D Channel, an ISDN term, refers to the channel that carries control and signaling information. (The "D" stands for "delta" channel.) The B-channel ("B" for "bearer") carries the main data. The D-channel carries control and signaling information.
D type Channel Bank refers to the terms used in T1 technology. Channel Bank defines the type of formatting that is required for transmission on T1 trunk. The purpose of a Channel Bank in the telephone company is to form the foundation of multiplexing and demultiplexing the 24 voice channels (DS0). D type Channel Bank is one of the type of Channel Bank which is used for digital signals. There are five kinds of Channel Banks that are used in the System: D1, D2, D3, D4, and DCT (Digital Carrier Trunk)
Directory Assistance (DA) is a telephone service in which a customer will be connected to an operator at a DA bureau by dialing the proper service code or number and shall be told the directory number of the customer whom he/she desired to call, provided that the customer's number is, or will be, published (listed) in the telephone directory.
DACS: Digital Access and Cross-Connect System
Digital access and cross-connect system (DACS, DCS or DCCS) is a digital switching device in telecommunications for routing T1 lines. The DACS can cross-connect any T1 line in the system with any other T1 line also in the system. DACS is a simple form of channel switch which works at the DS0, DS1(T1/E1) and DS3(T3/E3), as well as STS-level.
Dedicated Access Line (DAL) refers to a direct connection between customer location and telecommunication service facility to eliminate all local switching aspects of interexchange calling to/from this specific customer location
Dark fiber refers to unused fiber-optic cables that have been laid out in the field. Oftentimes companies lay more lines than what's needed in order to curb costs of having to do it again and again. The dark strands can be leased to others who want to establish optical connections among their own locations.
Data Set Answer Back Tone is one of telephone system audible tones that it will be heard when manually initiating a data call. It normally occurs shortly after the start of audible ringing and means that the remote data set has answered. The data set at the calling end should then be put into the data mode. Data Set Answer Back Tone is 2025 Hz steady at -13 dBm/frequency.
Data Strobe Encoding is a coding scheme for transmitting data in digital circuits which uses two signal lines, Data and Strobe. These have the property that either Data or Strobe changes its logical value in one clock cycle, but never both. This allows for easy clock recovery with a good jitter tolerance by XORing the two signal line values.
Datakit is proprietary packet switching system similar to X.25 widely deployed by the RBOCs. Datakit supports host-to-host connections and EIA-232 connections for terminals, printers, and hosts.
Datacasting is broadcast of digital information over networks to receivers and players. Datacasting is sometimes used as an alternative to traditional video broadcasting, because the receivers and player units can have the "intelligence" to customize their playback programming for the location and intended audience. The system of receivers set up to receive messages from a particular datacasting is known as Datacasting Networks, which are a venue for advertisers.
Direct Access Test Unit (DATU) is a loop conditioning system which is installed in the Metallic Facility Terminal (MFT) frame and connected through a No-Test trunk to a switching facility. DATU is then accessed by dialing a telephone number and following the voice prompts.
Digital Channel Bank (DCS) is a device at a telephone company central office (public exchange) that converts analog signals from home and business users into digital signals to be carried over higher-speed lines between the central office and other exchanges. The analog signal is converted into a digital signal that transmits at a rate of 64 thousand bits per second (Kbps). This 64 Kbps signal is a standard known as a DS0 signal. The signal is multiplexed with other DS0 signals on the same line using time-division multiplexing (TDM) . Usually, the digital information is put on each DS0 signal using pulse code modulation (PCM). The channel bank is the foundation for all digital telecommunication transmissions. It is the part of a carrier-multiplex terminal that multiplexes a group of channels into a higher bit-rate digital channel and demultiplexes these aggregates back into individual channels. A channel bank changes analog voice and data signals into a digital format. It is called a "bank" because it can contain enough processing power to convert a bank of up to 24/32 individual channels to a digital format, and then back to analog again.
