Dynamic Bandwidth Allocation.
Database administrator. The individual in the organization with the responsibility for the design and control of databases.
dBA. dBA is a measure of sound level. The ratio for determining dB in this case is the ratio between the sound level measured with a microphone and an implicit reference sound level, namely 0db, which is defined to be approximately equal to the threshold of human hearing. 45dBA is a very faint whisper, 75 dBA is typical conversation, 100 dBA is about how loud a Walkman can get, and 120dBA is a jet plane taking off at 20 feet away from the engine. The "A" represents a special filter which is used to take into account the fact that people are less sensitive to very low and very high frequencies. The dBA system is used for measuring background sounds like computer fans or office noise. A system with a different filter called dbC is used when very loud sounds are being measured. This definition courtesy APC.
Decibels dipole. A measurement of signal gain used in radio antenna design. Specifically, dBd refers to signal gain in a dipole radiator, which is a basic transmitting antenna consisting of two rods with their ends slightly separated. In the most basic form, the dipole radiator comprises two parallel horizontal rods. See also dB, dBd, and Decibel.
Decibel relative to a carrier level. See also dB.
dBi. Decibels isotropic. A measurement of signal gain used in radio antenna design. Specifically, dBi refers to signal gain in an isotropic radiator, which is a transmitting antenna that radiates a signal equally well in all directions. See also dB, dBd, and Decibel.
Don't Believe It. This is used in telecontrol systems for electricity transmission/distribution systems to denote an unreliable state change at a substation RTU (Remote Termination Unit) i.e. both inputs have either gone high or low. They should normally be different. An alarm legend is then generated and sent to the NMS (Network Management System) with a status of DBI instead of the normal ON or OFF i.e.
BREAKER DBI 00
See also RTU.
Also called D-BIT. The delivery confirmation bit in an X.25 packet that is used to indicate whether or not the DTE wishes to receive an end-to-end acknowledgment of delivery. In short, a bit in the X.25 packet header that assures data integrity between the TPAD and the HPAD.
dBm. Decibel (dB) ratio (log10) of Watts (W) to one milliwatt (1mW). In other words, the output power of a signal referenced to an input signal of 1mW (milliWatt). Similarly, dBm0 refers to output power, expressed in dBm, with no input signal. (O dBm = 1 milliwatt and -30 dBm = 0.001 milliwatt). See also dB and Decibel.
Identifier meaning "decibels referred to one milliwatt and corrected to a zero dBm effective power level;" used to state the relation of a signal level on a transmission line at other than a one-milliwatt point.
An identifier meaning decibels below reference noise referred to one milliwatt using psophometric weighting , dBmp is the ITU-T method for noise measurements. dBmp has a variance of approximately 2 dB from dBrn methods . See also dBrn.
Database management system. A computer program that manages data by providing the services of centralized control, data independence, and complex physical structures. Advantages include efficient access, integrity, recovery, concurrency control, privacy, and security. A DBMS enables users to perform a variety of operations on data, including retrieving, appending, editing, updating, and generating reports .
A decibel measure in relation to one millivolt across a specific impedance. In CATV the impedance used is 75 ohms. See Cable TV.
DeciBels above Reference Noise. A ratio of power level in dB relative to a noise reference. dBrnC uses a noise reference of -90 dBrn, as measured with a noise meter, weighted by a frequency function known as C-message weighting which expresses average subjective reaction to interference as a function of frequency. dBrn is used mostly in North American telecommunications work. See also dB and dBmp.
An identifier meaning deciBels above Reference Noise using C-message weighting. The measurement is accomplished through a filter approximating a type C voice messaging channel, and is the North American nomenclature for a DDD (Direct Distance Dialing) trunk channel. The reference is 90 dB below one milliwatt of power. See also dBrn and dBrnC0.
Pronounced "de-brink-o," it is an identifier meaning deciBels above Reference Noise using a filter approximating a type C voice messaging channel adjusted for equivalence to a 0 dBm equivalent circuit point. It is the same as dBrnC, except that it is corrected to a TLP (Transmission Level Point) of 0dB. See also dBrnC and TLP.
Direct Broadcast Satellite. A term for a satellite which sends relatively powerful signals to small (typically 18-inch diameter) dishes installed at homes . See C Band , 1994 and Direct Broadcast Satellite.
