Understanding Computers
Today and Tomorrow 12th Edition
Chapter 7:
Computer Networks
Learning Objectives
• Define a network and its purpose.
• Describe several uses for communications
technology.
• Understand the various topologies and architectures a
computer network might use.
• Explain the difference between a LAN, a WAN, and a
PAN, and between an intranet, an extranet, and a
VPN.
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Learning Objectives
• Understand characteristics about data and how it
travels over a network.
• Name specific types of wired and wireless
transmission media and explain how they transmit
data.
• Identify different protocols that can be used to connect
the devices on a network.
• List several types of networking hardware and explain
the purpose of each.
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Overview
• This chapter covers:
– Networking concepts and terminology
– Common networking and communications
applications
– Technical issues related to networks, including the
major types of networks, how data is transmitted
over a network, and types of transmission media
involved
– Explanation of the various ways networked devices
communicate with one another
– Various types of hardware used in conjunction with
a computer network
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What Is a Network?
• Network: A connected system of
objects or people
• Computer network: A collection of
computers and other hardware
devices connected together so that
users can share hardware,
software, and data, as well as
electronically communicate with
each other
• Internet: Largest computer network
in the world
• Types of networks
– Business networks
– Phone networks
– Home and multimedia networks
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Networking and
Communications Applications
• Mobile phones (wireless phones)
– Cellular (cell) phones
• Must be within range of cell tower to function
– Satellite phones
• Used where cell service isn’t available
– Dual-mode phones
• Allows users to make telephone calls on more
than one network
• Cellular / Wi-Fi dual mode phone are most
popular
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Networking and
Communications Applications
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Networking and
Communications Applications
• Paging
– Sending short
numeric or text
messages to a
person’s pager
– Most often used for
onsite paging
applications
• Messaging
– Two-way paging
– Most often takes
place today via a
mobile phone
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Networking and
Communications Applications
• Global positioning system (GPS): Uses satellites and
a receiver to determine the exact geographic location
of the receiver
– Commonly found in cars today
– Available as handheld units
– Used by the military, hikers, travelers,
and others who need to know their
precise location
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Networking and
Communications Applications
• Monitoring systems: Monitor status or location of
individuals, vehicles, assets, etc.
– RFID-based systems
– GPS-based monitoring systems
– Electronic medical monitors and other types of
home health monitoring
• Digital entertainment
– High-definition television/radio: HDTV is replacing
analog broadcasts
– Satellite radio: Delivers digital radio content to
satellite receivers
– Multimedia networking and digital data distribution
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Networking and
Communications Applications
• Videoconferencing: Use of communications
technology for real-time, face-to-face meetings
between individuals located in different places
– Technology continues to improve and mimic reallife meeting environments
– Telepresence
videoconferenceing
– Online conferencing
(via the Internet)
– Video phone calls
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Networking and
Communications Applications
• Collaborative computing (workgroup computing):
Using a computer and communications technology to
work together on documents and other project
– Tools include Microsoft Office markup tools and
collaboration software
• Telecommuting: Individuals work at home and
communicate with their place of business and clients
via communications technologies
– Possible because of the Internet and other
communications technologies
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Networking and
Communications Applications
• Telemedicine: Use of communications technology to
provide medical information and services
– Remote monitoring
and consultations
– Remote diagnosis
– Telesurgery
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Types of Networks
• Topology: How the devices in the network (called
nodes) are arranged
– Star networks: All devices connect to a central
device or hub)
– Bus networks: All devices connect to a central
cable
– Ring networks: Devices connect to one another in
a ring
– Mesh networks: Multiple connections between
devices
– Some networks use a combination of topologies
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Network Topologies
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Types of Networks
• Architecture : The way networks are designed to
communicate
• Client-server networks
– Client: PC or other
device on the network
that requests and
utilizes network
resources
– Server: Computer
dedicated to
processing client
requests
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Types of Networks
• Peer-to-peer networks: All computers at the same
level)
– Internet peer-to-peer (P2P) computing: Performed
via the Internet
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Types of Networks
• Local area network (LAN): Small geographical area
(office, campus, etc.)
