System Essential Report

ACKNOWLEDGEMENT

The fact that I have been able to prepare this project report is due to help and support of many sources. I could not have achieved anything without those sources.

First of all I would like to express my enormous gratitude to my system essential Professor Ms. Sanjana Sapra for her continuous encouragement and guidance throughout the project. Her way of thinking and converting ideas into something concrete helped me a lot. She was always there to encourage me, whenever I was down and looking for some support. She helped me to think in right direction and gave me her precious time in spite of having very busy schedule. I thank him for her timely guidance and the pains she took to make me complete this project report.

I am also thankful to my parents and friends who are a constant source of inspiration to me.

Thank you

System Essential Page 2

CONTENTS

ACKNOWLEDGEMENT ---------------------------------------------------------------------------------------------------------------------- 2

CONTENTS ---------------------------------------------------------------------------------------------------------------------------------------------- 3

COMPUTER NETWORKING -------------------------------------------------------------------------------------------------------- 4

NETWORKING METHODS ------------------------------------------------------------------------------------------------------------- 5

INTERNET ------------------------------------------------------------------------------------------------------------------------------------------------- 7

INTRANET -------------------------------------------------------------------------------------------------------------------------------------------------- 14

NETWORK TOPOLOGY ------------------------------------------------------------------------------------------------------------------- 16

PROTOCOLS --------------------------------------------------------------------------------------------------------------------------------------------- 20


NETWORK ARCHITECTURE ------------------------------------------------------------------------------------------------------- 23

BROWSING -------------------------------------------------------------------------------------------------------------------- 24

WEB SEARCH ENGINE ----------------------------------------------------------------------------------------------------------------- 24

Computer Networkingomputer networking is concerned with communication between computer devices or devices. Computer networking is sometimes

considered a sub-discipline of telecommunications, computer science, information technology and/or computer engineering. Computer networks rely heavily upon the theoretical and practical application of these scientific and engineering disciplines.

C


A computer network is any set of computers or devices connected to each other with the ability to exchange data. Examples of different networks are:

a) Local area network (LAN) – It is usually a small network constrained to a small geographic

area.lan is used where a person need to connect devices in small area. E.g. if a person wants

to connect devices present in a building then he will use LAN.

b) Metropolitan area network (MAN) - It is usually a network bigger then LAN but not too

bigger as it can work for a city only.

c) Wide area network (WAN) - It is usually a larger network that covers a large geographic

area.

d) Wireless LANs and WANs (WLAN & WWAN) - these are the wireless equivalent of the

LAN and WAN.

All networks are interconnected to allow communication with a variety of different kinds of media, including twisted-pair copper wire cable, coaxial cable, optical fiber, and various wireless technologies. The devices can be separated by a few meters (e.g. via Bluetooth) or nearly unlimited distances (e.g. via the interconnections of the Internet).

Networking Methodsetworking is a complex part of computing that makes up most of the IT Industry. Without networks, almost all communication in the world would cease to happen. It is because of

networking those telephones, televisions, the internet, etc. work. NOne way to categorize computer networks is by their geographic scope, although many real-world networks interconnect Local Area Networks (LAN) via Wide Area Networks (WAN) and wireless networks [WWAN]. These three (broad) types are:

Local area network (LAN)


A local area network is a network that spans a relatively small space and provides services to small number of people.

A peer-to-peer or client-server method of networking may be used. A peer-to-peer network is where each client shares their resources with other workstations in the network. Examples of peer-to-peer networks are: Small office networks where resource use is minimal and a home network.

A client-server network is where every client is connected to the server and each other. Client-server networks use servers in different capacities.

These can be classified into two types:

a) Single-service serverb) Print server

where the server performs one task such as file server, ; while other servers can not only perform in the capacity of file servers and print servers, but they also conduct calculations and use these to provide information to clients (Web/Intranet Server). Computers are linked via Ethernet Cable, can be joined either directly (one computer to another), or via a network hub that allows multiple connections.

Wide area network (WAN)

A wide area network is a network where a wide variety of resources are deployed across a large domestic area or internationally. An example of this is a multinational business that uses a WAN to interconnect their offices in different countries. The largest and best example of a WAN is the Internet, which is a network comprised of many smaller networks.

The Internet is considered the largest network in the world. The PSTN (Public Switched Telephone Network) also is an extremely large network that is converging to use Internet technologies, although not necessarily through the public Internet.

A Wide Area Network involves communication through the use of a wide range of different technologies. These technologies include Point-to-Point WANs such as Point-to-Point Protocol (PPP) and High-Level Data Link Control (HDLC), Frame Relay, ATM (Asynchronous Transfer


Mode) and Sonet (Synchronous Optical Network). The difference between the WAN technologies is based on the switching capabilities they perform and the speed at which sending and receiving bits of information (data) occur.

