56217 25910 Unit2 the Internet

8/3/2019 56217 25910 Unit2 the Internet

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B.S. Anangpuria Institute of Technology & Management

Subject Code: CSE-208 E

Subject Name: Internet Fundamentals

UNIT: 2 (The Internet)

2.1 Computer Network & Internet

A computer network may be defined as an interconnected collection of autonomous computers. Two

computers are said to be interconnected if they are able to exchange information. The connection need not

be via a copper wire; fiber optics, microwaves, and communication satellites can also be used. The term

autonomous computers means, the computer system that can be controlled by itself by having own

memory unit, control unit, and processor.

Types of Computer Networks:

2.1.1 Local Area Network (LAN)

Privately-owned networks within a single building or campus of upto a few kilometers in size.

LANs often use a transmission technology consisting of a single cable to which all the machines the

machines are attached.

Traditional LANs run at speeds of 10 to 100 Mbps, have low delay (tens of microseconds) and make very

few errors.

Newer LANs may operate at higher speeds, upto hundreds of megabits/seconds.

LANs might be related to the telephone lines.

2.1.2 Metropolitan Area Network (MAN)

A bigger version of a LAN.

It cover a group of nearby corporate offices or a city and might be either private or public.

Might be related to the local cable television network.

2.1.3 Wide Area Network (LAN)

Spans a large geographical area, often a country or continent.

It contains a collection of machines intended for running user (i.e., application) programs. These machines

are called as hosts.

2.1.4 Internetworks

Internetwork is a collection of interconnected networks is called anInternetworkorInternet


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2.2 Introduction to Internet

The Internet sometimes called the Information Superhighway, is a world wide publicly accessible series

of interconnected computer networks that transmit data by packet switching using the standard Internet

Protocol (IP).

It is a network of networks that consists of millions of smaller domestic, academic, business, and

government networks, which together carry various information and services, such as electronic mail,

online chat, file transfer, and the interlinked web pages and other resources of the World Wide Web.

Internet is a collection of interconnected computer networks, linked by copper wires, fiber-optic cables,

wireless connections, etc.

2.2.1 Services Provided by Internet

(Covered in Unit-1)

2.3 History of Internet

The foundation of Internet is found by the global interconnection of hundreds of thousands of independent

computers, communication entities, and the information systems.

What makes the interconnection possible is the use of a set of communication standards, procedures and

formats in common among the networks and the various devices and computational facilities connected to

them.

The procedures by which computers communicate with each other are calledprotocols.

The history of Internet can be explained as follows:

2.3.1 In 1970s.

Initially the protocols used by the Internet were the Transmission Control Protocol/Internet

Protocol (TCP/IP). TCP/IP is the protocol that determines how computers connect, send, and

receive information on the Internet. TCPpermits communication between the various computerson the Internet andIP specify how the data is routed from computer to computer.

In 1969, the U.S. Defense Advanced Research Projects Agency (variously called ARPA/DARPA),

an agency within the Department of Defense, commissioned a wide area computer network called

ARPANET, to share super-computing power. This network made use of the new packet

switching concepts for interconnecting computers and initially linked computers at Universities

and other research institutions in the United States and in selected NATO countries.

In 1970s, the ARPANET was essentially the only realistic wide-area computer network in

existence with a base of several dozens organizations, perhaps twice that number of computers and

numerous researchers at those sites.

In Packet Switching, the data to be transmitted is divided into small packets of information and

labeled to identify the sender and receiver. The packets were sent over a network and thenreassembled at their destination.

2.3.2 In 1980s.


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In 1980s, as the Internet grew, the Domain Name System (DNS) was developed, to allow the

network to expand more easily by assigning names to host computers in a distributed fashion.

2.3.2 In 1990s.

In 1990s, lots of commercial organizations started getting online. Graphical browsing tools were

developed, and the programming language HTML allowed users all over the world to publish on

what was called the World Wide Web. Millions of people went online to work, shop, bank and be

entertained.

TheKey reasons for the Internets great success:

1. Decisions were made on a technical rather than political basis.

2. The Internet did not require a centralized structure that would not scale up; it was and is a

distributed operation.

3. The Internet allowed people to do things of inherent interest, such as sending and receiving

emails.4. The software involved was free or very low cost.

Based on the past history, it can be assumed that the Internet will continue to grow, change,

support new applications.

2.4 Working of Internet

Working of Internet can be better explained by considering various issues as mentioned below:

Network Benefits

Interconnected Networks & Communication

Physical Components

Network Connections

IP Addresses

IPv6

Web Page Retrieval

2.4.1 Network Benefits

Provide Convenience : Computers on network can backup their files over the network.

