Developing of telecommunications

Late in the nineteenth century communications facilities were augmented by a new invention – telephone. In the USA its use slowly expanded, and by 1900 the American Telephone and Telegraph Company controlled 855,000 telephones; but elsewhere the telephone made little headway until the twentieth century. After 1900, however, telephone installations extended much more rapidly in all the wealthier countries. The number of telephones in use in the world grew at almost 100 per cent per decade. But long-distance telephone services gradually developed and began to compete with telegraphic business. A greater contribution to long-range communication came with the development of wireless. Before the outbreak of the First World War wireless telegraphy was established as a means of regular communication with ships at sea, and provided a valuable supplement to existing telegraph lines and cables. In the next few years the telephone systems of all the chief countries were connected with each other by radio. Far more immediate was the influence that radio had through broadcasting and by television, which followed it at an interval of about twenty-five years.

Telephones are as much a form of infrastructure as roads or electricity, and competition will make them cheaper. Losses from lower prices will be countered by higher usage, and tax revenues will benefit from the faster economic growth that telephones bring about. Most important of all, by cutting out the need to install costly cables and microwave transmitters, the new telephones could be a boon to the remote and poor regions of the earth. Even today, half the world’s population lives more than two hours away from a telephone, and that is one reason why they find it hard to break out of their poverty. A farmer’s call for advice could save a whole crop; access to a handset could help a small rural business sell its wares. And in rich places with reasonable telephone systems already in place, the effect of new entrants – the replacement of bad, overpriced services with clever, cheaper ones – is less dramatic but still considerable.

Global phones are not going to deliver all these benefits at once, or easily. Indeed, if the market fails to develop, it could prove too small to support the costs of launching satellites. Still, that is a risk worth taking. And these new global telephones reflect a wider trend. Lots of other new communication services – on-line film libraries, personal computers that can send video-clips and sound-bites as easily as they can be used for writing letters, terrestrial mobile-telephone systems cheap enough to replace hard-wired family sets – are already technically possible. What they all need is deregulation. Then any of them could bring about changes just as unexpected and just as magical as anything that Alexander Graham Bell’s telephone has already achieved.

SATTELITE SIRVICES

Our world has become an increasingly complex place in which, as individuals, we are very dependent on other people and on organizations. An event in some distant part of the globe can rapidly and significantly affect the quality of life in our home country.

This increasing independence, on both a national and international scale, has led us to create systems that can respond immediately to dangers, enabling appropriate defensive or offensive actions to be taken. These systems are operating all around us in military, civil, commercial and industrial fields.

A worldwide system of satellites has been created, and it is possible to transmit signals around the globe by bouncing them from on satellite to an earth station and thence to another satellite.

Originally designed to carry voice traffic, they are able to carry hundreds of thousands of separate simultaneous calls. These systems are being increasingly adopted to provide for business communications, including the transmission of traffic for voice, facsimile, data and vision.

It is probable that future satellite services will enable a great variety of information services to transmit directly into the home, possibly including personalized electronic mail. The electronic computer is at the heart of many such systems, but the role of telecommunications is not less important. There will be a further convergence between the technologies of computing and telecommunications. The change will be dramatic: the database culture, the cashless society, the office at home, the gigabit-per-second data network.

We cannot doubt that the economic and social impact of these concepts will be very significant. Already, advanced systems of communication are affecting both the layman and the technician. Complex functions are being performed by people using advanced terminals which are intended to be as easy to use as the conventional telephone.

The new global satellite-communications systems will offer three kinds of service, which may overlap in many different kinds of receivers:

Voice. Satellite telephones will be able to make calls from anywhere on earth to anywhere else. That could make them especially useful to remote, third-world villages (some of which already use stationary satellite telephones), explorers and disaster-relief teams. Today’s mobile phones depend on earth-bound transmitters, whose technical standards vary from country to country. So business travelers cannot use their mobile phones on international trips. Satellite telephones would make that possible.

Massaging. Satellite messagers have the same global coverage as satellite telephones, but carry text alone, which could be useful for those with laptop computers. Equipped with a small screen like today’s pagers, satellite messagers will also receive short messages.

Tracking. Voice and messaging systems will also tell their users where they are to within a few hundred metres. Combined with the messaging service, the location service could help rescue teams to find stranded adventurers, the police to find stolen cars, exporters to follow the progress of cargoes, and haulage companies to check that drivers are not detouring to the pub. Satellite systems will provide better positioning information to anyone who has a receiver for their signals.

 

WHAT IS COMPUTER VIRUS?

A virus is a piece of software designed and written to adversely affect your computer by altering the way it works without your knowledge or permission. In more technical terms, a virus is a segment of program code that implants itself to one of your executable files and spreads systematically from one file to another. Computer viruses do not spontaneously generate: They must be written and have a specific purpose.

