits from a subscriber and route the
call to any of 100 numbers. The selector 'wipers' always start in their
resting 'home' position. The first digit moves the selector vertically up to
the corresponding level and then the second digit moves the wipers
around the contacts of that level. This is shown in figure 3, below.
A Two-Motion "Final" Selector
The type of selector shown above is known as a Final Selector as it
takes the final two digits of the number dialed. Most numbers dialed are
several digits longer, and therefore pass through a chain of selectors.
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Selectors previous to the Final Selectors are different; they are
called Group Selectors. Group selectors take only ONE digit from the
caller, and step up the number of levels according to the digit dialed. The
rotary movement is then automatic; the wipers search around that level
to find a free outlet - i.e. the next free selector in the chain. This is
covered in more depth later.
CROSS BAR EXCAHNGE
In, a crossbar switch (also known as cross-point switch, cross point
switch, or matrix switch) is a connecting multiple inputs to multiple
outputs in a matrix manner. Originally the term was used literally, for a
matrix switch controlled by a grid of crossing. A crossbar switch is an
assembly of individual switches between multiple inputs and multiple
outputs. The switches are arranged in a matrix. If the crossbar switch
has M inputs and N outputs, then a crossbar has a matrix with M x N
cross-points or places where the "bars" cross. At each crosspoint is a
switch; when closed, it connects one of M inputs to one of N outputs. A
given crossbar is a single layer, non-blocking switch. Collections of
crossbars can be used to implement multiple layer and/or blocking
switches. A crossbar switching system is also called a co-ordinate
switching system.
ELECTRONICS EXCHANGE
It is based on the automatic control by stored programmed in computer
linked to it. It cover all the main drawbacks of above mentioned
exchange. It may be digital or analog but mostly digital electronics
exchanges are now common. It base on the principal time division
switching or space division switching. Space division switching is used
for analog electronics exchange and time division switching is used for
digital exchange.
1.3: CARRIER ROOM:
Leased line connectivity is provided in carrier room. This room
has two parts:
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1. Conventional leased line system
2. MLLN
1.4: 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.
FIG 1.2 MDF
(REF- 1.4.1)
1.4.1: 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.
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It provides testing of calls.
It checks whether fault is indoor or external.
All lines terminate individually.
1.5: POWER PLANT:
It provides -48V to the switch rooms and 48V to the connections.
Batteries are artificially discharged once in a year for their
maintenance.
Cooling is provided through fans & AC.
There is earth region too for protection.
1.6: HOW A TELECOM EXCHANGE WORKS:
It require -48 Vdc.
A telephone exchange or telephone switch is a system of
electronic components that
connects telephone calls. A central office is the physical b
uilding used to house inside plant equipment including
telephone switches, which make telephone calls “work” in
the sense of making connections and relaying the speech
information.
The basic block diagram for a telecom exchange is as follows-
Fig 1.3: Block diagram of telephone exchange
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1.7: Engine and Alternator
It provides AC output in the event of commercial power supply failure.
The diesel engine provides the prime mover to the alternator so that the
alternating current is generated to support the exchange systems.
150 KV Generator with 6 Silencer, and it require 24 V DC for Starting
System
1.8: OMC (Operation and Maintenance Control)
It contains input-output processor terminals, visual display units, printers,
cartridges, etc. It controls the entire operation of exchange data
and billing data. The new connections, adding and removing of facilities
to the subscriber is done in the OMC room.
1.9: Switch
It provides the switching facility and connection to the outside of the
exchange. The switch room contains actual telephone switching
hardware such as cabinets, racks, slots and cards. Switching is the most
important part of the exchange process.
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2. SWITCHING
A switch is defined as establishing a temporary connection from the
calling subscriber to the called subscriber. Switch is a device that makes
the connection and breaks the connection. It is a device that channels
incoming data from any of the multiple input ports to the specific input
that will take the data toward its intended destination.
A Digital switching system, in general, is one in which signals are
switched in digital form. These signals may represent speech or data.
The digital signals of several speech samples are time multiplexed on
a common media before being switched through the system.
To connect any two subscribers, it is necessary to interconnect the time-
slots of the two speech samples which may be on same or different PCM
highways. The digitalized speech samples are switched in two modes,
viz., Time Switching and Space Switching.
Fig 2.1: General Diagram of a Digital Switch
AU : Subscriber rack for feeding current and other functionalities
Interface: Interface between main exchange and
subscribers/Trunks
Switch: Main switching network and other exchange equipment
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MDD: Magnetic Disk Drive for storing data
MTD: Magnetic Tape Drive for backup and regeneration of the
exchange
OMT: Operation and Maintenance terminal to issue various
commands.
Control: Processor to control peripherals and interfacing Main
Exchange.