DCE: Data Circuit-Terminating Equipment
Data Circuit-terminating Equipment (DCE) is a device that establishes, maintains and terminates a session on a network. It may also convert signals for transmission. DCE is typically the modem, contrast with DTE which is a terminal or computer.
DCF: Dispersion Compensating Fiber
Dispersion Compensating Fiber (DCF) is a type optical fiber installed in a network which is a good way to compensate for dispersion. What is not widely known, however, is that to achieve adequate results with DCF, highly precise dispersion test must be carried out several times, at various levels.
DCS: Digital Cross Connect System
Digital Cross Connect System (DCS) is a digital system in which: (a) access is performed by T-1 hardware architecture in private and public networks with centralized switching, and (b) cross-connection is performed by D3/D4 framing for switching digital-signal-0 (DS-0) channels to other DS-0 channels. Modern digital access and cross-connect systems are not limited to the T-carrier system, and may accommodate high data rates such as those of SONET.
Direct Distance Dialing (DDD) is a telecommunications service feature in North American Numbering Plan, in which a call originator may call any other user outside the local calling area without any operator assistance. It requires more digits in the dialing than are required for calling within the local area. DDD also extends beyond the boundaries of national public telephone networks.
Direct Dialing In (DDI), also known as Direct Inward Dialing (DID), is the ability or service feature for a caller outside a company to call an internal extension without having to pass through an operator or attendant. In large PBX systems, the dialed digits are passed down the line from the CO (central office). The PBX then completes the call. Direct Inward Dialing is often proposed as Centrex's major feature. But automated attendants (a specialized form of interactive voice response systems) also provide a similar service.
Decode is the process of interpreting previously coded information back into the usable form in which it existed before the coding process.
Decoder, in telecommunication, refers to a device in some telephone switching for translating dial digits into control signals.
Dedicated Line is a communications cable in telecommunications that is dedicated to a specific application, in contrast with a shared resource such as the telephone network. Practically, Dedicated Line may not be implemented by using a single, discrete, end-to-end cable, but they do provide guarantees of constant bandwidth availability and near-constant latency, properties that cannot be guarantied for more public systems. Such properties add a considerable premium to the price charged.
Degree of Start-Stop Distortion
Degree of start-stop distortion refers to the following definitions: 1. In asynchronous data transmission, the ratio of a) the absolute value of the maximum measured difference between the actual and theoretical intervals separating any significant instant of modulation or demodulation from the significant instant of the start element immediately preceding it to, b) the unit interval. 2. The highest absolute value of individual distortion affecting the significant instants of a start-stop modulation.
The degree of distortion of a start-stop modulation (or demodulation) is usually expressed as a percentage.
Distinction can be made between the degree of late ( positive) distortion and the degree of early ( negative) distortion.
Delay Dial Signaling is one of the Start Dial Supervision Protocol. The Originating switch and trunk circuit will go off-hook. After a timing interval (75 to 300 mS), the Originating switch will look at the status of the incoming signaling from the Remote switch. If the supervision is on-hook, the Originating office will output digits to the Remote switch. If the supervision is off-hook, the Originating office will wait for the supervision to return to an on-hook state, then output digits. There is no minimum time to wait for a delay-dial pulse from the Remote switch. In fact, if the remote switch was in an on-hook state, there is no waiting at all prior to output of digits. If the Remote switch was not ready to receive digits, improper call completions can result.
Delay Distortion is the signal distortion caused by the differing transmission delays of signals of different frequencies to pass through a telecommunications transmission line.
Delay Equalizer is a device used to equalize the signal distortion caused by the differing frequency delay characteristics of a transmission line. The delay equalizer operates by adding delay to the faster transmitting frequencies.
Delta Modulation is a method of sampling and converting analog signals such as voice to digital signals. It is based on encoding the direction of signal change, indicating the direction of signal change with a single bit.
Demodulation is the process of recovering the original modulating signal from a modulated carrier. The original modulating signal is usually the information being transmitted, typically voice or data.
