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- 2. To be transmitted,data must be transformed to electromagnetic signals. 2
- 3. • Digital signal –discrete, discontinuous voltage pulses – each pulse is a signal element – binary data encoded into signal elements Digital Data, Digital Signal 3
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- 5. All signal levelsare on one side of the time axis - either above or below NRZ - Non Return to Zero scheme is an example of this code. The signal level does not return to zero during a symbol transmission. Scheme is prone to baseline wandering and DC components. It has no synchronization or any error detection. It is simple but costly in power consumption. Unipolar 5
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- 7. The voltages areon both sides of the time axis. Polar NRZ scheme can be implemented with two voltages. E.g. +V for 1 and -V for 0. There are two versions: ◦ NZR - Level (NRZ-L) - positive voltage for one symbol and negative for the other ◦ NRZ - Inversion (NRZ-I) - the change or lack of change in polarity determines the value of a symbol. E.g. a “1” symbol inverts the polarity a “0” does not. Polar - NRZ 7
- 8. Polar NRZ-L andNRZ-I schemes 8
- 9. In NRZ-L thelevel of the voltage determines the value of the bit. In NRZ-I the inversion or the lack of inversion determines the value of the bit. 9
- 10. NRZ-L and NRZ-Iboth have a DC component problem and baseline wandering, it is worse for NRZ-L. Both have no self synchronization &no error detection. Both are relatively simple to implement. 10
- 11. The Return toZero (RZ) scheme uses three voltage values. +, 0, -. Each symbol has a transition in the middle. Either from high to zero or from low to zero. This scheme has more signal transitions (two per symbol) and therefore requires a wider bandwidth. No DC components or baseline wandering. Self synchronization - transition indicates symbol value. More complex as it uses three voltage level. It has no error detection capability. Polar - RZ 11
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- 13. Manchester coding consistsof combining the NRZ-L and RZ schemes. ◦ Every symbol has a level transition in the middle: from high to low or low to high. Uses only two voltage levels. Differential Manchester coding consists of combining the NRZ-I and RZ schemes. ◦ Every symbol has a level transition in the middle. But the level at the beginning of the symbol is determined by the symbol value. One symbol causes a level change the other does not. Polar - Biphase: Manchester and Differential Manchester 13
- 14. Polar biphase: Manchesterand differential Manchester schemes 14
- 15. Comparison of analogand digital signals 15
- 16. In data communications,we commonly use periodic analog signals and nonperiodic digital signals. 16
- 17. PERIODIC ANALOG SIGNALSPERIODICANALOG SIGNALS Periodic analog signals can be classified as simple or composite. APeriodic analog signals can be classified as simple or composite. A simple periodic analog signal, a sine wave, cannot be decomposedsimple periodic analog signal, a sine wave, cannot be decomposed into simpler signals. A composite periodic analog signal isinto simpler signals. A composite periodic analog signal is composed of multiple sine waves.composed of multiple sine waves. Sine Wave Wavelength Time and Frequency Domain Composite Signals Bandwidth 17
- 18. Frequency and periodare the inverse of each other. 18
- 19. Units of periodand frequency 19
- 20. A composite periodicsignal 20
- 21. The bandwidth ofa composite signal is the difference between the highest and the lowest frequencies contained in that signal. 21
- 22. TRANSMISSION IMPAIRMENTTRANSMISSION IMPAIRMENT Signalstravel through transmission media, which are not perfect.Signals travel through transmission media, which are not perfect. The imperfection causes signal impairment. This means that theThe imperfection causes signal impairment. This means that the signal at the beginning of the medium is not the same as the signal atsignal at the beginning of the medium is not the same as the signal at the end of the medium. What is sent is not what is received. Threethe end of the medium. What is sent is not what is received. Three causes of impairment are attenuation, distortion, and noise.causes of impairment are attenuation, distortion, and noise. 22
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- 24.
