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Time-division Duplex
A duplex communication system is a point-to-point system composed of two or more connected parties or devices that can communicate with one another in both directions. Duplex systems are employed in many communications networks, either to allow for simultaneous communication in both directions between two connected parties or to provide a reverse path for the monitoring and remote adjustment of equipment in the field. There are two types of duplex communication systems: full-duplex (FDX) and half-duplex (HDX). In a full-duplex system, both parties can communicate with each other simultaneously. An example of a full-duplex device is plain old telephone service; the parties at both ends of a call can speak and be heard by the other party simultaneously. The earphone reproduces the speech of the remote party as the microphone transmits the speech of the local party. There is a two-way communication channel between them, or more strictly speaking, there are two communication channel ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Communication System
A communications system or communication system is a collection of individual telecommunications networks, transmission systems, relay stations, tributary stations, and terminal equipment usually capable of interconnection and interoperation to form an integrated whole. The components of a communications system serve a common purpose, are technically compatible, use common procedures, respond to controls, and operate in union. Telecommunications is a method of communication (e.g., for sports broadcasting, mass media, journalism, etc.). Communication is the act of conveying intended meanings from one entity or group to another through the use of mutually understood signs and semiotic rules. Types By media An optical communication system is any form of telecommunication that uses light as the transmission medium. Equipment consists of a transmitter, which encodes a ''message'' into an optical '' signal'', a '' communication channel'', which carries the signal to i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cell Phone
A mobile phone, cellular phone, cell phone, cellphone, handphone, hand phone or pocket phone, sometimes shortened to simply mobile, cell, or just phone, is a portable telephone that can make and receive calls over a radio frequency link while the user is moving within a telephone service area. The radio frequency link establishes a connection to the switching systems of a mobile phone operator, which provides access to the public switched telephone network (PSTN). Modern mobile telephone services use a cellular network architecture and, therefore, mobile telephones are called ''cellular telephones'' or ''cell phones'' in North America. In addition to telephony, digital mobile phones ( 2G) support a variety of other services, such as text messaging, multimedia messagIng, email, Internet access, short-range wireless communications ( infrared, Bluetooth), business applications, video games and digital photography. Mobile phones offering only those capabilities are known ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
ITU-T V-Series Recommendations
The ITU-T V-Series Recommendations on Data communication over the telephone network specify the protocols that govern approved modem communication standards and interfaces. ''Note:'' the '' bis'' and '' ter'' suffixes are ITU-T standard designators of successive iterations of a standard (''bis'' and ''ter'' are derived from the Latin for "twice" and "thrice"). General standards ''Applies to V.1–V.9'' *V.1 is an ITU-T recommendation, entitled ''Equivalence between binary notation symbols and the significant conditions of a two-condition code.'' *V.2 is an ITU-T recommendation, approved in November 1988, titled ''Power levels for data transmission over telephone lines.'' *V.4 is an ITU-T recommendation, approved in November 1988, titled ''General structure of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks.'' *V.5 was an ITU-T recommendation, approved in November 1988, titled ''Standardization of data signal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Modem
A modulator-demodulator or modem is a computer hardware device that converts data from a digital format into a format suitable for an analog transmission medium such as telephone or radio. A modem transmits data by modulating one or more carrier wave signals to encode digital information, while the receiver demodulates the signal to recreate the original digital information. The goal is to produce a signal that can be transmitted easily and decoded reliably. Modems can be used with almost any means of transmitting analog signals, from light-emitting diodes to radio. Early modems were devices that used audible sounds suitable for transmission over traditional telephone systems and leased lines. These generally operated at 110 or 300 bits per second (bit/s), and the connection between devices was normally manual, using an attached telephone handset. By the 1970s, higher speeds of 1,200 and 2,400 bit/s for asynchronous dial connections, 4,800 bit/s for synch ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Echo Cancellation
Echo suppression and echo cancellation are methods used in telephony to improve voice quality by preventing echo from being created or removing it after it is already present. In addition to improving subjective audio quality, echo suppression increases the capacity achieved through silence suppression by preventing echo from traveling across a telecommunications network. Echo suppressors were developed in the 1950s in response to the first use of satellites for telecommunications. Echo suppression and cancellation methods are commonly called acoustic echo suppression (AES) and acoustic echo cancellation (AEC), and more rarely line echo cancellation (LEC). In some cases, these terms are more precise, as there are various types and causes of echo with unique characteristics, including acoustic echo (sounds from a loudspeaker being reflected and recorded by a microphone, which can vary substantially over time) and line echo (electrical impulses caused by, e.g., coupling between ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1000BASE-T
