FUNDAMENTAL OF INTERNET CONCEPTS

Overview

History of the Internet Web Environment Overview TCP/IP HTTP URL DNS

Definition of the Internet

An electronic network of computers that includes nearly every university, government, and research facility in the world. Also included are many commercial sites. It started with four interconnected computers in 1969 and was known as ARPAnet.www.orafaq.com/glossary/faqglosi.htm

A network of computer networks which operates world-wide using a common set of communications protocols.www.utas.edu.au/library/etutor/main/webzglos.htm

The vast collection of inter-connected networks across the world that all use the TCP/IP protocols.www.liv.ac.uk/webteam/glossary/

What Is the Internet?

A network of networks, joining many government, university and private computers together and providing an infrastructure for the use of E-mail, bulletin boards, file archives, hypertext documents, databases and other computational resources

The vast collection of computer networks which form and act as a single huge network for transport of data and messages across distances which can be anywhere from the same office

to anywhere in the world.

History of the Internet

Brief History of the Internet 1968 - DARPA (Defense Advanced Research

Projects Agency) contracts with BBN (Bolt, Beranek & Newman) to create ARPAnet

1970 - First five nodes: UCLA Stanford UC Santa Barbara U of Utah, and BBN

1974 - TCP specification by Vint Cerf 1984 – On January 1, the Internet with its 1000 hosts

converts en masse to using TCP/IP for its messaging

Internet History

A Brief Summary of the Evolution of the Internet

1945 1995

Memex Conceived

1945

WWWCreated

1989

MosaicCreated

1993

A Mathematical

Theory of Communication

1948

Packet Switching Invented

1964

SiliconChip1958

First Vast ComputerNetwork

Envisioned1962

ARPANET1969

TCP/IPCreated

1972

InternetNamed

and Goes

TCP/IP1984

HypertextInvented

1965

Age ofeCommerce

Begins1995

From Simple, But Significant Ideas Bigger Ones Grow1940s to 1969

1945 1969

We can access information using

electronic computers

We do it reliably with “bits”, sending and receiving data

We can do it cheaply by using Digital circuits etched in silicon.

We can accomplish a lot by having a vast network of computers to use for

accessing information and exchanging ideas

We will prove that packet switching works over a WAN.

Packet switching can be used to send digitized data though

computer networks

Hypertext can be used to allow rapid access to text data

From Simple, But Significant Ideas Bigger Ones Grow1970s to 1995

1970 1995

Ideas from1940s to 1969

We need a protocol for Efficient and Reliable transmission of

Packets over a WAN: TCP/IP

The ARPANET needs to convert to a standard protocol and be renamed to

The Internet

Computers connected via the Internet can be used more easily if hypertext links are enabled using HTML

and URLs: it’s called World Wide Web

The World Wide Web is easier to use if we have a browser thatTo browser web pages, running in a graphical user interface context.

Great efficiencies can be accomplished if we useThe Internet and the World Wide Web to conduct business.

The Creation of the Internet

The creation of the Internet solved the following challenges: Basically inventing digital networking Survivability of an infrastructure to send / receive high-speed

electronic messages Reliability of computer messaging

Web Environment Overview

… continued

Web browsers communicate with Web servers via the TCP/IP protocol. The browser sends HTTP requests to the server, which responds with HTML pages and possibly additional programs in the form of ActiveX controls or Java applets.

HTTP

A protocol used to request and transmit files, especially webpages and webpage components, over the Internet or other computer network.

URL

Uniform Resource Locator, or URL, is a fancy name for the address of a web page on the world wide web.

URL

The first part of the URL is called the protocol. It tells the browser how to deal with the file that it is about to open. One of the most common protocols you will see it HTTP, or Hypertext Transfer Protocol.

The second part of the URL is the name of the server where the file is located, followed by the path that leads to the file and the file's name itself, as illustrated below:

Sometimes, a URL ends in a trailing forward slash with no file name given, as below.

"http://www.site.com/fun/" In this case the URL refers to the default file in the last directory in

the path, which is a file named "index.html." An equivalent URL to the one above would be

"http://www.site.com/fun/index.html

Absolute URLs

A URL that specifies the full path to the document page, which includes the domain name and protocol.

Also known as an "explicit URL“. Example: http://www.unikl.edu.my/network.htm

Relative URLs

Relative URLs are analogous to giving directions to someone such as "go down the hall and turn right." In other words, the directions refer to where you are starting from. In the same way, a relative URL describes the location of the desired file with reference to the location of the file that contains the URL itself.

For example, a relative URL for a file that is in the same directory as the current file (that is, the one with the link that points to that file) is merely the file name and extension, such as "index.html"

You create a URL for a file in a subdirectory of the current directory by placing the name of the subdirectory first and following it with a forward slash and then the name and extension of the desired file, as shown below.

Relative URLs To reference a file in a directory at a higher level of

the file hierarchy, use two periods ( .. ) as shown below.

You can combine and repeat the two periods and forward slash to reference any file on the same server as the current file.

DNS: Domain Name System

A system for converting host names and domain names into IP addresses on the Internet or on local networks that use the TCP/IP protocol. For example, when a Web site address is given to the DNS either by typing a URL in a browser or behind the scenes from one application to another, DNS servers return the IP address of the server associated with that name.

