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Basics of TCP/IP communications

Networks

The first networks appeared as people wanted to have a computer of higher productivity. They decided that they can achieve it if they combine several computers. One more advantage of such combination was the ability of the connected computers to use shared resources and to exchange information.

Computers are connected to the network by cables. Cables differ by their options and it is classified according to the rate of transmission of data and the frequency of the mistakes to appear.

Most of the networks use the following 3 categories of cables:

Twisted-pair, which consists of 2 isolated copper wires twisted together. UTP (Unshielded) and STP (Shielded) are the two types of twisted pair. These are the most widespread types of cables used for networks; they can transmit signals for distances about 100 meters;

Coaxial cable is used for data transmission over longer distances and for reliable support of high speed transmissions using less complicated equipment. Terminals are to be set up on both sides of coaxial cable;

In fiber-optic cables optical fibers are used, through which digital data signals are transmitted in form of modulated light impulses. Fiber-optic is used for the high-speed transmission of big volumes of data. A disadvantage of the fiber-optic is its fragility.

Wireless networks work in similar way except for the fact that instead of cables is used one of the following technologies: infrared transmission, which uses infrared beams, or narrow-band arrow transmission, when radio waves are used.

To satisfy growing requirements it is necessary to expand the size of the network or to improve its performance. You can not do it by adding computers or cable, but you should set up special devices that allow expanding the network. They are:

Repeaters and hubs allow expanding the network by adding 2 or more segments of cable. They transmit the electrical signal received from one port to all the other ports. These often-used devices are cheap and easy-to-install;

Bridges are devices that transmit the information packets between the segments of the network that use the same protocol. If the packet is going to the computer of the same segment as the sender, the bridge holds the packet in this segment. If the packet is going to another segment, it forwards the packet to that segment. Plus to this a bridge makes it available to connect different categories of cable;

Switchers are similar to bridges, but ensure a more direct network connection between the sending and the receiving computers.

Routers can determine a route to any segment of the network. A router allows to send packets directly to the destination computer, located in another network or segment and to prevent overloading of the network;

Gateways ensure the communication between dissimilar types of networks. A gateway receives data from one network and arranges it in the way clear for the other network.

The term “network area” is connected with the territorial size of the network. Networks are divided into 2 categories according to the area they cover:



Local area networks (LAN) - connect computers located nearby to each other. Corporate area network that integrates several closely located buildings can also be considered as local.

Global area networks - integrate computers, situated far away from each other. For example, the Internet is a global area network.

 

 

Multimedia.

The Multimedia is a combination of two or more concurrent communication Medias, such as text, image, sound and video.

One of the key features of Multimedia file is its interactivity. This means, that they can be controlled by the human involvement, for example, mouse manipulation. MM files can be stored in a different ways. They can be stored on a PC’s hard disk, or on some flash memory drives, Memory stick cards. Files can be archived by some programs, for example Win Zip or WinRar. Archived files require much less space on the hard drives.

All types of MM files are digitized in order to make data transmission simpler and faster. There are different types of transmission of MM files: they can be transferred by the Internet, or by using some kind of memory cards. If you want to copy some MM file, you shouldn’t worry about the loss of quality after the copying. If you copy the MM file without saving it to a different format, this operation will be lossless.

There are two main questions connected with MM: the reduction in amount of space, needed to store MM files on hard drives, and saving the quality of MM files after compression. Compression is the reduction in size of data in order to safe space or transmission time. So there are different formats, different types of compression for each communication media.

Text is the oldest and the simplest communication Media. The idea of compression of the text files is very simple. First of all, we have to calculate the repetition rate of some letter combinations, and then encode the combinations with the highest repetition rate with the shortest combinations of bits, and the combinations with the lowest frequency – with the longest combinations of bits. I think, that the idea of text compression is not very important, because usually all text files are rather small and don’t need much space for storage and transmission.

Sound and video files allow us to store the past. That means that we can store the best moments of our life not only in our unreliable memory, but also on different hard drives.

In order to store sound files, for example music, there were invented many audio formats. The most popular format is an MP3 that stands for MPEG Audio Layer 3. MP3 competes with another audio file format, called WAV. The key difference is that MP3 files are much smaller than WAV files. An MP3 file can store a minute of sound per megabyte, while a WAV file needs 11 or 12 Mb to hold the same amount. The idea of MP3 compression is that MP3 significantly reduces the stored information by stripping out sounds most people can’t hear. For example, most people can’t hear notes above the frequency of 16 kHz, so it eliminates them from the mix.

A ripper is a program that rips songs from a CD in your CD-ROM drive and turns them into WAV files. An encoder converts WAV files or vice versa.

