Chapter 3 Flashcards
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 efficient
- 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.
- dedicated circuits.
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.
- walkie-talkie.
- 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.
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.
What are guardbands?
-used in FDM to separate frequencies from each other(unused).
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.
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.
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.
Describe WDM
- 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.
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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.
Describe ASCII
- 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.
Describe Unicode.
- 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.
Describe amplitude.
-in sound waves measured in decibels.
Describe phase.
-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).
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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.
Describe codecs.
-used to send analog voice data over digital networks.
Describe quantizing error>
-different between the original signal and the digitized signal.
