14. Computer Systems and Networks
Transcript of 14. Computer Systems and Networks
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Indrajith Hapuarachchie
Computer Systems and Networks
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Computer Hardware
Types of Computers
Super Computers
Extremely powerful computers
With massive computing power
Large banks of processors Used for scientific purposes
Mainframe Computers
Very large and powerful
Hundreds of simultaneous users Kept in data centers
Temp. Humidity and dust is controlled
Specialized computer operators use them
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Computer Hardware
Types of Computers
Mini Computers
Much smaller
Fewer than 100 users
Can be used in office environment Staff can use it after training
Micro Computers ( PC / workstation)
On desktop
Generally one user Connected to a network (W/S) or can be standalone (PC)
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Computer Hardware Servers
Powerful micro computers (PC servers )
That server applications (web servers )
Routers Are computers or computer software that looks at the
destination of information and determines how best to get it
there Allows the connectivity of two different type of networks (LAN to
WAN )
Gateways / Communication servers Connect LAN to WAN
Connect different types of LANs
Repeaters Amplifies the signal
Bridges Connect two LANS of same type to each other
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Computer Hardware
Standards and Protocols
There should be a standard to allow
communication between computers and this is
called Protocols
Most are governed by OSI (Open System
Interconnection ) model developed by ISO
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Computer Hardware
OSI reference Model
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Computer Hardware Computer Addresses IP Address
Eg. 203.118.0.1 , 192.168.50.1, 172.16.5.
Address of each computer in the network
Internet routable addresses (Public IP) LAN only addresses ie. Private IP addresses
10.0.0.0 through 10.255.255.255
172.16.0.0 through 172.31.255.255
192.168.0.0 through 192.168.255.255
URL Uniform Resource Locator
Used instead of IP addresses
Central list is used to translate URLs in to IPs
Domain Name Servers (DNS)7
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Computer Hardware
Components of a URL Protocol
Host name
Port number (FTP 20,21,telnet 23, smtp 25, pop3
110, http 80, 53 Dns)
Directory/ path
File name
http://www.cbsl.gov.lk/htm/english/04_mp/mp.html
http://www.smib.lk:8080/user/Login.jsp
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http://www.cbsl.gov.lk/htm/english/04_mp/mp.htmlhttp://www.cbsl.gov.lk/htm/english/04_mp/mp.htmlhttp://203.94.66.193:8080/user/Login.jsphttp://203.94.66.193:8080/user/Login.jsphttp://www.cbsl.gov.lk/htm/english/04_mp/mp.htmlhttp://www.cbsl.gov.lk/htm/english/04_mp/mp.html -
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Computer Hardware HTTP (Hyper Text Transfer Protocol ) Basic communication mechanisum in the web
Four stages of information retrieval Connect
Connection between the web client ( browser ) and webserver (site) is made
Request Request an object from the server
Respond Responds to the request
Disconnect
Separate connection is made for each object
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Computer Hardware
Cookies HTTP is a stateless protocol
No information is maintained across series of connections
between the server and the client
No way to know that we have already connected toa particular web site
This was over come by placing a small file in the
users computer with values
Privacy issues are associated with cookies
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LAN & WAN Local Area Network Components
File server SAN
architecture to attach remote computer storage devices (such as disk arrays,tape libraries, and optical jukeboxes) to servers in such a way that thedevices appear as locally attached to the operating system
NAS
uses file-based protocols such as NFS where it is clear that the storage is
remote, and computers request a portion of an abstract file rather than a diskblock
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http://en.wikipedia.org/wiki/Disk_arrayhttp://en.wikipedia.org/wiki/Tape_libraryhttp://en.wikipedia.org/wiki/Optical_jukeboxhttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Direct-attached_storagehttp://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Network_File_System_(protocol)http://upload.wikimedia.org/wikipedia/commons/c/ce/Compingles.GIFhttp://en.wikipedia.org/wiki/Network_File_System_(protocol)http://en.wikipedia.org/wiki/Operating_systemhttp://en.wikipedia.org/wiki/Direct-attached_storagehttp://en.wikipedia.org/wiki/Server_(computing)http://en.wikipedia.org/wiki/Optical_jukeboxhttp://en.wikipedia.org/wiki/Tape_libraryhttp://en.wikipedia.org/wiki/Disk_array -
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LAN & WAN
Local Area Network Components
Print server
Print spooling Microcomputers (PC or W/S)
Gateway to connect other LANs or WAN
Repeaters to extend the LAN
Bridges and routers to connect to other LANs
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BUS LAN
Most simplest network
Use of Carrier Sense Multiple Access with Collision Detect (CSMA/CD)
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STAR LAN
Use of Carrier Sense Multiple Access with Collision Detect (CSMA/CD)
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Ring LANMulti-station Access Unit
MAU
Use of Token to pass data15
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Wide Area Network - WAN
Main Frame
Modem Modem
Simple WAN
Modem Modem
Multiplexor
Multiplexor
Multiplexed WAN16
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WAN Technology
Multiplexing Frequency Division
Multiplexing (FDM) Transmit all of the signals along
the same high speed linksimultaneously
Each signal set at a differentfrequency.
