Internet

1. A global network connecting millions of computers. More than 100 countries are linked into exchanges of data, news and opinions. There are a variety of ways to access the Internet It is also possible to gain access through a commercial Internet Service Provider (ISP). Internet

2. In 1969,the Advanced Research Project Agency (ARPA) funded by US department of Defense, created the first version of what we now term the internet called as ARPANET. The first version linked four computer located in US. The first e-mail program was created by Ray Tomlinson of BBN in 1972. ARPANET was currently using the Network Control Protocol or NCP to transfer data. This allowed communications between hosts running on the same network. 1973 Development began on the protocol later to be called TCP/IP, it was developed by a group headed by Vinton Cerf from Stanford and Bob Kahn from DARPA. This new protocol was to allow diverse computer networks to interconnect and communicate with each other. 1976 Dr. Robert M. Metcalfe develops Ethernet, which allowed coaxial cable to move data extremely fast. This was a crucial component to the development of LANs. In 1992 World-Wide Web released by Corporation for Research and Educational Networking (CREN). History

3. Internet Service Provider, a company that provides access to the Internet. For a monthly fee, the service provider gives you a software package, username, password and access phone number. Equipped with a modem, you can then log on to the Internet , browse the World Wide Web and send and receive e-mail. ISP

4. Modem

5. (mō´dem) (n.) Short for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over, for example, telephone or cable lines. Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves. A modem converts between these two forms. Fortunately, there is one standard interface for connecting external modems to computers called RS-232.

6. Difference between Internet and WWW The Internet and the Web are two separate but related things. The Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet. Information that travels over the Internet does so via a variety of languages known as protocols. The World Wide Web, or simply Web, is a way of accessing information over the medium of the Internet. The Web uses the HTTP protocol, only one of the languages spoken over the Internet, to transmit data. Web also utilizes browsers, such as Internet Explorer or Firefox, to access Web documents called Web pages that are linked to each other via hyperlinks. Web documents also contain graphics, sounds, text and video.

7. The protocol determines the following: 1.the type of error checking to be used 2.data compression method, if any 3.how the sending device will indicate that it has finished sending a message 4.how the receiving device will indicate that it has received a message • The protocol can be implemented either in hardware or in software. protocols

8. A system of Internet servers that support specially formatted documents. The documents are formatted in a markup language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. W W W

9. Short for Web browser, a software application used to locate and display Web pages. The two most popular browsers are Microsoft Internet Explorer and Firefox. Both of these are graphical browsers, which means that they can display graphics as well as text. In addition, most modern browsers can present multimedia information, including sound and video, though they require plug-ins for some formats Browser

10. Abbreviation of Uniform Resource Locator, the global address of documents and other resources on the World Wide Web. ftp://www.pcwebopedia.com/stuff.exe http://www.pcwebopedia.com/index.html The first part of the address is called a protocol identifier and it indicates what protocol to use, and the second part is called a resource name and it specifies the IP address or the domain name where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes. For example, the two URLs point to two different files at the domain pcwebopedia.com. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies a Web page that should be fetched using the HTTP protocol. URL

11. A name that identifies one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particular Web pages. For example, in the URL http://www.pcwebopedia.com/index.html, the domain name is pcwebopedia.com. • Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains. For example: gov - Government agencies edu - Educational institutions org - Organizations (nonprofit) mil - Military com - commercial business net - Network organizations ca - Canada th - Thailand • Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses. Domain name

12. The internet works by defining an address for each resource attached to it. In the case of attached computer and some devices , this is internet protocol address. IP add it’s a 32 bit address. Eg : 158.162.131.2 The number break down to a country, to a specific domain, right down to machine itself. of course we don’t use numbers to find resources and machines – we use name like vesit.ce.edu The name will actually have an associate number, but when a name is entered into a web browser ,the a web browser ,the computer will use a special system called Domain Name System (DNS) to look up the associate number which it will then use to get in contact with the desired server. IP address

13. web Email server DNS Internet Service Provider How computer links to internet Internet 81.155.138.148 Router/Gateway 192.168.1.1 192.168.1.4 192.168.1.2 192.168.1.3

14. Any communication that takes place on the internet uses the TCP/IP suite. This is a set of communication protocols for dialogs between computers and devices. These protocols implements a stack ,each layer of which solve problems relating to the transmission of data , as well providing services to higher layers than itself. Higher layers are logically closer to the user.

