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Training ReportTraining Report

SSA level in-plant summerSSA level in-plant summer training in BSNL (TEZPUR)training in BSNL (TEZPUR)

IITT COLLEGE OFIITT COLLEGE OF ENGINEERING pojewalENGINEERING pojewal

(sbs nagar)(sbs nagar)

Submitted to:Submitted to:HOD of IT BranchHOD of IT Branch

Submitted by:Submitted by:Dushmanta NathDushmanta Nath

Roll no: 81301113016Roll no: 81301113016

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Branch: ITBranch: IT (5(5thth SEM) 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

Job opportunities in telecom Market, government and statutory bodies

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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 isin-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 in1997 – 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 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

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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 isthe eighth largest in the world and the second largest among emerging economies. A brief ontelecom echo system and various key elements in institutional framework is given below:Summer Training, Overview of Telecommunication Networks-II Page 2 of 12Compiled 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:

Telecom Engineering Center (TEC) USO Fund Wireless Planning & Coordination Wing (WPC) Telecom Enforcement, Resource and Monitoring (TERM) Cell Telecom Centers of Excellence (TCOE)

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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 arebriefed 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.

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

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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.

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

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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..

Telecom Centers of Excellence (TCOE): (www.tcoe.in) The growth of Indian Telecommunications sector has been astounding, particularly in the last decade. This growthhas 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

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(i) enhancing talent pool, (ii) technological innovation, (iii) secure information infrastructure and (iv) bridging of digitaldivide. 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 SponsorNext 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 consortiumTelecom Regulatory Authority of India (TRAI): TRAI was established under TRAI Act1997 enacted on 28.03.1997. The act was amended in 2000. Its Organization setup consists ofOne Chairperson, Two full-time members & Two part-time members. Its primary role is todeals with regulatory aspects in Telecom Sector & Broadcasting and Cable services. TRAIhas 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

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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

• 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 andaddressed 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

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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, 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, SatelliteCommunication, 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,

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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 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 GeneralAssembly 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 fourthlargest 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 5lakh 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

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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. 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 Areasfor 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

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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 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.

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o Resale of IPLC: For promoting competition and affordability in International PrivateLeased 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.

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 arrivalin 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.

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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. Outwarddialing 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 (CUGs) whereas in the captive VSAT service only one CUG can be set up for the captive use of the licensee. The scope of theservice 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.

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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 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.

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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 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.

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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 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

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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.

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

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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 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.

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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 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

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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, 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.

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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

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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

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QuantizationIn 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

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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

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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.

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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 Signal Amplitude Range

Quantizing Interval

(mid value)

Quantizing Level

Binary Code

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

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(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

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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

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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.

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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

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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.

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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 B8FAW digit value X 0 0 1 1 0 1 1

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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

Numbers

B1 B2

B3

B4

B5

B6

B7

B8

FO X 0 0 1 1 0 1 1 FAW

F1 X 1 Y Y Y 1 1 1 ALARM

F2 X 0 0 1 1 0 1 1 FAW

F3 etc X 1 Y Y Y 1 1 1 ALARM

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

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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).

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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.

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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

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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.

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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. lineFirst level 1544 kbit/s T1Second level 6312 kbit/s T2Third 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. 1Encoded 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

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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 transmission medium so that the medium does not call for different bit rates.

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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

EQUIPMENTFor 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”. There should be two methods of achieving the 4th order bit

rate :

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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

as given in Fig.3. Fig. 3

Encoded TDM (European)

139.264

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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.

CAS potentially results in lower available bandwidth for the payload. For example, in the PSTN the use of out-of-band

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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. CCS allows the transfer of additional information along

with the signaling traffic providing features such as caller ID.

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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 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.

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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 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.

