Download Lecture 11

UEC01: Computer Skills & Programming
Concepts I
Lecture 11: Computer
Networks and Internet
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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
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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
• ISDN
• DSL
• Cable Modems
• Cellular Modems
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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
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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 FullDuplex 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
 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
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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
of 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
of 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
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HyperText Transfer Protocol – allows communication by using
links to transfer data between sites
 Domain name – address of site’s host computer
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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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