Dial Back-Up. A method of providing redundancy in the event of the failure of a leased line or even a network, dial back-up automatically re-establishes the connection through the PSTN (Public Switched Telephone Network) on a dial-up basis. For example, ISDN commonly is used for dial back-up for Frame Relay networks.
Decibels below 1uW. Decibels relative to microwatts. See also dB.
Decibel ratio of Volts to one microvolt. See also dB and Decibel.
A decibel measure referenced to one watt without reference to any impedance.
Direct Current. The flow of free electrons in one direction within an electrical conductor, such as a wire. The current may be constant or it may pulsate, but it always is in one direction. See also AC.
A device which blocks direct current but passes radio frequencies, audio frequencies, or alternating current depending upon the function of the block.
See Power Supply.
A collection of ways of transmitting communications signals using direct current ” the type of current produced by a dry cell household "D" cell battery. DC signaling is only used on cable. It's an out-of-band signal.
Defense Communication Agency. The U.S. government agency under the DOD (Department of Defense) that was responsible for installation and operation of Defense Data Networks, including the ARPANET and MILNET, and PSNs. DCA was folded into DISA (Defense Information Systems Agency) in 1991. See also DISA.
Document Content Architecture. The IBM approach to storing documents as two types of document group : draft documents and final form documents. For presentation, the draft document is transformed into a final document through an office system.
Direct Carrier Administration System.
Data Communications Channel. Channels contained within section and line overhead used as embedded operations channels to communicate to each network element. An AT&T SONET term.
An ATM term. Data Country Code: This specifies the country in which an address is registered. The codes are given in ISO 3166. The length of this field is two octets. The digits of the data country code are encoded in Binary Coded Decimal (BCD) syntax. The codes will be left justified and padded on the right with the hexadecimal value "F" to fill the two octets.
Digital Compact Cassette. A digital version of the familiar analog audio cassette. A DCC recorder can play and record both analog and digital cassettes. But the digital ones will sound a lot better.
Digital Control CHannel. A channel used in most newer digital cellular and PCS systems for signal and control purposes between the mobile terminal device and the radio base station. See also Cellular and PCS.
Data Carrier Detect. Signal from the DCE (modem or printer) to the DTE (typically your PC), indicating it (the modem) is receiving a carrier signal from the DCE (modem) at the other end of the telephone circuit.
Dynamically Configurable Device. A dynamically configurable device is a fancy name for a Plug and Play device, so-called because you don't have to reboot the system after installing one.
Duty Cycle Distortion. See Jitter.
Data Communications Equipment. Also known as DCTE (Data Circuit Terminating Equipment). The classic definition of DCE is that it resolves issues of interface between Data Terminal Equipment (DTE) and a transmission circuit. Examples include LAN Network Interface Cards (NICs), CSUs and DSUs, modems, and ISDN Terminal Adapters (TAs). DCE may accomplish such functions as changes in electrical coding schemes, electro-optical conversion, and data formatting. The physical interfaces between DTE and DCE can take a variety of forms, one of which is the RS-232 "standard" developed by the Electronic Industries Alliance (EIA). The main difference between a DCE and DTE in RS-232 is the wiring of pins two and three in the male and female 25-pin connectors. But there is, of course, no standardization. When wiring one RS-232 device to another, it's good to know which device is wired as a DCE and which as a DTE. But it's actually best to go straight to the wiring diagram in the appendix of the device's instruction manual. Then you compare the wiring diagram of the device you want to connect and build yourself a cable that takes into account the peculiar (i.e., strange ) vagaries of the engineers who designed each product. In short, with an RS-232 connection, the modem is usually regarded as DCE, while the user device (terminal or computer) is DTE. In a X.25 connection, the network access and packet switching node is viewed as the DCE. DCE devices typically transmit on pin 3 and receive on pin 2. DTE (Data Terminal Equipment) devices typically transmit on pin 2 and receive on pin 3. See also DTE and RS-232. See also the Appendix for an excellent graphic representation of the RS-232 pinout.
Distributed Computing Environment. An industry-standard , vendor-neutral set of distributed computing technologies developed by the Open Software Foundation (OSF). According to The Open Group, successor to the OSF, DCE provides security services to protect and control access to data, name services that make it easy to find distributed resources, and a highly scalable model for organizing widely scattered users, services and data. DCE runs on all major computing platforms, supporting distributed applications in heterogeneous hardware and software environments.
