1. Internet Overview (Chapter 1 in [2])

2. 2 Outline History of the Internet History of the Internet Seven Layers of the OSI Model Seven Layers of the OSI Model TCP/IP and the OSI Model TCP/IP and the OSI Model History of the World Wide Web History of the World Wide Web World Wide Web Consortium (W3C) World Wide Web Consortium (W3C) Hypertext Transfer Protocol (HTTP) Hypertext Transfer Protocol (HTTP)

3. 3 History of the Internet (1/5) ARPAnet ARPAnet Implemented in late 1960 ’ s by ARPA (Advanced Research Projects Agency of DOD) Implemented in late 1960 ’ s by ARPA (Advanced Research Projects Agency of DOD) Networked computer systems of a dozen universities and institutions with 56KB communications lines Networked computer systems of a dozen universities and institutions with 56KB communications lines Grandparent of today ’ s Internet Grandparent of today ’ s Internet Intended to allow computers to be shared Intended to allow computers to be shared Became clear that key benefit was allowing fast communication between researchers – electronic-mail (email) Became clear that key benefit was allowing fast communication between researchers – electronic-mail (email)

4. 4 History of the Internet (2/5) ARPA ’ s Goals ARPA ’ s Goals Allow multiple users to send and receive info at same time Allow multiple users to send and receive info at same time Network operated packet switching technique Network operated packet switching technique Digital data sent in small packages called packets Digital data sent in small packages called packets Packets contained data, address info, error-control info and sequencing info Packets contained data, address info, error-control info and sequencing info Greatly reduced transmission costs of dedicated communications lines Greatly reduced transmission costs of dedicated communications lines Network designed to be operated without centralized control Network designed to be operated without centralized control If portion of network fails, remaining portions still able to route packets If portion of network fails, remaining portions still able to route packets

5. 5 History of the Internet (3/5) Transmission Control Protocol (TCP) Transmission Control Protocol (TCP) Name of protocols for communicating over ARPAnet Name of protocols for communicating over ARPAnet Ensured that messages were properly routed and that they arrived intact Ensured that messages were properly routed and that they arrived intact Organizations implemented own networks Organizations implemented own networks Used both for intra-organization and communication Used both for intra-organization and communication

6. 6 History of the Internet (4/5) Huge variety of networking hardware and software appeared Huge variety of networking hardware and software appeared ARPA achieved inter-communication between all platforms with development of the IP ARPA achieved inter-communication between all platforms with development of the IP Internet Protocol Internet Protocol Current architecture of Internet Current architecture of Internet Combined set of protocols called TCP/IP Combined set of protocols called TCP/IP The Internet The Internet Limited to universities and research institutions Limited to universities and research institutions Military became big user Military became big user Next, government decided to access Internet for commercial purposes Next, government decided to access Internet for commercial purposes

7. 7 History of the Internet (5/5) Internet traffic grew Internet traffic grew Businesses spent heavily to improve Internet Businesses spent heavily to improve Internet Better service their clients Better service their clients Fierce competition among communications carriers and hardware and software suppliers Fierce competition among communications carriers and hardware and software suppliers Result Result Bandwidth (info carrying capacity) of Internet increased tremendously Bandwidth (info carrying capacity) of Internet increased tremendously Costs plummeted Costs plummeted

8. 8 Seven Layers of the OSI Model (1/4)

9. 9 Seven Layers of the OSI Model (2/4) Physical layer Physical layer Be concerned with transmitting raw bits over a communication channel. Be concerned with transmitting raw bits over a communication channel. Data-link layer Data-link layer To take a raw transmission facility and transform it into a line that appears free of undetected transmission errors to the network layer. To take a raw transmission facility and transform it into a line that appears free of undetected transmission errors to the network layer. Network layer Network layer Determining how packets are routed from source to destination Determining how packets are routed from source to destination

10. 10 Seven Layers of the OSI Model (3/4) Transport layer Transport layer To accept data from the session layer, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end. To accept data from the session layer, split it up into smaller units if need be, pass these to the network layer, and ensure that the pieces all arrive correctly at the other end. Session layer Session layer It establishes, maintains, and synchronizes the dialog between communicating systems. It also adds what called synchronization points for backup delivery in case of system or network failure. It establishes, maintains, and synchronizes the dialog between communicating systems. It also adds what called synchronization points for backup delivery in case of system or network failure.

11. 11 Seven Layers of the OSI Model (4/4) Presentation layer Presentation layer Be requested sufficiently often to warrant finding a general solution for them, rather than letting each user solve the problems. A typical example is encoding data in a standard agreed upon way. Be requested sufficiently often to warrant finding a general solution for them, rather than letting each user solve the problems. A typical example is encoding data in a standard agreed upon way. Application layer Application layer The application layer contains a variety of protocols that are commonly needed. The application layer contains a variety of protocols that are commonly needed. File transfer, Email, WWW File transfer, Email, WWW

12. 12 TCP/IP and the OSI Model (1/2) The TCP/IP is a suite or a stack of protocols that officially controls the Internet. TCP/IP was developed before the OSI model. The TCP/IP is a suite or a stack of protocols that officially controls the Internet. TCP/IP was developed before the OSI model.

13. 13 TCP/IP and the OSI Model (2/2)

14. 14 History of the World Wide Web WWW WWW Allows computer users to locate and view multimedia-based documents Allows computer users to locate and view multimedia-based documents Introduced in 1990 by Tim Berners-Lee Introduced in 1990 by Tim Berners-Lee Internet today Internet today Mixes computing and communications technologies Mixes computing and communications technologies Makes information constantly and instantly available to anyone with a connection Makes information constantly and instantly available to anyone with a connection

15. 15 World Wide Web Consortium (W3C) (1/2) W3C W3C Founded in 1994 by Tim Berners-Lee Founded in 1994 by Tim Berners-Lee Devoted to developing non-proprietary and interoperable technologies for the World Wide Web and making the Web universally accessible Devoted to developing non-proprietary and interoperable technologies for the World Wide Web and making the Web universally accessible Standardization Standardization W3C Recommendations: technologies standardized by W3C W3C Recommendations: technologies standardized by W3C include Extensible HyperText Markup Language (XHTML), Cascading Style Sheets (CSS) and the Extensible Markup Language (XML) include Extensible HyperText Markup Language (XHTML), Cascading Style Sheets (CSS) and the Extensible Markup Language (XML) Document must pass through Working Draft, Candidate Recommendation and Proposed Recommendation phases before considered for W3C Recommendation Document must pass through Working Draft, Candidate Recommendation and Proposed Recommendation phases before considered for W3C Recommendation

16. 16 World Wide Web Consortium (W3C) (2/2) W3C Structure W3C Structure 3 Hosts 3 Hosts Massachusetts Institute of Technology (MIT) Massachusetts Institute of Technology (MIT) European Research Consortium for Informatics and Mathematics (ERCIM) European Research Consortium for Informatics and Mathematics (ERCIM) Keio University of Japan Keio University of Japan 400 Members 400 Members W3C homepage at www.w3.org W3C homepage at www.w3.org www.w3.org W3C Goals W3C Goals User Interface Domain User Interface Domain Technology and Society Domain Technology and Society Domain Architecture Domain and Web Accessibility Initiatives Architecture Domain and Web Accessibility Initiatives

17. 17 Hypertext Transfer Protocol (HTTP) Hypertext Transfer Protocol (HTTP) is a client- server program for accessing and transferring documents on the World Wide Web (WWW), a collection of multimedia documents. The Uniform Resource Locator (URL) is a standard identifier for specifying information on the Internet. URL: