Chapter 8
Data and Network
Communication Technology
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Systems Architecture
Chapter 8
Chapter Goals
• Explain communication protocols.
• Describe signals and the media used to
transmit digital signals
• Compare and contrast methods of encoding
and transmitting data using analog and digital
signals.
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Chapter 8
Chapter Goals
• Describe methods for efficiently using
communication channels.
• Describe methods for detecting and
correcting data transmission errors.
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Chapter Topics
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Communication protocols
Encoding and transmitting bits
Transmission media
Channel organization
Clock synchronization
Error detection and correction
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Communication Protocols
• A message is a unit of data or information
transmitted from a sender to one or more
recipients.
• A communication protocol is a set of rules
and conventions for communication.
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Communication Protocols
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Chapter 8
Encoding and Transmitting Bits
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Carrier Waves
Modulation Methods
Analog Signals
Digital Signals
Signal Capacity Errors
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Encoding and Transmitting Bits
Carrier Waves
• Amplitude
• Phase
• Frequency
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Encoding and Transmitting Bits
Amplitude - is a measure of wave height or
power. The maximum distance between a
wave peak and its zero value.
Phase - a specific time point within a wave’s
cycle.
Frequency - the number of cycles that occur in
one second.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
• Bit are encoded within a wave by precisely
manipulating or modulating.
• Data can be encoded as bits by any shared
coding method. For example, text messages
could be encoded with Morse code.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Modulation Methods
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Amplitude Modulation
Frequency Modulation
Phase Modulation
Multilevel Coding
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Encoding and Transmitting Bits
Amplitude Modulation
• Represents bit values as specific wave
amplitudes.
• Amplitude modulation holds frequency
constant while varying amplitude to represent
data.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Frequency Modulation
• Represents bit values by varying carrier wave
frequency while holding amplitude constant.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Phase Modulation
The phase of a wave is used to represent
data by making an instantaneous shift in the
phase of a signal or switching quickly
between two signals of different phases.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Multilevel Coding
• A technique for embedding multiple bit values
within a single wave characteristic.
• Groups of bits are treated as a single unit for
the purposes of signal encoding.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Analog Signals
• Uses the full range of a carrier wave
characteristic to encode continuous data
values.
• Analog signals are continuous in nature.
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Encoding and Transmitting Bits
Digital Signals
• Can contain one of a finite number of
possible values.
• Digital signals can be generated using a
square wave instead of a sine wave.
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
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Encoding and Transmitting Bits
Signal Capacity and Errors
• Analog signals can carry a greater amount of
information than digital signals within a fixed
time interval.
• Higher data carrying capacity results from the
large number of possible messages that can
be encoded within an analog signal during a
period of time.
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Encoding and Transmitting Bits
• A digital signal is not as susceptible to noise
and interference.
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Transmission Media
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Definition for transmission media
Characteristics of transmission media
Speed and Capacity
Frequency and Bandwidth
Signal-to-Noise Ratio
Electrical and Optical Cabling
Wireless Data Transmission
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Transmission Media
• Transmission medium – the communication
path used to transport signals.
• Communication channel – consists of a
sending device, receiving device and the
transmission medium that connects them.
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Transmission Media
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Transmission Media
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Transmission Media
Characteristics of transmission media:
• Speed and capacity
• Bandwidth
• Noise, distortion, and susceptibility to external
interference
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Transmission Media
Speed and Capacity
• A raw data transfer rate is the maximum
number of bits or bytes per second that the
channel can carry.
• The effective data transfer rate describes
the transmission capacity actually achieved
with a particular communication protocol.
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Transmission Media
Frequency and Bandwidth
• Frequency is a measure of data carrying
capacity.
• The difference between the maximum and
minimum frequencies of a signal is the signal
bandwidth.
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Transmission Media
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Transmission Media
Modulator-demodulator (modem) technology is used to send digital signals
over voice-grade telephone channels.
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Transmission Media
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Transmission Media
Signal-to-Noise Ratio
Noise – refers to any extraneous signals that
might be interpreted incorrectly as data.
