Data Encryption Standard (DES)
A U.S. government standard for encrypting information. In 1972, the National Bureau of Standards called for proposals for an encryption standard. IBM responded with an algorithm called Lucifer, which was accepted, renamed Data Encryption Algorithm (DEA), and then further developed by the National Security Agency (NSA) and the National Bureau of Standards. In 1977, DEA was adopted as the Data Encryption Standard (DES). It is now the official encryption standard of the Department of Defense. DES is the name of the Federal Information Processing Standard FIPS 46-1, which explains the operation of the Data Encryption Algorithm
Data Service Unit (DSU)
A digital communication device that works with a Channel Service Unit (CSU) to connect a local area network (LAN) to an external communication carrier service or a wide area network (WAN) link (such as a T1 line). Data Service Units (DSUs) provide a modem-like interface between data terminal equipment (DTE) such as a router and the CSU connected to the digital service line. DSUs also serve to electrically isolate the telcos digital telecommunication line from the networking equipment at the customer premises.
A device on a TCP/IP internetwork that can forward Internet Protocol (IP) packets to another network, usually a router. In an internetwork, a given subnet might have several router interfaces that connect it to other, remote subnets. One of these router interfaces is usually selected as the default gateway of the local subnet. When a host on the network wants to send a packet to a destination subnet, it consults its internal routing table to determine whether it knows which router to forward the packet to in order to have it reach the destination subnet. If the routing table does not contain any routing information about the destination subnet, the packet is forwarded to the default gateway (one of the routers with an interface on the local subnet).
A host on a TCP/IP internetwork that is capable of having its IP address information dynamically assigned using Dynamic Host Configuration Protocol (DHCP). The term "DHCP client" can also describe the software component on a computer that is capable of interacting with a DHCP server to lease an IP address.
An umbrella term for various kinds of digital telecommunications services. The distinguishing feature of a digital line is that it is digital from end to end and does not employ any kind of analog modem technologies. As a result, digital lines have higher traffic-carrying capacities, less noise, and better error-handling features than analog lines. The term "digital line" can refer to circuits based on the following:
Any type of modem used for synchronous transmission of data over circuit-switched digital lines. One example of a digital modem is an ISDN terminal adapter. Digital modems are not used for changing analog signals into digital signals because they operate on end-to-end digital services. Instead, they use advanced digital modulation techniques for changing data frames from a network into a format suitable for transmission over a digital line such as an Integrated Services Digital Network (ISDN) line. They are basically data framing devices, rather than signal modulators.
Digital Subscriber Line (DSL)
A telecommunications technology for providing high-speed transmission to subscribers over the existing copper wire twisted-pair local loop between the customer premises and the telcos central office (CO). The Digital Subscriber Line (DSL) technology was designed to provide high-speed data and video-on-demand services to subscribers at speeds much faster than Integrated Services Digital Network (ISDN). The essential advantage of using DSL is that it allows much faster data transmission rates over existing copper local loop telephone lines than traditional modems.
DSL standards are still evolving, and implementation is not yet widespread in most locations. In addition, DSL is competing with cable modem technologies to replace ISDN for high-speed Internet access.
Direct burial fiber-optic cabling
A cable consisting of multiple fiber-optic cables bundled
together and enclosed in a protective sheath. Direct burial fiber-optic cabling is
designed to be buried in trenches and contains a gel filling that protects the individual
fibers from temperature and moisture variations. A strip of strengthening material runs
axially down the cable to prevent excessive bending, which can fracture the individual
fibers. Direct burial cabling can have steel-armor construction with heavy waterproof
polyethylene jackets and can contain either multimode or single-mode fiber-optic strands.