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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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INTRODUCTIONINTRODUCTION

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

business operations. The rapid growth of distributed business

applications, e-commerce, and bandwidth-intensive

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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: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: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 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 Band2.4 kbps – 128kbps

Broadband256kbps – 8000kbps

LAN1000kbps – 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

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Fig 2. Connection of Parallel telephones to Broadband line

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Fig 3. Broadband Network Connectivity Diagram

Broadband RAS

Tier 1 switchGigE

GigE

GigE

Tier 2 Switch FE

CoreRouter

GigE

FE

240 Port DSLAM

ADSL terminals

CUSTOMER

Broadband deployment

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ADSL DEPLOYMENT

DSLAMFDF

TIER 2

FE

PSTN

MDF

ER

Fiber Connectivity

Copper Pair

MDF

ER – Equipment Room

From Subscriber

Central Office

(Exchange)

Home/Office

ADSL

CPE

ADSL up to 4Km

Splitter

DSLAM

Data switch(Internet)

Voice Switch(PSTN)

Copper

TYPICAL NETWORK CONFIGURATION

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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

1Power light is out.

1. Ensure power adapter is well connected; 2. Ensure the right power adapter is used.

2ADSL LINK light is out.

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 connecting the Modem, which has such components like capacitors or diodes that could hinder back high frequency signals. 4. Ensure the Modem and telephones are connected in the right way.

3LAN LINK light is out.

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. 4. Ensure your Network Adapter works normally 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.

4USB LINK is out

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

with proper driver and ‘the device is working 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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5Can’t access theInternet.

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; 3. Ensure that you have entered the right user name and password.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.

6

Cannot log in the configuration page

1. Make sure the PC indicator at the task bar is on. 2. Make sure the configuration of TCP/IP is correct. 3. Make sure the data indicator (Blinking PC Indicator) of device is on when using Ping 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.

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INTRODUCTION

Optical communication systems date back to the 1790s, to the optical semaphore telegraph invented by French inventor Claude Chappe. In 1880, Alexander Graham Bell patented an optical telephone system, which he called the Photophone. However, his earlier invention, the telephone, was more practical and took tangible shape.

By 1964, a critical and theoretical specification was identified by Dr. Charles K. Kao for long-range communication devices, the 10 or 20 dB of light loss per kilometer standard. Dr. Kao also illustrated the need for a purer form of glass to help reduce light loss. By 1970 Corning Glass invented fiber-optic wire or "optical waveguide fibers" which was capable of carrying 65,000 times more information than copper wire, through which information carried by a pattern of light waves could be decoded at a destination even a thousand miles away. Corning Glass developed an SMF with loss of 17 dB/km at 633 nm by doping titanium into the fiber core. By June of 1972, multimode germanium-doped fiber had developed with a loss of 4 dB per kilometer and much greater strength than titanium-doped fiber. Prof. Kao was awarded half of the 2009 for "groundbreaking achievements concerning the transmission of light in fibers for optical communication". In April 1977, General Telephone and Electronics tested and deployed the world's first live telephone traffic through a fiber-optic system running at 6 Mbps, in Long Beach, California. They were soon followed by Bell in May 1977, with an optical telephone communication system installed in the downtown Chicago area, covering a distance of 1.5 miles (2.4 kilometers). Each optical-fiber pair carried the equivalent of 672 voice channels and was equivalent to a DS3 circuit. Today more than 80 percent of the world's long-distance voice and data traffic is carried over optical-fiber cables.

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FIBER_OPTIC APPLICATIONS

FIBRE OPTICS: The use and demand for optical fiber has grown tremendously and optical-fiber applications are numerous. Telecommunication applications are widespread, ranging from global networks to desktop computers. These involve the transmission of voice, data, or video over distances of less than a meter to hundreds of kilometers, using one of a few standard fiber designs in one of several cable designs.

Carriers use optical fiber to carry plain old telephone service (POTS) across their nationwide networks. Local exchange carriers (LECs) use fiber to carry this same service between central office switches at local levels, and sometimes as far as the neighborhood or individual home (fiber to the home [FTTH]).

Optical fiber is also used extensively for transmission of data. Multinational firms need secure, reliable systems to transfer data and financial information between buildings to the desktop terminals or computers and to transfer data around the world. Cable television companies also use fiber for delivery of digital video and data services. The high bandwidth provided by fiber makes it the perfect choice for transmitting broadband signals, such as high-definition television (HDTV) telecasts. Intelligent transportation systems, such as smart highways with intelligent traffic lights, automated tollbooths, and changeable message signs, also use fiber-optic-based telemetry systems.

