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Bridge Tap
Bridged tap or bridge tap is a long-used method of cabling for telephone lines. One cable pair (of wires) will "appear" in several different terminal locations (poles or pedestals). This allows the telephone company to use or " assign" that pair to any subscriber near those terminal locations. Once that customer disconnects, that pair becomes usable at any of the terminals. In the days of party lines, 2, 4, 6, or 8 users were commonly connected on the same pair which appeared at several different locations. A bridge tap has no hybrid coil or other impedance matching components, just a “T” (or branch) in the cable. Thus the bridge presents an impedance mismatch. The unused branch of the T is usually left with no device connected to its end, thus has no electrical termination. Both the tap and its unterminated branch cause unwanted signal reflections, also called echoes. Digital subscriber lines (DSL) can be affected by a bridged tap, depending on where the tap is bridged. D ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Serving Area Interface
The serving area interface or service area interface (SAI) is an outdoor enclosure or metal box that allows access to telecommunications wiring. Alternate names *Access point (AP) *Cabinet (cab) *B-box (breakout box) *Cross box *Cross-connect box *Jumper wire interface (JWI) *Outside plant interface (OPI) *Pedestal (ped) *Primary cross-connection point (PCP) (UK)"Multimedia Telecommunications" (BT Telecommunications Series), B. Whyte (Ed.), Springer 1997 *Secondary cross-connection point (SCP) (UK) *Telecom cabinet Function The SAI provides the termination of individual twisted pairs of a telephony local loop for onward connection back to the nearest telephone exchange (US: " central office" (CO)) or remote switch, or first to transmission equipment such as a subscriber loop carrier multiplexer and then to the exchange main distribution frame (MDF). In the United Kingdom, the components from the PCP onwards to the customer are known as "D-side" (distribution side), and from ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Provisioning
In telecommunication, provisioning involves the process of preparing and equipping a network to allow it to provide new services to its users. In National Security/Emergency Preparedness telecommunications services, ''"provisioning"'' equates to ''"initiation"'' and includes altering the state of an existing priority service or capability. The concept of network provisioning or service mediation, mostly used in the telecommunication industry, refers to the provisioning of the customer's services to the network elements, which are various equipment connected in that network communication system. Generally in telephony provisioning this is accomplished with network management database table mappings. It requires the existence of networking equipment and depends on network planning and design. In a modern signal infrastructure employing information technology (IT) at all levels, there is no possible distinction between telecommunications services and "higher level" infrastructure. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Party Line (telephony)
A party line (multiparty line, shared service line, party wire) is a local loop telephone circuit that is shared by multiple telephone service subscribers. Party line systems were widely used to provide telephone service, starting with the first commercial switchboards in 1878. A majority of Bell System subscribers in the mid-20th century in the United States and Canada were served by party lines, which had a discount over individual service. During wartime shortages, these were often the only available lines. British users similarly benefited from the party line discount. Farmers in rural Australia and South Africa used party lines, where a single line spanned miles from the nearest town to one property and on to the next. History Telephone companies offered party lines beginning in the late 1800s, although subscribers in all but the most rural areas may have had the option to upgrade to individual line service at an additional monthly charge. The service was common in s ... [...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 sequential se ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Impedance Matching
In electronics, impedance matching is the practice of designing or adjusting the input impedance or output impedance of an electrical device for a desired value. Often, the desired value is selected to maximize power transfer or minimize signal reflection. For example, impedance matching typically is used to improve power transfer from a radio transmitter via the interconnecting transmission line to the antenna. Signals on a transmission line will be transmitted without reflections if the transmission line is terminated with a matching impedance. Techniques of impedance matching include transformers, adjustable networks of lumped resistance, capacitance and inductance, or properly proportioned transmission lines. Practical impedance-matching devices will generally provide best results over a specified frequency band. The concept of impedance matching is widespread in electrical engineering, but is relevant in other applications in which a form of energy, not necessarily el ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electrical Termination
In electronics, electrical termination is the practice of ending a transmission line with a device that matches the characteristic impedance of the line. Termination prevents signals from reflecting off the end of the transmission line. Reflections at the ends of unterminated transmission lines cause distortion which can produce ambiguous digital signal levels and mis-operation of digital systems. Reflections in analog signal systems cause such effects as video ghosting, or power loss in radio transmitter transmission lines. Transmission lines Signal termination often requires the installation of a terminator at the beginning and end of a wire or cable to prevent an RF signal from being reflected back from each end, causing interference, or power loss. The terminator is usually placed at the end of a transmission line or daisy chain bus (such as in SCSI), and is designed to match the AC impedance of the cable and hence minimize signal reflections, and power losses. Less com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Signal Reflection