Usually a virus has two distinct functions:

· Spreads itself from one file to another without your input or knowledge. Technically, this is known as self-replication and propagation.

· Implements the symptom or damage planned by the perpetrator. This could include erasing a disk, corrupting your programs or just creating havoc on your computer. Technically, this is known as the virus payload, which can be benign or malignant at the whim of the virus creator.

A benign virus is one that is designed to do no real damage to your computer. For example, a virus that conceals itself until some predetermined date or time and then does nothing more than display some sort of message is considered benign.

A malignant virus is one that attempts to inflict malicious damage to your computer, although the damage may not be intentional. There are a significant number of viruses that cause damage due to poor programming and outright bugs in the viral code. A malicious virus might alter one or more of your programs so that it does not work, as it should. The infected program might terminate abnormally, write incorrect information into your documents. Or, the virus might alter the directory information on one of your system area. This might prevent the partition from mounting, or you might not be able to launch one or more programs, or programs might not be able to locate the documents you want to open.

Some of the viruses identified are benign; however, a high percentage of them are very malignant. Some of the more malignant viruses will erase your entire hard disk, or delete files.

WHAT VIRUSES DO

Some viruses are programmed specifically to damage the data on your computer by corrupting programs, deleting files, or erasing your entire hard disk. Many of the currently known Macintosh viruses are not designed to do any damage. However, because of bugs (programming errors) within the virus, an infected system may behave erratically.

WHAT VIRUSES DON'T DO

Computer viruses don't infect files on write-protected disks and don't infect documents, except in the case of Word macro viruses, which infect only documents and templates written in Word 6.0 or higher. They don't infect compressed files either. However, applications within a compressed file could have been infected before they were compressed. Viruses also don't infect computer hardware, such as monitors or computer chips; they only infect software.

In addition, Macintosh viruses don't infect DOS-based computer software and vice versa. For example, the infamous Michelangelo virus does not infect Macintosh applications. Again, exceptions to this rule are the Word and Excel macro viruses, which infect spreadsheets, documents and templates, which can be opened by either Windows or Macintosh computers.

Finally, viruses don't necessarily let you know that they are there - even after they do something destructive.

TYPES OF COMPUTER VIRUSES

Nowadays number of viruses is about 55000. It increases constantly. New unknown types of viruses appear. To classify them becomes more and more difficult. In common they can be divided by three basic signs: a place of situating, used operation system and work algorithms. For example according these three classifications virus Chernobyl can be classified as file infector and resident Windows virus. Further it will be explained what it means.

A PLACE OF EXISTENCE

File Infectors

These are viruses that attach themselves to (or replace).COM and.EXE files, although in some cases they can infect files with extensions.SYS,

.DRV,.BIN,.OVL and.OVY. With this type of virus, uninfected programs usually become infected when they are executed with the virus in memory. In other cases they are infected when they are opened (such as using the DOS DIR command) or the virus simply infects all of the files in the directory is run from (a direct infector).There are three groups of file infectors.

Viruses of the first group are called overwriting viruses because they overwrite their code into infected file erasing contents. But these viruses are primitive and they can be found very quickly.

Other group is called parasitic or cavity viruses. Infected file is capable of work fully or partly but contents of last one are changed.

Viruses can copy itself into begin, middle or end of a file. They record their code in data known not to be used.

Third group is called companion viruses. They don’t change files. They make double of infected file so when infected file is being started a double file becomes managing, it means virus. For example companion viruses working with DOS use that DOS firstly runs COM. file and after if this file is not found runs EXE. file. Viruses make double file with a same name and with extension COM and copies itself in this file. During start of infected file DOS runs a COM. file with a virus firstly and then a virus starts an EXE. file.

Sometime companion viruses rename file will be infected and record their code in a double file with old name. For example the file XCOPY.EXE is renamed into XCOPY.EXD and virus record itself in file XCOPY.EXE. When this file is started computer runs a virus code firstly and after virus starts original XCOPY, saved as XCOPY.EXD. Viruses like this were found not only in DOS. They were found in Windows and OS/2.

It is not only one way to make double files. For example there is subgroup of companion viruses called path-companion viruses. They use special feature of DOS - PATH: hierarchical record of file location. Virus copies itself in file with the same name but situated one level higher. In this case DOS will find file with virus.

Boot Viruses

Every logical drive, both hard disk and floppy, contains a boot sector.This is true even of disks that are not bootable. This boot sector contains specific information relating to the formatting of the disk, the data stored there and also contains a small program called the boot program(which loads the DOS system files). The boot program displays the familiar "Non-system Disk or Disk Error" message if the DOS system files are not present. It is also the program that gets infected by viruses. You get a boot sector virus by leaving an infected diskette in a drive and rebooting the machine. When the boot sector program is read and executed, the virus goes into memory and infects your hard drive. Remember, because every disk has a boot sector, it is possible (and common) to infect a machine from a data disk. NOTE: Both floppy diskettes and hard drives contain boot sectors.

