T1

This leased line provides point-to-point connections and transmits a total of 24 channels across two wire pairs – one pair for sending and one for receiving – for a transmission rate of 1.544 Mbps. A T1 is known as an E1 line in Europe. Also, the interval used by dirsync requestors to send their postoffice address list to the designated dirsync server.

T2

The interval used by the dirsync server to compile a new Global Address List and to send that list to the dirsync requestors.

T3

T3 (E3 in Europe) is similar to T1, but T3 has an even higher capacity. In fact, a T3 line can transmit at up to 45 Mbps. This is because a T3 line is made up of 672 64 Kbps channels. Also, the interval used by the dirsync requestors to rebuild their postoffice address list.

T.120

A standards-based protocol used with Exchange Data Conferencing. Clients such as Microsoft NetMeeting are T.120 compatible.

T Reference Point

Used with an S reference point to change a 4-wire ISDN network to a 2-wire ISDN network.

Table

In a SQL Server database, the object that contains rows and columns of data.

Tag Switching

Based on the concept of label swapping, where packets or cells are designated to defined-length labels that control the manner in which data is to be sent, tag switching is a high-performance technology used for forwarding packets. It incorporates Data Link layer (Layer 2) switching and Network layer (Layer 3) routing and supplies scalable, high-speed switching in the network core.

Tagged Traffic

ATM cells with their cell loss priority (CLP) bit set to 1. Also referred to as discard-eligible (DE) traffic. Tagged traffic can be eliminated in order to ensure trouble-free delivery of higher priority traffic, if the network is congested. See also Cell Loss Priority.

Target Server

An Exchange server in a remote site that is designated to receive messages from the local site.

Taskbar

The gray bar at the bottom of the screen; it replaces the Task Manager in previous versions of Windows. The Taskbar holds the Start menu button and buttons that represent running programs. It is used to switch between running programs and to choose the Start menu.

Task Manager

A Windows utility that can be used to start, end, or prioritize applications. The Task Manager shows the applications and processes that are currently running on the computer, as well as CPU and memory usage information.

Task Scheduler

A Windows utility used to schedule tasks to occur at specified intervals.

TB

See Terabyte.

T-Carrier

A type of multiplexed, high-speed, leased line. T-carrier service levels include T1, T2, T3, and T4. T-carriers offer transmission rates of up to 274Mbps.

T-Connector

A T-shaped device used to connect network cards to Thinnet cable.

TCO

See Total Cost of Ownership.

TCP

See Transmission Control Protocol.

TCP/IP

See Transmission Control Protocol/Internet Protocol.

TCP/IP Port

A logical port, used when a printer is attached to the network by installing a network card in the printer. Configuring a TCP/IP port requires the IP address of the network printer to connect to. See also Logical Port.

TDI

See Transport Driver Interface.

TDM

See Time Division Multiplexing.

TE

See Terminal Equipment.

TE1

A device with a four-wire, twisted-pair digital interface is referred to as terminal equipment type 1. Most modern ISDN devices are of this type.

TE2

Devices known as terminal equipment type 2 do not understand ISDN signaling techniques, and a terminal adapter must be used to convert the signaling.

TechNet

Microsoft’s monthly CD-ROM set that contains patches to existing programs, technical notes about issues (bugs), and white papers describing technologies in more detail. Most of the information in TechNet can also be found on Microsoft’s Web site.

Technical and Office Protocol (TOP)

An Ethernet implementation for use in an engineering environment, developed by Boeing Corporation. See also Manufactuing Automation Protocol.

Telco

A common abbreviation for the telephone company.

Telnet

A TCP/IP terminal emulation protocol that permits a node, called the Telnet client, to log in to a remote node, called the Telnet server. The client simply acts as a dumb terminal, displaying output from the server. The processing is done at the server. See also Internet.

Tempdb Database

A SQL Server database reserved for storing temporary objects. These may be tables or stored procedures and can be created implicitly by SQL Server or explicitly by the user. The Tempdb database is also used to store server-side cursors.

Template

Certain applications use template files to pre-load default configuration settings. Microsoft Word uses a template called NORMAL.DOT to store information about page setup, margins and other document information.

Terabyte

A computer storage measurement that equals 1,024 gigabytes.

Terminal Adapter

A hardware interface between a computer without a native ISDN interface and an ISDN line. In effect, a device to connect a standard async interface to a non-native ISDN device, emulating a modem.

Terminal Emulation

The use of software, installed on a PC or LAN server, that allows the PC to function as if it were a “dumb” terminal directly attached to a particular type of mainframe.

Terminal Equipment (TE)

Any peripheral device that is ISDN-compatible and attached to a network, such as a telephone or computer. TE1s are devices that are ISDN-ready and understand ISDN signaling techniques. TE2s are devices that are not ISDN-ready and do not understand ISDN signaling techniques. A terminal adapter must be used with a TE2.