Another important application for optical fiber is the biomedical industry. Fiber-optic systems are used in most modern telemedicine devices for transmission of digital diagnostic images. Other applications for optical fiber include space, military, automotive, and the industrial sector.

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ADVANTAGES OF FIBRE OPTICS

Fiber Optics has the following advantages:

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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FIBER OPTIC SYSTEM

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.

- Inexpensive light sources available.

- Repeater spacing increases along with operating speeds because low loss fibers are used at high data rates.

Fig. 1

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Principle of Operation – Theory

Total Internal Reflection - The Reflection that Occurs when a Ligh Ray Travelling in One Material Hits a Different Material and Reflects Back into the Original Material without any Loss of Light.

Fig. 2

Speed of light is actually the velocity of electromagnetic energy in vacuum such as space. Light travels at slower velocities in other materials such as glass. Light travelling from one material to another changes speed, which results in light changing its direction of travel. This deflection of light is called Refraction.

The amount that a ray of light passing from a lower refractive index to a higher one is bent towards the normal. But light going from a higher index to a lower one refracting away from the normal, as shown in the figures.

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ø1

Angle of incidence

n1

n2

ø2

n1

n2

ø1

ø2

n1

n2

ø1 ø2

Angle ofreflection

Light is bent away from normal

Light does not enter second material

Fig. 3

As the angle of incidence increases, the angle of refraction approaches 90o to the normal. The angle of incidence that yields an angle of refraction of 90o is the critical angle. If the angle of incidence increases amore than the critical angle, the light is totally reflected back into the first material so that it does not enter the second material. The angle of incidence and reflection are equal and it is called Total Internal Reflection.

PROPAGATION OF LIGHT THROUGH FIBRE

The optical fibre 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. Typical values for example are a core refractive index of 1.47 and a cladding index of 1.46. Fiber manufacturers control this difference to obtain desired optical fiber characteristics. 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 fibre. Figure shows the idea of light travelling through a fibre. Light injected into the fibre and striking core to cladding interface at grater than the critical angle, reflects back into core, since the angle of

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incidence and reflection are equal, the reflected light will again be reflected. The light will continue zigzagging down the length of the fibre. Light striking the interface at less than the critical angle passes into the cladding, where it is lost over distance. The cladding is usually inefficient as a light carrier, and light in the cladding becomes attenuated fairly. Propagation of light through fibre is governed by the indices of the core and cladding by Snell's law.

Such total internal reflection forms the basis of light propagation through a optical fibre. This analysis consider only meridional rays- those that pass through the fibre axis each time, they are reflected. Other rays called Skew rays travel down the fibre without passing through the axis. The path of a skew ray is typically helical wrapping around and around the central axis. Fortunately skew rays are ignored in most fibre optics analysis.

The specific characteristics of light propagation through a fibre

depends on many factors, including

- The size of the fibre.

- The composition of the fibre.

- The light injected into the fibre.

Jacket

CladdingCore

Cladding

Angle of reflection

Angle of incidence

Light at less thancritical angle isabsorbed in jacket

Jacket

Light is propagated by total internal reflection

Jacket

Cladding

Core

(n2)

(n2)

Fig. Total Internal Reflection in an optical FibreFig. 4 Propagation of light through fiber

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GEOMETRY OF FIBRE

A hair-thin fiber consist of two concentric layers of high-purity silica glass the core and the cladding, which are enclosed by a protective sheath as shown in Fig. 5. Light rays modulated into digital pulses with a laser or a light-emitting diode moves along the core without penetrating the cladding.

Fig. 5 Geometry of fiber

The light stays confined to the core because the cladding has a lower refractive index—a measure of its ability to bend light. Refinements in optical fibers, along with the development of new lasers and diodes, may one day allow commercial fiber-optic networks to carry trillions of bits of data per second.The diameters of the core and cladding are as follows.

Core (m) Cladding ( m)

8 125

50 125

62.5 125

100 140

Fibre sizes are usually expressed by first giving the core size followed by the cladding size. Thus 50/125 means a core diameter of 50m and a cladding diameter of 125m.

