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Flashcards in Chapter 3 Deck (62):
1

What is a physical circuit?

-the actual wire used to connect two devices.
-the physical media that carry the message we transmit.

2

What is a logical circuit?

-the transmission characteristics of the connection.
-T1 connection, refers to hw fast data can be sent trhough the connection

3

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.

4

What is a codec?

-translates analog voice data into digital form for transmission over digital computer circuits.

5

Why is digital transmission better?

-produces fewer errors and errors are easier to detect and correct
-permits higher max transmission rates.
-more efficient
-more secure, easier to encrypt
-integrating voice, video and data on same circuit is simpler.

6

What is a symbol?

-patters of electricity, light or radio wave that will be used to represent a 0 and a 1.

7

What is a symbol rate?

-How many symbols are sent over the circuit per second.

8

What is circuit configuration?

-the basic physical layout of the circuit.

9

What is a point-to-point circuit?

-goes from one computer to another computer.
-dedicated circuits.

10

What is a multipoint circuit?

-manyy computers are connected on the same circuit.
-each computer must share the circuit with the others.

11

What is simplex transmission?

-one-way transmission such as radios and TVs

12

What is half-duplex transmission?

-two-way transmission but you can only transmit in only one direction at a time.
-walkie-talkie.
-use of control signals to determine which will send and receive data.

13

What is turnaround time?

-the amount of time half-duplex communication takes to switch between sending and receiving.
-also called retrain time.

14

What is full-duplex?

-you can transmit in both directions simultaneously with no turnaround time.

15

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

16

What is the benefit of multiplexing?

-save money by reducing the amount of cable or the number of network circuits that must be installed.

17

What are the four types of multiplexing?

-Frequency division multiplexing, Time division multiplexing, statistical time division multiplexing, wave length division multiplexing.

18

Describe FDM.

-divides the circuit horizontally
-divided into series of separate channels each transmitting on a different frequency.
-exist on the media at the same time.

19

What are guardbands?

-used in FDM to separate frequencies from each other(unused).

20

Describe TDM.

-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.

21

Describe STDM.

-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.

22

What are benefits of STDM?

-provides more efficient use of the circuit and saves money.

23

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.

24

Describe WDM

-wavelength division multiplexing.
-version of FDM used in fiber-optic cables.
-transmit different frequencies of light.

25

Describe Dense WDM.

-variant of WDM by adding TDM to WDM

26

What is inverse-multiplexing?

-combines several low-speed circuits to make them appear as one high-speed circuit.
-T1 circuits for WANs

27

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.

28

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.

29

What is guided media?

-those in which the message flows through a physical media such as twisted pair wire, coaxial, etc.

30

What is wireless media?

-broadcast through the air(unguided.)

31

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.

32

What is graded-index multimode fiber?

-changes refractive properties of glass fiber so light arrives at the same time.

33

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

34

What is microwave transmission?

-extremely high frequency radio communication beam
-line of sight path between two points.
-

35

Describe satellite transmission.

-geosynchronous: satellite remains stationary.
-has propagation delay.

36

What is a coding scheme?

-the language that computers use to represent data.

37

What is a character?

-a symbol that has a common, constant meaning.

38

Describe ASCII

-American Standard Code for Information Interchange
-has 7-bit code with 128 valid character combinations
-80bit code with 256 valid combinations.

39

Describe ISO 8859.

-8-bit code that includes ASCII codes and non-english letters.

40

Describe Unicode.

-UTF-8: 8-bit version
-UTF-16: 16 bit version

41

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.

42

Describe serial transmission?

-stream of data is sent over a communication circuit sequentially in a bit-by-bit fashion.

43

Describe digital transmission.

-transmission of binary electrical or light pulses in that it only has two possible states.

44

Describe unipolar signaling?

-voltage is always positive or negative in which 0 volts transmits zeros and +5 volts transmits a 1.

45

Describe bipolar signaling.

-the ones and zeros vary from a plus voltage to a minus voltage.

46

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.

47

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.

48

Describe alternate mark inversion(AMI) signaling.

-0 is always sent using 0 volts, 1's alternate between +5 volts and -5 volts.

49

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

50

Describe analog transmission.

-signal sent over the transmission media continuously varies from one state to another in a wave-like pattern.

51

Describe amplitude.

-in sound waves measured in decibels.

52

Describe phase.

-direction in which the wave begins.

53

Describe amplitude modulation.

-amplitude shift keying
-amplitude of the wave is changed.
-one amplitued represents a 1 and another one represents a 0.

54

Describe Frequency modulation.

-frequency shift keying
-each 0 or 1 represented by a certain number of waves per second.( a different frequency).
-

55

Describe phase modulation.

-phase shift keying(PSK)
-one phase is a 0, the other phase is a 1.

56

What is QAM?

-quadrature amplitude modulation.
-splits symbol into 8 different phases and two different amplitudes

57

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.

58

Describe data rate.

-calculated by multiplying the number of bits sent on each symbol by the maximum sybol rate.

59

What is bandwidth?

-difference between the highest and lowest frequencies in a band or set of requencies.

60

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.

61

Describe codecs.

-used to send analog voice data over digital networks.

62

Describe quantizing error>

-different between the original signal and the digitized signal.