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Alttc report Alttc report Document Transcript

  • ALTTC TRAINING REPORT On TELECOMMUNICATION NETWORK AND TECHNOLOGY Submitted By AMBRISH KUMAR SHUKLA (1002931012) (ELECTRONICS AND COMMUNICATION ENGINEERING) Krishna Institute of Engineering & Technology Ghaziabad – Meerut Highway (NH – 58) Ghaziabad Uttar Pradesh, INDIA September-2013
  • Acknowledgement “It is not possible to prepare a training report without the assistance & encouragement of other people. This one is certainly no exception.” On the very outset of this report, I would like to extend my sincere and heartfelt obligation towards all the personages who have helped me in this endeavor. Without their active guidance, help, cooperation and encouragement, I would not have made head way in the report. First and foremost, I would like to express my sincere gratitude to my training guide, Pratibha Gupta. I was privileged to experience a sustained enthusiastic and involved interest from her side. This fuelled my enthusiasm even further and encouraged me to boldly step into what was a totally dark and unexplored expanse before me.She always fuelled my thoughts to think broad and out of the box. I would also like to thank all employee of ALTTC for organizing and permitting the Vocational training program for us. Thanking you Ambrish Kumar Shukla
  • Objectives and Scope of Training The objective of training is to fetch the information about various technical areas concerning Telecommunication fundamental, Digital communication, Broadband, GSM, CDMA, Wi-MAX, Wi-Fi, Satellite Communication, Microwave communication, Digital Switching, Advance Optical Network, Radio Communication and Mobile Communication. The training made me learn about the transmitting and receiving the signal and finally establishing communication path. The practical use of electronics as well as communication can be understood with this training.
  • TABLE OF CONTENTS: (1) About ALTTC (2) Broadband (3) Wi-MAX (4) Power Line Communication (PLC) (5) Free Space Optics (FSO) (6) GSM (7) CDMA
  • ABOUT ALTTC Advanced Level Telecom Training Centre (ALTTC), Ghaziabad is the apex training institute of BSNL.ALTTC was set up as a joint venture of International Telecommunication Union, Geneva, UNDP and the Government of India in 1975. ALTTC functions on the frontiers of telecom technology, finance and management and imparts training to the leaders in the business. The strength of ALTTC lies in the state of art labs, massive infrastructure and trained, talented and qualified human resource pool. The Centre's Mission statement is: "To Deliver Excellence Through Training" The training areas cover vast spectrum of topics such as Digital Switching and IN; Mobile Communication: GSM, 3G, CDMA; Data communication and Information Technology: MPLS, VPN, Broadband, IPv6, Database Administration, Server administartion, IT Security; Optical Networks: SDH, DWDM, NGSDH, NGN, Access Networks, Management, Telecom Finance, Building Science (Civil and Electrical) and Telecom Network Planning.
  • ORGANIZATIONAL STRUCTURE
  • BROADBAND INTRODUCTION: The term BROADBAND refers to high speed internet access. It is non-specific term. In fact there is no specific international definition for broadband. As the Internet market continues to grow, demand for greater BW and faster connection speed have led to broadband access to all consumer. The rapid growth of distributed business application, e-commerce and BW intensive application (such as multimedia, video conferencing and video-ondemand generate the demand for BW and access network. NEED OF BROADBAND PROFESSIONAL ACTIVITIES:1. Telecommuting 2. Video conferencing 3. Home based business 4. Home office ENTERTAINMENT ACTIVITIES:1. Web surfing 2. Video on-demand 3. Video games CONSUMER ACTIVITIES:1. Telemedicine 2. Distance learning 3. Information gathering 4. Photography
  • 5. Video conferencing among friends and family Definition: In India DoT has issued a broadband policy in 2004, keeping in mind, Broadband connectivity is defined as“A data connection which has capability of minimum download speed of 256 kbps is said to be broadband.” In 2012 new NTP was announced and Broadband speed was revised to 2 mbps in place of 256 kbps. Practically obtained speed is 56 kbps. Types of Broadband Services: WIRED: WIRELESS: DSL 3G/4G Cable MODEM Wi-Fi OFC WIMAX PLC FSO DIGITAL SUBSCRIBER LINE (DSL) DSL is a family of technology that provides high speed Internet access by transmitting digital data over the wires of a local telephone network. DSL service is delivered simultaneously with wired telephone service on the same telephone line. DSL uses higher frequency band for data transmission. The bit rate of consumer DSL service typically ranges from 256 kbps-40mbps in downstream direction depending on DSL technology used, line condition and service level implementation.
  • WHY USE DSL? Traditional MODEM can provide data rate up to 56 kbps, to achieve high speed internet access another techniques named DSL was used. Sampling rate of telephone company =8000 samples /sec. Each sample is represented by 8 bits. One bit is used for control purpose. Hence each sample is effectively represented by 7 bits. Data rate =8000*7=56000 bits/sec i.e 56 kbps . WHERE DSL IS USED DSL service is used on a local telephone line. As telephone line is twisted pair cable capable of handling BW upto 1.1 MHz. But voice utilizes only 4 KHz BW. So to enhance the efficiency of cable pair , a portion of large BW is utilized for data communication.
