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Introduction to-telecommunication-rf
The document provides an overview of telecommunication networks and their components. It discusses: 1) The major components of telecommunication networks including transmission facilities, local loops, interoffice facilities, switching systems, and customer premise equipment. 2) How transmission facilities such as local loops and trunks connect different parts of the network and carry traffic. 3) Analog and digital transmission methods, including frequency division multiplexing, time division multiplexing, and pulse code modulation to convert analog signals to digital formats.
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Introduction to-telecommunication-rf
- 1.
- 2. 2 •Describe the majorcomponents of the network and their interrelationships. •Describe how your voice is converted to electrical signals and transmitted over the network. Objectives Network Overview
- 3. 3 • A systemof interconnected elements • A system of various departments to support these elements • Traffic is the flow of information or messages throughout the network Definition of a network:
- 4. 4 • A systemof interconnected elements linked by facilities (i.e., physical connections) over which traffic will flow. • The traffic may be conversations, information, or complex video or audio services. The telecommunications network must also be able to control the interconnected elements What is a telecommunications network?
- 5. 5 • Physical componentsrequired for telecommunication network – Transmission Facilities – Local Loop – IOF - Interoffice facilities – Switching Systems – Customer Premise Equipment (CPE) Network Components and Architecture
- 6. 6 •In its simplestform, a transmission facility is a communication between two end points. This communication path can also be referred to as: •Channel •Circuit •Trunk •For telephony purposes, the communication path (also known as network facilities) can be classified into two broad categories: •Local Loop •Interoffice Facilities (IOF)/Trunk Transmission Facilities
- 7. 7 • The localloop: – is a circuit that connects a customer to the telephone network. – provides the customer with access to the switching system. • The term "loop" is derived from the pair of wires that forms the electrical path between the customer and the central office. • The local loop is also referred to as the subscriber loop. • A simple local loop architecture is depicted in Figure Transmission Facilities………..
- 8. 8 •The primary functionsof switching systems are to provide: •Call setup and routing •Call supervision •Customer I.D. and phone numbers •These are accomplished by interconnecting facilities Switching systems located at the central office (CO) that are used to provide dial tone and ringing are referred to as end offices or local switches. These switches can also be interconnected with other switches. •Another type of switch, tandem, is used as a hub to connect switches and provide routing. (No dial tone is provided to the customer.) Switching Systems
- 9. 9 •Three components ofany transmission system are the •The transmitter •The receiver •The communication path •In its simplest form, the CPE or customer premises equipment, is the transmitter and receiver. The media (twisted pair copper, coaxial cable, optical fiber, radio waves) that connects the CPE is the path. Components for Transmission
- 10. 10 •Many customers' telephonesare connected to the central office by a pair of wires within a cable •Why two wires? •Because your telephone is an electro- mechanical instrument, it requires a battery source and a ground source. •The battery source is supplied from the central office equipment to your telephone set by a wire called the ring lead. The ground source is transmitted from the central office by a wire called the tip lead. Together, the tip and ring of the telephone set are commonly referred to as a cable pair. Telephone Connection to the Central Office
- 11. 11 Analog and DigitalTransmission
- 12. 12 •Describe a carriersystem. •Describe the major differences between analog and digital signals. •Describe the analog to digital and digital to analog conversion process. •Compare and contrast Frequency Division Multiplexing and Time Division Multiplexing. Objectives Analog and Digital Transmission
- 13. 13 •The telecommunications networkcan transmit a variety of information, in two basic forms, analog and digital. In this lesson we will examine both. This information may be transmitted over a circuit/channel or over a carrier system. •Where: A circuit/channel is a transmission path for a single type of transmission service (voice or data) and is generally referred to as the smallest subdivision of the network. A carrier, on the other hand, is a transmission path in which one or more channels of information are processed, converted to a suitable format and transported to the proper destination. The two types of carrier systems we will be discussing in this lesson are: 1. FDM (Frequency Division Multiplexing) -- analog 2. TDM (Time Division Multiplexing) - digital Introduction
- 14. 14 • Multiplexing isthe process of transmitting two or more individual signals over a common path. In effect, it increases the amount of information transmitted, while decreasing the requirement for the physical media (no longer a 1:1 ratio). • Frequency Division Multiplexing • The first type of multiplexing was an analog multiplexing technique. Frequency Division Multiplexing (FDM). In FDM, the bandwidth of the transmission path serves as the frame of reference for all of the information being transmitted. The total bandwidth is divided into subchannels consisting of smaller segments of the available bandwidth Each subchannel is capable of carrying a separate signal. Signals are transmitted simultaneously. Thus, with FDM each channel is: • Assigned a different frequency • Separated into channels 4000 Hz. wide. • The different channels are then stacked and transported over a common path. In other words, each channel occupies a portion of the total frequency bandwidth. Multiplexing
- 15. 15 • Digital Transmission,demanded by our customers, has continually increased since its introduction in 1962. This is due, in large part, to the fact that more of our customers require a high degree of accuracy in the information they are transmitting over our network. And with a digital transmission (as opposed to analog) system we are able to manage the quality of the signal by managing the previously discussed transmission impairments. Thus, digital systems: 1). are a better switching interface 2.) are easier to multiplex 3.)produce clearer signals • Digital Signals A digital signal is a discrete signal. It is depicted as discontinuous -- Discretely variable (on/off) as opposed to an analog signal which is continuously variable (sine wave) A digital signal has the following characteristics: 1.) Holds a fixed value for a specific length of time 2.) Has sharp, abrupt changes 3.) A preset number of values allowed Why Digital Transmission?
