Page |1 Training ReportSSA level in-plant summer training in BSNL (TEZPUR) IITT COLLEGE OF ENGINEERING pOjEwaL (sbs NaGaR)Submitted to:HOD of IT Branch Submitted by: Dushmanta Nath Roll no: 81301113016
Page |2 Branch: IT (5 th SEM) INTRODUCTIONAll industries operate in a specific environment which keepschanging and the firms in the business need to understand it todynamically adjust their actions for best results. Like mindedfirms get together to form associations in order to protect theircommon interests. Other stake holders also develop a system totake care of their issues. Governments also need to intervene forensuring fair competition and the best value for money for itscitizens. This handouts gives exposure on the TelecomEnvironment in India and also dwells on the role of internationalbodies in standardizing and promoting Telecom Growth in theworld.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
Page |3 Job opportunities in telecom Market, government and statutory bodiesAssignment: Explore designated websites of institutions andcompaniesInstitutional Framework: It is defined as the systems offormal laws, regulations, and procedures, and informalconventions, customs, and norms, that broaden, mold, andrestrain socio-economic activity and behaviour. In India, TheIndian telegraph act of 1885 amended from time to time governsthe telecommunications sector. Under this act, the government isin-charge of policymaking and was responsible for provisioningof services till the opening of telecom sector to privateparticipation. The country has been divided into units calledCircles, Metro Districts, Secondary Switching Areas (SSA),Long Distance Charging Area (LDCA) and Short DistanceCharging Area (SDCA). Major changes in telecommunicationsin India began in the 1980s. The initial phase of telecom reformsbegan in 1984 with the creation of Center for Department ofTelematics (C-DOT) for developing indigenous technologiesand private manufacturing of customer premise equipment.Soon after, the Mahanagar Telephone Nigam Limited (MTNL)and Videsh Sanchar Nigam Limited (VSNL) were set up in1986. The Telecom Commission was established in 1989. Acrucial aspect of the institutional reform of the Indian telecomsector was setting up of an independent regulatory body in1997 – the Telecom Regulatory Authority of India (TRAI), toassure investors that the sector would be regulated in a balancedand fair manner. In 2000, DoT corporatized its services wingand created Bharat Sanchar Nigam Limited. Further changes inthe regulatory system took place with the TRAI Act of 2000that aimed at restoring functional clarity and improvingregulatory quality and a separate disputes settlement body wasset up called Telecom Disputes Settlement and AppellateTribunal (TDSAT) to fairly adjudicate any dispute between
Page |4licensor and licensee, between service provider, between serviceprovider and a group of consumers. In October 2003, UnifiedAccess Service Licenses regime for basic and cellular serviceswas introduced. This regime enabled services providers to offerfixed and mobile services under one license. Since then, Indiantelecom has seen unprecedented customer growth crossing 600million connections. India is the fourth largest telecom market inAsia after China, Japan and South Korea. The Indian telecomnetwork isthe eighth largest in the world and the second largest amongemerging economies. A brief ontelecom echo system and various key elements in institutionalframework is given below:Summer Training, Overview of Telecommunication Networks-II Page 2 of 12Compiled by MC Faculty ALTTC, GhaziabadDepartment of Telecommunications: In India, DoT is thenodal agency for taking care of telecom sector on behalf ofgovernment. Its basic functions are: Policy Formulation Review of performance Licensing Wireless spectrum management Administrative monitoring of PSUs Research & Development Standardization/Validation of Equipment International RelationsMain wings within DoT:
Page |5 Telecom Engineering Center (TEC) USO Fund Wireless Planning & Coordination Wing (WPC) Telecom Enforcement, Resource and Monitoring (TERM) Cell Telecom Centers of Excellence (TCOE)Public Sector Units Bharat Sanchar Nigam Limited(BSNL) Indian Telephone Industries Limited (ITI) Mahanagar Telephone Nigam Limited(MTNL) Telecommunications Consultants India Limited(TCIL)R & D Unit• Center for development of Telematics (C-DoT)The other key governmental institutional units are TRAI &TDSAT. Important units arebriefed below:Telecom Engineering Center (TEC): It is a technical bodyrepresenting the interest ofDepartment of Telecom, Governmentof India. Its main functions are: Specification of common standards with regard to Telecom network equipment, services and interoperability.
Page |6 Summer Training, Overview of Telecommunication Networks-II Page 3 of 12 Compiled by MC Faculty ALTTC, Ghaziabad Generic Requirements (GRs), Interface Requirements (IRs) Issuing Interface Approvals and Service Approvals Formulation of Standards and Fundamental Technical Plans Interact with multilateral agencies like APT, ETSI and ITU etc. for standardisation Develop expertise to imbibe the latest technologies and results of R&D Provide technical support to DOT and technical advice to TRAI & TDSAT Coordinate with C-DOT on the technological developments in the Telecom Sector for policy planning by DOT www.tec.gov.inUniversal Service Obligation Fund (USO): This fundwas created in 2002. This fund is managed by USOadministrator. All telecom operators contribute to this fund asper government policy. The objective of this fund is to bridgethe digital divide i.e. ensure equitable growth of telecomfacilities in rural areas. Funds are allocated to operators who bidlowest for providing telecom facilities in the areas identified byUSO administrator.
Page |7 WIRELESS PLANNING & COORDINATION (WPC)This unit was created in 1952 and is the National RadioRegulatory Authority responsible for Frequency SpectrumManagement, including licensing and caters for the needs of allwireless users (Government and Private) in the country. Itexercises the statutory functions of the Central Government andissues licenses to establish, maintain and operate wirelessstations. WPC is divided into major sections like Licensing andRegulation (LR), New Technology Group (NTG) and StandingAdvisory Committee on Radio Frequency Allocation (SACFA).SACFA makes the recommendations on major frequencyallocation issues, formulation of the frequency allocation plan,making recommendations on the various issues related toInternational Telecom Union (ITU), to sort out problemsreferred to the committee by various wireless users, Sitingclearance of all wireless installations in the country etc.Telecom Enforcement, Resource and Monitoring(TERM) Cell: In order to ensure that service providers adhereto the licence conditions and for taking care of telecom networksecurity issues, DoT opened these cells in 2004 and at present34 cells are operating in various Circles and big districts in thecountry. Key functions of these units are Inspection of premisesof Telecom and Internet Service Providers, Curbing illegalactivities in telecom services, Control over clandestine / illegaloperation of telecom networks by vested interests having nolicense, To file FIR against culprits, pursue the cases, issuenotices indicating violation of conditions of various Acts inforce from time to time, Analysis of call/subscription/traffic dataof various licensees, arrangement for lawful interception /monitoring of all communications passing through the licensee’snetwork, disaster management, network performancemonitoring, Registration of OSPs and Telemarketers in LicenseService Areas etc..