In computer networking, Gigabit Ethernet (GbE or 1 GigE) is the term applied to transmitting Ethernet frames at a rate of a gigabit per second. The most popular variant, 1000BASE-T, is defined by the IEEE 802.3ab standard. It came into use in 1999, and has replaced Fast Ethernet in wired local networks due to its considerable speed improvement over Fast Ethernet, as well as its use of cables and equipment that are widely available, economical, and similar to previous standards. History Ethernet was the result of research conducted at Xerox PARC in the early 1970s, and later evolved into a widely implemented physical and link layer protocol. Fast Ethernet increased the speed from 10 to 100 megabits per second (Mbit/s). Gigabit Ethernet was the next iteration, increasing the speed to 1000 Mbit/s. * The initial standard for Gigabit Ethernet was produced by the IEEE in June 1998 as IEEE 802.3z, and required optical fiber. 802.3z is commonly referred to as 1000BA ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Twisted Pair
Twisted pair cabling is a type of wiring used for communications in which two conductors of a single circuit are twisted together for the purposes of improving electromagnetic compatibility. Compared to a single conductor or an untwisted balanced pair, a twisted pair reduces electromagnetic radiation from the pair and crosstalk between neighboring pairs and improves rejection of external electromagnetic interference. It was invented by Alexander Graham Bell. For additional noise immunity, twisted-pair cabling may be shielded. Cable with shielding is known as shielded twisted pair (STP) and without as unshielded twisted pair (UTP). Explanation A twisted pair can be used as a balanced line, which as part of a balanced circuit can greatly reduce the effect of noise currents induced on the line by coupling of electric or magnetic fields. The idea is that the currents induced in each of the two wires are very nearly equal. The twisting ensures that the two wires are on aver ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ethernet
Ethernet () is a family of wired computer networking technologies commonly used in local area networks (LAN), metropolitan area networks (MAN) and wide area networks (WAN). It was commercially introduced in 1980 and first standardized in 1983 as IEEE 802.3. Ethernet has since been refined to support higher bit rates, a greater number of nodes, and longer link distances, but retains much backward compatibility. Over time, Ethernet has largely replaced competing wired LAN technologies such as Token Ring, FDDI and ARCNET. The original 10BASE5 Ethernet uses coaxial cable as a shared medium, while the newer Ethernet variants use twisted pair and fiber optic links in conjunction with switches. Over the course of its history, Ethernet data transfer rates have been increased from the original to the latest , with rates up to under development. The Ethernet standards include several wiring and signaling variants of the OSI physical layer. Systems communicating over ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telephone Hybrid
A telephone hybrid is the component at the ends of a subscriber line of the public switched telephone network (PSTN) that converts between two-wire and four-wire forms of bidirectional audio paths. When used in broadcast facilities to enable the airing of telephone callers, the broadcast-quality telephone hybrid is known as a broadcast telephone hybrid or telephone balance unit. The need for hybrids comes from the nature of analog plain old telephone service (POTS) home or small business telephone lines, where the two audio directions are combined on a single two-wire pair. Within the telephone network, switching and transmission are almost always four-wire circuits with the two signals being separated. Hybrids perform the necessary conversion. In older analog networks, conversion to four-wire was required so that repeater amplifiers could be inserted in long-distance links. In today's digital systems, each speech direction must be processed and transported independently. The li ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hybrid Coil
A hybrid coil (or bridge transformer, or sometimes hybrid) is a transformer that has three windings, and which is designed to be configured as a circuit having four ports that are conjugate in pairs. A signal arriving at one port is divided equally between the two adjacent ports but does not appear at the opposite port. In the schematic diagram, the signal into W splits between X and Z, and no signal passes to Y. Similarly, signals into X split to W and Y with none to Z, etc. Correct operation requires matched characteristic impedance at all four ports. Hybrids are a class of directional coupler in which the input port power is split equally between the two output ports. Forms of hybrid other than transformer coils are possible; any format of directional coupler can be designed to be a hybrid. These formats include transmission lines and waveguides. Explanation The primary use of a voiceband hybrid coil is to convert between 2-wire and 4-wire operation in sequenti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Two-wire Circuit
In telecommunication, a two-wire circuit is characterized by supporting transmission in two directions simultaneously, as opposed to four-wire circuits, which have separate pairs for transmit and receive. The subscriber local loop from the telco central office are almost all two wire for analog baseband voice calls (and some digital services like ISDN), and converted to four-wire at the line card back when telephone switching was performed on baseband audio. Today the audio is digitized and processed completely in the digital domain upstream from the local loop. The reason for using two wires rather than four is simple economics—half the materials cost half as much to purchase and install. Note the use of the past-tense "cost," as installation of two-wire copper local loops for telephony was done primarily during the mid 20th century. In the first world there is no new infrastructure planning for new copper-based technology, and as customers are migrating to cellular telephony ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Telephone
A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into electronic signals that are transmitted via cables and other communication channels to another telephone which reproduces the sound to the receiving user. The term is derived from el, τῆλε (''tēle'', ''far'') and φωνή (''phōnē'', ''voice''), together meaning ''distant voice''. A common short form of the term is ''phone'', which came into use early in the telephone's history. In 1876, Alexander Graham Bell was the first to be granted a United States patent for a device that produced clearly intelligible replication of the human voice at a second device. This instrument was further developed by many others, and became rapidly indispensable in business, government, and in households. The essential elements of a telephone are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