Attenuation – is a reduction in the strength of
a signal as it passes through a transmission
medium.
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Chapter 8
Transmission Media
Signal-to-Noise Ratio
Signal to Noise Ratio – the effective speed
limit of any given channel is determined by
the power of the message-carrying signal in
relation to the power of the noise in the
channel.
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Transmission Media
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Transmission Media
Electrical and Optical Cabling
• Electrical signals usually are transmitted
through copper wire.
• Optical cabling:
– Fiber optic cable
• Electrical cabling:
– Twisted Pair wire
– Coaxial cable
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Transmission Media
Electrical and Optical Cabling - Twisted Pair
Wire
• The most common transmission medium for
telephone and local area network
connections.
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Transmission Media
Electrical and Optical Cabling - Twisted Pair
Wire
• Disadvantages:
– High susceptibility to noise
– Limited transmission capacity
• Advantages:
– Low cost
– Ease of installation
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Transmission Media
Electrical and Optical Cabling – Coaxial
Cabling
Contains a single copper conductor
surrounded by a thick plastic insulator, a
metallic shield, and a tough outer plastic
wrapping.
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Transmission Media
Electrical and Optical Cabling – Coaxial
Cabling
• Advantages:
– Very resistant to EMI
– High bandwidth
– High data transmission capacity
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Transmission Media
Electrical and Optical Cabling – Coaxial
Cabling
• Disadvantages:
– More costly than twisted pair
– Harder to install
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Transmission Media
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Transmission Media
Fiber-optic cable
• Contains one or more strands of lightconducting filaments made of plastic or glass.
• Cable types – multimode and single mode.
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Transmission Media
Fiber-optic cable
• Advantages
– Transmission speed
– Low error rate
• Disadvantages
– High cost
– Difficult installation
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Transmission Media
Wireless Data Transmission
Uses short wave radio or infrared light waves
to transmit data through the atmosphere or
space.
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Channel Organization
• Simplex, Half Duplex and Full Duplex
• Parallel and Serial Transmission
• Channel Sharing
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Channel Organization
Simplex, Half Duplex and Full Duplex
• A single communication channel requires two
wires – signal wire (carries data), return wire
(complete the electrical circuit between the
sending and receiving devices)
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Channel Organization
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Channel Organization
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Channel Organization
Simplex Mode
• Messages flow in one direction.
• Used when data flows in one direction and
there is a small chance for transmission error.
• The receiver can not notify the sender of the
error.
• Used the send status messages from the host
computer.
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Channel Organization
Half-Duplex Mode
• Uses a single shared channel.
• Each node takes turns using the transmission
line to transmit and receive.
• If an error is detected, the receiver can
request to have the message resent.
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Channel Organization
Full-Duplex Mode
• The receiver can communicate with the
sender at any time by using the second
transmission line.
• If an error is sensed, the receiver immediately
can notify the sender and halt the
transmission.
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Channel Organization
Simplex, Half-Duplex and Full-Duplex
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Channel Organization
Parallel Transmission
• Uses a separate transmission line for each bit
position.
• The number of lines is typically one word.
• Parallel communication is relatively
expensive.
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Channel Organization
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Channel Organization
Serial Transmission
• Uses only a single transmission line or line
pair for electrical signals.
• Bits are sent sequentially through the single
transmission line and reassembled by the
receiver.
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Channel Organization
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Channel Organization
Channel Sharing
• Transmission capacity typically is needed for
short periods, or bursts.
• Channel sharing techniques combine the
traffic of multiple.
• Result in more efficient utilization of available
data transfer capacity.
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Channel Organization
Channel Sharing
• Time Division Multiplexing (TDM)
• Frequency Division Multiplexing (FDM)
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Channel Organization
Time Division Multiplexing
• Describes any technique by which data
transfer capacity is split into small time slices
and allocated to multiple users and/or
applications.
• Types of TDM – Packet Switching and Circuit
Switching.
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Channel Organization
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Channel Organization
Frequency Division Multiplexing (FDM)
• A single broadband channel is partitioned into
multiple baseband subchannels.