Dispersion Compensation Grating. DCG overcomes the distortion of optical signals as they are transmitted through a network. Instead of trying to compensate for large amounts of signal dispersion at the end of a network, DCG periodically removes the distortion where needed along the transmission line. See Solitons.
A CLEC which specializes in delivering only data, most typically DSL services. See CLEC.
Digital Circuit Multiplication. A means of increasing the effective capacity of primary rate and higher level PCM hierarchies, based upon speech coding at 64 Kbit/s. Also a Digital Carrier Module.
Distributed Order Management.
Digital circuit multiplication equipment is a compression equipment capable of handling voice, data and facsimile signals. This equipment is utilized as a means of augmenting the capacity of digital transmission systems. It can be used in Satellite as well as cable. Some can compress as high as 20:1. See Digital Circuit Multiplication.
Disconnect frame. Indicates the fax call is done. The sender transmits before hanging up. It does not wait for a response.
Distributed Component Object Model. DCOM is Microsoft's distributed version of its COM, a language-independent component architecture (not a programming language). It is meant to be a general purpose, object-oriented means to encapsulate commonly used functions and services. COM encompasses everything previously known as OLE Automation (Object Linking and Embedding). Microsoft describes DCOM as "COM with a longer wire." See also COM.
Digital Communications Protocol.
Detailed Continuing Property Records. See PICS/DCPR.
Distributed Communications System. See Distributed Switching.
Digital Crossconnect System. A device for switching and rearranging private line voice, private line analog data and T-1 lines. A DCS performs all the functions of a normal "switch," except that connections are typically set up in advance of when the circuits are to be switched ” not together with the call. You make those "connections" by calling an attendant who makes them manually, or by dialing in on a computer terminal ” one similar to an airline agent's. See also Network Reconfiguration Service.
Digital Cellular System.
Digital Communications System.
DCS. A packet-switched network implemented in Belgium and operated by the Belgian government.
DCS is also the Avaya PBX-to-PBX private networking protocol over point-to-point or ISDN-PRI T-1s, (not unlike the Siemens' CORNET service.)
See DCS1000 below.
Digital Cellular System at 1800 MHz. A GSM (Global System for Mobile Communications) standard for cellular mobile telephony established by ETSI (European Telecommunications Standards Institute) for operation at 1800 MHz. In short, DCS 1800 is GSM adopted to the 1800 Mhz frequency band. This means that existing GSM phones won't be able to talk on the DCS 1800.
DCS stands for Digital Collection System or Data Collection System, according to unconfirmed reports. (The FBI doesn't particularly like to confirm things.) DCS1000 is a surveillance program developed by the FBI (Federal Bureau of Investigation) for the interception and analysis of e-mail. DCS1000 was originally known as Carnivore, a poorly- chosen name that created quite a controversy as the public conjured up visions of the FBI indiscriminately examining and eating their mail. DCS1000 is packet-sniffing program that is installed, on the basis of a federal warrant under U.S. wiretap laws, at an ISP site. Once installed, the program sorts through packet traffic to find the subject of e-mail packets on the basis of various criteria, including IP addresses. Privacy advocates fear that the program will be used to capture and analyze other packet traffic, indiscriminately.
Digital Carrier Termination.
Discrete Cosine Transform. A compression algorithm used in most of the current image compression systems for bit rate reduction, including the ITU-T Px64 standard for video conferencing. DCT represents a discrete signal or image as a sum of sinusoidal wave forms.
Digital Consumer Terminal. A set-top box that receives and converts digital video and audio signals to standard television format. The box also processes addressability transactions and stores and transmits pay-per-view (PPV) transaction information back to the MSO. Some advanced units include support for digital video recording (also called Personal Video Recorder), video-on-demand, and/or HDTV signal processing. See PVR.
Data Circuit Terminating Equipment. Also known as DCE (Data Communications Equipment). See DCE.
Desktop Computer Telephone Integration. Basically, providing a way for your computer to control your telephone set.
Digital Cordless Telephone US.
Digital Compressed Video.
Dotted Decimal Notation. See Dotted Quad.
