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List of netowrking, wireless, broadband, satellite, telephony, general computing and other technical terms used throughout the site.
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Term Description
DARPA Defense Advanced Research Projects Agency
datagram The term has been generally replaced by the term packet. Datagrams or packets are the message units that the Internet Protocol (IP) transports over the Internet.

According to RFC 1594 a datagram is "a self-contained, independent entity of data carrying sufficient information to be routed from the source to the destination computer without reliance on earlier exchanges between this source and destination computer and the transporting network."
DBS Direct Broadcast Satellite
DCCP DCCP (Datagram Congestion Control Protocol) is a computer networking transport layer protocol.

DCCP provides provides bidirectional unicast connections of congestion-controlled unreliable datagrams. It is suitable for applications that transfer fairly large amounts of data and that can benefit from control over the tradeoff between timeliness and reliability. Such applications include streaming media, multiparty online games and Internet telephony (where getting new data is preferred to resending lost packets).

DCCP is published as RFC 4340, a proposed standard by the IETF in March 2006. See also: RFC 4336, RFC 4341, RFC 4342. Linux had an implementation of DCCP first released in Linux kernel version 2.6.14
DCLI Data Link Connection Identifier (DSLAM) is a number of a private or switched virtual circuit in a frame relay network. Located in the frame header, the DLCI field identifies which logical circuit the data travels over, and each DLCI has a Committed Information Rate (CIR) associated with it.

The DLCI number is local to the FRAD and frame relay switch it connects to, and it is generally changed by the switch within the network, because the receiving switch uses a different DLCI for the same connection.
DCOM DCOM (Distributed Component Object Model) is a protocol that enables software components to communicate directly over a network. Previously called "Network OLE," DCOM is designed for use across multiple network transports, including Internet protocols such as HTTP. DCOM is based on the Open Software Foundation's DCE-RPC spec. For more information about DCOM visit the following Web site:
DDNS DDNS (Dynamic Domain Name System) - the capability of having server software on a dynamic IP address to have a fixed domain name.
DDoS DDoS (Distributed Denial of Service) is a type of external Internet attack, in which multiple sources attack a single target system, with the goal being denial of service for its users. DDoS attacks flood the target system with incoming messages at a rate much higher than it can process, therefore slowing it down to a level where it is rendered useless to users.

Usualy the intruders that initiate DDoS attacks break into a system (or a few systems) and make it the DDoS master that (by using some DDoS daemon software) manages other (100s even 1000s) "slave" compromised systems, whose sole purpose is to distribute the attack over multiple sources, when initiated. Whenever the DDoS attack is initiated, the multiple slave systems are instructed by the master to launch the DDoS attack and flood the end target system simultaneously, rendering it useless for legitimate users.

Note: The multiple systems involved in a DDoS that initiate the flood are most often compromised systems that can be considered victims of the attacker as well as the final target system.
DECT DECT (Digital Enhanced Cordless Telecommunication) is an ETSI standard for digital cordless phones.

The DECT standard fully specifies a means for a portable unit such as a cordless telephone to access a fixed telecoms network via radio, but unlike the GSM standards does not specify any internal aspects of the fixed network itself. Connectivity to the fixed network (which may be of many different kinds) is done through a base station or "Radio Fixed Part" to terminate the radio link, and a gateway to connect calls to the fixed network. In most cases the base station connection is to the public switched telephone network or telephone jack, although connectivity with newer technologies such as Voice over IP has become available. There are also other devices such as some baby monitors utilizing DECT, and in these devices there is no gateway functionality.
demodulation Conversion of a carrier signal or wave form (analog) into an electrical signal (digital).
DES DES (Data Encryption Standard) is a cryptographic algorighm used to protect data when transmitted through an unsecured network.
DHCP DHCP (Dynamic Host Configuration Protocol) is a protocol for automatic assignment of IP addresses in an organization's network.

Using the Internet Protocol, each device that can connect to the Internet needs a unique IP address assigned to it. The DHCP server assigns a dynamic IP address to each client, using the concept of a "lease" (amount of time) that the IP will be valid for a particular network node. Assigning short lease times to clients allows for a dynamic network with more nodes than available IP addresses.

With DHCP there is no need to statically assign IPs to each node locally, and there is no need to reconfigure clients if they are moved to a different place in the network. The only disadvantage of using DHCP is the fact clients have no permanent IP addresses; when the DHCP lease expires IPs can be reassigned to a different client.

