Lecture 11 : Computer Networks and Internet 1 This Lecture Covers: - - PowerPoint PPT Presentation

UEC01: Computer Skills & Programming Concepts I

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Lecture 11: Computer Networks and Internet

This Lecture Covers:  Types of Computer Networks.

 Communication devices and media.  Network Topology.  LAN Components  Network Uses  Internet Protocols.  Internet Services.

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Objectives

 Describe the basic components of a network  Explain the methods of data transmission, including

types of signals, modulation, and choices among transmission nodes

 Differentiate among the various kinds of

communications links and appreciate the need for protocols

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Objectives

 Describe various network configurations  List the components, types, and protocols of a local

area network

 Describe some examples of networking  List and describe the non-Web services of the Internet

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Computer Network

 Computer systems that transmit data over communications

lines such as telephone lines or cables

 Uses communications equipment to connect two or more

computers and resources

 Distributed data processing systems are networks

Network types

 Local area network (LAN) designed to share data and

resources among several users in office or building

 Metropolitan Area Network (MAN) - networks that cover a

single city

 Wide Area Network (WAN) Can span the world or link

computers across town

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LAN

Putting Together a Network

 Basic Components

 Sending device  Communications link  Receiving device

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Digital and Analog Transmission

 Digital signal (data) from computer must be converted

to analog form to be transmitted over analog (voice) phone lines

 Conversion from digital to analog called modulation  Conversion from analog to digital called demodulation  Modem

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Modem

 Communication device  Short for modulator/demodulator  Converts digital signal to analog and vice versa

 Cable connects modem to standard phone jack

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Types of Modems

 External modem separate from computer  Internal modem inserted into computer  PC Card modem slides into slot on laptop  Modem Data Speed is Measured in bits per second

(bps)

 Early modems transmitted at 300 bps  Fastest current modems transmit at 56,000 bps

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Other Communications Devices

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• ISDN
• DSL
• Cable Modems
• Cellular Modems

Integrated Service Digital Network (ISDN)

 Special type of telephone circuit

 Can move data at 128,000 bps  Includes two phone lines, so you can talk on the phone

while online

 Drawbacks

 Expensive, especially at installation  Not available in all areas

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Digital Subscriber Line (DSL)

 Uses advanced electronics to send data over

telephone line at very high speeds

 Always on - no need to dial a connection  Can use phone while online

 Drawbacks

 You must be within three miles of telephone

company’s switching office

 That office must have DSL equipment

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Cable Modems

 Uses coaxial cable already in place for your TV

 Very fast transmission speed, especially for downloading  Always on: no need to dial a connection

 Drawbacks

 All users share a cable segment’s capacity

 As more users in neighborhood go online, speed

decreases

 No security for individual users or data

 Purchase a firewall program for security

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Cellular Modems

 Transmit data over the cellular telephone system

 Roughly half the speed of a regular telephone network

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Simplex, Half-Duplex, and Full- Duplex Transmission

 Simplex transmission sends data in one direction only

 Example: television broadcasting

 Half-duplex transmission sends data in both directions,

but only one way at a time

 Example: bank teller sends data about a deposit; after

data received, a confirmation returns

 Full-duplex transmission allows transmission in both

directions at same time

 Example: a conversation  Typically used for high-speed data communication

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Communications Media

 Physical means of data transmission  Bandwidth is measure of the capacity of the

communications link

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Types of Communications Media



Wire pairs

 known as twisted pair: Two wires twisted

around each other to reduce electrical interference



Coaxial cables

 A center conductor wire surrounded by layer of insulation and metallic sheath, as used

to connect to cable TV, higher bandwidth .



Fiber optics

 Use light instead of electricity to send data, Much higher bandwidth.



Microwave transmission

 Uses line-of-sight transmission, Requires relay stations (antenna) or repeaters every 30

miles, used by mobile phone. Offers high speed and cost-effectiveness.



Satellite transmission



A form of microwave transmission where Satellite acts as relay station and signal travels thousands of miles

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Wireless transmission



Transmits data over short distances without wires. Ex: IrDA, Bluetooth,802.11 standards

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Network Topology



The physical layout of a network



Node - each computer, printer, or server on network



Three common topologies

a) Star

 Central (hub or switch) computer manages network

b) Ring

 Links all nodes in a circular chain

c) Bus

 All nodes connected to single line (bus)

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LAN Components

 Network cable

 Twisted pair wire, coaxial or fiber optic cable  Wireless access point

 Network interface card (NIC)

 Circuit board Connects each computer to wiring in the network,

Handles sending, receiving, and error checking of transmitted data

 Router

 Router directs communications traffic when several networks

connected together

 Gateway

 Lets a node communicate with a computer on another dissimilar

network with different protocol

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Client/Server Network

 Server computer controls network

 Often has several hard drives, fastest printer

 Client computer requests services from server

 Thin client has little or no storage

 Processing approaches

 Client/server

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Peer-to-Peer Networks

 All computers have equal status  Users share each other’s files, printers, etc. as needed  Common in small offices  Networks tend to be slow

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Network Uses

 Electronic mail (e-mail)  Facsimile (fax) technology  Teleconferencing  Electronic data interchange  Electronic fund transfers  Computer commuting  The Internet

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The Internet

 A global network of hundreds of thousands of

computers

 Widely considered to be the defining technology

• f the beginning of this century

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The Internet Service Provider

 An Internet service provider (ISP)

provides the server computer and software to connect to the Internet

 Online service, such as America

Online, includes Internet access, Internet service, and a browser

 When you connect to the Internet,

the browser displays a home page

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Browser

 Interface software used to explore

the Internet

 Early browsers were text-only  Mosaic was the first graphical

browser

 Graphical browsers combine ease

• f links with attractive graphical

interface

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Uniform Resource Locator (URL)

 The complete, unique address of a Web page

 Web page URL begins with http

 HyperText Transfer Protocol – allows communication by using

links to transfer data between sites

 Domain name – address of site’s host computer

 Last part of domain name is called a top-level domain  Identifies country or purpose of organization

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Internet Links

 A link on a Web site is easy to

see

 Either underlined and

colored text or an icon

 Clicking the link transfers

data from that site to the user’s computer

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A Little About the Technology

 Protocol - a set of rules for the exchange of data

between a terminal and a computer or two computers

 Agreement on how data is to be sent and receipt

acknowledged

 Needed to allow computers from different vendors to

communicate

 Transmission Control Protocol/Internet Protocol

(TCP/IP) permits any computer to communicate with the Internet

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Searching the Internet

 Search Engine – lets a user specify

search terms

 Search engine builds database of sites

that match those terms

 Uses spider software to build database  Metasearch – searches search engines

and builds comprehensive list

 Internet directory – database is

developed by human researchers rather than spider

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Non-Web Services of the Internet

 Newsgroups  FTP  Telnet  E-mail  E-Commerce

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