Systems Architecture,
Sixth Edition
Chapter 8
Data and Network Communication
Technology
Chapter Objectives
•  In this chapter, you will learn to:
–  Explain communication protocols
–  Compare methods of encoding and transmitting
data with analog or digital signals
–  Describe signals and the media used to transmit
digital signals
–  Describe wireless transmission technology and
compare wireless LAN standards
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Chapter Objectives (continued)
–  Describe methods for using communication
channels efficiently
–  Explain methods of coordinating communication,
including clock synchronization and error
detection and correction
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FIGURE 8.1 Topics covered in this chapter
Courtesy of Course Technology/Cengage Learning
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Communication Protocols
•  Set of rules and conventions for communication
•  Message: a unit of data or information
transmitted from a sender to a recipient
•  Command message
•  Common method of encoding, transmitting, and
interpreting these bits
•  Complete communication protocol
–  Complex combination of subsidiary protocols
–  Technologies to implement them
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FIGURE 8.2 Components of a communication protocol
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Encoding and Transmitting Bits
•  Carrier waves
•  Modulation methods
•  Data bits can be encoded into analog or digital
signals
•  Signals
–  Electrical, optical, or radio frequency
–  Capacity and errors
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Carrier Waves
•  A sine wave with encoded bits (transports bits
from one place to another)
•  Characteristics of sine waves: amplitude, phase,
frequency
•  Importance of waves in communications
–  Travel through space, wires, and fibers
–  Can have patterns encoded in them
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FIGURE 8.3 Characteristics of a sine wave
Courtesy of Course Technology/Cengage Learning
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Modulation Methods
•  Techniques used to encode bits in sine waves
–  Amplitude modulation (AM)
–  Frequency modulation (FM)
–  Phase-shift modulation
–  Multilevel coding
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FIGURE 8.6 The bit string 11010001 encoded in a carrier wave with
amplitude modulation
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FIGURE 8.7 The bit string 11010001 encoded in a carrier wave with
frequency modulation
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FIGURE 8.8 The bit string 11010001 encoded in a carrier wave with
phase-shift modulation
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FIGURE 8.9 The bit string 11100100 encoded in a carrier wave with
2-bit multilevel coding
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Analog Signals
•  Uses full range of carrier wave characteristics to
encode continuous data values
•  Can represent any data value within a
continuum of values
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Digital Signals
•  Can contain one of a finite number of possible
values
•  Types of digital signals
–  Binary
–  Trinary
–  Quadrary
•  Square wave: contains abrupt amplitude shifts
between two different values
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FIGURE 8.10 The bit string 11010001 encoded in square waves
(digital signals)
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FIGURE 8.12 A binary signaling method using voltage ranges
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Signal Capacity and Errors
•  Analog signals compared with digital signals
–  Carry more information
–  Are more susceptible to transmission error
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FIGURE 8.13 Margin of transmission error (voltage drop or surge) before the
data value encoded in a digital binary signal is altered
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Transmission Media
•  Communication path that transports signals
(e.g., copper wire, optical fiber)
•  Characteristics
–  Speed and capacity
–  Frequency
–  Bandwidth
–  Noise, distortion, and susceptibility to external
interference
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FIGURE 8.14 Elements of a communication channel
Courtesy of Course Technology/Cengage Learning
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Speed and Capacity
•
•
•
•
Interdependent
Jointly described as data transfer rate
Raw data transfer rate
Effective data transfer rate
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Frequency and Bandwidth
•  Carrier wave frequency
–  Basic measure of data-carrying capacity (i.e.,
limits capacity)
•  Bandwidth
–  Difference between maximum and minimum
frequencies of a signal
–  High-bandwidth channels can carry multiple
messages simultaneously
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FIGURE 8.16 The spectrum of
electromagnetic frequency between 101
and 1019 Hz
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Signal-to-Noise (S/N) Ratio
•  Noise: unwanted signal components
•  Measure of the difference between noise power
and signal power
•  Effective data transfer rate can be much lower
than raw data transfer rate due to
–  Electromagnetic interference (EMI)
–  Attenuation
–  Distortion
–  Internal or external noise
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FIGURE 8.17 S/N ratio as a function of distance for a channel
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Electrical Cabling
•  Transmits signals through copper wire
•  Two types
–  Twisted pair
•  Relatively cheap; limited in bandwidth, S/N ratio,
and transmission speed
–  Axial (coaxial and twin-axial)
•  More expensive; offers higher bandwidth, greater
S/N ratio, and lower distortion; resistant to EMI
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Optical Cabling
•  Provides very high bandwidth, little internally
generated noise and distortion, immunity to EMI
•  Requires amplifiers and repeaters for long
distances to increase signal strength and
remove noise and distortion
•  Two types
–  Multimode
–  Single mode (higher transmission rates at greater
cost)
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Wireless Transmission
•  Uses shortwave radio frequency wave or light