Metropolitan Area Network (MAN)

A metropolitan network is a network that is too large for even the largest of LAN's but is not on the scale of a WAN. It also integrates two or more LAN networks over a specific geographical area (usually a city) so as to increase the network and the flow of communications. The LAN's in question would usually be connected via "backbone" lines.

.

Wireless networks (WLAN, WWAN)

A wireless network is basically the same as a LAN or a WAN but there are no wires between hosts and servers. The data is transferred over sets of radio transceivers. These types of networks are beneficial when it is too costly or inconvenient to run the necessary cables. For more information, see Wireless LAN and Wireless wide area network. The media access protocols for LANs come from the IEEE.The most common IEEE 802.11 WLANs cover, depending on antennas, ranges from hundreds of meters to a few kilometers. For larger areas, either communications satellites of various types, cellular radio, or wireless local loop (IEEE 802.16) all have advantages and disadvantages. Depending on the type of mobility needed, the relevant standards may come from the IETF or the ITU.

Internethe Internet is a global system of interconnected computer networks that interchange data by packet switching using the standardized Internet Protocol Suite (TCP/IP). It is a "network of networks" that consists of millions of private and public, academic,

business, and government networks of local to global scope that are linked by copper wires, fiber-optic cables, wireless connections, and other technologies.

TThe Internet carries various information resources and services, such as electronic mail, online chat, file transfer and file sharing, online gaming, and the inter-linked hypertext documents and other resources of the World Wide Web (WWW).

Terminology


The terms "Internet" and "World Wide Web" are often used in every-day speech without much distinction. However, the Internet and the World Wide Web are not one and the same. The Internet is a global data communications system. It is a hardware and software infrastructure that provides connectivity between computers. In contrast, the Web is one of the services communicated via the Internet. It is a collection of interconnected documents and other resources, linked by hyperlinks and URLs.

Creation

Lawrence Roberts to head a project to implement a network, and Roberts based the technology on the work of Paul Baran who had written an exhaustive study for the U.S. Air Force that recommended packet switching (as opposed to circuit switching) to make a network highly robust and survivable. After much work, the first two nodes of what would become the ARPANET were interconnected between UCLA and SRI International in Menlo Park, California, on October 29, 1969. The ARPANET was one of the "eve" networks of today's Internet. Following on from the demonstration that packet switching worked on the ARPANET, the British Post Office, Telenet, DATAPAC and TRANSPAC collaborated to create the first international packet-switched network service. In the UK, this was referred to as the International Packet Switched Service (IPSS), in 1978.

The first TCP/IP-based wide-area network was operational by January 1, 1983 when all hosts on the ARPANET were switched over from the older NCP protocols. In 1985, the United States' National Science Foundation (NSF) commissioned the construction of the NSFNET, a university 56 kilobit/second network backbone using computers called "fuzzballs" by their inventor, David L. Mills. The following year, NSF sponsored the conversion to a higher-speed 1.5 megabit/second network. A key decision to use the DARPA TCP/IP protocols was made by Dennis Jennings, then in charge of the Supercomputer program at NSF.

Today's Internet

The My Opera Community server rack. From the top, user file storage (content of files.myopera.com), "bigma" (the master MySQL database server), and two IBM blade centers containing multi-purpose machines (Apache front ends, Apache back ends, slave MySQL database servers, load balancers, file servers, cache servers and sync masters).


Aside from the complex physical connections that make up its infrastructure, the Internet is facilitated by bi- or multi-lateral commercial contracts (e.g., peering agreements), and by technical specifications or protocols that describe how to exchange data over the network. Indeed, the Internet is defined by its interconnections and routing policies.

As of March 31, 2008, 1.407 billion people use the Internet according to Internet World Stats.

Internet protocols

The complex communications infrastructure of the Internet consists of its hardware components and a system of software layers that control various aspects of the architecture. While the hardware can often be used to support other software systems, it is the design and the rigorous standardization process of the software architecture that characterizes the Internet.

The responsibility for the architectural design of the Internet software systems has been delegated to the Internet Engineering Task Force (IETF). The IETF conducts standard-setting work groups, open to any individual, about the various aspects of Internet architecture. Resulting discussions and final standards are published in Request for Comments (RFCs), freely available on the IETF web site.

The principal methods of networking that enable the Internet are contained in a series of RFCs that constitute the Internet Standards. These standards describe a system known as the Internet Protocol Suite. This is a model architecture that divides methods into a layered system of protocols (RFC 1122, RFC 1123).