- 16. 16 • Pulse CodeModulation (PCM) converts analog signals to a digital format (signal). This process has four steps The Pulse Code Modulation (PCM) Process
- 17. 17 •Frequencies below 300Hz and above 3400 Hz (Voice Frequency range) are filtered from the analog signal •The lower frequencies are filtered out to remove electrical noise induced from the power lines. •The upper frequencies are filtered out because they require additional bits and add to the cost of a digital transmission system. •The actual bandwidth of the filtered signal is 3100 Hz (3400 - 300). It is often referred to as 4 kHz. Step One: Filtering
- 18. 18 •The analog signalis sampled 8000 times per second. The rate at which the analog signal is sampled is related to the highest frequency present in the signal. This is based on the Nyquist sampling theorem. In his calculations, Nyquist used a voice frequency range of 4000 Hz (which represents the voice frequency range that contains "intelligent" speech). Thus, the standard became a sampling rate of 8000 Hz, or twice the bandwidth. The signal that is the result of the sampling process contains sufficient information to accurately represent the information contained in the original signal. The output of this sampling procedure is a Pulse Amplitude Modulated, or PAM, signal. Step Two: Sampling
- 19. 19 •In the thirdstep of the A/D conversion process, we quantize the amplitude of the incoming samples to one of 255 amplitudes on a quantizing scale •Thus, in this step the sampled signal is matched to a segmented scale. The purpose of step three is to measure the amplitude (or height) of the PAM signal and assign a decimal value that defines the amplitude. Based on the quantizing scale, each sampled signal is assigned a number between 0 and +127 to define its amplitude. Step Three and Four: Quantizing and Encoding •In the fourth step of the A/D conversion process, the quantized samples are encoded into a digital bit stream (series of electrical pulses).
- 20. 20 • Time divisionmultiplexing (TDM) is a digital multiplexing technique. In TDM, a number of low rate channels are fed into a multiplexer (e.g., D Bank), which combines them into one high rate digital signal. Each of the 24 VF(voice frequency)/DS0 channels is assigned a specific time slot by the TDM(Time Division Multiplexer). Thus, TDM is a process by which several digital signals are combined onto a single path and sent sequentially. Relating this back to the PAM process: The analog signal is sampled 8000 times a second. There will be 8,000 eight-bit words transmitted per second. These words will be 1/8000 second (or 125 microseconds) apart. Time division multiplexing (TDM)
- 21. 21 •The digital hierarchyrepresents the standard rates by which digital communications are sent in North America. •The basic building block of the digital hierarchy is the DS0 rate at 64 Kbps. Remember that multiplying 8-bit words by the sampling rate of 8000 times/second produces the 64,000 bps rate. With Time Division Multiplexing, multiplexing by an additional 24 time slots and including 8000 framing bits for timing information produces the 1,544,000 bps or 1.544 Mbs. DS1 is considered the beginning of high capacity digital transmission rates. Digital Hierarchy
- 22.
- 23. 23 Identify the majorfunctions of switching. State the meaning of electronic switching systems (ESS) and stored program control (SPC) switching systems. Describe how this family of switches differs from earlier switches. Describe the major components of a digital switch and the main functions of those components. Identify and describe the basic traffic measurements. Objectives Fundamentals of Switching
- 24. 24 The purpose ofa switch is to provide a path for the call. To process a call the switch performs three main functions: 1) Identifies the customer 2) Sets up the communication path 3) Supervises the call Functions of a Switch
- 25. 25 Initially customers wereidentified by the jack position they occupied on the switchboard. With the introduction of electromechanical switches, customers were as signed telephone numbers. (Also called line or station numbers.) The customer's cable pair is terminated and cross- connected to the office equipment at the main distributing frame. Office equipment terminated on the MDF represents a physical location in the switch and a specific telephone number. With the introduction of electronic switches, a telephone number is no longer wired to a specific component of the switch. The telephone number is now associated with a customer record which exists in the translations (or memory) of the switch. Identify the Customers
- 26. 26 Early in theprocessing of a call, the switch needs to determine what type of a call is being made. By analyzing either the first digit (is it a 0 or a 1?) or the first three digits (prefix), the switch will determine whether the call is intraswitch or inter-switch. If the call being processed is an intra-switch call, the path that the switch will allocate is called a line (i.e., "on the line side of the network"). If the call is an inter-switch call, the path that the switch will allocate is a trunk. Set Up the Path
- 27. 27 The supervision functionsof the switch tend to be overlooked because they are transparent to the customer. They are, however, extremely important because they directly impact the efficient functioning of the switch itself. Supervise the Call
- 28.