Allow Sharing :Networked computers can share resources, such as disks & printers.

Fac ilitate Communications : Sending and receiving email, transferring files, and

videoconferencing.

Generate Savings : Networked computers can provide more computing power for less money.

Several small computers connected on a network can provide as mush as or more computing power than a

single, large computer and will cost much less. Also, since resources can be shared, not everyone needs

their own peripherals, which can result in a substantial cost savings.

Provide Reliability : If one part of a network is down, useful work may still be possible using a

different network path.

Simplify Scalability : It is relatively easy to add more computers to an existing network.


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2.4.2 Interconnected Networks & Communication

The Internet is essentially a network of networks, the communication among which depends on a

common set of protocols.

The protocol that determines how the computers connect, send, and receive information on the

Internet is Transmission Control Protocol/Internet Protocol (TCP/IP).

The TCP permits communication between the various computers on the Internet, and IP specifies

how data is routed from computer to computer.

The TCP/IP provides Simple Mail Transfer Protocol (SMTP) for sending an email message,and Hypertext Transfer Protocol (HTTP) for a Web Page request.

TCP/IP divides the information to be sent into smaller pieces called packets and then transmit

them over Internet.

Advantages of Packets:-

Error Recovery. If a packet gets corrupted, only that packet needs to be resent, not the

entire message.

Load Distribution. If one area of the network is congested, packets can be routed to lessbusy areas.

Flexibility. If the network experiences a failure or disruption in one locale, packet can be

rerouted.

In addition to the message pieces, each packet of data also contains information about the

computer that sent it, the computer it is being sent to, a sequence number indicating where the

packet fits in the overall message and error checking information to ensure that packet is not

corrupted while in transit.

The packets are reassembled after being received at the destination computer.

A message is sent from the destination computer to the sending computer to resend any missing or

corrupted packets. This method of packet switching does not require the packets to be sent in

sequential order.

Packets

IP is used to

Route the

TCP converts message

message into

a stream ofpackets

Source

1 2 3

4 5 6

7 8 9

Original Message

1 2 3

4 5 6

7 8 9

Network

5

81 2 3

4 6

7 9


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Destination

2.4.3 Physical Components

In addition to various software protocols, Internet includes a host of physical components as well:

Servers

Routers

Communication Media

Server: Servers are the computers that answers the requests for services, such as list servers, mail

servers, & news servers.

Router: Routers are the special-purpose computers that directs data packets along the network.

Routers can detect whether the part of the network is down or congested and can then reroute

traffic just like a traffic cop.

Communication Media: Communication media provides means to transport packets of

information like: Copper Wires transmit messages as electrical impulses.

Fiber Optic Cables uses light waves to transmit messages.

Radio waves, Microwaves, Infrared Light & Visible Light all carry messages through air.

2.4.4 Network Connections

Connecting to the Internet from homes generally requires the use of a modem and a regular

telephone line (copper wire) to connect to an Internet Service Provider (ISP).

A second modem at the ISPs end completes the connection and slower the two modem speedsdetermines the maximum connection speed, usually 56 kbps.

Modem (Modulator Demodulator), is a device needed to convert data from digital to analog and

analog to digital.

Business, organization, network typically uses Network Interface Cards (NIC) instead of

modems. These systems have a higher speed connection, usually 56 kbps or better, to their ISPs.

Such connections are usually leased from the telephone company.

Another option is an Integrated Services Digital Network (ISDN) which is slightly more

expensive but uses regular telephone lines and replaces modems with special adaptors upto fivetimes faster than traditional modems.

Senders Computer

Network

Via phoneMessage

ISP

ModemNSP

Route

r


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line

Local Area Network

Network

Destination Computer

2.4.5 Client Server Model

The client server model consists of two parts:

Client, that request for some service

Server, that serves the client for any request.

Request

Service

The client server model is based on the request serve principle as shown above.

The client makes a request to the server for any information or resources over network by sendinga request message.

Then the server serves the client on his request by providing the required information or resources.

2.4.6 IP Addresses

Each computer connected over a network must have a unique name or address to be identified

uniquely. Computers are best suited to manipulate numbers, thus every computer is assigned a

numeric address, calledIP Address.

An IP Address is a 32 bit or four byte address, each byte separated by a dot. One byte represent a

number from 0 (00000000) to 255 (11111111).

Each IP Address consists of a network component and a Host Component.