JPEG (Joint Photographic Experts Group) is an image format, developed specially for storing photos and other pictures which has a lot of colors. Each pixel in this format takes 24 bits, so it can represent over 16 millions of colors. Storing BMP files with color depth 24 bits per pixel occupies a lot of disk space, however JPEG files requires much less storage. It is achieved by complicated compression algorithm which is used by JPEG format. It greatly reduces file size, however it has one disadvantage - this algorithm is lossless.

In conclusion, I want to say that the most common formats are MPEG, JPEG and MP3. In every music shop you could find the whole MP3 collection of albums of your favorite artist on only one CD. The majority of all music that can be downloaded from the Internet is compressed using the MP3 technology. And if you check the format of your digital photos, made by digital camera you will notice, that they are compressed into the JPEG format.

 

 

The Internet

To get to the origins of the Internet, we have to go back in time to 1957. That time is associated with the strong scientific competition between the USA and the USSR. Launching the satellite into Earth orbit by the USSR shocked the government of the USA. One of the immediate reactions was the creation of the Advanced Research Projects Agency within the Ministry of Defense. Its mission was to apply modern technology to US defense and to avoid being surprised by technological advances of the enemy. The creation of network (called APRANET) which connected 4 computers in different locations was the first step to the modern internet. APRANET started to grow and develop. New networks appeared. And finally, in 1982, when TCP/IP was adopted, the Internet was born.

The Internet is the connection of computer networks across the world. The Internet is the unlimited space, where you can find all information. There are some services: special devices, which help to find necessary information; chat; email and others. One of the greatest things about the Internet is that nobody really owns it. It is a global collection of networks, both big and small. These networks connect together in many different ways to form the single entity that we know as the Internet.

Every machine or node in the Internet has its unique identifying number, called an IP Address. The IP stands for Internet Protocol, which is the language that computers use to communicate over the Internet. The four numbers in an IP address are called octets, because they each have eight positions when viewed in binary form. Each of the eight positions can have two different states (1 or zero), the total number of possible combinations per octet is 28 or 256. So each octet can contain any value between zero and 255. Out of the almost 4.3 billion possible combinations.

But when we surf the Internet we use URL (Uniform Resource Locator) instead of IP-addresses. How does a browser find web pages? When you enter a URL or click on a webpage hyperlink, the browser sends the URL to a DNS server. It uses a table to find the IP-address of the Web server referred to in the URL. After this the IP-address is sent back to the browser. The browser then uses the IP-address to send a request to the Web server. The request is sent through the routers of the network as a series of separate data packets. The Web server now services the request by sending the webpage back to the browser computer. It is sent again as several packets which are combined together at the browser computer. And as a result you can see the requested webpage displayed in your browser.

While surfing the Internet we are working in the World Wide Web. The WWW is a network of sites that can be searched and retrieved by a special protocol known as a Hypertext Transfer protocol (HTTP). The WWW concept was designed in 1989 by Tim Berners-Lee and scientists, who were interested in making easier to retrieve research documentation. The World Wide Web provides a single interface for accessing all these protocols. This creates a convenient and user-friendly environment. The Web gathers together these protocols into a single system. Because of this feature, and because of the Web's ability to work with multimedia and advanced programming languages, the Web is the fastest-growing component of the Internet

What is the difference between the Internet and the Web?

The Web is an abstract space of information. On the Net, you find computers - on the Web, you find information. On the Net, the connections are cables between computers; on the Web, connections are hypertext links. The Web exists because of programs which communicate between computers on the Net. The Web could not be without the Net. The Web made the net useful because people are really interested in information and don't really want to have know about computers and cables.

In conclusion I would like to say that the Internet is continuing to grow at 40% a year, with about 20 million users. You can do many things on the Internet, such as shop for just about anything, bank and manage money, watch and listen to live cable television and radio broadcasts, talk to other users with voice like a telephone, conduct international meetings, and access all kinds of information on any subject imaginable.

 

Basics of TCP/IP communications

 

The Transmission Control Protocol (TCP) is a protocol providing a communication service at an intermediate level between an application program and the Internet Protocol (IP). That is, when an application program desires to send a large piece of data across the Internet using IP, instead of breaking the data into IP-sized pieces and issuing a series of IP requests, the software can issue a single request to TCP and let TCP handle the IP details.

The history of TCP/IP began in May, 1974, when the Institute of Electrical and Electronic Engineers published a paper entitled "A Protocol for Packet Network Interconnection." The paper's authors, Vint Cerf and Bob Kahn, described an internetworking protocol for sharing resources using packet-switching among the nodes. A central control component of this model was the Transmission Control Program that was monolithic. Transmission Control Program was later divided into a modular architecture consisting of the Transmission Control Protocol at the connection-oriented layer and the Internet Protocol at the internetworking (datagram) layer. The model became known informally as TCP/IP, although formally it was called the Internet Protocol Suite. In 1982 the TCP/IP was adopted.

IP works by exchanging pieces of information called packets. A packet is a sequence of bytes and consists of a header followed by a body. The header describes the packet's destination. The body contains the data which IP is transmitting.