The layers correspond to the environment or scope in which their services operate. At the top is the space (Application Layer) of the software application, e.g., a web browser application, and just below it is the Transport Layer which connects applications on different hosts via the network (e.g., client-server model). The underlying network consists of two layers: the Internet Layer which enables computers to connect to one-another via intermediate (transit) networks and thus is the layer that establishes internetworking and the Internet, and lastly, at the bottom, is a software layer that provides connectivity between hosts on the same local link (therefor called Link Layer), e.g., a local area network (LAN) or a dial-up connection. This model is also known as the TCP/IP model of networking. While other models have been developed, such as the Open Systems Interconnection (OSI) model, they are not compatible in the details of description, nor implementation.

Internet structure


There have been many analyses of the Internet and its structure. For example, it has been determined that the Internet IP routing structure and hypertext links of the World Wide Web are examples of scale-free networks.

Similar to the way the commercial Internet providers connect via Internet exchange points, research networks tend to interconnect into large sub networks such as the following:

• GEANT • GLORIAD • The Internet2 Network (formally known as the Abilene Network) • JANET (the UK's national research and education network)

These in turn are built around relatively smaller networks. See also the list of academic computer network organizations.

In computer network diagrams, the Internet is often represented by a cloud symbol, into and out of which network communications can pass.

Languages


After English (30% of Web visitors) the most requested languages on the World Wide Web are Chinese (17%), Spanish (9%), Japanese (7%), French (5%) and German (5%).

30

17

97

5

5

27

Languages

EnglishChineseSpanishJapaneseFrenchGermanOthers

By continent, 38% of the world's Internet users are based in Asia, 27% in Europe, 18% in North America, 10% in Latin America and the Caribbean, and 7% in Australia.

38

27

18

107

Continental Usage

Asia Europe North AmericaLatin America Australia

The Internet's technologies have developed enough in recent years, especially in the use of Unicode that good facilities are available for development and communication in most widely


used languages. However, some glitches such as mojibake (incorrect display of foreign language characters, also known as kryakozyabry) still remain.

Internet and the workplace

The Internet is allowing greater flexibility in working hours and location, especially with the spread of unmetered high-speed connections and Web applications.

The Internet viewed on mobile devices

The Internet can now be accessed virtually anywhere by numerous means. Mobile phones, data cards, handheld game consoles and cellular routers allow users to connect to the Internet from anywhere there is a cellular network supporting that device's technology.

E-mail

The concept of sending electronic text messages between parties in a way analogous to mailing letters or memos predates the creation of the Internet. Even today it can be important to distinguish between Internet and internal e-mail systems. Internet e-mail may travel and be stored unencrypted on many other networks and machines out of both the sender's and the recipient's control.

The World Wide Web

Graphic representation of a minute fraction of the WWW, demonstrating hyperlinks

Many people use the terms Internet and World Wide Web (or just the Web) interchangeably, but, as discussed above, the two terms are not synonymous.

The World Wide Web is a huge set of interlinked documents, images and other resources, linked by hyperlinks and URLs. These hyperlinks and URLs allow the web servers and other machines that store originals, and cached copies, of these resources to deliver them as required using HTTP (Hypertext Transfer Protocol). HTTP is only one of the communication protocols used on the Internet. Web services also use HTTP to allow software systems to communicate in order to share and exchange business logic and data.


Software products that can access the resources of the Web are correctly termed user agents. In normal use, web browsers, such as Internet Explorer and Firefox, access web pages and allow users to navigate from one to another via hyperlinks. Web documents may contain almost any combination of computer data including graphics, sounds, text, video, multimedia and interactive content including games, office applications and scientific demonstrations.

Through keyword-driven Internet research using search engines like Yahoo! and Google, millions of people worldwide have easy, instant access to a vast and diverse amount of online information. Many individuals and some companies and groups use "web logs" or blogs, which are largely used as easily updatable online diaries.

Some commercial organizations encourage staff to fill them with advice on their areas of specialization in the hope that visitors will be impressed by the expert knowledge and free information, and be attracted to the corporation as a result. One example of this practice is Microsoft, whose product developers publish their personal blogs in order to pique the public's interest in their work.

Remote access

The Internet allows computer users to connect to other computers and information stores easily, wherever they may be across the world. They may do this with or without the use of security, authentication and encryption technologies, depending on the requirements.

This is encouraging new ways of working from home, collaboration and information sharing in many industries. An accountant sitting at home can audit the books of a company based in another country, on a server situated in a third country that is remotely maintained by IT specialists in a fourth. These accounts could have been created by home-working bookkeepers, in other remote locations, based on information e-mailed to them from offices all over the world. Some of these things were possible before the widespread use of the Internet, but the cost of private leased lines would have made many of them infeasible in practice.