DD, as in 600 DD. It represents the number of circuit pairs that are terminated , but not spliced. It seems that 600 DD is the term used in the West, while 600 XD would be used by those trained in the East.
Domain Defined Attribute. A way of adding additional information to the address of your electronic mail in order to avoid confusion between people of the same or similar name.
Digital Data Bank.
Direct Department Calling.
Digital Data Communications Message Protocol. A byte-oriented, link-layer protocol from Digital Equipment Corp., used to transmit messages between stations over a communications line. DDCMP supports half- or full-duplex modes, and either point-to-point or multipoint lines in a DNA (Digital Network Architecture) network.
Direct Distance Dialing. The "brand name" the Bell System used to call its Message Toll Telephone Network. It used the words "Direct Distance Dialing" to convince the public to dial their own long distance calls directly without the help of an operator.
See Dynamic Data Exchange.
Dynamic Data Exchange Management Library. A feature of Microsoft Windows.
Direct Dialing Inward. A British term. It is a service where a call made to a DDI number arrives direct, without the intervention of an organization's operator, at an extension or, if routed via an ACD, to a group of extensions. A specific DDI number can be assigned to each campaign. When an agent answers a call made to one of these DDI numbers, the relevant script and screen are displayed. This way the agent can give an appropriate response. British Telecom, the U.K.'s biggest phone company typically allocates DDI in contiguous ranges of 1,000-10,000 numbers .
Data Dependent Jitter. See Jitter.
Distributed Data Management Architecture. An IBM SNA LU 6.2 transaction providing users with facilities to locate and access data in the network. It involves two structures: DDM Source, and DDM Target. The DDM Source works with a transaction application to retrieve distributed data and transmits commands to the DDM Target program on another system where the data that has been requested is stored. The DDM Target interprets the DDM commands, retrieves the data and sends it back to the DDM Source that originated the request.
Defense Data Network. A network that provides long haul and area data communications and interconnectivity for DOD (Department of Defense) systems, and supports the DOD suite of protocols ( especially TCP and IP). All equipment attached to the DDN by military subscribers must incorporate , or be compatible with, the DOD Internet and transport protocols. The packet-switched portion of DDN was split off from ARPANET to handle U.S. military needs, at which time is was renamed MILNET (MILitary NETwork). The remaining ARPANET evolved into the public Internet. DISA (Defense Information Systems Agency) is responsible for the DDN. See also DDN NIC and MILNET.
Defense Data Network Network Information Center. Also called the "NIC," by those in the defense domain, the DDN NIC is responsible for the assignment of Internet addresses and Autonomous System numbers, the administration of the root domain, and the provision of information and support services to the DDN. See also DDN, INTERNIC and NIC.
Dynamic Domain Name Servers. See DNS.
Distributed Denial of Service. See Denial of Service Attack.
See Distributed Data Processing.
Datagram Delivery Protocol is an AppleTalk protocol that provides for datagram delivery to higher-layer protocols. DDP supports connectionless service between network sockets at the network layer (Layer 3) of the OSI Reference Model. See also AARP and AppleTalk.
Double Data Rate-Synchronous Dynamic Random Access Memory. A next -generation SDRAM that transfers data twice per CPU (Centralized Processing Unit) clock cycle, which doubles the data transfer of SDRAM. While the resulting performance level is higher, so is the cost. See also DRAM, EDO RAM, Flash RAM, FRAM, Microprocessor, RAM, RDRAM, SDRAM, SRAM, and VRAM.
Dataphone Digital Service, also called Digital Data System. DDS is private line digital service, offered in point-to-point and point-to-multipoint configurations. Data rates available include 2,400 bps; 4,800 bps; 9,600 bps; 56/64 Kbps; and 1.544 Mbps (T-1). DDS is offered on an inter-LATA basis by AT&T, MCI and Sprint, and on an intraLATA basis by the ILECs (Incumbent Local Exchange Carriers ). CLECs (Competitive LECs) often use DDS circuits for local loops , leasing the DDS facilities from the ILECs. DDS originally was an AT&T tariff offering, but now is considered to be a generic term.
Digital Data Storage. A DAT format for storing data. It is sequential ” all data that is recorded to the tape falls after the previous block of data.
Delay Dial Start Dial. A start-stop protocol for dialing into a switch.
