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Transmission Basics ITNW 1325, Chapter III

Transmission Basics ITNW 1325, Chapter III. OSI Physical Layer. Physical Layer. Overview : Facilitates transmission of signals over network media – copper cable, fiber optics cable, or a wireless medium

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Transmission Basics ITNW 1325, Chapter III

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  1. Transmission Basics ITNW 1325, Chapter III

  2. OSI Physical Layer

  3. Physical Layer Overview: • Facilitates transmission of signals over network media – copper cable, fiber optics cable, or a wireless medium • Signals travel as electrical current in a copper cable, as light pulses, and as EM waves in these media • Defines and implements physical communications principles – signaling, multiplexing, duplex modes, etc. • Communications problems that occur have affect all other layers and thus security of communications • Better understanding of its principles and technologies enables fast recovery from network failures

  4. Physical Layer Network Media:

  5. Physical Layer Network Media (continued):

  6. Physical Layer Network Media (continued):

  7. Signaling Types

  8. Signaling Types Analog: • Implies continuously changing voltage or intensity – signal appears as a wavy line when graphed over time • Possesses four common characteristics – amplitude, frequency, wavelength, and phase • Amplitude – the measure of the wave’s strength at any given point in time (maximum deviation from center) • Frequency – the number of full cycles of the amplitude in a second (measured in Hz, KHz, MHz, GHz, etc.) • Wavelength – the distance between consequent similar points on a wave (measured in length units)

  9. Signaling Types Analog (continued): • Phase – a measure of the progress of a wave over time in relation to a fixed initial point • Quite variable – can convey greater subtleties with less energy (human vs. computer voice) • Continuous in nature – carry imprecise signal levels that are further affected by interference and environment

  10. Signaling Types Analog (continued):

  11. Signaling Types • Digital: • Implies encoding logical bits – binary zeroes and ones – into precise levels of voltages or medium intensities • Fit perfectly the binary nature of computer data – both wired and wireless LANs use digital signaling only • Transmission of discrete pulses is more resistant to interference – brings lower compensation overhead • Requires more complex communication equipment

  12. Signaling Types Compared:

  13. Analog Modulation

  14. Analog Modulation Overview: • Enables modification of analog signals to carry useful data – not all media can carry digital signals • Employs two devices – transmitter and receiver – and two waves – a carrier wave and a data wave • Acarrier wave has well-known wavelength, frequency, amplitude, and phase – conveys information • Adata wave carries data to be transmitted – used for alteration of one of the carrier wave’s parameters • A transmitter combines the two waves for data – by modifying one of the the carrier wave’s parameters

  15. Analog Modulation Overview (continued): • Alterations of the carrier wave’s amplitude, frequency, or phase produce AM, FM, or PM analog modulations • The resultant analog wave carries useful information – transmitted over the medium to the receiver • The receiver is aware of the carrier wave’s original parameters – reads information from it by comparing the actual wave received to the original one

  16. Analog Modulation • Amplitude (AM): • Implies modifying the maximum amplitude at each peak of the carrier wave – with higher peaks standing for logical 1s and lower peaks representing logical 0s • Susceptible to interference • Frequency (FM): • Implies modifying the duration of consequent carrier wave’s cycles – with shorter cycles representing logical 1s and longer cycles representing logical 0s • Less susceptible to interference than AM

  17. Analog Modulation Amplitude, Illustration:

  18. Analog Modulation Frequency, Illustration:

  19. Analog Modulation • Phase (PM): • Implies modifying the carrier wave’s phase according to bit changes between 1 and 0 in the data signal • Requires most complex equipment types of all

  20. Analog Modulation • Use Examples: • Radio broadcast stations use AM or FM • Television broadcast stations use AM for video, FM for sound, and PM for color

  21. Digital Modulation

  22. Digital Modulation Overview: • Employs three techniques that are similar to AM, FM, and PM – abbreviated ASK, FSK, and PSK • Relies on discrete signal levels – not affected by interference as much as analog signals • Digitally modulated signals enable effective error-correcting techniques and require less power • Used broadly by modern communication systems