- 29. 29 •Off Hook •Dial Tone •DialingDigits •RBT •Conversation •Ring •Off Hook & Conversation •Signaling •Traffic SWITCH / EXCHANGE BASIC Telephony
- 30.
- 31. 31 • Till 1982Cellular Systems were exclusively Analog Radio Technology. • Advanced Mobile Phone Service (AMPS) – U.S. standard on the 800 MHz Band • Total Access Communication System (TACS) – U.K. standard on 900 MHz band • Nordic Mobile Telephone System (NMT) – Scandinavian standard on the 450 & 900 MHz band Different Standards Worldwide
- 32.
- 33. 33 • End of1980’s Analog Systems unable to meet continuing demands – Severely confined spectrum allocations – Interference in multipath fading environment – Incompatibility among various analog systems – Inability to substantially reduce the cost of mobile terminals and infrastructure required Analog Mobile Telephony
- 34. 34 • Spectrum space- most limited and precious resource • Solution - further multiplex traffic (time domain) • Can be realized with Digital Techniques only Digital Mobile Telephony
- 35. 35 • A cellularsystem links Mobile subscribers to Public Telephone System or to another Mobile subscribers. • It removes the fixed wiring used in a traditional telephone installation. • Mobile subscriber is able to move around, perhaps can travel in a vehicle or on foot & still make & receive call. Cellular Communication
- 36. 36 • Mobility • Flexibility •Convergence • Greater QOS • Network Expansion • Revenue/Profit Advantage of Cellular Communication
- 37. 37 Courtesy of RichHoward First Mobile Radio Telephone (1924)
- 38. 38 • Advanced MobilePhone Service (AMPS) – US trials 1978; deployed in Japan (’79) & US (’83) – 800 MHz band — two 20 MHz bands – TIA-553 – Still widely used in US and many parts of the world • Nordic Mobile Telephony (NMT) – Sweden, Norway, Demark & Finland – Launched 1981; now largely retired – 450 MHz; later at 900 MHz (NMT900) • Total Access Communications System (TACS) – British design; similar to AMPS; deployed 1985 – Some TACS-900 systems still in use in Europe First Generation
- 39. 39 • Digital systems •Leverage technology to increase capacity – Speech compression; digital signal processing • Utilize/extend “Intelligent Network” concepts • Improve fraud prevention • Add new services • There are a wide diversity of 2G systems – IS-54/ IS-136 North American TDMA; PDC (Japan) – iDEN – DECT and PHS – IS-95 CDMA (cdmaOne) – GSM Second Generation — 2G
- 40. 40 • Speech codedas digital bit stream – Compression plus error protection bits – Aggressive compression limits voice quality • Time division multiple access (TDMA) – 3 calls per radio channel using repeating time slices • Deployed 1993 (PDC 1994) – Development through 1980s; bakeoff 1987 • IS-54 / IS-136 standards in US TIA • ATT Wireless & Cingular use IS-136 today – Plan to migrate to GSM and then to W-CDMA • PDC dominant cellular system in Japan today – NTT DoCoMo has largest PDC network D-AMPS/ TDMA & PDC
- 41. 41 • Used byNextel • Motorola proprietary system – Time division multiple access technology – Based on GSM architecture • 800 MHz private mobile radio (PMR) spectrum – Just below 800 MHz cellular band • Special protocol supports fast “Push-to-Talk” – Digital replacement for old PMR services • Nextel has highest APRU in US market due to “Direct Connect” push-to- talk service iDEN
- 42. 42 • Also basedon time division multiple access • Digital European Cordless Telephony – Focus on business use, i.e. wireless PBX – Very small cells; In building propagation issues – Wide bandwidth (32 kbps channels) – High-quality voice and/or ISDN data • Personal Handiphone Service – Similar performance (32 kbps channels) – Deployed across Japanese cities (high pop. density) – 4 channel base station uses one ISDN BRI line – Base stations on top of phone booths – Legacy in Japan; new deployments in China today DECT and PHS
- 43. 43 • Code DivisionMultiple Access – All users share same frequency band – Discussed in detail later as CDMA is basis for 3G • Qualcomm demo in 1989 – Claimed improved capacity & simplified planning • First deployment in Hong Kong late 1994 • Major success in Korea (1M subs by 1996) • Used by Verizon and Sprint in US • Simplest 3G migration story today North American CDMA (cdmaOne)
- 44. 44 • TIA standardIS-95 (ANSI-95) in 1993 • IS-95 deployed in the 800 MHz cellular band – J-STD-08 variant deployed in 1900 MHz US “PCS” band • Evolution fixes bugs and adds data – IS-95A provides data rates up to 14.4 kbps – IS-95B provides rates up to 64 kbps (2.5G) – Both A and B are compatible with J-STD-08 • All variants designed for TIA IS-41 core networks (ANSI 41) cdmaOne — IS-95
- 45. 45 • « Groupe SpecialMobile », later changed to « Global System for Mobile » – Joint European effort beginning in 1982 – Focus on seamless roaming across Europe • Services launched 1991 – Time division multiple access (8 users per 200KHz) – 900 MHz band; later extended to 1800MHz – Added 1900 MHz (US PCS bands) • GSM is dominant world standard today – Well defined interfaces; many competitors – Network effect (Metcalfe’s law) took hold in late 1990s – Tri-band GSM phone can roam the world today GSM
- 46.
