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Chapter Three

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

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