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Lecture #9: Wireless Transmission. Telephone System.

Lecture #9: Wireless Transmission. Telephone System. C o n t e n t s Physical basics of wireless signaling radio waves microwaves infrared light Telephone system: Structure Multiplexing Switching methods. 2. 5. 6. 8. 9. 10. 21. 38. Physical Basics in Wireless Signaling.

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Lecture #9: Wireless Transmission. Telephone System.

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  1. Lecture #9: Wireless Transmission. Telephone System. C o n t e n t s • Physical basics of wireless signaling • radio waves • microwaves • infrared • light • Telephone system: • Structure • Multiplexing • Switching methods 2 5 6 8 9 10 21 38

  2. Physical Basics in Wireless Signaling • Electromagnetic waves, frequency (f)  Hz and length (l)  m • Broadcasting and receiving of the electromagnetic waves - antennas • Vacuum speed of the electromagnetic waves (c). Speeds of the electrical and light pulses in conductors. Main relation: lf = c (i.e.: l[m] 104 1km 100 10 1m 1dm 1cm 1mm f[Hz] 30k 300k 3M 30M 300M 3G 30G 300G) • Differential form of f(l) = c/l is: f=c/l| d/dl df = -(c/l2)dl i.e. for finite differences Df = (c/l2)Dl

  3. Physical Basics in Wireless Signaling • Since Df = (c/l2)Dlit is possible to calculate from the physical diagrams the frequency bandwidth of given material or media: on (2/6) for Dl one has: l 0.85 mm 1.3 mm 1.55 mm Dl0.08 mm 0.17 mm 0.185 mm Df 33.22 THz 30.18 THz 23.1 THz • Data rate[b]  Df[Hz] and vary from 1b/HzLF to 30-50b/Hz >UHF Frequency bandwidth

  4. Electromagnetic Spectrum • Electromagnetic spectrum: RadioMicrowave  Infrared  Light  UV  X  Gamma. • ITU standard “radio” bands • Application of bands and correspondence to the transmission media • Spectrum allocation: ITU-R/WARC and FCC • Narrow frequency band (Df << f) • Spread spectrum (military but also business applications; regular hops between frequencies in wide band for higher security/privacy) 2/11 International Telecommunication Union - Radio Communication Sector/ World Agency for Radio Communications

  5. Radio Transmission Radio-frequency waves are: • easy to generate • with high penetration (buildings, forest, but not hills/mountains) • omnidirectional • with mutual interference • with frequency-dependant properties: • power losses with the distance • absorption and reflection (by LF/MF and HF/VHF) 2/12

  6. Microwave Transmission Microwaves have: • straight spreading (require straight line connection between the transmitter and receiver: on the Earth surface they need repeaters on each 100 km) • possibility of ray concentration (focusing) • no interference between non-collinear transmissions • low penetration (buildings and even rain are non transparent) • possible refraction in the dense atmosphere layers  multipath fading (phase shifting) • frequency-dependant properties: • power losses with the distance • absorption by water (f above 8Ghz/l 40cm and less )

  7. Microwave Transmission Microwave applications: • long-distance phone transmissions (incl. POTS and cellular phones): mW compete in this area with fiber optic. • Advantages: cheap, non-wired communication • Drawbacks: crowded spectrum, possible interference with other devices, low level of security, possible atmospheric disturbance • non licensed free bands • 902  928 MHz - industrial use (cordless home devices and distanced controllers); cheapest transceivers (transmitters or receivers) and lower level of interference • 2400  2484 MHz • 5725  5859 MHz

  8. Infrared Waves • 1012 1014 Hz band(invisible light with thermal impact). • Properties: • do not pass solid or non-transparent objects • strong attenuation in relatively short distance of air • can be focused in a ray but also dispersed in omnidirectional way • Application • house remote control devices • implementation of indoor wireless LANs (of portable computers) and communications.

