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Monday, August 5, 2013

PPT On Internet And World Wide Web


Internet And World Wide Web Presentation Transcript:
1.The World Wide Web

2.The World Wide Web
1989-1990 – Tim Berners-Lee invents the World Wide Web
Means for transferring text and graphics simultaneously
Client/Server data transfer protocol
Communication via application level protocol
Text mark up language
Simple and easy to use
Requires a client application to render text/graphics

The WWW today is a distributed client-server service, in which a client using a browser can access a service using a server. However, the service provided is distributed over many locations called sites. Each site holds one or more documents, referred to as Web pages. Each Web page, however, can contain some links to other Web pages in the same or other sites. In other words, a Web page can be simple or composite.

4.    Assume we need to retrieve a Web page that contains the biography of a famous character with some pictures, which are embedded in the page itself. Since the pictures are not stored as separate files, the whole document is a simple Web page. It can be retrieved using one single request/ response transaction.

5.    Now assume we need to retrieve a scientific document that contains one reference to another text file and one reference to a large image. The main document and the image are stored in two separate files in the same site (file A and file B); the referenced text file is stored in another site (file C). Since we are dealing with three different files, we need three transactions if we want to see the whole document. The first transaction (request/response) retrieves a copy of the main document (file A), which has a reference (pointer) to the second and the third files.

6. A very important point we need to remember is that file A, file B, and file C in Example 2 are independent Web pages, each with independent names and addresses. Although references to file B or C are included in file A, it does not mean that each of these files cannot be retrieved independently. A second user can retrieve file B with one transaction. A third user can retrieve file C with one transaction.

7.The World Wide Web Components
Structural Components
Clients/browsers – to dominant implementations
Servers – run on sophisticated hardware
Caches – many interesting implementations
Internet – the global infrastructure which facilitates data transfer
Semantic Components
Hyper Text Transfer Protocol (HTTP)
Hyper Text Markup Language (HTML)
eXtensible Markup Language (XML)
Uniform Resource Identifiers (URIs)

8.The World Wide Web Structure
Clients use browser application to send URIs via HTTP to servers requesting a Web page
Web pages constructed using HTML (or other markup language) and consist of text, graphics, sounds plus embedded files
Servers (or caches) respond with requested Web page
Or with error message
Client’s browser renders Web page returned by server
Page is written using Hyper Text Markup Language (HTML)
Displaying text, graphics and sound in browser
Writing data as well
The entire system runs over standard networking protocols (TCP/IP, DNS,…)

9.Uniform Resource Identifiers
Web resources need names/identifiers – Uniform Resource Identifiers (URIs)
Resource can reside anywhere on the Internet
URIs are a some what abstract notion
A pointer to a resource to which request methods can be applied to generate potentially different responses
A request method is eg. fetching or changing the object
Most popular form of a URI is the Uniform Resource Locator (URL)

10.WEB Documents

11.Overview of Network Security

12.What is “Security”
Freedom from risk or danger; safety.
2.     Freedom from doubt, anxiety, or fear; confidence.

3.     Something that gives or assures safety, as:
 A group or department of private guards: Call building security if a visitor acts suspicious.
 Measures adopted by a government to prevent attack.
 Measures adopted, as by a business or homeowner, to prevent a crime

13.Why do we need security?
Protect vital information while still allowing access to those who need it
Trade secrets, medical records, etc.
Provide authentication and access control for resources
Guarantee availability of resources

14.Who is vulnerable?
Financial institutions and banks
Internet service providers
Pharmaceutical companies
Government and defense agencies
Contractors to various government agencies
Multinational corporations

15.The Problem of Network Security
The Internet allows an attacker to attack from anywhere in the world from their home desk.
They just need to find one vulnerability:  a security analyst need to close every vulnerability.

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