Created By Dushmanta Nath

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Training Report
SSA level in-plant summer training in
BSNL (TEZPUR)
IITT COLLEGE OF
ENGINEERING pOjEwaL
(sbs NaGaR)
Submitted to:
HOD of IT Branch
Submitted by:
Dushmanta Nath
Roll no: 81301113016

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Branch: IT (5 th
SEM)
INTRODUCTION
All industries operate in a specific environment which keeps
changing and the firms in the business need to understand it to
dynamically adjust their actions for best results. Like minded
firms get together to form associations in order to protect their
common interests. Other stake holders also develop a system to
take care of their issues. Governments also need to intervene for
ensuring fair competition and the best value for money for its
citizens. This handouts gives exposure on the Telecom
Environment in India and also dwells on the role of international
bodies in standardizing and promoting Telecom Growth in the
world.
Lesson Plan
 Institutional Mechanism and role & Telecom Eco system
 National DOT, TRAI,TDSAT, TEC,CDOT
 International Standardization bodies- ITU,APT,ETSI etc
 Licensed Telecommunication services of DOT
 Various Trade associations, Network Operators,
Manufacturers, service providers, service provisioning and
retailing, billing and OSS

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 Job opportunities in telecom Market, government and
statutory bodies
Assignment: Explore designated websites of institutions and
companies
Institutional Framework: It is defined as the systems of
formal laws, regulations, and procedures, and informal
conventions, customs, and norms, that broaden, mold, and
restrain socio-economic activity and behaviour. In India, The
Indian telegraph act of 1885 amended from time to time governs
the telecommunications sector. Under this act, the government is
in-charge of policymaking and was responsible for provisioning
of services till the opening of telecom sector to private
participation. The country has been divided into units called
Circles, Metro Districts, Secondary Switching Areas (SSA),
Long Distance Charging Area (LDCA) and Short Distance
Charging Area (SDCA). Major changes in telecommunications
in India began in the 1980s. 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. Further changes in
the regulatory system took place with the TRAI Act of 2000
that aimed at restoring functional clarity and improving
regulatory quality and a separate disputes settlement body was
set up called Telecom Disputes Settlement and Appellate
Tribunal (TDSAT) to fairly adjudicate any dispute between

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licensor and licensee, between service provider, between service
provider and a group of consumers. In October 2003, Unified
Access Service Licenses regime for basic and cellular services
was introduced. This regime enabled services providers to offer
fixed and mobile services under one license. Since then, Indian
telecom has seen unprecedented customer growth crossing 600
million connections. 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 world and the second largest among
emerging economies. A brief on
telecom echo system and various key elements in institutional
framework is given below:
Summer Training, Overview of Telecommunication Networks-
II Page 2 of 12
Compiled by MC Faculty ALTTC, Ghaziabad
Department of Telecommunications: In India, DoT is the
nodal agency for taking care of telecom sector on behalf of
government. Its basic functions are:
 Policy Formulation
 Review of performance
 Licensing
 Wireless spectrum management
 Administrative monitoring of PSUs
 Research & Development
 Standardization/Validation of Equipment
 International Relations
Main wings within DoT:

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 Telecom Engineering Center (TEC)
 USO Fund
 Wireless Planning & Coordination Wing (WPC)
 Telecom Enforcement, Resource and Monitoring (TERM) Cell
 Telecom Centers of Excellence (TCOE)
Public Sector Units
 Bharat Sanchar Nigam Limited(BSNL)
 Indian Telephone Industries Limited (ITI)
 Mahanagar Telephone Nigam Limited(MTNL)
 Telecommunications Consultants India Limited(TCIL)
R & D Unit
• Center for development of Telematics (C-DoT)
The other key governmental institutional units are TRAI &
TDSAT. Important units are
briefed below:
Telecom Engineering Center (TEC): It is a technical body
representing the interest ofDepartment of Telecom, Government
of India. Its main functions are:
 Specification of common standards with regard to Telecom
network equipment, services and interoperability.

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 Summer Training, Overview of Telecommunication
Networks-II Page 3 of 12 Compiled by MC Faculty ALTTC,
Ghaziabad
 Generic Requirements (GRs), Interface Requirements (IRs)
 Issuing Interface Approvals and Service Approvals
 Formulation of Standards and Fundamental Technical Plans
 Interact with multilateral agencies like APT, ETSI and ITU
etc. for standardisation
 Develop expertise to imbibe the latest technologies and
results of R&D
 Provide technical support to DOT and technical advice to
TRAI & TDSAT
 Coordinate with C-DOT on the technological developments
in the Telecom Sector for policy planning by DOT
www.tec.gov.in
Universal Service Obligation Fund (USO): This fund
was created in 2002. This fund is managed by USO
administrator. All telecom operators contribute to this fund as
per government policy. The objective of this fund is to bridge
the digital divide i.e. ensure equitable growth of telecom
facilities in rural areas. Funds are allocated to operators who bid
lowest for providing telecom facilities in the areas identified by
USO administrator.

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WIRELESS PLANNING & COORDINATION
(WPC)
This unit was created in 1952 and is the National Radio
Regulatory Authority responsible for Frequency Spectrum
Management, including licensing and caters for the needs of all
wireless users (Government and Private) in the country. It
exercises the statutory functions of the Central Government and
issues licenses to establish, maintain and operate wireless
stations. WPC is divided into major sections like Licensing and
Regulation (LR), New Technology Group (NTG) and Standing
Advisory Committee on Radio Frequency Allocation (SACFA).
SACFA makes the recommendations on major frequency
allocation issues, formulation of the frequency allocation plan,
making recommendations on the various issues related to
International Telecom Union (ITU), to sort out problems
referred to the committee by various wireless users, Siting
clearance of all wireless installations in the country etc.
Telecom Enforcement, Resource and Monitoring
(TERM) Cell: In order to ensure that service providers adhere
to the licence conditions and for taking care of telecom network
security issues, DoT opened these cells in 2004 and at present
34 cells are operating in various Circles and big districts in the
country. Key functions of these units are Inspection of premises
of Telecom and Internet Service Providers, Curbing illegal
activities in telecom services, Control over clandestine / illegal
operation of telecom networks by vested interests having no
license, To file FIR against culprits, pursue the cases, issue
notices indicating violation of conditions of various Acts in
force from time to time, Analysis of call/subscription/traffic data
of various licensees, arrangement for lawful interception /
monitoring of all communications passing through the licensee’s
network, disaster management, network performance
monitoring, Registration of OSPs and Telemarketers in License
Service Areas etc..

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Telecom Centers of Excellence (TCOE): (www.tcoe.in)
The growth of Indian Telecommunications sector has been
astounding, particularly in the last decade. This growth
has been catalysed by telecommunications sector liberalization
and reforms. Some of the areas needing immediate attention to
consolidate and maintain the growth are:
• Capacity building for industry talent pool
• Continuous adaptation of the regulatory environment to
facilitate induction/ adoptation of high potential new
technologies and business models
• Bridging of high rural - urban teledensity/digital divide
• Faster deployment of broadband infrastructure across the
country Summer Training, Overview of Telecommunication
Networks-II Page 4 of 12 Compiled by MC Faculty ALTTC,
Ghaziabad Centres of Excellence have been created to work on
(i) enhancing talent pool, (ii) technological innovation, (iii)
secure information infrastructure and (iv) bridging of digital
divide.
These COEs are also expected to cater to requirements of South
Asia as regionaleaders. The main sponsor (one of the telecom
operators), the academic institute where the Centers are located
and the tentative field of excellence are enumerated in the table
below:
Field of Excellence in Telecom Associated Institute Sponsor
Next Generation Network & Network Technology IIT,
Kharagpur Vodafone Essar Telecom Technology &
Management IIT, Delhi Bharti Airtel Technology Integration,
Multimedia & Computational Maths IIT, Kanpur BSNL
Telecom Policy, Regulation, Governance, Customer Care &
Marketing IIM, Ahmadabad IDEA Cellular Telecom
Infrastructure & Energy IIT, Chennai Reliance Disaster
Management of Info systems & Information Security IISc,
Bangalore Aircel Rural Application IIT Mumbai Tata Telecom
Spectrum Management (Proposed) WPC, Chennai Govt with
Industry consortium

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Telecom Regulatory Authority of India (TRAI): TRAI
was established under TRAI Act
1997 enacted on 28.03.1997. The act was amended in 2000. Its
Organization setup consists of
One Chairperson, Two full-time members & Two part-time
members. Its primary role is to
deals with regulatory aspects in Telecom Sector & Broadcasting
and Cable services. TRAI
has two types of functions as mentioned below:
 Mandatory Functions
 Tariff policies
 Interconnection policies
 Quality of Service
 Ensure implementation of terms and conditions of license
 Recommendatory Functions
 New license policies
 Spectrum policies
 Opening of sector
Telecom Dispute Settlement Appellate Tribunal
(TDSAT): TDSAT was established in year 2000 by an
amendment in TRAI act by transferring the functions of dispute
handling to new entity i.e. TDSAT. The organization setup
consists of one Chairperson & two full-time members. Its
functions are:
• Adjudicate any dispute between
 licensor and licensee
 two or more licensees
 group of consumers