In this hypothetical example, WWW.COMPANY.COM would be converted into the IP address 204.0.8.51. Without DNS, you would have to type the four numbers and dots into your browser to retrieve the Web site, which of course, you can do.

DNS Hierarchy

The DNS system is a hierarchy of database servers that start with the root servers for all the top level domains (.com, .net, etc.).

The root servers point to authoritative servers residing within ISPs and companies that resolve the host names to complete the name resolution.

Using the example WWW.COMPANY.COM, COMPANY.COM is the domain name, and WWW is the host name. The domain name is the organization's identity on the Web, and the host name is the name of the actual Web server within that domain

Getting a Web Page

Turning a URL in a Web browser into an IP address can take numerous queries. This is a simplified diagram because the original requester actually talks to each name server in turn, and there can be more name servers in between. A request can also be satisfied from a DNS cache along the way and not need to reach the authoritative server.

OSI Model

The Open Systems Interconnection Reference Model (OSI Model or OSI Reference Model for short) is a layered abstract description for communications and computer network protocol design, developed as part of the Open Systems Interconnection initiative. It is also called the OSI seven layer model.

OSI Model

7 Application layer 6 Presentation

layer 5 Session layer 4 Transport layer 3 Network layer 2 Data link layer 1 Physical layer

Upper & Lower Layers

Layers 7 through 4 comprise the upper layers of the OSI protocol stack. They are more geared to the type of application than the lower layers, which are designed to move packets, no matter what they contain, from one place to another.

Layers 3 through 1 are responsible for moving packets from the sending station to the receiving station.

Layer 7: Application

This top layer defines the language and syntax that programs use to communicate with other programs. The application layer represents the purpose of communicating in the first place. For example, a program in a client workstation uses commands to request data from a program in the server. Common functions at this layer are opening, closing, reading and writing files, transferring files and e-mail messages, executing remote jobs and obtaining directory information about network resources.

Layer 6: Presentation

When data are transmitted between different types of computer systems, the presentation layer negotiates and manages the way data are represented and encoded. For example, it provides a common denominator between ASCII and EBCDIC machines as well as between different floating point and binary formats. Sun's XDR and OSI's ASN.1 are two protocols used for this purpose. This layer is also used for encryption and decryption.

Layer 5: Session

Provides coordination of the communications in an orderly manner. It determines one-way or two-way communications and manages the dialog between both parties; for example, making sure that the previous request has been fulfilled before the next one is sent. It also marks significant parts of the transmitted data with checkpoints to allow for fast recovery in the event of a connection failure.

Layer 4: Transport

This layer is responsible for overall end to end validity and integrity of the transmission. The lower layers may drop packets, but the transport layer performs a sequence check on the data and ensures that if a 12MB file is sent, the full 12MB is received.

"OSI transport services" include layers 1 through 4, collectively responsible for delivering a complete message or file from sending to receiving station without error.

Layer 3: Network

The network layer establishes the route between the sender and receiver across switching points, which are typically routers. The most ubiquitous example of this layer is the IP protocol in TCP/IP (see TCP/IP). IPX, SNA and AppleTalk are other examples of routable protocols, which means that they include a network address and a station address in their addressing system. This layer is also the switching function of the dial-up telephone system. If all stations are contained within a single network segment, then the routing capability in this layer is not required.

Layer 2: Data Link

The data link is responsible for node to node validity and integrity of the transmission. The transmitted bits are divided into frames; for example, an Ethernet, Token Ring or FDDI frame in local area networks (LANs). Frame relay and ATM are also at Layer 2.

Layers 1 and 2 are required for every type of communications.

Layer 1: Physical

The physical layer is responsible for passing bits onto and receiving them from the connecting medium. This layer has no understanding of the meaning of the bits, but deals with the electrical and mechanical characteristics of the signals and signaling methods. For example, it comprises the RTS and CTS signals in an RS-232 environment, as well as TDM and FDM techniques for multiplexing data on a line. SONET also provides layer 1 capability.

TCP/IP

A protocol for communication between computers, used as a standard for transmitting data over networks and as the basis for standard Internet protocols.

TCP (Transmission Control Protocol)

A protocol developed for the internet to get data from one network device to another

Using TCP, applications on networked hosts can create connections to one another, over which they can exchange data or packets. The protocol guarantees reliable and in-order delivery of sender to receiver data.

TCP also distinguishes data for multiple, concurrent applications (e.g. Web server and e-mail server) running on the same host.

IP address

(Internet Protocol address) The address of a device attached to an IP network (TCP/IP network). Every client, server and network device must have a unique IP address for each network connection (network interface). Every IP packet contains a source IP address and a destination IP address.

Static and Dynamic IP

Each device in an IP network is either assigned a permanent address (static IP) by the network administrator or is assigned a temporary address (dynamic IP) via DHCP software.

Routers, firewalls and proxy servers use static addresses as do most servers and printers that serve multiple users.

Client machines may use static or dynamic IP addresses. The IP address assigned to your service by your cable or DSL Internet provider is typically dynamic IP. In routers and operating systems, the default configuration for clients is dynamic IP