Glossary of Telecom Terms : D

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D Channel
The D channel is a packet-switched channel that carries signaling and control for B channels. In Basic Rate ISDN (BRI) applications, it can also support customer packet data traffic at speeds up to 9.6 kilobits per second.


Daily Usage Files (DUF)
Daily reports providing data enabling CLECs to bill end users for usage charges incurred. Learn more.


Dark Fiber
A Verizon Wholesale solution offered to customers that provides an unlit, continuous fiber optic strand within an existing, in-place Verizon fiber optic cable sheath without fiber optic transmission equipment or intermediate repeaters. Learn more.


Database (DB)
A collection of data organized in a structured manner so that information can be readily retrieved.


Data Communication Equipment (DCE)
Devices and connections, such as printers or modems, of a communications network; connect the communication circuit between the data source and destination. See Data Terminal Equipment (DTE).


Data Local Exchange Carrier (DLEC)
A carrier that primarily transports data with no voice grade services.


Data Service Unit or Digital Service Unit (DSU)
Device that connects data terminal equipment (such as a personal computer or a LAN) to a digital telephone line to allow fully digital communications; in effect, the digital equivalent of a modem.


Data Terminal Equipment (DTE)
Refers to devices such as personal computers or data terminals, as opposed to Data Communications Equipment (DCE) such as printers or modems.


Date Call Day Indicator
The calendar day on which the call was placed.


Date Call Month Indicator
The calendar month in which the call was placed.


See decibel.


A unit used to express power level in decibels relative to one milliwatt.


A unit used to express power level referred to, or measured at, a zero transmission level point (0TLP).


A unit used to express noise power relative to one picowatt measured with C message weighting.


A unit used to express noise power relative to one picowatt measured with C message weighting.


A unit used to express noise power in dBrnC referred to, or measured at, a zero transmission level point (0TLP).


See Direct Access Customer Service.


See Data Communication Equipment.


See Digital Cross-Connect System Functionality.


Decibel (dB)
The logarithmic unit of signal power ratio most commonly used in telephony. It is used to express the relationship between two signal powers, usually between two acoustic, electric, or optical signals.


Dedicated LAN
Network segment allocated to a single device. Used in LAN switched network topologies.


Dedicated Line

  1. A communications circuit or channel provided for the exclusive use of a particular subscriber. Dedicated lines are used for computers when large amounts of data need to be moved between points. Also known as a private line.
  2. A transmission circuit installed between two sites of a private network; it is "open," or available, at all times.

Dedicated SONET Ring
A private dedicated fiber-based optical ring service offered by Verizon Wholesale. Learn more.


Default Route
Entry in a routing table that can redirect any frames for which the table has no definitive listing for the next hop.


Amount of time a call spends waiting to be processed.


Destination Point Code (DPC)
The part of a routing label that identifies where an SS7 signaling message should be sent.


Dial Pulse (DP)
A type of switched access line address signaling that uses rapid loop open and loop closure signals (pulses) to indicate the digit being dialed. The digits, 1 through 9, are represented by a defined number of pulses; the digit zero is represented by ten pulses.


Dial Up
A type of communication that is established by a switched-circuit connection using the telephone network.


Dialing Parity
A property of a dialing plan under which all end users dial the same number of digits regardless of which competing carrier is selected to provide transport. Under a plan that provides dialing parity, end users do not have to dial extra digits to use the service of a non-dominant carrier. For example, if a Verizon end user must dial 11 digits (10 +1) to make an intraLATA toll call from community A to community B, a competing carrier's intraLATA toll end user must also be able to make the call by dialing 11 digits.


See Dispatch In/Dispatch Out.


Digital or Digitized
Any type of information that can be output, transmitted and interpreted as individual bits of binary information (the use of the numbers 0 and 1), using electrical or electronmagnetic signals that can be modulated to convey their specific content.


Digital Certificate
An electronic identifier that ensures a Certification Authority, such as Verizon, that a computer requesting access to specific applications has been verified, registered and secured via message encryption, by Verizon Security.


Digital Cross-Connect System Functionality (DCS, DSX)
Functionality that provides electronic cross connection for individual constituent digital signals within a high-speed digital line. There are two unbundled types of DCS available: Narrowband and Wideband. In both cases, the DCS functions are: demultiplexing an incoming higher-rate, electronic digital line into its constituent signals and switching those signals via the matrix to a different time slot on an outgoing higher-rate line. The combination of these functions allows for aggregation, grooming and redistribution of traffic in order to increase network use and efficiency.


Digital Data Service
Low-cost, digital connections for transmitting simultaneous two-way synchronous data at speeds of 2.4, 4.8, 9.6, 19.2, 56 and 64 Kbps. Learn more.


Digital Signal 0 (DS0)
A Special Access Service offering a 64 Kbps high-bandwidth dedicated circuit, that delivers quality that typically can't be duplicated with unconditioned analog circuits. Learn more.


Digital Signal 1 (DS1)
A Special Access Service that provides virtually error-free voice, video and data transmission at speeds up to 1.544 Mbps. Learn more.