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• Hear & dispose off appeal against any direction, decision or
order of the Authority under TRAI Act www.tdsat.nic.in
Key International Standardization Bodies for
Telecom sector:
ITU is the leading United Nations agency for information and
communication technology issues, and the global focal point
for governments and the private sector in developing networks
and services. For nearly 145 years, ITU has coordinated the
shared global use of the radio spectrum, promoted international
cooperation in assigning satellite orbits, worked to improve
telecommunication infrastructure in the developing world,
established the worldwide standards that foster seamless
interconnection of a vast range of communications systems and
addressed the global challenges of our times, such as mitigating
climate change and strengthening cyber security. Vast spectrum
of its work area includes broadband Internet to latest-generation
wireless technologies, from aeronautical and maritime
navigation to radio astronomy and satellite-based meteorology,
from convergence in fixed-mobile phone, Internet access, data,
voice and TV broadcasting to next-generation networks. ITU
also organizes worldwide and regional exhibitions and forums,
such as ITU TELECOM WORLD, bringing together the most
influential representatives of government and the
telecommunications and ICT industry to exchange ideas,
knowledge and technology for the benefit of the global
community, and in particular the developing world. ITU is based
in Geneva, Switzerland, and its membership includes 191
Member States and more than 700 Sector Members and
Associates. On 1 January 2009, ITU employed 702 people from
83 different countries. The staff members are distributed
between the Union's Headquarters in Geneva, Switzerland and
eleven field offices located around the world.
Asia Pacific Telecommunity: Headquartered at Bangkok,
the APT is a unique organization of Governments, telecom
service providers, manufactures of communication equipment,

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research & development organizations and other stake holders
active in the field of communication and information
technology. APT serves as the focal organization for
communication and information technology in the Asia Pacific
region. The APT has 34 Members, 4 Associate Members and
121 Affiliate Members. The objective of the Telecommunity is
to foster the development of telecommunication services and
information infrastructure throughout the region with a
particular focus on the expansion thereof in less developed
areas. APT has been conducting HRD Programme for
developing the skills of APT Members to meet the objectives of
APT. The topics include Information Communication
Technologies (ICT), Network and Information Security, Finance
and Budget, Telecommunication Management, Mobile
Communications, Multimedia, Satellite
Communication, Telecommunications and ICT Policy and
Regulation, Broadband Technologies, e-Applications, Rural
Telecommunications Technologies, IP Networks and Services,
Customer Relations, etc.
The European Telecommunications Standards Institute
(ETSI) produces globally applicable standards for Information
and Communications Tec hnologies(ICT), including fixed,
mobile, radio, converged, broadcast and internet technologies. It
is officially recognized by the European Union as a European
Standards Organization. ETSI is a not-for-profitorganization
with more than 700 ETSI member organizations drawn from 62
countries across 5 continents world-wide. ETSI unites
Manufacturers, Network operators, National Administrations,
Service providers, Research bodies, User groups, Consultancies.
This cooperation has resulted in a steady stream of highly
successful ICT standards in mobile, fixed, and radio
communications and a range of other standards that cross these
boundaries, including Security, Satellite, Broadcast, Human
Factors, Testing & Protocols, Intelligent transport, Power-line
telecoms, health, Smart Cards, Emergency communications,
GRID & Clouds, Aeronautical etc. ETSI is consensus-based and

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conducts its work through summer Training, Overview of
Telecommunication Networks-II Page 6 of 12 Compiled by MC
Faculty ALTTC, Ghaziabad Technical Committees, which
produce standards and specifications, with the ETSI General
Assembly and Board.
BSNL: Bharat Sanchar Nigam Limited was formed in year 2000
and took over the service providers role from DoT. Today,
BSNL has a customer base of over 9 crore and is the fourth
largest integrated telecom operator in the country. BSNL is the
market leader in Broadband, landline and national transmission
network. BSNL is also the only operator covering over 5
lakh village with telecom connectivity. Area of operation of
BSNL is all India except Delhi & Mumbai.
MTNL: Mahanagar Telephone Nigam Limited, formed in 1984
is the market leader in landline and broadband in its area of
operation.
TCIL: TCIL, a prime engineering and consultancy company, is
a wholly owned Government of India Public Sector Enterprise.
TCIL was set up in 1978 for providing Indian telecom expertise
in all fields of telecom, Civil and IT to developing countries
around the world. It has its presence in over 70 countries.
ITI: Indian telephone Industries is the oldest manufacturing unit
for telephone instruments. To keep pace with changing times, it
has started taking up manufacturing of new technology
equipment such as GSM, OFC equipment, Invertors, Power
plants, Defense equipments, Currency counting machines etc.
Centre for Development of Telematics (CDoT): This is the R
& D unit under DoT setup in 1984. The biggest contribution of
this centre to Indian telecom sector is the development of low
capacity (128 port) Rural automatic Exchange (RAX) which
enabled provisioning of telephone in even the smallest village.

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This was specially designed to suit Indian environment, capable
of withstanding natural temperature and dusty conditions.
Prominent Licenses provided by DoT:
o Access Service (CMTS & Unified Access Service): The
Country is divided into 23 Service Areas consisting of 19
Telecom Circle Service Areas and 4 Metro Service Areas
for providing Cellular Mobile Telephone Service (CMTS).
Consequent upon announcement of guidelines for Unified
Access (Basic& Cellular) Services licenses on 11.11.2003, some
of the CMTS operators have been permitted to migrate from
CMTS License to Unified Access Service License (UASL). No
new CMTS and Basic service licenses are being awarded after
issuing the guidelines for Unified access Service
Licence(UASL). As on 31st March 2008, 39 CMTS and 240
UASL licenses operated.
o 3G & BWA (Broadband Wireless Access): Department of
Telecom started the auction process for sale of spectrum for 3G
and BWA (WiMax) in April 2010 for 22 services areas in the
country. BSNL & MTNL have already been given spectrum for
3G and BWA and they need to pay the highest bid amount as
per auction results. BSNL & MTNL both are providing 3G
services. BSNL has rolled out its BWA service by using WiMax
technology.
o Mobile Number Portability (MNP) Service: Licenses have
been awarded to two operators to provide MNP in India. DoT is
ensuring the readiness of all mobile operators and expects to
start this service any time after June 2010.
o Infrastructure Provider: There are two categories IP-I and
IP-II. For IP-I the applicant company is required to be registered
only. No license is issued for IP-I. Companies registered as IP-I
can provide assets such as Dark Fibre, Right of Way, Duct space
and Tower. This was opened to private sector with effect from
13.08.2000. An IP-II license Summer Training, Overview of
Telecommunication Networks-II Page 7 of 12 Compiled by MC

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Faculty ALTTC, Ghaziabad can lease / rent out /sell end to end
bandwidth i.e. digital transmission capacity capable to carry a
message. This was opened to private sector with effect from
13.08.2000. Issuance of IP-II Licence has been discontinued
w.e.f. 14.12.05
o INMARSAT : INMARSAT (International Maritime Satellite
Organisation) operates constellation of geo-stationary satellites
designed to extend phone, fax and data communications all over
the world. Videsh Sanchar Nigam Ltd (VSNL) is permitted to
provide Inmarsat services in India under their International Long
Distance(ILD) licence granted by Department of
Telecommunications(DoT). VSNL has commissioned their new
Land Earth Station (LES) at Dighi, Pune compatible with 4th
generation INMARSAT Satellites (I-4) and INMARSAT-B, M,
Mini-M & M-4 services are now being provided through this
new LES after No Objection Certificate (NOC) is issued by DoT
on case by case basis.
o National Long Distance: There is no limit on number of
operators for this service and license is for 20 years.
o International Long Distance: This was opened to private
sector on 1st April 2002 with no limit on number of operators.
The license period is 20 years.
o Resale of IPLC: For promoting competition and affordability
in International Private
Leased Circuits (IPLC) Segment, Government permitted the
“Resale of IPLC” by introducing a new category of License
called as – “Resale of IPLC” Service License with effect from
24th September 2008. The Reseller can provide end-to-end
IPLC between India and country of destination for any capacity
denomination. For providing the IPLC service, the Reseller has
to take the IPLC from International Long Distance (ILD)
Service Providers licensed and permitted to enter into an
arrangement for leased line with Access Providers, National
Long Distance Service Providers and International Long
Distance Service Providers for provision of IPLC to end
customers.