Page |8Telecom Centers of Excellence (TCOE): (www.tcoe.in)The growth of Indian Telecommunications sector has beenastounding, particularly in the last decade. This growthhas been catalysed by telecommunications sector liberalizationand reforms. Some of the areas needing immediate attention toconsolidate and maintain the growth are:• Capacity building for industry talent pool• Continuous adaptation of the regulatory environment tofacilitate induction/ adoptation of high potential newtechnologies and business models• Bridging of high rural - urban teledensity/digital divide• Faster deployment of broadband infrastructure across thecountry Summer Training, Overview of TelecommunicationNetworks-II Page 4 of 12 Compiled by MC Faculty ALTTC,Ghaziabad Centres of Excellence have been created to work on(i) enhancing talent pool, (ii) technological innovation, (iii)secure information infrastructure and (iv) bridging of digitaldivide.These COEs are also expected to cater to requirements of SouthAsia as regionaleaders. The main sponsor (one of the telecomoperators), the academic institute where the Centers are locatedand the tentative field of excellence are enumerated in the tablebelow: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 BSNLTelecom Policy, Regulation, Governance, Customer Care &Marketing IIM, Ahmadabad IDEA Cellular TelecomInfrastructure & Energy IIT, Chennai Reliance DisasterManagement of Info systems & Information Security IISc,Bangalore Aircel Rural Application IIT Mumbai Tata TelecomSpectrum Management (Proposed) WPC, Chennai Govt withIndustry consortium
Page |9Telecom Regulatory Authority of India (TRAI): TRAIwas established under TRAI Act1997 enacted on 28.03.1997. The act was amended in 2000. ItsOrganization setup consists ofOne Chairperson, Two full-time members & Two part-timemembers. Its primary role is todeals with regulatory aspects in Telecom Sector & Broadcastingand 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 Spectrum policies Opening of sectorTelecom Dispute Settlement Appellate Tribunal(TDSAT): TDSAT was established in year 2000 by anamendment in TRAI act by transferring the functions of disputehandling to new entity i.e. TDSAT. The organization setupconsists of one Chairperson & two full-time members. Itsfunctions are:• Adjudicate any dispute between licensor and licensee two or more licensees group of consumers
P a g e | 10• Hear & dispose off appeal against any direction, decision ororder of the Authority under TRAI Act www.tdsat.nic.inKey International Standardization Bodies forTelecom sector:ITU is the leading United Nations agency for information andcommunication technology issues, and the global focal pointfor governments and the private sector in developing networksand services. For nearly 145 years, ITU has coordinated theshared global use of the radio spectrum, promoted internationalcooperation in assigning satellite orbits, worked to improvetelecommunication infrastructure in the developing world,established the worldwide standards that foster seamlessinterconnection of a vast range of communications systems andaddressed the global challenges of our times, such as mitigatingclimate change and strengthening cyber security. Vast spectrumof its work area includes broadband Internet to latest-generationwireless technologies, from aeronautical and maritimenavigation to radio astronomy and satellite-based meteorology,from convergence in fixed-mobile phone, Internet access, data,voice and TV broadcasting to next-generation networks. ITUalso organizes worldwide and regional exhibitions and forums,such as ITU TELECOM WORLD, bringing together the mostinfluential representatives of government and thetelecommunications and ICT industry to exchange ideas,knowledge and technology for the benefit of the globalcommunity, and in particular the developing world. ITU is basedin Geneva, Switzerland, and its membership includes 191Member States and more than 700 Sector Members andAssociates. On 1 January 2009, ITU employed 702 people from83 different countries. The staff members are distributedbetween the Unions Headquarters in Geneva, Switzerland andeleven field offices located around the world.Asia Pacific Telecommunity: Headquartered at Bangkok,the APT is a unique organization of Governments, telecomservice providers, manufactures of communication equipment,
P a g e | 11research & development organizations and other stake holdersactive in the field of communication and informationtechnology. APT serves as the focal organization forcommunication and information technology in the Asia Pacificregion. The APT has 34 Members, 4 Associate Members and121 Affiliate Members. The objective of the Telecommunity isto foster the development of telecommunication services andinformation infrastructure throughout the region with aparticular focus on the expansion thereof in less developedareas. APT has been conducting HRD Programme fordeveloping the skills of APT Members to meet the objectives ofAPT. The topics include Information CommunicationTechnologies (ICT), Network and Information Security, Financeand Budget, Telecommunication Management, MobileCommunications, Multimedia, SatelliteCommunication, Telecommunications and ICT Policy andRegulation, Broadband Technologies, e-Applications, RuralTelecommunications Technologies, IP Networks and Services,Customer Relations, etc.The European Telecommunications Standards Institute(ETSI) produces globally applicable standards for Informationand Communications Tec hnologies(ICT), including fixed,mobile, radio, converged, broadcast and internet technologies. Itis officially recognized by the European Union as a EuropeanStandards Organization. ETSI is a not-for-profitorganizationwith more than 700 ETSI member organizations drawn from 62countries across 5 continents world-wide. ETSI unitesManufacturers, Network operators, National Administrations,Service providers, Research bodies, User groups, Consultancies.This cooperation has resulted in a steady stream of highlysuccessful ICT standards in mobile, fixed, and radiocommunications and a range of other standards that cross theseboundaries, including Security, Satellite, Broadcast, HumanFactors, Testing & Protocols, Intelligent transport, Power-linetelecoms, health, Smart Cards, Emergency communications,GRID & Clouds, Aeronautical etc. ETSI is consensus-based and
P a g e | 12conducts its work through summer Training, Overview ofTelecommunication Networks-II Page 6 of 12 Compiled by MCFaculty ALTTC, Ghaziabad Technical Committees, whichproduce standards and specifications, with the ETSI GeneralAssembly and Board.BSNL: Bharat Sanchar Nigam Limited was formed in year 2000and 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 themarket leader in Broadband, landline and national transmissionnetwork. BSNL is also the only operator covering over 5lakh village with telecom connectivity. Area of operation ofBSNL is all India except Delhi & Mumbai.MTNL: Mahanagar Telephone Nigam Limited, formed in 1984is the market leader in landline and broadband in its area ofoperation.TCIL: TCIL, a prime engineering and consultancy company, isa wholly owned Government of India Public Sector Enterprise.TCIL was set up in 1978 for providing Indian telecom expertisein all fields of telecom, Civil and IT to developing countriesaround the world. It has its presence in over 70 countries.ITI: Indian telephone Industries is the oldest manufacturing unitfor telephone instruments. To keep pace with changing times, ithas started taking up manufacturing of new technologyequipment such as GSM, OFC equipment, Invertors, Powerplants, 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 ofthis centre to Indian telecom sector is the development of lowcapacity (128 port) Rural automatic Exchange (RAX) whichenabled provisioning of telephone in even the smallest village.
P a g e | 13This was specially designed to suit Indian environment, capableof withstanding natural temperature and dusty conditions.Prominent Licenses provided by DoT:o Access Service (CMTS & Unified Access Service): TheCountry is divided into 23 Service Areas consisting of 19Telecom Circle Service Areas and 4 Metro Service Areasfor providing Cellular Mobile Telephone Service (CMTS).Consequent upon announcement of guidelines for UnifiedAccess (Basic& Cellular) Services licenses on 11.11.2003, someof the CMTS operators have been permitted to migrate fromCMTS License to Unified Access Service License (UASL). Nonew CMTS and Basic service licenses are being awarded afterissuing the guidelines for Unified access ServiceLicence(UASL). As on 31st March 2008, 39 CMTS and 240UASL licenses operated.o 3G & BWA (Broadband Wireless Access): Department ofTelecom started the auction process for sale of spectrum for 3Gand BWA (WiMax) in April 2010 for 22 services areas in thecountry. BSNL & MTNL have already been given spectrum for3G and BWA and they need to pay the highest bid amount asper auction results. BSNL & MTNL both are providing 3Gservices. BSNL has rolled out its BWA service by using WiMaxtechnology.o Mobile Number Portability (MNP) Service: Licenses havebeen awarded to two operators to provide MNP in India. DoT isensuring the readiness of all mobile operators and expects tostart this service any time after June 2010.o Infrastructure Provider: There are two categories IP-I andIP-II. For IP-I the applicant company is required to be registeredonly. No license is issued for IP-I. Companies registered as IP-Ican provide assets such as Dark Fibre, Right of Way, Duct spaceand Tower. This was opened to private sector with effect from13.08.2000. An IP-II license Summer Training, Overview ofTelecommunication Networks-II Page 7 of 12 Compiled by MC
P a g e | 14Faculty ALTTC, Ghaziabad can lease / rent out /sell end to endbandwidth i.e. digital transmission capacity capable to carry amessage. This was opened to private sector with effect from13.08.2000. Issuance of IP-II Licence has been discontinuedw.e.f. 14.12.05o INMARSAT : INMARSAT (International Maritime SatelliteOrganisation) operates constellation of geo-stationary satellitesdesigned to extend phone, fax and data communications all overthe world. Videsh Sanchar Nigam Ltd (VSNL) is permitted toprovide Inmarsat services in India under their International LongDistance(ILD) licence granted by Department ofTelecommunications(DoT). VSNL has commissioned their newLand Earth Station (LES) at Dighi, Pune compatible with 4thgeneration INMARSAT Satellites (I-4) and INMARSAT-B, M,Mini-M & M-4 services are now being provided through thisnew LES after No Objection Certificate (NOC) is issued by DoTon case by case basis.o National Long Distance: There is no limit on number ofoperators for this service and license is for 20 years.o International Long Distance: This was opened to privatesector on 1st April 2002 with no limit on number of operators.The license period is 20 years.o Resale of IPLC: For promoting competition and affordabilityin International PrivateLeased Circuits (IPLC) Segment, Government permitted the“Resale of IPLC” by introducing a new category of Licensecalled as – “Resale of IPLC” Service License with effect from24th September 2008. The Reseller can provide end-to-endIPLC between India and country of destination for any capacitydenomination. For providing the IPLC service, the Reseller hasto take the IPLC from International Long Distance (ILD)Service Providers licensed and permitted to enter into anarrangement for leased line with Access Providers, NationalLong Distance Service Providers and International LongDistance Service Providers for provision of IPLC to endcustomers.
