A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
D
D-4 framing format - (1) Method of dividing a T1 ro DS-1 level circuit into 24 equal channels with each channel carrying digitized voice and signaling information in each eight-bit byte. Consists of 193 information bits. (2) Used to identify both the channel and signaling frames.
D Bank - Aka Channel Bank. A device that breaks down a T1 circuit into its 24 channels.
Dark Fiber - Fiber optic cables without multiplexers or amplifiers. Carriers can lay dark fiber and add SONET, Gigabit Ethernet and wavelength division multiplexers at a later date.
Data - Anything that is transmitted or processed digitally.
Data Above Voice (DAV) - Transmission system which carries digital data on a portion of the microwave radio spectrum above the frequency used for voice transmission.
Data Channel (D-channel) - (1) Unidirectional data transmission path with transmission terminal equipment at both ends. (2) A 16 kpbs or 64 kpbs channel reserved for signaling and other packetized services in an integrated services digital network (ISDN) configuration.
Data Communications - (1) Transfer of information between a source and a destination via one or more data links, according to appropriate protocols. (2) Transmission and reception of data, often including operations such as coding, decoding, and validation.
Data Encapsulation - Used for transferring application or user data from one layer of the OSI/SNA/DNA protocol stack to another. At the upper 3 layers, the units are called Packet Data Units. At the transport layer, they are called Segments. At the network and data-link layer, the units are called frames; each layer adds its own header info.
Data Link - Physical resources that form a path for data communication.
Data Link Connection (DLC) - Half duplex data channel (one way) - from the user connection to a frame relay network. Combining DLC's from each user provides full-duplex communications ability, aka Permanent Virtual Circuit (PVC).
Data Link Connection Identifier (DLCI) - A number given to a DLC - part of the frame-relay packet header that is used to name the logical channel the frame will be routed to. The header has space for 10 bits of data - this DLCI is embedded in the data stream from beginning to end of the transmission, and the values are different for every individual router in a network. Very similar to a Logical Channel Number (LCN) - and performs the same tasks as a LCN.
Data Rate - Data transmission speed measured in bits per second (bps).
Data Transfer Mode - Virtual circuit condition after a call is successfully established. Circuit remains in data transfer mode until it is cleared or until an escape-to-command mode is accomplished. Data packets carrying customer information and exchange in this virtual circuit mode.
Data Service Unit (DSU) - See CSU.
Dedicated Access - Connection between a customer's premises and an interexchange carrier (IXC). All transmissions on this dedicated line are automatically routed to the IXC. Provided by a local exchange carrier (LEC), alternate access provider or IXC.
Dedicated Channel - A channel dedicated to a specific customer within a T1 or T3 circuit.
Dedicated Circuit - Aka Private Line. A pair of wire, or two pairs of wire in a T1, that provides a dedicated high speed connection between your location and a specific location of your choice. As it does not go through switching circuitry, it is on all day, every day, with no dialing.
Dedicated Line - Permanently assigned path to specific data terminals which is not part of a switched network. Synonym: private line or dedicated transport.
Demarc (Dmarc, Demarcation Point) - Where the local phone company hands off a telephone circuit, separating the customer owned equipment from the telephone company equipment - where responsibility for the circuit's performance separates.
Dial Exchange - Automated switching junction or central office.
Dial Tone - A analog method of signaling - from the PBX or telephone company central office switch that signals the caller that a call can be placed.
Dial-up Line - (1) Communications circuit that is established by a switched circuit connection. (2) Any circuit available over the public switched network.
Digital - A signal that has only two levels per cycle, rather than infinite levels found in an analog signal. Easy to regenerate, and as the regenerating device only looks at two levels of signal, unwanted noise is eliminated.
Digital to Analog Converter (DAC) - The part of a channel bank that encodes analog voice streams into a stream of binary digits, sampling the callers voice at 8000 times per second, within one of 256 possible sample levels. When the data stream reaches its destination, the process then occurs in reverse.