Terminal Server User Group

A Windows special group that includes users who log on through Terminal Services. See also
Special Group.

Terminal Services

A Windows Server service that allows thin clients to connect to a Terminal Services server and access many Windows features. In Terminal Services application server mode, clients can access the Windows Desktop environment and run applications. In Terminal Services remote administration mode, administrators can perform server administrative tasks remotely from a client. See also Thin Client, Terminal Services Server, and Desktop.

Terminal Services Client

A client that uses thin client technology to deliver the Windows Server Desktop to the user. The client only needs to establish a connection with the server and display the graphical user interface information that the server sends. This process requires very little overhead on the client’s part, and it can be run on older machines that would not otherwise be able to use the latest version of Windows. See also Thin Client.

Terminal Services Client Creator

A Windows Server utility used to create 32-bit and 16-bit Terminal Services client software diskettes for use with client machines. See also Terminal Services.

Terminal Services Configuration

A Windows Server utility used to change the properties of the RDP-TCP connection that is created when Terminal Services is installed and to add new connections. See also Terminal Services.

Terminal Services Manager

A Windows Server utility used to manage and monitor users, sessions, and processes that are connected to or running on any Terminal Services server on the network. See also Terminal Services Server.

Terminal Services Server

A server that has Terminal Services installed. The Terminal Services server controls all of the Terminal Services clients that are connected to it. All Terminal Services operations take place on the Terminal Services server. See also Terminal Services and Terminal Services Client.

Terminate and Stay Resident (TSR)

TSR programs stay in memory after being executed. TSR programs allow the user to quickly switch back and forth between programs in a non-multitasking environment, such as MS-DOS. Some viruses are TSR programs that stay in memory to infect other files and programs. Also known as Memory-Resident Program.

Terminator

A device at the end of a cable segment that indicates that the last node has been reached. In the case of Ethernet cable, a 50-ohm resistor (a terminator) at both ends of the cable prevents signals from reflecting back through the cable.

Terrestrial Microwave

Terrestrial microwave communication employs Earth-based transmitters and receivers. The frequencies used are in the low-gigahertz range, which limits all communications to line-of-sight.

Text File

A file saved in ASCII format. It contains text characters, but no formatting codes.

TFTP

See Trivial File Transfer Protocol.

Thicknet

Also called 10Base5. Bus network that uses a thick cable and runs Ethernet up to 500 meters.

Thin Client

A client that has minimal requirements. With Terminal Services, a thin client can be run on a variety of machines, including older computers and terminals that would not otherwise be able to run the latest version of Windows. See also Terminal Services.

Thinnet

Also called 10Base2. Bus network that uses a thin coax cable and runs Ethernet media access up to 185 meters.

Thread

A list of instructions running in a computer to perform a certain task. Each thread runs in the context of a process, which embodies the protected memory space and the environment of the threads. Multithreaded processes can perform more than one task at the same time. See also Process, Preemptive Multitasking, and Program.

Throughput

The amount of data that has been sent over a given time. For example, 10baseT Ethernet has a theoretical maximum throughput of 10Mbps. In practice, the throughput depends on the quality and length of wiring and is usually slightly less than 10Mbps.

Tic Count

This method provides an actual time estimate used in routers. A tic is a time unit as defined by the routing implementation.

TIME

Displays or sets the system time.

Time Bomb

Usually malicious action triggered at a specific date or time. See also Logic Bomb.

Time-Division Multiplexing (TDM)

A technique for assigning bandwidth on a single wire, based on preassigned time slots, to data from several channels. Bandwidth is allotted to each channel regardless of a station’s ability to send data. See also Asynchronous Time-Division Multiplexing, Frequency-Division Multiplexing, and Multiplexing.

Time-Domain Reflectometer (TDR)

TDRs send sound waves along a cable and look for imperfections that might be caused by a break or a short in the line. A good TDR will often be able to detect faults on a cable to within a few feet.

Timestamp

The time of creation or last modification recorded on a file or another object. Users can usually find the timestamp in the Properties section of a file.

Time To Live (TTL)

A field in an IP header, indicating the length of time a packet is valid.

Title Bar

A horizontal bar across the top of each screen in DOSSHELL that contains the name of the screen.

Toggle

A term used to describe something that turns on and off with the same switch.

Token

The packet of security information a certification authority sends to a client during advanced security setup. Information in the packet includes the client’s public key and its expiration. A token is synonymous with a certificate.

Token Bus

LAN architecture that is the basis for the IEEE 802.4 LAN specification and employs token passing access over a bus topology. See also Institute of Electrical and Electronics Engineers.

Token Passing

The computers take turns using the transmission medium. This is facilitated by the passing of a token. The machine in possession of the token is allowed to transmit. See Token Ring.

