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

UEC 01 : Computer Skills & Programming Concepts I Lecture 11 : Computer Networks and Internet 1

This Lecture Covers:  Types of Computer Networks.  Communication devices and media.  Network Topology.  LAN Components  Network Uses  Internet Protocols.  Internet Services. 2

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 3

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 4

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 5

LAN 6

Putting Together a Network  Basic Components  Sending device  Communications link  Receiving device 7

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 8

Modem  Communication device  Short for modulator/demodulator  Converts digital signal to analog and vice versa  Cable connects modem to standard phone jack 9

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 10

Other Communications Devices • ISDN • DSL • Cable Modems • Cellular Modems 11

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 12

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 13

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 14

Cellular Modems  Transmit data over the cellular telephone system  Roughly half the speed of a regular telephone network 15

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 16

Communications Media  Physical means of data transmission  Bandwidth is measure of the capacity of the communications link 17

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  Wireless transmission  Transmits data over short distances without wires. Ex: IrDA, Bluetooth,802.11 standards 18

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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) 20

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 21

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 22

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 23

Network Uses  Electronic mail (e-mail)  Facsimile (fax) technology  Teleconferencing  Electronic data interchange  Electronic fund transfers  Computer commuting  The Internet 24

The Internet  A global network of hundreds of thousands of computers  Widely considered to be the defining technology of the beginning of this century 25

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 26

Browser  Interface software used to explore the Internet  Early browsers were text-only  Mosaic was the first graphical browser  Graphical browsers combine ease of links with attractive graphical interface 27

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 28

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 29

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 30

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 31

Non-Web Services of the Internet  Newsgroups  FTP  Telnet  E-mail  E-Commerce 32