32 bits

132.170.4.124

Network Host

10000100 10101010 00000100 01111100

Modem

Route

r

Message

Client Server Network


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IP Address plays an important role in the routing of packets over the Internet. Source and

Destination IP Addresses are included in each packet. In essence, the address provide directions on

where the packets should go.

A central authority manages IP Addresses; otherwise conflicts might arise.

The Network Information Center (NIC) is in charge of assigning IP Addresses.

IP Addresses are 32 bit numbers, whereas Domain Names are easy to remember symbolic

strings.

A program called aResolvertakes care of the translation i.e., conversion of a symbolic name into

its corresponding IP Address.

Types of IP Addresses:

2.4.6.1 Static IP Address.

A permanently assigned IP Address, one that is given to a computer or router connected to the

Internet is called astatic IP address.

2.4.6.2 Dynamic IP Address.

If one is connected to the Internet through an ISP, then typically each time the user connects, he

will be assigned a different IP address, called a dynamic IP address, from the ISPs pool of IP

addresses.

2.4.7 IPv6 (Internet Protocol Version 6)

IPv6 is the latest version of the IP routing protocol. It was originally called IPng (Next

Generation).

The new protocol is necessary to accommodate the greater demands being placed on the Internet.

The major changes will be:

More addresses:by increasing the IP address size from 32 bits to 128 bits.

Simplified IP headers: The number of header fields needed in an IP packet will be

reduced.

Added Security Features: The new protocol will provide greater support for privacy and

security.

2.4.8 Web Page Retrieval

Suppose a URL is selected as:


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http://www.bsaitm.org/cs.php

The Web Page is retrieved using following steps:

1. Based on the actions, the browser determines that the URL selected was

http://www.bsaitm.org/cs.php

using the http protocol.

2. The browser queries the Domain Name System for the IP Address www.bsaitm.org.

3. Suppose the Domain Name System responds with the IP Address

192.1.123.25

4. The browser next establishes the TCP connection to 192.1.123.25. The default port for web

servers is Port 80.

5. The browser then sends a message asking for the what part of the URL i.e.,

cs.php

6. The server, www.bsaitm.org, services this request and sends back the file cs.php.

7. The TCP connection is closed. This ends the conversation between the client and the server.

8. The browser renders the text portion of the HTML code contained in the file cs.php.

9. The browser repeats these steps to obtain any in line images contained in the file cs.php.

10. The browser displays the image as they are retrieved.

2.5 Internet Congestion

The number of users and their demands continue to grow almost without bound, causing the congestion onthe Internet.

Once a user get a network connection, the factor limiting how quickly one can view Web Pages often

becomes the speed with which the computer renders the pages. The computer speed depends on a complex

balance of CPU speed, bus speed, memory quantity, disc speed, and so on.

The slowest link speed involved in a connection determines the overall level of performance.

2.5.1 World Wide Wait Problem

World Wide Wait refers to the ever increasing delays experienced when trying to access

information on the Internet. The literal translation of this phrase is wait in the world network.

With the advent of the WWW and the development of graphical browsers came a surge of interest

in the Internet. This increase in the number of Internet users, coupled with the accompanying

requests for Web Pages containing elaborate in line images, sound, and video clips, has degraded

the speed of the Internet to the point where the Information Superhighway sometimes appear to

have a traffic jam.

2.5.2 Technical Solutions

Researchers working in conjunction with the World Wide Web Congestion are addressing the

issue of network congestion with a goal to save the Internet from the Web.
http://www.bsaitm.org/cs.phphttp://www.bsaitm.org/http://www.bsaitm.org/http://www.bsaitm.org/cs.phphttp://www.bsaitm.org/http://www.bsaitm.org/


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Some of the solutions offered involve HTTP itself, as well as improvements in the way HTTP and

TCP/IP interact. The researchers have focused on the following issues:

Improving the process of connecting to a Web Server.

Introducing new techniques to expedite Web Page requests.

Refining how a URL is resolved, using persistent connections that make it more efficient

to retrieve pages from the same Web server.

Since the Web page content (i.e. the graphics, sound, text, and/or video) dictates download time,

one recommendation is to avoid unnecessary graphics.

Cascading Style Sheets (CSS), Web page design tool also has the potential to improve

download time.

Researchers recommend using PNG (Portable Network Graphics) format over the GIF

(Graphics Interchange Format) for images on Web pages, since images are generally smaller than GIF and

they render more quickly.

Another step being taken is, reduction in size of router tables by rearranging how blocks ofaddresses are identified.

