The Internet Lecture 16 CSCI 1405, CSCI 1301 Introduction to Computer Science Fall 2009

The Internet Which originated from research projects going back to the early 1960s. most of this original work was sponsored by the U.S. government through the Defense Advanced Research Projects Agency (DARPA). Over the years, the development of the Internet shifted from the defense project to an academic research project, and today it is largely a commercial undertaking that links a worldwide combination of WANs, MANs, and LANs involving millions of computers 2

Internet Architecture: The Internet can be viewed as a collection of domains, each of which consists of network or a relatively small internet operated by a single organization such as university, company, or government agency. It might consist of a single computer or a complex internet consisting of many LANs, MANs, and even WANs. 3

The establishment of domains is overseen by the Internet Corporation for Assigned Names and Numbers (ICANN), which is a nonprofit corporation established to coordinate the naming of domains and the assignment of Internet addresses To establish a domain on the Internet, the domain must first be registered via one of the companies, called registrars, that have been delegated for this purpose by ICANN. Once a domain has been registered, it can be attached to the existing Internet by means of a router that connects one of the networks in the domain to a network already in the Internet. Router is often referred to as the domain's gateway, it represents the domain's gate to the rest of the Internet Internet Architecture: 4

The portion of the Internet lying outside of its gateway is sometimes called the cloud One popular structure, is for the gateways of a number of domains to be connected to form a regional network of gateways. For instance, a group of universities could choose to pool their resources to construct such a network. This regional network would be connected to a more global network to which other regional networks attached. 5

Internet Architecture: 6

Connecting to the Internet: To simplify the process of connecting to the Internet, numerous companies, called Internet service providers (ISP), allow customers to connect their domains to the Internet via the ISP's equipment or to become a part of a domain already established by the ISP. 7

: Dialup Connection The least expensive connections to an ISP are obtained through temporary telephone links called dial-up connections. An individual connects his or her computer to the local telephone line and executes a software package that places a call to a computer at the ISP. At this point the ISP provides Internet access for the duration of the telephone call. 8

DSL In fixed location applications it is rabidly giving way to permanent connections through higher bandwidth systems such as DSL, cable television line, and satellite links. These technologies have greatly reduced the expense of broadband (high-capacity) Internet access, making today's multimedia applications accessible to home users. 9

Home System Another development taking place at the household level is that home computer systems are expanding from single computer installations to multicomputer networks, usually implemented as Ethernet bus networks. These networks gain access to the Internet by means of a router within the home that is permanently connected to an ISP via DSL, cable television line, or a satellite link, making a home system a local network within a domain established by the ISP. 10

In Internet, internet address is called (Internet Protocol Address) IP address. IP address is a 32 bits pattern: it has two parts: 1.The network identifier to identify the domain and it is assigned by ICANN at the time the domain registered 2.The host address to identify a particular computer within a domain and is assigned by the domain local authority. IP ad dress is written using dotted decimal notation Ex: IP address of a computer on the Internet may be: The red is the network identifier The green is the host address Each domain is also assigned a Domain Name, for example the aw.com The domain local authority extends it to obtain a name for each machine within its domain. Ex: ssenterprise.aw.com Internet Addressing: 11

Internet Addressing: Each domain local authority is responsible for maintaining a directory of the name and the corresponding IP address of all computers within the domain. This directory is on a computer called name server All the name servers are part of a system on the Internet called domain name system (DNS) DNS is used to convert from names to IP addresses and vice versa 12

13 Internet Applications: Electronic Mail : Mail server: is a machine within a domain to handle activities To send messages: –every message sent from the domain is sent to the mail server first –then the domain server send this message to the destination To receives messages: every message with an address for a person on the domain is received first by the mail server the mail server holds the message in person mail box until he requests to see his mail box

Electronic Mail : Send message to Mail server at iugaza Domain iugaza Router Domain hotmail Mail server at hotmail hotmail.com Receives message from 14

Internet Applications: FTP: File Transfer Protocol (FTP): It is a client /server protocol for transferring file s(File Transfer Protocol). The machine which request the FTP is the client and the other is server A request to establish contact with FTP server is done by first entering the user name and password. If it is OK, the FTP server establishes the connection and files can then be transferred. 15

Internet Applications: Telnet: It is a client /server protocol allowing the access from one computer to another from great distance. communication via the telnet is not encrypted The communication via the SSH is more secure than telnet because the data is encrypted 16

Internet Applications: The World Wide Web (WWW) The fastest growing area of the Internet It uses hypertext as a way of linking documents to each other. A highlighted word or phrase in one document acts as a pointer to another document that amplifies or relates to the first document. Documents on the WWW include text, but they may also include images, video, and audio WWW is another example of client/server computing. Each time a link is followed, the client is requesting a document (or graphic or sound file) from a server (also called a Web server) that's part of the World Wide Web that "serves" up the document. The server uses a protocol called HTTP or HyperText Transport Protocol. The standard for creating hypertext documents for the WWW is HyperText Markup Language or HTML. HTML essentially codes plain text documents so they can be viewed on the Web. 17

Internet Applications: The World Wide Web (WWW) The program you use to access the WWW is known as a browser because it "browses" the WWW and requests these hypertext documents. All of these programs understand http and other Internet protocols such as FTP, telnet and others 18

Internet Applications: The World Wide Web (WWW) Uniform Resource Locators, or URLs: is the address of a document you'll find on the WWW. Your WWW browser interprets the information in the URL in order to connect to the proper Internet server and to retrieve your desired document. Each time you click on a hyperlink in a WWW document, you're actually instructing your browser to find the URL that's embedded within the hyperlink. The elements in a URL: Protocol://server's address/filename Hypertext protocol: File Transfer Protocol: ftp://ftp.dartmouth.edu Telnet Protocol: telnet://pac.carl.org 19