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55 terms

Network+ Guide to Networks

Chapter Three
STUDY
PLAY
Transmit
To issue signals along a network medium.
Transmission
the process of transmitting or the progress of signals after they have been transmitted.
Transceiver
A device that transmit and receives signal
Voltage
measurement of the strength of an electrical signal;
Electrical current pressure
analog
characterized by four fundamental properties: amplitude, frequency, wavelength, and phase.
amplitude
is a measure of its strength at any given point in time
frequency
is the number of times that a wave's amplitude cycles from its starting point.
hertz (Hz)
cycles per second
wavelength
the distance between corresponding points on a wave's cycle.
Digital Signals
Pulses of voltages
Positive voltage represents a 1
Zero voltage represents a 0
Binary system
1s and 0s represent information
Bit (binary digit)
Possible values: 1 or 0
Digital signal pulse
Phase
refers to the progress of a wave over time in relationship to a fixed point.
Overhead
Describe Nondata information
Required for proper signal routing and interpretation
Modem
Accomplishes translation
Modulator/demodulator
Data modulation
Technology modifying analog signals
Make data suitable for carrying over communication path
Carrier wave
Combined with another analog signal
Produces unique signal -Transmitted from one node to another
Preset properties
Purpose: Convey information
Information wave (data wave)
Added to carrier wave
Modifies one carrier wave property
Frequency modulation (FM)
Carrier frequency modified
By application of data signal
Amplitude modulation
Carrier signal amplitude modified
By application of data signal
Simplex
Signal transmission: one direction
Half-duplex transmission
Signal transmission: both directions
One at a time
One communication channel
Shared for multiple nodes to exchange information
Full-duplex
Signals transmission: both directions simultaneously
Used on data networks
Channel
Distinct communication path between nodes
Separated physically or logically
Full duplex advantage
Increases speed
Multiplexing
Multiple signals
Travel simultaneously over one medium
Subchannels
Logical multiple smaller channels
Multiplexer (mux)
Combines many channel signals
Demultiplexer (demux)
Separates combined signals
Regenerates them
TDM (time division multiplexing)
Divides channel into multiple time intervals
Statistical multiplexing
Transmitter assigns slots to nodes
According to priority, need
More efficient than TDM
FDM (frequency division multiplexing)
Unique frequency band for each communications subchannel
Two types:
Cellular telephone transmission
DSL Internet access
WDM (wavelength division multiplexing)
One fiber-optic connection
Carries multiple light signals simultaneously
DWDM (dense wavelength division multiplexing)
Used on most modern fiber-optic networks
Extraordinary capacity
Point-to-point transmission
One transmitter and one receiver
Point-to-multipoint transmission
One transmitter and multiple receivers
Broadcast transmission
One transmitter and multiple, undefined receivers
Used on wired and wireless networks
Simple and quick
Nonbroadcast
One transmitter and multiple, defined receivers
Throughput
Most frequently discussed

Measures amount of data transmitted
During given time period
Capacity or bandwidth
Quantity of bits transmitted per second
Bandwidth (strict definition)
Measures difference between highest and lowest frequencies medium can transmit
Range of frequencies
Measured in hertz (Hz)
Baseband transmission
Digital signals sent through direct current (DC) pulses applied to wire
Requires exclusive use of wire's capacity
Transmit one signal (channel) at a time
Example: Ethernet
Broadband transmission
Signals modulated
Radiofrequency (RF) analog waves
Uses different frequency ranges
Does not encode information as digital pulses
Noise
Any undesirable influence degrading or distorting signal:
Form of noise is cross talk
Types of noise
EMI (electromagnetic interference)
EMI/RFI (radiofrequency interference)
Cross talk
NEXT (near end cross talk)
Potential cause: improper termination
Environmental influences
Heat
Attenuation
Loss of signal's strength as it travels away from source
Signal boosting technology
Analog signals pass through amplifier
Noise also amplified
Regeneration
Digital signals retransmitted in original form
Repeater: device regenerating digital signals
Amplifiers and repeaters
OSI model Physical layer
Latency
Delay between signal transmission and receipt
Causes
Cable length
Intervening connectivity device
RTT (round trip time)
Time for packet to go from sender to receiver, then back from receiver to sender
Measured in milliseconds
Transmission Flaws
Attneuation, Signal boosting Tech, Latency, Causes, RTT, May cause network transmission errors
Physical Media Characteristics
Throughput
Cost
Size and scalability
Connectors
Noise immunity
Cross Talk
Form of noise. Occurs when a signal traveling on one wire or cable infringes on the signal traveling over an adjacent wire or cable.
Throughput
Most significant transmission method factor
Causes of limitations:Laws of physics
Signaling and multiplexing techniques
Noise, Devices connected to transmission medium
Fiber-optic cables allows faster throughput - Compared to copper or wireless connections