LESSON 5-6 signals

Broadcast Network

a communication network where one shared channel is used and all nodes receive the message

Broadcast Network Characteristics

all devices receive the same data; efficient for one-to-many; uses a shared medium; can have congestion

Broadcast Network Advantages

efficient for sending the same message to many receivers

Broadcast Network Disadvantages

not ideal for large networks due to congestion and no personalization

Point-to-Point Network

a direct private connection between two endpoints

Point-to-Point Network Characteristics

dedicated connection, high reliability, less interference, more expensive

Simplex

unidirectional communication

Half Duplex

bidirectional but not simultaneous communication

Full Duplex

bidirectional and simultaneous communication

Transmission Medium

the path data travels between transmitter and receiver

Guided Media

physical medium that guides signals such as fiber, coaxial, twisted pair

Unguided Media

wireless medium where waves propagate freely

Signal

a physical quantity carrying information

Digital Signal

signal with discrete values like 0 and 1

Analog Signal

signal that varies continuously

Periodic Signal

signal that repeats after a time interval T

Amplitude

height or strength of a signal

Frequency

number of cycles per second

Phase

position of a signal relative to a cycle

Period

time needed for one full cycle

Sine Wave

smooth periodic oscillating signal

Network Interface Device

device that converts data to electrical, optical, or radio signals and back

Data Rate

bits transmitted per second

Bit Duration

time required to send one bit

Modulation Rate

rate at which signal levels change, measured in baud

NRZ-L

0 is low level and 1 is high level

NRZ-I

0 means no transition; 1 means transition at the start of interval

Bipolar AMI

0 has no signal; 1 alternates between positive and negative

Pseudoternary

1 has no signal; 0 alternates positive and negative

Manchester

0 is high-to-low center transition; 1 is low-to-high transition

Differential Manchester

0 has transition at start; 1 has no transition at start; always has center transition

ASK

amplitude shift keying, amplitude changes per bit

FSK

frequency shift keying, frequency changes per bit

PSK

phase shift keying, phase changes per bit

QPSK

modulation with four phase shifts representing 2 bits per symbol

QAM

modulation that changes both amplitude and phase

PCM

converts analog to digital using sampling, quantizing, and coding

Sampling

taking periodic samples of an analog signal

Quantizing

rounding sampled values to nearest level

Coding

converting quantized values to binary

AM

amplitude modulation varying strength of carrier

FM

frequency modulation varying carrier frequency

Phase Shift Modulation

modulation by abrupt changes in carrier phase

Modem

device used to modulate and demodulate signals

Attenuation

reduction of signal strength

Capacitance

stored electrical energy between conductors affecting signals

Time Delay

time taken for a signal to reach a destination

Noise

unwanted disturbance added to a signal

Thermal Noise

noise from thermal vibrations of charge carriers

Intermodulation Noise

noise from mixing signals of different frequencies

Crosstalk

noise induced on a wire from another wire

Impulse Noise

short high-energy spikes from disturbances like lightning

EMI

electromagnetic interference from motors or power lines

RFI

radio frequency interference

NEXT

near-end crosstalk

FEXT

far-end crosstalk