  • TYPES OF DSL SERVICE: 1. SDSL- Symmetric Digital Subscriber Line 2. ADSL- Asymmetric Digital Subscriber Line 3. HDSL- High Bit Rate Digital Subscriber Line 4. VDSL- Very High Bit Rate Digital Subscriber Line Symmetric DSL (SDSL) UPLOAD SPEED = DOWNLOAD SPEED Upstream= 768 kbps Downstream= 768 kbps Ex. - Suitable for residential subscriber who need equal speed in both direction
  • HDSL AND VDSL HDSL Downstream = 1.544 - 2 Mbps Upstream = 1.544 – 2 Mbps VDSL Downstream = Upstream = 22 – 55 Mbps 3.2 Mbps Downstream = Upstream = 34 Mbps (If Symmetric) Asymmetrical DSL (ADSL) 1. ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses. 2. Downstream data rate is greater than upstream data rate. 3. Downstream = 1.5 – 8 Mbps Upstream = 16 – 640 Kbps
  • MODULATION TECHNIQUE FOR ADSL The modulation technique that is used for ADSL is Discrete Multi-tone Modulation (DMT). It combines FDM and QAM. In DMT an available BW of 1.104 MHz is divided into 256 parallel stream. Each parallel stream is known as sub channel or tone or bin or bucket. Each channel uses a BW of 4.312 KHz and can carry maximum 15 bits. Voice – Channel 0 Upstream = Channel 6 to 30 (25 channels) Downstream = Channel 31 to 255 (255 channels)
  • DMT FREQUENCY SPECTRUM DSLAM Digital Subscriber line Access Multiplexer Definition: A DSLAM is a Network Device, usually placed at a Telephone Company Central Office, That Receives Signals from multiple customer of DSL Connections and puts the signals on a high-speed backbone line using Multiplexing Techniques. DSLAM enables a phone company to offer business or home users the fastest Phone Line Technology (DSL) with the fastest backbone Network Technology.
  • WI-MAX WiMAX is a standards-based technology enabling the delivery of last mile wireless broadband access as an alternative to wired broadband like cable and DSL. Wi-MAX provides fixed, nomadic, portable and, soon, mobile wireless broadband connectivity without the need for direct line-of-sight with a base station. In a typical cell radius deployment of three to ten kilometers, Wi-MAX Forum Certified systems can be expected to deliver capacity of up to 40 Mbps per channel, for fixed and portable access applications. This is enough bandwidth to simultaneously support hundreds of businesses with T-1 speed connectivity and thousands of residences with DSL speed connectivity. Mobile network deployments are expected to provide up to 15 Mbps of capacity within a typical cell radius deployment of up to three kilometers. It is expected that WiMAX technology will be incorporated in notebook computers and PDAs by 2007, allowing for urban areas and cities to become "metro zones" for portable outdoor broadband wireless access. USES: The bandwidth and range of Wi-MAX make it suitable for the following potential applications: • Connecting Wi-Fi hotspots with other parts of the house hold. • Providing a wireless alternative to cable and DSL for "last mile” broadband access. • Providing data and telecommunications services. • Providing a source of Internet connectivity as part of a business continuity plan. That is, if a business has a fixed and a wireless Internet connection, especially from unrelated providers, they are unlikely to be affected by the same service.
  • Standards Associated With Wimax Wireless Standards IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks. More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. (By contrast, in cell-based networks data is transmitted in short, uniformly sized units called cells. Isochronous networks, where data is transmitted as a steady stream of octets, or groups of octets, at regular time intervals, are also out of the scope of this standard.) The number 802 was simply the next free number IEEE could assign, though “802” is sometimes associated with the date the first meeting was held — February 1980. IEEE 802.16 : The IEEE 802.16 Working Group on Broadband Wireless Access Standards, which was established by IEEE Standards Board in 1999, aims to prepare formal specifications for the global deployment of broadband Wireless Metropolitan Area Networks. The Workgroup is a unit of the IEEE 802 LAN/MAN Standards Committee. A related future technology Mobile Broadband Wireless Access (MBWA) is under development in IEEE 802.20. Although the 802.16 family of standards is officially called Wireless MAN, it has been dubbed “Wi-MAX” (from "Worldwide Interoperability for Microwave
  • Access") by an industry group called the Wi-MAX Forum. The mission of the Forum is to promote and certify compatibility and interoperability of broadband wireless products. In January 2003, the IEEE approved 802.16a as an amendment to IEEE 802.162001, defining (Near) Line-Of- Sight capability. • In July 2004, IEEE 802.16REVd, now published under the name IEEE 802.16-2004,introduces support for indoor CPE (NLOS) through additional radio capabilities such as antenna beam forming and OFDM sub-channeling. • Early 2005, an IEEE 802.16e variant will introduce support for mobility. Possible services provided by Wi-MAX are widespread over various data communication services including entertainment, information and commerce services. The first round of Wi-MAX technology is expected to be nomadic, meaning that CPEs will be portable, but not truly mobile. But with Samsung’s new developments on hand-over, the technology may become truly mobile, offering the 20 Mb/s to 30 Mb/s at speeds up to 120 km/h Wi-MAX enthusiasts are touting. For entertainment services, Wi-MAX will provide high quality VoD/MoD/AoD, real- time streaming broadcasting, 3G network games and MMS. Web Browsing, file downloading and interactive information services will be provided as information services by Wi-MAX.