- 47. 47 30 KHz 30 KHz 30KHz 30 KHz 30 KHz 30 KHz 30 KHz 30 KHz Frequency FDMA — Frequency Division Multiple Access 1G — Separate Frequencies
- 48. 48 Frequency Time 200 KHz 200 KHz 200KHz 200 KHz One timeslot = 0.577 ms One TDMA frame = 8 timeslots 2G — TDMA Time Division Multiple Access
- 49. 49 • Spread spectrummodulation – Originally developed for the military – Resists jamming and many kinds of interference – Coded modulation hidden from those w/o the code • All users share same (large) block of spectrum – One for one frequency reuse – Soft handoffs possible • Almost all accepted 3G radio standards are based on CDMA – CDMA2000, W-CDMA and TD-SCDMA 2G & 3G — CDMA Code Division Multiple Access
- 50. 50 Courtesy of PetriPossi, UMTS World Multi-Access Radio Techniques
- 51. 51 • Universal globalroaming • Multimedia (voice, data & video) • Increased data rates – 384 kbps while moving – 2 Mbps when stationary at specific locations • Increased capacity (more spectrally efficient) • IP architecture • Problems – No killer application for wireless data as yet – Vendor-driven 3G Vision
- 52. 52 • ITU (InternationalTelecommunication Union) – Radio standards and spectrum • IMT-2000 – ITU’s umbrella name for 3G which stands for International Mobile Telecommunications 2000 • National and regional standards bodies are collaborating in 3G partnership projects – ARIB, TIA, TTA, TTC, CWTS. T1, ETSI - refer to reference slides at the end for names and links • 3G Partnership Projects (3GPP & 3GPP2) – Focused on evolution of access and core networks International Standardization
- 53.
- 54. 54 • IMT-SC* SingleCarrier (UWC-136): EDGE – GSM evolution (TDMA); 200 KHz channels; sometimes called “2.75G” • IMT-MC* Multi Carrier CDMA: CDMA2000 – Evolution of IS-95 CDMA, i.e. cdmaOne • IMT-DS* Direct Spread CDMA: W-CDMA – New from 3GPP; UTRAN FDD • IMT-TC** Time Code CDMA – New from 3GPP; UTRAN TDD – New from China; TD-SCDMA • IMT-FT** FDMA/TDMA (DECT legacy) * Paired spectrum; ** Unpaired spectrum IMT-2000 Radio Standards
- 55. 55 • Evolution fromoriginal Qualcomm CDMA – Now known as cdmaOne or IS-95 • Better migration story from 2G to 3G – cdmaOne operators don’t need additional spectrum – 1xEVD0 promises higher data rates than UMTS, i.e. W-CDMA • Better spectral efficiency than W-CDMA(?) – Arguable (and argued!) • CDMA2000 core network less mature – cmdaOne interfaces were vendor-specific – Hopefully CDMA2000 vendors will comply w/ 3GPP2 CDMA2000 Pros and Cons
- 56. 56 • Wideband CDMA –Standard for Universal Mobile Telephone Service (UMTS) • Committed standard for Europe and likely migration path for other GSM operators – Leverages GSM’s dominant position • Requires substantial new spectrum – 5 MHz each way (symmetric) • Legally mandated in Europe and elsewhere • Sales of new spectrum completed in Europe – At prices that now seem exorbitant W-CDMA (UMTS) Pros and Cons
- 57. 57 • Time divisionduplex (TDD) • Chinese development – Will be deployed in China • Good match for asymmetrical traffic! • Single spectral band (1.6 MHz) possible • Costs relatively low – Handset smaller and may cost less – Power consumption lower – TDD has the highest spectrum efficiency • Power amplifiers must be very linear – Relatively hard to meet specifications TD-SCDMA
- 58. 58 CDMA GSM TDMA PHS (IP-Based) 64 Kbps GPRS 115 Kbps CDMA1xRTT 144 Kbps EDGE 384 Kbps cdma2000 1X-EV-DV Over 2.4 Mbps W-CDMA (UMTS) Up to 2 Mbps 2G 2.5G 2.75G 3G 1992 - 2000+ 2001+ 2003+ 1G 1984 - 1996+ 2003 - 2004+ TACS NMT AMPS GSM/ GPRS (Overlay) 115 Kbps 9.6 Kbps 9.6 Kbps 14.4 Kbps / 64 Kbps 9.6 Kbps PDC Analog Voice Digital Voice Packet Data Intermediate Multimedia Multimedia PHS TD-SCDMA 2 Mbps? 9.6 Kbps iDEN (Overlay) iDEN Source: U.S. Bancorp Piper Jaffray Migration To 3G
- 59. 59 ARIB (Japan) T1 (USA) ETSI (Europe) TTA (Korea) CWTS (China) TTC (Japan) TIA (USA) Third Generation Patnership Project (3GPP) ThirdGeneration Partnership Project II (3GPP2) ITU Mobile Operators ITU Members IS-95), IS-41, IS- 2000, IS-835 GSM, W-CDMA, UMTS Mobile Standard Organizations
Editor's Notes
- #4 If there would have been only 3-4 telephones within one locality, it would make sense to connect each phone to all others to find simple method of selecting the desired one. However if there are 3-4 thousand subscribers within same locale, the solution mentioned above is out of question. Certainly there is a need of architecture where all telephone within a locale are connected to some central office where connection can take place as required either by very simple means of dot and probe or sophisticated cross-connect i.e. SPC switch. This central office (CO) solution is the one that has been widely accepted by telecommunication industry.