waves to transmit data through the atmosphere
or space
•  Advantages
–  Relatively high bandwidth, avoidance of wired
infrastructure, simultaneous broadcast
transmission
•  Disadvantages
–  Susceptibility to external interference, cost, high
demand for unused radio frequencies, security
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Channel Organization
•  Configuration and organization issues
–  Number of transmission wires or bandwidth
assigned to each channel
–  Assignment of those wires or frequencies to carry
specific signals
–  Sharing, or lack thereof, of channels among
multiple senders and receivers
•  Three types: simplex, half-duplex, full duplex
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Channel Organization
Simple
Uses one optical fiber or copper wire pair to
transmit data in one direction only
Half-duplex Identical to a simplex channel but sends a
control signal to reverse transmission
direction
Full duplex
Uses two fibers or wire pairs to support
simultaneous transmission in both directions
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FIGURE 8.22 Configurations for simplex (a), half-duplex (b), and
full-duplex (c) modes
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Parallel and Serial Transmission
Parallel
Serial
•  Uses a separate
•  Uses a single line to
transmission line for each bit
send one bit at a time
position
•  Reliable over much
•  Unreliable over distances
longer distances
greater than a few meters
•  Lower wiring and cable
due to skew and crosstalk
cost
•  Provides higher channel
throughput
•  Relatively expensive
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FIGURE 8.23 Parallel transmission of a data byte (8 bits)
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FIGURE 8.24 Serial transmission of a data byte (8 bits)
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Channel Sharing
•  Uses available capacity by combining traffic of
multiple users
•  For use when no single user or application
needs a continuous supply of data transfer data
capacity
•  Techniques
–  Circuit switching
–  Packet switching
–  Frequency division multiplexing
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Channel Sharing Techniques
Circuit switching
•  Allocates an entire channel to a single user
for duration of one data transfer operation
•  Only used where data transfer delay and
available data transfer capacity must be
within precise and predictable limits (e.g.,
telephone service)
Packet switching
•  Allocates time on the channel by dividing
many message streams into smaller units
(packets) and intermixing them during
transmission
Frequency division
multiplexing (FDM)
•  Divides a broadband channel into several
baseband channels (e.g., cable television)
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FIGURE 8.27 Packet switching—the most common form of TDM
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FIGURE 8.28 Channel sharing with FDM
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Communication Coordination
•  Sender and receiver must coordinate their
approaches to various aspects of communication
in a channel
–  Start and end times of bits or signal events
–  Error detection and correction
–  Encryption methods (or lack thereof)
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Clock Synchronization
•  Ensures that sender/receiver use same time
periods and boundaries to encode/decode bit
values
•  Synchronous transmission
–  Ensures that sender/receiver clocks are always
synchronized by sending continuous data
streams
•  Asynchronous transmission
–  Relies on specific start and stop signals to
indicate beginning and end of a message unit
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FIGURE 8.32 Typical format for messages transmitted with
synchronous character-framing methods
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FIGURE 8.33 Asynchronous character framing for serial transmission,
including a start bit
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Error Detection and Correction
•  Error detection
–  Based on a form of redundant transmission
–  Increasing redundancy increases chances of
error detection at the expense of reducing
channel throughput
•  Common error detection methods
–  Parity checking
–  Block checking
–  Cyclical redundancy checking
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How Methods of Error Detection and
Correction Vary
•
•
•
•
Size and content of redundant transmission
Efficient use of the communication channel
Probability that an error will be detected
Probability that an error-free message will be
identified as an error
•  Complexity of the error detection method
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Parity Checking
•
•
•
•
Also called vertical redundancy checking
Can be based on even or odd bit counts
Has a high Type I error rate
Reliability issues
–  Unreliable in channels subject to error bursts
affecting many adjacent bits
–  More reliable in channels with rare errors that are
usually confined to widely spaced bits
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FIGURE 8.34 Sample parity bits
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Block Checking
•  Also called longitudinal redundancy checking
(LRC)
•  Sending device counts number of 1-valued bits
at each bit position within a block
•  Sender combines parity bits for each position
into a block check character (BCC) and appends
it to the end of the block
•  Receiver counts 1-valued bits in each position
and derives its own BCC to compare with that
transmitted by sender
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FIGURE 8.35 Block checking
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Cyclic Redundancy Checking (CRC)
•  Most widely used error detection technique
•  Produces a BCC usually more than 8 bits long;
can be as large as 128 bits
•  Much lower Type I and Type II error rates than
parity checking and LRC checking
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Summary
•  Communication protocols
•  How bits are represented and transported
among computer systems and hardware
components
•  Transmission media
•  Channel organization
•  Clock synchronization
•  Detecting and correcting errors in data
transmission, reception, or interpretation
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