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Police Technology
Chapter Four
Networks
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Learning Objectives
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Understand the importance and use of
Networks
Understand the different types of
technologies necessary to establish a
network
Be exposed to several different types of
networks
Understand the necessity for network
security and several of the means of
providing network security.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Network Basics
A network is about
two or more people
establishing a way
to communicate.
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There are formal
and informal
networks.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Network Basics
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Networks are founded on the concept of
client-server architecture. Architecture
refers to the design of a system or
technology.
The individual work station, called a node,
is provided networking services by a
server.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Network Basics

The server is a computer that
provides files, printers, and
processing power to the
individual workstations. The
server is a special type of
computer linked into a
network. It is used only to
manage the network, shared
data, and shared resources.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Why Network?

Law enforcement agencies may have
many buildings and offices in different
physical locations. A network allows them
to share computer, data, and information
resources. Much of the information used
by law enforcement comes from agencies
outside their organization (e.g., DMV,
Corrections, other agencies, etc.).
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Why Network?

Networks also provide organizations with
the capability to back up data. If one
computer fails, the network can take over
the processing load.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Back to …..
Analog and Digital Signals
An analog signal weakens as it travels
through wire because of the resistance
the signal meets in the medium that is
carrying it (air, wire, coaxial cable).
Digital signals are subject to the same
decrease in strength as analog signals.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Back to …..
Analog and Digital Signals
Digital signals are the primary means of
transmitting data communications.
Digital signals have several advantages
over analog:
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Fewer errors;
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Can be transmitted at higher speeds

Peripheral devices are less complex.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Analog stuff
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The analog wave is called a baud.
Bits are essentially added to the
analog wave.
Public networks tend to run at about
2,400 baud (waves) per second.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Analog stuff

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Our technology adds more bits to each
baud generally in multiples of four.
A 2,400 baud analog signal that adds
12 bits to each baud would give an
effective transmission rate of 28,800
bits per second (BPS).
This about
Modem Speed!
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Error Detection
One of the schemes commonly used to
prevent data corruption is bit parity.
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Take a stream of binary, add up the
numbers, you get an odd or an even
number.
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Add a digit at the end of the data to indicate
if the sum is odd or even.

The receiving computer compares the sum of
the data stream to the bit parity digit.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Data Transmission
Information travels between computers
in a network in one of three ways:

Simplex transmission – information
travels in one direction only

Half-duplex – information travels in
both directions, one way at a time

Full duplex – data is transmitted in
both directions simultaneously
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Designing a Network
Look at three things:

The fastest throughput and response
time possible

The least-cost path – the data flows
through the fewest devices possible
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Design reliability
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Things That Connect
Networks accomplish data transfer with a
concept called packet switching.
 Unused (available) portions of a
network are chosen
 Data passes through the most efficient
available means
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Things That Connect
In networks, the connection point between
your computer and the network is commonly
a modem.
Modems have become asymmetric digital
subscriber line (ADSL). The word
asymmetrical is used because these modems
send data faster in one direction than the
other.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Asymmetric Digital Subscriber
Line - DSL
Most homes and offices have a dedicated copper
wire running between them and the telephone
company’s central office.

The copper wire can carry far more data than the
3,000 Hz signal of a typical telephone conversation
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The copper wire can act as a purely digital high-speed
transmission channel (1 million bps).

The same line can transmit both a telephone
conversation and the digital data.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Other ways
of connecting to a network
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Use a hub
Most hubs include a switch. A switch
determines how data will travel along its
path to the intended destination – to
look for the optimal route
A router is like a switch. A router is a
bridge between two networks. The
router determines the best path between
two different networks
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Network Terms
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A remote switch is one that is at your
location but controlled by someone else at
different location.
A trunk is a circuit between different types
of switching equipment.
Middleware describes a software that is
used to connect different applications (the
translator).
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Data Compression

Techniques to reduce
the size of data in
order to improve
storage and
bandwidth
(transmission)
capacity.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Bandwidth
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Refers to the capacity of
the medium that carries
the signal.
Analog bandwidth is
measured in Hz.
Digital bandwidth is
measured in the number
of bits per second the
medium can carry.
Determines the speed at
which data can be moved
through a network
More bandwidth = more data, faster
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Protocols
An agreement between people on how
a transaction should take place.
Many networks use the Transmission
Control Protocol/Internet Protocol
(TCP/IP). Your computer must use
TCP/IP to go on the Internet.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Basic Network Types
Hierarchical - vertical
or tree structure
 Local Area Network
(LAN) - horizontal
network. Allows each
device on the network
to receive every
network transmission.
 Star Configuration –
All transmissions
come
Copyright 2005-2009: Hi Tech
Criminal from a hub.

Justice, Raymond E. Foster
Basic Network Types
LAN is a network that operates in one
specific location.
 Wide Area Network (WAN) is used to
connect geographically separated
networks together.

Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Basic Network Types

Wireless Local Area
Network (WLAN)
uses radio waves
to connect among
the mobile node,
mobile computer,
and the hardwired
network.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Data Security
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Could be called Network security or
Computer security.
What we are most trying to protect is
the information contained in the
various systems.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Physical Security is . . .
Anything we do to physically protect
our systems and information:
 Placing servers, routers and
switching equipment behind locked
doors
 Backing up data in one or more
location
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Virtual Security is…..
Firewall - operates by controlling
access to the network based upon the
contents of the data packets being
transmitted on the network.
 Encryption - changing text or data
into a form that is unreadable without
a key (secret code)

Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
Virtual Security is…..
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Intrusion Detection –
security management
system that gathers
and analyses info
from different part of
the network. Scans
network looking for
user and system
activity and any
pattern of abnormal
behavior.
Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster
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Copyright 2005-2009: Hi Tech Criminal
Justice, Raymond E. Foster