  23. Digital Modulation • Amplitude Shift Keying (ASK): • Carrier signal (positive voltage or intensity) encodes a binary 1 and no carrier signal encodes a binary 0 • Resembles analog amplitude modulation

  24. Digital Modulation • Frequency Shift Keying (FSK): • Higher frequency (tighter wave) encodes a binary 1 and lower frequency (wider wave) encodes a binary 0 • Resembles analog frequency modulation

  25. Digital Modulation • Phase Shift Keying (PSK): • One change in phase encodes transition to a binary 1 while other change encodes transition to a binary 0 • Resembles analog phase modulation

  26. Duplex Modes

  27. Duplex Modes Overview: • Reflect possible directions of a data flow – as well as possible utilization of both directions at a time • Simplex – signals can travel in only one direction (example – a broadcast radio station) • Half-duplex – signals can travel in both directions but in only one direction at a time (example – a walkie-talkie) • Full-duplex – signals can travel in both directions simultaneously (example – a telephone conversation) • The duplex mode can be specified by humans or negotiated between computer devices

  28. Duplex Modes Overview (continued):

  29. Duplex Modes Full Duplex: • Maximizes data rates in both directions – beneficial for modern computer networks that use it widely • One physical channel would commonly be used for transmitting data while another one – for receiving it • Example – multiple wires used for sending and receiving data combined into single network cable • Must be supported by both communication peers in order for them to communicate – may be negotiated too

  30. Duplex Modes Full Duplex (continued):

  31. Relationships

  32. Relationships • Overview: • Reflect possible numbers and types of hosts sending and receiving data over a network • Point-to-Point (PtP, Unicast) – implies one specific sender and one specific intended receiver (example – a WAN connection between business locations) • Point-to-Multipoint (PtM) – implies one specific sender and multiple defined or undefined receivers • Broadcast – a point-to-multipoint relationship that implies one specific sender and multiple undefined receivers (example – TV and radio stations)

  33. Relationships • Overview (continued): • Multicast – a point-to-multipoint relationship that implies one specific sender and multiple defined receivers (example – audio and video conferences)

  34. Relationships Overview (continued):

  35. Relationships Overview (continued):

  36. Relationships Overview (continued):

  37. Throughput and Bandwidth

  38. Throughput and Bandwidth • Overview: • Bandwidth – a difference between the highest and lowest frequencies that the medium can transmit (Hz) • Throughput – a number of bits transmitted per second (reflects a real communication data rate) • Bandwidth correlates with maximum achievable data rate while throughput measures the actual data rate • The two are not the same thing but get mixed up often

  39. Throughput and Bandwidth • Examples: • Bit per second – equivalent to 1 bit per second, abbreviated bps • Kilobit per second – equivalent to 1000 bits per second, abbreviated Kbps • Megabit per second – equivalent to 1,000,000 bits per second, abbreviated Mbps • Gigabit per second – equivalent to 1,000,000,000 bits per second, abbreviated Gbps

  40. Throughput and Bandwidth • Examples (continued): • Hertz – equivalent to 1 oscillation per second, abbreviated Hz • Kilohertz – equivalent to 1000 oscillations per second, abbreviated KHz • Megahertz – equivalent to 1,000,000 oscillations per second, abbreviated MHz • Gigahertz – equivalent to 1,000,000,000 oscillations per second, abbreviated GHz

  41. Throughput and Bandwidth • Examples (continued): • Residential cable and DSL connections provide throughput of up to 30 and 3 Mbps, respectively • Modern wired and wireless local area networks provide up to 10 Gbps and up to 1.3 Gbps, respectively

  42. Multiplexing

  43. Multiplexing • Overview: • Enables splitting the network medium into multiple data channels in order for multiple signals to travel at once • Effectively increases the amount of data transmitted over the medium available during a time frame • A multiplexer combines signals at the sending end – with a demultiplexer separating them at the receiving end to obtain the original separate data streams back • Type of multiplexing used depends on what the media, transmission, and reception equipment can handle, with several types used most commonly

  44. Multiplexing Overview (continued):

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