D

Data Encryption Standard

(DES) A standard defined by the National Institute of Standards and Technology, for encryption of digital data transmissions within the United States.

data link layer

The second of the seven layers in the International Organization for Standardization's Open Systems Interconnection (OSI) model for standardizing computer-to-computer communications. The data link layer is one level above the physical layer. It is involved in packaging and addressing information and in controlling the flow of separate transmissions over communications lines. The data link layer is the lowest of the three layers (data link, network, and transport) that help move information from one device to another. See also transport layer.

data service

A mechanism provided by a service provider for sending broadcast data to broadcast clients. Such data can include Program Guide information, Web pages, software, and other digital information. The data service mechanism can be any broadcast process, including Internet channel broadcasting.

data stream

See stream.

datagram

One packet of information and associated delivery information, such as the destination address, that is routed through a packet-switching network. In a packet-switching network, data packets are routed independently of each other and may follow different routes and arrive in a different order from which they were sent. An Internet Protocol (IP) multicast packet is an example of a datagram.

DBS

See direct broadcast satellite.

dependency

A file that must be downloaded for an enhancement page to display properly, for example an image file in .gif format embedded in an HTML page. The image must be sent to clients first, so that it will be there when the page is displayed.

DES

See Data Encryption Standard.

device class

A group into which devices and buses are placed for the purposes of installing and managing device drivers and allocating resources. The hardware registry tree is organized by device class. Windows 98 uses class installers to install the drivers for the different classes of hardware.

device object

A programming object used to represent a physical, logical, or virtual hardware device whose device driver has been loaded into the operating system.

direct broadcast satellite

(DBS) A satellite communications technology that allows use of a very small (18 inches to 3 feet in diameter) receiver dish packaged as a consumer electronics product, enabling consumers to receive satellite television signals directly.

DirectShow

The DirectShow (formerly ActiveMovie) application programming interface (API) is a multimedia technology designed to play video, audio, and other multimedia streams in a variety of formats that are stored locally or acquired from Internet servers. DirectShow relies on a modular system of components called filters arranged in a configuration called a filter graph. A component called the filter graph manager oversees the connection of these filters and controls the data flow of the stream. See also DirectShow filter.

DirectShow filter

A DirectShow component that processes data streams. Each filter handles part of the operation involved in receiving, decoding, transforming, scheduling, and displaying interdependent video, audio, or other data streams. Filters connect to each other in a configuration called a filter graph.

A DirectShow filter is a user-mode entity that is an instance of a Component Object Model (COM) object, usually implemented by a dynamic-link library (DLL). A Broadcast Architecture DirectShow filter can be a source filter, a transform filter, a renderer filter, or a utility filter.

See also KSProxy filter.

downstream

One-way data flow from head end to broadcast client. See also upstream.