- #5 A telecommunication network is the combination of numerous network elements that are required to support voice, data or video services in local or long distance applications. A telecommunication network is the foundation of all telephony activity, it is the networks that connects the end user to virtually anywhere in world though copper cable, coaxial cable, optical fiber cable or through a wireless technology such as microwave or satellite.
- #6 ‘Telecommunication’ as the name suggests is meant to ‘connect’ i.e. to perform desired connection. Physical entities required are mainly classified into following :- The subscriber premises equipment Telephone set Fax Modem DSL Modem The local loop The Telephone line ISDN Line The local exchange Telephone exchange DSLAM Inter exchange transmission media E1s over copper/fiber/microwave/satellite
- #7 Transmission means transmission of data between two equipments, all modern transport equipments are mainly digital one. Starting from digitization of information, coding and modulation to transmit to desired destination and vice versa is achieved through various components. The widely adopted standard for digitization of voice information is Pulse Code Modulation. The basic voice channel is 64kbps PCM. 32 such channels form an E1(2MBPS) trunk. These channels/trunks are interconnected to form circuits by means of physical media and equipments. There are four types of media that can be used in transmitting information in telecommunication world: Copper Wire Coaxial Cable (actually an adaptation of copper wire) Optical Fiber Wireless Signals are multiplexed before transmission over media. Various multiplexing hierarchies are available, equipments are designed and manufactured based upon hierarchies.
- #8 The CPE is connected to the central office by means of the drop wire, distribution cable, and feeder cable which are cross-connected at specific points. (terminals) SAI = Serving Area Interface. Also known as a B-Box. (cross-connect box) Interoffice Facilities (IOF): Consist of trunks that connect switching systems. Carry multiple transmissions over a single path rather than a single transmission over a single path. Consist of the necessary equipment on each end, and the facility (i.e. cable) itself. Historically, copper cable was the facility used. Today, the facility may also be: coaxial cable radio links (microwave) fiber optics
- #9 The switch is basically a cross connect which performs connection between originating and terminating subscriber loop. Initially customers were identified by the jack position they occupied on the switchboard. With the introduction of electromechanical switches, customers were as signed telephone numbers. (Also called line or station numbers.) The customer's cable pair is terminated and cross-connected to the office equipment at the main distributing frame. Office equipment terminated on the MDF represents a physical location in the switch and a specific telephone number. With the introduction of electronic switches, a telephone number is no longer wired to a specific component of the switch. The telephone number is now associated with a customer record which exists in the translations (or memory) of the switch. Initial phases of switches were manual, where actual functioning was done by human using plug/cord/jack. Followed by ‘step-by-step’ and ‘cross-bar’ switching which were electromechanical switches. All above switches were analog type and method of switching was space switching. The revolution started when ‘stored program control’ switches were introduced which were digital switches using time switching. All modern switches in today’s telecom networks are time switches.
- #10 As discussed earlier transmission link consists of end equipments and media. Equipment design is dependent on multiplexing hierarchy while media is mostly independent of same. Few basic hierarchies and multiplexing/modulation algorithms used are : PDH SONET/SDH ATM ADSL
- #11 The basic loop connection is two wire half duplex. To discuss :- Simplex/Duplex
- #14 Basic function of telephone networks is to ensure voice communication between two subscribers. The voice is basic analog signal in the range of 20Hz to 20KHz. Most of today’s transmission system are digital one, analog transmission is only used in last mile i.e. subscriber loop.