P a g e | 15o Sale of International Roaming SIM cards /Global CallingCards in India: The cards being offered to Indian Customerswill be for use only outside India. However, if it is essential toactivate the card for making test calls/emergent calls before thedeparture of customer and /or after the arrival of the customer,the same shall be permitted for forty eight (48) hours only priorto 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 startingfrom 6.11.98 on non-exclusive basis. Three category of licenseexist 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 toPC/Telephone outside India, IP based calls from India to othercountries.o VPN: Internet Service Providers (ISPs) can provide VirtualPrivate Network (VPN) Services. VPN shall be configured asClosed User Group(CUG) only and shall carry only the trafficmeant for the internal use of CUG and no third party traffic shallbe carried o the VPN. VPN shall not have any connectivity withPSTN /ISDN / PLMN except when the VPN has been set upusing 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 ofCUG VSAT licenses : (i) Commercial CUG VSAT license and(ii) Captive CUG VSAT license. The commercial VSAT serviceprovider can offer the service on commercial basis to thesubscribers by setting up a number of Closed User Groups
P a g e | 16(CUGs) whereas in the captive VSAT service only one CUGcan be set up for the captive use of the licensee. The scope of theservice is to provide data connectivity between various sitesscattered within territorial boundary of India via INSATSatellite System using Very Small Aperture Terminals(VSATs). However, these sites should form part of a ClosedUser Group (CUG). PSTN connectivity is not permitted.o Radio Paging: The bids for the Radio Paging Service in 27cities were invited in 1992, the licenses were signed in 1994 andthe service was commissioned in 1995. There was a provisionfor a fixed license fee for first 3 years and review of the licensefee afterwards. The license was for 10 years and in 2004 Govtoffered a extended 10 years license with certain license feewaivers but with the wide spread use of mobile phones, thisservice has lost its utility.o PMRTS: Public Mobile Radio Trunking service allows citywide connectivity through wireless means. This service iswidely used by Radio Taxi operators and companies whoseworkforce is on the move and there is need to locate the presentposition of employee for best results. PSTN connectivity ispermitted.o INSAT MSS: INSAT Mobile Satellite System ReportingService (INSAT MSS Reporting Service) is a one way satellitebased messaging service available through INSAT. The basicnature of this service is to provide a reporting channel viasatellite to the group of people, who by virtue of their nature ofwork are operating from remote locations without any telecomfacilities and need to send short textual message or short dataoccasionally to a central station.o Voice Mail/ Audiotex/ UMS (Unified Messaging Service):Initially a seprate license was issued for these services. ForUnified Messaging Service, transport of Voice Mail Messages toother locations and subsequent retrieval by the subscriber must
P a g e | 17be on a nonreal time basis. For providing UMS under thelicence, in addition to the license for VoiceMail/Audiotex/UMS, the licensee must also have an ISP license.The ISP licence as well as Voice Mail/Audiotex/ UMS licenseshould 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 theseservices as Value Added Service (VAS) under their licenseconditions.o Telemarketing: Companies intending to operate asTelemarketer need to obtain this license from DoT.o Other Service Provider (including BPO): As per NewTelecom Policy (NTP) 1999, Other Service Providers (OSP),such as tele-banking, tele-medicine, tele-trading, ecommerce,Network Operation Centers and Vehicle Tracking Systems etcare allowed to operate by using infrastructure provided byvarious access providers for non-telecom services. INTRODUCTION A long distance or local telephone conversation betweentwo persons could be provided by using a pair of open wirelines or underground cable as early as early as mid of 19thcentury. However, due to fast industrial development andincreased telephone awareness, demand for trunk and local trafficwent on increasing at a rapid rate. To cater to the increaseddemand of traffic between two stations or between twosubscribers at the same station we resorted to the use of anincreased number of pairs on either the open wire alignment, or
P a g e | 18in underground cable. This could solve the problem for sometime only as there is a limit to the number of open wire pairs thatcan be installed on one alignment due to headwayconsideration and maintenance problems. Similarly increasingthe number of open wire pairs that can be installed on onealignment due to headway consideration and maintenanceproblems. Similarly increasing the number of pairs to theunderground cable is uneconomical and leads tomaintenance problems. It, therefore, became imperative to think of new technicalinnovations which could exploit the available bandwidth oftransmission media such as open wire lines or undergroundcables to provide more number of circuits on one pair. Thetechnique used to provide a number of circuits using a singletransmission link is called Multiplexing. MULTIPLEXING TECHNIQUES There are basically two types of multiplexing techniques I. Frequency Division Multiplexing (FDM) II. Time Division Multiplexing (TDM) Frequency Division Multiplexing Techniques (FDM) The FDM techniques are the process of translatingindividual speech circuits (300-3400 Hz) into pre-assignedfrequency slots within the bandwidth of the transmission
P a g e | 19medium. The frequency translation is done by amplitudemodulation of the audio frequency with an appropriate carrierfrequency. At the output of the modulator a filter network isconnected to select either a lower or an upper side band. Sincethe intelligence is carried in either side band, single side bandsuppressed carrier mode of AM is used. This results insubstantial saving of bandwidth mid also permits the use of lowpower amplifiers. Please refer Fig. 1. FDM techniques usually find their application in analoguetransmission systems. An analogue transmission system is onewhich is used for transmitting continuously varying signals. Fig. 1 FDM Principle Time Division Multiplexing Basically, time division multiplexing involves nothing morethan sharing a transmission medium by a number of circuits intime domain by establishing a sequence of time slots duringwhich individual channels (circuits) can be transmitted. Thus theentire bandwidth is periodically available to each channel.Normally all time slots1 are equal in length. Each channel isassigned a time slot with a specific common repetition periodcalled a frame interval. This is illustrated in Fig. 2.
