This chapter discusses networks and their importance for law enforcement agencies. It covers the basics of networks including client-server architecture, formal and informal networks, and why networks are useful for sharing resources across multiple locations. The chapter also discusses different types of network connections including digital and analog signals, modems, switches, routers, and remote switches. Network security is also mentioned as an important concept to understand.

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Police TechnologyPolice Technology
Chapter FourChapter Four
NetworksNetworks

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Learning ObjectivesLearning Objectives
 Understand the importance and use ofUnderstand the importance and use of
NetworksNetworks
 Understand the different types ofUnderstand the different types of
technologies necessary to establish atechnologies necessary to establish a
networknetwork
 Be exposed to several different types ofBe exposed to several different types of
networksnetworks
 Understand the necessity for networkUnderstand the necessity for network
security and several of the means ofsecurity and several of the means of
providing network security.providing network security.

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Network BasicsNetwork Basics
 AA networknetwork is aboutis about
two or more peopletwo or more people
establishing a wayestablishing a way
to communicate.to communicate.
 There are formalThere are formal
and informaland informal
networks.networks.

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Network BasicsNetwork Basics
 Networks are founded on the concept ofNetworks are founded on the concept of
client-server architectureclient-server architecture. Architecture. Architecture
refers to the design of a system orrefers to the design of a system or
technology.technology.
 The individual work station, called aThe individual work station, called a nodenode,,
is provided networking services by ais provided networking services by a
server.server.

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Network BasicsNetwork Basics
 TheThe serverserver is a computer thatis a computer that
provides files, printers, andprovides files, printers, and
processing power to theprocessing power to the
individual workstations. Theindividual workstations. The
server is a special type ofserver is a special type of
computer linked into acomputer linked into a
network. It is used only tonetwork. It is used only to
manage the network, sharedmanage the network, shared
data, and shared resources.data, and shared resources.

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Why Network?Why Network?
 Law enforcement agencies may haveLaw enforcement agencies may have
many buildings and offices in differentmany buildings and offices in different
physical locations. A network allows themphysical locations. A network allows them
to share computer, data, and informationto share computer, data, and information
resources. Much of the information usedresources. Much of the information used
by law enforcement comes from agenciesby law enforcement comes from agencies
outside their organization (e.g., DMV,outside their organization (e.g., DMV,
Corrections, other agencies, etc.).Corrections, other agencies, etc.).

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 Networks also provide organizations withNetworks also provide organizations with
the capability to back up data. If onethe capability to back up data. If one
computer fails, the network can take overcomputer fails, the network can take over
the processing load.the processing load.
Why Network?Why Network?

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Back to …..Back to …..
Analog and Digital SignalsAnalog and Digital Signals
An analog signal weakens as it travelsAn analog signal weakens as it travels
through wire because of the resistancethrough wire because of the resistance
the signal meets in thethe signal meets in the mediummedium that isthat is
carrying it (air, wire, coaxial cable).carrying it (air, wire, coaxial cable).
Digital signals are subject to the sameDigital signals are subject to the same
decrease in strength as analog signals.decrease in strength as analog signals.

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Digital signals are the primary means ofDigital signals are the primary means of
transmitting data communications.transmitting data communications.
Digital signals have several advantagesDigital signals have several advantages
over analog:over analog:
 Fewer errors;Fewer errors;
 Can be transmitted at higher speedsCan be transmitted at higher speeds
 Peripheral devices are less complexPeripheral devices are less complex..
Back to …..Back to …..
Analog and Digital SignalsAnalog and Digital Signals

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 The analog wave is called aThe analog wave is called a baudbaud..
Bits are essentially added to theBits are essentially added to the
analog wave.analog wave.
 Public networks tend to run at aboutPublic networks tend to run at about
2,400 baud (waves) per second.2,400 baud (waves) per second.
Analog stuffAnalog stuff

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 Our technology adds more bits to eachOur technology adds more bits to each
baud generally in multiples of four.baud generally in multiples of four.
 A 2,400 baud analog signal that addsA 2,400 baud analog signal that adds
12 bits to each baud would give an12 bits to each baud would give an
effective transmission rate of 28,800effective transmission rate of 28,800
bits per second (BPS).bits per second (BPS).
Analog stuffAnalog stuff
This about
Modem Speed!