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FIBRE TYPES

The refractive Index profile describes the relation between the indices of the core and cladding. Two main relationships exists:

(I) Step Index

(II) Graded Index

The step index fibre has a core with uniform index throughout. The profile shows a sharp step at the junction of the core and cladding. In contrast, the graded index has a non-uniform core. The Index is highest at the center and gradually decreases until it matches with that of the cladding. There is no sharp break in indices between the core and the cladding.

By this classification there are three types of fibres :

(I) Multimode Step Index fibre (Step Index fibre)

(II) Multimode graded Index fibre (Graded Index fibre)

(III) Single- Mode Step Index fibre (Single Mode Fibre)

STEP-INDEX MULTIMODE FIBER 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. These alternative pathways cause the different groupings of light rays, referred to as modes, to arrive separately at a receiving point. The pulse, an aggregate of different modes, begins to spread out, losing its Well-defined shape. The need to leave spacing between pulses to prevent overlapping limits bandwidth that is, the amount of information that can be sent. Consequently, this type of fiber is best suited for transmission over short distances, in an endoscope, for instance.

Fig. 6 STEP-INDEX MULTIMODE FIBER

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GRADED-INDEX MULTIMODE FIBER 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.

Fig.7 GRADED-INDEX MULTIMODE FIBER

Also, rather than zigzagging off the cladding, light in the core curves helically because of the graded index, reducing its travel distance. The shortened path and the higher speed allow light at the periphery to arrive at a receiver at about the same time as the slow but straight rays in the core axis. The result: a digital pulse suffers less dispersion.

 

SINGLE-MODE FIBER 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.

Fig. 8 SINGLE-MODE FIBER

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OPTICAL FIBRE PARAMETERS

Optical fiber systems have the following parameters.

(I) Wavelength.

(II) Frequency.

(III) Window.

(IV) Attenuation.

(V) Dispersion.

(VI) Bandwidth.

WAVELENGTH

It is a characteristic of light that is emitted from the light source and is measures in nanometers (nm). In the visible spectrum, wavelength can be described as the colour of the light.

For example, Red Light has longer wavelength than Blue Light, Typical wavelength for fibre use are 850nm, 1300nm and 1550nm all of which are invisible.

FREQUENCY

It is number of pulse per second emitted from a light source. Frequency is measured in units of hertz (Hz). In terms of optical pulse 1Hz = 1 pulse/ sec.

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WINDOW A narrow window is defined as the range of wavelengths at which a fibre best

operates. Typical windows are given below :

WindowOperational Wavelength

800nm - 900nm 850nm

1250nm - 1350nm 1300nm

1500nm - 1600nm 1550nm

ATTENUATION

Attenuation is defined as the loss of optical power over a set distance, a fibre with lower attenuation will allow more power to reach a receiver than fibre with higher attenuation. Attenuation may be categorized as intrinsic or extrinsic.

INTRINSIC ATTENUATION

It is loss due to inherent or within the fibre. Intrinsic attenuation may occur as

(1) Absorption - Natural Impurities in the glass absorb light energy.

Fig. 9 Absorption of Light

(2) Scattering - Light Rays Travelling in the Core Reflect from small Imperfections into a New Pathway that may be Lost through the cladding.

LightRay

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LightRay

Light is lost

Fig. 10 Scattering

EXTRINSIC ATTENUATION

It is loss due to external sources. Extrinsic attenuation may occur as –

(I) Macrobending - The fibre is sharply bent so that the light travelling down the fibre cannot make the turn & is lost in the cladding.

Fig. 11 Micro and Macro bending

(II) Microbending - Microbending or small bends in the fibre caused by crushing contraction etc. These bends may not be visible with the naked eye.

Attenuation is measured in decibels (dB). A dB represents the comparison between the transmitted and received power in a system.

BANDWIDTH

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It is defined as the amount of information that a system can carry such that each pulse of light is distinguishable by the receiver.