- 25. In networking, weuse the term bandwidth in two contexts. ❏The first, bandwidth in hertz, refers to the range of frequencies in a composite signal or the range of frequencies that a channel can pass. ❏The second, bandwidth in bits per second, refers to the speed of bit transmission in a channel or link. 25
- 26. • has transitionin middle of each bit period • transition serves as clock and data • low to high represents one • high to low represents zero • used by IEEE 802. Manchester Encoding 26
- 27. midbit transition isclocking only transition at start of bit period representing 0 no transition at start of bit period representing 1 ◦ this is a differential encoding scheme used by IEEE 802.5 Differential Manchester Encoding 27
- 28. • phase ofcarrier signal is shifted to represent data • binary PSK – two phases represent two binary digits • differential PSK – phase shifted relative to previous transmission rather than some reference signal Phase Shift Keying 28
- 29. • bandwidth – ASK/PSKbandwidth directly relates to bit rate – multilevel PSK gives significant improvements • in presence of noise: – bit error rate of PSK and QPSK are about 3dB superior to ASK and FSK – for MFSK & MPSK have tradeoff between bandwidth efficiency and error performance Performance of Digital to Analog Modulation Schemes 29
- 30. • digitization isconversion of analog data into digital data which can then: – be transmitted using NRZ-L – be transmitted using code other than NRZ-L – be converted to analog signal • analog to digital conversion done using a codec – pulse code modulation – delta modulation Analog Data, Digital Signal 30
- 31. • Amplitude Modulation •Frequency Modulation • Phase Modulation Analog Modulation Techniques 31
- 32. • modulate carrierfrequency with analog data • why modulate analog signals? – higher frequency can give more efficient transmission – permits frequency division multiplexing (chapter 8) • types of modulation – Amplitude – Frequency – Phase Analog Data, Analog Signals 32
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- 34. Bit rate andbit interval 34
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- 37. • NIC providesthe physical interface between computer and cabling. • It prepares data, sends data, and controls the flow of data. It can also receive and translate data into bytes for the CPU to understand. • The following factors should be taken into consideration when choosing a NIC: 1. - Preparing data 2. - Sending and controlling data 3. - Configuration 4. - Drivers 5. - Compatibility 6. - Performance 37 Network Interface Card (NIC)
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- 39. 39 IRQ COMMON USE 0Timer 1 Keyboard 2 Secondary IRQ controller 3 COM 2 and 4 4 Com 1 and 3 5 LPT2 or MIDI device 6 Floppy disk drive 7 LPT1 8 Real-time clock 9 Free or sound card 10 Free or primary SCSI adapter 11 Free or secondary SCSI adapter 12 PS/2 Mouse 13 Floating-Point processor 14 Primary hard disk controller 15 Free or secondary hard disk controller
- 40. Classes of TransmissionMediaClasses of Transmission Media 40
- 41. GUIDED MEDIAGUIDED MEDIA Guidedmedia: Are those that provide a conduit from oneGuided media: Are those that provide a conduit from one device to another, include twisted-pair cable, coaxialdevice to another, include twisted-pair cable, coaxial cable, and fiber-optic cable.cable, and fiber-optic cable. 41
- 42. Coaxial Cable • Wasthe predominant form of network cabling • Shielding: protective layer(s) wrapped around cable to protect it from external interference • Less susceptible to interference and attenuation than twisted-pair, but more susceptible than fiber-optic 42
- 43.
- 44. • Ethernet’s beginningsare in coaxial cable – First, it was run on a very thick, rigid cable, usually yellow, referred to as thicknet (10Base5) – Later, a more manageable coaxial cable called thinnet (10Base2) was used • 10Base5 is an IEEE designation – 10 Mbps – Baseband – Maximum segment length is 500 meters The Use of Coaxial Cable for Ethernet 44
- 45. Coaxial Cable inCable Modem Applications Coaxial cable in LANs has become obsolete The standard cable (75 ohm, RG-6; RG stands for “radio grade”) that delivers cable television (CATV) to millions of homes nationwide is also being used for Internet access 45
- 46.