Printer: To get hard copy for all the report.
2.1 Electronic Switches
Different types of Electronic Switches are: –
C-DOT : Indian Made
E10B : France Made
OCB : France Made
EWSD : Germany Made
Of these, the most important ones include C-DOT and EWSD. Which are
mostly used now a days.
In BSNL EXCHANGE, KATHUA the switches used are of C-DOT.
Switches developed by C-DOT have 50% of the fixed line Indian market
share in terms of number of lines. C-DOT has brought out new state-of-
the-art versions of rural as well as urban digital switches of variable
capacities from over 200 subscribers to 100,000 subscribers both in
stand-alone versions and multiple-module versions respectively. All the
switches have contemporary features and are built in such a way that
the same can also support emerging features and service requirements.
Rural Automatic Exchange
Main Automatic Exchange
Access Network Rural Automatic Exchange
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2.2 GENERAL DESCRIPTION OF C-DOT MAX DSS
SYSTEM
1. GENERAL
1.1 C-DOT DSS MAX –XL is a universal digital switch, which can be
configured for different application as local, transit or integrated local cum
transit switch. The hardware architecture of C-DOT DSS MAX – XL utilizes
state of the art microircuitry & modular packaging. It utilizes advanced concept
in hardware design such as duplicated & distributed microprocessor based
control, hybrid integrated circuit & single chip digital signal processors for
MF& DTMF receivers. The software has been written in high level
language(C) & the man machine interface language is a simple English like
language. Now CDOT DSS Exchange can upgrade to provide ISDN service
by adding minimum additional hardware units.
1.2 The system employs a T-S-T switching configuration and is based on a 32 channel PCM structure. It uses a basic rate of 64 Kbps & 2 mbps primary multiplexing rate. Basic memory unit has been implemented as a 16MB dynamic RAM board with 256 KB as basic dynamic RAM chip. Single chip digital signal processors are used for implementing DTMF & MF receivers.
2. BASIC GROWTH/BUILDING MODULES
C-DOT DSS MAX exchanges can be configured using four basic modules
Base Module
Central Module
Administrative Module
Input Output Module.
3. Hardware Architecture
3.1 GENERAL
The hardware architecture of C-DOT DSS MAX is mapped closely on the
System Overview described in the previous chapter. In the following sections,
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the hardware architecture of each constituent module is described.
3.2 BASE MODULE (BM)
Base Module (BM) is the basic building block of C-DOT DSS MAX. It
interfaces the subscribers, trunks and special circuits. The subscribers
may be individual or grouped PBX lines, analog or digital lines. The
trunks may be Two Wire Physical, E&M Four Wire, E&M Two Wire,
Digital CAS or CCS.
The basic functions of a Base Module:
Analog to digital conversion of all signals on analog lines
and trunks
Interface to digital trunks and digital subscribers
Switching the calls between terminals connected to the
same Base Module
Communication with the Administrative Module via the
Central Module for administrative and maintenance
functions and also for majority of inter-BM switching (i.e.
call processing) functions
Provision of special circuits for call processing support
e.g. digital tones,
announcements, MF/DTMF senders/receivers
Provision for local switching and metering in standalone
mode of Remote Switch Unit as well as in case of Single
Base Module Exchange (SBM-RAX)
For these functions, the Base Module hardware is spread over
different types of Units.
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(Ref. fig. 3.1)
Analog Terminal Unit - to interface analog lines/trunks,
and providing special circuits as conference,
announcements and terminal tester.
Digital Terminal Unit - for interfacing digital trunks i.e.
2Mbps E-1/PCM
Links
#7 Signalling Unit Module - to support SS7 protocol
handlers and some call processing functions for CCS7
calls.
ISDN Terminal Unit - to support termination of BRI/PRI
interfaces and
Implementation of lower layers of DSS1 signaling protocol.
Time Switch Unit - for voice and message switching and
provision of service circuits.
Base Processor Unit - for control message communication
and call processing functions.
3.2.1. Analog Terminal Unit (ATU) (Figure 3.2A)
The Analog Terminal Unit (ATU) is used for interfacing 128 analog
terminations which may be lines or trunks. It consists of terminal cards which
may be a combination of Line Circuit Cards (LCC), CCB with Metering (CCM)
cards, Two Wire Trunk (TWT) cards, E&M Two wire (EMT) Trunk cards and
E&M Four wire (EMF) trunk cards, depending upon the module configuration.
Also, provision has been made to equip Conference (CNF) card to support “six
party” conference, Announcement (ANN) to support 15 user-friendly
announcement messages, and Terminal Test Controller (TTC) for testing of
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analog terminations. Power Supply Unit (PSU-I) provides logical voltages and
ringing current in the ATU.