Digital-Access Cross-Connect System (DACS) - Also known as Digital Cross-Connect System (DCS). Part of both a local and long-distance company's network that enables any circuit it interfaces with to be cross-connected from one path to another within the network.
Digital Cross Connect System (DCS) - See DACS.
Digital Loop Back - A transmission equipment feature; allows user to reroute a signal back to the source, rather than into the termination or end equipment to determine if signal is good or bad.
Digital Loop Carrier (DLC) - Equipment that provides two dial tones over a single twisted copper pair - allows two phone to work on one phone line.
Digital Multiplex System (DMS) - (1) Means of utilizing technologies that provide digital switched service for voice and data transmission. (2) Switched network method characterized by the use of pulse code modulation (PCM) and time division multiplexing (TDM). Allows the direct switching of PCM signals used in transmission systems without conversion to analog format.
Digital Service (DS) - Prefix for digital service circuits.
Digital Service Cross Connect (DSX) - Digital service termination/patch panel, allowing DS1 and DS3 circuits to be monitored by test equipment.
Digital Subscriber Line Access Multiplexer (DSLAM) - Refers to x Digital Subscriber Loop (xDSL) service from a central office; the distribution device for this service that combines and separates different formats of communications (voice, data, video, etc.) and routes them to their respective hosts.
Digital Subscriber Line (DSL) - Aka ISDN Basic Rate Interface (BRI).
Digital Switched Service (DSS) - Switched telephone line that is offered in digital form. As most telephone lines that leave a customer's location via a T1 line are converted to analog when they reach the telephone company central office - a DSS line is run in digital form.
Direct Inward Dial (DID) - The line from the local phone company to a PBX switch, without going to a console operator.
Direct Outward Dial (DOD) - PBX feature that allows telephone stations to access (or not access) an outside dial tone.
Discard Eligibility (DE) - One of the bits in the 16 bit header of a frame-relay frame, and is set to 1 to notify the network that its frame should be discarded at the first onset of congestion on the network.
Disco (Disconnect) - What many cable and telephone companies call their disconnect orders (i.e. "Disco Orders")
Distinctive Ringing - PBX system feature, allowing for different rings depending on the type of call; for example, a call coming from outside the system can be set to ring differently than internal calls from co-workers.
Domain - An internet address, such as 225.225.225.10, which can be identified through DNS as a name.
Domain Name System (DNS) - Aka domain name server. A way of identifying network addresses on the Internet or in LAN's; for example, allows a server to be named, or a website URL to be listed, rather than using an identifier like 225.225.225.10. It is easier to remember a domain name, rather than a number.
Downstream - In an asymmetrical broadband transmission - the bandwidth/information flow away from the service provider to the customer. ADSL and cable modem/internet services are asymmetrical; where the downstream flow is larger than the upstream flow.
Drop - (1) Portion of an outside telephone plant which extends from the telephone distribution cable to the subscribers premises. (2) Connection point for terminal to a line.
DS-0 - Transmission rate of 64 kbps - equals one voice line.
DS-1 - T-1 transmission rate of 1.54 million bits per second - 24 channels of 64 kpbs.
DS-3 - Transmission rate of 44 mbps with 672 channels (equivalent to 28 T-1 lines)
Dual Tone Multiple Frequency (DTMF) - When you push the buttons on a touch-tone phone; these are the tones you hear, which are a combination of two frequencies. For example, the numbers 1,2, and 3 all generate a tone at 697 Hz, and the numbers 2,5,8, and 0 generate tones at 1336 Hz. When you push the 5 button - it generates two tones - one at 697 Hz, the other at 1336 Hz.
Dual Homing - Aka alternate routing, redundancy, or self healing.
Dynamic Host Configuration Protocol (DHCP) - A protocol that is capable of automatically configuring the iP address, subnet mask, default gateway, and DNS addresses within a network.
Dynamic Routing - Where a router's operating system adjusts its routing/address tables automatically when changes occur in the internetwork.