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Module E: Network BASICS
INTRODUCTION

Computer network – two or more
computers connected so that they can
communicate with each other and share
information, software, peripheral devices,
and/or processing power
INTRODUCTION
Number of connections



For n nodes, you would need n(n-1)/2
connections
For examples to connect 5 nodes
we would need 5 (5-1)/2=10
connections
Basic Principles of Networks

1.
2.
3.
Four main principles
Each computer must have a network
interface to provide a doorway for
information
The network usually has at least one
connecting device
The network must have communications
media to transport information
Basic Principles of Networks
4.

Each computer must have software to
move information in and out of the
computer
These four principles apply to all
networks, large and small
HOME NETWORKS

A typical home network setup has
1.
2.
3.
An Ethernet network card in each
computer or a wireless card in each laptop
Network cables to transmit signals, or no
cables for wireless
A DSL or cable modem connection and a
broadband/home router
Network Cards

Network interface card (NIC) – an
expansion card or PC card that connects
your computer to a network


Ethernet card – the most common type of
network interface card
Built into the motherboards of many new
computers – looks like a telephone jack,
but wider
Wired Transmission Media

Cat 5 (Category 5) cable – better-
constructed version of phone twisted-pair
cable
Wireless Transmission Media



Wireless Access Point (WAP) – device
that allows a computer to use radio waves to
access a network
Connects to hub or switch with a cable like a
wired computer
May be built into broadband router and not
require separate cabling
Home Internet Service

Broadband router or home router – a
device to connect computers together to
share DSL or cable Internet service in a
home or small office


One port to plug into DSL or cable connection to
connect to the Internet
Usually several ports to build a network for
home computers or printers and share Internet
connection
Network Software



Makes each computer's hardware work
Can use Windows
Turn on filesharing to make files available to
other computers on the network
NETWORK COMPONENTS

Hub – a device that connects computers
into a network and repeats all
transmissions to every connected
computer



Only one computer can transmit at a time
All computers see every message
Can have collisions when two computers try
to transmit at the same time
NETWORK COMPONENTS

Switch – a device that connects
computers and repeats transmissions
only to intended recipient



Multiple conversations can occur
simultaneously between different sets of
computers
Only recipient computer sees each message
Computers can still broadcast messages to
all other computers on the network
NETWORK COMPONENTS

Router – a device that connects
subnetworks (subnets) of a larger
network



Can connect different buildings at same or
different locations
Passes transmissions from one network to
another
May pass through multiple routers on the
way from source to destination
NETWORK COMPONENTS

More on routers



Home/broadband routers often have builtin switches or hubs
Corporate routers generally require
separate switches or hubs
Routers must be configured with
information about the networks they
connect
NETWORKS BY DISTANCE

Large networks can be classified by the
proximity of the area(s) they serve:

Local Area Network (LAN) – network
that serves a building or buildings in a
contiguous area
NETWORKS BY DISTANCE

More networks by distance

Wide Area Network (WAN) – a set of
connected networks serving areas not
immediately contiguous

Metropolitan Area Network (MAN) – a
set of connected networks within the same
city or metropolitan area but not in
immediate proximity to each other
THE INTERNET



A vast network of computers that
connects people all over the world
Computers pass messages through
routers to their ultimate destinations
Each router determines whether it has a
direct path to the recipient or whether to
send the message on to another router
Bandwidth



The amount of information that can be
transferred in a given amount of time
Usually expressed as bits per second (bps)
Higher bandwidths expressed as
 kilobits per second (Kbps) – thousands of bits
per second
 megabits per second (Mbps) – millions of bits
per second
 gigabits per second (Gbps) – billions of bits
per second
Internet Connection Types





Phone line and dialup modem
Phone line and DSL modem
Cable TV line and cable modem
Satellite modem
Dedicated high-speed business lines
Broadband Internet
Connection


Broadband – high-capacity
telecommunications line capable of
providing high-speed Internet service
All Internet access methods on the
previous slide are broadband except the
dialup modem
Dialup Connection



Modem – connects a computer to a phone
line to access another computer or network
Modulates outgoing signal from digital to
analog form
Demodulates incoming signal from analog to
digital form
Digital Subscriber Line (DSL)


Digital Subscriber Line (DSL) – high-
speed Internet connection using phone
lines, which allows you to use your
phone for voice communications at the
same time
Runs at a higher frequency than voice
conversations, so not supported on some
older phone lines
Cable Modem

Cable modem – uses your TV cable to
deliver an Internet connection
Satellite Modem



Satellite modem – delivers Internet
access from satellite dish
Satellite TV and modem may share same
dish or may be separate
Connects to computer or broadband
router like cable modem
T1 and DS3 Business Lines




T1 and DS3 developed by phone
companies to carry many long-distance
voice conversations
T1 runs up to about 1.5 Mbps
DS3 runs up to about 45 Mbps
Can carry both voice and network over
the same lines
Frame Relay and ATM Business
Services