- #15 Add Notes for Students:
- #17 In retrospect, PCM, like many other great inventions, appears to be simple and obvious. In the history of electrical communications, the earliest reason for sampling a signal was to interlace samples from different telegraphy sources, and convey them over a single telegraph cable. Telegraph time-division multiplexing (TDM) was conveyed as early as 1853, by the American inventor M.B. Farmer. The electrical engineer W.M. Miner, in 1903, used an electro-mechanical commutator for time-division multiplex of multiple telegraph signals, and also applied this technology to telephony. He obtained intelligible speech from channels sampled at a rate above 3500–4300 Hz: below this was unsatisfactory. This was TDM, but pulse-amplitude modulation (PAM) rather than PCM. Paul M. Rainey of Western Electric in 1926 patented a facsimile machine using an optical mechanical analog to digital converter. The machine did not go into production. British engineer Alec Reeves, unaware of previous work, conceived the use of PCM for voice communication in 1937 while working for International Telephone and Telegraph in France. He described the theory and advantages, but no practical use resulted. Reeves filed for a French patent in 1938, and his U.S. patent was granted in 1943. The first transmission of speech by digital techniques was the SIGSALY vocoder encryption equipment used for high-level Allied communications during World War II from 1943. It was not until about the middle of 1943 that the Bell Labs people who designed the SIGSALY system, became aware of the use of PCM binary coding as already proposed by Alec Reeves. PCM in the 1950s used a cathode-ray coding tube with a grid having encoding perforations. As in an oscilloscope, the beam was swept horizontally at the sample rate while the vertical deflection was controlled by the input analog signal, causing the beam to pass through higher or lower portions of the perforated grid. The grid interrupted the beam, producing current variations in binary code. Rather than natural binary, the grid was perforated to produce Gray code lest a sweep along a transition zone produce glitches.
- #20 In conventional PCM, the analog signal may be processed (e.g. by amplitude compression) before being digitized. Once the signal is digitized, the PCM signal is usually subjected to further processing (e.g. digital data compression). Some forms of PCM combine signal processing with coding. Older versions of these systems applied the processing in the analog domain as part of the A/D process, newer implementations do so in the digital domain. These simple techniques have been largely rendered obsolete by modern transform-based audio compression techniques. Pulse-code modulation can be either return-to-zero (RZ) or non-return-to-zero (NRZ). For a NRZ system to be synchronized using in-band information, there must not be long sequences of identical symbols, such as ones or zeroes. For binary PCM systems, the density of 1-symbols is called ones-density. Ones-density is often controlled using precoding techniques such as Run Length Limited encoding, where the PCM code is expanded into a slightly longer code with a guaranteed bound on ones-density before modulation into the channel. In other cases, extra framing bits are added into the stream which guarantee at least occasional symbol transitions. Another technique used to control ones-density is the use of a scrambler polynomial on the raw data which will tend to turn the raw data stream into a stream that looks pseudo-random, but where the raw stream can be recovered exactly by reversing the effect of the polynomial. In this case, long runs of zeroes or ones are still possible on the output, but are considered unlikely enough to be within normal engineering tolerance. In other cases, the long term DC value of the modulated signal is important, as building up a DC offset will tend to bias detector circuits out of their operating range. In this case special measures are taken to keep a count of the cumulative DC offset, and to modify the codes if necessary to make the DC offset always tend back to zero. Many of these codes are bipolar codes, where the pulses can be positive, negative or absent. In the typical alternate mark inversion code, non-zero pulses alternate between being positive and negative. These rules may be violated to generate special symbols used for framing or other special purposes.
- #21 In the standard North American PCM system, 24 channels are time division multiplexed together and transmitted over a common path. This common path is known as a digital carrier system and operates at the DS1 rate (1.544 Mbps). Using TDM, the 24 channels are sampled sequentially. First, channel one is sampled Then channel two is sampled, and so on. These samples are then passed on to a common quantizer/encoder where they are converted into a single bit stream. In comparison: FDM is simultaneous. TDM is sequential. The multiplexing equipment counts the bits. 24 channels X 8 bit words = 192 bits When it reaches 192, it will add one framing bit for timing, and start over. Additionally, throughout the digital network regenerative repeaters are used to "recreate" the original signal, thus reducing transmission impairments found in the analog network. The "Regen" also filters out noise.
- #22 In telecommunications, a digital multiplex hierarchy is a hierarchy consisting of an ordered repetition of tandem digital multiplexers that produce signals of successively higher data rates at each level of the hierarchy. Digital multiplexing hierarchies may be implemented in many different configurations depending on; (a) the number of channels desired, (b) the signaling system to be used, and (c) the bit rate allowed by the communications media. Some currently available digital multiplexers have been designated as Dl-, DS-, or M-series, all of which operate at T-carrier rates. In the design of digital multiplex hierarchies, care must be exercised to ensure interoperability of the multiplexers used in the hierarchy.