Demodulator is a device for assembling signals after they have been received by an antenna. A demodulator is typically the first major device downstream from an antenna receiving system. The corresponding device on the transmission side of a system is a modulator.
Deposit Coin Tone is one of the audible tone in telephone system. It is sent from a Community Dial Office to a post-pay coin telephone, informs the calling party that the called party has answered and that the coin should be deposited. Deposit Coin Tone is a steady Low Tone.
Dial Around is a telephone service feature which allows customers to dial a toll-free number before entering the destination number for long-distance calling. Dial around is especially convenient for residential customers and cellular users who wish to bypass their primary long-distance provider and take advantage of discounted calling rates.
Dial Jack Tone is used as a start-dial signal to tell a DSA operator that the connection reached through a dial jack is ready to receive dialing. Dial Jack Tone is a steady Low Tone.
Dial Long Line is an equipment (usually located in a central office) that extends the dialing, supervision and other signaling range of a loop.
Dial Off-Normal Tone is a steady Low Tone. It is returned to an operator after he/she has completed a call into a step-by-step office and after the calling party has answered to remind him/her to restore the dial key
Dial Pulse is regular, momentary interruption of signaling current used to transmit numerical information either into a register or to control a switch directly. There are different ways of generating Dial Pulses. When end-users pick up the receiver on a telephone, an electrical connection is made to the lines leading to the central office. When end-users replace the receiver on the cradle the connection is broken or interrupted. This applies to both push-button and rotary dial telephones. By periodically breaking the connections leading to the central office, a number can be dialed. The number of interruptions is equal to the digit dialed, with the exception that ten interruptions correspond to zero. These pulses may be generated at the rate of ten times per second and there should be a 1/2 second delay between each two digits. The rotary dial on the telephone is a mechanical device which periodically breaks the connection leading to the central office.
Dial Pulsing is a means of signaling consisting of regular momentary interruption of a direct or alternating current path at the sending end in which the number of interruptions corresponds to the value of a digit or character. The interruptions are usually produced by a rotary telephone dial, but may be produced by a sender in a switching system.
Dial Tone is sent to a calling customer or operator to indicate that the receiving end is ready to receive dial pulses or DTMF signals. It is used in all types of dial offices when dial pulses are produced by the customer's or operator's dials. Normally dial tone means that the entire wanted number may be dialed; however, there are some cases where the calling party must await a second dial tone or where an operator, after dialing an initial group of digits, must wait for a second dial tone before the rest of the number can be dialed. Some dialing switchboards are arranged to permit listening for dial tone between certain digits. Dial Tone is 350 Hz and 440 Hz held steady at -13 dBm0/frequency.
Dial Tone Delay is a measure of time required to provide dial tone to customers. This measures one aspect of the performance of a switching system
Dial Tone Marker is the common control equipment used to control call-operating operations in a Number 5 Crossbar System.
Dial Train is the series of pulses or tones that is sent from the originating station and the switching equipment in order to specify the destination of the desired call.
Dialing Parity is equal dialing access provided to consumers. No additional codes or numbers are necessary to access a different telephone service provider.
Dial-Normal Transmission Signal
Dial-Normal Transmission Signal is a second dial tone returned to an operator between digits indicating that he/she may dial the remainder of the number. For example, when an operator reaches a link-type Community Dial Office via a step-by-step office after dialing a routing code, he/she must pause until an idle link at the Community Dial Office returns dial tone. This method of operation is not recommended or considered standard. Dial-Normal Transmission Signal is a steady Low Tone.
Dialup is the technique of initiating and routing a call by means of dial signals from the originating station.
Dial-up Access refers to the method of accessing a telecommunications system via dialup.
Dial-up Line is a communications circuit that is established by a switched-circuit connection using the telephone company network.
Diaphragm is a thin, flexible sheet that can be vibrated by sound waves as in a microphone, or by magnetic waves as in a telephone receiver.