System bandwidth is measured in MHz or GHz. In general, when we say that a system has bandwidth of 20 MHz, means that 20 million pulses of light per second will travel down the fibre and each will be distinguishable by the receiver.

NUMBERICAL APERTURE

Numerical aperture (NA) is the "light - gathering ability" of a fibre. Light injected into the fibre at angles greater than the critical angle will be propagated. The material NA relates to the refractive indices of the core and cladding.

NA = n12 - n2

2

Where n1 and n2 are refractive indices of core and cladding respectively.

NA is unitless dimension. We can also define as the angles at which rays will be propagated by the fibre. These angles form a cone called the acceptance cone, which gives the maximum angle of light acceptance. The acceptance cone is related to the NA

= arc sing (NA) or

NA = sin

where is the half angle of acceptance

The NA of a fibre is important because it gives an indication of how the fibre accepts and propagates light. A fibre with a large NA accepts light well, a fibre with a low NA requires highly directional light.

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In general, fibres with a high bandwidth have a lower NA. They thus allow fewer modes means less dispersion and hence greater bandwidth. A large NA promotes more modal dispersion, since more paths for the rays are provided NA, although it can be

defined for a single mode fibre, is essentially meaningless as a practical characteristic. NA in a multimode fibre is important to system performance and to calculate anticipated performance.

Fig. 12 Numerical Aperture of fiber

* Light Ray A : Did not Enter Acceptance Cone - Lost

* Light Ray B : Entered Acceptance Cone - Transmitted through the Core by Total Internal Reflection.

DISPERSION

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Dispersion is the spreading of light pulse as its travels down the length of an optical fibre as shown in figure 13. Dispersion limits the bandwidth or information carrying capacity of a fibre. The bit-rates must be low enough to ensure that pulses are farther apart and therefore the greater dispersion can be tolerated.

There are three main types of dispersion in a fibre -

(I) Modal Dispersion

(II) Material dispersion

(III) Waveguide dispersion

Fig. 13 Dispersion

BANDWIDTH AND DISPERSION: A bandwidth of 400 MHz -km means that a 400 MHz-signal can be transmitted for 1 km. It means that the product of frequency and the length must be 400 or less. We can send a lower frequency for a longer distance, i.e. 200 MHz for 2 km or 100 MHz for 4 km. Multimode fibres are specified by the bandwidth-length product or simply bandwidth.

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Single mode fibres on the other hand are specified by dispersion, expressed in ps/km/nm. In other words for any given single mode fibre dispersion is most affected by the source's spectral width. The wider the source spectral width, the greater the dispersion.

Conversion of dispersion to bandwidth can be approximated roughly by the following equation.

0.187

BW = --------------------------

(Disp) (SW) (L)

Disp = Dispersion at the operating wavelength in seconds/ nm/ km.

SW = Spectral width of the source in nm.

L = Fibre length in km.

So the spectral width of the source has a significant effect on the performance of a single mode fibre.

OPTICAL WINDOWS : Attenuation of fibre for optical power varies with the wavelengths of light. Windows are low-loss regions, where fiber carry light with little attenuation. The first generation of optical fibre operated in the first window around 820 to 850 nm. The second window is the zero-dispersion region of 1300 nm and the third window is the 1550 nm region as shown in figure 14.

Fig. 14 Optical Windows

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CABLE CONSTRUCTION

There are two basic cable designs are:

1. Tight Buffer Tube Cable

2. Loose Buffer Tube Cable

Loose-tube cable, used in the majority of outside-plant installations and tight-buffered cable, primarily used inside buildings.

Tight-Buffered CableWith tight-buffered cable designs, the buffering material is

in direct contact with the fiber. This design is suited for "jumper cables" which connect outside plant cables to terminal equipment, and also for linking various devices in a premises network. Single-fiber tight-buffered cables are used as pigtails, patch cords and jumpers to terminate loose-tube cables directly into opto-electronic transmitters, receivers and other active and passive components.

Multi-fiber tight-buffered cables also are available and are used primarily for alternative routing and handling flexibility and ease within buildings.The tight-buffered design provides a rugged cable structure to protect individual fibers during handling, routing and connectorization. Yarn strength members keep the tensile load away from the fiber.