- #25 Initially customers were identified by the jack position they occupied on the switchboard. With the introduction of electromechanical switches, customers were as signed telephone numbers. (Also called line or station numbers.) The customer's cable pair is terminated and cross-connected to the office equipment at the main distributing frame. Office equipment terminated on the MDF represents a physical location in the switch and a specific telephone number. With the introduction of electronic switches, a telephone number is no longer wired to a specific component of the switch. The telephone number is now associated with a customer record which exists in the translations (or memory) of the switch. Initial phases of switches were manual, where actual functioning was done by human using plug/cord/jack. Followed by ‘step-by-step’ and ‘cross-bar’ switching which were electromechanical switches. All above switches were analog type and method of switching was space switching. The revolution started when ‘stored program control’ switches were introduced which were digital switches using time switching. All modern switches in today’s telecom networks are time switches.
- #26 Add Notes for the Students:
- #27 Add Notes for the Students:
- #28 Many RBOCs use two primary vendors of digital switches: The #5ESS switch manufactured by AT&T The DMS100 switch manufactured by Northern Telecom Inc. (NTI). At the overview level these switches have similar components and operating characteristics. - Administration Module (AM) - Communications Module (CM) - Remote Switch Module (RSM) - Switch Module (SM) - Main Memory (MM) - Input/Output (I/O) - Time Multiplex Switch Unit (TMSU) Advantages of digital switches are: - Call processing is executed in nanoseconds (1/1,000,000,000 second) - A/D & D/A conversion is performed in the SM. - Digital switches with the appropriate generic (i.e., software or operating system) are required for providing ISDN or remote switch services. - Digital switches with the proper upgrades are required for AIN - Digital switches are more efficient in the way they allocate paths through the switch, virtual (time slots vs physical). - Digital switches with appropriate hardware/software can reduce D-Banks in the Central Office.
- #30 Plane Old Telephony System
- #31 Cellular is one of the fastest growing and most demanding telecommunications applications. Today, it represents a continuously increasing percentage of all new telephone subscriptions around the world. Currently there are more than 45 million cellular subscribers worldwide, and nearly 50 percent of those subscribers are located in the United States. It is forecasted that cellular systems using a digital technology will become the universal method of telecommunications. Mobile (radio) communication is understood as exchange of information between two or more users of which at least one user equipment is not located at a fixed position and may be moving around. In cellular systems, radio communication takes place between a mobile station (MS) and a fixed station which is referred to as radio base station (RBS). Normally, in a cellular system, there is no direct communication between two mobile stations (there may be however extensions to cellular systems which allow also direct communication between MSs). The geographic area in which a mobile station is able to exchange radio signals with a radio base station is called a (radio) cell. A cellular system consists of set of (possibly overlapping) cells where each cell is served by one radio base station. At one (antenna) site (“Standort”) several radio base stations may be co-located. By using sector antennas it is possible to establish several cells from a single site. The transmission direction from an MS to a RBS is denoted as uplink (sometimes also referred to as reverse link). The transmission direction from an RBS to an MS is denoted as downlink(sometimes also referred to as forward link).
- #32 The concept of cellular service is the use of low-power transmitters where frequencies can be reused within a geographic area. The idea of cell-based mobile radio service was formulated in the United States at Bell Labs in the early 1970s. However, the Nordic countries were the first to introduce cellular services for commercial use with the introduction of the Nordic Mobile Telephone (NMT) in 1981. Cellular systems began in the United States with the release of the advanced mobile phone service (AMPS) system in 1983. The AMPS standard was adopted by Asia, Latin America, and Oceanic countries, creating the largest potential market in the world for cellular. In the early 1980s, most mobile telephone systems were analog rather than digital, like today's newer systems. One challenge facing analog systems was the inability to handle the growing capacity needs in a cost-efficient manner. As a result, digital technology was welcomed. The advantages of digital systems over analog systems include ease of signaling, lower levels of interference, integration of transmission and switching, and increased ability to meet capacity demands.
- #33 The Development of Mobile Telephone Systems Year Mobile System 1981 Nordic Mobile Telephone (NMT) 450 1983 American Mobile Phone System (AMPS) 1985 Total Access Communication System (TACS) 1986 Nordic Mobile Telephony (NMT) 900 1991 American Digital Cellular (ADC) 1991 Global System for Mobile Communication (GSM) 1992 Digital Cellular System (DCS) 1800 1994 Personal Digital Cellular (PDC) 1995 PCS 1900—Canada 1996 PCS—United States
- #35 Add Notes for the Students:
- #39 1G - AnalogIntroduced in the late 1970s and early 1980s, the first cellular systems were analog. They were used for data just like land-based telephone lines are used for dial-up with analog modems. A handful of cellphone models could be adapted to laptop modems and transfer data at less than 15 Kbps while traveling
- #40 2G - 2.5G - Digital The second generation refers to digital voice cellphone systems deployed in the 1990s, which were based on GSM, TDMA or CDMA. Several so-called 2.5G (or 2G+) technologies added data services for Internet access and e-mail with typical downstream speeds ranging from 64 to 200 Kbps for the user. These include GPRS, EDGE and IS-95B.