DIB: Directory Information Base
Directory Information Base (DIB) is the complete set of information to which the directory provides access, and which includes all of the pieces of information which can be read or manipulated using the operations of the directory
DID/DNIS: Direct Inward Dialing/Dialed Number Identification Service
Direct Inward Dialing/Dialed Number Identification Service (DID/DNIS) refers to a service when a call arrives at an ACD or PBX, the carrier sends a digital code on the trunk line. The switch can read this code to determine how it should dispatch the call. Typically, this value is the specific number dialed by the user. By mapping each possible code with an internal extension, the switch can provide direct inward dialing (DID).
Direct-Inward-Dial (DID), also known as Direct Dialing In (DDI), is a service offered by telephone companies that enables callers to dial directly into an extension on a PBX and not use an auto-attendant. Direct-inward-dial (DID) is the call in which the gateway uses the number initially dialed (DNIS) to make the call, as opposed to a prompt to dial additional digits.
Differential Signaling is a method of digital data transmission using two wires for each electrical path for high immunity to noise and crosstalk. The signals are sent down one wire as positive and the other as negative, and the circuit at the receiving end derives the signal from the difference between the two. It is superior to single-ended signaling, where the reference voltage is ground and can vary over long distances. In differential signaling, the reference voltage is controlled. Typically, twisted pairs are used so that external radiation impacts both wires at the same place, and the noise can be detected more easily.
Digital refers to, in telecommunications system, a means for encoding information of communication signals through the use of bits (binary digits). Digital transmission is increasingly replacing analog transmission because it provides more efficiency and flexibility for networking.
Digital Carrier System is a carrier system for digital signals that uses regenerative versus linear repeaters and time division multiplexing.
Digital Transmission is the transmission of a digital signal between two or more points. The usual definition applies to the manner in which the transmission carrier is modified to carry the transmitted information. For example, in digital microwave systems, the radio frequency carrier is an analog signal, but its information modulation is derived from the digital signal.
Digitize is the process of converting any information from its base states to a digital form; i.e., a form in which only a limited number of states exist. It should be noted that a digital form does not necessarily imply a character encoded form of information.
Direct Interlata Connecting Trunk Groups
Direct Interlata Connecting Trunk Groups refer to those trunk groups used for switched LATA access that interconnect an IC's POP directly with a BOC end office switching systems.
Direct Progressive System is a switching system in which the switches are at least partially under the direct control of a customer's dial and in which the path through the switching office is selected progressively one step at a time.
Directive Gain, usually expressed in dB, refers to the following definitions: 1. Of an antenna, the ratio of (a) 4Ï€ times the radiance, i.e., power radiated per unit solid angle (watts per steradian), in a given direction to (b) the total power, i.e., the power radiated to 4Ï€ steradians. 2. Of an antenna, for a given direction, the ratio of the radiance produced in the given direction to the average value of the radiance in all directions. If the direction is not specified, the direction of maximum radiance is assumed.
Directory Assistance Trunk Group
Directory Assistance Trunk Group is a trunk group that provides the means for customers or operators to obtain listed directory numbers and newly connected numbers. Applications commonly employ the following types of trunk groups: End Office to Trunk, Concentrator, End Office to Desk, Tandem to Trunk Concentrator, Tandem to Desk, Cord Switchboard to Trunk Concentrator, End Office to Automatic Call Distributor, and Tandem to Automatic Call Distributor.
Directory Number is the telephone numbers assigned to subscribers' main stations, which is typically listed in the phone book or directory.
Disparity refers to the digital algebraic sum of set of signal elements in Pulse-code modulation (PCM). The disparity will be zero and there will be no cumulative or drifting polarization if there are many positive elements ("1s") as there are negative elements ("0s").
Dispersion-limited operation is operation of a communications link in which signal waveform degradation attributable to the dispersive effects of the communications medium is the dominant mechanism that limits link performance. Dispersion is the filter-like effect that a link has on the signal, due to the different propagation speeds of the eigenmodes of the link. Practically, this means that the waveform at the input will be different from the waveform at the output of the link.