Frame Relay and ATM are used
to connect many branch offices
to the main office
Use virtual circuits to simulate
having a line from every office
to every other office
Virtual Circuits
Comparison of Connection
Types

Telephone modem



+ Inexpensive and available anywhere
there's a phone line
- Slow, and ties up the line for voice calls
too
DSL

+ Higher-speed connection, doesn't tie up
the phone line for voice calls, and can be
left on all the time
Comparison of Connection
Types

Cable modem



+ Higher-speed connection, doesn't use the
phone line at all, and always-on
- Connection shared with the
neighborhood, so speed may vary
Satellite modem


+ Available in remote locations where DSL
and cable aren't
- High cost
Comparison of Connection
Types


T1 and DS3
 + High-speed to very-high-speed
connections, can transmit both voice and
data
 - High cost that may be mileage-dependent
Frame relay and ATM
 + Use virtual circuits to simulate more interoffice connections than are physically present
 - High cost normally affordable only by midto large-scale enterprises
Voice Over IP


Voice over IP – allows you to send
voice communications over the Internet
and avoid long-distance toll charges
No long-distance calling cost
NETWORK COMMUNICATIONS
MEDIA



Communications media – the paths in
a network over which information travels
Wired communications media –
transmit information over a closed,
connected path
Wireless communications media –
transmit information through the air
Wired Communications Media



Twisted-pair cable – a bundle of copper
wires for transmitting voice or data
Cat 5 and Cat 5e are common for modern
networks
Coaxial cable (coax) – one central wire
surrounded by insulation, a metallic shield,
and a covering of insulation
Wired Communications Media

Optical fiber – uses a very thin glass or
plastic fiber through which pulses of light
travel
Wireless Communications
Media

Infrared – uses red light to send and receive
information


Bluetooth – a standard for transmitting
information in the form of short-range radio
waves over distances of up to 30 feet and is
used for purposes such as wirelessly connecting
a cell phone or PDA to a computer
Microwave – a type of radio transmission
 Repeater – receives a radio signal,
strengthens it, and sends it on
Wireless Communications
Media
Wireless Communications
Media

Communications Satellite – microwave
repeater in space
NETWORK SECURITY

The four principles of network security
are:
1.
2.
3.
4.
Confidentiality
Authenticity
Integrity
Availability
NETWORK SECURITY

Confidentiality – information can be
obtained only by those authorized to
access it


Bank statements, credit reports, employee
evaluations
Threatened by capture of network
transmissions and easily-guessed
passwords
NETWORK SECURITY

Authenticity – information really comes
from the source it claims to come from


Military orders, medical diagnoses,
stockbroker directions
Threatened by fraudulent e-mails and
misspellings of popular Web site names
NETWORK SECURITY

Integrity – information has not been
altered


Bank balance, corporate Web site,
prescriptions, credit card charges
Threatened by forged network
transmissions and faulty server software
NETWORK SECURITY

Availability – a service or resource is
available when it's supposed to be


Mail-order Web site, corporate e-mail
server
Threatened by network failures, faulty
server software, and high volumes of
malicious network traffic
Firewalls & Intrusion Detection
Systems

Firewall – protects a computer from
intruders

Intrusion detection system (IDS) –
watches for and reports intrusion
attempts

Intrusion prevention system (IPS) –
type of IDS that also takes action against
intrusion attempts
Encryption

Encryption – scrambles data so you
can't read it without having the
decryption key

Virtual Private Network (VPN) –
encrypts all network transmissions
between two endpoints to protect
confidentiality and integrity of data
Firewalls & Intrusion
Detection Systems
Malware

Malware – software designed to harm
your computer or security
1.
2.
3.
Virus – software written with malicious
intent to cause annoyance or damage
Worm – spreads itself from computer to
computer via e-mail and other network
traffic
Spyware – collects information about you
and reports it to someone else without
your permission
CLIENT/SERVER SOFTWARE
MODEL

Client/server network – a network in
which one or more computers are
servers and provide services to the other
computers, called clients
Client/Server: A Business View

Client/server networks differ according
to
1.
2.
3.
Where the processing for the presentation
of information occurs
Where the processing of logic or business
rules occurs
Where the data management component
(DBMS) and information (database) are
located
Client/Server: Model 5
Five Models of Client/Server
Five Models of Client/Server
1.
2.
3.
Distributed Presentation
 The server handles almost all functions,
including a major portion of the presentation
Remote Presentation
 The client handles all presentation functions
Distributed Logic
 The server handles all data management,
the client handles all presentation
formatting, and the logic processing is
shared
Five Models of Client/Server
4.
Remote Data Management

5.
The server handles data management
only, and the client processes business
rules and formats the presentation of
results
Distributed Data Management

The client handles all presentation
formatting and business rule processing,
and both the server and client share data
management duties