An office worker away from his desk, perhaps on the other side of the world on a business trip or a holiday, can open a remote desktop session into his normal office PC using a secure Virtual Private Network (VPN) connection via the Internet. This gives the worker complete access to all of his or her normal files and data, including e-mail and other applications, while away from the office.This concept is also referred to by some network security people as the Virtual Private Nightmare, because it extends the secure perimeter of a corporate network into its employees' homes; this has been the source of some notable security breaches, but also provides security for the workers.


File sharing

A computer file can be e-mailed to customers, colleagues and friends as an attachment. It can be uploaded to a website or FTP server for easy download by others. It can be put into a "shared location" or onto a file server for instant use by colleagues. The load of bulk downloads to many users can be eased by the use of "mirror" servers or peer-to-peer networks.

In any of these cases, access to the file may be controlled by user authentication; the transit of the file over the Internet may be obscured by encryption, and money may change hands before or after access to the file is given.

Internet access

Common methods of home access include dial-up, landline broadband (over coaxial cable, fiber optic or copper wires), and Wi-Fi, satellite and 3G technology cell phones.

Public places to use the Internet include libraries and Internet cafes, where computers with Internet connections are available. There are also Internet access points in many public places such as airport halls and coffee shops, in some cases just for brief use while standing. Various terms are used, such as "public Internet kiosk", "public access terminal", and "Web payphone". Many hotels now also have public terminals, though these are usually fee-based. These terminals are widely accessed for various usage like ticket booking, bank deposit, online payment etc. Wi-Fi provides wireless access to computer networks, and therefore can do so to the Internet itself. Hotspots providing such access include Wi-Fi cafes, where would-be users need to bring their own wireless-enabled devices such as a laptop or PDA.Commercial Wi-Fi services covering large city areas are in place in London, Vienna, Toronto, San Francisco, Philadelphia, Chicago and Pittsburgh.

Social impact

The Internet has made possible entirely new forms of social interaction, activities and organizing, thanks to its basic features such as widespread usability and access.

Social networking websites such as Facebook and MySpace have created a new form of socialization and interaction. Users of these sites are able to add a wide variety of items to their personal pages, to indicate common interests, and to connect with others.

Political organization and censorship

In democratic societies, the Internet has achieved new relevance as a political tool. The presidential campaign of Howard Dean in 2004 in the United States became famous for its ability to generate donations via the Internet. Many political groups use the Internet to achieve a whole new method of organizing, in order to carry out Internet activism.


Some governments, such as those of Cuba, Iran, North Korea, Myanmar, the People's Republic of China, and Saudi Arabia, restrict what people in their countries can access on the Internet, especially political and religious content. This is accomplished through software that filters domains and content so that they may not be easily accessed or obtained without elaborate circumvention.

Complex architecture

Many computer scientists see the Internet as a "prime example of a large-scale, highly engineered, yet highly complex system”. The Internet is extremely heterogeneous. (For instance, data transfer rates and physical characteristics of connections vary widely.) The Internet exhibits "emergent phenomena" that depend on its large-scale organization. For example, data transfer rates exhibit temporal self-similarity. Further adding to the complexity of the Internet is the ability of more than one computer to use the Internet through only one node, thus creating the possibility for a very deep and hierarchal sub-network that can theoretically be extended infinitely (disregarding the programmatic limitations of the IPv4 protocol). However, since principles of this architecture date back to the 1960s, it might not be a solution best suited to modern needs, and thus the possibility of developing alternative structures is currently being looked into.

According to a June 2007 article in Discover magazine, the combined weight of all the electrons moved within the Internet in a day is 0.2 millionths of an ounce. Others have estimated this at nearer 2 ounces (50 grams).

Marketing

The Internet has also become a large market for companies; some of the biggest companies today have grown by taking advantage of the efficient nature of low-cost advertising and commerce through the Internet, also known as e-commerce. It is the fastest way to spread information to a vast number of people simultaneously. The Internet has also subsequently revolutionized shopping—for example; a person can order a CD online and receive it in the mail within a couple of days, or download it directly in some cases. The Internet has also greatly facilitated personalized marketing which allows a company to market a product to a specific person or a specific group of people more so than any other advertising medium.

Examples of personalized marketing include online communities such as MySpace, Friendster, Orkut, Facebook and others which thousands of Internet users join to advertise themselves and make friends online. Many of these users are young teens and adolescents ranging from 13 to 25 years old. In turn, when they advertise themselves they advertise interests and hobbies, which online marketing companies can use as information as to what those users will purchase online, and advertise their own companies' products to those users.