  9. Light Waves • Visible light is called optics. • Optic signals are transmitted usually in form of coherent directed lightrays (transmitters called LASERs). • Unidirectional transmission needs very precise alignment between the transmitter and receiver (photodetector); often application of defocusing lenses • Same Properties like infrared rays • Atmosphere distortions Light Amplification by Stimulated Emis- sion of Radiation 8 2/13

  10. Telephone System • Public Switched Telephone Network (PSTN) - used to for communication media between computers that cannot share one common LAN because they are: • of large number; • too distanced; • separated by other property. • Communication properties of switched phone lines: • low data rate - 104 b/S (108 b/S for direct wire) • high error rate - 10-5 Err/b (10-12 Err/b for direct wires)

  11. Telephone System - Structure • Development of the Telephone system from non-switched fully interconnected graph to centralized switching system and then to hierarchical system of [routable] switches • Structure of the connectivity of the hierarchical switched telephone system: • local loops twisted pair  analog • toll connecting trunks coax, mW, fiber  analog, digital • intertoll trunks coax, mW, fiber  digital, analog 2/14 2/15

  12. Telephone System - Transmission Technologies • The transmission and switching are shifting towards fully optical systems: all electric optical transmission electric switching all optical

  13. Analog Transmission • In analog transmission the physical quantity of the signal carrying the information (amplitude, frequency, phase) varies in a direct relationship to the information to be transmitted. • The nature of information transfer is continuous.

  14. Digital Transmission • In digital transmission the continuous signal is first sampled by slicing the signal at regular intervals into discrete values. • Signal samples are then quantified, their amplitudes are approximated to the nearest pre-defined value. • Quantified samples are coded into binary words. • After this, the binary words are transmitted. • The length of a coded binary sample depends on that how accurate the quantization must be. • For example, if the signals are presented with 256 different (voltage) levels, the coded binary word is 8 bits long (28 = 256).

  15. Digital Transmission Samples Quantization 010 100 011 Binary words

  16. Telephone System - Digital vs. Analog Signaling • Digital vs. Analog signaling in Telephone system: • stronger attenuation but • possibility for multiple consecutive signal regeneration • possibility congestion of data rates on the lines • possibility for 1:1 data transmission (incl. image, voice, stored data) between two points (i.e. high QoS) • easier equipment implementation • possibility for automation of maintenance • the ability to add redundant information (e.g. for error detection and correcting purposes) to the true information stream … 17

  17. Telephone System - Digital vs. Analog Signaling • Digital vs. Analog signaling in Telephone system - continue: • not so sensitive for interference as the analogue transmission. • the binary representation of the signal can be transmitted, for example, by frequency modulation when a frequency F1 represents the binary digit ‘0’ and a frequency F2 is associated with the binary ‘1’.

  18. Local Loops by Inter-computer Communication • Doubled digital-to/from-analog conversion in local loops of switched lines • Main distortions: • attenuation A(log10d, f)  dB/km - signal power losses and signal shape wrapping • delay - different for the signal frequency components  overlapping of the components of different consecutive bits • noise - caused by line/relay commutations and junctions, signal inductive interference or random energy sources 2/17

  19. Local Loops - Modulation/Demodulation • Modems: Digital-to-analog-and-analog-to-digital converters. Analog coding is called modulation. Digital [de]coding is called demodulation. • Analog signal is transmitted by sine carrier off = 12kHz. Modulation (i.e. analog coding) can be performed by carrier tension amplitude, by carrier frequency shifting or by carrier phase shifting. Nyquist’s Theorem boundary: 3kHz local loop bandwidth transmits up to 6kHz carrier • Advanced modulation techniques transmit multiple (3-4) bits per baud by combination of amplitude and phase shifting (QAM - Quadrature Amplitude Modulation). 2/18 2/19

  20. Local Loops - Circuitry • Electrical Modem/Computer interfaces (DCE/DTE interface): • RS232C (CCITT: V.24 standard): serial interface, 25 pin connectors including lines for in/out bit stream, control, synchronization, clock. Null modem - crossed transmit/receive data lines for computer/computer (no modem) interface. • RS232 variations ( RS422, RS423, RS 449 - difference in ground lines for the signals) • Optical interfaces - for arising new telecom services • FTTH (Fiber To The Home) - straight but expensive • FTTC (Fiber To The Curb) - fiber to junction box (for group of users); end connection[s] is twisted pair or coax. 2/18

  21. Multiplexing • Multiplexing by Physical layer means splitting off (and thus sharing) the media transmission capacity between multiple users/processes/channels • 2 methods: • multiplexing by frequency - FDM. Frequency spectrum is divided into smaller bands which are assigned to each active user. Example: Radio broadcasting stations over fixed frequency channel (static assignment/multiplexing) • multiplexing by time - TDM. The channel time is split into [small] even periods, that are repeatedly assigned to a fixed (for given instant) list of active users/channels - in round-robin manner

