telephone
There are four principal means by which an end user using a telephone handset may connect to a telephone network: a traditional fixed phone "landline", which uses dedicated physical wire connections connected to a single location; wireless and radio telephones, which use either analog or digital radio signals; satellite telephones, which utilize telecommunications satellites; and voice over internet protocol (VoIP) telephones, which use broadband internet connections. Between end users, transmissions across a network may be carried by fiber optic cable, point to point microwave or satellite relay. Until relatively recently, a "telephone" generally referred only to landlines. Cordless and mobile phones are now common in many places around the world, with mobile phones expected to gradually displace the conventional landline telephone. Unlike a mobile phone, a cordless telephone is considered to be landline because it is only useable within a short distance of a small personal or domestic base station connected to a fixed phone line. The identity of the inventor of the electric telephone remains in dispute. Antonio Meucci, Johann Philipp Reis, and Alexander Graham Bell, amongst others, have all been credited with the invention. The very early history of the telephone is a confusing morass of claim and counterclaim, which was not clarified by the huge mass of lawsuits which hoped to resolve the patent claims of individuals. Much money was expended, particularly in the Bell Telephone companies, and the aggressive defense of the Bell patents resulted in much confusion. Additionally, the earliest investigators preferred publication in the popular press and demonstration to investors instead of scientific publication and demonstration to fellow scientists. It is important to note that there is probably no single "inventor of the telephone". The modern telephone is the result of work done by many hands, all worthy of recognition of their addition to the field. Only in the last ten years, however, has the British government announced that it now recognises (primarily for educational purposes) Antonio Meucci (see below) as the 'first inventor' of the telephone. The Public Switched Telephone Network (PSTN) has gradually evolved towards digital telephony which has improved the capacity and quality of the network. End-to-end analog telephone networks were first modified in the 1970s by upgrading long-haul transmission networks with SONET technology and fiber optic transmission methods. Digital transmission made it possible to carry multiple digitized switched circuits on a single transmission medium (known as multiplexing). While today the end instrument remains analog, the analog signals reaching the aggregation point (Serving Area Interface (SAI) or the central office (CO) ) are typically converted to digital signals. Digital loop carriers (DLC) are often used, placing the digital network ever closer to the customer premises, relegating the analog local loop to legacy status. While the term "wireless" means radio and can refer to any telephone that uses radio waves, it is primarily used for cell phones. In the United States wireless companies tend to use the term wireless to refer to a wide range of services while the cell phone itself is called a mobile phone, mobile, PCS phone, cell phone or simply cell with the trend now moving towards mobile. The changes in terminology is partially due to providers using different terms in marketing to differentiate newer digital services from older analog systems and services of one company from another. Cordless telephones, first invented by Teri Pall in 1965, consist of a base unit that connects to the land-line system and also communicates with remote handsets by low power radio. This permits use of the handset from any location within range of the base. Because of the power required to transmit to the handset, the base station is powered with an electronic power supply. Thus, cordless phones typically do not function during power outages. Initially, cordless phones used the 1.7 MHz frequency range to communicate between base and handset. Because of quality and range problems, these units were soon superseded by systems that used frequency modulation (FM) at higher frequency ranges (49 MHz, 900 MHz, 2.4 GHz, and 5.8 GHz). The 2.4 GHz cordless phones can interfere with certain wireless LAN protocols (802.11b/g) due to the usage of the same frequencies. On the 2.4 GHz band, several "channels" are utilized in an attempt to guard against degradation in the quality of the voice signal due to crowding. The range of modern cordless phones is normally on the order of a few hundred meters. Most modern mobile phone systems are cell-structured. Radio is used to communicate between a handset and nearby cell sites. When a handset gets too far from a cell site, a computer system commands the handset and a closer cell site to take up the communications on a different channel without interrupting the call. Radio frequencies are a limited, shared resource. The higher frequencies used by cell phones have advantages over short distances. Connection distance is somewhat predictable and can be controlled by adjusting the power level. By only using enough power to connect to the "nearest" cell site phones using one cell site will cause almost no interference with phones using the same frequencies on another cell site. The higher frequencies also work well with various forms of multiplexing which allows more than one phone to connect to the same tower with the same set of frequencies. Some mobile telephones, especially those used in remote locations, where constructing a cell network would be too unprofitable or difficult, instead communicate directly with an orbiting satellite. Such devices tend to be bulkier than cell-based mobile phones, as they require a large antenna or dish for communicating with the satellite, but do not require ground based transmitters, making them useful for communicating from remote areas and disaster zones. There are phones that work as a cordless phone when near their corresponding base station (and sometimes other base stations) and work as a wireless phone when in other locations but for a variety of reasons did not become popular. Some kinds of cordless phones work like cellular phones but only within a small private network covering a building or group of buildings. These kinds of systems using VoIP are popular in hospitals and factories where the same wireless network can be used for both data and voice. Also known as Internet telephony or Voice over IP (VoIP), digital telephony is a disruptive technology that is rapidly replacing traditional telephone networks. In Japan and Korea up to 10% of subscribers, as of January 2005, have switched from analog to digital telephone service. A recent Newsweek article suggested that Internet telephony may be "the next big thing." [2] Digital telephones use a broadband Internet connection to transmit conversations as data packets. In addition to replacing the PSTN, digital telephony is also competing with mobile phone networks by offering free or lower cost connections via WiFi hotspots. As mentioned above VoIP is also used on private wireless networks which may or may not have a connection to the outside telephone network.3gpp - a-law - abbreviated dialing - adsl - ani - answering machine - apn - automatic ring back - b-channel - baud - bell 202 modem - bit rate - bonding - bri - busy signal - cable modem - call-progress tones - call accounting - call capture - call forwarding - call originator - call park - call pick-up - call transfer - call waiting - call waiting deluxe - called party - caller id - caller id spoofing - calling party - carrier wave - cbr - ccitt - cdma - cdma2000 - cellular repeater - celp - channel - clec - clock rate - codec - collect call - conference - conference call - crc - csd - d-channel - data compression - device driver - dial-up - dial - dial tone - direct-inward-dialing - direct distance dialing - distinctive ring - dnis - dsl - dsp - dtmf - dtr - duplex - echo cancellation - edge - extension - fax - fcc - fdma - fidonet - follow-me - g.711 - g.723.1 - g.723 - g.726 - g.lite - gprs - gps - gsm - h.323 - harmonic - headphones - hscsd - hspda - iad - idsn - internet call waiting - isp - ivr - jack plug - local loop - long distance - microcontroller - mobile phone - modem - modulation - mu-law - music-on-hold - night service - off-hook - on-hook - pabx - pager - payphone - pbx - pcm - pots - prank call - precise tone plan - pstn - pulse dialling - push to talk - ring modulation - ring tone - ringback - ringing signal - rj11 - roaming - serial communications - serial port - signal noise - sim - simplex - sit - sms - softmodem - switchboard operator - tapi - tdma - telecommunications - telemarketing - telephone - telephone call - telephone card - telephone company - telephone exchange - telephone line - telephone number - telephone numbering plan - telephone operator - telephone switchboard - telephony - tts - twisted pair - umts - v.32 - v.32bis - v.34 - v.42bis - vbr - vertical service code - voicemail - voip - vox - wap - wav - wi-fi - wimax - wire
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