In telecommunications, signal reflection occurs when a signal is transmitted along a transmission medium, such as a copper cable or an optical fiber. Some of the signal power may be reflected back to its origin rather than being carried all the way along the cable to the far end. This happens because imperfections in the cable cause impedance mismatches and non-linear changes in the cable characteristics. These abrupt changes in characteristics cause some of the transmitted signal to be reflected. In radio frequency (RF) practice this is often measured in a dimensionless ratio known as voltage standing wave ratio (VSWR) with a VSWR bridge. The ratio of energy bounced back depends on the impedance mismatch. Mathematically, it is defined using the reflection coefficient. Because the principles are the same, this concept is perhaps easiest to understand when considering an optical fiber. Imperfections in the glass create mirrors that reflect the light back along the fiber. Impe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Digital Subscriber Line
Digital subscriber line (DSL; originally digital subscriber loop) is a family of technologies that are used to transmit digital data over telephone lines. In telecommunications marketing, the term DSL is widely understood to mean asymmetric digital subscriber line (ADSL), the most commonly installed DSL technology, for Internet access. DSL service can be delivered simultaneously with wired telephone service on the same telephone line since DSL uses higher frequency bands for data. On the customer premises, a DSL filter on each non-DSL outlet blocks any high-frequency interference to enable simultaneous use of the voice and DSL services. The bit rate of consumer DSL services typically ranges from 256 kbit/s to over 100 Mbit/s in the direction to the customer (downstream), depending on DSL technology, line conditions, and service-level implementation. Bit rates of 1 Gbit/s have been reached. In ADSL, the data throughput in the upstream direction (the direction ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attenuation Distortion
Attenuation distortion is the distortion of an analog signal that occurs during transmission when the transmission medium does not have a flat frequency response across the bandwidth of the medium or the frequency spectrum of the signal.Rowe, Standord H. II, ''Network Technology & Service Integration'' (5th Edition), 2002, Prentice-Hall, Inc., 2002 Attenuation distortion occurs when some frequencies are attenuated more than other frequencies. When an analog signal of constant amplitude across its frequency spectrum suffers attenuation distortion, some frequencies of the received signal arrive being greater in amplitude (louder), relative to other frequencies. To overcome the effects of attenuation distortion, communications circuits have special equalization equipment attached at the ends of the circuit or in between, designed to attenuate the signal evenly across the frequency spectrum, or to allow the signal to be received at equal amplitude for all frequencies. Attenuation di ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Synchronization
Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronous or ''in sync''—and those that are not are '' asynchronous''. Today, time synchronization can occur between systems around the world through satellite navigation signals and other time and frequency transfer techniques. Navigation and railways Time-keeping and synchronization of clocks is a critical problem in long-distance ocean navigation. Before radio navigation and satellite-based navigation, navigators required accurate time in conjunction with astronomical observations to determine how far east or west their vessel traveled. The invention of an accurate marine chronometer revolutionized marine navigation. By the end of the 19th century, important ports provided time signals in the form of a signal gun, flag, or dropping time ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates. Hearing protectors help reduce acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs). In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field. Background In many cases, attenuation is an exponential function of the path length through the medium. In optics and in chemical spectroscopy, this is known as the Beer–Lambert law. In engineering, attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc.) and is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Local Loop
In telephony, the local loop (also referred to as the local tail, subscriber line, or in the aggregate as the last mile) is the physical link or circuit that connects from the demarcation point of the customer premises to the edge of the common carrier or telecommunications service provider's network. At the edge of the carrier access network in a traditional public telephone network, the local loop terminates in a circuit switch housed in an incumbent local exchange carrier or telephone exchange. Infrastructure Traditionally, the local loop was an electrical circuit in the form of a single pair of conductors from the telephone on the customer's premises to the local telephone exchange. Single-wire earth return lines had been used in some countries until the introduction of electric tramways from the 1900s made them unusable. Historically the first section was often an aerial open-wire line, with several conductors attached to porcelain insulators on cross-arms on "telegra ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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