Analog Subscriber Line Cards:
Two variants of subscriber line cards as LCC or CCM with interfaces up
to 8 subscribers, provide basic BORSCHT functions for each line.
Analog to digital conversion is done by per-channel CODEC according
to A-law of Pulse Code Modulation. Each CCM card has the provision of
battery reversal for all the 8 lines with the last two lines having
provision to generate 16 KHz metering pulses to be sent to subscriber's
metering equipment.
The 8-bit digital (voice) output of four LCCs is multiplexed to form a
32-channel, 2 Mbps PCM link - also called a terminal group (TG). Since
a Terminal Unit has a maximum of 16 terminal cards, there are four
such terminal groups. The signaling information is separated by a
scan/drive logic circuit and is sent to the signaling processor on four
different scan/drive signals. The LCC/CCM also provides test access
relay to isolate the exchange side and line side to test it separately by
using the Terminal Test Controller (TTC).
Analog Trunk Cards:
Analog trunk cards interface analog inter-exchange trunks which may be of
three types as TWT, EMT and EMF. These interfaces are similar to Subscriber
Line Card, with only difference that the interfaces are designed to can/drive
events on the trunks as per predefined signalling requirement.
Signalling Processor (SP) Card
Signalling Processor (SP) processes the signalling information received from
the terminal cards. This signalling information consists of scan/drive functions
like origination detection, answer detection, digit reception, reversal
detection, etc. The validated events are reported to Terminal Interface
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Controller for further processing to relieve itself from real-time intensive
functions. Based on the information received from the Terminal Interface
Controller, it also drives the event on the selected terminal through scan/drive
signals.
Terminal Interface Controller (TIC) Card
Terminal Interface Controller (TIC) controls the four terminal groups
(TG) of 32 channels, and multiplex them to form a duplicated 128-
channel, 8 Mbps link towards the Time Switch (TS). For signalling
information of 128- channels, it communicates with Signalling Processor
(SP) to receive/send the signalling event on analog terminations. It also
uses one of the 64 kbps channel out of 128 channels towards Time
Switch, to communicate with Base Processor Unit (BPU). In
concentration mode, three other Terminal Units share this 128-channel
link towards the Time Switch to have 4:1 concentration.
Terminal Interface Controller is built around 8-bit microprocessor with
associated memory and interface and it is duplicated for redundancy.
Special Service Cards:
A Terminal Unit has some special service cards such as Conference (CNF) Card
to provide six party conference. Speech samples from five parties are added
by inbuilt logic and sent to the sixth party to achieve conferencing. Terminal
Test Controller (TTC) Card is used to test analog terminal interfaces via the
test access relays on the terminal cards.
Announcement Controller (ANN) Card provides 15 announcements on
broadcast basis. Only one service card of each type is equipped in a
Base Module with provision of fixed slot for TTC and variable slots for
CNF/ANNC.
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Announcement and Conference Cards are equipped in Terminal Unit through
S/W MMC command. Two slots are occupied by each card i.e. 16 channels for
each card is used out of 128 channels available on a Bus between a TU &TS.
3.2.2. Digital Terminal Unit (DTU) (Ref. Fig. 3.2B) Digital Terminal Unit (DTU) is used exclusively to interface digital trunks. One
set of Digital Trunk Synchronization (DTS) card along with the Digital Trunk
Controller (DTC) card is used to provide one E-1 interface.
Each interface occupies one TG of 32 channels and four such interfaces share
4 TGs in a Digital Terminal Unit. The functions performed by TIC and SP in
Analog Terminal Unit, are collectively performed by the Terminal Unit
Controller (TUC) in the Digital Terminal Unit. The scan functions are - HDB3 to
NRZ code conversion, frame alignment and reconstitution of the received
frame. The drive functions include insertion of frame alignment pattern and
alignment information. Each interface can be configured as CAS or CCS
interface.
3.2.3. SS7 Signalling Unit Module (SUM) (Ref. Fig.3.2D)
Any one of the ATU or DTU in a BM can be replaced by SUM frame to support
CCS7 signalling. Only one such unit is equipped in the exchange irrespective of
its configuration or capacity. For details of SUM architecture, refer to chapter
no.4.
3.2.4. ISDN - Terminal Unit (ISTU) (Ref. Fig. 3.2C) One of the four ATUs/ DTUs in a BM can be replaced by ISTU to
provide BRI/PRI interfaces in C-DOT DSS. The only constraint is that
ISTU has to be principal TU i.e. directly connected to TSU on 8 Mbps
PCM link. The ATU/DTU cannot be used in concentration with ISTU. By
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equipping one ISTU in the exchange, a max. Of 256 B channels are
available to the administrator which can be configured as BRI, PRI or
any mix as per site requirement. Depending on the requirement of
number of ISDN-Interfaces, one or more ISTUs can be integrated in C-
DOT DSS, either in one BM or distributed across different BMs. For
details, refer chapter no. 4.