Frequency overlap must beavoided
Operates similar way to radiobroadcasting
In order to prevent signaloverlap there are strips offrequency that separate thesignals called guard bands.17
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WAN Technology
Multiplexing
Time Division Multiplexing (TDM)
Multiplexor collect and store the incoming
transmissions and allocating a time slice on the fast
link to each in turn.
Messages are sent down the high speed link one
after the other.
Two ways of implementing TDM are:
Synchronous TDM
Asynchronous TDM
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WAN Technology
Multiplexing
Time Division Multiplexing (TDM)
Synchronous TDM
Gives exactly the same amount of time toeach device even if a device has nothing to
transmit
Asynchronous TDM
Length of time allocated is not fixed for each
device Time is given to devices that have data to
transmit.
Works by tagging each frame with an
identification number to note which device it
belongs to.
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WAN Technology
Packet Switched
Networks
Data is Broken in to
small parts called
packets Packets are given the
IP address that they
should reach
Then they are
dropped to thenetwork
They will use the best
path to reach the
destination
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Complex Networks
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Internet Technology
Hypertext Mark-up Language (HTML) Form of text
Information includes links
Used to connect to another page
Load more information like pictures, video etc.
XML (Extensible Markup Language)
Is a set of rules for encoding documents in machine-
readable form
It is a textual data format
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Internet Technology
Java & ActiveX Java
Programming language
Browsers have inbuilt java interpreters
Is a object-oriented programming language (OOP) Can be run on any platform
It runs on Java Run time environment
Features
Increased Interaction
Graphics
Reduced Server Load
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Internet Technology
Java Applets Is a Java Program specifically written for the
browsers
Strictly controlled access to host machine
Can not normally read or write files to the computer
Java Script
Programming script that can be embedded in HTML
Developed by Netscape ( this is different to java
programming )
Used to provide dynamic content in web pages
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Internet Technology
JavaBeans Reusable components of java programming
Created by JavaSoft (business unit of SUN)
Application Programming Interface (API)
This is where JavaBeans comes in
JavaBeans offers platform independent and
Architecture independent API for java software
ActiveX
Microsofts answer to Java
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Other Devices
Mobile Telephones
SMS
GSM
WAP ( Wirelessapplication protocol)
Strips complex graphics
from websites
Slow
3G (3rd Generationtelephony)
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Other Devices
How WAP works
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Other Devices
Use of 3G in Enterprises
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Other Devices
Bluetooth is an openwireless technology standard
for exchanging data over short distances (using
short length radio waves)
from fixed and mobile devices,
creating personal area networks (PANs)
with high levels of security
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http://en.wikipedia.org/wiki/Open_standardhttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Personal_area_networkhttp://en.wikipedia.org/wiki/File:Bluetooth.svghttp://en.wikipedia.org/wiki/Personal_area_networkhttp://en.wikipedia.org/wiki/Wirelesshttp://en.wikipedia.org/wiki/Open_standard -
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Other Devices
Bluetooth Network
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From Viruses to Cybercrime
In the past, PCs were mainly under threat fromviruses and worms. The main purpose of theseprograms was to spread; however, some programswere also designed to cause damage to files andPCs. Such malicious software, or malware, could bedescribed as cyber vandalism. In the majority ofcases, the goal of viruses and worms was to spreadas much as possible, with a high infection rate leadingto fame for that program.
But in recent years, the situation has changeddrastically.
Today, the biggest threat faced by computers iscrimeware. This malicious software is written bycybercriminals with the purpose of making money
illegally Crimeware may take the form of viruses
Computer Threats
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