Chapter 3 – Physical Layer – Business Data Communications ; Networking 10th Edition – Flashcards
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Network circuits
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physical media and special purpose devices for networking, such as cables, routers, and hubs
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Physical circuits
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connect devices and include actual wires
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Logical circuits
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transmission characteristics of the circuit
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digital data
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binary produced by a computer and passed along a circuit
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analog data
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electrical signals shaped like the sound wave they stransfer
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codec
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translates analog into digital
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symbol rate
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how many symbols will be sent over a circuit per second
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point-to-point circuit
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goes from one point to another; dedicated circuit
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multipoint circuit (shared circuit)
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many computers are connected on the same circuit
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simplex
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one-way transmission
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half-duplex
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"walkie talkie" transmission
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full duplex
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transmit in both directions
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turnaround time
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time for a specific circuit to switch between sending and receiving
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Multiplexing
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breaking one high speed physical communication circuit into several lower speed logical circuits
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Frequency Division Multiplexing (FDM)
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dividing a circuit into several channels "horizontally"
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guardbands
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unused portions of a circuit used to separate channels in FDM
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Time Divison Multiplexing (TDM)
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shares a circuit by dividing circuit "vertically", allocates time to each device whether or not data is being transmitted
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Statistical Time Division Multiplexing (STDM)
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Sends data with address packages across a circuit, allows for more efficient use of a circuit
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Wavelength Division Multiplexing (WDM)
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version of FDM used with Fiber Optic Cables using different frequencies of light,can be combined with TDM
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Inverse Multiplexing (IMUX)
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combining several low-speed circuits into one high-speed circuit
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Bandwidth on Demand Interoperability Networking Group (BONDING)
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a recently adopted standard for IMUX
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Digital subscriber line (DSL)
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combines analog and FDM to send voice and data across copper telephone lines
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Customer premises equipment (CPE)
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DSL modem installed in a customer's home
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guided media
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media flows through a physical media
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wireless media
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message is broadcast through the air
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Twisted Pair wires (TP)
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insulated pairs of wires, reduce electromagnetic interference by twisting two wires together
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Coaxial Cable
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copper ore with outer cylindrical shell for insulation. Less prone to interference than TP, but more expensive.
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Fiber optic cable
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high capacity wire, light sends signal down a thin glass or plastic fiber
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Multimode
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50 micron core fiber optic cable. Signal spreads out over short distances
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Graded index multimode
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reduces signal weakening by changing the refractive properties of glass fiber so that as the light approaches the outer edge of the fiber, it speeds up, which compensates for the slightly longer distance it must travel.
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Single-mode
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cable that transmits a single direct beam of light through a cable that ensures the light reflects only in one patter. 5-10 micron core. Generally is more expensive because it must use lasers
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Radio Waves
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wireless transmission of electrical waves through air
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Microwave Radio
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High frequency form of radio communications that requires line of sight. Possesses similar properties as light
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propagation delay
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delay in transmission of a satellite signal due to the time it takes for a signal to travel out into space
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character
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symbol that has a common, constant meaning
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bits
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a binary zero or one
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byte
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group of consecutive bits that is treated as a unit or character
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coding scheme (code)
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the representation of a set of characters by a string of bits
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American Standard Code for Information Interchange (ASCII)
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a 7 bit (156 combination) and 8 bit (256 combination) coding scheme used on most microcomputers
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Digital transmission
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transmission of binary electrical or light pulses in that it only has two possible states, 1 or 0.
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Hertz (Hz)
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Thousand symbols per second
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symbol rate
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how often a sender can transmit data
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unipolar signaling
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voltage is always positive or negative, for example 0 volts = 0 and 5 volts = 1
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Bipolar signlaing
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positive = 1, negative = 0
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Manchester signaling
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A change from high to low is used to represent a 0 and a change from low to high is used to represent a 1. Used by ethernet.
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Modem
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translates digital data into an analog signal to be sent over a telephone line
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Plain Old Telephone Service (POTS)
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Sound waves converted to electrical signals by the sender then converted back to sound waves at the far end
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amplitude
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height (loudness of a wave) measured in dB
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Frequency
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Number of waves in a second, measured in Hertz
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modulation
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changing the shape of a wave to represent a 1 or a 0
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carrier wave
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a sound wave sent through a circuit representing a 1 or a 0
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Amplitude modulation (amplitude shift keying)
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changing the height of a wave to send a 1 or a 0. More susceptible to errors
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Frequency Modulation (frequency shift keying)
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each 0 or 1 is represented by a number of waves per second
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Phase Modulation
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changing the direction in which a wave starts to signal a 0 or a 1
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Quadrature amplitude modulation (QAM)
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splitting the symbol into eight different phases and two different amplitudes for a total of 16 possible values, sending 4 bits on the same symbol.
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bit rate
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number of bits sent per second
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baud rate (symbol rate)
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number of symbols per second
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bandwidth
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difference between the highest and lowest frequencies in a band or set of frequencies
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codec
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converts analog signal to digital form
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quantizing error
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the difference between an analog signal before and after being converted with a codec
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pulse code modification (PCM)
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NA telephone network, samples input voice 8000 times per second and generates 8 bits per sample, uses 64 Kbps
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Adaptive differential pulse code modulation (ADPCM)
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transmits the difference between two 8 bit values, only needs 4 bits and can thus be transmitted on a 32 Kbps circuit
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Phase
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refers to the point in each wave cycle at which the waves begins measured in degrees.
