Lecture 10: 9/26/2002CS149D Fall CS149D Elements of Computer Science Ayman Abdel-Hamid Department of Computer Science Old Dominion University Lecture 10: 9/26/2002

CS149D Fall Outline Skip section 3.4 Networks  Network classification  The Internet  World Wide Web Should cover section 3.5

Lecture 10: 9/26/2002CS149D Fall Network classification 1/3 Two broad categories LAN (Local area network)  University campus WAN (Wide area network)  Satellite links Ownership (public domain, private) Public domain  open network (Internet) Private  proprietary network Network configuration (pattern in which machines are connected) Ring, bus, star, irregular

Lecture 10: 9/26/2002CS149D Fall Network classification 2/3 Copyright © 2003 Pearson Education, Inc.

Lecture 10: 9/26/2002CS149D Fall Network classification 3/3 Copyright © 2003 Pearson Education, Inc.

Lecture 10: 9/26/2002CS149D Fall The Internet A network of networks  internet An example of an internet is the Internet Originated from a research program initiated in 1973 by the Defense Advanced Research Projects Agency (DARPA) Internet is a combination of WANs and LANs involving maybe millions of machines Each network connected to the other by a special machine called a router Router is a machine belonging to 2 networks that allows messages in one network to be transferred to the other network

Lecture 10: 9/26/2002CS149D Fall Internet Addressing 1/4 Internet  collection of network clusters known as domains Domain

Lecture 10: 9/26/2002CS149D Fall Internet Addressing 2/4 Address of a machine in the Internet is 32 bits IP address  IP is Internet Protocol Consists of 2 parts  identify the domain (network identifier)  identify the particular machine within the domain (host address) Network identifier assigned by InterNIC (Internet Network Information Center) at time of domain establishment and registration (guarantee uniqueness of network identifier) ODU machine addresses example  

Lecture 10: 9/26/2002CS149D Fall Internet Addressing 3/4 InterNIC assigns each domain a unique mnemonic address known as domain name odu.educs.odu.edupitfall.cs.odu.edu (edu, gov, org, com,.. first-level domains) Break domain into subdomainscs.odu.eduece.odu.edu We need a mapping between numeric addresses and mnemonic addresses (Each local authority maintains such directory) Directory is implemented within the domain in the form of a server called a name server(DNS  Domain Name System) Name server provides lookup for mnemonic addresses to obtain the corresponding numeric addresses

Lecture 10: 9/26/2002CS149D Fall Internet Addressing 4/4 Organization to become part of Internet Become part of an existing domain Establish a new domain (need to register with InterNic) Individual obtains access to Internet Through membership in an organization with a domain Through an ISP (Internet Service Provider) Dialup, Cable Modem, DSL

Lecture 10: 9/26/2002CS149D Fall World Wide Web 1/3 Hypertext Text containing words, phrases, or images that are linked to other documents (a link to my home page)a link to my home page When hypertext contains sounds, and video, it is called hypermedia Reader of hypertext documents can explore related documents A web of related information is formed Web that has evolved on the Internet spans the entire globe and is known as World Wide Web Client machine Browser Server machine Serves web pages Request Reply Netscape Internet Explorer

Lecture 10: 9/26/2002CS149D Fall World Wide Web 2/3 Each document is identified by a unique address This unique address is called a URL (Uniform Resource Locator) The URL allows to identify the server, the protocol in use, and a desired document Sometimes a URL does not explicitly identify a document, in such case a predetermined document is often returned (usually a home page) Protocol required to access document (Hypertext transfer protocol) Mnemonic of host holding the document Directory path indicating the location of the document within the host’s file system Document name

Lecture 10: 9/26/2002CS149D Fall World Wide Web 3/3 A hypertext document contains special markers that describe  How the document should appear within the browser  Which items within the document are to be linked to other documents Systems of markers known as Hypertext Markup Language (HTML) Finding information on the WWW  Search Engines How the Internet Infrastructure works? (from howstuffworks.com)