Английский язык в сфере компьютерных и телекоммуникационных технологий (стр. 37 )

This short word is more often Hashes on news in our days. Everybody heard that it is technology of wireless networks. However, the similar technologies existed earlier, but am of them was not supported such powerful all-round, and about one of them was not spoken so much. What is Bluetooth?

What Is In A Name? (The History Of Bluetooth)

The word Bluetooth does not describe neither essence of technology nor something else Bluetooth was a nickname of the Danish King Harald Blatand - or Harold Bluetooth in English - severe Viking, lived in 10 century lie had been instrumental in uniting warring factions in parts of what is now Norway, Sweden and Denmark. This name was chosen as the name of technology because originally Bluetooth reflected as a means for connection of computers and telecommunication devices, like mobile telephones. In Jelling, Denmark a monument can be found in a church yard that celebrates both his achievements and those of his father the first king of Denmark "Gorrn the Old" It is interesting that this particular stone was lost for nearly six-hundred years after Harald had a small war with his own son, Sven Forkbeard, over control of the country Sven "won" the argument (exiling his father in the process), and since this runic stone also glorified Harald, Sven had it buried Only years later a fanner, curious about a large mound in his farm, rediscovered the stone.

The logo itself was originally designed by a Scandinavian firm at the time the trade association was announced to the public Keeping to the traditions of the name, the logo combines the runic alphabetic characters "H" which looks similar to an asterisk and a "B". Look carefully you can seen both represented in the logo.

SIC (Special Interest Croup)

The kingdom of first Bluetooth did not become eternal, but modern developers Bluetooth are not afraid of it. And. from our day's situation, they have all bases on these. The developed technology has appeared so successful, that maybe this technology will be everywhere in some years, from computers and mobile telephones (as well as it was supposed originally), to refrigerators and microwaves oven (that originally it was not supposed).

In the beginning of 1998 year companies Nokia, Ericsson, IBM, Intel and Toshiba have formed a consortium, which has engaged in development of wireless communication technology, which have named Bluetooth. Initially consortium was open for cooperation Now Bluetooth SIG (Special Interest Group) Promoters includes 3Com, Ericsson, IBM, Intel, Lucent, Microsoft, Motorola, Nokia, and Toshiba. Any company, which plans to make or to develop devices and software on the basis of the Bluetooth technology can enter in group Bluetooth absolutely free-of-charge. At present already about 2000 companies of the various kind of business have come in this group. So Bluetooth has really quite good prospects.

Used frequencies

Physically typical Bluetooth device represents the radio receiver and radio transmitter working on frequencies 2400-2483.5 MHz. These frequencies are chosen not casually, they are open and free from licensing in the majority of the countries of the world. Exceptions make Spain and France. Until recently exceptions make and Japan, hut since October, 1999 there this problem is partially solved, and now Bluetooth devices in Japan can use a complete spectrum of radiofrequencies stipulated by the specifications Bluetooth. Though, some restrictions have remained still in Japan. In Spain the spectrum of radiofrequencies solved for use Bluetooth devices is limited 2445-2475 Mhz, in France this spectrum is limited up to 2446.5-2483.5 MHz. Therefore Bluetooth device developed specially for France, Spam or Japan will not work together with devices developed for all other world. Accordingly, the return statement is correct also. Now members Bluetooth S1G work with authorities of these countries, and there are bases to believe that such situation to not be prolonged.

Bluetooth ability

The used frequencies determine opportunities Bluetooth to the data transfer. Width of the channel for Bluetooth devices makes 723 2 Kbit/second with in asynchronous modes (however, even in this mode all the same remain up to 57.6 Kb/sec with for simultaneous transfer m the opposite direction), or 4339 Kb/sec with in completely synchronous mode. If data is not transferred, then the connection can be transmitted through Bluetooth up to 3 audio channels. Each of audio channels supports synchronous channels with speed 64 Kb/sec in each direction. Besides, it is possible combined transfer of data and vote.