2.5.3 Issues & Predictions

The various issues and predictions involved in Internet Congestion may be:

People may start using Internet during less busy periods.

There may be reduced usage of Internet due to Internet Congestion.

Business or organizations might be using Intranets instead of Internets World Wide.

2.6 Internet Culture

Internet has emerged from being a research medium to one that includes advertising, commerce, and

forums for exchanging ideas on a nearly infinite set of subjects.

2.6.1 Critical Evaluation of Information

Since the Internet is not regulated for content, anything and everything can be found on the Web.

To find valuable information, one needs to go through several Web pages, and separate the useful

from the useless, the valid from the invalid information.

To evaluate the valuable information, one must consider several issues as mentioned below:

Who wrote the information? Was the person who wrote the material knowledgeable

and careful? Was he aware of what others have written? Can he be trusted?

Is the writing quality high? A document riddled with types is more likely to have

inaccurate content than carefully created Web page.

Is the document up to date? Try to determine whether the information is current orup to date.

Are there obvious errors in the content? For example, if the user knows that the same

of baseball requires 9 players on a team and the document says it only requires 6 players, be varying.


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2.6.2 Freedom of Expression

The Internet facilitates the interchange of ideas. Anyone with an Internet connection can express

their views globally. This also allows small groups of people with something in common to share

their views.

Internet provides the facility of personal expression, but it is not necessary that everything and

anything should be published. For example, some people find the availability of offensive material

like articles encouraging violence (such as encouraging terrorism).

Unfortunately, some people lose sight of all the great benefits that the Internet provides:

More educational opportunities

Sharing of research ideas and information.

Convenience of performing many functions, such as banking and shopping on line.

Opportunity for entertainment like playing games, listening to music.

World Wide discussion forums to promote solutions to global problems.

The Platform for internet Content Selection (PICS) provides a set of technical specifications for

designating labels to identify the content of Web pages. The PICS specifications works with

vendor supplied filtering software and rating services like pop up blockers.

Although PICS provides an alternative to government control of Internet content, many are still

concerned about promoting any censorship technology.

2.6.3 Communication Mechanism

People from all over the world can exchange ideas via email, Internet Relay Chat (IRC), Instant

Messaging, Mailing Lists, newsgroups, and so on.

Since there are no facial expressions, voice inflections, or body language to convey or interpret

these communications, users must avoid ambiguity or misunderstanding by either spelling things

out completely or using emoticons like:

angel devil

laugh smile

surprise wink

While video conferencing is a way to include the otherwise missing audio and video, this

technology is still in its infancy.

To save time when typing messages, users sometimes employ a friendly shorthand for commonly

used phrases like:

BRB Be Right BackBTW By The Way

LOL Laughing Out Loud

TTYL Talk To You Later

GM Good Morning


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HRU How Are You

Being rude or overly confrontational is called flaming, and such messages are called flames.

Some people find it easy to be rude when they do not have to confront a person face to face.

Flaming is not considered appropriate on the Internet; it violates the commonly accepted

guidelines of netiquettes.

2.6.4 Advertising

Ads generate huge incomes for companies like Yahoo, Rediffmail, India Times, and so on. The

web pages of these companies get millions of hits per day, so an ad placed on one of their web

pages has a tremendous audience and provides the marketing experts a potential consumer base.

Most of the ads shown on web pages are clickable images.

Many of the most popular web pages have revolving advertisements; i.e. each time the

user revisit the page, or while the user is visiting the page, he gets a different ad.

Many users manage to browse the web without paying too much attention to theadvertisements, other than noticing that the ads slow down the loading process.

Obviously, the ads influence some people, because companies continue to invest huge

amounts of money in them.

The style, forms and content of ads is a rapidly emerging part of the Internet culture.

2.6.5 Societal Impact

The Internet has had an enormous impact on society, and its influence will be continued.

Nearly all facets of life have been affected.

Many people work in Internet related jobs, either building computer network

components, writing software, creating web pages, performing marketing research, designing graphics, or

conducting business on the web.

Many people obtain required information and perform most of their communication using

the Internet.

Weather, news, stock prices, and travel information are accessed by millions of users every

day.

2.7 Business Culture

Many businesses are recognizing opportunities in on line activities. So Internet is being used for

business purposes very widely.

2.7.1 On line Business

The Internet provides a way to facilitate communications both within and between companies.

Internet is an excellent venue for advertising and conducting trade with consumers.

It is currently possible to shop goods and services through on line catalogs; subscribe to on line

versions of magazines and newspapers; and purchase software.