Intranetn intranet is a private computer network that uses Internet protocols and network connectivity to securely share any part of an organization's information or operational systems with its employees. Sometimes the term refers only to the organization's

internal website, but often it is a more extensive part of the organization's computer infrastructure and private websites are an important component and focal point of internal communication and collaboration...

AAn intranet is built from the same concepts and technologies used for the Internet, such as clients and servers running on the Internet Protocol Suite (TCP/IP). Any of the well known Internet protocols may be found in an intranet, such as HTTP (web services), SMTP (e-mail), and FTP (file transfer). There is often an attempt to employ Internet technologies to provide modern interfaces to legacy information systems hosting corporate data.

An intranet can be understood as a private version of the Internet, or as a private extension of the Internet confined to an organization. The term first appeared in print on April 19, 1995, in Digital News & Review in an article authored by technical editor Stephen Lawton.

Intranet-Site content is almost always private and requires authorization for each web viewer, provided either through specific user authentication or by default, based on the location of the viewer's computer on the private network.

Intranets differ from extranets in that the former are generally restricted to employees of the organization while extranets may also be accessed by customers, suppliers, or other approved parties. Extranets extend a private network onto the Internet with special provisions for access, authorization and authentication (see also AAA protocol).

An organization's intranet does not necessarily have to provide access to the Internet. When such access is provided it is usually through a network gateway with a firewall, shielding the intranet from unauthorized external access. The gateway often also implements user authentication, encryption of messages, and often virtual private network (VPN) connectivity for off-site employees to access company information, computing resources and internal communications.


Increasingly, intranets are being used to deliver tools and applications, e.g., collaboration (to facilitate working in groups and teleconferencing) or sophisticated corporate directories, sales and Customer relationship management tools, project management etc., to advance productivity.

Intranets are also being used as corporate culture-change platforms. For example, large numbers of employees discussing key issues in an intranet forum application could lead to new ideas in management, productivity, quality, and other corporate issues.

Benefits of intranets

1. Workforce productivity: Intranets can help users to locate and view information faster and use applications relevant to their roles and responsibilities. With the help of a web browser interface, users can access data held in any database the organization wants to make available, anytime and - subject to security provisions - from anywhere within the company workstations, increasing employees' ability to perform their jobs faster, more accurately, and with confidence that they have the right information. It also helps to improve the services provided to the users.

2. Time: With intranets, organizations can make more information available to employees on a "pull" basis (i.e., employees can link to relevant information at a time which suits them) rather than being deluged indiscriminately by emails.

3. Communication: Intranets can serve as powerful tools for communication within an organization, vertically and horizontally. From a communications standpoint, intranets are useful to communicate strategic initiatives that have a global reach throughout the organization. The type of information that can easily be conveyed is the purpose of the initiative and what the initiative is aiming to achieve, who is driving the initiative, results achieved to date, and who to speak to for more information. By providing this information on the intranet, staff have the opportunity to keep up-to-date with the strategic focus of the organization.

4. Web publishing allows 'cumbersome' corporate knowledge to be maintained and easily accessed throughout the company using hypermedia and Web technologies. Examples include: employee manuals, benefits documents, company policies, business standards, newsfeeds, and even training, can be accessed using common Internet standards (Acrobat files, Flash files, CGI applications). Because each business unit can update the online copy of a document, the most recent version is always available to employees using the intranet.


Planning and creating an intranet

Most organizations devote considerable resources into the planning and implementation of their intranet as it is of strategic importance to the organization's success. Some of the planning would include topics such as:

The purpose and goals the intranet Persons or departments responsible for implementation and management Implementation schedules and phase-out of existing systems Defining and implementing security of the intranet How they'll ensure to keep it within legal boundaries and other constraints Level of interactivity (eg wikis, on-line forms) desired. Is the input of new data and updating of existing data to be centrally controlled or

devolved?

These are in addition to the hardware and software decisions (like Content Management Systems), participation issues (like good taste, harassment, confidentiality), and features to be supported.

The actual implementation would include steps such as

1. User involvement to identify users' information needs.

2. Setting up web server(s) with the appropriate hardware and software.

3. Setting up web server access using a TCP/IP network.

4. Installing required user applications on computers.

5. Creation of document framework for the content to be hosted.

6. User involvement in testing and promoting use of intranet.


Network Topologyetwork topology is the study of the arrangement or mapping of the elements (links, nodes, etc.) of a network, especially the physical (real) and

logical (virtual) interconnections between nodes. A local area network (LAN) is one example of a network that exhibits both a physical topology and a logical topology. Any given node in the LAN will have one or more links to one or more other nodes in the network and the mapping of these links and nodes onto a graph results in a geometrical shape that determines the physical topology of the network. Likewise, the mapping of the flow of data between the nodes in the network determines the logical topology of the network. It is important to note that the physical and logical topologies might be identical in any particular network but they also may be different.

