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Understanding Computers: Today and Tomorrow, 13th Edition
Computer Networks
Learning Objectives
1. Define a network and its purpose.
2. Describe several uses for networks.
3. Understand the various characteristics of a network,
such as topology, architectures, and size.
4. Understand characteristics about data and how it
travels over a network.
5. Name specific types of wired and wireless networking
media and explain how they transmit data.
6. Identify the most common communications protocols
and networking standards used with networks today.
7. List several types of networking hardware and explain
the purpose of each.
Understanding Computers: Today and Tomorrow, 13th Edition
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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 users can
share hardware, software, and data, and electronically
communicate
• Computer networks converging with telephone and other
communications networks
• Networks range from small private networks to the
Internet (largest network in the world)
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Why Network
• Resource Sharing
• File Sharing
• Communication
• PCs’ Administration and Security
Understanding Computers: Today and Tomorrow, 13th Edition
Networking Applications
•
•
•
•
•
The Internet
Telephone service
An Intranet
Television and Radio Broadcasting
Videoconferencing,
• Please refer to page 259 for more about networking
Applications
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Basic Components of data communication
system
1. Message: data  text, number, audio …
2. Sender: device that sends the data – computer, telephone, camera
3. Receiver: device that receives the data – computer, telephone,
camera
4. Transmission medium: physical path by which message travels.
5. Rules or Protocols: Set of rules that govern data communications/
an agreement between the communicating devices
Understanding Computers: Today and Tomorrow, 13th Edition
Network Characteristics
• Wired vs. wireless networks
– Wired: A network in which computers and other
devices are connected to the network via physical
cables
• Found in homes, schools, businesses, and
government facilities
– Wireless: A network in which computers and other
devices are connected to the network without physical
cables; data is typically sent via radio waves
• Found in homes, schools, and businesses
• Wi-Fi hotspots found in coffeehouses, businesses,
airports, hotels, and libraries
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Network Topology
•Topology: How the devices in the network (called nodes)
are arranged
• Physical layout
A. Star
B. Ring
C. Bus
D. Mesh
• Node – any device
connected to the network
– Server
– Computer
– Printer
– Other peripheral
Understanding Computers: Today and Tomorrow, 13th Edition
Network Topology
• Star
– A network that uses a host device (Central
hub) connected directly to several other
devices
– All messages routed through hub
– Node failure – no effect on overall network
– Hub failure – network fails
• Ring
– Travel around circular connection in one
direction
– Node looks at data as it passes
• Addressed to me?
• Pass it on if not my address
– No danger from collisions
– Node failure – network fails
Understanding Computers: Today and Tomorrow, 13th Edition
Network Topology
•
Bus
– network consisting of a central cable to which
all network devices are attached
–
–
–
–
•
Single pathway
All nodes attached to single line
Collisions result in re-send
Node failure – no effect on overall network
Mesh networks:
– A network in which there are multiple
connections between the devices on the
network so that messages can take any one of
several paths
Understanding Computers: Today and Tomorrow, 13th Edition
Network Architecture
• Client-Server Networks
• Peer-to-Peer (P2P) Networks
• internet Peer-to-Peer
Understanding Computers: Today and Tomorrow, 13th Edition
Network Architecture: client /server
•Server are computers that dedicated to processing client requests
•Client are computers and other devices on the network that request
and utilize (use) network resources.
•
•
How it works
– Client sends request for service to server
– Server fulfills request and send results to client
– Client and server may share processing
Benefits
–
–
–
•
Centralization - access, resources, and data security are
controlled through the server
Scalability - any element can be upgraded when needed
Flexibility - new technology (clients) can be easily integrated
into the system
Nodes can be less expensive computers
Understanding Computers: Today and Tomorrow, 13th Edition
Network Architecture: client /server
• Examples
– Network server
• To manage network traffics
– File server
• Manage shared files
– When client retrieve files from a server it is
called downloading
– Transferring data from a client to a server is
called uploading
– Print server
• Handle printing related activities
– Mail or web server
• To handle email and web pages requests.
Understanding Computers: Today and Tomorrow, 13th Edition
Network Architecture: Peer-to-Peer
• All computers have equal status
• Users have direct access to the
computers and other devices
attached to the network.