• Each subchannel represents a single different
frequency range (band).
• Signals are transmitted within each
subchannel at a fixed frequency.
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Channel Organization
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Clock Synchronization
• Data must be sent using a common
transmission rate.
• Senders place bits into a transmission line at
precise intervals.
• Receivers examine the signal at or during
specific time intervals.
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Clock Synchronization
Two synchronization problems:
• Keeping sender and receiver clocks
synchronized during transmission.
• Synchronizing the start of each message.
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Clock Synchronization
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Clock Synchronization
Synchronous transmission – ensures that
sender and receiver clocks are always
synchronized by sending continuous data
streams.
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Clock Synchronization
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Clock Synchronization
Asynchronous transmission – messages
are sent on an as-needed basis. Messages
can be sent one after another or there can be
periods of inactivity between messages.
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Clock Synchronization
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Chapter 8
Error Detection and Correction
Methods of Error Detection:
• Parity Checking
• Block Checking
• Cyclic Redundancy Checking
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Error Detection and Correction
• All error detection methods are based on
some form of redundant transmission.
• A redundant message is transmitted after the
original message.
• The receiver compares the two messages for
a match.
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Error Detection and Correction
• If the two match, then the message is
assumed to have been transmitted, received
and interpreted correctly.
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Error Detection and Correction
Parity Checking (Vertical Redundancy
Check)
• Used for character data.
• One bit (parity bit) is appended to each
character.
• Two parity schemes are used – Odd and
Even Parity.
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Error Detection and Correction
Parity Checking (Vertical Redundancy
Check) – Odd Parity
• The parity bit is set to 0 if the number of 1 bits
within the character is odd.
• The parity bit is set to 1 if the number of 1 bits
within the character is even.
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Error Detection and Correction
Parity Checking (Vertical Redundancy
Check) – Even Parity
• The parity bit is set to 0 if the number of 1 bits
within the character is even.
• The parity bit is set to 1 if the number of 1 bits
within the character is odd.
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Error Detection and Correction
Block Checking (Longitudinal Redundancy
Checking)
• Used for blocks of characters.
• The number of 1 bits is counted in a block of
characters by the sending computer.
• The parity bits for each position are combined
into a Block Check Character (BCC) and
appended to the end of the block.
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Error Detection and Correction
Block Checking (Longitudinal Redundancy
Checking)
• The receiver counts the number of 1 bits in
the block of characters and generates a Block
Check Character.
• If the two Block Check Characters match,then
the message is assumed to have been sent,
transmitted and received correctly.
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Error Detection and Correction
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Error Detection and Correction
Cyclic Redundancy Checking
• Most widely used error detection technique.
• A block check character is produced.
• A Cyclic Redundancy Checking character is
generated mathematically.
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Technology Focus
Wireless Network Standards
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Chapter 8
Summary
• A communication protocol is a set of rules and
conventions covering many communication aspects.
• Data bits can be encoded into analog or digital
signals.
• Important characteristics of transmission media
include raw data transfer rate, bandwidth, and
susceptibility to noise, distortion, external
interference, and attenuation.
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Systems Architecture
Chapter 8
Summary
• The effective data transfer rate can be much
less than the raw data transfer rate due to
attenuation, distortion, and noise.
• Electrical cables are of two primary types –
twisted pair and coaxial.
• Optical cables are of two types – multimode
and single mode.
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Summary
• Data can be transmitted without wires via
radio waves and infrared light.
• Channel organization describes the number
of lines dedicated to a channel and the
assignment of specific signals to those
channels.
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Summary
• Parallel transmission uses multiple lines to
send several bits per signal event. Serial
transmission uses a single line to send one
bit at a time.
• Channels often are shared among users and
applications when no one user or application
needs a continuous supply of data transfer
capacity.
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Summary
• Sender and receiver must synchronize clocks
to ensure that they use the same time periods
and boundaries to encode and decode bit
values.
• Error detection always is based on some form
of redundant transmission.
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