3.2.5. Time Switch Unit (TSU) (Ref. Fig. 3.2 F) Time Switch Unit (TSU) implements three basic functions as time switching
within the Base Module, routing of control-messages within the Base Module
and across Base Modules and support services like MF/DTMF circuits,
answering circuits, tones, etc. These functions are performed by three
different functional units, integrated as time switch unit in a single frame
(Refer Fig. 3.2).
3.2.6. Base Processor Unit (BPU) (Ref. Fig. 3.2 E)
Base Processor Unit (BPU) is the master controller in the Base Module. It is
implemented as a duplicated controller with memory units. These duplicated
sub-units are realised in the form of the following cards:
Base Processor Controller (BPC) Card
Base Memory Extender (BME) Card
BPC controls time switching within the Base Module via the Base Message
Switch and the Time Switch Controller. It communicates with the
Administrative Processor via Base Message Switch for operations and
maintenance functions. In a SBM configuration, BPC directly interfaces with
the Alarm Display Panel and the Input Output Module.
To support 8, 00,000 BHCA, the BPC card is replaced by High performance
Processor Card (HPC). It is pin to pin compatible for hardware and also for
software so that they are interchangeable at any site to meet specific traffic
requirement.
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3.3. CENTRAL MODULE (CM)
Central Module (CM) is responsible for space switching of inter-Base Module calls,
communication between Base Modules and the Administrative Module, clock
distribution and network synchronisation. For these functions, Central Module has a
Space Switch, Space Switch Controller and a Central Message Switch. Figure 3.3
summarises the various units and sub-units of the CENTRAL MODULE.
3.4. ADMINISTRATIVE MODULE (AM) Administrative Module (AM) consists of a duplicated 16/32-bit controller called the
Administrative Processor (APC). It communicates with Base Processors via the
Central Message Switch for control messages and with the duplicated Input Output
Processors in the Input Output Module for interfacing peripheral devices
Administrative processor is responsible for global routing, translation, and resource
allocation and all other functions that are provided centrally in C-DOT DSS MAX.
The implementation of AM is similar to Base Processor Complex of BM, using the
same hardware configuration. As explained earlier, HPC instead of BPC is used to
NOTE: 1) REPLACE TSS CARDS BY ETS CARDS IN CASE OF REMOTE
BASE MODULES (RSU)
2) MSC AND MSD CARDS ARE REPLACED BY HMS FOR 800K BHCA
FIG: 3.2F TIME SWITCH UNIT (TSU) CONFIGURATION
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C-DOT MAX DSS SYSTEM ARCHITECTURE
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2.3 C-DOT 256P RAX It is a digital, stored, program-controlled switching system with 256 terminations or ports. It employs a non-blocking 4-wire PCM switching network. Offering a low investment telephone service in rural areas, however far flung they may be. It is ideal for rural applications since it provides immediate basic telephone connection with minimum infrastructure. It is easy to install and possesses a fault-tolerant system with inbuilt redundancy. Besides requiring no air-conditioning, it withstands dust, wide temperature fluctuations (-5 to 50 C), humidity and salinity. Moreover, it consumes very little power, sustaining itself despite frequent power failures due to low battery drain. A distinguishing feature of the C-DOT 256P RAX is its simple and flexible connectivity through a satellite wide range of transmission systems such as UHF, VHF, radio and satellite. Because it is program-controlled, it can be easily integrated as per the network requirement through man machine commands. Thus, proving to be an extremely cost-effective and viable
proposition. How can C-DOT 256P RAX suit differing requirements? It can act as a terminal exchange, an Integrated Local-cum-Transit exchange (ILT) to a purely transit exchange. And it can be placed in the secondary switching area as a tertiary center, providing connectivity among RAXs, TAXs and manual trunk positions, in addition to local subscribers, it also features Network Synchronization that is essential for satisfactory fax and Internet access applications. As an independent exchange, the C-DOT 256P RAX provides man-machine interface for operation and maintenance form the exchange. These functions can be carried out either from the exchange itself, or remotely through Central Operation and Maintenance Centers.