Discard Eligible. The frame relay standard specifies that data sent across a virtual circuit in excess of that connection's Committed Information Rate (CIR) will be marked by the user as being eligible for discard in the event of network congestion. DE data is the first to be discarded by the network when congestion occurs, thus providing protection for data sent within the parameters of the CIR. It is the responsibility of the intelligent end equipment and/or protocol to recognize the discard and respond by resending the information. As a practical matter, few users are likely to volunteer to have frames discarded, and few manufacturers provide for the setting of the DE bit. See Oversubscription.
Designated Entities. Small businesses, businesses owned by members of minority groups and/or women, and rural telephone companies that meet size or other criteria established for specific services. Specifically, companies are either "entrepreneurs" (defined as entities, together with affiliates, having gross revenues of less than $125 million and total assets of less than $500 million) or "small businesses" (defined as entities, together with affiliates , having gross revenues of less than $40). The blocks reserved, in part, at the FCC for designated entities are the C and F blocks.
Used to describe a standard reflecting current or actual practice, but not having approval or sanction by any official standards-setting organization. In other words, a de facto standard is an unofficial standard that exists because sufficient companies adhere to it or because of market acceptance. Usually created by an individual manufacturer or developer ” hence, often used as a synonym for proprietary. The Hayes AT auto-dial modem command language is an example of a de facto standard. Very often, de facto standards form the basis for de jure standards. Ethernet was the basis of Institute of Electrical and Electronics Engineers (IEEE) or IEEE standard 802.3. Contrast with de jure.
Lee de Forest invented the vacuum tube in 1907. Until the invention of the transistor after World War II, all radio, long distance telephony and complicated electronics, including electronic computers, were derived from de Forest's invention.
Used to describe standards approved or sanctioned by an official standards setting organization. ITU-T Recommendation X.25 for packet data networks is an example of a de jure standard. Contrast with De Facto.
A telephone subscriber frequently pays a rate based on the average amount it costs a phone company to provide service to a group of subscribers, as opposed to the actual amount it costs the company to provide the particular service to that particular subscriber. As we move towards a more competitive, deregulated environment, costs are frequently being "deaveraged". When rates are "deaveraged", a subscriber's rate is based on the amount it actually costs a company to serve that subscriber, as opposed to the average cost. Of course, when you have a factory ” a gigantic phone system ” that serves many subscribers with many different services, fast, slow, analog, digital, long, short, etc. ” it's really very difficult, if not impossible , to figure out the cost of various services. So the term "de-average" tends to mean the phone companies drop the price of competitive services and raise the price of non-competitive services.
The reverse of pre-emphasis. A process used in frequency modulation detectors to reverse transmission pre-emphasis. See Pre-emphasis.
The process of extracting a data packet from the user data field of the encapsulating data packet.
De-install means to remove a piece of equipment that has been installed, but keep it in good condition so that it can be successfully installed some place else. When much of the telecom industry overexpanded in the late 1990s, several companies came along to offer "de-installing" services. Here's a description of one: Somera Communications, Inc. provides telecommunications carriers with a broad range of infrastructure equipment and related services designed to meet their specific and changing equipment needs. The Company offers its customers a combination of new and de-installed equipment from a variety of manufacturers, allowing them to make fast multi-vendor purchases from a single cost-effective source. See deinstall.
The process used by a correlator to recover narrowband information from a spread-spectrum signal.
This is a service that Bell Canada offers. It gives the customer a local number and access to their digital equipment where the number resides.
Dead Air refers to the silence received when placing a call to a valid telephone number. Dial tone is received, the valid number is dialed but you do not receive ring back tone, only dead silence. See also High and Dry.
When a telephone company worker begins work in a manhole, he or she must first open the manhole cover, and pump fresh air into the manhole for at least 20 minutes. The reason is that the air in the manhole will likely lack oxygen or contain toxic gases ” possibly leaked in from adjacent natural gas pipes. Should a worker descend into the manhole without first pumping fresh air in, he could die from breathing the air. This has happened . Most phone companies have lost workers in manholes. Telephone company workers have a generic name for the bad air in manholes. They call it dead air.
A dead cat bounce occurs when the price of a stock has fallen so constantly so far, that sufficient people think it can't fall any further and they buy it and the stock rises. The expression comes from the Wall Street saying: "Even a dead cat will bounce once if it is dropped from high enough."