These are just a few types of business transactions taking place on the on line market place.


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For companies, this means a greater selection of services and products.

For consumers, this means a greater selection of services and products.

Internet provides various options for business like:

Advertising

Marketing

Software Availability

Communication

2.7.2 On line Business Hurdles

The most significant consumer concerns about doing business on line are privacy and security.

When disclosing personal information and revealing spending habits on line, consumers want

assurance that the information will go no further.

Some users could also get nervous if their favorite on line catalog remembers their hat sizes,shoe sizes, and credit card numbers.

What is to prevent this information from falling into the wrong hands?

These data are actually stored on the hard disk in a file usually called cookies.

Cookies.

Sometimes when a user visit a Web page, information about the user is collected.

It might be the name, password, preferences, credit card number, phone number, address,

etc.

A web server sends this information to the users browser, and the data is written to the

cookies file stored on the users disk. This process is known as setting a cookie.

Using cookies file, a web server can keep track of the web page the user visits.

The next time the user visit a particular web page, the server will search the cookies file,

retrieve the information stored there, and use that to customize its web page to accommodate the user.

As the amount of data that can be stored in a cookie is very limited, the server stores an id for

the user, fetches that id from the cookie, and then looks up in the server database for users more

detailed profile and history.

The purpose of putting information in the cookies file on the hard disk is to reduce the servers

search time in locating a specific cookie, as the cookies file is limited in size.

The information stored in cookies file may be retrieved and used to determine ones personal

habits.

Credit card security is a valid concern, but such numbers are encrypted.

But it is generally considered to be harmful.


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2.7.3 Business and Safety / Security on web

The biggest concern of consumers conducting business on line is the issue of secure payments. Is

it safe to use credit card on line?

Mechanisms for ensuring secure payments are currently being developed in the private sector.

Secure Electronic Transaction (SET) is a new technical standard to be implemented by Visa and

MasterCard to make credit card payments over Internet more secure.

Other payment option being developed includes Electronic Money.

Business transactions over Internet are becoming more widespread and also more secure.

2.7.4 Legal Environment

While concerns about secure payments may scare some potential on line consumers, issues

concerning legal implications of doing business on line discouraged some companies from takingtheir business on line.

Without a predictable legal structure and without a guarantee that governments will not suddenly

impose taxes and tariffs on trade conducted over Internet, a number of companies find it risky.

2.8 Collaborative Computing

Collaborative computing is defined as application that allow the sharing of information and resources

between two or more people. It is also referred to as teamware or groupware.

The World Wide Web, with its collection of Web pages, is a collaborative computing platform that

employs HTML and Web Browsers.

For example, Lotus Notes, Novells GroupWise, and Microsoft Exchange.

2.8.1 Need for Collaborative Computing

As business and individual must cope with more and more information and the cost of travel for

face to face meetings continues to increase, the need for collaborative computing is clear.

Employees spend too much time sorting through data in email, faxes, reports, and voice messages.

This problem is compounded by downsizing and restructuring in many companies, which

translates to fewer people doing more work.

Organizing the information and correctly forwarding it is also time consuming. To staycompetitive, businesses and organizations are turning to collaborative computing to share

knowledge and resources and to move information efficiently.

2.8.2 Applications


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From customer and account service to research and product development, collaborative computing

can enhance many aspects of business.

1. E-mail. The most basic collaborative computing application is email.

Email has replaced the written memo in many organizations, saving time (distributing

the memo) as well as more (paper cost).

2. Intelligent Form. Collaborative computing can simplify the process of

filling out an expense report. Using an intelligent form, an employee need only enter

expense amount; the expense figures are then automatically calculated and the report is

electronically submitted.

At any point in the process, the employee can track the report to determine its status.

Similarly, purchase orders can be filled in and dispatched. This method permits the fast

and easy distribution, as well as convenient tracking.

3. Version Control. In this application, the software makes it possible for

more than one people to work on a document at the same time. The software keeps the

track of the latest versions of the document, and updates all other copies as needed.

4. Video Conferencing. One of the most exciting applications ofcollaborative computing involves real time interaction through video teleconferencing

or simply videoconferencing (VC).

Business communication has involved the exchange of data and voice information; VC

enables the real time exchange of colorful video images and audio.

2.8.3 Impact

The major benefits of collaborative computing are convenience and time savings; these amount to

money.

1. Employees can examine, organize and rout data efficiently, while managers can have access todata easily and can find information in a timely manner.

2. Electronically forwarding and accessing information saves time, since paper does not have to

be physically distributed.

