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Lecture-1 Prepared by: Abdul Hasib Lecture, IICT BUET

Lecture-1 Prepared by: Abdul Hasib Lecture, IICT BUET. Frequency, Spectrum and Bandwidth. Time domain (examining the signal over time): Continuous signal - signal with no breaks or discontinuities Discrete signal - signal with a finite number of values

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Lecture-1 Prepared by: Abdul Hasib Lecture, IICT BUET

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  1. Lecture-1 Prepared by: Abdul Hasib Lecture, IICT BUET

  2. Frequency, Spectrum and Bandwidth • Time domain (examining the signal over time): • Continuous signal - signal with no breaks or discontinuities • Discrete signal - signal with a finite number ofvalues • Amplitude - the instantaneous value of a signal • Frequency - inverse of the period in cycles per second,Hertz • Phase - measure of relative position in time within a singleperiod

  3. Frequency, Spectrum and Bandwidth Digital signal Audio signal • Frequency Domain (signal viewed as a function of frequency): • any signal is made up of components atvarious frequencies, each sinusoid • Spectrum- the range of frequencies in a signal • Absolute bandwidth - is the width of the spectrum (fn - f1) where, fn is largest frequency in signal and f1 is the smallest

  4. Signal Strength • Effective bandwidth (bandwidth) - width of spectrum containingmost of the energy in the signal • Signal strength gain, losses and relative levels are expressed indecibels: • Decibel measuredifference in two power levels:

  5. Communication mode • Point-to-point - if direct link is shared between only two • devices • Multipoint - if direct link shared between multiple devices • Simplex- one way transmission (commercial radio/TV) • Half-duplex - one way transmission at a time, endpoints take • turns • Full-Duplex - simultaneous two way transmission • » NOTE: These are US (ANSI) definitions, in Europe (CCITT) • simplex refers to half-duplex and duplex to full-duplex

  6. Data versus signal • Data: Convey meaning within a computer (stored in files)  Need to be converted into a signal before transfer • Signals: Electric or electromagnetic encoding of data Networks and communication systems transmit signals • Data and signal can be analog or digital • Analog information can be audio or video • Digital information is binary • Issues related to the transmission of signals • Impairments (also transmission flaws) • Capacity of the media

  7. AnalogtoDigitalConversion : Why? • Digital Technology : a. VLSI, LSI • b. lower cost • Data Integrity : Use repeaters instead of amplifiers • => Noise not accumulated, i.e., transmit data • for longer distance • Capacity utilization : More easily to multiplex digital data than analog • Security and privacy • Integration : integrate voice , data ( when digitize analog data)

  8. Modulation and Encoding schemes Modulation: Encoding:

  9. Conversion • Encoding: • Digital data to digital signal : less complex and less expensive equipment than analogmodulation equipment • Analog data to digital signal : To use the modern digital transmission and switchingequipment • Modulation: • Digital data to analog signal : Some transmission media can propagate analog signals only. Example: fibre , wire • Analog data to analog signal : • 1. Transmit baseband signal over wire transmission(Microwave) • => Low frequency baseband means few kilometer antenna !!! • 2. shift baseband signals of several voice channel (FDM)

  10. Digital data , Digital signals • Factors to improve receiving data: • Decrease data rate => decrease error rate • Increase S/N ratio => decrease bit error rate • Increase bandwidth => Increase data rate • Digital signal encoding formats: • Nonreturn-to-zero-level (NRZ-L) • Nonreturn-to-zero Interted (NRZI) • Bipolar-AMI • Manchester • Differential Manchester etc.

  11. Digital signal encoding formats

  12. Analog Data, Digital Signals • Codec : Coder – decoder • Device to convert analog to digitaland digital to analog at • transmitting and receiving side • Sampling Theorem : “If a signal f(t) is sampled at a regular intervals oftimeand at a rate higher than twice the highest significant signal frequency, then thesamples contains all the information of theoriginal signal.” • example: voice data < 4000Hz, then 8000 samples/sec (Nyquist formula) • Data Rate: • C = capacity or data transfer rate in bps • B = bandwidth (in hertz) • M = number of possible signaling levels

  13. Analog to Digital Conversion (PCM)

  14. Modulation • The process of encoding source data onto a carrier signal with frequency f. • Three basic modulation technique: • -> Amplitude • -> Frequency • -> Phase • Baseband signal : • Input signal (digital or analog) to modulator.

  15. Digital data, Analog signals • Transmitting digital data through public telephonenetwork (0.3 - 3.4 KHz) • Example : Modem (modulator, demodulator) • Digital Modulation techniques: • 1. Amplitude-Shift Keying (ASK): • amplitude of carrier freqency vary betwwen two level • susceptible to sudden gain changes and is ratherinefficient technique • up to 1200 bps on voice-grade lines

  16. Digital Modulation techniques: • 2. Frequency-Shift Key (FSK) • A cos(2 f1 t + Qc) binary 1 • s(t) = • A cos(2  f2 t + qc) binary 0 • f1 and f2 are carrier frequency • Used in early low bit modem

  17. E E 2 M= Digital Modulation techniques • 3. Phase Shift Key (PSK) • The phase of the carrier signal is shifted torepresent data • Fig: Phase coherent PSK • Zero : represented by a signal with the same phase of the preceding one • One: represent by signal of opposite phase (180° shift)to thepreceding one • Disadvantage: - Reference carrier signal phase is required at the recever • - Bit rate= Signalling rate

  18. Figure 7.2: amplitude modulation of a sinusoidal carrier by the baseband PAM signal Analog Data, Analog Signals • Techniques: • AM, FM, and PM • Amplitude Modulation

  19. 1 r W- W 0 f 0 fc - fc - W - fc - fc + W fc - W fc + W Amplitude-modulation. Figure: Spectra of (a) baseband and (b) amplitude-modulated signal.