• Wide area network (WAN): Large geographical area
(Internet)
• Metropolitan area network (MAN): Serves a
metropolitan area
– Municipal Wi-Fi projects
• Personal area network
(PAN): Connects personal
devices for one individual,
such as his or her portable
PC, mobile phone, and
portable printer
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Types of Networks
• Wireless sensor networks (WSNs): Contain sensors
(devices that respond to a stimulus and generate an
electrical signal that can be measured or interpreted)
• Intranet: Private network set up by an organization for
use by its employees
• Extranet: Intranet that is at least partially accessible to
authorized outsiders
• Virtual private network (VPN): Secure path over the
Internet that provide authorized users a secure means
of accessing a private network via the Internet
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Data Transmission Characteristics
• Analog vs. digital (waves vs. discrete)
• Bandwidth: The amount of data
that can be sent at during a given
period of time
– Measured in bits per second (bps)
• Serial vs. parallel
transmission
– Serial = 1 bit
– Parallel = at
least 1 byte at
a time
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Data Transmission Characteristics
• Transmission timing
– Synchronous transmission (at regular, specified
intervals)
– Asynchronous transmission (sent when ready)
– Isochronous transmission (sent at the same time
as other, related, data)
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Data Transmission Characteristics
• Transmission directions
– Simplex transmission (one way only)
– Half-duplex transmission (one way at a time)
– Full-duplex transmission (both ways at the same
time)
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Data Transmission Characteristics
• Type of connections
– Circuit-switched: Dedicated path over a network is
established and all data follows that path
– Packet-switched: Messages are separated into
small units called packets and travel along the
network separately
• Used to send data over the Internet
– Broadcast: Data is sent out to all other nodes on
the network
• Primarily used with LANs
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Type of Connections
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Data Transmission Characteristics
• Wired connections: The PC is physically cabled to the
network
– Common in schools, business, and government
facilities
• Wireless connections: Typically use radio waves to
send data through the air
– Rapidly becoming more popular in homes and
businesses
– Wireless hotspots are commonly available in public
locations
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Wired Network Transmission Media
• Twisted-pair cable
– Pairs of wires twisted together
– Used for telephone and network connections
• Coaxial cable
– Thick center wire
– Used for computer networks, short-run telephone
transmissions, cable television delivery
• Fiber-optic cable
– Glass or fiber strands through which light can pass
– Used for high-speed communications
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Wired Network Transmission Media
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Wireless Network Transmission Media
• Use radio signals
– Short-range (such as Bluetooth) can connect a
wireless keyboard or mouse to a PC
– Medium-range (such as Wi-Fi) are used for
wireless LANs and to connect portable PC users to
the Internet at public hotspots
– Longer-range (WiMAX) can be used to provide
Internet access to wide geographic areas
• Radio frequencies are assigned by the FCC and are
measured in hertz (Hz)
• The electromagnetic spectrum is the range of
common electromagnetic radiation (energy) that
travels in waves
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Wireless Network Transmission Media
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Cellular Radio Transmissions
• Use cellular towers within cells
• Calls are transferred from cell tower to cell tower as
the individual moves
• Different transmission frequencies are used to avoid
interference and allow multiple conversations to take
place via a single tower at one time
• Widely used, but cell service not available everywhere
• Cell phone technology is referred to in generations
– Today’s phones are third-generation
– 4G service is beginning to become available
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Cellular Radio Transmissions
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Microwave and Satellite Transmissions
• Microwaves: High-frequency radio signals
– Sent and received using microwave stations or
satellites
– Microwave stations are earth-based and can
transmit signals to each other over distances of
about 30 miles
– Signals are line of sight, so stations are usually
built on tall buildings, towers, mountaintops
• Communication satellites: Space-based devices
launched into orbit to send and receive microwave
signals from earth
– Traditional satellites use geosynchronous orbit
– Low earth orbit (LEO) satellites were developed to
combat delay
– Medium earth orbit (MEO) satellites are most often
used for GPS systems
• Can send large quantities of data at high speed over
long distances
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Microwave and Satellite Transmissions
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Infrared (IR) Transmissions
• Sends data as infrared light
• Like an infrared television remote, IR requires line of
sight
• Because of this limitation, many formerly IR devices
(wireless mice, keyboards) now use RF technology
• IR is still sometimes used to beam data between
handheld PCs or gaming systems, or send documents
from portable PCs to printers
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Networking Standards and
Communications Protocols
• Standards: A set of criteria or requirements
considered to be the approved model for something
• Networking standards: Address how networked
computers communicate and connect
• Communications protocol: An agreed-upon standard
for transmitting data between two devices on a
network
• In networking, standards and protocols specify how:
– Devices physically connect to a network
– Data is packaged for transmission
– Receiving devices acknowledge signals
– Errors are handled
– Also ensure products can work together
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Ethernet
• Ethernet: Most widely used communications protocol
for wired LANs
– Typically used a bus or star topology and twistedpair, coaxial, or fiber-optic cables
– Original (10Base-T) Ethernet networks run at 10
Mbps
– Newer 100 Mbps, 1Gbps, and 10 Gbps versions
are common
– 100 Gbps is in development
• Power over Ethernet: Allows electrical power to be
sent along with data on an Ethernet network
– Most often used by businesses
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Ethernet