Token-Ring

IBM’s token-passing LAN technology. It runs at 4Mbps or 16Mbps over a ring topology. Defined formally by IEEE 802.5. See Data Link Layer, Ring Topology, and Token Passing.

Token-Ring Frame

There are two types of token-ring frames. One is used to carry management information and the other is used to transfer data. Token-ring frames are used on token-ring networks, and not Ethernet networks.

Token Ring Interface Processor (TRIP)

A high-speed interface processor used on Cisco 7000 series routers. The TRIP provides two or four ports for interconnection with IEEE 802.5 and IBM media with ports set to speeds of either 4Mbps or 16Mbps set independently of each other.

Token-Ring_SNAP Frame

The Token-Ring_SNAP provides a similar function as the Ethernet_SNAP frame type, but for token-ring networks.

Toll Network

WAN network that uses the Public Switched Telephone Network (PSTN) to send packets.

TOM

See Top of Memory.

Tombstone

Information created by the DS about a deleted directory object. The tombstone is replicated to other Exchange servers in a site to inform them of the deletion.

Tombstone Lifetime

The length of time a tombstone is kept before it is deleted.

TOP

See Technical and Office Protocol.

Top of Memory (TOM)

A design limit at the 640kb-mark on most PCs. Often the boot record does not completely reach the top of memory, thus leaving empty space. Boot sector infectors often try to conceal themselves by hiding around the top of memory. Checking the top of memory value for changes can help detect a virus, though there is also non-viral reasons this value can change.

Topology

A type of network connection or cabling system. Networks are usually configured in bus, ring, star, or mesh topology.

Total Cost of Ownership (TCO)

A term first used by Gardener Group in an attempt to quantify the real cost of a particular computer solution. TCO encompasses the direct costs of the hardware and the software required and then adds in costs for maintenance and support, costs for the users performing their own technical support rather than their official job, and system productivity costs. See also NetPC, Network Computer, Thin Client, and
Zero Administration for Windows.

trace

IP command used to trace the path a packet takes through an internetwork.

Trace Log

A log file that can be created through the use of the Windows Performance tool. Trace logs record specific events and can be analyzed through the use of compatible utilities.

TRACERT

A tool used to map out the path that the packets are taking as they flow to a remote system.

Transaction

A logical set of one or more commands that need to be processed as a whole in order to make a complete unit of work.

Transaction Log

A file used to quickly write data. That data is later written to the relevant Exchange database file. It is quicker to write to a transaction log file because the writes are done sequentially (i.e., one right after the other). Transaction log files can also be used to recreate data that has been lost in an Exchange database.

Transaction Processing

A processing method in which transactions are executed immediately when they are received by the system, rather than at some later time as in batch-processing systems. Airline reservation databases and automatic teller machines are examples of transaction-processing systems. See also Online Transaction Processing, Roll Back, Roll Forward, and Two-Phase Commit.

Transaction SQL

See Transact-SQL.

Transact-SQL (T-SQL)

SQL is a database language, originally designed by IBM, that can be used not only for queries but also to build databases and manage security of the database engine. Microsoft SQL Server uses Transact-SQL (T-SQL), an enhanced version of the SQL language, as its native database language.

Transceiver

The device that performs both the transmission and reception of signals on a given medium.

Transformation File

A type of file used by the Windows Installer to modify the behavior of the application-installation process.

Transient

A high-voltage burst of electric current, usually lasting less than 1 second, occurring randomly. Transients are often referred to as spikes.

Transitive Trust

A trust relationship that allows for implicit trusts between domains. For example, if Domain A trusts Domain B and Domain B trusts Domain C, then Domain A implicitly trusts Domain C. See also Trust and Two-Way Trust.

Transmission Control Protocol (TCP)

An internetwork connection-oriented protocol that corresponds to the OSI Transport layer. TCP provides full-duplex end-to-end connections. See also Transmission Control Protocol/Internet Protocol and Internet Protocol.

Transmission Control Protocol/Internet Protocol (TCP/IP)

A set of protocols (protocol suite) and services used by many different operating systems and the Internet. See also Transmission Control Protocol, Internet Protocol, Simple Network Management Protocol, Routing Information Protocol, User Datagram Protocol and all other acronyms ending in the letter P.

Transmission Medium

A pathway used to connect different resources on a network.

Transparent Bridge

See Learning Bridge.

Transparent Bridging

The bridging scheme used in Ethernet and IEEE 802.3 networks, it passes frames along one hop at a time, using bridging information stored in tables that associate end-node MAC addresses within bridge ports. This type of bridging is considered transparent because the source node does not know that it has been bridged, because the destination frames are sent directly to the end node. See also Source-Route Bridging.

