D

daisy chain
A daisy-chain network is created by linking multiple devices by means of a cabling system. In an AppleTalk network, the daisy-chain topology is created using PhoneNet connectors and twisted pair wiring (regular phone wire). A daisy-chain configuration must be terminated at both ends using terminating resistors.

Data Exchange Interface (DXI)
DXI is an ATM interface that converts variable-length network frames to fixed-length ATM cells. ATM DXI converts LAN frames to the variable-length DXI frame format. The ATM CSU/DSU then converts the DXI frames to fixed-length ATM cells. This two-step conversion simplifies processing on the ATM CSU/DSU, because it only needs to convert one type of frame.

Data Link Control (DLC)
DLC is a generic term that refers to a protocol (such as Token Ring or Ethernet) used to transfer information across a single link.

data service unit/channel service unit (DSU/CSU)
The hardware required to connect a common carrier connection (leased line) to a router is referred to as the DSU/CSU. Frame relay service requires one DSU/CSU, whereas private line service requires two DSU/CSUs.

datagram (packet)
A datagram is a unit of information processed by the Network Layer of the OSI reference model. The packet header contains the logical (network) address of the destination node. Intermediate nodes forward a packet until it reaches its destination. A packet can contain an entire message generated by higher OSI layers, or a segment of a much larger message.

detector
A detector is a device that receives optical signals and converts them into electrical signals.

direct memory access (DMA)
DMA is the type of memory access that does not involve the main processor in a computer to transfer data directly from memory to a peripheral device, such as a hard drive or NIC.

Distributed Queue Dual Bus (DQDB)
DQDB is the IEEE 802.6 standard for MANs. See SMDS.

Domain Name System (DNS)
DNS is an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they are easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.

Dynamic Host Configuration Protocol (DHCP)
DHCP is a proprietary approach from Microsoft that simplifies IP network management by dynamically assigning IP addresses to logical end-stations for fixed periods of time.