N

Any particular network topology is determined only by the graphical mapping of the configuration of physical and/or logical connections between nodes. LAN Network Topology is, therefore, technically a part of graph theory. Distances between nodes, physical interconnections, transmission rates, and/or signal types may differ in two networks and yet their topologies may be identical.

Basic types of topologies

The arrangement or mapping of the elements of a network gives rise to certain basic topologies which may then be combined to form more complex topologies (hybrid topologies). The most common of these basic types of topologies are (refer to the illustration at the top right of this page):

• Bus (Linear, Linear Bus) • Hybrid • Point to Point


http://en.wikipedia.org/wiki/Image:NetworkTopologies.png

Classification of network topologies

There are also three basic categories of network topologies:

• Physical topologies • Signal topologies • Logical topologies

The terms signal topology and logical topology are often used interchangeably even though there is a subtle difference between the two and the distinction is not often made between the two.

Physical topologies

The mapping of the nodes of a network and the physical connections between them – i.e. the layout of wiring, cables, the locations of nodes, and the interconnections between the nodes and the cabling or wiring system.

Classification of physical topologies

The simplest topology is a permanent link between two endpoints. Switched point-to-point topologies are the basic model of conventional telephony. The value of a permanent point-to-point network is the value of guaranteed, or nearly so, communications between the two endpoints.

Linear bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has exactly two endpoints (this is the 'bus', which is also commonly referred to as the backbone, or trunk) – all data that is transmitted between nodes in the network is transmitted over this common transmission medium and is able to be received by all nodes in the network virtually simultaneously (disregarding propagation delays).

Distributed bus

The type of network topology in which all of the nodes of the network are connected to a common transmission medium which has more than two endpoints that are created by adding branches to the main section of the transmission medium – the physical distributed bus topology functions in exactly the same fashion as the physical linear bus topology (i.e., all nodes share a common transmission medium).


Tree

The type of network topology in which a central 'root' node (the top level of the hierarchy) is connected to one or more other nodes that are one level lower in the hierarchy (i.e., the second level) with a point-to-point link between each of the second level nodes and the top level central 'root' node, while each of the second level nodes that are connected to the top level central 'root' node will also have one or more other nodes that are one level lower in the hierarchy (i.e., the third level) connected to it, also with a point-to-point link, the top level central 'root' node being the only node that has no other node above it in the hierarchy – the hierarchy of the tree is symmetrical, each node in the network having a specific fixed number, f, of nodes connected to it at the next lower level in the hierarchy, the number, f, being referred to as the 'branching factor' of the hierarchical tree.

Hybrid network topologies

The hybrid topology is a type of network topology that is composed of one or more interconnections of two or more networks that are based upon different physical topologies or a type of network topology that is composed of one or more interconnections of two or more networks that are based upon the same physical topology, but where the physical topology of the network resulting from such an interconnection does not meet the definition of the original physical topology of the interconnected networks

Signal Topology

The mapping of the actual connections between the nodes of a network, as evidenced by the path that the signals take when propagating between the nodes.

Logical Topology

The mapping of the apparent connections between the nodes of a network, as evidenced by the path that data appears to take when traveling between the nodes.

Classification of Logical topologies

The logical classification of network topologies generally follows the same classifications as those in the physical classifications of network topologies, the path that the data takes between nodes being used to determine the topology as opposed to the actual physical connections being used to determine the topology.

Centralization

The star topology reduces the probability of a network failure by connecting all of the peripheral nodes (computers, etc.) to a central node. When the physical star topology is applied to a logical


bus network such as Ethernet, this central node (traditionally a hub) rebroadcasts all transmissions received from any peripheral node to all peripheral nodes on the network, sometimes including the originating node. All peripheral nodes may thus communicate with all others by transmitting to, and receiving from, the central node only. The failure of a transmission line linking any peripheral node to the central node will result in the isolation of that peripheral node from all others, but the remaining peripheral nodes will be unaffected.

Decentralization

In a mesh topology (i.e., a partially connected mesh topology), there are at least two nodes with two or more paths between them to provide redundant paths to be used in case the link providing one of the paths fails.

This decentralization is often used to advantage to compensate for the single-point-failure disadvantage that is present when using a single device as a central node (e.g., in star and tree networks). A special kind of mesh, limiting the number of hops between two nodes, is a hypercube. The number of arbitrary forks in mesh networks makes them more difficult to design and implement, but their decentralized nature makes them very useful. This is similar in some ways to a grid network, where a linear or ring topology is used to connect systems in multiple directions. A multi-dimensional ring has a toroidal topology, for instance.