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o Sale of International Roaming SIM cards /Global Calling
Cards in India: The cards being offered to Indian Customers
will be for use only outside India. However, if it is essential to
activate the card for making test calls/emergent calls before the
departure of customer and /or after the arrival of the customer,
the same shall be permitted for forty eight (48) hours only prior
to departure from India and twenty four (24) hours after arrival
in India.
o Internet without Telephony: The Internet Service Provider
(ISP) Policy was announced in November, 98. ISP Licenses ,
which prohibit telephony on Internet ,are being issued starting
from 6.11.98 on non-exclusive basis. Three category of license
exist namely A,B and C. A is all India, B is telecom Circles,
Metro Districts and major districts where as C is SSA wide.
o Internet with Telephony: Only ISP licensees are permitted,
within their service area, to offer Internet Telephony service.
The calls allowed are PC to PC in India, PC in India to
PC/Telephone outside India, IP based calls from India to other
countries.
o VPN: Internet Service Providers (ISPs) can provide Virtual
Private Network (VPN) Services. VPN shall be configured as
Closed User Group(CUG) only and shall carry only the traffic
meant for the internal use of CUG and no third party traffic shall
be carried o the VPN. VPN shall not have any connectivity with
PSTN /ISDN / PLMN except when the VPN has been set up
using Internet access dial-up facility to the ISP node. Outward
dialing facility from ISP node is not permitted.
o VSAT & Satellite Communication: There are two types of
CUG VSAT licenses : (i) Commercial CUG VSAT license and
(ii) Captive CUG VSAT license. The commercial VSAT service
provider can offer the service on commercial basis to the
subscribers by setting up a number of Closed User Groups

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(CUGs) whereas in the captive VSAT service only one CUG
can be set up for the captive use of the licensee. The scope of the
service is to provide data connectivity between various sites
scattered within territorial boundary of India via INSAT
Satellite System using Very Small Aperture Terminals
(VSATs). However, these sites should form part of a Closed
User Group (CUG). PSTN connectivity is not permitted.
o Radio Paging: The bids for the Radio Paging Service in 27
cities were invited in 1992, the licenses were signed in 1994 and
the service was commissioned in 1995. There was a provision
for a fixed license fee for first 3 years and review of the license
fee afterwards. The license was for 10 years and in 2004 Govt
offered a extended 10 years license with certain license fee
waivers but with the wide spread use of mobile phones, this
service has lost its utility.
o PMRTS: Public Mobile Radio Trunking service allows city
wide connectivity through wireless means. This service is
widely used by Radio Taxi operators and companies whose
workforce is on the move and there is need to locate the present
position of employee for best results. PSTN connectivity is
permitted.
o INSAT MSS: INSAT Mobile Satellite System Reporting
Service (INSAT MSS Reporting Service) is a one way satellite
based messaging service available through INSAT. The basic
nature of this service is to provide a reporting channel via
satellite to the group of people, who by virtue of their nature of
work are operating from remote locations without any telecom
facilities and need to send short textual message or short data
occasionally to a central station.
o Voice Mail/ Audiotex/ UMS (Unified Messaging Service):
Initially a seprate license was issued for these services. For
Unified Messaging Service, transport of Voice Mail Messages to
other locations and subsequent retrieval by the subscriber must

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be on a nonreal time basis. For providing UMS under the
licence, in addition to the license for Voice
Mail/Audiotex/UMS, the licensee must also have an ISP license.
The ISP licence as well as Voice Mail/Audiotex/ UMS license
should be for the areas proposed to be covered by UMS service.
Since start of NTP-99, all access provider i.e. CMTS, UASL,
Fixed service providers are also allowed to provide these
services as Value Added Service (VAS) under their license
conditions.
o Telemarketing: Companies intending to operate as
Telemarketer need to obtain this license from DoT.
o Other Service Provider (including BPO): As per New
Telecom Policy (NTP) 1999, Other Service Providers (OSP),
such as tele-banking, tele-medicine, tele-trading, ecommerce,
Network Operation Centers and Vehicle Tracking Systems etc
are allowed to operate by using infrastructure provided by
various access providers for non-telecom services.
INTRODUCTION
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 early as mid of 19th
century. However, due to fast industrial development and
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

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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.
MULTIPLEXING TECHNIQUES
There are basically two types of multiplexing techniques
I. Frequency Division Multiplexing (FDM)
II. Time Division Multiplexing (TDM)
Frequency Division Multiplexing Techniques (FDM)
The FDM techniques are the process of translating
individual speech circuits (300-3400 Hz) into pre-assigned
frequency slots within the bandwidth of the transmission

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medium. The frequency translation is done by amplitude
modulation of the audio frequency with an appropriate carrier
frequency. At the output of the modulator a filter network is
connected to select either a lower or an upper side band. Since
the intelligence is carried in either side band, single side band
suppressed carrier mode of AM is used. This results in
substantial saving of bandwidth mid also permits the use of low
power amplifiers. Please refer Fig. 1.
FDM techniques usually find their application in analogue
transmission systems. An analogue transmission system is one
which is used for transmitting continuously varying signals.
Fig. 1 FDM Principle
Time Division Multiplexing
Basically, time division multiplexing involves nothing more
than sharing a transmission medium by a number of circuits in
time domain by establishing a sequence of time slots during
which individual channels (circuits) can be transmitted. Thus the
entire bandwidth is periodically available to each channel.
Normally all time slots1 are equal in length. Each channel is
assigned a time slot with a specific common repetition period
called a frame interval. This is illustrated in Fig. 2.

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Fig. 2 Time Division Multiplexing
Each channel is sampled at a specified rate and transmitted
for a fixed duration. All channels are sampled one by, the cycle is
repeated again and again. The channels are connected to
individual gates which are opened one by one in a fixed
sequence. At the receiving end also similar gates are opened in
unison with the gates at the transmitting end.
The signal received at the receiving end will be in the form
of discrete samples and these are combined to reproduce the
original signal. Thus, at a given instant of time, only one channel
is transmitted through the medium, and by sequential sampling a
number of channels can be staggered in time as opposed to
transmitting all the channel at the same time as in EDM
systems. This staggering of channels in time sequence for
transmission over a common medium is called Time Division
Multiplexing (TDM).
Pulse Code Modulation
It was only in 1938; Mr. A.M. Reaves (USA) developed
a Pulse Code Modulation (PCM) system to transmit the
spoken word in digital form. Since then digital speech

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transmission has become an alternative to the analogue
systems.
PCM systems use TDM technique to provide a number
of circuits on the same transmission medium viz open wire or
underground cable pair or a channel provided by carrier,
coaxial, microwave or satellite system.
Basic Requirements for PCM System
To develop a PCM signal from several analogue signals,
the following processing steps are required
•Filtering
•Sampling
•Quantization
•Encoding
•Line Coding
FILTERING
Filters are used to limit the speech signal to the frequency
band 300-3400 Hz.
SAMPLING
It is the most basic requirement for TDM. Suppose we
have an analogue signal Fig. 3 (b), which is applied across a
resistor R through a switch S as shown in Fig. 3 (a) . Whenever
switch S is closed, an output appears across R. The rate at which
S is closed is called the sampling frequency because during the
make periods of S, the samples of the analogue modulating
signal appear across R. Fig. 3(d) is a stream of samples of the
input signal which appear across R. The amplitude of the sample

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is depend upon the amplitude of the input signal at the instant of
sampling. The duration of these sampled pulses is equal to the
duration for which the switch S is closed. Minimum number of
samples are to be sent for any band limited signal to get a good
approximation of the original analogue signal and the same is
defined by the sampling Theorem.
Fig. 3: Sampling Process
Sampling Theorem
A complex signal such as human speech has a wide
range of frequency components with the amplitude of the signal
being different at different frequencies. To put it in a different
way, a complex signal will have certain amplitudes for all
frequency components of which the signal is made. Let us say
that these frequency components occupy a certain bandwidth B.
If a signal does not have any value beyond this bandwidth B,

23. P a g e | 23
then it is said to be band limited. The extent of B is determined
by the highest frequency components of the signal.
Sampling Theorem States
"If a band limited signal is sampled at regular intervals of
time and at a rate equal to or more than twice the highest signal
frequency in the band, then the sample contains all the
information of the original signal." Mathematically, if fH is the
highest frequency in the signal to be sampled then the sampling
frequency Fs needs to be greater than 2 fH.
i.e. Fs>2fH
Let us say our voice signals are band limited to 4 KHz and let
sampling frequency be 8 KHz.
Time period of sampling Ts = 1 sec
8000
or Ts = 125 micro seconds
If we have just one channel, then this can be sampled every
125 microseconds and the resultant samples will represent the
original signal. But, if we are to sample N channels one by one
at the rate specified by the sampling theorem, then the time
available for sampling each channel would be equal to Ts/N
microseconds.

24. P a g e | 24
FIG. 4: Sampling and combining Channels
Fig. 4 shows how a number of channels can be sampled
and combined. The channel gates (a, b ... n) correspond to the
switch S in Fig. 3. These gates are opened by a series of pulses
called "Clock pulses". These are called gates because, when
closed these actually connect the channels to the transmission
medium during the clock period and isolate them during the OFF
periods of the clock pulses. The clock pulses are staggered so
that only one pair of gates is open at any given instant and,
therefore, only one channel is connected to the transmission
medium. The time interval during which the common
transmission medium is allocated to a particular channel is called
the Time Slot for that channel. The width of. this time slot will
depend, as stated above, upon the number of channels to be
combined and the clock pulse frequency i.e. the sampling
frequency.
In a 30 channel PCM system. TS i.e. 125 microseconds are
divided into 32 parts. That is 30 time slots are used for 30 speech
signals, one time slot for signaling of all the 30 chls, and
one time slot for synchronization between Transmitter &
Receiver.
The time available per channel would be Ts/N = 125/32 =
3.9 microseconds. Thus in a 30 channel PCM system, time slot is
3.9 microseconds and time period of sampling i.e..the interval

25. P a g e | 25
between 2 consecutive samples of a channel is 125 microseconds.
This duration i.e. 125 microseconds is called Time Frame.
The signals on the common medium (also called the
common highway)
of a TDM system will consist of a series of pulses, the
amplitudes of which are proportional to the amplitudes of the
individual channels at their respective sampling instants. This is
illustrated in Fig. 5
i
Fig 5: PAM Output Signals
The original signal for each channel can be recovered at
the receive end by applying gate pulses at appropriate instants
and passing the signals through low pass filters. (Refer Fig. 6).
Fig. 6 : Reconstruction of Original Signal