  • Power line communication (PLC) Power line communication (PLC) carries data on a conductor that is also used simultaneously for AC electric power transmission or electric power distribution to consumers. It is also known as power line carrier, power line digital subscriber line (PDSL), mains communication, power line telecommunications, or power line networking (PLN). A wide range of power line communication technologies are needed for different applications, ranging from home automation to Internet access which is often called broadband over power lines (BPL). Most PLC technologies limit themselves to one type of wires (such as premises wiring within a single building), but some can cross between two levels (for example, both the distribution network and premises wiring). Typically transformers prevent propagating the signal, which requires multiple technologies to form very large networks. Various data rates and frequencies are used in different situations. A number of difficult technical problems are common between wireless and power line communication, notably those of spread spectrum radio signals operating in a crowded environment. Radio interference, for example, has long been a concern of amateur radio groups.
  • FREE SPACE OPTICS (FSO) Free-space optical communication (FSO) is an optical communication technology that uses light propagating in free space to transmit data for telecommunications or computer networking. "Free space" means air, outer space, vacuum, or something similar. This contrasts with using solids such as optical fiber cable or an optical transmission line. The technology is useful where the physical connections are impractical due to high costs.
  • OPTICAL COMMUNICATION SYSTEM Fundamentals of Optical Fiber Systems:
  • Light plays a vital role in our daily lives. It is used in compact disc (CD) players, in which a laser reflecting off a CD transforms the returning signal into music. It is used in grocery store checkout lines, where laser beams read bar codes for prices. It is used by laser printers to record images on paper. It is used in digital cameras that capture our world and allow pictures to be displayed on the Internet. It is the basis of the technology that allows computers and telephones to be connected to one another over fiber-optic cables. And light is used in medicine, to produce images used in hospitals and in lasers that perform eye surgery. BASIC FIBER OPTIC COMMUNICATION SYSTEM Fiber optics is a medium for carrying information from one point to another in the form of light. Unlike the copper form of transmission, fiber optics is not electrical in nature. A basic fiber optic system consists of a transmitting device that converts an electrical signal into a light signal, an optical fiber cable that carries the light, and a receiver that accepts the light signal and converts it back into an electrical signal. The complexity of a fiber optic system can range from very simple (i.e., local area network) to extremely sophisticated and expensive (i.e., long- distance telephone or cable television trunking). For example, the system shown in Figure 1 could be built very inexpensively using a visible LED, plastic fiber, a silicon photo-detector, and some simple electronic circuitry. On the other hand, a typical system used for long-distance, highbandwidth telecommunication could cost tens or even hundreds of thousands of dollars.
  • Basic fiber optic communication system The basic question is, "How much information is to be sent and how far does it have to go?" With this in mind we will examine the various components that make up a fiber optic communication system and the considerations that must be taken into account in the design of such systems.
  • Figure : Typical Fiber Optic Cable Advantage of Optical Fiber Communication: Enormous potential bandwidth: The optical carrier frequency has a far greater potential transmission BW than metallic cable systems. Small size and weight: Optical fiber has small diameters. Hence, even when such fibers are covered with protective coating they are far smaller and lighter than corresponding copper cables.
  • Electrical Isolation: Optical fibers which are fabricated from glass or sometimes a plastic polymer are electrical insulators and unlike their metallic counterpart, they do not exhibit earth loop or interface problems. This property makes optical fiber transmission ideally suited for communication in electrically hazardous environments as fiber created no arcing or spark hazard at abrasion or short circuits. Signal security: The light from optical fiber does not radiate significantly and therefore they provide a high degree of signal security. This feature is attractive for military, banking and general data transmission i.e. computer networks application. Low transmission loss: The technological developments in optical fiber over last twenty years has resulted in optical cables which exhibits very low attenuation or transmission loss in comparison with best copper conductors. Potential low cost: The glass which provides the optical fiber transmission medium is made from sand. So, in comparison to copper conductors, optical fiber offers the potential for low cost line communication. Disadvantage of Optical Fiber Communication: 1. It requires a higher initial cost in installation 2. Although the fiber cost is low, the connector and interfacing between the fiber optic costs a lot. 3. Fiber optic requires specialized and sophisticated tools for maintenance and repairing.