- 47. • 10BaseT – Maximumlength is 100 meters • UTP is now the most popular form of LAN cabling • The UTP cable used for networking usually includes one or more pairs of insulated wires • UTP specifications govern the number of twists per foot (or per meter), depending on the cable’s intended use • UTP is used for telephony, but requirements for networking uses differ from the telephony ones Unshielded Twisted Pair (UTP) 47
- 48. UTP cabling israted according to a number of categories devised by the TIA and EIA; since 1991, ANSI has also endorsed these standards ◦ ANSI/TIA/EIA 568 Commercial Building Wiring Standard for commercial environments includes: Category 1 (voicegrade) Category 2: up to 4 Mbps Category 3: up to 10 Mbps (16 MHz) Category 4 (datagrade): up to 16 Mbps (20 MHz) Category 5: up to 100 Mbps (100 MHz) Category 5e: up to 1000 Mbps (100 MHz) Category 6: up to 1000 Mbps (200 MHz) UTP Cabling Categories 48
- 49. • Shielding reducescrosstalk and limits external interference – Usually, wiring includes a wire braid inside cladding or sheath, and a foil wrap around each wire pair • Enables support of higher bandwidth over longer distances than UTP – No set of standards for STP corresponds to the ANSI/TIA/EIA 568 Standard, yet it’s not unusual to find STP cables rated according to those standards – Uses two pairs of 150 ohm wire (defined by the IBM cabling system), and was not designed to be used in Ethernet applications, but it can be adapted to Shielded Twisted Pair (STP) 49
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- 51. One of theskills required of a network technician is making a twisted-pair patch cable To do this, you need: ◦ Wire cutters or electrician’s scissors ◦ Wire stripper ◦ Crimp tool ◦ RJ-45 plugs There are two standards for the arrangement of wires: TIA/EIA 568A and TIA/EIA 568B ◦ You must stick to one throughout your network 51 Making Twisted-Pair Cable Connections
- 52. Making Twisted-Pair CableConnections (continued) 52
- 53. Making Twisted-Pair CableConnections (continued) 53
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- 57. • Installation offiber-optic networks is more difficult and time-consuming than copper media installation • Connectors and test equipment are considerably more expensive than their copper counterparts • Two types – Single-mode: costs more and generally works with laser-based emitters, but spans the longest distances – Multimode: costs less and works with light emitting diodes (LEDs), but spans shorter distances Fiber-Optic Cable (continued) 57
- 58. Radio, satellite transmissions,and infrared light are all different forms of electromagnetic waves that are used to transmit data. •LANs use radio waves •WANs use microwave signals Wireless Media 58
- 59. •Land-based, line-of-sight transmission •Approximately20-30 miles maximum between towers •Transmits data at hundreds of millions of bits per second •Popular with telephone companies and business to business transmissions Terrestrial Microwave 59
- 60. Similar to terrestrialmicrowave except the signal travels from a ground station on earth to a satellite and back to another ground station. Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, and HEO). Satellite Microwave 60
- 61. Data Communications andComputer Networks Chapter 3 61
- 62. •LEO - LowEarth Orbit - 100 miles to 1000 miles. Used for pagers, wireless e-mail, special mobile telephones, spying, videoconferencing. •MEO - Middle Earth Orbit - 1000 to 22,300 miles. Used for GPS and government. •GEO - Geosynchronous Orbit - 22,300 miles. Used for weather, television, and government operations. •HEO – Highly Elliptical Orbit A fourth type of orbit used by the military for spying and by scientific organizations for photographing celestial bodies. When satellite is far out into space, it takes photos. When satellite is close to earth, it transmits data. Satellite Microwave 62