26. P a g e | 26
Quantization
In FDM systems we convey the speech signals in their
analogue electrical form. But in PCM, we convey the speech in
discrete form. The sampler selects a number of points on the
analogue speech signal (by sampling process) and measures their
instant values. The output of the sampler is a PAM signal as
shown in Fig. 3; The transmission of PAM signal will require
linear amplifiers at trans and receive ends to recover distortion
less signals. This type of transmission is susceptible to all the
disadvantages of AM signal transmission. Therefore, in PCM
systems, PAM signals are converted into digital form by using
Quantization Principles. The discrete level of each sampled
signal is quantified with reference to a certain specified level on
an amplitude scale.
The process of measuring the numerical values of the
samples and giving them a table value in a suitable scale is
called "Quantizing". Of course, the scales and the number of
points should be so chosen that the signal could be effectively
reconstructed after demodulation.
Quantizing, in other words, can be defined as a process of
breaking down a continuous amplitude range into a finite
number of amplitude values or steps.
A sampled signal exists only at discrete times but its
amplitude is drawn from a continuous range of amplitudes of an
analogue signal. On this basis, an infinite number of amplitude
values is possible. A suitable finite number of discrete values
can be used to get an. approximation of the infinite set. The
discrete value of a sample is measured by comparing it with
a scale having a finite number of intervals and identifying
the interval in which the sample falls. The finite number of
amplitude intervals is called the "quantizing interval". Thus,
quantizing means to divide the analogue signal's total
amplitude range into a number of quantizing intervals and
assigning a level to each. intervals.
For example, a 1 volt signal can be divided into 10mV
ranges like 10-20mV, 30-40mV and so on. The interval 10-20

27. P a g e | 27
mV, may be designated as level 1, 20-30 mV as level 2 etc. For
the purpose of transmission, these levels are given a binary code.
This is called encoding. In practical systems-quantizing and
encoding are combined processes. For the sake of
understanding, these are treated separately.
Quantizing Process
Suppose we have a signal as shown in Fig. 7 which is
sampled at instants a, b, c, d and e. For the sake of explanation,
let us suppose that the signal has maximum amplitude of 7 volts.
In order to quantize these five samples taken of the signal,
let us say the total amplitude is divided into eight ranges or
intervals as shown in Fig. 7. Sample (a) lies in the 5th range.
Accordingly, the quantizing process will assign a binary code
corresponding to this i.e. 101, Similarly codes are assigned for
other samples also. Here the quantizing intervals are of the
same size. This is called Linear Quantizing.
FIG. 7: QUANTIZING-POSITIVE SIGNAL
Assigning an interval of 5 for sample 1, 7 for 2 etc. is the
quantizing process. Giving, the assigned levels of samples,
the binary code are called coding of the quantized samples.
Quantizing is done for both positive and negative swings. As
shown in Fig.6, eight quantizing levels are used for each
direction of the analogue signal. To indicate whether a

28. P a g e | 28
sample is negative with reference to zero or is positive with
reference zero, an extra digit is added to the binary code. This
extra digit is called the "signbit".In Fig.8. Positive values have
a sign bit of ' 1 ' and negative values have sign bit of'0'.
FIG. 8: QUANTIZING - SIGNAL WITH + Ve & - Ve
VALUES
Relation between Binary Codes and Number of levels.
Because the quantized samples are coded in binary form,
the quantization intervals will be in powers of 2. If we have a 4
bit code, then we can have 2" = 16 levels. Practical PCM
systems use an eight bit code with the first bit as sign bit. It
means we can have 2" = 256 (128 levels in the positive
direction and 128 levels in the negative direction) intervals for
quantizing.

29. P a g e | 29
Quantization Distortion
Practically in quantization we assign lower value of each
interval to a sample falling in any particular interval and this
value is given as:
Table-1: Illustration of Quantization Distortion
Analogue Quantizing Quantizing Binary Code
Signal Interval Level
Amplitude (mid value)
Range
0-10 mv 5 mv 0 1000
10-20mv 15mv 1 1001
20-30 mv 25 mv 2 1010
30-40 mv 35 mv 3 1011
40-50 mv 45 mv 4 1100
If a sample has an amplitude of say 23 mv or 28 mv, in
either case it will be assigned he eve "2". This Is represented
in binary code 1010. When this is decoded at the receiving end,
the decoder circuit on receiving a 1010 code will convert this
into an analogue signal of amplitude 25 mv only. Thus the
process' of quantization leads to an approximation of the input
signal with the detected signal having some deviations in
amplitude from the actual values. This deviation between the
amplitude of samples at the transmitter and receiving ends (i.e.
the difference between the actual value & the reconstructed
value) gives rise to quantization distortion.
If V represent the step size and 'e' represents the
difference in amplitude fe' must exists between - V/2 & + V/2)
between the actual signal level and its quantized equivalent then
it can be proved that mean square quantizing error is equal to

30. P a g e | 30
(V2). Thus, we see that the error depends upon the size of the
step.
In linear quantization, equal step means equal degree of
error for all input amplitudes. In other words, the signal to noise
ratio for weaker signals will be poorer.
To reduce error, we, therefore, need to reduce step size or
in other words, increase th,e number of steps in the given
amplitude range. This would however, increase the
transmission bandwidth because bandwidth B = fm log L.
where L is the number of quantum steps and fm is the highest
signal frequency. But as we knows from speech statistics that
the probability of occurrence of a small amplitude is much
greater than large one, it seems appropriate to provide more
quantum levels (V = low value) in the small amplitude region
and only a few (V = high value) in the region of higher
amplitudes. In this case, provided the total number of specified
levels remains unchanged, no increase in transmission
bandwidth will be required. This will also try to bring about
uniformity in signal to noise ratio at all levels of input signal.
This type of quantization is called non-uniform quantization.
In practice, non-uniform quantization is achieved using
segmented quantization (also called companding). This is shown
in Fig. 9 (a). In fact, there is equal number of segments for both
positive and negative excursions. In order to specify the location
of a sample value it is necessary to know the following:
1.The sign of the sample (positive or negative excursion)
2.The segment number
3.The quantum level within the segment

31. P a g e | 31
Fig. 9 (a) Segmented coding curve
As seen in Fig. 9 (b), the first two segment in each
polarity are collinear, (i.e. the slope is the same in the central
region) they are considered as one segment. Thus the total
number of segment appear to be 13. However, for purpose of
analysis all the 16 segments will be taken into account.
Encoding
Conversion of quantized analogue levels to binary signal
is called encoding. To represent 256 steps, 8 level code is
required. The eight bit code is also called an eight bit "word".
The 8 bit word appears in the form
P ABC
WXYZ
Polarity bit ‘1’ Segment Code
Linear encoding
for + ve 'O' for - ve. In the
segment

32. P a g e | 32
The first bit gives the sign of the voltage to be coded. Next
3 bits gives the segment number. There are 8 segments for the
positive voltages and 8 for negative voltages. Last 4 bits give
the position in the segment. Each segment contains 16
positions. Referring to Fig. 9(b), voltage Vc will be encoded as
1 1 1 1 0101.
FIG. 9 (b) : Encoding Curve with Compression 8 Bit Code
The quantization and encoding are done by a circuit called
coder. The coder converts PAM signals (i.e. after sampling)
into an 8 bit binary signal. The coding is done as per Fig. 9
which shows a relationship between voltage V to be coded and
equivalent binary number N. The function N = f(v) is not linear.
The curve has the following characteristics.
It is symmetrical about the origins. Zero level
corresponds to zero voltage to be encoded.
It is logarithmic function approximated by 13 straight segments
numbered 0 to 7 in positive direction and 'O' to 7 in the
negative direction. However 4 segments 0, 1, 0, 1 lying between
levels + vm/64 -vm/64 being collinear are taken as one segment.

33. P a g e | 33
The voltage to be encoded corresponding to 2 ends of
successive segments are in the ratio of 2. That is vm, vm/2, vm/
4, vm/8, vm/16, vm/32, vm/64, vm/128 (vm being the maximum
voltage).
There are 128 quantification levels in the positive part of
the curve and 128 in the negative part of the curve. In a PCM
system the channels are sampled one by one by applying the
sampling pulses to the sampling gates. Refer Fig. 10. The gates
open only when a pulse is applied to them and pass the analogue
signals through them for the duration for which the gates remain
open. Since only one gate will be activated at a given instant, a
common encoding circuit is used for all channels. Here the
samples are quantized and encoded. The encoded samples of all
the channels and signals etc are combined in the digital combiner
and transmitted.
Fig. 10
The reverse process is carried out at the receiving end to
retrieve the original analogue signals. The digital combiner
combines the encoded samples in the form of "frames". The
digital separator decombines the incoming digital streams into

34. P a g e | 34
individual frames. These frames are decoded to give the PAM
(Pulse Amplitude Modulated) samples. The samples
corresponding to individual channels are separated by
operating the receive sample gates in the same sequence i.e. in
synchronism with the transmit sample gates.
CONCEPT OF FRAME
In Fig. 10, the sampling pulse has a repetition rate of Ts
sees and a pulse width of "St". When a sampling pulse arrives,
the sampling gate remains opened during the time "St" and
remains closed till the next pulse arrives. It means that a channel
is activated for the duration "St". This duration, which is the
width of the sampling pulse, is called the "time slot" for a given
channel.
Since Ts is much larger as compared to St. a number of
channels can be sampled each for a duration of St within the time
Ts. With reference to Fig. 10, the first sample of the first channel
is taken by pulse 'a', encoded and is passed on the combiner.
Then the first sample of the second channel is taken by pulse 'b'
which is also encoded and passed on to the combiner, likewise the
remaining channels are also sampled sequentially and are
encoded before being fed to the combiner. After the first sample
of the Nth channel is taken and processed, the second sample of
the first channel is taken, this process is repeated for all
channels. One full set of samples for all channels taken within
the duration Ts is called a "frame". Thus the set of all first
samples of all channels is one frame; the set of all second
samples is another frame and so on.
For a 30 chl PCM system, we have 32 time slots.
Thus the time available per channel would be 3.9 microsecs.
Thus for a 30 chl PCM system,
Frame = 125 microseconds
Time slot per chl = 3.9 microseconds.