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TCP/IP and Wireless Application
Protocol (WAP)
• TCP/IP (Transmission Control Protocol/Internet
Protocol): Used for transferring data over the Internet
– Uses packet switching
– TCP/IP support built into virtually all Oss
– IPv4 uses 32-bit addresses
– IPv6 uses 128-bit addresses and expected to
eventually replace IPv4
• Wireless Application Protocol (WAP):
A standard for delivering Internet
content to mobile devices
– Microbrowser: Used to access
WAP content
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TCP/IP
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Wi-Fi (802.11)
• Wi-Fi (Wireless Fidelity): A family of wireless
networking standards using the IEEE standard 802.11
– Also called wireless Ethernet
– Current standard for wireless networks in home
and office
– Designed for medium-range transmission
– Wi-Fi hardware built into most notebook PCs and
many consumer devices today
– Hotspots rapidly multiplying
– Speed and distance of Wi-Fi networks depends on
• Standard and hardware being used
• Number of solid objects between the access
point and the PC or wireless device
• Possible interference
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Wi-Fi (802.11)
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Wi-Fi (802.11)
• Various standards
– Current standard is 802.11g
– Emerging standard is 802.11n
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WiMAX, Mobile WiMAX, and Mobile-Fi
• WiMAX (Worldwide Interoperability for Microwave
Access or 802.16): Fairly new wireless standard for
longer range wireless networking connections
– Designed to deliver broadband to homes,
businesses, other fixed locations
– Mobile WiMAX is the mobile version of the
standard
– 4G mobile phones may be WiMAX-based
• Mobile-Fi (802.20): Currently in development for
providing high-speed mobile Internet access in cars,
trains, and other moving vehicles
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WiMAX, Mobile WiMAX, and Mobile-Fi
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Short-Range Wireless Networking
• Bluetooth: Very short range (less than 10 feet)
– For communication between computers or mobile
devices and peripheral devices
– Bluetooth devices are automatically networked with
each other when they are in range (piconets)
• Ultra Wideband (UWB or WiMedia): Originally
developed by the military for locating tanks, enemies,
hidden objects
– Designed for wireless multimedia networking
– Range of 100 feet or less
– Speed depends on distance between devices
– New Bluetooth standards will use UWB to speed
up transfers of large amounts of data
– Wireless USB is UWB-based
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Bluetooth
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Short-Range Wireless Networking
• Wireless HD (WiHD): In development, designed for
networking home electronics devices
• ZigBee: Emerging, designed for inexpensive, simple
short-range networking like sensor networks
– Intended for application that require low data
transfer rates and several years of battery life
– Can accommodate more than 65,000 devices on a
single network
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Phoneline and Powerline
• Phoneline (HomePNA): Allows computers to be
networked through regular phone lines and jacks
– Geared for quick and easy networking
– HomePNA 3.0 is fast (320 Mbps) and designed for
both computers and multimedia networking
• Powerline: Allows computers to be networked over
power lines and conventional outlets
– Also designed for quick and easy networks
– HomePlug AV is fast (200 Mbps) and designed for
both computers and multimedia networking
• Broadband over power lines (BPL): An emerging
technology that allows Internet data to be sent over
existing power-pole infrastructure
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Cellular Standards
• Second-generation wireless standards
– GSM (Global System for Mobile communications)
– CDMA (Code Division Multiple Access)
• Third-generation standards
– GPRS (General Packet Radio Service)
– EDGE (Enhanced Data Rates for GSM Evolution)
– UMTS (Universal Mobile Telecommunications
System)
– HSDPA (High Speed Downlink Packet Access)’
– EV-DO (Evolution Data Optimized)
– SMS (Short Message Service)
• Fourth generation standards are under development
– Some are WiMAX-based
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Networking Hardware
• Network adapter: Used to connect a PC to a network
or the Internet
– Also called network interface card (NIC) when in
the form of an expansion card
– Available in a variety of formats
• PCI and PCIe
• USB
• PC Card and ExpressCard
– Adapter must match the type of network being
used (Ethernet, Wi-Fi, Bluetooth, etc.)
– Are often built into portable computers
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Network Adapters
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Networking Hardware
• Modem: Device that connects a computer to the
Internet or to another computer
– Term used for Internet connection device, even if
not connecting via a phone line
– Type of modem needed depends on the type of
Internet access being used
• Conventional dial-up
• Cable
• Fixed wireless
• DSL
• These and other types of Internet access are
discussed in Chapter 8
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Modems
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Networking Hardware for Connecting
Devices and Networks
• Hub: Central device that connects all of the devices on
the network
• Switch: Connects devices and identifies the device on
the network for which the data is intended and sends
the data only to that node
• Wireless access point: Used to connect devices to a
network wirelessly
• Gateway: A devices that connects two different
networks
– Bridge: Usually connects wired LANs
– Router: Connects networks and plans path (routes
traffic)
• Can be wired or wireless
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Other Networking Hardware
• Repeater: Amplifies signals along a network
• Range extender: Repeater for a wireless network
• Antenna: Used when Wi-Fi networks need to go
further than hardware normally allows
– Higher-gain antennas can be used with routers
– Some network adapters can use an external
antenna
• Multiplexer: Combines transmissions from several
different devices to send them as one message
• Concentrator: Combines messages and sends them
via a single transmission medium in such a way that
all of the messages are active
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Networking Hardware
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Summary
• What Is a Network?
• Networking and Communications Applications
• Types of Networks
• How Does Data Travel Over a Network?
• Networking Standards and Communications Protocols
• Networking Hardware
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