Preferred stock that has no recession and no conversion rights.
In the 1500s, local folks started running out of places to bury people. So they would dig up coffins and would take the bones to a "bone-house" and reuse the grave. When reopening these coffins, 1 out of 25 coffins were found to have scratch marks on the inside and they realized they had been burying people alive . So they thought they would tie a string on the wrist of the corpse, lead it through the coffin and up through the ground and tie it to a bell. Someone would have to sit out in the graveyard all night the ("graveyard shift") to listen for the bell; thus, someone could be "saved by the bell" or was considered a "dead ringer."
In facsimile, the elapsed time between the end of scanning of one line and the start of scanning of the following line.
A cellular radio term. It denotes an area within a cell where service is not available. A dead spot is usually caused by hilly terrain which blocks the signal to or from the cell tower. It can also occur in tunnels and indoor parking garages. Excessive foliage or electronic interference can also cause dead spots. If you encounter a dead spot, tell your cellular radio supplier. They often will do something.
The paper version of a publication available in both paper and electronic forms. If you are reading my dictionary on paper, you are reading the dead tree edition.
During the Civil War, captured troops were placed in a field. They were told they could move wherever they wanted in the field except beyond a line that was drawn around the field. If they did, they would be shot. Thus the origin of the word deadline.
See Deadly Embrace.
Stalemate that occurs when two elements in a process are each waiting for the other to respond. For example, in a network, if one user is working on file A and needs file B to continue, but another user is working on file B and needs file A to continue, each one waits for the other. Both are temporarily locked out. The software must be able to deal with this.
Venture capitalists need to invest monies in promising new companies. But where to find them? You have to hang out a shingle, have a neat web site inviting submissions for money and have oodles of contacts who know millions of people. The key is deal flow. The more potential great deals that can flow your way, the better.
A dealer is simply a person who sells equipment ” hardware or software ” made by someone else. That dealer may be a distributor of Novell LAN software. Or that dealer may be in the secondary telecom equipment business, i.e. a company that buys and sells secondary market telephone equipment. Generally in the secondary equipment business, a dealer takes ownership of the equipment (see BROKER). He tests and refurbishes it before remarketing. An authorized dealer has a contract with the manufacturer to buy equipment at a preset price. He also has the added support of a manufacturer's warranty. An independent dealer has no formal agreement with the manufacturer. He uses a variety of sources to obtain equipment and his warranty is backed only by the company's internal resources.
British term meaning "trading turret ."
An application of ANI (Automatic Number Identification) technology that matches the caller's phone number with a database of dealer locations. The caller can then be transferred automatically or manually referred to the closest location.
British term meaning "trading room."
Suburbs around New Jersey where many AT&T employees live. Makes reference to the AT&T logo, which employees have dubbed "The Death Star" (from the Star Wars films ).
Does Everything But Eat. DEBE (pronounced Debbie) applies to any and all all-inone devices that seemingly does everything you could ever want. In other words, it does everything but eat.
The term telephone "debit card" covers three categories of a new type of telephone calling card, variously called "calling card" and "prepaid telephone card." The definitions are in flux. Here's the best shot at debit card: A telephone debit card is a piece of credit-card size plastic with some technology on it or embedded into it which represents the value of the money remaining on the debit card. Such money can be used to make phone calls. The technology on the card is most typically an integrated circuit, a magnetic strip, or bar codes which can be read by an optical reader. See Breakage, Calling Card and Prepaid Telephone Card.
A big provider of mobile telephone services in Germany. It is owned mainly by Daimler-Benz and Metro, a big retail group.
A MS-DOS program to examine or alter memory, load and look at sectors of data from disk and create simple assembly-language programs. MS-DOS DEBUG.COM lets you write some small programs. You can use DEBUG to correct problems in some programs.
A tool (program) that is used by programmers to help identify and fix problems ( bugs ) in a program.