P a g e | 20 Fig. 2 Time Division Multiplexing Each channel is sampled at a specified rate and transmittedfor a fixed duration. All channels are sampled one by, the cycle isrepeated again and again. The channels are connected toindividual gates which are opened one by one in a fixedsequence. At the receiving end also similar gates are opened inunison with the gates at the transmitting end. The signal received at the receiving end will be in the formof discrete samples and these are combined to reproduce theoriginal signal. Thus, at a given instant of time, only one channelis transmitted through the medium, and by sequential sampling anumber of channels can be staggered in time as opposed totransmitting all the channel at the same time as in EDMsystems. This staggering of channels in time sequence fortransmission over a common medium is called Time DivisionMultiplexing (TDM). Pulse Code Modulation It was only in 1938; Mr. A.M. Reaves (USA) developeda Pulse Code Modulation (PCM) system to transmit thespoken word in digital form. Since then digital speech
P a g e | 21transmission has become an alternative to the analoguesystems. PCM systems use TDM technique to provide a numberof circuits on the same transmission medium viz open wire orunderground 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 CodingFILTERING Filters are used to limit the speech signal to the frequency band 300-3400 Hz. SAMPLING It is the most basic requirement for TDM. Suppose wehave an analogue signal Fig. 3 (b), which is applied across aresistor R through a switch S as shown in Fig. 3 (a) . Wheneverswitch S is closed, an output appears across R. The rate at whichS is closed is called the sampling frequency because during themake periods of S, the samples of the analogue modulatingsignal appear across R. Fig. 3(d) is a stream of samples of theinput signal which appear across R. The amplitude of the sample
P a g e | 22is depend upon the amplitude of the input signal at the instant ofsampling. The duration of these sampled pulses is equal to theduration for which the switch S is closed. Minimum number ofsamples are to be sent for any band limited signal to get a goodapproximation of the original analogue signal and the same isdefined by the sampling Theorem. Fig. 3: Sampling Process Sampling Theorem A complex signal such as human speech has a widerange of frequency components with the amplitude of the signalbeing different at different frequencies. To put it in a differentway, a complex signal will have certain amplitudes for allfrequency components of which the signal is made. Let us saythat these frequency components occupy a certain bandwidth B.If a signal does not have any value beyond this bandwidth B,
P a g e | 23then it is said to be band limited. The extent of B is determinedby the highest frequency components of the signal. Sampling Theorem States "If a band limited signal is sampled at regular intervals oftime and at a rate equal to or more than twice the highest signalfrequency in the band, then the sample contains all theinformation of the original signal." Mathematically, if fH is thehighest frequency in the signal to be sampled then the samplingfrequency Fs needs to be greater than 2 fH.i.e. Fs>2fHLet 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 every125 microseconds and the resultant samples will represent theoriginal signal. But, if we are to sample N channels one by oneat the rate specified by the sampling theorem, then the timeavailable for sampling each channel would be equal to Ts/Nmicroseconds.
P a g e | 24 FIG. 4: Sampling and combining Channels Fig. 4 shows how a number of channels can be sampledand combined. The channel gates (a, b ... n) correspond to theswitch S in Fig. 3. These gates are opened by a series of pulsescalled "Clock pulses". These are called gates because, whenclosed these actually connect the channels to the transmissionmedium during the clock period and isolate them during the OFFperiods of the clock pulses. The clock pulses are staggered sothat only one pair of gates is open at any given instant and,therefore, only one channel is connected to the transmissionmedium. The time interval during which the commontransmission medium is allocated to a particular channel is calledthe Time Slot for that channel. The width of. this time slot willdepend, as stated above, upon the number of channels to becombined and the clock pulse frequency i.e. the samplingfrequency. In a 30 channel PCM system. TS i.e. 125 microseconds aredivided into 32 parts. That is 30 time slots are used for 30 speechsignals, one time slot for signaling of all the 30 chls, andone 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 is3.9 microseconds and time period of sampling i.e..the interval
P a g e | 25between 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 thecommon highway)of a TDM system will consist of a series of pulses, theamplitudes of which are proportional to the amplitudes of theindividual channels at their respective sampling instants. This isillustrated in Fig. 5 i Fig 5: PAM Output Signals The original signal for each channel can be recovered atthe receive end by applying gate pulses at appropriate instantsand passing the signals through low pass filters. (Refer Fig. 6). Fig. 6 : Reconstruction of Original Signal
P a g e | 26 Quantization In FDM systems we convey the speech signals in theiranalogue electrical form. But in PCM, we convey the speech indiscrete form. The sampler selects a number of points on theanalogue speech signal (by sampling process) and measures theirinstant values. The output of the sampler is a PAM signal asshown in Fig. 3; The transmission of PAM signal will requirelinear amplifiers at trans and receive ends to recover distortionless signals. This type of transmission is susceptible to all thedisadvantages of AM signal transmission. Therefore, in PCMsystems, PAM signals are converted into digital form by usingQuantization Principles. The discrete level of each sampledsignal is quantified with reference to a certain specified level onan amplitude scale. The process of measuring the numerical values of thesamples and giving them a table value in a suitable scale iscalled "Quantizing". Of course, the scales and the number ofpoints should be so chosen that the signal could be effectivelyreconstructed after demodulation. Quantizing, in other words, can be defined as a process ofbreaking down a continuous amplitude range into a finitenumber of amplitude values or steps. A sampled signal exists only at discrete times but itsamplitude is drawn from a continuous range of amplitudes of ananalogue signal. On this basis, an infinite number of amplitudevalues is possible. A suitable finite number of discrete valuescan be used to get an. approximation of the infinite set. Thediscrete value of a sample is measured by comparing it witha scale having a finite number of intervals and identifyingthe interval in which the sample falls. The finite number ofamplitude intervals is called the "quantizing interval". Thus,quantizing means to divide the analogue signals totalamplitude range into a number of quantizing intervals andassigning a level to each. intervals. For example, a 1 volt signal can be divided into 10mVranges like 10-20mV, 30-40mV and so on. The interval 10-20
P a g e | 27mV, may be designated as level 1, 20-30 mV as level 2 etc. Forthe purpose of transmission, these levels are given a binary code.This is called encoding. In practical systems-quantizing andencoding are combined processes. For the sake ofunderstanding, these are treated separately. Quantizing Process Suppose we have a signal as shown in Fig. 7 which issampled 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 orintervals as shown in Fig. 7. Sample (a) lies in the 5th range.Accordingly, the quantizing process will assign a binary codecorresponding to this i.e. 101, Similarly codes are assigned forother samples also. Here the quantizing intervals are of thesame size. This is called Linear Quantizing. FIG. 7: QUANTIZING-POSITIVE SIGNALAssigning an interval of 5 for sample 1, 7 for 2 etc. is thequantizing 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. Asshown in Fig.6, eight quantizing levels are used for eachdirection of the analogue signal. To indicate whether a
P a g e | 28sample is negative with reference to zero or is positive withreference zero, an extra digit is added to the binary code. Thisextra digit is called the "signbit".In Fig.8. Positive values havea sign bit of 1 and negative values have sign bit of0. FIG. 8: QUANTIZING - SIGNAL WITH + Ve & - Ve VALUESRelation 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 4bit code, then we can have 2" = 16 levels. Practical PCMsystems use an eight bit code with the first bit as sign bit. Itmeans we can have 2" = 256 (128 levels in the positivedirection and 128 levels in the negative direction) intervals forquantizing.
P a g e | 29 Quantization Distortion Practically in quantization we assign lower value of eachinterval to a sample falling in any particular interval and thisvalue is given as:Table-1: Illustration of Quantization Distortion Analogue Quantizing Quantizing Binary Code Signal Interval Level Amplitude (mid value) Range 0-10 mv 5 mv 0 1000 10-20mv 15mv 1 1001 20-30 mv 25 mv 2 1010 30-40 mv 35 mv 3 1011 40-50 mv 45 mv 4 1100 If a sample has an amplitude of say 23 mv or 28 mv, ineither case it will be assigned he eve "2". This Is representedin binary code 1010. When this is decoded at the receiving end,the decoder circuit on receiving a 1010 code will convert thisinto an analogue signal of amplitude 25 mv only. Thus theprocess of quantization leads to an approximation of the inputsignal with the detected signal having some deviations inamplitude from the actual values. This deviation between theamplitude of samples at the transmitter and receiving ends (i.e.the difference between the actual value & the reconstructedvalue) gives rise to quantization distortion. If V represent the step size and e represents thedifference in amplitude fe must exists between - V/2 & + V/2)between the actual signal level and its quantized equivalent thenit can be proved that mean square quantizing error is equal to
P a g e | 30(V2). Thus, we see that the error depends upon the size of thestep. In linear quantization, equal step means equal degree oferror for all input amplitudes. In other words, the signal to noiseratio for weaker signals will be poorer. To reduce error, we, therefore, need to reduce step size orin other words, increase th,e number of steps in the givenamplitude range. This would however, increase thetransmission bandwidth because bandwidth B = fm log L.where L is the number of quantum steps and fm is the highestsignal frequency. But as we knows from speech statistics thatthe probability of occurrence of a small amplitude is muchgreater than large one, it seems appropriate to provide morequantum levels (V = low value) in the small amplitude regionand only a few (V = high value) in the region of higheramplitudes. In this case, provided the total number of specifiedlevels remains unchanged, no increase in transmissionbandwidth will be required. This will also try to bring aboutuniformity 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 usingsegmented quantization (also called companding). This is shownin Fig. 9 (a). In fact, there is equal number of segments for bothpositive and negative excursions. In order to specify the locationof 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
P a g e | 31 Fig. 9 (a) Segmented coding curve As seen in Fig. 9 (b), the first two segment in eachpolarity are collinear, (i.e. the slope is the same in the centralregion) they are considered as one segment. Thus the totalnumber of segment appear to be 13. However, for purpose ofanalysis all the 16 segments will be taken into account. Encoding Conversion of quantized analogue levels to binary signalis called encoding. To represent 256 steps, 8 level code isrequired. The eight bit code is also called an eight bit "word".The 8 bit word appears in the formP ABC WXYZPolarity bit ‘1’ Segment Code Linear encodingfor + ve O for - ve. In thesegment
P a g e | 32 The first bit gives the sign of the voltage to be coded. Next3 bits gives the segment number. There are 8 segments for thepositive voltages and 8 for negative voltages. Last 4 bits givethe position in the segment. Each segment contains 16positions. Referring to Fig. 9(b), voltage Vc will be encoded as1 1 1 1 0101. FIG. 9 (b) : Encoding Curve with Compression 8 Bit Code The quantization and encoding are done by a circuit calledcoder. The coder converts PAM signals (i.e. after sampling)into an 8 bit binary signal. The coding is done as per Fig. 9which shows a relationship between voltage V to be coded andequivalent binary number N. The function N = f(v) is not linear.The curve has the following characteristics. It is symmetrical about the origins. Zero levelcorresponds to zero voltage to be encoded.It is logarithmic function approximated by 13 straight segmentsnumbered 0 to 7 in positive direction and O to 7 in thenegative direction. However 4 segments 0, 1, 0, 1 lying betweenlevels + vm/64 -vm/64 being collinear are taken as one segment.