Due to network congestion or other unpredictable network behavior, IP packets can be lost. TCP detects these problems by requesting retransmission of lost packets, rearranges out-of-order packets, and even helps minimize network congestion to reduce the occurrence of the other problems. Once the TCP receiver has finally reassembled a perfect copy of the data originally transmitted, it passes that datagram to the application program. Thus, TCP abstracts the application's communication from the underlying networking details.

TCP is used extensively by many of the Internet's most popular applications, including the World Wide Web, E-mail, File Transfer Protocol, and some streaming media applications.

TCP is optimized for accurate delivery rather than timely delivery, and therefore, TCP sometimes incurs relatively long delays (in the order of seconds) while waiting for out-of-order messages or retransmissions of lost messages. It is not suitable for real-time applications such as Voice over IP.

TCP is a reliable stream delivery service that guarantees delivery of a data stream sent from one host to another without duplication or losing data.

 

 

The WWW.

The WWW is a network of sites that can be searched and retrieved by a special protocol known as a Hypertext Transfer protocol (HTTP). The WWW concept was designed in 1989 by Tim Berners-Lee and scientists, who were interested in making easier to retrieve research documentation. The World Wide Web provides a single interface for accessing all these protocols. This creates a convenient and user-friendly environment. The Web gathers together these protocols into a single system. Because of this feature, and because of the Web's ability to work with multimedia and advanced programming languages, the Web is the fastest-growing component of the Internet

The first Web browser, written by the internet’s concept owner Tim Berners Lee and introduced in early 1991. It ran on the NeXT platform, which was also used as the first Web server.

Web pages are accessed by the user via a Web browser application such as Internet Explorer, Netscape, Safari, Opera and Firefox. The browser renders the pages on screen, executes embedded scripts and automatically invokes additional software as needed.
The World Wide Web is made up of "Web servers" that store and disseminate "Web pages," which are "rich" documents that contain text, graphics, animations and videos to anyone with an Internet connection.
The heart of the Web technology is the hyperlink, which connects each document to each other by its "URL" address, whether locally or in another country. It also enabled the concept of a "global server" that provides a source for all applications and data.
A Web page is a text document embedded with HTML tags that define how the text and graphics are displayed on screen. Web pages can be created with any text editor or word processor. They are also created in HTML authoring programs that provide a graphical interface for designing the layout. Authoring programs generate the HTML tags behind the scenes, but the tags can be edited if required. Many applications export documents directly to HTML, thus basic Web pages can be created in numerous ways without HTML coding. The ease of page creation helped fuel the Web's growth.
A collection of Web pages makes up a Web site. Very large organizations deploy their Web sites on inhouse servers or on their own servers co-located in a third party facility that provides power and Internet access. Small to medium sites are generally hosted by Internet service providers (ISPs). Millions of people have developed their own mini Web sites as ISPs typically host a small number of personal Web pages at no extra cost to individual customers.

In conclusion I would like to say that

 

Future of IT

 

IT is one of the fastest growing areas nowadays. New technologies are invented every day. IT is used in such spheres of human activity as science, education, medicine, entertainment, advertising, communications, etc. In future IT will greatly change our life in all these spheres. We can’t imagine how our life will be changed by IT technologies in 5, 10 or 15 years. For example, Ken Olson, founder and chairman of Digital Equipment Corp., said in 1977, “There is no reason anyone would want a computer in their home”, but we can see a PC in almost every home today.

Well, I want to talk about future of mobile technologies. I would like to tell you not about far future, but about next 3-5 years of development in this field. There are two main directions of development of mobile technology: mobile phones and mobile computers.

Lets focus on mobile phones technologies. This is a very rapidly growing sphere, every week a new phone model is put on the market. In next three years we can expect to see mobile phones with touch less displays that will be thinner and lighter than we can image. They will perform all basic functions of a PC; have full-fledged camera, hard disk with large amount of memory, multiple core processors. Maybe after next 5 years mobile phones will be more powerful than modern desktops. Such things as voice and handwriting recognition, augmented reality services, payment services etc will also be used in mobile phones. In general, mobile phone will be a helper in all spheres of our everyday life instead only communication device.

Now I move to mobile computers. The modern way of development in computer technologies is creating tablet PCs. In next 5 years tablet PCs will replace notebooks and netbooks, because they will be able to perform all their functions being smaller, thinner and more convenient. Maybe they will replace common desktops too, by using special devices that allow users to make all thing they do with their home computers like gaming, printing documents, watching films, web-surfing, communication with friends, reading news, editing photos and videos.

To sum up IT technologies change our everyday life from year to year. 5 years ago we couldn’t image that we would use mobile phones for web-surfing and document editing. In next 5 years world of IT technologies will be greatly changed and we can’t imagine how it will look like in next several years.

 


Date: 2015-12-24; view: 766


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