15. M2-Internet DNS: Domain Name System People: many identifiers: • SSN, name, passport # Internet hosts, routers: • IP address (32 bit) - used for addressing datagrams • “name”, e.g., ww.yahoo.com - used by humans Q: map between IP addresses and name ? Domain Name System: • distributed database implemented in hierarchy of many name servers • application-layer protocol host, routers, name servers to communicate to resolvenames (address/name translation) • note: core Internet function, implemented as application-layer protocol • complexity at network’s “edge”

16. Root DNS Servers org DNS servers edu DNS servers com DNS servers poly.edu DNS servers umass.edu DNS servers pbs.org DNS servers yahoo.com DNS servers amazon.com DNS servers M2-Internet Distributed, Hierarchical Database Client wants IP for www.amazon.com; 1st approx: • client queries a root server to find com DNS server • client queries com DNS server to get amazon.com DNS server • client queries amazon.com DNS server to get IP address for www.amazon.com

17. M2-Internet DNS DNS services • hostname to IP address translation • host aliasing • Canonical, alias names • mail server aliasing • load distribution • replicated Web servers: set of IP addresses for one canonical name Why not centralize DNS? • single point of failure • traffic volume • distant centralized database • maintenance doesn’t scale!

18. does not strictly belong to hierarchy • each ISP (residential ISP, company, university) has one. • also called “default name server” • when host makes DNS query, query is sent to its local DNS server • acts as proxy, forwards query into hierarchy M2-Internet Local Name Server

19. local DNS server dns.poly.edu M2-Internet DNS name resolution example root DNS server 2 • Host at cis.poly.edu wants IP address for gaia.cs.umass.edu 3 TLD DNS server 4 5 • iterated query: • contacted server replies with name of server to contact • “I don’t know this name, but ask this server” 6 7 1 8 authoritative DNS server dns.cs.umass.edu requesting host cis.poly.edu gaia.cs.umass.edu

20. root DNS server 2 3 6 7 TLD DNS server 4 local DNS server dns.poly.edu 5 1 8 authoritative DNS server dns.cs.umass.edu requesting host cis.poly.edu gaia.cs.umass.edu M2-Internet DNS name resolution example • recursive query: • puts burden of name resolution on contacted name server • heavy load?

22. Layer 7: The application layer ...This is the layer at which communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. (This layer is not the application itself, although some applications may perform application layer functions.) • Layer 6: The presentation layer ...This is a layer, usually part of an operating system, that converts incoming and outgoing data from one presentation format to another (for example, from a text stream into a popup window with the newly arrived text). Sometimes called the syntax layer. • Layer 5: The session layer ...This layer sets up, coordinates, and terminates conversations, exchanges, and dialogs between the applications at each end. It deals with session and connection coordination. • Layer 4: The transport layer ...This layer manages the end-to-end control (for example, determining whether all packets have arrived) and error-checking. It ensures complete data transfer. • Layer 3: The network layer ...This layer handles the routing of the data (sending it in the right direction to the right destination on outgoing transmissions and receiving incoming transmissions at the packet level). The network layer does routing and forwarding. • Layer 2: The data-link layer ...This layer provides synchronization for the physical level and does bit-stuffing for strings of 1's in excess of 5. It furnishes transmission protocol knowledge and management. • Layer 1: The physical layer ...This layer conveys the bit stream through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier.

23. A document on the World Wide Web. Every Web page is identified by a unique URL . Main protocol used for communication between a browser and a web server is HTTP. This protocol was designed to enable documents to be transferred but can be used with other type of data too. For web documents the http protocol works by sending command over a TCP connection. Web page

24. 192.168.18.32 Port 80 Server client GET index.html HTTP /1.1 http://www.mysports.com/index.html DSN 192.168.18.32

25. HTTP/ 1.1 200 OK Client server Contents of document

26. Client side prog. HTML DHTML XHTML CSS XML Java script, VB script Server side prog. ASP Servlet JSP