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One of the schemes commonly used toOne of the schemes commonly used to
prevent data corruption isprevent data corruption is bit paritybit parity..
 Take a stream of binary, add up theTake a stream of binary, add up the
numbers, you get an odd or an even number.numbers, you get an odd or an even number.
 Add a digit at the end of the data to indicateAdd a digit at the end of the data to indicate
if the sum is odd or even.if the sum is odd or even.
 The receiving computer compares the sumThe receiving computer compares the sum
of the data stream to the bit parity digit.of the data stream to the bit parity digit.
Error DetectionError Detection

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Information travels between computersInformation travels between computers
in a network in one of three ways:in a network in one of three ways:
 Simplex transmissionSimplex transmission – information– information
travels in one direction onlytravels in one direction only
 Half-duplexHalf-duplex – information travels in– information travels in
both directions, one way at a timeboth directions, one way at a time
 Full duplexFull duplex – data is transmitted in– data is transmitted in
both directions simultaneouslyboth directions simultaneously
Data TransmissionData Transmission

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Designing a NetworkDesigning a Network
Look at three things:Look at three things:
 TheThe fastest throughput and responsefastest throughput and response
time possibletime possible
 TheThe least-cost pathleast-cost path – the data flows– the data flows
through the fewest devices possiblethrough the fewest devices possible
 Design reliabilityDesign reliability

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Things That ConnectThings That Connect
Networks accomplish data transfer with aNetworks accomplish data transfer with a
concept calledconcept called packet switchingpacket switching..
 Unused (available) portions of aUnused (available) portions of a
network are chosennetwork are chosen
 Data passes through the most efficientData passes through the most efficient
available meansavailable means

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In networks, the connection point betweenIn networks, the connection point between
your computer and the network is commonlyyour computer and the network is commonly
aa modemmodem..
Modems have becomeModems have become asymmetric digitalasymmetric digital
subscriber line (ADSL).subscriber line (ADSL). The wordThe word
asymmetrical is used because these modemsasymmetrical is used because these modems
send data faster in one direction than thesend data faster in one direction than the
other.other.
Things That ConnectThings That Connect

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Most homes and offices have a dedicated copperMost homes and offices have a dedicated copper
wire running between them and the telephonewire running between them and the telephone
company’s central office.company’s central office.
 The copper wire can carry far more data than theThe copper wire can carry far more data than the
3,000 Hz signal of a typical telephone conversation3,000 Hz signal of a typical telephone conversation
 The copper wire can act as a purely digital high-speedThe copper wire can act as a purely digital high-speed
transmission channel (1 million bps).transmission channel (1 million bps).
 The same line can transmit both a telephoneThe same line can transmit both a telephone
conversation and the digital data.conversation and the digital data.
Asymmetric Digital SubscriberAsymmetric Digital Subscriber
Line -Line - DSLDSL

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Other waysOther ways
of connecting to a networkof connecting to a network
 Use aUse a hubhub
 Most hubs include aMost hubs include a switchswitch. A switch. A switch
determines how data will travel along itsdetermines how data will travel along its
path to the intended destination – to lookpath to the intended destination – to look
for the optimal routefor the optimal route
 AA routerrouter is like a switch. A router is ais like a switch. A router is a
bridge between two networks. Thebridge between two networks. The
router determines the best path betweenrouter determines the best path between
two different networkstwo different networks

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 AA remote switchremote switch is one that is at youris one that is at your
location but controlled by someone else atlocation but controlled by someone else at
different location.different location.
 AA trunktrunk is a circuit between different typesis a circuit between different types
of switching equipment.of switching equipment.
 MiddlewareMiddleware describes a software that isdescribes a software that is
used to connect different applications (theused to connect different applications (the
translator).translator).
Network TermsNetwork Terms

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Data CompressionData Compression
 Techniques to reduceTechniques to reduce
the size of data inthe size of data in
order to improveorder to improve
storage andstorage and
bandwidthbandwidth
(transmission)(transmission)
capacity.capacity.