Distinctive Call Waiting Tone is a feature in telecommunication system that enable a customer who has call waiting feature to hear a distinctive call waiting tone for those incoming calls from a preselected number while they are talking. This feature is sometimes called VIP Alert or Call Selector.
Distribution Cable is a hierarchical level of cable plant usually referring to that cable which is installed between the trunk or feeder cable and the drop cable to a customer's premises.
Diversity, in telecommunications system, refers to the technique of using one, two, or more separate transmission channels. These channels may be along the same paths, in which case the diversity is that of frequency or polarization. The channels may be along separate physical paths, in which case there is a space diversity.
Digital Loop Carrier (DLC) is an equipment that combines a number of individual phone line signals into a single multiplexed digital signal for local traffic between a central office (of a telephone company) and a business complex or other outlying service area. Typically, up to 24 analog voice calls are combined into a single signal and transmitted over a single copper T-carrier system or E-carrier line, an optical fiber cable, or a wireless connection. In a home, business, or other installations using digital loop carrier, the analog phone lines of individual users are connected to a local DLC box which then converts the analog signals into digital and combines (multiplexes) them into one signal that it sent to the phone company's central office on the single line. At the central office, the combined signal is separated back into the original signals. Digital loop carrier can carry traffic for regular phone calls (so-called plain old telephone service) and Integrated Services Digital Network (ISDN) service. Approaches have been developed for using DLC to handle the higher bandwidth of Digital Subscriber Line (DSL) service. Digital loop carrier is typically used as an efficient way to provide service to an office building or complex and to extend service to new areas outside the current local loop. DLC is also used to set up telephone services in emergency situations.
SS7 Diagonal Link (D-Link) connects a secondary (e.g., local or regional) STP pair to a primary (e.g., inter-network gateway) STP pair in a quad-link configuration. Secondary STPs within the same network are connected via a quad of D-links. The distinction between a "B" link and a "D" link is rather arbitrary. For this reason, such links may be referred to as "B/D" links.
DLTU: Digital Line and Trunk Unit
Digital Line and Trunk Unit (DLTU) is a Lucent term which refers to a telecommunication device or component of 5ESS switch that provides the interface to digital trunks and lines.
Delta Modulation (DM) is a method of sampling and converting analog signals to digital signals. It is based on encoding the direction of signal change, indicating the direction of signal change with a single bit.
Digital Multiplex System (DMS) refers to a family of switching systems made by Nortel Networks that provides digital circuit-switched service for voice and data transmission, and packet switched service for data transmission. DMS is characterized by the use of pulse code modulation (PCM) and time division multiplexing (TDM) throughout the switched network. The system allows the direct switching of PCM signals used in transmission systems without their conversion to analogue format
DMS-10 Digital Switching System
DMS-10 Digital Switching System is a family of time division multiplexed digital switching systems for local, tandem, and toll applications, by the Nortel Networks (formerly Northern Telecom). DMS-lOE digital switching system is a small Class 5 digital switch that can satisfy the need as a Community Dial Office (CDO) replacement vehicle. This system can be expanded to 8000 subscriber lines. The DMS-lOE digital switching system offers Custom Calling Features, CAMA, LAMA (Local Automatic Message Accounting), Integrated Business Services (IBS), Equal Access, and Operations Support System (OSS) interfaces.
DMS-100 Digital Switching System
DMS-100 Digital Switching System is a large local Class 5 digital switching system that can be expanded up to 100,000 subscriber lines. Major features offered include LAMA, Integrated Business Network (IBN), Equal Access and OSS interfaces. The DMS-100 digital switching system is manufactured by Northern Telecom Ltd., now called Nortel Networks.
DMS-200 Digital Switching System
DMS-200 digital switching system is a large toll/tandem digital switching system that can be expanded up to 60,000 trunk circuits. Major features offered include CAMA, Traffic Operator Position Service (TOPS), CCIS, Equal Access, and OSS interfaces. The DMS-200 digital switching system is manufactured by Northern Telecom Ltd., now called Nortel Networks.