  • Basic Law of Optics Total Internal Reflection: Optical fibers work on the principle of total internal reflection The angle of refraction at the interface between two media is governed by Snell’s law: Refraction & Total Internal Reflection •
  • Acceptance Angle: Multimode optical fiber will only propagate light that enters the fiber within a certain cone, known as the acceptance cone of the fiber. The half-angle of this cone is called the acceptance angle, θmax , Numerical Aperture : Numerical Aperture is the measurement of the acceptance angle of an optical fiber, which is the maximum angle at which the core of the fiber will take in light that will be contained within the core. Taken from the fiber core axis (center of core), the measurement is the square root of the squared refractive index of the core minus the squared refractive index of the cladding. The numerical aperture of the fiber is closely related to the critical angle and is often used in the specification for optical fiber and the components that work with it The numerical aperture is given by the formula:
  • Types of Optical Fiber Optical fibers come in two main types. Single-mode fiber has a small core that forces the light waves to stay in the same path, or mode. This keeps the light signals going farther before they need to be beefed up, or amplified. Most longdistance, or long-haul, fiber optic telephone lines use single-mode fiber. The second type, called multimode fiber, has a much larger core than singlemode fiber. This gives light waves more room to bounce around inside as they travel down the path. The extra movement eventually causes the pulses to smear, and lose information. That means multimode fiber signals can’t travel as far before they need to be cleaned up and re- amplified. Multimode fibers can carry only a third or less the Information carrying capacity—or bandwidth—than single-mode fiber and they won't work for long distances. Network engineers prefer multimode fiber for shorter-distance communication, such as in an office building or a local area network (LAN), because the technology is less expensive. However, with the growing demand for more bandwidth between computers and over the Internet, single-mode fiber is becoming more popular for smaller networks, too. Therefore, we can categorize the fiber optic communication in two categories: 1. Step Index a) Single Mode b) Multimode 2. Graded Index
  • Step Index: These types of fibers have sharp boundaries between the core and cladding, with clearly defined indices of refraction. The entire core uses single index of refraction. Single Mode: Single mode fiber has a core diameter of 8 to 9 Step Index microns, which only allows one light path or mode. Multimode Step-Index Fiber: Multimode fiber has a core diameter of 50 or 62.5 microns (sometimes even larger). It allows several light paths or modes . This causes modal dispersion – some modes take longer to pass through the fiber than others because they travel a longer distance Multimode Graded-Index Fiber Graded-index refers to the fact that the refractive index of the core gradually decreases farther from the center of the core. The increased refraction in the center of the core slows the speed of some light rays, allowing all the light rays to reach the receiving end at approximately the same time, reducing dispersion.
  • The light rays no longer follow straight lines; they follow a serpentine path being gradually bent back toward the center by the continuously declining refractive index. This reduces the arrival time disparity because all modes arrive at about the same time. The modes traveling in a straight line are in a higher refractive index, so they travel slower than the serpentine modes. These travel farther but move faster in the lower refractive index of the outer core region. Attenuation Attenuation and pulse dispersion represent the two most important characteristics of an optical fiber that determine the information-carrying capacity of a fiber optic communication system. The decrease in signal strength along a fiber optic waveguide caused by absorption and scattering is known as attenuation. Attenuation is usually expressed in dB/km.
  • Dispersion Dispersion, expressed in terms of the symbol ∆t, is defined as pulse spreading in an optical fiber. As a pulse of light propagates through a fiber, elements such as numerical aperture, core diameter, refractive index profile, wavelength, and laser line width cause the pulse to broaden. This poses a limitation on the overall bandwidth of the fiber .