Hybrids

Hybrid networks use a combination of any two or more topologies in such a way that the resulting network does not exhibit one of the standard topologies (e.g., bus, star, ring, etc.). For example, a tree network connected to a tree network is still a tree network, but two star networks connected together exhibit a hybrid network topology. A hybrid topology is always produced when two different basic network topologies are connected. Two common examples for Hybrid network are: star ring network and star bus network.

A Star ring network consists of two or more star topologies connected using a multistation access unit (MAU) as a centralized hub.

A Star Bus network consists of two or more star topologies connected using a bus trunk (the bus trunk serves as the network's backbone).


Protocolsn computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints. In its simplest form, a protocol can be defined as the rules governing the syntax, semantics, and synchronization of

communication. Protocols may be implemented by hardware, software, or a combination of the two. At the lowest level, a protocol defines the behavior of a hardware connection.

ITypical properties

It is difficult to generalize about protocols because they vary so greatly in purpose and sophistication. Most protocols specify one or more of the following properties:

Detection of the underlying physical connection (wired or wireless), or the existence of the other endpoint or node

Handshaking Negotiation of various connection characteristics How to start and end a message How to format a message What to do with corrupted or improperly formatted messages (error correction) How to detect unexpected loss of the connection, and what to do next Termination of the session and or connection.

Importance

The widespread use and expansion of communications protocols is both a prerequisite for the Internet, and a major contributor to its power and success. The pair of Internet Protocol (or IP) and Transmission Control Protocol (or TCP) are the most important of these, and the term TCP/IP refers to a collection (or protocol suite) of its most used protocols. Most of the Internet's communication protocols are described in the RFC documents of the Internet Engineering Task Force (or IETF).

The protocols in human communication are separate rules about appearance, speaking, listening and understanding. All these rules, also called protocols of conversation, represent different layers of communication. They work together to help people successfully communicate. The need for protocols also applies to network devices. Computers have no way of learning protocols, so network engineers have written rules for communication that must be strictly followed for successful host-to-host communication.


Common protocols

• IP (Internet Protocol) • UDP (User Datagram Protocol) • TCP (Transmission Control Protocol) • DHCP (Dynamic Host Configuration Protocol) • HTTP (Hypertext Transfer Protocol) • FTP (File Transfer Protocol) • Telnet (Telnet Remote Protocol) • SSH (Secure Shell Remote Protocol) • POP3 (Post Office Protocol 3) • SMTP (Simple Mail Transfer Protocol) • IMAP (Internet Message Access Protocol)

Protocol testing

In general, protocol testers work by capturing the information exchanged between a Device under Test (DUT) and a reference device known to operate properly. In the example of a manufacturer producing a new keyboard for a personal computer, the Device under Test would be the keyboard and the reference device, the PC.

Network Architecturen computing, network architecture is the design of a computer network.The design principles, physical configuration, functional organization, operational procedures, and data formats used as the bases for the design, construction, modification, and operation of a

communications network. The structure of an existing communications network, including the physical configuration, facilities, operational structure, operational procedures, and the data formats in use. It outlines the products and services required in data communication networks.

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Browsingeb browser is a software application which enables a user to display and interact with text, images, videos, music, games and other information typically located on a Web page at a website on the World Wide Web or a local area

network. Text and images on a Web page can contain hyperlinks to other Web pages at the same or different website. Web browsers allow a user to quickly and easily access information provided on many Web pages at many websites by traversing these links. Web browsers format HTML information for display, so the appearance of a Web page may differ between browsers.

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Therefore, Browing is nothing but surfing the webpapes located on the world wide web using a web browser.

Some of the Web browsers currently available for personal computers include Internet Explorer, Mozilla Firefox, Safari, Netscape, Opera, Avant Browser, Konqueror, Google Chrome, Flock, Arachne, Epiphany, K-Meleon and AOL Explorer. Web browsers are the most commonly used type of HTTP user agent. Although browsers are typically used to access the World Wide Web, they can also be used to access information provided by Web servers in private networks or content in file systems.

Protocols and standards

Web browsers communicate with Web servers primarily using HTTP (hypertext transfer protocol) to fetch webpages. HTTP allows Web browsers to submit information to Web servers as well as fetch Web pages from them. The most commonly used HTTP is HTTP/1.1, which is fully defined in RFC 2616. HTTP/1.1 has its own required standards that Internet Explorer does not fully support, but most other current-generation Web browsers do.

Pages are located by means of a URL (uniform resource locator, RFC 1738 ), which is treated as an address, beginning with http: for HTTP access. Many browsers also support a variety of other URL types and their corresponding protocols, such as gopher: for Gopher (a hierarchical hyperlinking protocol), ftp: for FTP (file transfer protocol), rtsp: for RTSP (real-time streaming protocol), and https: for HTTPS (an SSL encrypted version of HTTP).