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2.4 C-DOT 256P AN-RAX The 256P AN-RAX from C-DOT is a world-class cost-effective communication solution for rural areas. Development with the sole purpose of transforming the villages by removing natural barriers to progress through its versatility in any environment-hot tropical areas, subzero mountainous regions, vast deserts and coastal areas, the 256P AN-RAX A is an Access Network product. Salient Features The 256P AN-RAX caters to 256 terminations and is based on the 256P RAX switch, development by CDOT more than a decade ago. It avoids longer subscriber line loops and provides telecommunication facilities in remote areas. It interfaces to a Local Exchange (LE) over two E1 links, supporting V5.2 protocol, and automatically achieves network synchronization. It provides a Man-Machine Interface (MMI) for local operations and maintenance. This MMI can also be remoted to LE over V5 links using modems. Apart from supporting all the subscriber features of the 256P RAX, the 256P AN-RAX also supports some additional features such as conferencing, distinctive ringing and call waiting, in conjunction with LE. There are over 33,000 256P RAX switches installed in the Indian telecom network. All these switches can be easily converted to 256P AN-RAX.
System Features Control • 68302 Microprocessor based SPC Capacity • Maximum 248 subscriber lines Termination Types Supported • Normal /CCB/CCB with 16 KHz metering (CCM) Signaling between Subscriber & Exchange • Decadic /DTMF Loop Resistance • Subscriber line 1200 Ohm Insulation Resistance • 20 Ohm (minimum) Metering Scheme (Done at LE) • Software meters Subscriber meters • Subscriber traffic Service circuit traffic Printouts • Spontaneous /on command Periodic (Done at LE) Traffic • 4000 BHCA
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3. MOBILE COMMUNICATION
A mobile phone, cell phone or hand phone is an electronic device used
to make mobile telephone calls across a wide geographic area, served
by many public cells, allowing the user to be mobile. By contrast, a
cordless telephone is used only within the range of a single, private base
station, for example within a home or an office.
A mobile phone can make and receive telephone calls to and from
the public telephone network which includes other mobiles and fixed-line
phones across the world. It does this by connecting to a cellular network
provided by a mobile network operator. In addition to telephony, modern
mobile phones also support a wide variety
of other services such as text messaging, MMS, email, Internet access,
short range wireless communications (infrared, Bluetooth), business
applications, gaming and photography. Mobile phones that offer these
more general computing capabilities are referred to as smart phones.
3.1: Generation Gap
Generation#1
Analog [routines for sending voice]
All systems are incompatible
No international roaming
Generation#2
Digital [voice encoding]
Increased capacity
More security
Compatibility
Can use TDMA or CDMA for increasing capacity
Generation#2.5
Packet-switching
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Connection to the internet is paid by packets and not by
connection time.
Connection to internet is cheaper and faster [up to 56KBps]
Generation#3
The present future
Permanent web connection at 2Mbps
Internet, phone and media: 3 in 1
The standard based on GSM is called UMTS.
The EDGE standard is the development of GSM towards 3G.
The genius of the cellular system is the division of a city into
small cells. This allows extensive frequency reuse across a city,
so that millions of people can use cell phones simultaneously. In
a typical analog cell-phone system, the cell-phone carrier
receives about 800 frequencies to use across the city. The
carrier chops up the city into cells. Each cell is typically sized at
about 10squaremiles (26 square 34kilometers). Cells are
normally thought of as hexagons on a big hexagonal grid, like this:
Fig 3.1: Cell Phones and base Stations
3.2: HOW A CALL IS CONNECTED
When you first power up the phone, it listens for an SID on the
control channel. The control channel is a special frequency that
the phone and base station use to talk to one another about
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things like call set-up and channel changing. If the phone cannot
find any control channels to listen to, it knows it is out of range
and displays a “no service” message.
When it receives the SID, the phone compares it to the SID
programmed into the phone. If the SIDs match, the phone knows
that the cell it is communicating with is part of its home system.
Along with the SID, the phone also transmits a registration
request, and the MTSO keeps track of your phone’s location in a
database — this way, the MTSO knows which cell you are in
when it wants to ring your phone.
The MTSO gets the call, and it tries to find you. It looks in its
database to see which cell you are in.
The MTSO picks a frequency pair that your phone will use in
that cell to take the call.
The MTSO communicates with your phone over the control
channel to tell it which frequencies to use, and once your phone
and the tower switch on those frequencies, the call is connected.
Now, you are talking by two-way radio to a friend.
As you move toward the edge of your cell, your cell’s
base station notes that your signal strength is diminishing.
Meanwhile, the base station in the cell you are moving toward
(which is listening and measuring signal strength on all
frequencies, not just its own one-seventh) sees
o Your phone’s signal strength increasing. The two base
stations coordinate with each other through the MTSO, and
at some point, your phone gets a signal on a control
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channel telling it to change frequencies. This
hand off switches your phone to the new cell.
Let’s say you’re on the phone and you move from one cell to
another — but the cell you move into is covered by another
service provider, not yours. Instead of dropping the call, it’ll
actually be handed off to the other service provider.