Transport Driver Interface (TDI)

A specification to which all Windows transport protocols must be written in order to be used by higher level services such as programming interfaces, file systems, and interprocess communications mechanisms. See also Transport Protocol.

Transport Layer

Layer 4 of the OSI reference model, used for reliable communication between end nodes over the network. The Transport layer provides mechanisms used for establishing, maintaining, and terminating virtual circuits, transport fault detection and recovery, and controlling the flow of information. See also Application Layer, Data Link Layer, Network Layer, Physical Layer, Presentation Layer, and Session Layer.

Transport Mode

Another name for the end-to-end mode, in which IPSec is used to encrypt before data is sent and decrypted at the other end, while the data is protected during transport.

Transport Protocol

A service that delivers discrete packets of information between any two computers in a network. Higher level connection-oriented services are built upon transport protocols. See also Transmission Control Protocol/Internet Protocol, NetWare Link, NetBIOS Extended User Interface, Transport Layer, Internet Protocol, and Internet.

TREE

Graphically displays the directory structure of a drive or path.

Tree

A set of Active Directory domains that share a common namespace and are connected by a transitive two-way trust. Resources can be shared between the domains in an Active Directory tree.

Trigger

A SQL Server object that is a stored procedure. A trigger activates when data is added, updated, or deleted from a table. Triggers are used to ensure that tables linked by keys stay internally consistent with each other.

Triggered Event

An action built into a virus set off by a specific condition. Examples include a message displayed on a specific date or reformatting a hard drive after the 10th execution of a program.

TRIP

See Token Ring Interface Processor.

Trivial File Transfer Protocol (TFTP)

Conceptually, a stripped-down version of FTP, it is the protocol of choice if you know exactly what you want and where it is to be found. TFTP does not provide the abundance of functions that FTP does. In particular, it has no directory browsing abilities; it can do nothing but send and receive files.

Trivial File Transfer Protocol Daemon (TFTPD)

Used by Remote Installation Services (RIS) to transfer data to remote installation clients.

Trojan Horse Program

A Trojan horse program is a malicious program that pretends to be a benign application; a Trojan horse program purposefully does something the user does not expect. Trojans are not viruses since they do not replicate, but Trojan horse programs can be just as destructive. Many people use the term to refer only to non-replicating malicious programs, thus making a distinction between Trojans and viruses. Also known as Trojan.

Trunk Line

Link used between switches and from some servers to the switches. Trunk lines carry information about many VLANs. Access links are used to connect host devices to a switch and carry only VLAN information that the device is a member of.

Trunk Up-Down (TUD)

A protocol used in ATM networks for the monitoring of trunks. Should a trunk miss a given number of test messages being sent by ATM switches to ensure trunk line quality, TUD declares the trunk down. When a trunk reverses direction and comes back up, TUD recognizes that the trunk is up and returns the trunk to service.

Trust

A relationship between domains that allows for the sharing of resources.

Trusted Connection

See Integrated Security.

Trust Level

A numeric value given an object that is used to determine if that object should be replicated to another location, such as a foreign directory.

Trust Relationship

Administrative link that joins two or more domains. With a trust relationship users can access resources in another domain if they have rights, even if they do not have a user account in the resource domain.

TSInternetUser

A special domain user account that is used by Terminal Services. See also Domain User Account and Terminal Services.

T-SQL

See Transact-SQL.

TSR

See Terminate and Stay Resident.

TTL

See Time To Live.

TUD

See Trunk Up-Down.

Tunnel

A private, virtual circuit between a client and a server using the Internet as a transportation medium.

Tunnel Endpoint

The systems at the end of a two-way IPSec tunnel.

Tunnel Mode

The use of IPSec to secure traffic that is being passed over someone else’s wire.

Tunneling

1. A method of avoiding protocol restrictions by wrapping packets from one protocol in another protocol’s packet and transmitting this encapsulated packet over a network that supports the wrapper protocol. See also Encapsulation.
2. A virus technique designed to prevent anti-virus applications from working correctly. Anti-virus programs work by intercepting the operating system actions before the OS can execute a virus. Tunneling viruses try to intercept the actions before the anti-virus software can detect the malicious code. New anti-virus programs can recognize many viruses with tunneling behavior.

Twisted-Pair Cable

A type of cable that has two or more wires twisted around each other. Telephone wire is a twisted-pair cable.

Two-Phase Commit

A type of data replication for SQL Server. With two-phase commit, two or more SQL Server computers either complete a transaction simultaneously or not at all. The Distributed Transaction Coordinator (MS-DTC service) is designed to help manage these types of transactions. See also Online Transaction Processing, Roll Back, Roll Forward, and Transaction Processing.

Two-Way Trust

A trust relationship in which two domains trust each other. For example, a two-way trust might involve Domain A trusting Domain B and Domain B trusting Domain A.

TYPE

Displays the contents of a text file.