The first physical sector of every hard disk (Side III, Track III, Sector)

1) contains the disk's Master Boot Record and Partition Table. The Master Boot Record has a small program within it called the Master Boot Program, which looks up the values in the partition table for the starting location of the bootable partition, and then tells the system to go there and execute any code it finds. Assuming your disk is set up properly, what it finds in that location (Side 1, Track Ш, Sector 1) is a valid boot sector.

On floppy disks, these same viruses infect the boot sectors. You get a Master Boot Record virus in exactly the same manner you get a boot sector virus -- by leaving an infected diskette in a drive and rebooting the machine. When the boot sector program is read and executed, the virus goes into memory and infects the MBR of your hard drive. Again, because every disk has a boot sector, it is possible (and common) to infect a machine from a data disk.

Multi-Partite Viruses

Multi-partite viruses are a combination of the viruses listed above.They will infect both files and MBRs or both files and boot sectors. These types of viruses are currently rare, but the number of cases is growing steadily.

Macro Viruses

Until recently, the macro languages included with most applications were not powerful or robust enough to support writing an effective virus. However, many of the more advanced applications that are being developed today include built-in programming capabilities that rival some of the larger development packages. This has recently been demonstrated by the various strains of Microsoft Word viruses, including the so-called Word Concept and Word Nuclear viruses. These viruses transport themselves through Microsoft Word documents. When opened in Word, they perform various actions, including spreading themselves into the user's installation of Word, thus preparing to infect all future documents on the system. An additional concern is that macro viruses can be cross-platform. The Word Concept virus has the claim to fame of being the first prominent cross- platform virus, because it can infect both Windows and Macintosh systems. Because most application macro languages support passing execution to an external shell, such as COMMAND.COM or CMD.EXE, the power of the macro virus is not limited to the constraints of the macro language itself.

USED OPERATION SYSTEM

Any computer or net virus can infect files of one or more operation systems: DOS, Windows, OS/2, Linux, MacOS and others. It is a base of this way of classification. For example virus BOZA working with Windows only is classified as Windows virus, virus BLISS – as Linux virus.

Work Algorithms

Viruses can be differed by used algorithms making them danger and hard for catching. Firstly viruses can be divided on resident and nonresident. Resident virus having come in operation memory of computer doesn’t infect memory. They are capable of copying when they are started only. We can call any macro virus resident. They present in memory during application infected by them works. Second viruses are visible and invisible. To be invisible means that users and antivirus programs can’t notice changes of infected file done by virus. Invisible virus catches all requires of operation system to read file and to record in file and shows uninfected version of file. So we can see only ‘clear’ programs during virus works. One of first invisible file infectors was FRODO and boot infector – BRAIN. Almost any virus uses methods of self-coding or polymorphism to escape antivirus programs. It means that they can change itself. Changing itself helps virus to be able work.

In conclusion a few words about future of this classification. Nowadays computer technologies and all software develop very quickly. It helps new types of computer viruses to appear. Viruses are becoming more and more dangerous and ‘cleverer’. It means that viruses can be found more and more hard. But this classification can be saved a long time thank for principles of work of computer. It means that this classification will be changed when computers work by principles that differ from principles of von Neiman. So this classification can be change by adding new subtypes of basic types if virus makers have created something new.

RADIO

RADIO transmission or reception of electromagnetic radiation in the radio frequency range. The term is commonly applied also to the equipment used, especially to the radio receiver.

Uses Of Radio Waves

The prime purpose of radio is to convey information from one place to another through the intervening media (i.e., air, space, no conducting materials) without wires. Besides being used for transmitting sound and television signals, radio is used for the transmission of data in coded form. In the form of radar it is used also for sending out signals and picking up their reflections from objects in their path. Long-range radio signals enable astronauts to communicate with the earth from the moon and carry information from space probes as they travel to distant planets (see space exploration). For navigation of ships and aircraft the radio range, radio compass (or direction finder), and radio time signals are widely used. Radio signals sent from global positioning satellites can also be used by special receivers for a precise indication of position (see navigation satellite). Digital radio, both satellite and terrestrial provides improved audio clarity and volume. Various remote-control devices, including rocket and artificial satellite operations systems and automatic valves in pipelines, are activated by radio signals. The development of the transistor and other microelectronic devices (see microelectronics) led to the development of portable transmitters and receivers. Cellular and cordless telephones are actually radio transceivers. Many telephone calls routinely are relayed by radio rather than by wires; some are sent via radio to relay satellites. Some celestial bodies and interstellar gases emit relatively strong radio waves that are observed with radio telescopes composed of very sensitive receivers and large directional antennas (see radio astronomy).