Digital Equipment Corporation. An erstwhile leading manufacturer of minicomputers when there was still a market for minicomputers. The Unix operating system, developed at Bell Labs, ran on DEC computers. DEC, with its headquarters in Massachusetts and having sold so many computers to Western Electric for inclusion in central office switches and toll switches, used to be referred to as "Eastern Electric." Kenneth H. Olsen founded DEC in 1957 with three employees in 8,500 square feet of leased space in a corner of an old New England woolen mill. DEC fell upon hard times, when it completely ignored the PC, which quickly developed more power than the Dumb. Compaq bought DEC in June 1998 and fired many of its people and closed much of its production. The alleged reason for the costly acquisition was the DEC salesforce and its ultra -fast Alpha microprocessor. See DECnet.
A process used in networking in which the receiving system looks at the header of an arriving message to determine if the message contains data. If the message does contain data, the header is removed and the data decoded.
Group of communications products (including a protocol suite) developed and supported by Digital Equipment Corporation. DECnet/OSI (also called DECnet Phase V) is the most recent iteration and supports both OSI protocols and proprietary Digital protocols. Phase IV Prime supports inherent MAC addresses that allow DECnet nodes to coexist with systems running other protocols that have MAC address restrictions. See DEC.
A proprietary data communications protocol developed by DEC. See DEC.
dB. One tenth of a Bel, with "Bel" referring to Alexander Graham Bell. A unit of measure of the power of sound or the strength of a signal, usually expressed as the relationship between a transmitted signal and a standard signal source, known as a reference. The decibel was invented by the Bell System to measure the level of gain or loss in telephone transmission systems. Loss in such systems is the result of signal attenuation in passive devices (e.g., resistance/impedance in electrically-based conducted media such as copper cables, and the quality of the space between transmitting and receiving radio antenna or other airwave systems). Gain in such systems is the result of active devices such as amplifiers and repeaters, which serve to boost the strength of the signal. The ultimate objective of measuring the loss in such a passive system is to compensate for it with measured gain accomplished by an active device in order to produce a signal at the receiver which is of the same intensity as the signal created by the transmitter.
Specifically, decibel is a logarithmic unit, which, in this context, defines the level of gain or loss in a circuit or link, or device, as compared to a reference value. The logarithmic expression of gain or loss is much more effective than a linear expression for several reasons. First, the human ear interprets loudness (i.e., signal strength) on a scale much closer to a logarithmic scale than a linear scale. Likewise, the human eye has a logarithmic response to changes in light. Second, the quantities measured often exhibit huge ranges of variation that can be expressed more conveniently in logarithmic , rather than linear, terms. dB is expressed as the ratio of two values, each of which is taken at a specific point. Here is an composite explanation drawn from several editions of James Harry Green's excellent book, The Irwin Handbook of Telecommunications. Mr. Green writes , "The power in telecommunications circuits is so low that it is normally measured in milliwatts. However, the milliwatt is not a convenient way to express differences in power level between circuits...Therefore in telephony, the decibel...is used as a measure of relative power between circuits or transmission level points. A change in level of 1 dB is barely perceptible under ideal conditions. The number of dB corresponding to a power ratio is expressed as dB = 10 log P2/P1. The dB also can express voltage and current ratios if the impedance...is the same for both values of voltage or current. The dB ratio between voltage and current is expressed as dB = 20 log E2/E1 and dB = 20 log I2/I1, respectively. Increases or reductions of 3 dB result in doubling or halving the power in a circuit...The corresponding figure for doubling or halving voltage and current is 6 dB." (In terms of power, a loss of 6 dB translates into a drop in power of approximately 75%.)
Now, let's put this into human terms, courtesy of the Deafness Research Foundation: 30 dB equals a quiet library, soft whispers. 40 dB equals a living room, a refrigerator, a bedroom away from traffic. 50 dB equals light traffic, normal conversation or a quiet office. 60 dB equals an air conditioner at 20 feet or a sewing machine. 70 dB is the sound of a vacuum cleaner, a hair dryer, or a noisy restaurant. 80 dB equals the sound of average city traffic, garbage disposals, or an alarm clock at two feet. According to the foundation, the following noises can be dangerous under constant exposure: 90 dB is a subway , motorcycle, truck traffic or lawn mower; 100 dB is a garbage truck, chain saw, or pneumatic drill; 120 dB is a rock band concert (If you didn't listen to your parents' advice, and you're crazy enough to sit right in front of the speakers .) or a thunderclap; 140 dB is a gunshot blast or a jet plane taking off; 180 dB is the sound of a rocket launching pad.