Discrete Multitone (DMT) is a method of separating a Digital Subscriber Line (DSL) signal so that the usable frequency range is separated into 256 frequency bands (or channels) of 4.3125 kHz each. Discrete multitone uses the fast Fourier transform algorithm for modulation and demodulation. Dividing the frequency spectrum into multiple channels allows DMT to work better when AM radio transmitters are present. Within each channel, modulation uses quadratude amplitude modulation (QAM). By varying the number of bits per symbol within a channel, the modem can be rate-adaptive.
DNIS: Dialed Number Identification Service
Dialed Number Identification Service (DNIS) is a telephone service that identifies for the receiver of a call the number that the caller dialed. It's a common feature of 800 and 900 lines. If you have multiple 800 or 900 numbers to the same destination, DNIS tells which number was called. DNIS works by passing the touch tone digits (dual tone multi-frequency or MF digits) to the destination where a special facility can read and display them or make them available for call center programming.
Dynamic Overload Control (DOC) is a control application that is automatically activated by switching systems to speed up call processing and limit attempts from connected offices.
DOD communication system, the US Department Of Defense (DOD) communication system, is one of the most advanced communication systems in the world. DOD communication systems are used not only for the administration of the Department, but, most critically, for the command and control of force structures. To this end, the Defense Communications Agency (DCA) strives to ensure that the Department's missions are carried out with state-of-the-art communications systems.
Direct Outward Dialing (DOD) is a service of a local exchange carrier that allows subscribers within a company's private branch exchange (PBX) system to connect to outside lines directly. Using DOD, a company can offer each person or workstation within the company the ability to dial numbers directly, without the need to go through an operator or dial other numbers first. DOD is often used together with Direct Inward Dialing (DID).
Double Order Tone is one of the Order Tones. For the double-order tone, the signal is two short spurts of High Tone in quick succession, and means that the operator should pass only the desired number.
Double-ended Synchronization is a synchronization control scheme used in two connected exchanges in a telecommunications network. In Double-ended synchronization, the phase error signals used to control the clock at one telephone exchange are derived by comparison with the phase of the incoming digital signal and phase of the internal clocks at both exchanges.
Dial Pulse (DP) is a short, direct current signal which is produced by, or simulated to look like, the opening and closing of contacts in a rotary-dial telephone when numbers are dialed. Dial pulses control the action of telephone switching equipment.
Destination Point Code (DPC) refers to the scheme in SS7 signaling to identify the receiving signaling point. In SS7 network, the point codes are numeric addresses which uniquely identify each signaling point.
DPCM: Differential Pulse-Code Modulation
Differential Pulse-Code Modulation (DPCM) is a PCM technique that codes the difference between sample points to compress the digital data. Because audio waves propagate in predictable patterns, DPCM predicts the next sample and codes the difference between the prediction and the actual point. The differences are smaller numbers than the numerical value of each sample on the full scale and thereby reduce the resulting bitstream
DPSK: Differential Phase Shift Keying
Differential Phase Shift Keying (DPSK) is a digital modulation format where information is conveyed in phase difference of a carrier signal between consecutive symbols.
DRE: Directional Reservation Of Equipment
Directional Reservation Of Equipment (DRE) is a control application that reserves trunk capacity for incoming traffic.
Drift is a term in telecommunication system that is a comparatively long-term change in an attribute or value of a system or equipment operational parameter. Drift is usually undesirable and unidirectional, but may be bidirectional, cyclic, or of such a long-term duration and low excursion rate as to be negligible. The drift can be characterized as "diurnal frequency drift" and "output level drift".
Drop refers to the following meanings in telecommunications: 1. the portion of a device directly connected to the internal station facilities, such as toward a switchboard or toward a switching center. 2. a wire or cable between a building and a pole or cable terminus. 3. test jacks on the central office side.