  20. Analog Modulation Techniques

  21. Simple switching network end node Network node -- provide routing Purpose: - provide interconnection between all the nodes on a network without the need for single connections between each pair of nodes

  22. Digital Telephone Networks, Mobile Networks • Circuit switched of fixed bit rate (n x 64 kbps / 13 kbps) • Connection oriented

  23. Public switched telephone network (PSTN)

  24. Circuit Switching (CS) • Communication in which a dedicated communications path is established between two devices through one or more intermediate switching nodes • Dominant in both voice and data communications today (PSTN is a circuit-switched network) • Relatively inefficient (100% dedication even without 100% utilization) • Three stages: • Circuit establishment • Transfer of information • Circuit disconnect

  25. Circuit-Switching Stages • Circuit establishment • Based on routing information • Transfer of information • Point-to-point from endpoints to node • Internal switching among nodes • Usually a full-duplex connection throughout • Circuit disconnect • Signal initiated by one of the stations and propagated to used nodes to de-allocate the dedicated resources

  26. Example: space division switch • The interconnection of network consists of a rectangular matrix of cross-points

  27. Multiplexing • Multiplexing provides a mechanism to share the use of a common channel or circuitby two or more devices. • Multiplexing minimizes number of transmission lines.

  28. Type of multiplexer • FDM (Frequency Division Multiplex) • TDM (Time Division Multiplex) • WDM (Wave Length division Multiplex) • CDM (Code division Multiplex)

  29. Frequency Division Multiplex • FDM is a broadband analog transmission technique. • Each data signal is modulatedonto a carrier with a different frequency • All signal travel simultaneously over achannel.

  30. Time Division Multiplex • TDM is a base-band technique. • Individuals circuit are identified by their position ina stream. • Analog inputs are digitized using PCM • Digitized information areinsert into the pre-allocated, fixed timing called timed slot.

  31. Wave Length division Multiplex • Used for photonic communication. • Realised by laser modulation of different wave length. • Superposition of optical signals of different channels on one fibre

  32. Code division Multiplex • Each channel uses a different code sequence for modulation • Codes are mutually orthogonal • Spread spectrum technique • Multiplexing is acheived by superposition of the products of • the signal with their code.

  33. Digital Carrier Systems • T-carrier • North America,Japan • E-carrier • Europe,South America • SONET/SDH • world-wide new standard

  34. E1-frame 30 voice channels+2 control channels E1 bit rate :(32x8 bit)/125 microsec =2.048Mbps

  35. Transfer Modes • The type of switching depends on connectionnature. • Transfer modes: • Circuit Switching (CS) • Packet switching • Problems of Circuit Switch: • Collisions: when more than one inputs are destined for the same output. • Blocking:when the progress of one message through the network is stopped by a message that is not destined for the same output.

  36. Local Area Networks (LAN) • Connectionless

  37. Internet

  38. Alternate Routing

  39. Packet-Switching • Data is broken into packets, each of which can be routed separately • Datagram • Connectionless service • Individual packets can follow different routes • Packets can arrive out of sequence and are reassembled on the destination host.

  40. Packet Switching • Virtual Circuit • Establishes an end-to-end circuit between the sender and receiver • All packets for that transmission take the same route over the virtual circuit • Similar to circuit switching, but the circuit is not dedicated

  41. Packet-Switching Networks:Pros and Cons • Advantages: • Better line efficiency, • Signals can always be routed • Prioritization option • Disadvantages: • Transmission delay in nodes, • Variable delays can cause jitter • Extra overhead for packet addresses

  42. Example: Virtual Connection

  43. Development of Internet Hosts and Web

  44. Internet History • Arpanet • 1960s : studies of packet switching • 1980-1983: Introduction of TCP/IP • 1989: first proposal for Web (Tim Berners, Robert Cailliau) • 1994: Internet known to public • Everything over IP, IP over everything

  45. Arpanet History

  46. Growth • Number of users • Traffic demand per application • Web item sizes (imazes, java applets, audio, video) • New applications • Access line bit rate • Number of servers • Penetration into leisure / entertainment sector

  47. Worldwide Ranks

  48. Challenges • Connectivety: • connecting various systems to support communication among disparate technologies • reliability • network management: • must provide centralized support and troubleshooting capabilities • configuration, security, performance • flexibility: • to change with new demands.

  49. Standardization Body • create formal standards by: • organizing ideas • discussing the approach • developing draft standards • voting on draft • formally releasing the completed standard to the public • Internet Activities Board (IAB): • discuss issues pertinent to the Internet and set Internet policies through decisions and task forces. The IAB designates some Request For Comments (RFC) documents as Internet standards, including Transmission Control Protocol/Internet Protocol (TCP/IP) and the Simple Network Management Protocol (SNMP).

  50. Standardization Body

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