  • Figure Pulse broadening caused by dispersion
  • GSM GSM (Global System for Mobile Communications, originally Groupe Spécial Mobile), is a standard set developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones. It became the de facto global standard for mobile communications with over 80% market share. The GSM standard was developed as a replacement for first generation (1G) analog cellular networks, and originally described a digital, circuit-switched network optimized for full duplex voice telephony. This was expanded over time to include data communications, first by circuit-switched transport, then packet data transport via GPRS (General Packet Radio Services) and EDGE (Enhanced Data rates for GSM Evolution or EGPRS). Further improvements were made when the 3GPP developed third generation (3G) UMTS standards followed by fourth generation (4G) LTE Advanced standards. "GSM" is a trademark owned by the GSM Association. It may also refer to the initially most common voice codec used, Full Rate
  • NETWORK STRUCTURE The network is structured into a number of discrete sections: • Base Station Subsystem – the base stations and their controllers. Network and Switching Subsystem – the part of the network most similar to a fixed network, sometimes just called the "core network" • GPRS Core Network – the optional part which allows packet-based Internet connections. • • Operations support system (OSS) – network maintenance Base Station Subsystem GSM is a cellular network, which means that cell phones connect to it by searching for cells in the immediate vicinity. There are five different cell sizes in a GSM network—macro, micro, pico, femto, and umbrella cells. The coverage area of each cell varies according to the implementation environment. Macro cells can be regarded as cells where the base station antenna is installed on a mast or a building above average rooftop level. Micro cells are cells whose antenna height is under average rooftop level; they are typically used in urban areas. Pico cells are small cells whose coverage diameter is a few dozen metres; they are mainly used indoors. Fem to cells are cells designed for use in residential or small business environments and connect to the service provider’s network via a broadband internet connection. Umbrella cells are used to cover shadowed regions of smaller cells and fill in gaps in coverage between those cells. Cell horizontal radius varies depending on antenna height, antenna gain, and propagation conditions from a couple of hundred metres to several tens of kilometres. The longest distance the GSM specification supports in practical use
  • is 35 kilometres (22 mi). There are also several implementations of the concept of an extended cell, where the cell radius could be double or even more, depending on the antenna system, the type of terrain, and the timing advance. Indoor coverage is also supported by GSM and may be achieved by using an indoor pico cell base station, or an indoor repeater with distributed indoor antennas fed through power splitters, to deliver the radio signals from an antenna outdoors to the separate indoor distributed antenna system. These are typically deployed when significant call capacity is needed indoors, like in shopping centres or airports. However, this is not a prerequisite, since indoor coverage is also provided by in-building penetration of the radio signals from any nearby cell. GSM carrier frequency GSM networks operate in a number of different carrier frequency ranges (separated into GSM frequency ranges for 2G and UMTS frequency bands for 3G), with most 2G GSM networks operating in the 900 MHz or 1800 MHz bands. Where these bands were already allocated, the 850 MHz and 1900 MHz bands were used instead (for example in Canada and the United States). In rare cases the 400 and 450 MHz frequency bands are assigned in some countries because they were previously used for first-generation systems. Most 3G networks in Europe operate in the 2100 MHz frequency band. For more information on worldwide GSM frequency usage, see GSM frequency bands. Regardless of the frequency selected by an operator, it is divided into timeslots for individual phones. This allows eight full-rate or sixteen halfrate speech channels per radio frequency. These eight radio timeslots (or burst periods) are grouped into a TDMA frame. Half-rate channels use alternate frames in the same timeslot. The channel data rate for all 8 channels is 270.833 kb it/s, and the frame duration is 4.615 msec. The transmission power in the handset is limited to a maximum of 2 watts in GSM 850/900 and 1 watt in GSM 1800/1900. Voice codecs GSM has used a variety of voice codecs to squeeze 3.1 kHz audio into between 6.5 and 13 kbit/s. Originally, two codecs, named after the types of data channel they were allocated, were used, called Half Rate (6.5 kbit/s) and Full Rate (13 kbit/s). These used a system based on linear predictive coding (LPC). In addition to being efficient with bitrates, these codecs also made it easier to identify more important parts of the audio, allowing the air interface layer to prioritize and better protect these parts of the signal.
  • As GSM was further enhanced in 1997 with the Enhanced Full Rate (EFR) codec, a 12.2 kb it/s codec that uses a full-rate channel. Finally, with the development of UMTS, EFR was refactored into a variable-rate codec called AMR-Narrowband, which is high quality and robust against interference when used on full-rate channels, or less robust but still relatively high quality when used in good radio conditions on half-rate channels. Subscriber Identity Module (SIM) One of the key features of GSM is the Subscriber Identity Module, commonly known as a SIM card. The SIM is a detachable smart card containing the user's subscription information and phone book. This allows the user to retain his or her information after switching handsets. Alternatively, the user can also change operators while retaining the handset simply by changing the SIM. Some operators will block this by allowing the phone to use only a single SIM, or only a SIM issued by them; this practice is known as SIM locking Phone locking Sometimes mobile network operators restrict handsets that they sell for use with their own network. This is called locking and is implemented by a software feature of the phone. A subscriber may usually contact the provider to remove the lock for a fee, utilize private services to remove the lock, or use software and websites to unlock the handset themselves. In some countries (e.g., Bangladesh, Brazil, Chile, Hong Kong, India, Lebanon, Malaysia, Nepal, Pakistan, Singapore) all phones are sold unlocked. In others (e.g., Singapore) it is unlawful for operators to offer any form of subsidy on a phone's price. The Switching System The switching system (SS) is responsible for performing call processing and subscriber-related functions. The switching system includes the following functional units: • Home location register (HLR)—The HLR is a database used for storage and management of subscriptions. The HLR is considered the most important database, as it stores permanent data about subscribers, including a subscriber's service profile, location information, and activity status. When an individual
  • buys a subscription from one of the PCS operators, he or she is registered in the HLR of that operator. • Mobile services switching centre (MSC)—The MSC performs the telephony switching functions of the system. It controls calls to and from other telephone and data systems. It also performs such functions as toll ticketing, network interfacing, common channel signaling, and others. • Visitor location register (VLR)—The VLR is a database that contains temporary information about subscribers that is needed by the MSC in order to service visiting subscribers. The VLR is always integrated with the MSC. When a mobile station roams into a new MSC area, the VLR connected to that MSC will request data about the mobile station from the HLR. Later, if the mobile station makes a call, the VLR will have the information needed for call setup without having to interrogate the HLR each time. • Authentication centre (AUC)—A unit called the AUC provides authentication and encryption parameters that verify the user's identity and ensure the confidentiality of each call. The AUC protects network operators from different types of fraud found in today's cellular world. • Equipment identity register (EIR)—The EIR is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. The AUC and EIR are implemented as stand-alone nodes or as a combined AUC/EIR node. The Base Station System (BSS) All radio-related functions are performed in the BSS, which consists of base station controllers (BSCs) and the base transceiver stations (BTSs). BSC—The BSC provides all the control functions and physical links between the MSC and BTS. It is a high-capacity switch that provides functions such as handover, cell configuration data, and control of radio frequency (RF) power levels in base transceiver stations. A number of BSCs are served by an MSC. BTS—The BTS handles the radio interface to the mobile station. The BTS is the radio equipment (transceivers and antennas) needed to service each cell in the network. A group of BTSs are controlled by a BSC.