Distance on which Bluetooth connection can be established is insignificant, and makes from 10 up to 100 meters. But even now for Bluetooth it is not required direct visibility or directed aerial. The connection can be established even through a wall (certainly, if the wall is not shielded).

The main feature of Bluetooth is that various Bluetooth devices connect with each other automatically, if it only appears within the limits of reach. Cables, drivers and so on are not required to the user. The user will take care only that Bluetooth devices would be closely to each other enough. Bluetooth device and software would take care about all the rest.

How is connection established?

Being situated beside, Bluetooth device can establish not only connection of a type a point -  - to - point, when there are only two devices, but also the point to - many points, when one device works simultaneously with several others. At connection of one device with several by others, the device which serves some connections is called master, and connected devices –slave. To one master can be connected up to seven active slaves. There are can be a set inactive slave, which can not exchange data with master while all channels are engaged, except for active slave (that is, devices which actively exchange data), remain are synchronized with it (Such structure is called piconet).

There can be only one master in one piconet but everyone slave can be master for other devices simultaneously, and form piconet. Several piconets connected thus form scatternet. In scatternet different devices can not only to be at the same time master and slave simultaneously for various piconet, but also only slave for different piconets.

It is possible to familiarize with this structure in the submitted below figure more evidently.

Moreover, in case of necessity any slave can become master in piconet. Previous master thus  becomes slave.

Thus, in scatternet can be united so much Bluetooth devices, how much it is necessary. The logic connections can be formed how it is required, and can change somehow, m case of necessity. A unique condition, various piconet included in one scatternet should have the different channels of communication, that is work on various frequencies and have various hopping channel. Hopping is a regular change of frequencies determined in parameters hopping sequence. Specification provides 10 variants hopping sequence, 5 with a cycle in 79 changes and 5 with a cycle in 23 changes. With any hopping sequence of frequency are replaced 1600 hops/ sec.  Hopping used to prevent attenuation of a radio signal and interference.

As was already spoken, the automatic installation of connection between Bluetooth devices situated within the limits of reach is one of major Bluetooth features. Therefore, Bluetooth device starts its work in a unfamiliar environment from device discovery, in other words search others Bluetooth devices. For this purpose the inquiry is sent, and the answer to it depends not only on presence in radius of communication active Bluetooth devices, but also from a mode in which there are these devices. On this stage it is possible three basic modes.

Discoverable mode

The devices, being in this mode, always answer all inquiries, received by them.

Limited discoverable mode

In this mode there are devices which can answer inquiries only limited time, or should answer only at observance of the certain conditions.

Non-discoverable mode

The devices, taking place in this mode, as it is visible from the name of a mode, do not answer new inquiries.

But it is not all. Even if device finds out success, it can be in connectable mode or in non-connectable mode. In non-connectable mode the device does not allow to adjust some important parameters of connection, and, thus, though it can be revealed but to exchange the data with it, it will be impossible. If the device is in connectable mode, at this stage Bluetooth device agree among themselves about a used range of frequencies, size of pages, quantity both order of hops, and other physical parameters of connection

If the process of detection of devices has passed normally, new Bluetooth device receives a set of addresses accessible of Bluetooth devices, and it follows device name discovery, when the new device finds out names of all accessible Bluetooth devices from the list Everyone Bluetooth device should have the unique address (like as MAC-addresses at network payments), but at a level of the user not this address is usually used, and name of the device, which can be any, and it is no necessary to be global unique. The name of the Bluetooth device can be length up to 248 bytes, and use code page according to Unicode UTF-8 (at use UCS-2. the name can be short up to 82 symbols). The specification provides, that Bluetooth of the device are not obliged to accept more first 40 symbols of a name of another Bluetooth device. If Bluetooth the device has the limited size and limited computing power screen, quantity of symbols, which it will accept can be reduced up to 20.

Another major Bluetooth features is the automatic connection of Bluetooth devices to services given by others Bluetooth devices. Therefore, after there is a list of names and addresses, the search of accessible services given by accessible devices is carried out service discovery. The reception or granting any services are main courses of Bluetooth creation, therefore for search of possible services there is special protocol named is Service Discovery Protocol (SOP).