P a g e | 33 The voltage to be encoded corresponding to 2 ends ofsuccessive 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 maximumvoltage). There are 128 quantification levels in the positive part ofthe curve and 128 in the negative part of the curve. In a PCMsystem the channels are sampled one by one by applying thesampling pulses to the sampling gates. Refer Fig. 10. The gatesopen only when a pulse is applied to them and pass the analoguesignals through them for the duration for which the gates remainopen. Since only one gate will be activated at a given instant, acommon encoding circuit is used for all channels. Here thesamples are quantized and encoded. The encoded samples of allthe channels and signals etc are combined in the digital combinerand transmitted. Fig. 10 The reverse process is carried out at the receiving end toretrieve the original analogue signals. The digital combinercombines the encoded samples in the form of "frames". Thedigital separator decombines the incoming digital streams into
P a g e | 34individual frames. These frames are decoded to give the PAM(Pulse Amplitude Modulated) samples. The samplescorresponding to individual channels are separated byoperating the receive sample gates in the same sequence i.e. insynchronism with the transmit sample gates. CONCEPT OF FRAME In Fig. 10, the sampling pulse has a repetition rate of Tssees and a pulse width of "St". When a sampling pulse arrives,the sampling gate remains opened during the time "St" andremains closed till the next pulse arrives. It means that a channelis activated for the duration "St". This duration, which is thewidth of the sampling pulse, is called the "time slot" for a givenchannel. Since Ts is much larger as compared to St. a number ofchannels can be sampled each for a duration of St within the timeTs. With reference to Fig. 10, the first sample of the first channelis taken by pulse a, encoded and is passed on the combiner.Then the first sample of the second channel is taken by pulse bwhich is also encoded and passed on to the combiner, likewise theremaining channels are also sampled sequentially and areencoded before being fed to the combiner. After the first sampleof the Nth channel is taken and processed, the second sample ofthe first channel is taken, this process is repeated for allchannels. One full set of samples for all channels taken withinthe duration Ts is called a "frame". Thus the set of all firstsamples of all channels is one frame; the set of all secondsamples 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 microsecondsTime slot per chl = 3.9 microseconds.
P a g e | 35 Structure of Frame A frame of 125 microsecond’s duration has 32 time slots.These slots are numbered Ts 0 to Ts 31. Information forproviding synchronization between Trans and receive ends ispassed through a separate time slot. Usually the slot Ts 0carries the synchronization signals. This slot is also calledFrame alignment word (FAW). The signaling information is transmitted through time slotTs 16. Ts 1 to Ts 15 are utilized for voltage signal ofchannels 1 to 15 respectively. Ts 17 to Ts 31 are utilized forvoltage signal of channels 16 to 30 respectively. SYNCHRONIZATION The output of a PCM terminal will be a continuous streamof bits. At the receiving end, the receiver has to receive theincoming stream of bits and discriminate between frames andseparate channels from these. That is, the receiver has torecognise the start of each frame correctly. This operation iscalled frame alignment or Synchronization and is achievedby inserting a fixed digital pattern called a "Frame AlignmentWord (FAW)" into the transmitted bit stream at regularintervals. The receiver looks for FAW and once it is detected,it knows that in next time slot, information for channel onewill be there and so on.The digits or bits of FAW occupy seven out of eight bits of Ts0 in the following pattern.Bit position of Ts 0 B1 B2 B3 B4 B5 B6B7 B8FAW digit value X 0 0 11 0 1 1
P a g e | 36The bit position B1 can be either 1 or 0. However, whenthe 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 fortransmitting supervisory and alarm signals. To distinguish theTs 0 of frame carrying supervisory/alarm signals from thosecarrying the FAW, the B2 bit position of the former are fixedat T. The FAW and alarm signals are transmitted alternativelyas shown in Table - 2. TABLE-2 Frame Remark Numbe B1 B B B B B B B8 rs 2 3 4 5 6 7 FO X 0 0 1 1 0 1 1 FAW F1 X 1 Y Y Y 1 1 1 ALAR M F2 X 0 0 1 1 0 1 1 FAW F3 etc X 1 Y Y Y 1 1 1 ALAR M In frames 1, 3, 5, etc, the bits B3, B4, B5 denotevarious types of alarms. For example, in B3 position, if Y = 1,it indicate Frame synchronization alarm. If Y = 1 in B4, itindicates high error density alarm. When there is no alarmcondition, bits B3 B4 B5 are set 0. An urgent alarm isindicated by transmitting "all ones". The code word for anurgent alarm would be of the form. X 111 1111
P a g e | 37 SIGNALLING IN PCM SYSTEMS In a telephone network,-the signaling information isused for proper routing of a call between two subscribers, forproviding certain status information like dial tone, busytone, ring back. NU tone, metering pulses, trunk offeringsignal etc. All these functions are grouped under the generalterms "signaling" in PCM systems. The signalinginformation can be transmitted in the form of DC pulses (as instep by step exchange) or multi-frequency pulses (as in crossbar systems) etc. The signaling pulses retain their amplitude for a muchlonger period than the pulses carrying speech information.It means that the signaling information is a slow varyingsignal in time compared to the speech signal which is fastchanging in the time domain. Therefore, a signaling channelcan be digitized with less number of bits than a voice channel.In a 30 chl PCM system, time slot Ts 16 in each frame isallocated for carrying signaling information. The time slot 16 of each frame carries thesignaling data corresponding to two VF channels only.Therefore, to cater for 30 channels, we must transmit 15frames, each having 125 microsecond’s duration. Forcarrying synchronization data for all frames, oneadditional frame is used. Thus a group of 16 frames (eachof 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, theencoded samples of all channels plus the signaling andsynchronization data. Each sample has eight bits of duration0.400 microseconds (3.9/8 = 0.488) each. The relationshipbetween the bit duration frame and multi-frame is illustrated inFig. 11 (a) & 11 (b).
P a g e | 38 Fig. 11 (a) Multi-frame Formation FIG. 11 (b) 2.048 Mb/s PCM Multi-frameWe have 32 time slots in a frame; each slot carries an 8 bit word.The total number of bits per frame = 32 x 8 = 256The total number of frames per seconds is 8000The total number of bits per second is 256 x 8000 = 2048 K/bits.Thus, a 30 channel PCM system has 2048 Kbits/sec.