35. P a g e | 35
Structure of Frame
A frame of 125 microsecond’s duration has 32 time slots.
These slots are numbered Ts 0 to Ts 31. Information for
providing synchronization between Trans and receive ends is
passed through a separate time slot. Usually the slot Ts 0
carries the synchronization signals. This slot is also called
Frame alignment word (FAW).
The signaling information is transmitted through time slot
Ts 16. Ts 1 to Ts 15 are utilized for voltage signal of
channels 1 to 15 respectively. Ts 17 to Ts 31 are utilized for
voltage signal of channels 16 to 30 respectively.
SYNCHRONIZATION
The output of a PCM terminal will be a continuous stream
of bits. At the receiving end, the receiver has to receive the
incoming stream of bits and discriminate between frames and
separate channels from these. That is, the receiver has to
recognise the start of each frame correctly. This operation is
called frame alignment or Synchronization and is achieved
by inserting a fixed digital pattern called a "Frame Alignment
Word (FAW)" into the transmitted bit stream at regular
intervals. The receiver looks for FAW and once it is detected,
it knows that in next time slot, information for channel one
will be there and so on.
The digits or bits of FAW occupy seven out of eight bits of Ts
0 in the following pattern.
Bit position of Ts 0 B1 B2 B3 B4 B5 B6
B7 B8
FAW digit value X 0 0 1
1 0 1 1

36. P a g e | 36
The bit position B1 can be either ' 1 ' or '0'. However, when
the PCM system is to be linked to an international network,
the B1 position is fixed at '1'.
The FAW is transmitted in the Ts O of every alternate frame.
Frame which do not contain the FAW, are used for
transmitting supervisory and alarm signals. To distinguish the
Ts 0 of frame carrying supervisory/alarm signals from those
carrying the FAW, the B2 bit position of the former are fixed
at T. The FAW and alarm signals are transmitted alternatively
as shown in Table - 2.
TABLE-2
Frame Remark
Numbe B1 B B B B B B B8
rs 2 3 4 5 6 7
FO X 0 0 1 1 0 1 1 FAW
F1 X 1 Y Y Y 1 1 1 ALAR
M
F2 X 0 0 1 1 0 1 1 FAW
F3 etc X 1 Y Y Y 1 1 1 ALAR
M
In frames 1, 3, 5, etc, the bits B3, B4, B5 denote
various types of alarms. For example, in B3 position, if Y = 1,
it indicate Frame synchronization alarm. If Y = 1 in B4, it
indicates high error density alarm. When there is no alarm
condition, bits B3 B4 B5 are set 0. An urgent alarm is
indicated by transmitting "all ones". The code word for an
urgent alarm would be of the form.
X 111 1111

37. P a g e | 37
SIGNALLING IN PCM SYSTEMS
In a telephone network,-the signaling information is
used for proper routing of a call between two subscribers, for
providing certain status information like dial tone, busy
tone, ring back. NU tone, metering pulses, trunk offering
signal etc. All these functions are grouped under the general
terms "signaling" in PCM systems. The signaling
information can be transmitted in the form of DC pulses (as in
step by step exchange) or multi-frequency pulses (as in cross
bar systems) etc.
The signaling pulses retain their amplitude for a much
longer period than the pulses carrying speech information.
It means that the signaling information is a slow varying
signal in time compared to the speech signal which is fast
changing in the time domain. Therefore, a signaling channel
can be digitized with less number of bits than a voice channel.
In a 30 chl PCM system, time slot Ts 16 in each frame is
allocated for carrying signaling information.
The time slot 16 of each frame carries the
signaling data corresponding to two VF channels only.
Therefore, to cater for 30 channels, we must transmit 15
frames, each having 125 microsecond’s duration. For
carrying synchronization data for all frames, one
additional frame is used. Thus a group of 16 frames (each
of 125 microseconds) is formed to make a "multi-frame".
The duration of a multi-frame is 2 milliseconds. The multi-
frame has 16 major time slots of 125 microsecond’s duration.
Each of these (slots) frames has 32 time slots carrying, the
encoded samples of all channels plus the signaling and
synchronization data. Each sample has eight bits of duration
0.400 microseconds (3.9/8 = 0.488) each. The relationship
between the bit duration frame and multi-frame is illustrated in
Fig. 11 (a) & 11 (b).

38. P a g e | 38
Fig. 11 (a) Multi-frame Formation
FIG. 11 (b) 2.048 Mb/s PCM Multi-frame
We have 32 time slots in a frame; each slot carries an 8 bit word.
The total number of bits per frame = 32 x 8 = 256
The total number of frames per seconds is 8000
The total number of bits per second is 256 x 8000 = 2048 K/bits.
Thus, a 30 channel PCM system has 2048 K
bits/sec.

39. P a g e | 39
DEFINITION AND DESCRIPTION OF DIGITAL
HIERARCHIES
INTRODUCTION AND DEFINITION
The term “digital hierarchy” has been created when
developing digital transmission systems. It was laid down when
by multiplexing a certain number of PCM primary multiplexers
were combined to form digital multiplexers of higher order (e.g.
second-order multiplex equipments).
Consequently, a digital hierarchy comprises a number of
levels. Each level is assigned a specific bit rate which is formed
by multiplexing digital signals, each having the bit rate of the
next lower level. In CCITT Rec. G.702, the term “digital
multiplex hierarchy” is defined as follows :
“A series of digital multiplexes graded according to
capability so that multiplexing at one level combines a defined
number of digital signals, each having the digit rate prescribed
for the next lower order, into a digital signal having a prescribed
digit rate which is then available for further combination with
other digital signals of the same rate in a digital multiplex of the
next higher order”.
WHY HIERARCHIES?
1) Before considering in detail the digital hierarchies under
discussion we are going to recapitulate in brief, why there
are several digital hierarchies instead of one only. It has
always been pointed out that as far as the analogue FDM
technique is concerned, the C.C.I.T.T. recommends the
world wide use of the 12-channel group (secondary
group). Relevant C.C.I.T.T. Recommendation exists also
for channel assemblies with more than 60 channels so that
with certain exceptions – there is only one world-wide
hierarchy for the FDM system (although the term
“hierarchy” is not used in the FDM technique).
2) In the digital transmission technique it was unfortunately
not possible to draw up a world-wide digital hierarchy. In

40. P a g e | 40
practice, equipment as specified in C.C.I.T.T.
Recommendation G.732 and 733, they do not only differ
completely in their bit rates, but also in the frame
structures, in signaling, frame alignment, etc. Needless to
say that, as a consequence, the higher order digital
multiplexers derived from the two different PCM primary
multiplexers and thus the digital hierarchies differ as well.
3) Since these two PCM primary multiplexers are available,
two digital hierarchies only would have to be expected. In
reality, however, two digital hierarchies with several
variants are under discussion because the choice of the
fundamental parameters of a digital hierarchy depends not
only on the PCM primary multiplex, which forms the basic
arrangement in that hierarchy, but on many other factors
such as :
(a) The bit rate of the principal signal sources.
(b) Traffic demand, network topology, operational
features, flexibility of the network.
(c) Time division and multiplexing plant
requirements.
(d) Compatibility with analog equipment.
(e) Characteristics of the transmission media to be
used at the bit rates for the various levels of the
hierarchies.
Since today these factors which are essential for
forming digital hierarchies vary from country to
country, it is no wonder that we now have to consider
more than two proposals for digital hierarchies.