Fig. 15 Tight Buffer Tube Cable

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Loose-Tube CableThe modular design of loose-tube cables typically holds 6,

12, 24, 48, 96 or even more than 400 fibers per cable. Loose-tube cables can be all-dielectric or optionally armored. The loose-tube design also helps in the identification and administration of fibers in the system.

In a loose-tube cable design, color-coded plastic buffer tubes house and protect optical fibers. A gel filling compound impedes water penetration. Excess fiber length (relative to buffer tube length) insulates fibers from stresses of installation and environmental loading. Buffer tubes are stranded around a dielectric or steel central member, which serves as an anti-buckling element.

The cable core, typically uses aramid yarn, as the primary tensile strength member. The outer polyethylene jacket is extruded over the core. If armoring is required, a corrugated steel tape is formed around a single jacketed cable with an additional jacket extruded over the armor.

Loose-tube cables typically are used for outside-plant installation in aerial, duct and direct-buried applications.

Here are some common fiber cables types are given below:

(1) Distribution Cable

Distribution Cable (compact building cable) packages individual 900µm buffered fiber reducing size and cost. The connectors may be installed directly on the 900µm buffered fiber at the breakout box location.

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Fig. 16 Distribution Cable

(2) Loose Tube Cable Loose tube cable is designed to endure outside temperatures

and high moisture conditions. The fibers are loosely packaged in gel filled buffer tubes to repel water. Recommended for use between buildings that are unprotected from outside elements. Loose tube cable is restricted from inside building use.

Fig.17 Loose Tube Cable

(3) Aerial Cable/Self-Supporting Aerial cable provides ease of installation and reduces time

and cost. Figure 8 cable can easily be separated between the fiber and the messenger. Temperature range (-55ºC to +85ºC)

Fig. 18 Aerial Cable/Self-Supporting

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(4) Hybrid & Composite Cable

Hybrid cables offer the same great benefits as our standard indoor/outdoor cables, with the convenience of installing multimode and single mode fibers all in one pull. Our composite cables offer optical fiber along with solid 14 gauge wires suitable for a variety of uses including power, grounding and other electronic controls

Fig. 19 Hybrid & Composite Cable

(5) 5.Armored Cable

Armored cable can be used for rodent protection in direct burial if required. This cable is non-gel filled and can also be used in aerial applications. The armor can be removed leaving the inner cable suitable for any indoor/outdoor use. (Temperature rating -40ºC to +85ºC)

Fig. 20 Armored Cable

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Fibre Optic Cables (Loose Buffer Tube) have the following parts in common ;

(I) Optical Fibre

(II) Buffer

(III) Strength member

(IV) Jacket

Component Function Material

BufferProtect fibre From

OutsideNylon, Mylar, Plastic

Central Member

Facilitate Stranding

Temperature Stability

Anti-Buckling

Steel, Fibreglass

Primary Strength Member

Tensile Strength Aramid Yarn, Steel

Cable Jacket

Contain and Protect

Cable Core

Abrasion Resistance

PE, PUR, PVC, Teflon

Cable Filling

Compound

Prevent Moisture

intrusion and Migration

Water Blocking

Compound

ArmoringRodent Protection

Crush ResistanceSteel Tape

Table-1 Cable Components

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OFC SPLICING

Splices are permanent connection between two fibres. The splicing involves cutting of the edges of the two fibres to be spliced.

Splicing Methods The following three types are widely used :

1. Adhesive bonding or Glue splicing.

2. Mechanical splicing.

3. Fusion splicing.

Adhesive Bonding or Glue Splicing This is the oldest splicing technique used in fibre splicing.

After fibre end preparation, it is axially aligned in a precision V–groove. Cylindrical rods or another kind of reference surfaces are used for alignment. During the alignment of fibre end, a small amount of adhesive or glue of same refractive index as the core material is set between and around the fibre ends. A two component epoxy or an UV curable adhesive is used as the bonding agent. The splice loss of this type of joint is same or less than fusion splices. But fusion splicing technique is more reliable, so at present this technique is very rarely used.