P a g e | 39 DEFINITION AND DESCRIPTION OF DIGITAL HIERARCHIESINTRODUCTION AND DEFINITION The term “digital hierarchy” has been created whendeveloping digital transmission systems. It was laid down whenby multiplexing a certain number of PCM primary multiplexerswere combined to form digital multiplexers of higher order (e.g.second-order multiplex equipments). Consequently, a digital hierarchy comprises a number oflevels. Each level is assigned a specific bit rate which is formedby multiplexing digital signals, each having the bit rate of thenext lower level. In CCITT Rec. G.702, the term “digitalmultiplex hierarchy” is defined as follows : “A series of digital multiplexes graded according tocapability so that multiplexing at one level combines a definednumber of digital signals, each having the digit rate prescribedfor the next lower order, into a digital signal having a prescribeddigit rate which is then available for further combination withother digital signals of the same rate in a digital multiplex of thenext 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
P a g e | 40 practice, equipment as specified in C.C.I.T.T. Recommendation G.732 and 733, they do not only differ completely in their bit rates, but also in the frame structures, in signaling, frame alignment, etc. Needless to say that, as a consequence, the higher order digital multiplexers derived from the two different PCM primary multiplexers and thus the digital hierarchies differ as well.3) Since these two PCM primary multiplexers are available, two digital hierarchies only would have to be expected. In reality, however, two digital hierarchies with several variants are under discussion because the choice of the fundamental parameters of a digital hierarchy depends not only on the PCM primary multiplex, which forms the basic arrangement in that hierarchy, but on many other factors such as : (a) The bit rate of the principal signal sources. (b) Traffic demand, network topology, operational features, flexibility of the network. (c) Time division and multiplexing plant requirements. (d) Compatibility with analog equipment. (e) Characteristics of the transmission media to be used at the bit rates for the various levels of the hierarchies. Since today these factors which are essential for forming digital hierarchies vary from country to country, it is no wonder that we now have to consider more than two proposals for digital hierarchies.
P a g e | 41 DIGITAL HIERARCHIES BASED ON THE 1544 KBIT/S PCM PRIMARY MULTIPLEX EQUIPMENT It was around 1968 that Bell labs. proposed a digitalhierarchy based on the 24-channel PCM primary multiplex atthe various levels of the hierarchy : Level in hierarchy Bit rate Trans. line First level 1544 kbit/s T1 Second level 6312 kbit/s T2 Third level 46304 kbit/s L5 (Jumbo Grp) Fourth level 280000 kbit/s WT4 (Wave guide) Fifth level 568000 kbit/s T5 This proposal was modified during the following years. Atthe end of the study period 1968/72, the following digitalnetwork hierarchy was finally proposed as given in Fig.1. Fig. 1 Encoded FDM (Master Group) USA & Canada 1) For the various bit rates at the higher levels of the two proposals, different reasons have been indicated. The bit rate of 44736 kbit/s was selected to provide a flexibility point for circuit interconnection and because it was a
P a g e | 42 suitable coding level for the 600 channel FDM mastergroup.2) It is also an appropriate bit rate for inter-connection to radio-relay links planned for use at various frequencies.3) At the same time, N.T.T. published its PCM hierarchy are concerned (1554 and 6112 kbit/s, respectively), these two proposals are identical. They differ, however, in the higher levels as shown in Fig.2. Fig. 2 Encoded TDM (Japanese)4) In the N.T.T. proposal the bit rate of 32064 kbit/s at the third level of the proposed hierarchy might be considered a suitable bit rate to be used on international satellite links perhaps for administrations operating different PCM primary multiplex equipments. It is also a convenient bit rate for encoding the standardized 300- channel FDM master group. Delta modulation and differential PCM for 4 MHz visual telephone are also suitable for this bit rate. Transmission of 32064 kbit/s via a special symmetrical cable of new design is also possible.5) The above fact shows that the differing bit rates of the third level indicated in the two hierarchy proposals can, therefore, be justified by technical arguments. As far as the differing bit rates of the fourth level are concerned, only a few technical reasons are included in the two proposal. In both cases coaxial cables are used as a
P a g e | 43 transmission medium so that the medium does not call for different bit rates.6) Moreover, it seems that at present the specifications of the fourth level (and higher ones) in the two proposed hierarchies is not yet considered so urgent. For the time being the third level seems to be more important.7) The C.C.I.T.T. faced with this situation has reached finally the solution which is covered by CCITT recommendation G.752 as one can see from this recommendation, two different hierarchical levels are existing in the third level of this hierarchy, namely 32064 kbits/s and 44736 kbit/s respectively. Higher level have not been specified so far.DIGITAL HIERARCHY BASED ON THE 2048 KBIT/S PCM PRIMARY MULTIPLEX EQUIPMENT For this digital hierarchy, two specifications have at present been laid down only for the first level at 2048 kbit/ s and for the second level at 8448 kbit/s. As for the higher levels, the situation is just contrary to that existing in the case of digital hierarchies derived from 1544 kbit/s primary multiplex, i.e. general agreement has more or less been reached on the fourth level having a bit rate of 139264 kbit/s. 5th order system where bit rate of 565 Mb/s have also been planned now.1) The critical point in this hierarchy is whether or not the third level at 34368 kbit/s should exist.2) 4.2 The C.C.I.T.T. has agreed after long discussions on the following (Recommendation G.751) “that there should be a 4th order bit rate of 139264 kbit/s in the digital hierarchy which is based on the 2nd order bit rate of 8448 kbit/s”.
P a g e | 44 There should be two methods of achieving the 4th order bitrate : Method 1 by using a 3rd order bit rate of 34368 kbit/s in the digital hierarchy. Method 2 by directly multiplexing sixteen digital signals at 8448 kbit/s. The digital signals at the bit rate of 139264 kbit/s obtained by these two methods should be identical. The existence of the above two methods implies that the use of the bit rate of 34368 kbit/s should not be imposed on an Administration that does not wish to realize the corresponding equipment. 3) In accordance with the above two methods the following realizations of digital multiplex equipments using positive justification are recommended : Method 1 : Realization by separate digital multiplex equipments : one type which operates at 34368 kbit/s and multiplexes four digital signals at 8448 kbit/s; the other type which operates at 139264 kbit/s and multiplexes four digital signals at 34368 kbit/s. Method 2 : Realization by a single digital multiplex equipment which operates at 139264 kbit/s and multiplexes sixteen digital signals at 8448 kbit/s. Method 1 has been put into practice. 4) Where the fifth level is concerned, some preliminary proposals (e.g. 565148 kbit/s) have been submitted which were not discussed in detail. Therefore, the present structure of this digital hierarchy is 139.264as given in Fig.3.
P a g e | 45 Fig. 3 Encoded TDM (European) SIGNALLING IN TELECOMMUNICATIONS The term signaling, when used in telephony,refers to the exchange of control information associated withthe establishment of a telephone call on a telecommunicationscircuit. An example of this control information is the digitsdialed by the caller, the callers billing number, and other call-related information. When the signaling is performed on the same circuit thatwill ultimately carry the conversation of the call, it is termedChannel Associated Signaling (CAS). This is the case for earlieranalogue trunks, MF and R2 digital trunks, and DSS1/DASSPBX trunks. In contrast, SS7 signaling is termed Common ChannelSignaling (CCS) in that the path and facility used by thesignaling is separate and distinct from the telecommunicationschannels that will ultimately carry the telephone conversation.With CCS, it becomes possible to exchange signaling withoutfirst seizing a facility, leading to significant savings andperformance increases in both signaling and facility usage.Channel Associated SignalingChannel Associated Signaling (CAS), also known as per-trunksignaling (PTS), is a form of digital communication signaling.As with most telecommunication signaling methods, it usesrouting information to direct the payload of voice or data to itsdestination. With CAS signaling, this routing information isencoded and transmitted in the same channel as the payloaditself. This information can be transmitted in the same band (in-band signaling) or a separate band (out-of-band signaling) to thepayload.