If the SID on the control channel does not match the SID
programmed into your phone, then the phone knows it is
roaming. The MTSO of the cell that you are roaming in contacts
the MTSO of your home system, which then checks its database
to confirm that the SID of the phone you are using is valid. Your
home system verify your phone to the local MTSO, which then
tracks your phone as you move through its cells. And the
amazing thing is that all of this happens within seconds.
3.3 Mobile Phone Towers
The mobile phone works on the frequency signal and each mobile phone connection
has its own frequency. These frequencies are sending from the basic lower station
tower. Each tower has a range of 5 km in the city circle and there are a number of
towers in the city to provide connectivity to each mobile phone subscriber. The city is
divided into imaginary hexagon as its area plans out and each hexagon point has a
tower for providing frequency signals to the mobile subscriber. When the mobile
sends signals to the base tower then it is called uplink signal. When the base tower
sends signal to the mobile then its downlink signals on the highways the range of base
tower of sending signal to the mobile phone subscribers is 25 km.
Basic terms in mobile communication are:-
1. MSC: TAX for mobile phones
2. HLR: Home Location Register
3. TRC: Traffic Controller
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4. VLR: Visitors Location Register
5. MNC: Mobile Network Code
6. BSC: Base Station Control
MSC:
It acts as a trunk automatic exchange (TAX). All the switching is done here in this TAX. Each and every call made by the mobile subscribers is first collected from the base station are send to the MSC where all the necessary verification of the subscriber is made and then the switching of the call is made by the MSC. The OSS is a component within the MSC which maintains the MSC. The functions of OSS are maintenance of MSC.
MSC
HLR:
The Home Location Register stores each and every data of the mobile subscriber. Before the call is switched for the mobile subscriber the MSC verifies the subscriber and all the verification data is provided by the HLR. When the subscriber is on roaming facility, the MSC of that area collects all the necessary information of the subscriber from its home MSC through its HLR.
TRC:
The traffic controller controls the traffic for MSC and also controls the traffic of subscriber trying to make contact with the MSC when call is made or received.
VLR:
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The Visitor Location Register keeps a track record of subscribers who are on roaming facility and all the records of the visitor coming from a different MSC area.
MNC:
Each and every country and its states have a unique Mobile Network Code (MNC) which makes a difference between the mobile subscriber of two different countries and also within the states. The MNC for India is 404and for Jharkhand BSNL mobile is INA76 where INA refers to the Indian Network.
BSC:
The Base Station acts as important media for call transfer and call receiving for the mobile subscribers. It sends frequency signals for the connectivity of mobile subscriber. The BSC is connected to its towers through 2 MB link and is directly connected to the MSC where all call switching takes place for the mobile subscribers. Each base station is provided 124 frequencies and a time slot of 8 channels for every call.
3.4 GSM Network Components
The GSM network is divided into two systems. Each of these systems is comprised of a number of functional units which are individual components of the mobile network. The two systems are: Switching System (SS) Base Station System (BSS)
GSM networks are operated, maintained and managed from computerized centers.
Subscriber Identity Module (SIM)
SIM card is the key feature of the GSM. It contains information about the subscriber and must be plugged into the ME to enable the subscriber to use the network with the exception of emergency calls MS can only be operated if a valid SIM is present. These store three types of subscriber related information:
1. Fixed data stored before the subscription is sold such as authentication key and security algorithms.
2. Temporary network data such as the location area of the subscriber and forbidden PLMNS.
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3. Service data such as language preference advice of charge.
There are two types of SIM cards:- ID-SIM: The format and layout of the ID-SIM complies with ISO
standards for integrated circuit cards. PLUG-In SIM: The plug-in SIM is smaller than the ID-SIM and is
intended for semi-permanent installation in the MNS.
3.5 INTODUCTION TO GSM TECHNOLOGY
What is GSM?
If you are in Europe, Asia or Japan and using a mobile phone then most probably you
must be using GSM technology in your mobile phone.
GSM stands for Global System for Mobile Communication and is an open, digital cellular technology used for transmitting mobile voice and data services.
The GSM emerged from the idea of cell-based mobile radio systems at Bell Laboratories in the early 1970s.
The GSM is the name of a standardization group established in 1982 to create a common European mobile telephone standard.
The GSM standard is the most widely accepted standard and is implemented globally.
The GSM is a circuit-switched system that divides each 200 kHz channel into eight 25 kHz time-slots. GSM operates in the 900MHz and 1.8GHz bands in Europe and the 1.9GHz and 850MHz bands in the US.
The GSM is owning a market share of more than 70 percent of the world's digital cellular subscribers.
The GSM makes use of narrowband technique for transmitting signals. The GSM was developed using digital technology. It has an ability to
carry 64 kbps to 120 Mbps of data rates. Presently GSM support more than one billion mobile subscribers in
more than 210 countries throughout of the world. The GSM provides basic to advanced voice and data services
including Roaming service. Roaming is the ability to use your GSM phone number in another GSM network.