  22. Frequency Division Multiplexing • Single phone voice-grade channel seizes 3kHz band (sound transmission in band 50/3000 Hz) • By FDM 4kHz band is allocated for each channel (3kHz signal + 2*500Hz separation bands) • The standard FDM: group of 12 channel bands * 4kHz placed in band 60108kHz (60 + 12*4 = 108) - . Option: second group in the band 1260kHz. • Overlapping between the adjacent channels (although the separation bands) because of nonperfect filtration. • Mastergroup = 5 supergroups = 25 groups = 300 vice-grade channels. 2/24

  23. Frequency Division Multiplexing • FDM variation used in fiber optics: WDM - Wavelength Division Mux. • Same physical principle: junction of two light transmitting fiber by a diffraction grid (e.g. optic prism) in one fiber transmitting the combined (two wavelengths/frequencies) signal to a common end point. The signal separation at the end point by diffraction grid. • WDM properties: • passive system (no frequency/wavelength shifting) • reliability • WDM based switches - light switching is harder then electricity switching. 1:n light switches are either of type “Passive star” (for n~102) or some kind of optical tunable filters like interferometrs (for n~106) 2/25 [24]

  24. [Interferometers] • Interferometers isolate a specific portion of the electromagnetic spectrum. Unlike prism or grid monochromators, interferometers are not dispersive instruments, but use interference to selectively transmit a certain wavelength. Two interferometer designs: Schematic of a Mach-Zender interferometer Schematic of a Fabry-Perot etalon

  25. WDM • WDM is the technique for fiber optics that uses a similar principle than FDM, except the channel discriminator is a wavelength instead of time. • Each input data stream is converted into separate wavelength. Each application creates a channel that operates at a separate wavelength. After that, the WDM system combines and at the same time transmits the channels through the same optical fiber. Since each wavelength is completely isolated from the other, protocols can be mixed within the same link. • This is a great benefit to WDM, since FDM creates high-speed time slots in the form of frames or cells, which allow multiple applications to share the channel only if all applications are of the same platform.

  26. WDM • Stable WDM systems today multiplex just a few wavelengths over fiber to extend capacity. However, some systems can now increase a fiber's capacity by multiplexing 32 wavelengths and more. Still newer multiplexers entering the market this year promise 40 to 80 discrete optical channels. • WDM is a costly solution, although it works with the existing fiber infrastructure, since it requires additional equipment like transmitters and optical amplifiers for each wavelength. That equipment is quite expensive nowadays. • The WDM market is predicted to increase dramatically over the next ten years as telephone companies, cable television and other carriers maximize their optical-fiber network capacity.

  27. WDM FDDI FDDI • Besides the telephone system trunks WDM is suitable for future LAN network environment: ATM ATM ETHERNET ... ... ETHERNET WDM WDM TOKEN RING TOKEN RING FIBER CHANNEL FIBER CHANNEL

  28. Time Division Multiplexing • Applicable only in digital electronics (while FDM is applicable only for analog data) - i.e. TDM condenses just digital data for the telephone company trunks. • Digitizing the analog signal by codec (Coder-DECoder). • PCM - Pulse Code Modulation • In the telephone systems PCM is performed with rate 8000S-1 samples in periods (i.e. 8kHz) of 125mS. According Niquist’s theorem 8kHz = 2*4kHz (telephone channel bandwidth - for avoiding information losses and information overload).

  29. Pulse Code Modulation • T1-carrier Method (USA, Japan): multiplexes 24 voice channels in Round-robin for each 125mS period [By data communication the 24th channel is reserved for a synchronization pattern]. • The instant state of each channel is coded by 7b + 1b control. • Transmission rate per each channel is 64kb/S (=8000*8b; 56kb/S data + 8kb/S control) • Frame size 193b (=24*8b + 1b framing code) • Transmission rate per multiplexed channel 1.544Mb/S (=193b*8000) • E1-carrier Method: multiplexes 32 channels (30 data + 2 control/synchronization) in Round-robin for each 125mS period . • Transmission rate per multiplexed channel 2.048Mb/S (=32ch*8b*8000) 2/26