P a g e | 46CAS potentially results in lower available bandwidth for thepayload. For example, in the PSTN the use of out-of-bandsignalling within a fixed bandwidth reduces a 64 kbit/s DS0 to56 kbit/s. Because of this, and the inherent security benefits ofseparating the control lines from the payload, most currenttelephone systems rely more on Common Channel Signaling(CCS).Common Channel SignalingIn telephony, Common Channel Signaling (CCS) is thetransmission of signaling information (control information) on aseparate channel from the data, and, more specifically, wherethat 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 thesole purpose of carrying signaling for establishment and Teardown of telephone calls. The remaining channels are usedentirely for the transmission of voice data. In most cases, asingle 64kbit/s channel is sufficient to handle the call setup andcall 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 channeldedicated to it.CCS offers the following advantages over CAS, in the contextof 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.
P a g e | 47 • CCS allows the transfer of additional information along with the signaling traffic providing features such as caller ID.The most common CCS signaling methods in use today areIntegrated Services Digital Network (ISDN) and SignalingSystem 7 (SS7).ISDN signaling is used primarily on trunks connecting end-userprivate branch exchange (PBX) systems to a central office. SS7is primarily used within the PSTN. The two signaling methodsare very similar since they share a common heritage and in somecases, the same signaling messages are transmitted in both ISDNand SS7.CCS is distinct from in-band or out-of-band signaling, which areto the data band what CCS and CAS are to the channel.Signaling System Number #7SS7 is a set of telephony signaling protocols which are used toset up most of the worlds public switched telephone networktelephone calls. The main purpose is to set up and tear downtelephone calls. Other uses include number translation, prepaidbilling mechanisms, short message service (SMS), and a varietyof other mass market services.It is usually abbreviated as Signaling System No. 7, SignalingSystem #7, or just SS7. In North America it is often referred to asCCSS7, an acronym for Common Channel Signaling System 7.In some European countries, specifically the United Kingdom, itis sometimes called C7 (CCITT number 7) and is also known asnumber 7 and CCIS7.There is only one international SS7 protocol defined by ITU-Tin its Q.700-series recommendations. There are however, manynational variants of the SS7 protocols. Most national variants arebased on two widely deployed national variants as standardizedby ANSI and ETSI, which are in turn based on the international
P a g e | 48protocol defined by ITU-T. Each national variant has its ownunique characteristics. Some national variants with ratherstriking characteristics are the China (PRC) and Japan (TTC)national variants.SS7 is designed to operate in two modes: Associated Mode andQuasi-Associated Mode. When operating in the Associated Mode, SS7 signalingprogresses from switch to switch through the PSTN followingthe same path as the associated facilities that carry the telephonecall. This mode is more economical for small networks. TheAssociated Mode of signaling is not the predominant choice ofmodes in North America. When operating in the Quasi-Associated Mode, SS7signaling progresses from the originating switch to theterminating switch, following a path through a separate SS7signaling network composed of STPs. This mode is moreeconomical for large networks with lightly loaded signalinglinks. The Quasi-Associated Mode of signaling is thepredominant choice of modes in North America.SS7 clearly splits the signaling planes and voice circuits. AnSS7 network has to be made up of SS7-capable equipment fromend to end in order to provide its full functionality. The networkis made up of several link types (A, B, C, D, E, and F) and threesignaling nodes - Service switching point (SSPs), signal transferpoint (STPs), and Service Control Point (SCPs). Each node isidentified on the network by a number, a point code. Extendedservices are provided by a database interface at the SCP levelusing the SS7 network.The links between nodes are full-duplex 56, 64, 1,536, or 1,984kbit/s graded communications channels. In Europe they areusually 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) orall (1,536 kbit/s) timeslots (DS0As or DS0s) within a T1facility. One or more signaling links can be connected to the
P a g e | 49same two endpoints that together form a signaling link set.Signaling links are added to link sets to increase the signalingcapacity of the link set.In Europe, SS7 links normally are directly connected betweenswitching exchanges using F-links. This direct connection iscalled associated signaling. In North America, SS7 links arenormally indirectly connected between switching exchangesusing an intervening network of STPs. This indirect connectionis called quasi-associated signaling. Quasi-associated signalingreduces the number of SS7 links necessary to interconnect allswitching 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) arecalled High Speed Links (HSL) in contrast to the low speed (56and 64 kbit/s) links. High Speed Links (HSL) are specified inITU-T Recommendation Q.703 for the 1.5 Mbit/s and 2.0 Mbit/srates, and ANSI Standard T1.111.3 for the 1.536 Mbit/s rate.There are differences between the specifications for the 1.5Mbit/s rate. High Speed Links utilize the entire bandwidth of aT1 (1.536 Mbit/s) or E1 (1.984 Mbit/s) transmission facility forthe transport of SS7 signaling messages.
P a g e | 50 INTRODUCTION With the evolution of computer networking and packetswitching concept a new era of integrated communication hasemerged in the telecom world. Rapid growth of datacommunication market and popularity of Internet, reflect theneeds of enhanced infrastructure to optimize the demand oftraffic. Integration of telecom and computer networkingtechnology trend has further amplified the importance oftelecommunications in the field of informationcommunication. It becomes a tool for the conveyance ofinformation, and thus can be critical to the developmentprocess. Telecommunications has become one of the mostimportant infrastructures that are very essential to the socio-economic well being of any nation. As the Internet marketcontinues to explode, demand for greater bandwidth andfaster connection speeds have led to several technologicalapproaches developed to provide broadband access to allconsumers. The demand for high-speed bandwidth is growingat a fast pace, driven mostly by growth in data volumes as theInternet and related networks become more central to
P a g e | 51 business operations. The rapid growth of distributed business applications, e-commerce, and bandwidth-intensive applications (such as multimedia, videoconferencing, and video on demand) generate the demand for bandwidth and access network.A concept of broadband services and the means of accesstechnologies to bridge the customer and service provider isemerged out throughout the world. "Broadband" refers to high-speed Internet access. Broadband Solutions represent theconvergence of multiple independent networks including voice,video and data into a single, unified, broadband network.
P a g e | 52 DEFINITION OF BROADBANDBroadband is the nonspecific term for high-speed digital Internetaccess. To state the obvious, ‘broadband’ indicates a means ofconnectivity at a high or ‘broad’ bandwidth. There are thevarious 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.
P a g e | 53In fact there is no specific International Definition for BroadbandIn India, Department of Telecommunications has issued aBroadband 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 supportinteractive services including Internet access and has thecapability of the minimum download speed of 256 kilo bits persecond (kbps) to an individual subscriber from the Point OfPresence (POP) of the service provider intending to provideBroadband service where multiple such individual Broadbandconnections are aggregated and the subscriber is able to accessthese interactive services including the Internet through thisPOP. The interactive services will exclude any services forwhich a separate license is specifically required, for example,real-time voice transmission, except to the extent that it ispresently 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
P a g e | 54 Broadband technology will allow for high-speed transmission of voice, video, and data over networks like the Internet IMPLEMENTATION OF BROADBANDTo 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.