  • The Operation and Support System The operations and maintenance centre (OMC) is connected to all equipment in the switching system and to the BSC. The implementation of OMC is called the operation and support system (OSS). The OSS is the functional entity from which the network operator monitors and controls the system. The purpose of OSS is to offer the customer cost-effective support for centralized, regional, and local operational and maintenance activities that are required for a GSM network. An important function of OSS is to provide a network overview and support the maintenance activities of different operation and maintenance organizations. Additional Functional Elements Message centre (MXE)—The MXE is a node that provides integrated voice, fax, and data messaging. Specifically, the MXE handles short message service, cell broadcast, voice mail, fax mail, email, and notification. Mobile service node (MSN)—The MSN is the node that handles the mobile intelligent network (IN) services. Gateway mobile services switching centre (GMSC)—A gateway is a node used to interconnect two networks. The gateway is often implemented in an MSC. The MSC is then referred to as the GMSC. GSM interworking unit (GIWU)—The GIWU consists of both Hard ware and software that provides an interface to various networks for data communications. Through the GIWU, users can alternate between speech and data during the same call. The GIWU hardware equipment is physically located at the MSC/VLR. GSM Network Areas The GSM network is made up of geographic areas. As shown in Figure 3, these areas include cells, location areas (LAs), MSC/VLR service areas, and public land mobile network (PLMN) areas.
  • The cell is the area given radio coverage by one base transceiver station. The GSM network identifies each cell via the cell global identity (CGI) number assigned to each cell. The location area is a group of cells. It is the area in which the subscriber is paged. Each LA is served by one or more base station controllers, yet only by a single MSC. Each LA is assigned a location area identity (LAI) number. Location Areas An MSC/VLR service area represents the part of the GSM network that is covered by one MSC and which is reachable, as it is registered in the VLR of the MSC. MSC/VLR Service Areas
  • The PLMN service area is an area served by one network operator. PLMN Network Areas GSM Specifications Before looking at the GSM specifications, it is important to understand the following basic terms: Bandwidth—the range of a channel's limits; the broader the bandwidth, the faster data can be sent Bits per second (bps)—a single on-off pulse of data; eight bits are equivalent to one byte Frequency—the number of cycles per unit of time; frequency is measured in hertz (Hz)
  • Kilo (k)—kilo is the designation for 1,000; the abbreviation kbps represents 1,000 bits per second Megahertz (MHz)—1,000,000 hertz (cycles per second) Milliseconds (msec)—one-thousandth of a second Watt (W)—a measure of power of a transmitter. Specifications for different personal communication services (PCS) systems vary among the different PCS networks. Listed below is a description of the specifications and characteristics for GSM. Frequency band—the frequency range specified for GSM is 1,850 to 1,990 MHz (mobile station to base station). Duplex distance—the duplex distance is 80 MHz. Duplex distance is the distance between the uplink and downlink frequencies. A channel has two frequencies, 80 MHz apart. Channel separation—the separation between adjacent carrier frequencies. In GSM, this is 200 kHz. Modulation—Modulation is the process of sending a signal by changing the characteristics of a carrier frequency. This is done in GSM via Gaussian minimum shift keying (GMSK). Transmission rate—GSM is a digital system with an over-the-air bit rate of 270 kbps. Access method—GSM utilizes the time division multiple access (TDMA) concept. TDMA is a technique in which several different calls may share the same carrier. Each call is assigned a particular time slot.
