Flashcards in Chapter 3 Deck (62):
What is a physical circuit?
-the actual wire used to connect two devices.
-the physical media that carry the message we transmit.
What is a logical circuit?
-the transmission characteristics of the connection.
-T1 connection, refers to hw fast data can be sent trhough the connection
What is a modem?
-used to send digital data over an analog telephone circuit.
-translates computer's digital data into analog data that can be transmitted through the voice communication circuits.
What is a codec?
-translates analog voice data into digital form for transmission over digital computer circuits.
Why is digital transmission better?
-produces fewer errors and errors are easier to detect and correct
-permits higher max transmission rates.
-more secure, easier to encrypt
-integrating voice, video and data on same circuit is simpler.
What is a symbol?
-patters of electricity, light or radio wave that will be used to represent a 0 and a 1.
What is a symbol rate?
-How many symbols are sent over the circuit per second.
What is circuit configuration?
-the basic physical layout of the circuit.
What is a point-to-point circuit?
-goes from one computer to another computer.
What is a multipoint circuit?
-manyy computers are connected on the same circuit.
-each computer must share the circuit with the others.
What is simplex transmission?
-one-way transmission such as radios and TVs
What is half-duplex transmission?
-two-way transmission but you can only transmit in only one direction at a time.
-use of control signals to determine which will send and receive data.
What is turnaround time?
-the amount of time half-duplex communication takes to switch between sending and receiving.
-also called retrain time.
What is full-duplex?
-you can transmit in both directions simultaneously with no turnaround time.
What is multiplexing?
-break one high-speed physical communication circuit into several lower-speed logical circuits so that many devices can simultaneously use it but still think they have their own separate circuits.
-done in multiples of four
What is the benefit of multiplexing?
-save money by reducing the amount of cable or the number of network circuits that must be installed.
What are the four types of multiplexing?
-Frequency division multiplexing, Time division multiplexing, statistical time division multiplexing, wave length division multiplexing.
-divides the circuit horizontally
-divided into series of separate channels each transmitting on a different frequency.
-exist on the media at the same time.
What are guardbands?
-used in FDM to separate frequencies from each other(unused).
-divides the circuit vertically
-one character taken from each computer in turn and transmitted down the circuit.
-time allocated evenly even if there is not transmision
-more efficient than FDM because it does not need guardbands.
-capacity of the multiplexed circuit dos not need to equal the sum of the circuits it combines.
-takes advantage of the fact that not all computers will need to transmit at the same time at their maximum speed.
What are benefits of STDM?
-provides more efficient use of the circuit and saves money.
What are disadvantages of STDM?
--needs internal memory to store incoming data if all users transmit at the same time.
-need to add addressing to packets that increases overhead.
-wavelength division multiplexing.
-version of FDM used in fiber-optic cables.
-transmit different frequencies of light.
Describe Dense WDM.
-variant of WDM by adding TDM to WDM
What is inverse-multiplexing?
-combines several low-speed circuits to make them appear as one high-speed circuit.
-T1 circuits for WANs
What is BONDING?
-Bandwidth on Demand Interoperability Network Group
-standard that allows IMUX circuits to communicate with other IMUX circuits.
-common in room to room video conferencing.
What is DSL?
-combines analog transmission and FDM to provide a set of voice and data circuits.
-uses a combination of amplitude and phase modulate to provide the desired data rate.
What is guided media?
-those in which the message flows through a physical media such as twisted pair wire, coaxial, etc.
What is wireless media?
-broadcast through the air(unguided.)
What are multimode fibe cables?
-light can reflect inside the cable at many different angles.
-plagued by excessive signal weakening(attenuation) and dispersion(different parts arrive at ddiferent times.
What is graded-index multimode fiber?
-changes refractive properties of glass fiber so light arrives at the same time.
What is single-mode fiber?
-transmits a single direct beam of light through a cable that ensues the light reflects in only one pattern.
-up to 100 kilometers
What is microwave transmission?
-extremely high frequency radio communication beam
-line of sight path between two points.
Describe satellite transmission.
-geosynchronous: satellite remains stationary.
-has propagation delay.
What is a coding scheme?
-the language that computers use to represent data.
What is a character?
-a symbol that has a common, constant meaning.
-American Standard Code for Information Interchange
-has 7-bit code with 128 valid character combinations
-80bit code with 256 valid combinations.
Describe ISO 8859.
-8-bit code that includes ASCII codes and non-english letters.
-UTF-8: 8-bit version
-UTF-16: 16 bit version
What id parallel transmission.
-internal transfer of binary data where the bits of data element are transferred between mainmemory and CPU simultaneously on 8 separate connections.
Describe serial transmission?
-stream of data is sent over a communication circuit sequentially in a bit-by-bit fashion.
Describe digital transmission.
-transmission of binary electrical or light pulses in that it only has two possible states.
Describe unipolar signaling?
-voltage is always positive or negative in which 0 volts transmits zeros and +5 volts transmits a 1.
Describe bipolar signaling.
-the ones and zeros vary from a plus voltage to a minus voltage.
Describe non return to zero (NRZ) signaling.
-alternates from +5 volts (indicates a 1) and -5 volts(indicates a zero) without returning to 0 volts.
Describe return to zero signaling(RZ)
-always returns to zero volts after each bit before going to +5 volts for a 1 or -5 volts for a zero.
Describe alternate mark inversion(AMI) signaling.
-0 is always sent using 0 volts, 1's alternate between +5 volts and -5 volts.
Describe manchester encoding.
-bipolar signaling in which teh signal is changed from high to low or low to high in the middle of the signal.
-high to low represents a 0
-low to high represents a 1
Describe analog transmission.
-signal sent over the transmission media continuously varies from one state to another in a wave-like pattern.
-in sound waves measured in decibels.
-direction in which the wave begins.
Describe amplitude modulation.
-amplitude shift keying
-amplitude of the wave is changed.
-one amplitued represents a 1 and another one represents a 0.
Describe Frequency modulation.
-frequency shift keying
-each 0 or 1 represented by a certain number of waves per second.( a different frequency).
Describe phase modulation.
-phase shift keying(PSK)
-one phase is a 0, the other phase is a 1.
What is QAM?
-quadrature amplitude modulation.
-splits symbol into 8 different phases and two different amplitudes
What is a baud?
-a unit of signaling speed used to indicate the number of times per second the signal on the communication circuit changes.
Describe data rate.
-calculated by multiplying the number of bits sent on each symbol by the maximum sybol rate.
What is bandwidth?
-difference between the highest and lowest frequencies in a band or set of requencies.
Describe a modem.
-takes digital data from a computer in the form of electrical pulses and converts them into the analog signal that is need d for transmission over an analog voice-grade circuit.
-used to send analog voice data over digital networks.