41. P a g e | 41
DIGITAL HIERARCHIES BASED ON THE 1544
KBIT/S PCM PRIMARY MULTIPLEX
EQUIPMENT
It was around 1968 that Bell labs. proposed a digital
hierarchy based on the 24-channel PCM primary multiplex at
the various levels of the hierarchy :
Level in hierarchy Bit rate Trans. line
First level 1544 kbit/s T1
Second level 6312 kbit/s T2
Third level 46304 kbit/s L5 (Jumbo Grp)
Fourth level 280000 kbit/s WT4 (Wave
guide)
Fifth level 568000 kbit/s T5
This proposal was modified during the following years. At
the end of the study period 1968/72, the following digital
network hierarchy was finally proposed as given in Fig.1.
Fig. 1
Encoded FDM (Master Group) USA & Canada
1) For the various bit rates at the higher levels of the two
proposals, different reasons have been indicated. The bit
rate of 44736 kbit/s was selected to provide a flexibility
point for circuit interconnection and because it was a

42. P a g e | 42
suitable coding level for the 600 channel FDM
mastergroup.
2) It is also an appropriate bit rate for inter-connection to
radio-relay links planned for use at various frequencies.
3) At the same time, N.T.T. published its PCM hierarchy
are concerned (1554 and 6112 kbit/s, respectively),
these two proposals are identical. They differ, however,
in the higher levels as shown in Fig.2.
Fig. 2
Encoded TDM (Japanese)
4) In the N.T.T. proposal the bit rate of 32064 kbit/s at the
third level of the proposed hierarchy might be
considered a suitable bit rate to be used on international
satellite links perhaps for administrations operating
different PCM primary multiplex equipments. It is also
a convenient bit rate for encoding the standardized 300-
channel FDM master group. Delta modulation and
differential PCM for 4 MHz visual telephone are also
suitable for this bit rate. Transmission of 32064 kbit/s
via a special symmetrical cable of new design is also
possible.
5) The above fact shows that the differing bit rates of the
third level indicated in the two hierarchy proposals can,
therefore, be justified by technical arguments. As far as
the differing bit rates of the fourth level are concerned,
only a few technical reasons are included in the two
proposal. In both cases coaxial cables are used as a

43. P a g e | 43
transmission medium so that the medium does not call
for different bit rates.
6) Moreover, it seems that at present the specifications of
the fourth level (and higher ones) in the two proposed
hierarchies is not yet considered so urgent. For the time
being the third level seems to be more important.
7) The C.C.I.T.T. faced with this situation has reached
finally the solution which is covered by CCITT
recommendation G.752 as one can see from this
recommendation, two different hierarchical levels are
existing in the third level of this hierarchy, namely
32064 kbits/s and 44736 kbit/s respectively. Higher
level have not been specified so far.
DIGITAL HIERARCHY BASED ON THE 2048
KBIT/S PCM PRIMARY MULTIPLEX
EQUIPMENT
For this digital hierarchy, two specifications have at
present been laid down only for the first level at 2048 kbit/
s and for the second level at 8448 kbit/s.
As for the higher levels, the situation is just contrary to
that existing in the case of digital hierarchies derived from
1544 kbit/s primary multiplex, i.e. general agreement has
more or less been reached on the fourth level having a bit
rate of 139264 kbit/s. 5th order system where bit rate of
565 Mb/s have also been planned now.
1) The critical point in this hierarchy is whether or not the
third level at 34368 kbit/s should exist.
2) 4.2 The C.C.I.T.T. has agreed after long discussions on
the following (Recommendation G.751) “that there should
be a 4th order bit rate of 139264 kbit/s in the digital
hierarchy which is based on the 2nd order bit rate of 8448
kbit/s”.

44. P a g e | 44
There should be two methods of achieving the 4th order bit
rate :
Method 1 by using a 3rd order bit rate of 34368 kbit/s in
the digital hierarchy.
Method 2 by directly multiplexing sixteen digital signals
at 8448 kbit/s. The digital signals at the bit rate of 139264
kbit/s obtained by these two methods should be identical.
The existence of the above two methods implies that the
use of the bit rate of 34368 kbit/s should not be imposed
on an Administration that does not wish to realize the
corresponding equipment.
3) In accordance with the above two methods the following
realizations of digital multiplex equipments using positive
justification are recommended :
Method 1 : Realization by separate digital multiplex
equipments : one type which operates at 34368 kbit/s and
multiplexes four digital signals at 8448 kbit/s; the other
type which operates at 139264 kbit/s and multiplexes four
digital signals at 34368 kbit/s.
Method 2 : Realization by a single digital multiplex
equipment which operates at 139264 kbit/s and
multiplexes sixteen digital signals at 8448 kbit/s.
Method 1 has been put into practice.
4) Where the fifth level is concerned, some preliminary
proposals (e.g. 565148 kbit/s) have been submitted which
were not discussed in detail.
Therefore, the present structure of this digital hierarchy is
139.264
as given in Fig.3.

45. P a g e | 45
Fig. 3
Encoded TDM (European)
SIGNALLING IN TELECOMMUNICATIONS
The term signaling, when used in telephony,
refers to the exchange of control information associated with
the establishment of a telephone call on a telecommunications
circuit. An example of this control information is the digits
dialed by the caller, the caller's billing number, and other call-
related information.
When the signaling is performed on the same circuit that
will ultimately carry the conversation of the call, it is termed
Channel Associated Signaling (CAS). This is the case for earlier
analogue trunks, MF and R2 digital trunks, and DSS1/DASS
PBX trunks.
In contrast, SS7 signaling is termed Common Channel
Signaling (CCS) in that the path and facility used by the
signaling is separate and distinct from the telecommunications
channels that will ultimately carry the telephone conversation.
With CCS, it becomes possible to exchange signaling without
first seizing a facility, leading to significant savings and
performance increases in both signaling and facility usage.
Channel Associated Signaling
Channel Associated Signaling (CAS), also known as per-trunk
signaling (PTS), is a form of digital communication signaling.
As with most telecommunication signaling methods, it uses
routing information to direct the payload of voice or data to its
destination. With CAS signaling, this routing information is
encoded and transmitted in the same channel as the payload
itself. This information can be transmitted in the same band (in-
band signaling) or a separate band (out-of-band signaling) to the
payload.

46. P a g e | 46
CAS potentially results in lower available bandwidth for the
payload. For example, in the PSTN the use of out-of-band
signalling within a fixed bandwidth reduces a 64 kbit/s DS0 to
56 kbit/s. Because of this, and the inherent security benefits of
separating the control lines from the payload, most current
telephone systems rely more on Common Channel Signaling
(CCS).
Common Channel Signaling
In telephony, Common Channel Signaling (CCS) is the
transmission of signaling information (control information) on a
separate channel from the data, and, more specifically, where
that signaling channel controls multiple data channels.
For example, in the public switched telephone network (PSTN)
one channel of a communications link is typically used for the
sole purpose of carrying signaling for establishment and Tear
down of telephone calls. The remaining channels are used
entirely for the transmission of voice data. In most cases, a
single 64kbit/s channel is sufficient to handle the call setup and
call clear-down traffic for numerous voice and data channels.
The logical alternative to CCS is Channel Associated Signaling
(CAS), in which each bearer channel has a signaling channel
dedicated to it.
CCS offers the following advantages over CAS, in the context
of the PSTN:
• Faster call setup.
• No falsing interference between signaling tones by
network and speech frequencies.
• Greater trunking efficiency due to the quicker set up and
clear down, thereby reducing traffic on the network.
• No security issues related to the use of in-band signaling
with CAS.

47. P a g e | 47
• CCS allows the transfer of additional information along
with the signaling traffic providing features such as caller
ID.
The most common CCS signaling methods in use today are
Integrated Services Digital Network (ISDN) and Signaling
System 7 (SS7).
ISDN signaling is used primarily on trunks connecting end-user
private branch exchange (PBX) systems to a central office. SS7
is primarily used within the PSTN. The two signaling methods
are very similar since they share a common heritage and in some
cases, the same signaling messages are transmitted in both ISDN
and SS7.
CCS is distinct from in-band or out-of-band signaling, which are
to the data band what CCS and CAS are to the channel.
Signaling System Number #7
SS7 is a set of telephony signaling protocols which are used to
set up most of the world's public switched telephone network
telephone calls. The main purpose is to set up and tear down
telephone calls. Other uses include number translation, prepaid
billing mechanisms, short message service (SMS), and a variety
of other mass market services.
It is usually abbreviated as Signaling System No. 7, Signaling
System #7, or just SS7. In North America it is often referred to as
CCSS7, an acronym for Common Channel Signaling System 7.
In some European countries, specifically the United Kingdom, it
is sometimes called C7 (CCITT number 7) and is also known as
number 7 and CCIS7.
There is only one international SS7 protocol defined by ITU-T
in its Q.700-series recommendations. There are however, many
national variants of the SS7 protocols. Most national variants are
based on two widely deployed national variants as standardized
by ANSI and ETSI, which are in turn based on the international

48. P a g e | 48
protocol defined by ITU-T. Each national variant has its own
unique characteristics. Some national variants with rather
striking characteristics are the China (PRC) and Japan (TTC)
national variants.
SS7 is designed to operate in two modes: Associated Mode and
Quasi-Associated Mode.
When operating in the Associated Mode, SS7 signaling
progresses from switch to switch through the PSTN following
the same path as the associated facilities that carry the telephone
call. This mode is more economical for small networks. The
Associated Mode of signaling is not the predominant choice of
modes in North America.
When operating in the Quasi-Associated Mode, SS7
signaling progresses from the originating switch to the
terminating switch, following a path through a separate SS7
signaling network composed of STPs. This mode is more
economical for large networks with lightly loaded signaling
links. The Quasi-Associated Mode of signaling is the
predominant choice of modes in North America.
SS7 clearly splits the signaling planes and voice circuits. An
SS7 network has to be made up of SS7-capable equipment from
end to end in order to provide its full functionality. The network
is made up of several link types (A, B, C, D, E, and F) and three
signaling nodes - Service switching point (SSPs), signal transfer
point (STPs), and Service Control Point (SCPs). Each node is
identified on the network by a number, a point code. Extended
services are provided by a database interface at the SCP level
using the SS7 network.
The links between nodes are full-duplex 56, 64, 1,536, or 1,984
kbit/s graded communications channels. In Europe they are
usually one (64 kbit/s) or all (1,984 kbit/s) timeslots (DS0s)
within an E1 facility; in North America one (56 or 64 kbit/s) or
all (1,536 kbit/s) timeslots (DS0As or DS0s) within a T1
facility. One or more signaling links can be connected to the

