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

Four main principles1. Each computer must have a

network interface to provide a doorway for information

2. The network usually has at least one connecting device

3. 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 has1. An Ethernet network card in each

computer or a wireless card in each laptop

2. Network cables to transmit signals, or no cables for wireless

3. 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

built-in 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

- Not available in all areas or on all lines

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

inter-office connections than are physically present

- High cost normally affordable only by mid- to 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. Confidentiality2. Authenticity3. Integrity4. 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 security1. Virus – software written with

malicious intent to cause annoyance or damage

2. Worm – spreads itself from computer to computer via e-mail and other network traffic

3. 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 to1. Where the processing for the

presentation of information occurs2. Where the processing of logic or

business rules occurs3. 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. Distributed Presentation The server handles almost all

functions, including a major portion of the presentation

2. Remote Presentation The client handles all presentation

functions 3. 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 The server handles data

management only, and the client processes business rules and formats the presentation of results

5. Distributed Data Management The client handles all presentation

formatting and business rule processing, and both the server and client share data management duties