– i.e., Share data and devices as
needed
• Less expensive and less
complicated to implement that clientserver networks because there no
dedicated servers
• Disadvantage – slow transmission
Understanding Computers: Today and Tomorrow, 13th Edition
Network Architecture: internet Peer-to-Peer
• Internet peer-to-peer (P2P)
– Is performed via the internet
– one user can copy a file from another user’s hard
drive to his or her own computer via the internet.
• Example
– Emule and Kazaa
Understanding Computers: Today and Tomorrow, 13th Edition
Network Size and Coverage Area
• Personal area network (PAN):
Connects an individual’s personal
devices that are located close together.
• Local area network (LAN): Connects
devices located in a small geographic
area
• Campus area network (CAN):
Interconnects a number of LANs (within a
limited geographical area)
• Metropolitan area network (MAN):
Serves a metropolitan area
• Wide area network (WAN)
– Large geographic area
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Network Size and Coverage Area
• 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 provides authorized users a secure means
of accessing a private network via the Internet
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Data Transmission Characteristics
• There are two fundamentally different types of
data:
• Digital data –
– Computer produced signals that are binary,
either on or off.
– Digital data have discrete states and take
discrete values.
• Analog –
– Electrical signals which are shaped like the
sound waves they transfer.
– Analog data are continuous and take
continuous values
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Data Transmission Characteristics
Signals: Electric representations of information. Can
be Analog or Digital
• An analog signal refers to something that is
continuous- a type of signal represented by
continuous waves.
– Analog signals can have an infinite number of
values in a range
• A digital signal refers to something that is discrete –a
type of signal where data represented by 0s and 1s
– digital signals can have only a limited number
of values.
Transmission can also be Analog or Digital
– Analog transmission system: continuous signals
– Digital transmission system: discrete signals
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encoder/decoder
modulator/demodulator
Understanding Computers: Today and Tomorrow, 13th Edition
Data Transmission Characteristics
Bandwidth:
The amount of data that can be transferred in a given
period of time
– Measured in bits per second (bps)
• Modulate
– Convert from digital data to analog signal
• Demodulate
– Convert from analog signal to digital data
•
Definition modem a device that converts a digital
to an analog and vice verse
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Data Transmission Characteristics
• Serial vs. parallel transmission
– Serial = 1 bit
• one bit is sent at a time
– Parallel = at least 1 byte at a time
• multiple bits are sent at the same time
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Transmission Timing (Timing of Serial
Transmission )
When data is sent using serial transmission, a technique must be
used to organize the bits being transferred so the data can be
reconstructed after it is received.
•Synchronous
transmission occurs
continuously with no gap
between the transmission
of two data items
•Asynchronous
transmission can occur at
any time with an arbitrary
delay between the
transmission of two data
items
•Isochronous (even in
duration ) transmission
occurs at regular intervals
with a fixed gap between
the transmission of two
data items
Understanding Computers: Today and Tomorrow, 13th Edition
Transmission Directions
Direction of data flow
• Simplex
• One direction
• Television broadcasting
• Half-duplex
• Either direction, but one
way at a time
• Full-duplex
• Both directions at once
• Telephone conversation
Understanding Computers: Today and Tomorrow, 13th Edition
Type of Connections (delivery method )
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NETWORKING MEDIA
• To connect the devices in a network,
– either wired media (physical cables) or
– wireless media (typically radio signals) can be
used.
Understanding Computers: Today and Tomorrow, 13th Edition
Wired Networking Media
Transmits using light
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Wireless Networking Media
• Wireless connections: Use radio signals to send data
– Short-range (such as Bluetooth) can connect a
wireless keyboard or mouse to a computer
– Medium-range (such as Wi-Fi, 802.11) are used for
wireless LANs and to connect portable computer
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 Federal
Communications Commission (FCC) and are
measured in hertz (Hz)
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The Electromagnetic Spectrum
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Cellular Radio Transmissions
•
•
•
•
•
Cellular radio transmissions are used with cell phones and are sent
and received via cellular (cell) towers—tall metal poles with antennas on
top.
Cellular service areas are divided into honeycomb-shaped zones called
cells; each cell contains one cell tower
When a cell phone user begins to make a call, it is picked up by the
appropriate cell tower (the one that is located in the cell in which the cell
phone is located and that belongs to the user’s mobile phone provider).
That cell tower then forwards the call to the mobile phone company’s Mobile
Telephone Switching Office (MTSO), which routes the call to the recipient’s
telephone via his or her mobile or conventional telephone service provider
The speed of cellular radio transmissions depends on the type of cellular
standard being used, the type of phone being used by the recipient.