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BandwidthBandwidth
 Refers to theRefers to the capacitycapacity ofof
the medium that carriesthe medium that carries
the signal.the signal.
 Analog bandwidth isAnalog bandwidth is
measured in Hz.measured in Hz.
 Digital bandwidth isDigital bandwidth is
measured in the numbermeasured in the number
of bits per second theof bits per second the
medium can carry.medium can carry.
 Determines the speed atDetermines the speed at
which data can be movedwhich data can be moved
through a networkthrough a network More bandwidth = more data, faster

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ProtocolsProtocols
An agreement between people on howAn agreement between people on how
a transaction should take place.a transaction should take place.
Many networks use theMany networks use the TransmissionTransmission
Control Protocol/Internet ProtocolControl Protocol/Internet Protocol
(TCP/IP).(TCP/IP). Your computer must useYour computer must use
TCP/IP to go on the Internet.TCP/IP to go on the Internet.

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Basic Network TypesBasic Network Types
 HierarchicalHierarchical - vertical- vertical
or tree structureor tree structure
 Local Area NetworkLocal Area Network
(LAN(LAN) - horizontal) - horizontal
network. Allows eachnetwork. Allows each
device on the networkdevice on the network
to receive everyto receive every
network transmission.network transmission.
 Star ConfigurationStar Configuration ––
All transmissionsAll transmissions

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 LANLAN is a network that operates inis a network that operates in oneone
specific location.specific location.
 Wide Area Network (WAN)Wide Area Network (WAN) is used tois used to
connect geographically separatedconnect geographically separated
networks together.networks together.
Basic Network TypesBasic Network Types

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Basic Network TypesBasic Network Types
 Wireless LocalWireless Local
Area NetworkArea Network
(WLAN)(WLAN) uses radiouses radio
waves to connectwaves to connect
among the mobileamong the mobile
node, mobilenode, mobile
computer, and thecomputer, and the
hardwired network.hardwired network.

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Data SecurityData Security
 Could be called Network security orCould be called Network security or
Computer security.Computer security.
 What we are most trying toWhat we are most trying to protect isprotect is
the informationthe information contained in thecontained in the
various systems.various systems.

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Physical Security is . . .Physical Security is . . .
Anything we do to physically protectAnything we do to physically protect
our systems and information:our systems and information:
 Placing servers, routers andPlacing servers, routers and
switching equipment behind lockedswitching equipment behind locked
doorsdoors
 Backing up data in one or moreBacking up data in one or more
locationlocation

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 FirewallFirewall - operates by controlling- operates by controlling
access to the network based upon theaccess to the network based upon the
contents of the data packets beingcontents of the data packets being
transmitted on the network.transmitted on the network.
 EncryptionEncryption - changing text or data- changing text or data
into a form that is unreadable withoutinto a form that is unreadable without
a key (secret code)a key (secret code)
Virtual Security is…..Virtual Security is…..

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Virtual Security is…..Virtual Security is…..
 Intrusion DetectionIntrusion Detection ––
security managementsecurity management
system that gatherssystem that gathers
and analyses infoand analyses info
from different part offrom different part of
the network. Scansthe network. Scans
network looking fornetwork looking for
user and systemuser and system
activity and anyactivity and any
pattern of abnormalpattern of abnormal
behavior.behavior.

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Police TechnologyPolice Technology
Go to theGo to the Student ResourcesStudent Resources page atpage at
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