  • Speech coder—GSM uses linear predictive coding (LPC). The purpose of LPC is to reduce the bit rate. The LPC provides parameters for a filter that mimics the vocal tract. The signal passes through this filter, leaving behind a residual signal. Speech is encoded at 13 kbps. GSM Subscriber Services There are two basic types of services offered through GSM: telephony (also referred to as Tele-services) and data (also referred to as bearer services). Telephony services are mainly voice services that provide subscribers with the complete capability (including necessary terminal equipment) to communicate with other subscribers. Data services provide the capacity necessary to transmit appropriate data signals between two access points creating an interface to the network. In addition to normal telephony and emergency calling, the following subscriber services are supported by GSM: Dual-tone multi frequency (DTMF)—DTMF is a tone signalling scheme often used for various control purposes via the telephone network, such as remote control of an answering machine. GSM supports full-originating DTMF. Facsimile group III—GSM supports CCITT Group 3 facsimile. As standard fax machines are designed to be connected to a telephone using analog signals, a special fax converter connected to the exchange is used in the GSM system. This enables a GSM–connected fax to communicate with any analog fax in the network. Short message services— A convenient facility of the GSM network is the short message service. A message consisting of a maximum of 160 alphanumeric characters can be sent to or from a mobile station. This service can be viewed as an advanced form of alphanumeric paging with a number of advantages. If the subscriber's mobile unit is powered off or has left the coverage area, the message is stored and offered back to the subscriber when the mobile is powered on or has reentered the coverage area of the network. This function ensures that the message will be received. Cell broadcast—A variation of the short message service is the cell broadcast facility. A message of a maximum of 93 characters can be broadcast to all mobile subscribers in a certain geographic area. Typical applications include traffic congestion warnings and reports on accidents. Voice mail—This service is actually an answering machine within the network, which is controlled by the subscriber. Calls can be forwarded to the subscriber's
  • voice-mail box and the subscriber checks for messages via a personal security code. Fax mail—With this service, the subscriber can receive fax messages at any fax machine. The messages are stored in a service center from which they can be retrieved by the subscriber via a personal security code to the desired fax number. Supplementary Services GSM supports a comprehensive set of supplementary services that can complement and support both telephony and data services. Supplementary services are defined by GSM and are characterized as revenue-generating features. A partial listing of supplementary services follows. Call forwarding—This service gives the subscriber the ability to forward incoming calls to another number if the called mobile unit is not reachable, if it is busy, if there is no reply, or if call forwarding is allowed unconditionally. Barring of outgoing calls—This service makes it possible for a mobile subscriber to prevent all outgoing calls. Barring of incoming calls—This function allows the subscriber to prevent incoming calls. The following two conditions for incoming call barring exist: baring of all incoming calls and barring of incoming calls when roaming outside the home PLMN. Advice of charge (AoC)—The AoC service provides the mobile subscriber with an estimate of the call charges. There are two types of AoC information: one that provides the subscriber with an estimate of the bill and one that can be used for immediate charging purposes. AoC for data calls is provided on the basis of time measurements. Call hold—This service enables the subscriber to interrupt an ongoing call and then subsequently re-establish the call. The call hold service is only applicable to normal telephony. Call waiting—This service enables the mobile subscriber to be notified of an incoming call during a conversation. The subscriber can answer, reject, or ignore the incoming call. Call waiting is applicable to all GSM telecommunications services using a circuit-switched connection. Multiparty service—The multiparty service enables a mobile subscriber to establish a multiparty conversation—that is, a simultaneous conversation
  • between three and six subscribers. This service is only applicable to normal telephony. Calling line identification presentation/restriction—These services supply the called party with the integrated services digital network (ISDN) number of the calling party. The restriction service enables the calling party to restrict the presentation. The restriction overrides the presentation. Closed user groups (CUGs)—CUGs are generally comparable to a PBX. They are a group of subscribers who are capable of only calling themselves and certain number. CDMA Code division multiple access (CDMA) is a channel access method used by various radio communication technologies. CDMA is an example of multiple access, which is where several transmitters can send information simultaneously over a single communication channel. This allows several users to share a band of frequencies (see bandwidth). To permit this to be achieved without undue interference between the users CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code). CDMA is used as the access method in many mobile phone standards such as cdmaOne, CDMA2000 (the 3G evolution of cdmaOne), and WCDMA(the 3G standard used by GSM carriers), which are often referred to as simply CDMA. Steps in CDMA modulation
  • CDMA is a spread spectrum multiple access technique. A spread spectrum technique spreads the bandwidth of the data uniformly for the same transmitted power. A spreading code is a pseudo-random code that has a narrow ambiguity function, unlike other narrow pulse codes. In CDMA a locally generated code runs at a much higher rate than the data to be transmitted. Data for transmission is combined via bitwise XOR (exclusive OR) with the faster code. The figure shows how a spread spectrum signal is generated. The data signal with pulse duration of (symbol period) is XOR’ed with the code signal with pulse duration of (chip period). (Note: bandwidth is proportional to = bit time) Therefore, the bandwidth of the data signal is bandwidth of the spread spectrum signal is . Since where and the is much smaller than , the bandwidth of the spread spectrum signal is much larger than the bandwidth of the original signal. The ratio is called the spreading factor or processing gain and determines to a certain extent the upper limit of the total number of users supported simultaneously by a base station. Each user in a CDMA system uses a different code to modulate their signal. Choosing the codes used to modulate the signal is very important in the performance of CDMA systems. The best performance will occur when there is