A GSM digitizes and compresses data, then sends it down through a channel with two other streams of user data, each in its own time slot. It operates at either the 900 MHz or 1,800 MHz frequency band. Specifications for different Personal Communication Services (PCS) systems vary among the different PCS networks. The GSM specification is listed below with important characteristics.
3.6 GSM SUBSYSTEMS:
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RADIO SUBSYSTEM (RSS)
NETWORK AND SWITCHING SUBSYSTEM (NSS)
3.6.1 RADIO SUBSYSTEM:
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
IMIE (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
3.6.2 NETWORK AND SWITCHING SUBSYSTEM:
This subsystem does mainly switching, mobility management, interconnection to
other networks, system control.
COMPONENTS:
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.
2. DATABASES:
Home Location Register (HLR):
Central master database containing user data, permanent and semi-permanent data of
all subscribers assigned to the HLR (one provider can have several HLRs).
Visitor Location Register (VLR):
Local database for a subset of user data, including data about all user currently in the
domain of the VLR.
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3.6.3 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
Modulation: Modulation is a form of change process where we change the input information into a suitable format for the transmission medium. We also changed the information by demodulating the signal at the receiving end. The GSM uses Gaussian Minimum Shift Keying (GMSK) modulation method.
Access Methods:
Because radio spectrum is a limited resource shared by all users, a method must be devised to divide up the bandwidth among as many users as possible. GSM chose a combination of TDMA/FDMA as its method. The FDMA part involves the division by frequency of the total 25 MHz bandwidth into 124 carrier frequencies of 200 kHz bandwidth. One or more carrier frequencies are then assigned to each BS. Each of these carrier frequencies is then divided in time, using a TDMA scheme, into eight time slots. One time slot is used for transmission by the mobile and one for reception. They are separated in time so that the mobile unit does not receive and transmit at the same time.
Transmission Rate:
The total symbol rate for GSM at 1 bit per symbol in GMSK produces 270.833 K symbols/second. The gross transmission rate of the time slot is 22.8 Kbps.
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GSM is a digital system with an over-the-air bit rate of 270 kbps.
Frequency Band:
The uplink frequency range specified for GSM is 933 - 960 MHz (basic 900 MHz
band only). The downlink frequency band 890 - 915 MHz (basic 900 MHz band
only).
Speech Coding:
GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit
rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal
passes through this filter, leaving behind a residual signal. Speech is encoded at 13
kbps.
EVOLUTION OF GSM :
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4. TRANSMISSION
4.1 Local and trunk Network Trunk Lines The term Trunk Line in telecommunications refers to the high-speed connection between telephone central offices in the. Trunk lines are always digital. The wiring between central offices was originally just pairs of twisted copper wire (the twists in the wiring prevented things known as crosstalk and noise). Because it is expensive to string up (or lay trenches for buried cables), the phone company researched ways in which to carry more data over the existing copper lines. This was achieved by using. Later, when fiber-optic technology became available, phone companies upgraded their trunk lines to fiber optics and used statistical time-division multiplexing, coarse or dense wave division multiplexing and optical switching to further improve transmission speeds. The signaling information exchanged between different exchanges via inter exchange trunks for the routing of calls is termed as Inter exchange Signaling. Earlier in band /out of band frequencies were used for transmitting signaling information. Later on, with the emergence of PCM systems, it was possible to segregate the signaling from the speech channel. A trunk line is a connecting (or other switching equipment), as distinguished from local loop circuit which extends from telephone exchange switching equipment to individual or information origination/termination equipment. When dealing with a private branch exchange (PBX), trunk lines are the phone lines coming into the PBX from the telephone provider. This differentiates these incoming lines from extension telephone lines that connect the PBX to (usually) individual phone sets. Trunking saves cost, because there are usually fewer trunk lines than extension lines, since it is unusual in most offices to have all extension lines in use for external calls at once. Trunk lines transmit voice and data in formats such as analog, digital signal 1, ISDN or primary rate interface. The dial tone lines for outgoing calls are called DDCO (Direct Dial Central Office) trunks. A travelling over a trunk line is not actually flowing any faster. The electrical signal on a voice line takes the same amount of time to traverse the wire as a similar length trunk line. What makes trunk lines faster is that it has been altered to carry more data in less time using more advanced multiplexing and techniques. If you compared a voice line and a trunk line and put them side by side and observed them, the first pieces of information arrive simultaneously on both the voice and trunk line. However, the last piece of information would arrive sooner on the trunk line. No matter what, you can't break the laws of physics. Electricity over copper or laser light over fiber optics, you cannot break the speed of light--though that has rarely stopped uneducated IT or IS managers from demanding that cabling perform faster instead of upgrading equipment. Trunk lines can contain thousands of simultaneous calls that have been combined using. These thousands of calls are carried from one central office
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to another where they can be connected to a de-multiplexing device and switched through digital access cross connecting switches to reach the proper exchange and local phone number. What is Trunking? In telecommunications systems, trunking is the aggregation of multiple user circuits into a single channel. The aggregation is achieved using some form of multiplexing.
