James Tam

Computer Networks

Concepts covered

•What is a computer network

•Benefits and issues of networks

•Types of networks

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What Is A Network?

2+ computers

A communication system that connects them

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Benefits Of Networks (Business View)1

1) Resource sharing• Programs, hardware, data etc.

2) Reliability• Multiple copies of files, multiple processors

3) Reducing costs• Initial cost of network and future upgrades

4) Communication• The network provides yet another means of communicating

1 From “Computer Networks” by Tanebaum

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4) Communication (Instant Messaging)

Instant Messenger (Microsoft)

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4) Communication (Instant Messaging Continued)

AIM (American online/Netscape)

ICQ (I seek you)

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Benefits Of Networks (Business View - Continued)

4) Communication - groupware

e.g. The TeamWave Workplace (Sonexis Inc.)

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Benefits of networks (person-based view)1

1) Access to remote information• E.g., access to information

2) Person-person communication• E.g., Instant messenger services, ICQ, email etc

3) Entertainment• Fun and games

1 From “Computer Networks” by Tanebaum

Diablo (Blizzard) Black Knight(Microsoft)

Ghost Recon (Red Storm)

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Social Issues Of Networks1

1) Determining what is acceptable

2) Privacy• Employers. Employees• The need for the storage of access to information vs. individual rights

3) Anonymity• Costs and benefits

1 From “Computer Networks” by Tanebaum

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What You Need For A Two Computer Network

Two computers (obvious)

A network interface card (NIC) for each computer

Ethernet connection

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A Picture Of A Two Computer Network

Computer name = “Fred”

Computer name = “Freda”

Network name = “Fland”

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What You Need For A Multi (3+) Computer Network

The computers

A network interface card for each computer

Ethernet connection

Network hub

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A Picture Of A Multi-Computer Network

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Connecting A Network To Other Networks

Router

• Avoids clogging computers with irrelevant data• Ensures that information reaches the proper destination

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Protecting Your Network From The Outside

Firewall

• Filters information- Offensive web sites

• Protects network- Hackers

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Types Of Networks

Local Area Network (LAN)• May be located within a single building or campus

Metropolitan Area Network (MAN)• A larger version of a LAN• May span several corporate offices or an entire city

•Wide Area Network (WAN)• May span a country or even a continent

LANMAN

LAN LAN

WAN

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Bandwidth

Determines the amount of information that can be transmitted by a network connection• Finite amount• Measured in bits per second (bps)

Transmission rate analogous to a road• Number of “lanes”• Speed

Categories• Narrow band: 40 – 100 bits/second (telegraph line)• Voice band: 110 – 9600 bits/second (phone line)• Broad band: several Megabits/second (next slides)

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Types Of Network Connections

Physical • Twisted pair• Coaxial cable• Fiber optic

Wireless• Microwave• Infrared• Light• Radio

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Twisted Pair Networks (Physical)

Twisting eliminates electrical interference from nearby pairs

Increased twisting increases the transmission rate

Category 1 Less than 1 Megabit/second (phone lines)

Category 2 Up to 4 Megabits/second

Category 3 10 Megabits/second (U of C)

Category 4 20 Megabits/second (Token Ring)

Category 5 100 Megabits/second (Fast Ethernet)

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Twisted Pair Networks (Physical - Continued)

Twisted pair can be:

•Unshielded – cheaper and takes up less space

•Shielded – protects against interference

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Coaxial Cable Networks (Physical)

Speed range• 10 – 100 Megabits per second

Copper core

Insulation

Braided outer conductor

Protective plastic covering

Metal connector

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Twisted pair vs. Coaxial cables

Both• Transmit signals through a metal cable

Coaxial cables can be longer• 100 meters (twisted pair) vs. 500 meters (coaxial cable)

Coaxial cables are linear (one break takes down an entire part of the network)

Hub

Twisted pair Coaxial cable

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Fiber Optic Networks (Physical)

Light is transmitted through a clear plastic tube

Fast with few errors• 100 Megabits per second

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Pros And Cons of Fiber (Physical Continued)

Advantages over copper wires (twisted pair and coax)• Long range• Not affected by electrical problems• Not effected by air borne corrosives • Thin and light• Secure

Disadvantages of fiber over copper• New and unfamiliar technology• Unidirectional – light travels in one direction

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Microwave-based Networks (Wireless)

No physical link required• May increase flexibility in location

Lower costs

Low error rate

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Microwave-based Networks (Wireless continued)

Slow transmission rate• 8 Megabits per second

Linear• Microwaves travel in a straight line

May be effected by atmospheric conditions• Transmissions called on account of rain…

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Infrared Networks (Wireless)

No physical link required

Cheap and easy to build

Need a clear line of sight• IR beams don’t pass well through solid objects

Slow transmission rate• 4 Megabits per second

Doesn’t work outside

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Light-based Networks (Wireless)

No physical link required

Unidirectional and limited range• ~ Several hundred meters

Highly dependent on the weather

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Radio-wave Networks (Wireless)

No physical link required

Works outdoors and indoors

Omni directional

Slow transmission• 1 Megabit per second

Subject to interference

Direct Indirect

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Radio-wave Networks: Bluetooth (Wireless)

No physical link required

Short range radio• 10 m (100 with antenna)

Works with any electronic device• Keyboard, computer, mouse, cell phone, head phone etc.

Slow• 1 Megabit per second

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SummaryWhat is a network and what a network consists of

Benefits and issues associating with computer networks

What are different types of networks• LAN, MAN, WAN

What are different types of network connections• Physical vs. wireless and examples of each.