Digital Signal 2 (DS2) refers to a higher level digital frame made of four T1 frames and transmitted at 6.312 Mbps.
DSB-RC: Double-SideBand Reduced Carrier
Double-SideBand Reduced Carrier (DSB-RC) is a transmission scheme in which (a) the frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier and (b) the carrier level is reduced for transmission at a fixed level below that which is provided to the modulator.
DSB-SC: Double-SideBand Suppressed Carrier
Double-SideBand Suppressed Carrier (DSB-SC) is a transmission scheme in which (a) frequencies produced by amplitude modulation are symmetrically spaced above and below the carrier frequency and (b) the carrier level is reduced to the lowest practical level, ideally completely suppressed.
Dispersion-shifted fiber (DSF) is a type of single-mode fiber designed to have zero dispersion near 1550 nm. Dispersion Shift Fiber (DSF) is specified in ITU-T G.653. It has had dopants added which shift the zero-dispersion wavelength from the natural 1300 nm in silica-glass fibers to the minimum-loss window at 1550 nm.
DSI: Digital Speech Interpolation
Digital Speech Interpolation (DSI) is a technique of sharing voice communication paths among a larger number of users by means of allocating the silent periods inherent in human speech to active uses. An earlier technology was called Time Assignment Speech Interpolation or TASI. The technique is somewhat analogous to that of the statistical multiplexing of data transmission.
Defense Switched Network (DSN) is a worldwide private-line telephone network. Multilevel precedence and preemption (MLPP) capabilities on the DSN are utilized by command and control users to ensure that the highest-priority calls achieve connection quickly, especially during a crisis situation. The DSN also provides global data and video services using dial-up switched 56 kbps or 64 kbps Integrated Services Digital Network (ISDN) services.
Data Signaling Rate (DSR) refers to the aggregate signaling rate at which data pass a point in the transmission path in a data transmission system.
DS-SMF: Dispersion-Shifted Single Mode Fiber
Dispersion-Shifted Single Mode Fiber (DS-SMF) is a type of optical fiber in a telecommunications transmission system using single-mode fiber that is best designed for longer transmission distances, making it suitable for long-distance telephony and multichannel television broadcast systems.
Data Service Unit(DSU), often referred to together with CSU as CSU/DSU, is the device used in digital transmission that adapts the physical interface on a Data Terminal Equipment(DTE) device to a transmission facility, such as T1 or E1. The DSU also is responsible for such functions as signal timing.
DSX: Digital Signal Cross-Connect
Digital Signal Cross-connect (DSX) is a cross-connection point for DS-1 signals.
Digital Signal Cross-connect Level 1(DSX-1) is a standard that defines the voltage, pulse width and plug and socket for connecting DS-1 (T1) signals.
DTMF: Dual Tone Multifrequency
Dual Tone Multifrequency(DTMF), also known as Touch Tone or Tone Dialing, is used for telephone signaling over the line in the voice frequency band to the call-switching center. DTMF is the tones generated when a button is pressed on a telephone, primarily used in the U.S. and Canada. DTMF is an example of a multifrequency shift keying (MFSK) system and is standardised by ITU-T Recommendation Q.23.
Data Transfer Process (DTP) refers to the process in telecommunications system that establishes and manages the data connection. The DTP can be passive or active.
Dual Access refers to the following meanings in telecommunication system 1. The connection of a user to two switching centers by separate access lines using a single message routing indicator or telephone number. 2. In satellite communications, the transmission of two carriers simultaneously through a single communication satellite repeater.
Dual seizure refers to the condition when two exchanges attempt to seize the same circuit at approximately the same time (kin to a two-way operation mode).
Duplex refers to a channel or a device which can communicate in both directions simultaneously. There are varous forms of duplex such as full duplex and half duplex.
DX Signaling is a signaling process used on long metallic circuits. The process uses a bridge circuit to detect the small current signals. The term DX is an old term used to refer to distant transmission.