3. The use of audio, graphics, and video plus text in a collaborative computing environment

provides the means for clearer communications.

4. This can result in fewer errors and misunderstandings.

5. Travel time and expenses can be significantly reduced by collaborative computing, since being

in the same location is no longer a prerequisite for the exchange of ideas.

2.8.4 Future Prospects

Collaborative computing may soon become a necessity for business that want to remain

competitive. Unfortunately, a number of the commercial groupware products are quite expensive.

However, some applications make use of Web technology and provide a cheaper alternative.

In addition to being cheaper, the web technology may be easier to use.

The infrastructure for a web based collaborative computing platform is an Intranet. Access

within an Intranet is limited to employees and business contacts only, by a security measure knownas a firewall.

Intranet to Intranet communication across the Internet is possible, if the user use a technology

that does not require dedicated bandwidth.


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In response, groupware providers are trying not to compete directly with the web technology.

Instead, they are trying to make their products compatible with the web by allowing browsers to

access their databases.

The ease and effectiveness with which groupware can meld with the Internet may determine its

success.

Many businesses are already improving workers productivity through the use of collaborative

computing. As developers overcome some of the current hurdles, collaborative computing will

become even more prevalent.

2.9 Domain Name

The term domain name has multiple related meanings:

A name that identifies a computer or computers on the internet. These names appear as a component

of a Web site's URL, e.g. wikipedia.org. This type of domain name is also called a hostname.

The following example illustrates the difference between a URL (Uniform Resource Locator) and a domain

name:

URL: http://www.example.net/index.html

Domain name: www.example.net

2.9.1Top-level domains

Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list ofgeneric names (three or more characters), or a two-character territory code.

2.9.2Other-level domains

In addition to the top-level domains, there are second-level domain (SLD) names. These are the names

directly to the left of .com, .net, and the other top-level domains. As an example, in the domainen.wikipedia.org, "wikipedia" is the second-level domain.

On the next level are third-level domains. These domains are immediately to the left of a second-level

domain. In the en.wikipedia.org example, "en" is a third-level domain. There can be fourth and fifth level

domains and so on, with virtually no limitation. An example of a working domain with five levels is

www.sos.state.oh.us. Each level is separated by a dot or period symbol between them.

Domains of third or higher level are also known as subdomains, though this term technically applies to a

domain of any level, since even a top-level domain is a "subdomain" of the "root" domain (a "zeroth-level"

domain that is designated by a dot alone).

Traditionally, the second level domain has been chosen based on the name of a company (i.e.

microsoft.com). The third level was commonly used to designate a particular host server.
http://en.wikipedia.org/wiki/Web_sitehttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Hostnamehttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Top-level_domainhttp://en.wikipedia.org/wiki/Second-level_domainhttp://en.wikipedia.org/wiki/Subdomainshttp://en.wikipedia.org/wiki/Web_sitehttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Hostnamehttp://en.wikipedia.org/wiki/Uniform_Resource_Locatorhttp://en.wikipedia.org/wiki/Top-level_domainhttp://en.wikipedia.org/wiki/Second-level_domainhttp://en.wikipedia.org/wiki/Subdomains


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The structure of domain names followed a strict hierarchy in which the top level domain indicated the type

of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or

further levels to express complex structures, where, for instance, branches, departments, and subsidiaries

of a parent organization would have addresses which were subdomains of the parent domain. Also,

hostnames were intended to correspond to actual physical machines on the network, generally with only

one name per machine.

Within a particular top-level domain, parties are generally free to select an unallocated domain name as

their own on a first come, first served basis

2.10 Domain Name System

The Domain Name System (DNS) associates various sorts of information with so-called domain names;

most importantly, it serves as the "phone book" for the Internet by translating human-readable computer

hostnames, e.g. www.example.com, into the IP addresses, e.g. 208.77.188.166, that networking equipmentneeds to deliver information. It also stores other information such as the list ofmail exchange servers that

accept email for a given domain. In providing a worldwide keyword-based redirection service, the

Domain Name System is an essential component of contemporary Internet use.

DNS servers

The Domain Name System consists of a hierarchical set of DNS servers. Each domain or subdomain has

one or more authoritative DNS servers that publish information about that domain and the name servers of

any domains "beneath" it. The hierarchy of authoritative DNS servers matches the hierarchy of domains.

At the top of the hierarchy stand the root nameservers: the servers to query when looking up (resolving) a

top-level domain name (TLD).

DNS resolvers

A resolver looks up the resource record information associated with nodes. A resolver knows how to

communicate with name servers by sending DNS queries and heeding DNS responses.