- 63. Special transmissions thatuse a focused ray of light in the infrared frequency range. Very common with remote control devices, but can also be used for device-to-device transfers, such as PDA to computer. Bluetooth is a Radio Frequency specification for short-range, point-to-multipoint voice and data transfer. Bluetooth can transmit through solid, non-metal objects. Its typical link range is from 10 cm to 10 m, but can be extended to 100 m by increasing the power. Infrared & Bluetooth Transmissions 63
- 64. This technology transmitsdata between workstations and local area networks using high speed radio frequencies. Current technologies allow up to 54 Mbps data transfer at distances up to hundreds of feet. Wireless LAN (IEEE 802.11) 64
- 65. FACTORS UTP STPCOAXIAL FIBEROPTICS Cost Lowest Moderate Moderate High Installation Easy Fairly easy Fairly easy Difficult Bandwidth 1-155Mbps 1-155Mbps 2-10 Mbps 2 Gbps Capacity per Segment (typically 10 Mbps) (typically 16 Mbps) (typically 10 Mbps) (typically 100Mbps) Node Capacity per Segment 2 2 30 (10base2) 100(10base5) 2 Attenuation High (range of hundreds of meters) High (range of hundreds of meters) lower(range of few kilometers) Lowest(range of tens of kilometers) EMI Most Vulnerable to EMI and eavesdropping Less Vulnerable than UTP but still vulnerable to EMI and eavesdropping Less Vulnerable than UTP but still vulnerable to EMI and eavesdropping Not effected by EMI or eavesdropping Characteristics of Cable Media 65
Editor's Notes
- #4 Encoding - Digital data to digital signals: A digital signal is a sequence of discrete, discontinuous voltage pulses, as illustrated in Stallings DCC8e Figure 3.13. Each pulse is a signal element. Binary data are transmitted by encoding each data bit into signal elements. In the simplest case, there is a one-to-one correspondence between bits and signal elements. More complex encoding schemes are used to improve performance, by altering the spectrum of the signal and providing synchronization capability. In general, the equipment for encoding digital data into a digital signal is less complex and less expensive than digital-to-analog modulation equipment
- #27 There is another set of coding techniques, grouped under the term biphase, that overcomes the limitations of NRZ codes. Two of these techniques, Manchester and differential Manchester, are in common use. In the Manchester code, there is a transition at the middle of each bit period. The midbit transition serves as a clocking mechanism and also as data: a low-to-high transition represents a 1, and a high-to-low transition represents a 0. Biphase codes are popular techniques for data transmission. The more common Manchester code has been specified for the IEEE 802.3 (Ethernet) standard for baseband coaxial cable and twisted-pair bus LANs.
- #28 In differential Manchester, the midbit transition is used only to provide clocking. The encoding of a 0 is represented by the presence of a transition at the beginning of a bit period, and a 1 is represented by the absence of a transition at the beginning of a bit period. Differential Manchester has the added advantage of employing differential encoding. Differential Manchester has been specified for the IEEE 802.5 token ring LAN, using shielded twisted pair.
- #29 In PSK, the phase of the carrier signal is shifted to represent data. The simplest scheme uses two phases to represent the two binary digits (Figure 5.7c) and is known as binary phase shift keying. An alternative form of two-level PSK is differential PSK (DPSK). In this scheme, a binary 0 is represented by sending a signal burst of the same phase as the previous signal burst sent. A binary 1 is represented by sending a signal burst of opposite phase to the preceding one. This term differential refers to the fact that the phase shift is with reference to the previous bit transmitted rather than to some constant reference signal. In differential encoding, the information to be transmitted is represented in terms of the changes between successive data symbols rather than the signal elements themselves. DPSK avoids the requirement for an accurate local oscillator phase at the receiver that is matched with the transmitter. As long as the preceding phase is received correctly, the phase reference is accurate.