See also: What is the difference between dynamic and static IP addresses ?
DLC DLC (Digital Loop Carrier) technology makes use of digital techniques to bring a wide range of services from the telecommunications network provider to users via twisted-pair copper phone lines.
DLEC Data Local Exchange Carrier
DMZ DMZ (De-Militarized Zone) refers to a computer/device on an internal protected network that is placed outside the firewall, but still available to the LAN.

The advantage of a DMZ computer is it has all communicatons ports open and it can use any special aplication that communicates on non-standard ports, such as many VoIP programs and online games. The disadvantage is that the device might be vulnerable to attacks, not being protected by the firewall.
DNS DNS (Domain Name System) is a protocol used to translate Internet domain and host names (such as to IP addresses. DNS implements a distributed database to store name and address information for all public hosts on the Net, assuming IP addresses are statically assigned.
DOCSIS DOCSIS ( Data Over Cable Service Interface Specification ) is the Cable Modem standard that defines the interface requirements of high-speed data transmission over cable networks. Cable modems often have a "CableLabs Certified" logo on the devices to indicate they are DOCSIS compliant.

DOCSIS 1.x (v1.0 1997, v1.1 1999) 38 Mbps downstream, 9 Mbps upstream. Version 1.1 standardized QoS support.
DOCSIS 2.0 (2001) 38 Mbps downstream, 27 Mbps upstream.
DOCSIS 3.0 (2006) 38 Mbps downstream, 27 Mbps upstream per channel, 4+ channel bonding, support for IPv6.
DOCSIS 3.1 (2013) 10 Gbps downstream, 1 Gbps upstream using 4096 QAM.

See also: CableLabs.
domain domain - a specific name for a network of computers.
downstream downstream (or download, downlink) is a transmission from a server toward the end user and upstream/upload is a transmission toward the server. Data rate can differ in the downstream and upstream directions.
DS0 DS0 (digital signal 0) is digital transmission rate of 64 Kbps, the bandwidth normally used for one telephone voice channel. It is the base multiple for both T (North America) and E (Europe and Japan) DS (digital signal) carriers.

A T1 for example is 24 DS0 (64 Kbps) signals, or 1.544 Mbps. E1 = 32 DS0s, or 2.048 Mbps.
DSL DSL ( Digital Subscriber Line ) is a method of high-speed data transfer over ordinary copper telephone lines. xDSL refers to different variations of DSL, such as ADSL, HDSL, SDSL and RADSL.
DSLAM DSLAM (Digital Subscriber Line Access Multiplexer) is a network device, usually at a telephone company central office, that receives signals from multiple customer DSL connections and puts the signals on a high-speed backbone line using multiplexing techniques.

Depending on the product, DSLAM multiplexers connect DSL lines with some combination of ATM (asynchronous transfer mode), frame relay, or IP networks.
DSSS DSSS (direct-sequence spread spectrum) is a modulation technology used in wireless network transmissions. DSSS is used as a kind of radio transmission that distributes the signal over many frequencies.

DSSS generates a redundant bit pattern (chipping code) for every bit of data to be transmitted. Data is then combined with the chipping code according to some spreading ratio. This chipping code allows for recovering lost data without retransmissions. DSSS improves pricacy, increases the signal's resistance to narrowband interference, and provides data redundancy.

See also: FHSS
DSU DSU (Data Service Unit) is a modem-like interface device that connects the computer as end user Data Terminal Equipment (DTE) to digital access lines (through a CSU), and which provides framing of sub-64Kbps customer access channels onto higher rate data circuits.

Often combined with a CSU into a single CSU/DSU (Channel Service Unit/Data Service Unit) device.
DTE DTE (Data Terminal/Termination Equipment) - a single piece or an interconnected subsystem of multiple pieces of equipment that perform all the required functions necessary to permit users to communicate. Typically the device that transmits data (computer, data terminal).
duplex Refers to the ability to transfer data in both directions. Full-duplex allows for data transfer in both directions simultaneously; half-duplex allows for data transfer only in one direction at the same time.

Most current NICs allow for full-duplex communication, theoretically doubling their throughput (i.e. for 100BaseT - 100 Mbps in one direction and 100 Mbps in the other at the same time). Curent Cable/DSL modems are usually half-duplex.
Term Description
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