A DNS query may be either a recursive query or a non-recursive query:

A non-recursive query is one where the DNS server may provide a partial answer to the query (or

give an error). DNS servers must support non-recursive queries.

A recursive query is one where the DNS server will fully answer the query (or give an error). DNS

servers are not required to support recursive queries.

The resolver (or another DNS server acting recursively on behalf of the resolver) negotiates use of

recursive service using bits in the query headers.

Resolving usually entails iterating through several name servers to find the needed information. However,some resolvers function simplistically and can only communicate with a single name server. These simple

resolvers rely on a recursive query to a recursive name server to perform the work of finding information

for them.
http://en.wikipedia.org/wiki/First-come%2C_first-servedhttp://en.wikipedia.org/wiki/Domain_namehttp://en.wikipedia.org/wiki/Telephone_directoryhttp://en.wikipedia.org/wiki/Hostnamehttp://en.wikipedia.org/wiki/Example.comhttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Mail_exchange_serverhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/Keywordhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Root_nameserverhttp://en.wikipedia.org/wiki/Top-level_domainhttp://en.wikipedia.org/wiki/First-come%2C_first-servedhttp://en.wikipedia.org/wiki/Domain_namehttp://en.wikipedia.org/wiki/Telephone_directoryhttp://en.wikipedia.org/wiki/Hostnamehttp://en.wikipedia.org/wiki/Example.comhttp://en.wikipedia.org/wiki/IP_addresshttp://en.wikipedia.org/wiki/Mail_exchange_serverhttp://en.wikipedia.org/wiki/Emailhttp://en.wikipedia.org/wiki/Keywordhttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Root_nameserverhttp://en.wikipedia.org/wiki/Top-level_domain


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2.11 Modems

2.11.1Introduction

(Self)

2.11.2Types of Modems

1. Long haul modems

In the 1960s, Bell began to digitize the telephone system, and developed early high-speed

radio modems for this purpose. Once digital long-haul networks were in place, they were

leased for every other purpose.

Optic fibre manufacturing was mastered in the 1980s, and optic modems were first

invented for these early systems. The first systems simply used light-emitting diodes and

PIN diodes. Faster modulation was quickly adopted for long-haul networks. In the 1990s,

multispectral optical modems were adopted as well.

2. Narrowband/Phone-line Dialup Modems

A standard modem of today contains two functional parts: an analog section for generating

the signals and operating the phone, and a digital section for setup and control. This

functionality is actually incorporated into a single chip, but the division remains in theory.

In operation the modem can be in one of two "modes", data mode in which data is sent to

and from the computer over the phone lines, and command mode in which the modem

listens to the data from the computer for commands, and carries them out. A typical session

consists of powering up the modem (often inside the computer itself) which automatically

assumes command mode, then sending it the command for dialing a number. After the

connection is established to the remote modem, the modem automatically goes into data

mode, and the user can send and receive data. When the user is finished, the escape

sequence, "+++" followed by a pause of about a second, is sent to the modem to return it to

command mode, and the command ATH to hang up the phone is sent.

3. Radio modems

Direct broadcast satellite,WiFi, and mobile phones all use modems to communicate, as do

most other wireless services today. Modern telecommunications and data networks also

make extensive use ofradio modems where long distance data links are required.

Such systems are an important part of the PSTN, and are also in common use for high-

speed computer networklinks to outlying areas where fibre is not economical.

Even where a cable is installed, it is often possible to get better performance or make other

parts of the system simpler by using radio frequencies and modulation techniques through a

cable.

4. Broadband

DSL modem

ADSL modems, a more recent development, are not limited to the telephone's "voiceband"