- #46 Global System for Mobile communications (GSM: originally from Groupe Spécial Mobile) is the most popular standard for mobile phones in the world. Its promoter, the GSM Association, estimates that 82% of the global mobile market uses the standard.[1] GSM is used by over 2 billion people across more than 212 countries and territories.[2][3] Its ubiquity makes international roaming very common between mobile phone operators, enabling subscribers to use their phones in many parts of the world. GSM differs from its predecessors in that both signalling and speech channels are digital call quality, and thus is considered a second generation (2G) mobile phone system. This has also meant that data communication was built into the system using the 3rd Generation Partnership Project (3GPP). The ubiquity of the GSM standard has been advantageous to both consumers (who benefit from the ability to roam and switch carriers without switching phones) and also to network operators (who can choose equipment from any of the many vendors implementing GSM[4]). GSM also pioneered a low-cost alternative to voice calls, the Short message service (SMS, also called "text messaging"), which is now supported on other mobile standards as well. Newer versions of the standard were backward-compatible with the original GSM phones. For example, Release '97 of the standard added packet data capabilities, by means of General Packet Radio Service (GPRS). Release '99 introduced higher speed data transmission using Enhanced Data Rates for GSM Evolution (EDGE).
- #48 Frequency Division Multiple Access or FDMA is an access technology that is used by radio systems to share the radio spectrum. The terminology “multiple access” implies the sharing of the resource amongst users, and the “frequency division” describes how the sharing is done: by allocating users with different carrier frequencies of the radio spectrum. This technique relies upon sharing of the available radio spectrum by the communications signals that must pass through that spectrum. The terminology “multiple access” indicates how the radio spectrum resource is intended to be used: by enabling more than one communications signal to pass within a particular band; and the “frequency division” indicates how the sharing is accomplished: by allocating individual frequencies for each communications signal within the band. In demand assigned multiple access (DAMA) systems, a control mechanism is used to establish or terminate voice and/or data links between the source and destination stations. Consequently, any of the subdivisions is used by any of the participating earth stations at any given time.
- #49 Time division multiple access (TDMA) is a channel access method for shared medium (usually radio) networks. It allows several users to share the same frequency channel by dividing the signal into different timeslots. The users transmit in rapid succession, one after the other, each using his own timeslot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only the part of its bandwidth they require. TDMA is used in the digital 2G cellular systems such as Global System for Mobile Communications (GSM), IS-136, Personal Digital Cellular (PDC) and iDEN, and in the Digital Enhanced Cordless Telecommunications (DECT) standard for portable phones. It is also used extensively in satellite systems, and combat-net radio systems. For usage of Dynamic TDMA packet mode communication, see below. TDMA frame structure showing a data stream divided into frames and those frames divided into timeslots.TDMA is a type of Time-division multiplexing, with the special point that instead of having one transmitter connected to one receiver, there are multiple transmitters. In the case of the uplink from a mobile phone to a base station this becomes particularly difficult because the mobile phone can move around and vary the timing advance required to make its transmission match the gap in transmission from its peers.
- #50 Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. It should not be confused with cdmaOne (often referred to as simply "CDMA"), which is a mobile phone standard that uses CDMA as its underlying channel access method. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency. CDMA is a form of "spread-spectrum" signaling, since the modulated coded signal has a much higher bandwidth than the data being communicated. An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speak at different pitches (frequency division), or speak in different directions (spatial division). In CDMA, they would speak different languages. People speaking the same language can understand each other, but not other people. 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 understand each other.
- #51 In contrast to FDMA, Time Division Multiple Access (TDMA) is an access technique whereby users are separated in time. Code Division Multiple Access CDMA is an access technology whereby users are separated by codes. Other access techniques include: SDMA – Space division multiple access, CSMA – Carrier sense multiple access, and MF-TDMA - Multi-Frequency TDMA
- #57 W-CDMA transmits on a pair of 5 MHz-wide radio channels, while CDMA2000 transmits on one or several pairs of 1.25 MHz radio channels. Though W-CDMA does use a direct sequence CDMA transmission technique like CDMA2000, W-CDMA is not simply a wideband version of CDMA2000. The W-CDMA system is a new design by NTT DoCoMo, and it differs in many aspects from CDMA2000. From an engineering point of view, W-CDMA provides a different balance of costs vs. capacity vs. performance vs. density, and promises to achieve a benefit of reduced cost for video phone handsets. W-CDMA may also be better suited for deployment in the very dense cities of Europe and Asia. However, hurdles remain, and cross-licencing of patents between Qualcomm and W-CDMA vendors has not eliminated possible patent issues due to the features of W-CDMA which remain covered by Qualcomm patents.[3] W-CDMA has been developed into a complete set of specifications, a detailed protocol that defines how a mobile phone communicates with the tower, how signals are modulated, how datagrams are structured, and system interfaces are specified allowing free competition on technology elements.