Telephone and Telecommunication

Telephone - a device for transmitting and receiving sound at a distance. Modern phones are performed through the transmission of electrical signals.

In general, the phone - a device that can transmit sound over long distances. The earliest telephones were mechanical devices with direct acoustic channel, ie their principle of operation is based on the propagation of sound vibrations in continuous media (air, etc.), in contrast to the modern electrical devices using electromagnetic signals.

Before the invention of Telegraphs (optical and electrical) and phone to send messages over long distances use primitive methods, such as a whistle, gong or drum beats.

Radiotelephones

Represent a system consisting of a base to which they connect analog or digital subscriber lines from the PBX and one or more cordless handsets that can both communicate with each other, and to call on external lines. Operate at different frequencies. Previously released only analog phones with the carrier frequency of several tens of megahertz. These devices were exposed to noise, and sometimes his pipe could hear conversations on the same phone from a neighboring apartment. Such telephones generally have only had one tube. Then went on sale phones with carrier frequency of 900 MHz and digitally encoded signal. In these devices, the sound quality is better, increased range of reliable operation and prevent accidental eavesdropping your neighbors talking. The next step had phones with a carrier frequency of 2.4 GHz. These devices are sometimes made with multiple handsets, increased the range and sound quality. Recently went on sale phones with carrier frequency 5.8 GHz, having the communication range is sometimes enough to work within a block with good sound quality. These phones often allow you to connect multiple handsets and usually can work without interference in apartments equipped with other wireless devices (such as wireless internet ). These carriers work phones are for phones sold in the U.S. and Canada.

In modern radiotelephones most popular is the use of protocol DECT ( Eng. Digital Enhanced Cordless Telecommunication) - wireless technology at frequencies of MHz with modulation GMSK (BT = 0,5). Range meters. DECT is not only got the widest distribution in Europe, and is the most popular standard for wireless phone in the world, thanks to the ease of deployment DECT- networks, a wide range of custom services and high quality communications. System designed to improve the quality of voice and allow multiplexing of voice and data on a single phone line. Subscriber Interface BRI ( Eng. basic rate interface) represents two user bcc (B- channels) and the signaling channel 16 kbit / s (D- channel) multiplexed in time division.

Mobile Phones

Cellphone A radio communication system that seeks to provide a coupling member at any location. Consists of a large number of base stations interconnected by a central switch, and cell phones. Cell phone when the recorded at the nearest base station, and if his number is called, the central switch finds the phone and puts it on the call via the nearest base station. During the movement of the call is transferred from one base station to another (handover). Base stations called cell towers exist mikrovyshki with broadcasting radius of m, the average of meters and makrovyshki meters. Modern cell phone, in most cases, has also built a set of additional functions. For example, even the already relatively outdated phone Philips Xenium X100 has a flashlight, calculator, FM- radio, voice recorder, MP3- player, sort of internet, SMS, diary, alarm clock, calendar.

Satellite phone Satellite phone - mobile phone sending the information directly through a dedicated communications satellite. Depending on the service provider, the scope can be either the entire Earth, or only specific regions. This is due to the fact that low-flying satellites are used or that a sufficient amount of coverage area cover the entire Earth, or satellites in geostationary orbit, where they do not move relative to the earth and not "see" it completely. Size satellite phone is comparable to a conventional mobile phone, released in the 1980s and 1990s, but usually has an additional antenna. There are also satellite phones in the fixed version. These phones are used for communication in areas where there is no cellular communications.

Phone field Phone field is the kind of phone designed for special operating conditions and have greater mobility in operation. Primarily designed for communication during combat. First field telephone was used by Germany during World War I, he replaced the flag is a system of communication and the telegraph.

IP-telephony Technology that seeks to transmit voice, digitized and compressed using digital techniques through networks based on IP-technology. For example, over the Internet. Can significantly reduce the cost of long distance calls. Weaknesses - the problem of signal delay associated with the peculiarities of IP-technology. Since 2005, the use of specialized software (eg, Skype) made ​​IP- telephony more affordable, though not free.