  30. Pulse Code Modulation • Differential PCM - codes not the amplitude but the difference between the two latest amplitudes. Differences of 7b-coded magnitude (0127) can be coded with less bits (i.e. 5b code difference 0  32 - 25% of the maximum of the magnitude for single sampling step). • Delta PCM - Differential PCM modification - 1b code for the difference: “0” means magnitude[t] = magnitude[t-1]-1; “1” means magnitude[t] = magnitude[t-1]+1. • Possibility for delay of the modulated signal to the analog original. • Predictive PCM - Delta PCM modification - magnitude[t] = magnitude[t-1, t-2,...] 2/27

  31. Hierarchy of the Time Division Multiplexing • Higher order multiplexing of the sequential bits of T1 channels - Round-robin for several T1 channels • USA standard hierarchy: 24ch  T1 4*T1T2 6*T2T3 7*T3T4 1.544Mb/S 6.312Mb/S 37.400Mb/S 260.500Mb/S • CCITT (ITU-T) standard hierarchy: 32ch  T1 4*T1T2 4*T2T3 4*T3T4 4*T4T5 2.048Mb/S 8.848Mb/S 34.304Mb/S 139.264Mb/S 565.148Mb/S 2/28 Known as PDH (Plesiochronous Digital Hierarchy). Coax, fiber and radio links are applied in PDH connections over 2 Mbps

  32. SONET Standard • SONET (Synchronous Optical NETwork) - standard for optical long-distance telephone traffic (CCITT [ITU-T] equivalent: SDH - Synchronous Digital Hierarchy) • SONET is the North American standard for synchronous multiplexing that corresponds to SDH • ITU-T has based the standardization work of SDH on SONET standards • In principle, SDH is an international extension of SONET • The terminology in SDH and SONET is similar and in some cases identical [33]

  33. SDH • Synchronous Digital Hierarchy (SDH) standardized by ITU-T has several improvements compared to the PDH: • Direct pointer based access to data without need of layers of hierarchical branching equipment • Centralized remote control of network elements • Increased use of the physical network • Shorter delivery time for leased lines • SDH is a standardized multiplexing hierarchy for both plesiochronous and synchronous purposes. • The multiplexing levels in the SDH can be divided into two groups: • multiplexing levels (virtual containers, VC) and line signal levels • (synchronous transport modules, STM).

  34. SONET Standard • SONET defines • internetworking parameters: wavelength / frequen-cies, timing and framing • Operations, Administrations and Maintenance (OAM) support - tools and procedures. • SONET is synchronous system with one master clock and TDM data congestion method (i.e. one carrier frequency in entire bandwidth) standard bit lasting varies 10-7%. • SONET is channel switching model. [ATM is cell switching model with asynchronous arrivals of cells].

  35. SONET System Model • SONET system structure: fiber-connected multiplexers, switches and repeaters. • Sections, lines and paths. • Physical topology is mesh; logical topology is ring (any path). • SONET frame: 810B/6480b frame, frame interval 125mS i.e. 8000frames/S = 6.48MB/S = 51.84Mb/S channel speed - STS-1 (Synchronous Transport Signal-1). • Each SONET frame contains: • Header of Section overheadfollowed byLine overheadandPath overhead. • Payload [SPE (Synchronous Payload Envelope)] - user data (might be empty!) pointed by the 3 leading bytes of the Line overhead. (SPE contains 9B of Path overload spread by each 87B intervals). 2/29 ? Why Path overload is aligned with SPE and Section/Line overloads are aligned with the frames generated and read at the start/ end of the section generated and read at the start/ end of the line 2/30

  36. SONET Multiplexing • 1st stage: The standard T1, 2, 3 input streams are converted to standard STS-1 channel (rounded to the STS-1 rate of 51.84 Mb/S). The input channels to a multiplexer are called tributaries. Multiplexing is Byte-level Round-robin of all the tributaries. Further steps of multiplexing: • 3 of STS-1 tributaries are multiplexed to STS-3 155.52 Mb/S channel rate • 4 of STS-3 tributaries are multiplexed to STS-12 622.08 Mb/S channel rate • 4 of STS-12 tributaries are multiplexed to STS-48 2.4883 Gb/S channel rate • 2nd stage: scrambling (disarranging the components of the transmission in order to make unintelligible to interception and avoid long sequences of “0” or “1” states to run out of the synchronizing clock; back arranging based on header information) • 3rd stage: Electric-to-optic conversion to optical carrier signal denoted OC-n. (when carries STS-n channel) E.g. OC-3 (starting), OC-9, -12, -36, -48. 2/31 SONET and SDH multiplex data rates 2/32