4.2 PCM
A long distance or local telephone conversation between two persons could be provided by using a pair of open wire lines or underground cable as early as mid of 19th century. However, due to fast industrial development and an increased telephone awareness, demand for trunk and local traffic went on increasing at a rapid rate. To cater to the increased demand of traffic between two stations or between two subscribers at the same station we resorted to the use of an increased number of pairs on either the open wire alignment, or in underground cable. This could solve the problem for some time only as there is a limit to the number of open wire pairs that can be installed on one alignment due to headway consideration and maintenance problems. Similarly increasing the number of open wire pairs that can be installed on one alignment due to headway consideration and maintenance problems. Similarly increasing the number of pairs to the underground cable is uneconomical and leads to maintenance problems. It, therefore became imperative to think of new technical innovations which could exploit the available bandwidth of transmission media such as open wire lines or underground cables to provide more number of circuits on one pair. The technique used to provide a number of circuits using a single transmission link is called Multiplexing. Basic Requirements for PCM System:
To develop a PCM signal from several analogue signals, the following processing steps are required:
1. Filtering
2. Sampling
3. Quantisation
4. Encoding
5. Line Coding
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Duplexing Methodology:
Duplexing is the technique by which the send and receive paths are separated over the medium, since transmission entities (modulator, amplifiers, demodulators) are involved. There are two types of Duplexing: Frequency Division Duplexing (FDD)
Time Division Duplexing (TDD)
Frequency Division Duplexing (FDD): Different frequencies are used for send and receive paths and hence there will be a forward band and reverse band. Duplexer is needed if simultaneous transmission (send) and reception (receive) methodology is adopted. Frequency separation between forward band and reverse band is constant. Time Division Duplexing (TDD): TDD uses different time slots for transmission and reception paths. Single radio frequency can be used in both the directions instead of two as in FDD. No duplexer is required. Only a fast switching synthesizer, RF filter path and fast antenna switch are needed. It increases the battery life of mobile phones.
4.3 FIBER OPTIC TRANSMISSION SYSTEM
INTRODUCTION:
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:
Information is encoded into Electrical Signals.
Electrical Signals are converted into light Signals.
Light Travels down the Fiber.
A Detector Changes the Light Signals into Electrical Signals.
Electrical Signals are decoded into Information.
OPTICAL FIBER TRANSMISSION (REF- 1)
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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.
Jacket
Cladding
Core
Cladding
Angle of
reflection
Angle of
incidence
Light at less than
critical angle is
absorbed in jacket
Jacket
Light is propagated by
total internal reflection
Jacket
Cladding
Core
(n2)
(n2)
Fig. Total Internal Reflection in an optical Fibre
PROPAGATION OF LIGHT THROUGH FIBRE (REF- 1)
CLASSIFICATION:
There are three types of fibers:
Multimode Step Index fiber (Step Index fiber)
Multimode graded Index fiber (Graded Index fiber)
Single- Mode Step Index fiber (Single Mode fiber)
(I) STEP-INDEX MULTIMODE FIBER: It has a large core, up to 100 microns in
diameter. 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 MULTIMODE FIBER: It contains a core in which the
refractive index diminishes gradually from the center axis out toward the cladding.
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 less
dispersion.
(III) SINGLE-MODE FIBER: It has a narrow core (eight microns or less), and the
index of refraction between the core and the cladding changes less than it does for
multimode fibers. Light thus travels parallel to the axis, creating little pulse
dispersion. Telephone and cable television networks install millions of kilometers of
this fiber every year.
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ADVANTAGES OF FIBRE OPTICS:
SPEED: Fiber optic networks operate at high speeds - up into the gigabits.
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.
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5. CONCLUSION
The working in the project was an interesting and an altogether learning experience. New technologies, new progress and new competition are the order of the day. The core area to look for is highly fragmented and information intense activity sequence that involves a number of player and audiences. The emphasis of the different parts of the project is to throw light on the systems working in KATHUA Main Exchange. The project also deals with modern technologies attributes and the scope of implementation of the same in KATHUA. The area under study was limited to KATHUA Main Exchange. The scope of the study is very vast and the topic under study deals with the volatile technology world. After the study, suggestions and strategy has been formulated keeping in view the limitations of the field. Evolution of this technological world is occurring every minute. Thanks to telecom and web technologies, countries are coming closer day by day.