P a g e | 55 NEED OF BROADBANDThe concept of socio economy has an important role in the fieldof communication of data, audio, video, speech or any otherkind of application. It is an era of CAPEX and OPEX. Serviceproviders and customers both are interested in economy withfastest tool of communication with more throughput. Traditionalcircuit switching network are not supporting the effective fastcommunication for new applications. This has emerged out withthe evolution of packet switching network. Communication ofdata for various applications is feasible to carry with differentthroughput.The service provider converged voice and data networkpromises to be implemented as nodes in a neighborhood orremote switches in regional locations.The Internet, e-mail, web sites, software downloads, filetransfers: they are all now part of the fabric of doing business.But until now, it has not been possible for businesses to fullytake advantage of the benefits that technology can truly deliver.The reason for this is a simple one - a lack of bandwidth. Evenfor small businesses, narrowband dial-up access is no longersufficient. It simply takes too long to do basic tasks, like
P a g e | 56downloading a large file, and is increasingly being recognized asinsufficient and inconvenient.Kim Maxwell in his book-"Residential Broadband: An InsidersGuide to the Battle for the Last Mile" has grouped potentialresidential broadband applications into three general categories:"professional activities” (activities related to usersemployment), "entertainment activities” (from game playing tomovie watching), and "consumer activities “(all other non-employment and non-entertainment activities).as follows: Professional Activities: Telecommuting (access to corporate networks and systems to support working at home on a regular basis) Video conferencing (one-to-one or multi-person video telephone calls) Home-based business (including web serving, e-commerce with customers, and other financial functions) Home office (access to corporate networks and e-mail to supplement work at a primary office location)
P a g e | 57Entertainment Activities: Web surfing (as today, but at higher speeds with more video content) Video-on-demand (movies and rerun or delayed television shows) Video games (interactive multi-player games)Consumer Activities: Shopping (as today, but at higher speeds with more video content) Telemedicine (including remote doctor visits and remote medical analyses by medical specialists) Distance learning (including live and pre-recorded educational presentations) Public services (including voting and electronic town hall meetings) Information gathering (using the Web for non- entertainment purposes) Photography (editing, distributing, and displaying of digital photographs) Video conferencing among friends and family
P a g e | 58These applications have different bandwidth requirements, andsome of them are still out of reach today. For example, all of the"professional" activities will likely be supported with less than1.0 Mbps of bandwidth. Similarly, web surfing and homeshopping will be supported with less than 1.0 Mbps ofbandwidth.Movies and video, however, demand more bandwidth. Featurelength movies can probably be delivered with 1.5 Mbps ofbandwidth, but broadcast quality video will probably requiremore— perhaps as much as 6.0 Mbps. Moreover, if highdefinition television ("HDTV") is widely accepted as a newbroadcast standard, that quality of video would require almost20.0 Mbps of bandwidth — much higher than the currentbroadband technologies will support. Thus, although thetechnology is moving toward flexible, high-quality video-on-demand, the necessary speed is probably still more than a fewyears away from becoming a reality.The Internet is poised to spin off thousands of specializedbroadband services. The access network needs to provide theplatform for delivery of these services. Following are thevarious applications or services, which are very popular insociety and needs broadband connectivity: -Virtual NetworksThe private virtual networks (LAN/WAN) can be used in anample variety of multimedia services, like bank accounts andcentral offices.Education by distanceEducation will not have any limits to reach from source todestination. Along with the traditional school a concept ofremote leaning center is emerged out and popular for various
P a g e | 59courses. There is no limit of distance, area or location in suchdistance learning. The student situated in the remote station canintervene directly to his class with a double system viavideoconference, whilst this happens, simultaneously, the file exchangeTeleworkOrganization firm workers that incorporate communicationsystems via satellite, can work remotely connecting directly totheir head offices Internet by a high speed connection thatpermits users to work efficiently and comfortable.TelemedicineDoctors situated in different clinics can stay in contact andconsult 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 ruralzone can have the opinion of specialists situated in remotehospitals quickly and efficiently.Electronic commerceElectronic commerce is a system that permits users to pay goodsand services by Internet. Thanks to this service, any personconnected to the network can ad quire such services withindependence from the place that he is situated and during the24 hours, simply using a portable computer.
P a g e | 60 TECHNOLOGY OPTIONS FOR BROADBAND SERVICESCommunication of data with different throughput is feasible byfollowing technologies: - Narrow Band 2.4 kbps – 128kbps Broadband 256kbps – 8000kbps LAN 1000kbps – 100Mbps / Giga Ethernet Various Access Technologies are used for the delivery of broadband services. Broadband communications technology can be divided broadly in to following categories: - Wire line Technology Wireless TechnologiesService providers according to available technology and accessprovide the broadband services to customers. The accesstechnologies that are adopted by the services providers aremainly Optical Fiber Technologies, DSL on copper loop, CableTV Network, Satellite Media, cellular and fixed wireless,Terrestrial Wireless etc.Technology options for broadband services may be classifiedaccording 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
P a g e | 61Wireless Technologies include Satellite Media Terrestrial Wireless 3G Mobile Wi-Fi (Wireless Fidelity) WiMax LMDS and MMDS FSO (Free Space Optics) BROADBAND NETWORKThe broadband services reached to customer from the threeproviders. Basically these are Service Provider, NetworkProvider and Access Provider. The role of Network Provider isto provide the services offered to customer through the accessextended by Access Provider. There are various types ofnetworks which are capable of transmitting and managing thebroadband traffic to desired nodes or locations.Wire line access technology through DSL, Fiber, and Cable etcare generally adopts: • IP based Network • ATM NetworkWireless access technology through Wi-Fi, Wi-Max. 3G mobileetc provides wireless access to ingress point of any core networkany migrates to Internet world.
P a g e | 62BROADBAND TECHNOLOGIES USED IN ASIAN COUNTRIESBroadband technologies go through two stages of developmentin Asian countries. In the early stage, sharp technologicaldivisions exist among players due to regulatory constraints.There are various mode of access used by service providers inthis field. Following was the beginning scenario in variouscountries like Hong Kong, Malaysia, Indonesia, India andSingapore: - • 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 areshaped by geography and infrastructure. The broadband startedestablishing and due to a progressive regulatory framework ithas matured in the market. In the countries like Korea andPhilippines service providers employ several technologies forthe broadband in their networks. DSL and cable modems are used where the PSTN and CATV are in place.
P a g e | 63 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, ISDNbecomes relatively less important. Established telephonecompanies are calculating the economics of converting the LastMile of existing networks to all-digital systems. Hong Kong andSingapore citizens already have broadband access, such asmovies on demand, through their local telecom network. Cable-TV operators, too, are venturing into high-speed Internet accessthrough modified networks and end-user "cable modems."Advances in wireless communications means that people startssurfing the net with cell phones at speeds comparable to orgreater than current home access.
P a g e | 64 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.
P a g e | 65Benefits 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)
P a g e | 66Fig 1. Connection of CPE at Sub Office
P a g e | 67Fig 2. Connection of Parallel telephones to Broadband line
P a g e | 68 Broadband deployment Core Router GigE Broadband RAS GigE GigE Tier 1 switchTier 2Switch GigE 240 Port DSLAM ADSL terminals CUSTOMER Fig 3. Broadband Network Connectivity Diagram
P a g e | 69 ADSL DEPLOYMENTHome/Office Central Office ADSL (Exchange) Data switch(Internet) CPE ADSL up to 4Km DSLAM Copper Splitter Voice Switch(PSTN) TYPICAL NETWORK CONFIGURATION PS T N ER MDF TIER 2 FD DSLAM F FE Fiber Connectivity MDF Copper Pair ER – Equipment RoomFrom Subscriber
P a g e | 70 TYPE I MODEM MT 882LED INDICATIONS FOR TYPE I MODEM
P a g e | 71 TYPE II MODEM WA1003ALED INDICATIONS FOR TYPE II MODEM
P a g e | 72 TYPE III/IV MODEM MT841LED INDICATIONS FOR TYPE III/IV MODEM
P a g e | 73 TROUBLE SHOOTING GUIDELINES Failure Instructions Power light 1. Ensure power adapter is well connected;1 is out. 2. Ensure the right power adapter is used. 1. Ensure the ADSL line is well connected; 2. Ensure the telephone line before entering the house is valid, try to test with a telephone; 3. Check that there is no junction box before ADSL LINK2 connecting the Modem, which has such light is out. components like capacitors or diodes that could hinder back high frequency signals. 4. Ensure the Modem and telephones are connected in the right way. 1. Ensure you use the right cables from the Modem to your PC. 2. Ensure the connection is secured. 3. Check if the NIC LED lights up. LAN LINK 4. Ensure your Network Adapter works normally3 light is out. by examining whether the item of “Networking Adapters” is labelled with ! or ?. If it is, you may delete it and then click “Refresh” to reinstall. Otherwise, you may try the NIC in another slot. As a last resort, you have to replace the NIC. 1. Ensure that USB cable connection is secure. 2. Ensure that the proper driver is installed in the PC. 3. Ensure that the modem is correctly installed USB LINK is with proper driver and ‘the device is working4 out properly’ message is available is device manager. 4. Ensure that USB port in the PC is working properly; otherwise connect the modem to another port.