  37. SONET Physical Layer • 4 sublayers architecture: • Photonic sublayer specifies the physical properties of the light rays and fiber guides. • Section sublayer transmits standard frames between each two consecutive repeaters by amplifying and regeneration of the single bits. • Line sublayer multiplexes several tributaries in a channel and demultiplexes it in the next consecutive multiplexer. Repeaters are transparent to this sublayer. • Path sublayer organize end-to-end connection between source and destination multiplexers. 2/33

  38. Switching Methods - Circuit Switching • Circuit switching - establishment of temporary dedicated physical connection from-end-to-end before and during the whole transfer. The connection exists: • from the moment of realization of the transmission initiative • till the moment of request for end of the transfer by either of the parties (or for some technical reason/problem). • Structure of circuit switching: user device (phone/computer…); end switching office; hierarchy of intermediate switching offices. • Time diagram of the processes by circuit switching: • propagation time for each signal (in copper 5mSm-6) • request/acknowledge signals before setting up the connection (by phones ack={signal, vabusy}); request delayed by: • time for propagation • time for finding outgoing trunks in the switching offices • Dedicated channel: no possibility of interruptions and clipped signal until the end of the connection 2/34 2/35

  39. Switching Methods – Connectionless Switching • Message switching: transmission of arbitrary long buffered blocks - “messages” - to the next switching office which is actually a router. • Time diagram of the processes by message switching: • propagation time for each message • queuing delay in the consecutive routers (interactive communications (e.g. phone calls) have priority over non-interactive ones  undefined delays for intercomputer communications; possibility for perceivable delays by interactive communications. • Packet switching: transmission of small fixed size buffered blocks - “packets”. Demonopolization of the channels capacity • Time diagram of the processes by packet switching: • propagation time for each packet (shorter than by the message sw.) • channel congestion, reduced delay; possible perceivable brakes in the interactive communications 2/34b 2/35b 2/35c

  40. Connection-oriented vs. Con-nectionless [Packet] Switching

  41. Switching Systems - Hierarchy • Basically tree structure of hierarchy levels (AT&T  5 levels) but: • the nearer the root - the denser connections in that level (up to full graph of connections) • interlevel shortcuts (“direct trunks) for overloaded routes • Service Access Points are at the lowest hierarchy level (at tree leaves) 2/37

  42. Switching Systems - Crossbars • nxn (in parallel computers: nxm) crossbar (“crosspoint”) connects n inputs full duplex to n outputs - one stage switch. • The matrix of elementary switches has n2 components. • The elementary switches are automatically controlled in manner : in:om requires im:on;no impossible combinations (full graph of connectivity) • Delays • by switching - hardly depends on hardware; down to mS • by signal propagation - no delay (commutation independence) 2/38

  43. Switching Systems - InterLAN Crossbars

  44. Switching Systems - Multistage Switches • Multistage switches consist of s stages • Each stage i consists of of ni independent n:k (e.g. 2:2, 4:4) crossbar elements (CE) • Static interstage connection scheme (usually so called Banyan switching) • NO intrastage and interstage loops • Less hardware than crossbars: 8:8 crossbar needs 64 elementary switches; 8:8 Banyan multistage needs 12 CE by 4 elementary switches = 48, BUT • Possible rejected connections • Delays: • by switching = delay for one switching element • by signal propagation = delay for one switching element x s

  45. Switching Systems - Time Division Switching • Components: n-input multiplexer; n-slots interchange buffer with associated n-pointers mapping table and n-output demultiplexer • Switching method: • Round robin scanning (multiplexing) of n input lines and storing the content in the indexed buffer • Reordering the contents of the buffer according to the scheme in the mapping table in n steps [for double space buffers: in one step  input and output process overlap - “conveyer”] • Output the contents of the reordered buffer to n serial output lines (demultiplexing) • Delays: • by reordering: for non-conveyered switching the delay depends on n; for conveyered switching the delay depends on the R/W RAM cycle of the buffer 2/40

  46. Electromagnetic spectrum

  47. Radio Transmission

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