Digital Signal 3 (DS3)
A Special Access Service comparable to having 672 voice-grade channels capable of handling multiple data streams in high volume at speeds up to 44.736 Mbps (commonly referred to as a 45 Megabit channel). Learn more.


Digital Subscriber Line (DSL)
A generic name for a group of enhanced speed digital services provided by telephone service providers. DSL services run on twisted-pair wires; they carry both voice and data. Learn more.


Digital Subscriber Line Access Multiplexer (DSLAM)
Technology that concentrates traffic in ADSL implementations. Located in the central office.


Digital Switch
A computer that electronically switches digitally encoded messages through the telephone network. Operates faster, more efficiently and more flexibly than an analog switch.


Digital Transmission
A mode of transmission in which all information is transmitted in digital form as a serial stream of pulses. Sound waves and other information are converted into binary computer code (a series of 0s and 1s) and transmitted to the end point. At the end point, binary code is converted back into the original format. Digital transmission provides sharper, clearer, faster transmission than analog transmission.


Digital Two-Wire Link or Loop
Provides an enhanced channel equivalent to a two-wire loop less than 18,000 feet with total bridge tap less than 6,000 feet from an end user's premises to a point of interconnection in Verizon's central office.


Digital Unbundled Port Services (DUPS)
An element, not bundled with a loop or transport facility, that provides digital access to the functionality of a local switching system.


Direct Access to Directory Assistance Listings DB
A Verizon Wholesale service that provides direct access to Verizon's Operator Services Directory Assistance regional databases. Learn more.


Direct Current (DC)
The uni-directional flow or movement of electric charge carriers (which are usually electrons) through a conducting material such as a metal wire.


Direct Customer Access Service (DCAS)
An electronic interface system provided by Verizon for CLECs and Resellers to facilitate the ordering, provisioning and maintenance of UNEs.


Direct Trunked Transport
Transport of Switched Access Service over facilities dedicated to the use of a single Interexchange Carrier, without switching at the tandem, either between the serving wire center and the end office, or between two Interexchange Carrier designated telephone service provider offices.


A database for end user Directory Listing information. Directories are offered in book form as well as via Web based applications.


Directory Assistance
A service that provides end user Directory Listing information to customers


Directory Assistance Enhanced Services
A Verizon Wholesale Operator Service that provides end user customers with information over the phone on restaurants, movies, businesses, weather, sports, and more. Learn more.


Directory Assistance Listing Service
A Verizon Wholesale Operator Service that provides access to Verizon's customer listing database. Learn more.


Directory Listing
A standard directory listing includes the name, address and telephone number of an organization/firm/individual.


Directory Listing Inquiry (DLI)
A Verizon Wholesale local pre-order transaction that allows the CLEC to access the listing data belonging to an end user. Learn more.


Disaster Recovery
The pre-defined use of alternative network circuits to re-establish communications channels in the event that primary channels are disconnected or malfunctioning.


Dispatch In/ Dispatch Out (DI/DO)
Refers to the source of a reported trouble on a telephone circuit: Dispatch In signifies the problem is likely within the central office and that an inside technician may be assigned to troubleshoot and fix the problem; Dispatch Out signifies the problem is likely on the loop portion of the circuit and that an outside technician has been assigned the problem.


See Data Local Exchange Carrier.


See Directory Listing Inquiry.


See Dial Pulse.


See Destination Point Code.


Disconnect Supervision
An on-hook supervisory signal end at the completion of a call.


See Digital Signal 0.


See Digital Signal 1.


A Verizon Wholesale UNE service offering providing a trunk port DS1 level electrical interface to the local switch for the termination of digital PBX systems. Learn more.


See Digital Signal 3.


DS3 Loop
A two-point digital channel which provides for simultaneous two-way transmission of serial, bipolar, return-to-zero isochronous digital electrical signals at a rate of 44.736 Mbps + 20 ppm. Learn more.


DS-1 Message Trunk (DS1MT)
A digital trunk-side port of a local switching system that operates at 1.544 megabits per second and is channelized to provide twenty-four 64 kilobits per second or 56 kilobits per second for the message telecommunications network.


See Digital Subscriber Line Access Multiplexer.


See Digital Service Unit (DSU).


Digital System Cross-Connect (DSX) Panel or Frame
A bay or panel to which high-speed lines such as T-1 lines are attached. Used in small office applications where only a few digital trunks are installed, a DSX permits cross connections.


See Digital Subscriber Line.


See Digital System Cross-Connect Panel or Frame.


See Data Terminal Equipment.


See Dual Tone Multi-Frequency.


Dual Homing
Where a device is connected to the network via two independent access points (points of attachment). One access point is the primary connection; the other is a standby connection that is activated in the event the primary connection fails.


Dual Tone Multi-Frequency (DTMF)
A type of switched access line address signaling that uses two tones transmitted simultaneously to indicate a digit (0 to 9) or character (* or #).


See Daily Usage Files.


Duplex Signaling
A type of Direct Current (DC) signaling that employs symmetrical and balanced signaling equipment at each end of the loop. One simplex conductor of the 4-wire loop is used for signaling and the other simplex conductor is used for ground potential compensation.



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