The file format for a Web page is usually HTML (hyper-text markup language) and is identified in the HTTP protocol using a MIME content type. Most browsers natively support a variety of formats in addition to HTML, such as the JPEG, PNG and GIF image formats, and can be extended to support more through the use of plugins. The combination of HTTP content type and URL protocol specification allows Web page designers to embed images, animations, video, sound, and streaming media into a Web page, or to make them accessible through the Web page.

Early Web browsers supported only a very simple version of HTML. The rapid development of proprietary Web browsers led to the development of non-standard dialects of HTML, leading to problems with Web interoperability. Modern Web browsers support a combination of standards- and defacto-based HTML and XHTML, which should display in the same way across all browsers. No browser fully supports HTML 4.01, XHTML 1.x or CSS 2.1 yet. Currently many sites are designed using WYSIWYG HTML generation programs such as Adobe Dreamweaver or Microsoft FrontPage. Microsoft FrontPage often generates non-standard HTML by default, hindering the work of the W3C in developing standards, specifically with XHTML and CSS (cascading style sheets, used for page layout). Dreamweaver and other more modern Microsoft HTML development tools such as Microsoft Expression Web and Microsoft Visual Studio conform to the W3C standards.

Some of the more popular browsers include additional components to support Usenet news, IRC (Internet relay chat), and e-mail. Protocols supported may include NNTP (network news transfer protocol), SMTP (simple mail transfer protocol), IMAP (Internet message access protocol), and POP (post office protocol). These browsers are often referred to as Internet suites or application suites rather than merely Web browsers.

Web search Engine Web search engine is a search engine designed to search for information on the World Wide Web. Information may consist of web pages, images, information and other types of files. Some search engines also mine data available in news books, databases, or

open directories. Unlike Web directories, which are maintained by human editors, search engines operate algorithmically or are a mixture of algorithmic and human input.

A Before there were search engines there was a complete list of all web servers. The list was edited by Tim Berners-Lee and hosted on the CERN web server. As more and more web servers went online the central list could not keep up. On the NCSA Site new servers were announced under the title "What's New!" but no complete listing existed any more.


The very first tool used for searching on the (pre-web) Internet was Archie. The first Web search engine was Wandex, a now-defunct index collected by the World Wide Web Wanderer, a web crawler developed by Matthew Gray at MIT in 1993. Another very early search engine, Aliweb, also appeared in 1993.

Search engines were also known as some of the brightest stars in the Internet investing frenzy that occurred in the late 1990s. Several companies entered the market spectacularly, receiving record gains during their initial public offerings. Some have taken down their public search engine, and are marketing enterprise-only editions, such as Northern Light. Many search engine companies were caught up in the dot-com bubble, a speculation-driven market boom that peaked in 1999 and ended in 2001.

Around 2000, the Google search engine rose to prominence. The company achieved better results for many searches with an innovation called PageRank. This iterative algorithm ranks web pages based on the number and PageRank of other web sites and pages that link there, on the premise that good or desirable pages are linked to more than others. Google also maintained a minimalist interface to its search engine. In contrast, many of its competitors embedded a search engine in a web portal.

By 2000, Yahoo was providing search services based on Inktomi's search engine. Microsoft first launched MSN Search (since re-branded Live Search) in the fall of 1998 using search results from Inktomi.As of late 2007, Google was by far the most popular Web search engine worldwide. A number of country-specific search engine companies have become prominent; for example Baidu is the most popular search engine in the People's Republic of China and guruji.com in India.

Web search engines work by storing information about many web pages, which they retrieve from the WWW itself. These pages are retrieved by a Web crawler (sometimes also known as a spider) — an automated Web browser which follows every link it sees.

Exclusions can be made by the use of robots.txt. The contents of each page are then analyzed to determine how it should be indexed (for example, words are extracted from the titles, headings, or special fields called meta tags). Data about web pages are stored in an index database for use in later queries. Some search engines, such as Google, store all or part of the source page (referred to as a cache) as well as information about the web pages, whereas others, such as AltaVista, store every word of every page they find. This cached page always holds the actual search text since it is the one that was actually indexed, so it can be very useful when the content of the current page has been updated and the search terms are no longer in it.


This problem might be considered to be a mild form of linkrot, and Google's handling of it increases usability by satisfying user expectations that the search terms will be on the returned webpage. This satisfies the principle of least astonishment since the user normally expects the search terms to be on the returned pages. Increased search relevance makes these cached pages very useful, even beyond the fact that they may contain data that may no longer be available elsewhere.


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