- #30 In looking at the performance of various digital-to-analog modulation schemes, the first parameter of interest is the bandwidth of the modulated signal. This depends on a variety of factors, including the definition of bandwidth used and the filtering technique used to create the bandpass signal. For ASK & PSK the bandwidth is directly related to the bit rate. With multilevel PSK (MPSK), significant improvements in bandwidth can be achieved. Nothing has yet been said of performance in the presence of noise. Stallings DCC8e Figure 5.4 shows the bit error rate plotted as a function of the ratio Eb/N0. As that ratio increases, the bit error rate drops. Further, DPSK and BPSK are about 3 dB superior to ASK and BFSK. Stallings DCC8e Figure 5.13 shows the same information for various levels of M for MFSK and MPSK. There is an important difference. For MFSK, the error probability for a given value Eb/N0 of decreases as M increases, while the opposite is true for MPSK. On the other hand, comparing Equations (5.10) and (5.11), the bandwidth efficiency of MFSK decrease as M increases, while the opposite is true of MPSK. Thus, in both cases, there is a tradeoff between bandwidth efficiency and error performance: an increase in bandwidth efficiency results in an increase in error probability.
- #31 In this section we examine the process of transforming analog data into digital signals. Analog data, such as voice and video, is often digitized to be able to use digital transmission facilities. Strictly speaking, it might be more correct to refer to this as a process of converting analog data into digital data; this process is known as digitization. Once analog data have been converted into digital data, a number of things can happen. The three most common are: 1.The digital data can be transmitted using NRZ-L. In this case, we have in fact gone directly from analog data to a digital signal. 2.The digital data can be encoded as a digital signal using a code other than NRZ-L. Thus an extra step is required. 3.The digital data can be converted into an analog signal, using one of the modulation techniques discussed in Section 5.2. The device used for converting analog data into digital form for transmission, and subsequently recovering the original analog data from the digital, is known as a codec (coder-decoder). In this section we examine the two principal techniques used in codecs, pulse code modulation and delta modulation.
- #32 Amplitude modulation (AM) is the simplest form of modulation, and involves the multiplication of the input signal by the carrier fc. The spectrum consists of the original carrier plus the spectrum of the input signal translated to fc. The portion of the spectrum for |f| > |fc| is the upper sideband, and the portion of the spectrum for |f| < |fc| is lower sideband. Both the upper and lower sidebands are replicas of the original spectrum M(f), with the lower sideband being frequency reversed. A popular variant of AM, known as single sideband (SSB), takes advantage of this fact by sending only one of the sidebands, eliminating the other sideband and the carrier. Frequency modulation (FM) and phase modulation (PM) are special cases of angle modulation. For phase modulation, the phase is proportional to the modulating signal. For frequency modulation, the derivative of the phase is proportional to the modulating signal. As with AM, both FM and PM result in a signal whose bandwidth is centered at fc, but can show that the magnitude of that bandwidth is very different, hence both FM and PM require greater bandwidth than AM. Stallings DCC8e Figure 5.24 illustrates these various techniques showing amplitude, phase, and frequency modulation by a sine wave. The shapes of the FM and PM signals are very similar. Indeed, it is impossible to tell them apart without knowledge of the modulation function.
- #33 Analog data can be modulated by a carrier frequency to produce an analog signal in a different frequency band, which can be utilized on an analog transmission system. The basic techniques are amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). Modulation has been defined as the process of combining an input signal m(t) and a carrier at frequency fc to produce a signal s(t) whose bandwidth is (usually) centered on fc. For digital data, the motivation for modulation should be clear: When only analog transmission facilities are available, modulation is required to convert the digital data to analog form. The motivation when the data are already analog is less clear. After all, voice signals are transmitted over telephone lines at their original spectrum (referred to as baseband transmission). There are two principal reasons for analog modulation of analog signals: A higher frequency may be needed for effective transmission, since for unguided transmission, it is virtually impossible to transmit baseband signals; Modulation permits frequency division multiplexing, an important technique explored in Chapter 8. In this section we look at the principal techniques for modulation using analog data: amplitude modulation (AM), frequency modulation (FM), and phase modulation (PM). As before, the three basic characteristics of a signal are used for modulation.
- #65 Movies – You go online at home, see which movies are playing, order tickets, download them to home computer, do a wireless transfer over to PDA. Take PDA with you to movies. PDA communicates with ticket booth at movie theatre, you just walk right in. Or you walk up to your front door and your PDA communicates with your house – unlocks door, turns on lights, sets the heat/cool temperature, turns on the TV, etc. Other examples?