A four-wire circuit allows for simultaneous communication in both directions, optimizing data transmission. It is commonly used for home and business data lines. DSL allows for voice and data communication over a single twisted pair, but signal loss may occur over distance. Copper wires were replaced by coaxial cable and fiber optics for faster transmission speeds. The four-wire circuit is still used inside buildings and can be preferred for data security.
A four-wire circuit is defined as two pairs of two communication wires that allow signals to be transmitted in both directions simultaneously. Simultaneous communication is called a full-duplex system, where two people can talk and be heard at the same time. Many home and business data lines use these circuits to optimize data transmission. An electrical circuit for supplying both 120 and 240 volt power to an appliance using two hot or current-carrying wires, as well as a neutral and a ground, is also called a four-wire circuit.
Ordinary home telephone equipment uses two-wire circuits for voice calls. Conversations can go both ways, but usually only a few telephones can be connected to a single two-wire line. Data communication would be limited in this type of circuit.
Adding two more wires to create a four-wire circuit allows the system to send data to a computer or modem in one direction with two wires and receive data from the device with the other two wires. Data rates are greatly improved with fewer errors and signal loss. This system is called a full-duplex line, which has been common since the 1980s for data systems such as Integrated System Digital Networks (ISDN). As the demand for data rates increased, digital systems expanded to digital systems Ethernet, which is a four-wire or eight-wire pair of circuits, capable of handling both voice and data communications.
A digital data system that can operate over a two-wire line is a digital subscriber line (DSL). This system uses voice and data communication over a single twisted pair by transmitting two different frequencies. Normally a filter is installed in any phone to prevent distortion of the higher frequency data signal. Due to signal losses over distance, DSL may not be available in areas that are too far from telephone company transmission equipment.
Until the late 20th century, communication systems were built with copper wires coated with non-conductive insulation. As the Internet grew and the demand for data increased, networks were increasingly limited and transmission speeds compromised. Network companies began converting wired networks first to coaxial cable, then to fiber optics which can carry more data using laser light transmitted through the glass fiber. Home and business users could subscribe to Internet service from various companies and bring cable or fiber-optic technology right into the building.
The four-wire circuit has been replaced by cable and fiber optic systems to transmit data to users. Inside the building, however, the four-wire circuit in single or multiple circuits continued to be used extensively into the 21st century. Wireless data networks can be used, but businesses or individuals concerned about data security can still choose a wired network to minimize the risk of data theft.
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