T

[This is preliminary documentation and subject to change.]

Task Scheduler: A scheduling service and user interface that is available as a common resource with the Microsoft® Windows® 98 operating system. Windows 98 includes Task Scheduler as a Component Object Model (COM) interface. Task Scheduler manages all aspects of job scheduling: starting jobs, enumerating currently running jobs, tracking job status, and so on. In Task Scheduler, the user works with a folder under My Computer called Scheduled Tasks, which lists currently scheduled items and enables creation of new tasks. The Task Scheduler replaces the Microsoft® Windows® 95 System Agent.
TCP/IP: See Transmission Control Protocol/Internet Protocol.
Television System Services: (TSS) An Automation interface designed to enable developers to write Windows 98 – based applications that use broadcast television. TSS provides a user model with password security and interapplication scheduling of television shows for viewing or recording. TSS is designed to be used with the Guide database, the Video control or its underlying Microsoft® DirectShow™ filters, the Video Access server, and Guide database loaders. See also Broadcast Architecture subsystems.
theme: A category to which individual television programs are assigned within the Guide database. A theme allows a program episode to be associated with multiple genre/subgenre pairs.
thread: One of several paths of execution in a program or process in which all paths can execute in parallel. Each thread can perform a different function, or many threads can cooperate to perform a larger task.
time to live: (TTL) A value in the range 0 through 255 that defines the scope within which multicast packets should be sent over a network using Internet Protocol (IP). The scope is defined in terms of how local or remote a packet's destination is. Each router decrements the TTL by one. When the value reaches a predefined lower limit, the router throws the packet away. Current multicast backbone (MBONE) requirements, available at the ftp://ftp.isi.edu/mbone/faq.txt site, define the following standard scopes: local network, 1; local site, 15; region, 63; world, 127. Other settings may have local meaning; for example, 31 might indicate all sites within a particular organization.
transform filter: A filter that modifies the contents of a stream. Transform filters usually have both input and output pins.
Transmission Control Protocol/Internet Protocol: (TCP/IP) A networking protocol that provides reliable communications across interconnected networks made up of computers with diverse hardware architectures and operating systems. The TCP portion of the protocol, a layer above IP, is used to send a reliable, continuous stream of data and includes standards for automatically requesting missing data, reordering IP packets that might have arrived out of order, converting IP datagrams to a streaming protocol, and routing data within a computer to make sure the data gets to the correct application. The IP portion of the protocol includes standards for how computers communicate and conventions for connecting networks and routing traffic. See also User Datagram Protocol/Internet Protocol (UDP/IP).
transponder: A device on a satellite that receives and amplifies uplink signals in radio frequencies that come from an earth station. Once the signal is received, the transponder redirects it back toward its destination earth station within the particular satellite's footprint. Each transponder is responsible for a small frequency range, and a satellite is typically made up of 10 to 40 transponders. Unlike in traditional broadcast television, each transponder has enough bandwidth to carry multiple television channels, as well as data. Any one transponder might carry anywhere from 10 low resolution television channels to 2 high-definition television (HDTV) channels, or some combination. See also multiplexer.
transport layer: The fourth of the seven layers in the International Organization for Standardization's Open Systems Interconnection (OSI) model for standardizing computer-to-computer communications. The transport layer is one level above the network layer and is responsible for error detection and correction, among other tasks. Error correction ensures that the bits delivered to the receiver are the same as the bits transmitted by the sender, in the same order and without modification, loss, or duplication. The transport layer is the highest of the three layers (data link, network, and transport) that help move information from one device to another. See also data link layer.
trigger: A notification that is sent to a broadcast client at specific times during an interactive television show to change enhancement display on the client. For example, you can use triggers to automatically change the content of an enhancement, as in an advertisement rotator.
Triple DES: A method of encryption in which the Data Encryption Standard (DES) algorithm is applied three times in a row using three different session keys. These three keys are combined into one Triple DES session key. Triple DES encryption is much more resilient to differential and plaintext attacks than DES.
TSS: See Television System Services.
tuner: An electronic component that locks onto a selected channel and filters signals such as audio and video from that frequency for amplification and display.
tuning space: A set of nonoverlapping channels that are all available through the same type of physical channel tuner, such as a broadcast receiver card or analog cable tuner. A broadcast client with multiple tuning devices can provide channels from multiple tuning spaces.
twisted-pair cable: A communications medium consisting of two thin, insulated wires, generally made of copper, that are twisted together. Standard telephone connections are often referred to as "twisted pair."