Understanding Computers: Today and Tomorrow, 13th Edition
Cellular Radio Transmissions
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Microwave station.
•
•
•
Microwave station.
– An earth-based device that sends and receives high-frequency, highspeed radio signals.
Microwaves are high-frequency radio signals that can send large quantities
of data at high speeds over long distances. Microwave signals can be sent
or received using microwave stations or communications satellites, but must
travel in a straight line from one station or satellite to another without
encountering any obstacles, since microwave signals are line of sight.
Microwave stations are earth-based stations that can transmit
microwave signals directly to each other over distances of up to about 30
miles. To avoid buildings, mountains, and the curvature of the earth
obstructing the signal, microwave stations are usually placed on tall
buildings, towers, and mountaintops. Microwave stations typically contain
both a dish-shaped microwave antenna and a transceiver. When one
station receives a transmission from another, it amplifies it and passes it on
to the next station.
Understanding Computers: Today and Tomorrow, 13th Edition
Communications satellites
• Communications satellites are space-based devices
launched into orbit around the earth to receive and
transmit microwave signals to and from earth.
•
Communications satellites were originally used to
facilitate microwave transmission when microwave
stations were not economically viable (such as over
large, sparsely populated areas) or were physically
impractical (such as over large bodies of water).
Understanding Computers: Today and Tomorrow, 13th Edition
Communications satellites
• Communications satellites are space-based devices
launched into orbit around the earth to receive and
transmit microwave signals to and from earth.
•
• Communications satellites were originally used to
facilitate microwave transmission when microwave
stations were not economically viable (such as over
large, sparsely populated areas) or were physically
impractical (such as over large bodies of water).
Understanding Computers: Today and Tomorrow, 13th Edition
Microwave and Satellite Transmissions
Traditional satellites use geosynchronous orbit
Low earth orbit (LEO) satellites were developed to combat delay
Medium earth orbit (MEO) satellites - often used for GPS systems
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Infrared (IR) Transmissions
• IR: 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
portable computers or gaming systems, or send
documents from portable computers to printers
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Communications Protocols and Networking
Standards
• Protocol: A set of rules for a particular situation
– Communications protocol: A set of rules that
determine how devices on a network communicate
• Standard: A set of criteria (guidelines) or requirements
approved by a recognized standards organization
– Networking standards: Address how networked
computers connect and communicate
– Needed to ensure products can work with other
products
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Transport Control Protocol /Internet Protocol
(TCP/IP)
• TCP/IP: The most
widely used
communications
protocols
• Used with the
Internet
• TCP responsible
for delivery of data
• IP provides
addresses and
routing information
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Ethernet (802.3)
• Ethernet: Most widely used standard for wired networks
– Original (10Base-T) Ethernet networks run at 10
Mbps
– Newer 100 Mbps, 1Gbps, and 10 Gbps versions are
common
– 100 Gbps and Terabit Ethernet are in development
• Power over Ethernet(POE): Allows electrical power to be
sent along with data on an Ethernet network
– Most often used by businesses
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Phoneline, Powerline, G.hn, and BPL
• Phoneline: Allows networking via ordinary telephone
wiring
• Powerline: Allows networking via ordinary electrical
outlets
• G.hn: An emerging standard designed as unified world
wide standard for home networks creating via phone
lines, power lines, and coaxial cable
• Broadband over powerline (BPL): Uses existing power
lines to deliver broadband internet to some homes
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Wi-Fi (802.11)
– Hotspots expanding
– Speed and distance of Wi-Fi networks depends on:
• Standard and hardware
being used (continually
evolving)
• Number of solid
objects between
the access point
and the
computer or
device
• Possible
interference
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WiMAX and Mobile WiMAX
• WiMAX (802.16): Fairly new
wireless standard for longer
range wireless networking
connections
– Designed to deliver
broadband to homes,
businesses, other fixed
locations
– Hotzones close to 2 miles
(similar in concept to cell
phone towers)
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Short-Range Wireless Standards
• 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
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Wireless Networking Standards
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Networking Hardware
• Networking hardware
– Network adapter: Used to connect a computer 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
– 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
– Cable
– Wi-Fi or WiMAX
– DSL
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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 in a network like a hub but
only sends data to the device for which the data is
intended
– Wireless access point: Used to grant network access
to wireless client devices
– Wireless router: Typically connects both wired and
wireless devices in a network
– Bridge: Used to connect two LANs together
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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
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Networking Hardware
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