audio frequencies. Some ADSL modems use coded orthogonal frequency division

modulation (DMT).
http://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/PIN_diodehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Direct_broadcast_satellitehttp://en.wikipedia.org/wiki/WiFihttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Radio_modemhttp://en.wikipedia.org/wiki/PSTNhttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/DSL_modemhttp://en.wikipedia.org/wiki/Asymmetric_Digital_Subscriber_Linehttp://en.wikipedia.org/wiki/DSL_modemhttp://en.wikipedia.org/wiki/Coded_orthogonal_frequency_division_modulationhttp://en.wikipedia.org/wiki/Coded_orthogonal_frequency_division_modulationhttp://en.wikipedia.org/wiki/Light-emitting_diodehttp://en.wikipedia.org/wiki/PIN_diodehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Escape_sequencehttp://en.wikipedia.org/wiki/Direct_broadcast_satellitehttp://en.wikipedia.org/wiki/WiFihttp://en.wikipedia.org/wiki/Mobile_phonehttp://en.wikipedia.org/wiki/Radio_modemhttp://en.wikipedia.org/wiki/PSTNhttp://en.wikipedia.org/wiki/Computer_networkinghttp://en.wikipedia.org/wiki/DSL_modemhttp://en.wikipedia.org/wiki/Asymmetric_Digital_Subscriber_Linehttp://en.wikipedia.org/wiki/DSL_modemhttp://en.wikipedia.org/wiki/Coded_orthogonal_frequency_division_modulationhttp://en.wikipedia.org/wiki/Coded_orthogonal_frequency_division_modulation


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Cable modems use a range of frequencies originally intended to carry RF television

channels. Multiple cable modems attached to a single cable can use the same frequency

band, using a low-level media access protocol to allow them to work together within the

same channel. Typically, 'up' and 'down' signals are kept separate using frequency division

multiple access.

New types ofbroadband modems are beginning to appear, such as doublewaysatellite and

powerline modems

5. Voice modem

Voice modems are regular modems that are capable of recording or playing audio over the

telephone line. They are used fortelephony applications. See Voice modem command set

for more details on voice modems. This type of modem can be used as FXO card for

Private branch exchange systems

2.12 Communication Softwares

Communications Software is a program or tool that makes it possible to send and receive data over

telephone lines, modems and the internet. Communication software it seems like a big word, eh? In reality,

it is already part of the tools we use for our daily lives but it is not often identified as communication

softwares.

2.12.1 Simple Communication Software

Radio Waves

Basically, Radio waves were the predecessor of mobile phone communications and though they are not as

popular as the next Ipod, it revolutionized communication technology as we knew it. Communications withairplanes, boats and individual radios are still being used by the military and a lot of individuals today.

Mobile Phone

There are actually many simple kinds of communications software in the market today. For instance, the

mobile phones program that allows us to call others through the phone by remitting sound is one of the

most used programs today; another set of tools are the instant messengers we use in our mobile phones and

the internet. You see, communication software have been around for a very long time but they havent been

recognized as software since we usually regard them as hardware or physical objects. But in reality, without

the technology working hand in hand with these objects, they wouldnt be able to function properly.

2.12.2 Complex Communications Software

There are a couple of complex communications softwares but most of them involve transferring of data

from, computer to computer, human to computer and vice versa.

Satellite Communications

One of the most complex functions for me is satellite communications. It would involve a lot of algorithm

and sophisticated tools in order to make the communication work, it is one of the programs, being utilize to

make our lives easier through tracking and allowing us to connect to it and seeing through its vision.
http://en.wikipedia.org/wiki/Cable_modemhttp://en.wikipedia.org/wiki/Frequency_division_multiple_accesshttp://en.wikipedia.org/wiki/Frequency_division_multiple_accesshttp://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/Doublewayhttp://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/Power_line_communicationhttp://en.wikipedia.org/wiki/Telephonyhttp://en.wikipedia.org/wiki/Voice_modem_command_sethttp://en.wikipedia.org/wiki/FXOhttp://en.wikipedia.org/wiki/Private_branch_exchangehttp://en.wikipedia.org/wiki/Cable_modemhttp://en.wikipedia.org/wiki/Frequency_division_multiple_accesshttp://en.wikipedia.org/wiki/Frequency_division_multiple_accesshttp://en.wikipedia.org/wiki/Broadbandhttp://en.wikipedia.org/wiki/Doublewayhttp://en.wikipedia.org/wiki/Satellitehttp://en.wikipedia.org/wiki/Power_line_communicationhttp://en.wikipedia.org/wiki/Telephonyhttp://en.wikipedia.org/wiki/Voice_modem_command_sethttp://en.wikipedia.org/wiki/FXOhttp://en.wikipedia.org/wiki/Private_branch_exchange


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Cell Sites

For me, Cellular technology is one of the best breakthroughs of the past 20 years since it now allows us to

have simple, quick and reliable communication between any two mobile phones and other modes of

communications in a push of a button.

Overall, Communications software has been around for a long while and they had always been one of the

most powerful programs out there however communication software always stays in the shadows of the

flashy hardware that use them.

Counter sites

Free Countersites also represent a good resource for webmasters and software developers. They enable you

to keep track on how many visitors your are recieving while at the same time providing the visitors with

feedback.
http://www.avencio.de/http://www.avencio.de/

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