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same two endpoints that together form a signaling link set.
Signaling links are added to link sets to increase the signaling
capacity of the link set.
In Europe, SS7 links normally are directly connected between
switching exchanges using F-links. This direct connection is
called associated signaling. In North America, SS7 links are
normally indirectly connected between switching exchanges
using an intervening network of STPs. This indirect connection
is called quasi-associated signaling. Quasi-associated signaling
reduces the number of SS7 links necessary to interconnect all
switching exchanges and SCPs in an SS7 signaling network.
SS7 links at higher signaling capacity (1.536 and 1.984 Mbit/s,
simply referred to as the 1.5 Mbit/s and 2.0 Mbit/s rates) are
called High Speed Links (HSL) in contrast to the low speed (56
and 64 kbit/s) links. High Speed Links (HSL) are specified in
ITU-T Recommendation Q.703 for the 1.5 Mbit/s and 2.0 Mbit/s
rates, and ANSI Standard T1.111.3 for the 1.536 Mbit/s rate.
There are differences between the specifications for the 1.5
Mbit/s rate. High Speed Links utilize the entire bandwidth of a
T1 (1.536 Mbit/s) or E1 (1.984 Mbit/s) transmission facility for
the transport of SS7 signaling messages.

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INTRODUCTION
With the evolution of computer networking and packet
switching concept a new era of integrated communication has
emerged in the telecom world. Rapid growth of data
communication market and popularity of Internet, reflect the
needs of enhanced infrastructure to optimize the demand of
traffic. Integration of telecom and computer networking
technology trend has further amplified the importance of
telecommunications in the field of information
communication. It becomes a tool for the conveyance of
information, and thus can be critical to the development
process. Telecommunications has become one of the most
important infrastructures that are very essential to the socio-
economic well being of any nation. As the Internet market
continues to explode, demand for greater bandwidth and
faster connection speeds have led to several technological
approaches developed to provide broadband access to all
consumers. The demand for high-speed bandwidth is growing
at a fast pace, driven mostly by growth in data volumes as the
Internet and related networks become more central to

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business operations. The rapid growth of distributed business
applications, e-commerce, and bandwidth-intensive
applications (such as multimedia, videoconferencing, and
video on demand) generate the demand for bandwidth and
access network.
A concept of broadband services and the means of access
technologies to bridge the customer and service provider is
emerged out throughout the world. "Broadband" refers to high-
speed Internet access. Broadband Solutions represent the
convergence of multiple independent networks including voice,
video and data into a single, unified, broadband network.

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DEFINITION OF BROADBAND
Broadband is the nonspecific term for high-speed digital Internet
access. To state the obvious, ‘broadband’ indicates a means of
connectivity at a high or ‘broad’ bandwidth. There are the
various ways to define the broadband: -
 Term for evolving digital technologies that provide
customers a high-speed data network connection
 Provides signal switched facility offering integrated access
to voice, data, video, and interactive delivery services
 The Federal Communications Commission (FCC) defines
broadband as an advanced telecommunications capability
 Delivers services & facilities with an upstream and
downstream speed of 200 Kbps or more. Range varies
from 128 Kbps to 100 Mbps.

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In fact there is no specific International Definition for
Broadband
In India, Department of Telecommunications has issued a
Broadband policy in 2004. Keeping in view the present status,
Broadband connectivity is defined at present as: -
“An ‘always-on’ data connection that is able to support
interactive services including Internet access and has the
capability of the minimum download speed of 256 kilo bits per
second (kbps) to an individual subscriber from the Point Of
Presence (POP) of the service provider intending to provide
Broadband service where multiple such individual Broadband
connections are aggregated and the subscriber is able to access
these interactive services including the Internet through this
POP. The interactive services will exclude any services for
which a separate license is specifically required, for example,
real-time voice transmission, except to the extent that it is
presently permitted under ISP license with Internet Telephony.
It reflects that: -
 One of the latest trends in enhancing communication
systems involves broadband technology.
 Broadband refers to greater bandwidth-or transmission
capacity of a medium

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 Broadband technology will allow for high-speed
transmission of voice, video, and data over networks like
the Internet
IMPLEMENTATION OF BROADBAND
To Strengthen Broadband Penetration, the Government of India
has formulated a Broadband Policy whose main
objectives are to:-
 Establish a regulatory framework for the carriage and the
content of information in the scenario of convergence.
 Facilitate development of national infrastructure for an
information based society.
 Make available broadband interactive multimedia services
to users in the public network.
 Provide high speed data and multimedia capability using
new technologies to all towns with a population greater
than 2 lakhs.
 Make available Internet services at panchayat (village)
level for access to information to provide product
consultancy and marketing advice.
 Deploy state of art and proven technologies to facilitate
introduction of new services.
 Strengthen research and development efforts in the
telecom technologies.

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NEED OF BROADBAND
The concept of socio economy has an important role in the field
of communication of data, audio, video, speech or any other
kind of application. It is an era of CAPEX and OPEX. Service
providers and customers both are interested in economy with
fastest tool of communication with more throughput. Traditional
circuit switching network are not supporting the effective fast
communication for new applications. This has emerged out with
the evolution of packet switching network. Communication of
data for various applications is feasible to carry with different
throughput.
The service provider converged voice and data network
promises to be implemented as nodes in a neighborhood or
remote switches in regional locations.
The Internet, e-mail, web sites, software downloads, file
transfers: they are all now part of the fabric of doing business.
But until now, it has not been possible for businesses to fully
take advantage of the benefits that technology can truly deliver.
The reason for this is a simple one - a lack of bandwidth. Even
for small businesses, narrowband dial-up access is no longer
sufficient. It simply takes too long to do basic tasks, like

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downloading a large file, and is increasingly being recognized as
insufficient and inconvenient.
Kim Maxwell in his book-"Residential Broadband: An Insider's
Guide to the Battle for the Last Mile" has grouped potential
residential broadband applications into three general categories:
"professional activities” (activities related to users'
employment), "entertainment activities” (from game playing to
movie watching), and "consumer activities “(all other non-
employment and non-entertainment activities).as follows:
Professional Activities:
 Telecommuting (access to corporate networks and systems
to support working at home on a regular basis)
 Video conferencing (one-to-one or multi-person video
telephone calls)
 Home-based business (including web serving, e-commerce
with customers, and other financial functions)
 Home office (access to corporate networks and e-mail to
supplement work at a primary office location)

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Entertainment Activities:
 Web surfing (as today, but at higher speeds with more
video content)
 Video-on-demand (movies and rerun or delayed television
shows)
 Video games (interactive multi-player games)
Consumer Activities:
 Shopping (as today, but at higher speeds with more video
content)
 Telemedicine (including remote doctor visits and remote
medical analyses by medical specialists)
 Distance learning (including live and pre-recorded
educational presentations)
 Public services (including voting and electronic town hall
meetings)
 Information gathering (using the Web for non-
entertainment purposes)
 Photography (editing, distributing, and displaying of
digital photographs)
 Video conferencing among friends and family

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These applications have different bandwidth requirements, and
some of them are still out of reach today. For example, all of the
"professional" activities will likely be supported with less than
1.0 Mbps of bandwidth. Similarly, web surfing and home
shopping will be supported with less than 1.0 Mbps of
bandwidth.
Movies and video, however, demand more bandwidth. Feature
length movies can probably be delivered with 1.5 Mbps of
bandwidth, but broadcast quality video will probably require
more— perhaps as much as 6.0 Mbps. Moreover, if high
definition television ("HDTV") is widely accepted as a new
broadcast standard, that quality of video would require almost
20.0 Mbps of bandwidth — much higher than the current
broadband technologies will support. Thus, although the
technology is moving toward flexible, high-quality video-on-
demand, the necessary speed is probably still more than a few
years away from becoming a reality.
The Internet is poised to spin off thousands of specialized
broadband services. The access network needs to provide the
platform for delivery of these services. Following are the
various applications or services, which are very popular in
society and needs broadband connectivity: -
Virtual Networks
The private virtual networks (LAN/WAN) can be used in an
ample variety of multimedia services, like bank accounts and
central offices.
Education by distance
Education will not have any limits to reach from source to
destination. Along with the traditional school a concept of
remote leaning center is emerged out and popular for various

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courses. There is no limit of distance, area or location in such
distance learning. The student situated in the remote station can
intervene directly to his class with a double system via
videoconference, whilst this happens, simultaneously, the file ex
change
Telework
Organization firm workers that incorporate communication
systems via satellite, can work remotely connecting directly to
their head offices Internet by a high speed connection that
permits users to work efficiently and comfortable.
Telemedicine
Doctors situated in different clinics can stay in contact and
consult themselves directly to other regional medical centers,
using videoconference and the exchange of high quality images,
giving out test results and any type of information. Also rural
zone can have the opinion of specialists situated in remote
hospitals quickly and efficiently.
Electronic commerce
Electronic commerce is a system that permits users to pay goods
and services by Internet. Thanks to this service, any person
connected to the network can ad quire such services with
independence from the place that he is situated and during the
24 hours, simply using a portable computer.