Mechanical Splicing This technique is mainly used for temporary splicing in

case of emergency repairing. This method is also convenient to connect measuring instruments to bare fibres for taking various measurements.

The mechanical splices consist of 4 basic components :

(i) An alignment surface for mating fibre ends.

(ii) A retainer

(iii) An index matching material.

(iv) A protective housing

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A very good mechanical splice for M.M. fibres can have an optical performance as good as fusion spliced fibre or glue spliced. But in case of single mode fibre, this type of splice cannot have stability of loss.

Fusion Splicing The fusion splicing technique is the most popular

technique used for achieving very low splice losses. The fusion can be achieved either through electrical arc or through gas flame.

The process involves cutting of the fibres and fixing them in micro–positioners on the fusion splicing machine. The fibres are then aligned either manually or automatically core aligning (in case of S.M. fibre) process. Afterwards the operation that takes place involve withdrawal of the fibres to a specified distance, preheating of the fibre ends through electric arc and bringing together of the fibre ends in a position and splicing through high temperature fusion.

If proper care taken and splicing is done strictly as per schedule, then the splicing loss can be minimized as low as 0.01 dB/joint. After fusion splicing, the splicing joint should be provided with a proper protector to have following protections:

(a) Mechanical protection

(b) Protection from moisture.

Sometimes the two types of protection are combined. Coating with Epoxy resins protects against moisture and also provides mechanical strength at the joint.

Now–a–days, the heat shrinkable tubes are most widely used, which are fixed on the joints by the fusion tools.

The fusion splicing technique is the most popular technique used for achieving very low splice losses. The introduction of single mode optical fibre for use in long haul network brought with it fibre construction and cable design different from those of multimode fibres.

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The splicing machines imported by BSNL begins to the core profile alignment system, the main functions of which are :

(1) Auto active alignment of the core.

(2) Auto arc fusion.

(3) Video display of the entire process.

(4) Indication of the estimated splice loss.

The two fibres ends to be spliced are cleaved and then clamped in accurately machined vee–grooves. When the optimum alignment is achieved, the fibres are fused under the microprocessor contorl, the machine then measures the radial and angular off–sets of the fibres and uses these figures to calculate a splice loss. The operation of the machine observes the alignment and fusion processes on a video screens showing horizontal and vertical projection of the fibres and then decides the quality of the splice.

The splice loss indicated by the splicing machine should not be taken as a final value as it is only an estimated loss and so after every splicing is over, the splice loss measurement is to be taken by an OTDR (Optical Time Domain Reflectometer). The manual part of the splicing is cleaning and cleaving the fibres. For cleaning the fibres, Dichlorine Methyl or Acetone or Alcohol is used to remove primary coating.

With the special fibre cleaver or cutter, the cleaned fibre is cut. The cut has to be so precise that it produces an end angle of less than 0.5 degree on a prepared fibre. If the cut is bad, the splicing loss will increase or machine will not accept for splicing. The shape of the cut can be monitored on the video screen, some of the defect noted while cleaving are listed below

(i) Broken ends.

(ii) Ripped ends.

(iii) Slanting cuts.

(iv) Unclean ends.

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INTRODUCTION

WCDMA (Wideband Code Division Multiple Access) Network is a Multi-Service “Network of Networks”

It provides traditional Telecom services & new Internet based services

It accommodates interconnections for varieties of networks-

Circuit-Switched & Packet Switched

Narrowband & Wideband

Voice & Data

Fixed & Mobile

WCDMA is a high bit rate Network

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3GPPREFERENCE MODEL

WCDMA is standardized by the Third Generation Partnership Project (3GPP).

WCDMA Network can be considered to consist of four major components-

User Equipments (UE)

Access Network (AN)

Core Network (CN)

Networks External to WCDMA

ERICSSON IMPLEMENTATION

Based on 3GPP standards, Vendors have designed, developed & implemented WCDMA Networks.

As a Vendor, Ericsson has its own way of realization of 3G Network covering both GSM & WCDMA Technologies.

