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Chapter 7
Networking: Computer
Connections
Networks
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Network - a computer system that uses
communications equipment to connect two or more
computers and their resources
– share hardware, software, and data
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Local Area Network (LAN) - a computer network that
spans a relatively small geographic area
– often connects users in an office or building
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Wide Area Network (WAN) - a computer network that
spans a large geographic area
Data Transmission Methods
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digital signal - data is sent as distinct pulses (on or
off) (0 or 1)
analog signal - data is sent as a continuous electrical
signal in the form of a wave
most in place communications media are analog
– phone lines, coaxial cable, microwave circuits
modem - device to convert digital signals to analog
(modulation) and analog signals to digital
(demodulation)
– may be internal or external
– transmission rates of 56,000 bps
Alternatives to modems
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ISDN - Integrated Services Digital Network
– transmission rates of 128,000 bps
– requires an adapter and phone service, possibly a
new phone line
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DSL - Digital Subscriber Line
– even slower services several times faster than
standard modems
– uses modulation/demodulation, but acts like many
modems working simultaneously
More alternatives

Cable modems
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uses coaxial television cables
speeds up to 10 million bps
always “on”, does not require dialing
users share capacity, decreasing performance
security can be an issue
Cellular modems
– convenient for mobile users
Asynchronous and Synchronous
Transmission
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Methods for keeping sending and receiving
systems “on the same page”
asynchronous - start signal is sent, then a
character, then a stop signal
– receiving system sets up a timing mechanism
when start signal is received
– slow transmission rates
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synchronous - sending and receiving systems
are synchronized by a bit pattern at the
beginning of the message
– large blocks transmitted
– more complex and expensive, faster
Communications Media

communications medium - physical means of
data transmission
– most networks use a combination of media
• twisted pair wire - traditional telephone lines
• coaxial cable - cable television lines
• fiber-optic cable - bundles of fine glass or plastic fibers,
guide light beams, very high transmission speeds
• microwave transmission - line-of-sight transmission from
station to station, susceptible to weather conditions
• satellite transmission - microwave transmission using
satellite as relay station

bandwidth - measure of the capacity of the
link
Protocols
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protocol - a set of rules for the
exchange of data
communicating systems must agree on
– transmission method, speed, duplex
setting, etc.
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TCP/IP - Transmission Control
Protocol/Internet Protocol - standard set
of rules for Internet communication
Topology
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topology - physical
layout of a network
node - any physical
device in the
network
star
bus
ring
Wide Area Networks
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communications services provided by common
carriers
– dedicated service permanently connects 2 or more
locations (may be leased)
– switched (dial-up) service provides a temporary
connection

WAN hardware and software
– host - mainframe to control network
– multiplexer - combines transmissions from many
sources into a single stream, decomposes stream
when received
– terminal emulation software - allows a mainframe
to view PC as a terminal
Local Area Networks
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components connected by some type of
network cable
each computer has a network interface card
bridge - hardware/software that connects
similar networks
gateway - hardware/software that connects
dissimilar networks (protocol conversion)
router - computer that directs
communications traffic, selects best path
– strategy used in e-mail transmission
Types of LAN’s

client/server
– server - computer that controls the network
– client - other computers that request
service from the server
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peer-to-peer
– all computers have equal status
– users share resources
– may be slow with heavy use
Uses and Advantages of
Networking
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electronic mail
fax technology
groupware - sharing software
teleconferencing - bring people together
despite geographical differences
telecommuting - working from home via
computer
electronic data interchange (EDI) - electronic
transfer of “paperwork”
sharing of hardware resources