  • good separation between the signal of a desired user and the signals of other users. The separation of the signals is made by correlating the received signal with the locally generated code of the desired user. If the signal matches the desired user's code then the correlation function will be high and the system can extract that signal. If the desired user's code has nothing in common with the signal the correlation should be as close to zero as possible (thus eliminating the signal); this is referred to as cross correlation. If the code is correlated with the signal at any time offset other than zero, the correlation should be as close to zero as possible. This is referred to as auto-correlation and is used to reject multi-path interference. An analogy to the problem of multiple access is a room (channel) in which people wish to talk to each other simultaneously. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different languages (code division). CDMA is analogous to the last example where people speaking the same language can understand each other, but other languages are perceived as noise and rejected. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can communicate. In general, CDMA belongs to two basic categories: synchronous (orthogonal codes) and asynchronous (pseudorandom codes) The Mobile Station (MS) In a cdma2000 1X network, the mobile station—the subscriber’s handset— functions as a mobile IP client. The mobile station interacts with the Access Network to obtain appropriate radio resources for the exchange of packets, and it keeps track of the status of radio resources (e.g. active, stand-by, dormant). It accepts buffer packets from the mobile host when radio resources are not in place or are insufficient to support the flow to the network. Upon power-up, the mobile station automatically registers with the Home Location Register (HLR) in order to: • Authenticate the mobile for the environment of the accessed network
  • • Provide the HLR with the mobile’s current location • Provide the Serving Mobile Switching Centre (MSC-S) with the mobile’s permitted feature set After successfully registering with the HLR, the mobile is ready to place voice and data calls. These may take either of two forms, circuit-switched data (CSD) or packet-switched data (PSD), depending on the mobile’s own compliance (or lack thereof) with the IS-2000 standard. This document defines protocols for several critical CDMA interfaces pertaining to packet transmission, namely A1, A7, A9, and A11. Mobile Stations must comply with IS-2000 standards to initiate a packet data session using the 1xRTT1 network. Mobile stations having only IS-95 capabilities are limited to CSD, while IS-2000 terminals can select either the PSD or CSD. Parameters forwarded by the terminal over the air link (AL) to the network will determine the type of service requested. Circuit-switched data has a maximum rate of 19.2 Kbps and is delivered over traditional TDM circuits. This service allows users to select the point of attachment into a data network using ordinary dialled digits. Packet-switched data service has a maximum data rate of 144 Kbps. For each data session a Point-to-Point Protocol (PPP) session is created between the mobile station and the Packet Data Serving Node (PDSN). IP address assignment for each mobile can be provided by either the PDSN or a Dynamic Host Configuration Protocol (DHCP) server via a Home Agent (HA). The Radio Access Network (RAN) The Radio Access Network is the mobile subscriber’s entry point for communicating either data or voice content. It consists of: • The air link • The cell site tower/antenna and the cable connection to the Base Station Transceiver Subsystem • The Base Station Transceiver Subsystem (BTS) • The communications path from the Base Station Transceiver Subsystem to the base station controller • The Base Station Controller (BSC)
  • • The Packet Control Function (PCF) The RAN has a number of responsibilities that impact the network’s delivery of packet services in particular. The RAN must map the mobile client identifier reference to a unique link layer identifier used to communicate with the PDSN, validate the mobile station for access service, and maintain the established transmission links. The Base Station Transceiver Subsystem (BTS) controls the activities of the air link and acts as the interface between the network and the mobile. RF resources such as frequency assignments, sector separation and transmit power control are managed at the BTS. In addition, the BTS manages the back-haul from the cell site to the Base Station Controller (BSC) to minimize any delays between these two elements. Normally a BTS connects to the BSC through un-channelized T1 facilities or direct cables in co-located equipment. The protocols used within this facility are proprietary and are based on High-level Data Link Control (HDLC). The Base Station Controller (BSC) routes voice- and circuit-switched data messages between the cell sites and the MSC. It also bears responsibility for mobility management: it controls and directs handoffs from one cell site to another as needed. It connects to each MTX using channelized T1 lines for voice and circuit switched data; and to un-channelized T1 lines for signalling and control messages to the PDSN using the 10BaseT Ethernet protocol. The Packet Control Function (PCF) routes IP packet data between the mobile station within the cell sites and the Packet Data Serving Node (PDSN). During packet data sessions, it will assign available supplemental channels as needed to comply with the services requested by the mobile and paid for by the subscribers.
  • ALTTC Satellite Earth Station
  • EWSD Switch
  • OCB Switch
  • OTDR
  • 5ESS Switch
  • REFRENCE 1. www.alttc.bsnl.co.in 2. training.bsnl.co.in 3. www.asktraining.com 4. wikimapia.org 5. Wikipedia.com