Two major components of WCDMA Network are -

WCDMA Radio Access Network WCDMA/GSM Core Network

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WCDMA RADIO ACCESSNETWORKS

WCDMA Radio Access Network (RAN) consists of – RBS & RNC which together constitute RNS (Radio Network System).

RBS ( Radio Base Station )-

Also Known as Node B within 3GPP

RBS provides the physical Radio resources

Converts data flow between UE & RNC

RNC ( Radio Network Controller )-

RNC controls the RBS & the Radio Resources

RNC is the access point for getting into WCDMA Core Network

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WCDMA/GSM CORENETWORKS

The Core Network architecture is based on an evolved GSM Core Network and consists of the following Nodes-

1. MSC Server (Soft switch)

2. MSC(GSM)

3. Gateway MSC Server (GMSC Server)

4. Mobile Media Gateway (M-MGW)

5. Serving GPRS Support Node (SGSN)

6. Home Location Register (HLR)

7. Authentication Centre (AUC)

8. Equipment Identity Register (EIR)

9. Flexible Number Register (FNR)

10. IP Multimedia Sub-System (IMS)

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CORE NODES (Contd.)

MSC Server-

Handles control functions within Mobile Soft-switch environment

Plays major role in circuit-mode working

Works in conjunction with M-MGW

MSC (GSM)-

Its roles are within a classical MSC architecture

Roles are related to circuit-mode working

Gateway MSC Server-

Main function is related to routing of I/C calls to Mobile Subscribers

GMSC obtains routing information from Subscribers’ HLR

Mobile Media Gateway-

It works in conjunction with MSC Server

M-MGW connects Core Network with- Radio Access Network of WCDMA & GSM, PSTN, ISDN & other Mobile Networks.

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Serving GPRS Support Node-

-Main role lies in session and mobility management related to packet-switched network

SGSN is an interface between GGSN on one side and RNC/BSC on the other side

Gateway GPRS Support Node-

Activities are related to transfer of high speed data with external IP based data networks

Home Location Register-

Serves as the primary database of subscriber information

Provides information related to control and intelligence within GSM & WCDMA network

Authentication Centre-

Contains functions for secure storage of individual subscriber identifiers and keys.

Also includes algorithms necessary for generating Authentication & Ciphering data based subscriber keys.

Works as interface between SGSN & external data networks.

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Equipment Identity Register-

Validates Mobile Sub Equipment Identity

MSC may request to check if the Mobile Sub Equipment belongs to black list, grey list or white list

Flexible Number Register-

FNR offers Mobile Number Portability (MNP) Flexible allocation of MSISDN for GSM &

WCDMA networks.

IP Multimedia Sub-system-

Its roles are related to NGN applications like Multimedia Conferencing, Multiplayer Gaming etc.

WCDMA USER EQUIPMENTS

There are hardly any specific standards for classifying the User Equipments (UEs) for WCDMA. A general classification is-

Mobile Phones

Personal Digital Assistant (PDA)

Smart Phones

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Mobile Phones are much enhanced ones with wide ranges of features. PDAs are basically Mobile Computers. Smart Phones are aggregation of Mobile Phones and PDAs.

WCDMA USER EQUIPMENTS (Contd.)

WCDMA Mobile Phone has two broad units-

UICC (Universal Integrated Circuit Card)

ME (Mobile Equipment)

UICC is a smart Card that contains a module called USIM (Universal Subscriber Identity Module). USIM is the user dependent part of the UE and is provided by the Service provider.

ME is manufacturer dependent. ME has two components-

MT (Mobile Termination)

TE (Terminal Equipment)

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LAYER CONCEPT IN WCDMA

WCDMA architecture works in three layers-

1. Application Layer

2. Control Layer

3. Connectivity Layer

Application Layer-

Responsible for providing services to users via applications regardless of devices and methods in which the user accesses the network.

Control Layer-

Contains the nodes that control and direct traffic of both CS and PS networks.

Nodes in control layers are- MSCs, HLR/HSS (Home Location Register/Home Service Server), GMSC/TSC, SGW, IMS etc.

Connectivity Layer-

It is related to transport nodes that have role to connect Access Network

Nodes in this layer are M-MGW, SGSN & GGSN.

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