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TECHNOLOGY OPTIONS FOR BROADBAND
SERVICES
Communication of data with different throughput is feasible by
following technologies: -
 Narrow Band
2.4 kbps – 128kbps
 Broadband
256kbps – 8000kbps
 LAN
1000kbps – 100Mbps / Giga Ethernet Various Access
Technologies are used for the delivery of broadband
services. Broadband communications technology can be
divided broadly in to following categories: -
 Wire line Technology
 Wireless Technologies
Service providers according to available technology and access
provide the broadband services to customers. The access
technologies that are adopted by the services providers are
mainly Optical Fiber Technologies, DSL on copper loop, Cable
TV Network, Satellite Media, cellular and fixed wireless,
Terrestrial Wireless etc.
Technology options for broadband services may be classified
according to the mode of access.
Wire line Technologies include
 Digital Subscriber Lines (DSL) on copper loop
 Optical Fiber Technologies
 Cable TV Network
 PLC (Power Line Communication

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Wireless Technologies include
 Satellite Media
 Terrestrial Wireless
 3G Mobile
 Wi-Fi (Wireless Fidelity)
 WiMax
 LMDS and MMDS
 FSO (Free Space Optics)
BROADBAND NETWORK
The broadband services reached to customer from the three
providers. Basically these are Service Provider, Network
Provider and Access Provider. The role of Network Provider is
to provide the services offered to customer through the access
extended by Access Provider. There are various types of
networks which are capable of transmitting and managing the
broadband traffic to desired nodes or locations.
Wire line access technology through DSL, Fiber, and Cable etc
are generally adopts:
• IP based Network
• ATM Network
Wireless access technology through Wi-Fi, Wi-Max. 3G mobile
etc provides wireless access to ingress point of any core network
any migrates to Internet world.

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BROADBAND TECHNOLOGIES USED IN ASIAN
COUNTRIES
Broadband technologies go through two stages of development
in Asian countries. In the early stage, sharp technological
divisions exist among players due to regulatory constraints.
There are various mode of access used by service providers in
this field. Following was the beginning scenario in various
countries like Hong Kong, Malaysia, Indonesia, India and
Singapore: -
• Basic Telecom service providers adopted the use of ISDN/
DSL
• CATV operators use cable modems
• Competitive players use wireless technologies.
In the later stage of development, technological divisions are
shaped by geography and infrastructure. The broadband started
establishing and due to a progressive regulatory framework it
has matured in the market. In the countries like Korea and
Philippines service providers employ several technologies for
the broadband in their networks.
 DSL and cable modems are used where the PSTN and
CATV are in place.

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 Where rainfall is light, an LMDS is used to serve densely
populated areas with little infrastructure and unwired
business districts.
 Satellite is used to service rural areas where population
densities are low
Once newer technologies are available in the market, ISDN
becomes relatively less important. Established telephone
companies are calculating the economics of converting the Last
Mile of existing networks to all-digital systems. Hong Kong and
Singapore citizens already have broadband access, such as
movies on demand, through their local telecom network. Cable-
TV operators, too, are venturing into high-speed Internet access
through modified networks and end-user "cable modems."
Advances in wireless communications means that people starts
surfing the net with cell phones at speeds comparable to or
greater than current home access.

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BSNL provides High speed
broadband internet access under the brand name
“Dataone” BSNL’s Broadband service let the customer to
transmit large amount of data at high speed. At the
minimum of 256 kbps, it is 4.5 times faster than the dial-up,
when connected to the internet such a connection allow
surfing or downloading at much faster speed with out the
hassle of dialing and disconnection. The Broadband service
is available on DSL technology (on the same copper cable
that is used for connecting telephone), on a countrywide
basis spanning more than 200 cities.
Customer needs in order to be able to use Broadband:-
1. BSNL’s Bfone (Basic phone ) connection
2. Personal Computer with Ethernet port or USB port.
3. ADSL CPE (Customer Premises Equipment). This can be
taken from BSNL at nominal rental or can be purchased
out rightly from BSNL.
4. Along with CPE, a splitter. The splitter is used to separate
voice and data.

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Benefits and services of Broadband
 Always on, fast internet connections with minimum speed
of 256 kbps up to 8 Mbps
 Fast downloads even for files with complex graphics and
pictures.
 Get streaming contents like radio, streaming video, Games
on demand without interruption.
 Simultaneous use of telephone and internet.
 Saves time and money.
 Simple monthly charges. No telephone call charges for
internet access.
 At present only postpaid broadband services are available.
Prepaid services are likely to be made available shortly.
 Content Base Services like Video on Demand, IPTV are to
be introduced shortly. ( Up to 100 TV channels on
broadband is available at Pune with a monthly rental of Rs.
250.00)

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Fig 1. Connection of CPE at Sub Office

67. P a g e | 67
Fig 2. Connection of Parallel telephones to Broadband line

68. P a g e | 68
Broadband deployment
Core
Router
GigE
Broadband
RAS
GigE
GigE Tier 1 switch
Tier 2
Switch
GigE
240 Port
DSLAM
ADSL
terminals
CUSTOMER
Fig 3. Broadband Network Connectivity Diagram

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ADSL DEPLOYMENT
Home/Office
Central Office
ADSL (Exchange)
Data switch(Internet)
CPE
ADSL up to 4Km
DSLAM
Copper
Splitter
Voice Switch(PSTN)
TYPICAL NETWORK CONFIGURATION
P
S T N
ER
MDF TIER 2
FD
DSLAM F
FE
Fiber Connectivity
MDF Copper Pair
ER – Equipment Room
From Subscriber

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TYPE I MODEM MT 882
LED INDICATIONS FOR TYPE I MODEM

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TYPE II MODEM WA1003A
LED INDICATIONS FOR TYPE II MODEM

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TYPE III/IV MODEM MT841
LED INDICATIONS FOR TYPE III/IV MODEM

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TROUBLE SHOOTING GUIDELINES
Failure Instructions
Power light 1. Ensure power adapter is well connected;
1
is out. 2. Ensure the right power adapter is used.
1. Ensure the ADSL line is well connected;
2. Ensure the telephone line before entering the
house is valid, try to test with a telephone;
3. Check that there is no junction box before
ADSL LINK
2 connecting the Modem, which has such
light is out.
components like capacitors or diodes that could
hinder back high frequency signals.
4. Ensure the Modem and telephones are
connected in the right way.
1. Ensure you use the right cables from the
Modem to your PC.
2. Ensure the connection is secured.
3. Check if the NIC LED lights up.
LAN LINK 4. Ensure your Network Adapter works normally
3
light is out. by examining whether the item of “Networking
Adapters” is labelled with ! or ?. If it is, you may
delete it and then click “Refresh” to reinstall.
Otherwise, you may try the NIC in another slot.
As a last resort, you have to replace the NIC.
1. Ensure that USB cable connection is secure.
2. Ensure that the proper driver is installed in
the PC.
3. Ensure that the modem is correctly installed
USB LINK is with proper driver and ‘the device is working
4
out properly’ message is available is device
manager.
4. Ensure that USB port in the PC is working
properly; otherwise connect the modem to
another port.

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Take the most common access mode as an
example, in which a dial-up application is
installed on the user’s computer:
1. Ensure that any of the problems above is not
the reason;
2. Ensure that the dial-up application is correctly
installed and set on your PC;
Can’t
3. Ensure that you have entered the right user
5 access the
name and password.
Internet.
4. Ensure “Use Proxy Server” is unchecked in
internet explorer (tools-internet options –
connections – LAN settings), if the problem still
remains even after you have log into
successfully;
5. Try more than one Websites, in case of some
Web server’s being in failure.
1. Make sure the PC indicator at the task bar is
on.
2. Make sure the configuration of TCP/IP is
Cannot log
correct.
in the
6 3. Make sure the data indicator (Blinking PC
configuration
Indicator) of device is on when using Ping
page
command.
4. Make sure the user name and password is
correct. Reset the device.
Safety Concerns for ADSL Modems
 Place the MODEM on a stable stand or table.
 Use the power adapter provided along with MODEM.
 Do not connect telephone directly to the ADSL line. Use
the splitter to connect the phone.
 Do not put heavy objects on top of the MODEM.

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 Do not spill liquid of any kind onto the MODEM. And
keep the unit clean and in a dry environment.
 Break off the power supply in a stormy weather.
 Do not expose the MODEM to direct sunlight.
 Do not put the MODEM on top of the cabinet of your PC.
 Use a soft and dry cloth for cleaning.
 When not in use, please power off the MODEM;
 Do not use junction boxes before connecting the MODEM,
which have such components like capacitors or diodes that
could hinder back high frequency signals.
 When the Modem has been used for a long time, the
surface will reach a certain temperature. This is a natural
phenomenon and the Modem can still work normally.
Line Parameters for Broadband
 The loop resistance should be less than 1100 ohms.
 Insulation resistance between the a limb and b limb, a limb
to earth & b limb to earth should be more than 2 Mega
ohms
 Wires should not contain any joints.
 The foreign potential between a limb to earth & b limb to
earth should be less than 6 volts.
 There should not be any cross talk in the line.
 There should not be any noise in the line.
 Usage of drop wire should be minimum
 The capacitance excluding the instrument should be in
between 0.3 to 0.5 microfarads.