T

T-line

A digital communication line used in WANs. Commonly used T designations are T1 and T3. It is also possible to use only part of a T1 line, which then becomes known as fractional T1.

TCP (Transmission Control Protocol)

A connection-oriented, reliable data transmission communication service that operates at the transport layer of the OSI model. TCP is part of the TCP/IP protocol suite.

TCP/IP (Transmission Control Protocol/Internet Protocol)

A suite of protocols that includes TCP and IP. TCP/IP was originally designed for use on large internetworks but has now become the de facto protocol for networks of all sizes.

TCP/IP socket

A socket, or connection to an endpoint, that is used in TCP/IP communication transmissions.

TDI (Transport Driver Interface)

A kernel-mode network interface that is exposed at the upper edge of all Windows NT transport protocol stacks. The highest-level protocol driver in every such stack supports the TDI interface for still higher-level kernel-mode network clients.

TDR (time-domain reflectometer)

A device that is used to test copper cables to determine whether and where a break is on the cable. For optical cables, an optical TDR is used.

Telnet

A standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used to perform terminal emulation over TCP/IP via remote terminal connections, enabling users to log in to remote systems and use resources as if they were connected to a local system.

Terminal Services

A service provided in Windows 2000 and as an add-on in Windows NT that allows clients to connect to the server as if it were a multiuser operating system. All the processing for the client session is performed on the server, with only screen updates and user input being transmitted across the network connection.

TFTP (Trivial File Transfer Protocol)

A simplified version of FTP that allows file transfers but does not offer any security or file management capabilities.

Thick Ethernet

The IEEE 802.3 standard 10Base5, which describes Ethernet networking using thick coaxial cabling.

thick coaxial

The thick cable most commonly used as the backbone of a coaxial network. It is approximately .375 inches in diameter.

thin client

An application that is run from a back-end server system such as Microsoft Terminal Services. The processing tasks are all performed at the terminal server rather than on the client.

Thin Ethernet

The 802.3 standard 10Base2, which describes Ethernet networking using thin coaxial cabling.

thin coaxial

Cable that is thinner than thick coaxial cable but still about .25 inches in diameter. It is commonly used in older bus topologies.

TIA (Telecommunications Industry Association)

An organization that, along with EIA, develops standards for telecommunications technologies.

token

A frame that provides controlling information. In a Token Ring network, the node that possesses the token is the one that is allowed to transmit next.

Token Ring

An IBM-proprietary token-passing LAN topology defined by IEEE standard 802.5. It operates at either 4Mbps or 16Mbps, in a star topology.

Token Ring adapter

Traditionally an ISA or a Microchannel device with 4Mbps or 16Mbps transfer capability that is used to connect nodes to a Token Ring network.

tone generator

A device that is used with a tone locator to locate and diagnose problems with twisted-pair cabling.

topology

The shape or layout of a physical network and the flow of data through the network.

See also [logical topology]

See also [physical topology]

trace route

A function of the TCP/IP protocol suite, implemented in utilities such as traceroute and tracert, that allows the entire path of a packet to be tracked between source and destination hosts. It is used as a troubleshooting tool.

transmit

To send data using light, electronic, or electric signals. In networking, this is usually done in the form of digital signals composed of bits.

transparent bridging

A situation in which the bridges on a network tell each other which ports on the bridge should be opened and closed, which ports should be forwarding packets, and which ports should be blocking packets—all without the assistance of any other device.

transport layer

Layer 4 of the OSI model, which controls the flow of information.

TTL (time to live)

A value that is assigned to a packet of data to prevent it from moving around the network indefinitely. The TTL value is decremented each time the packet crosses a router, until it reaches 0, at which point it is removed from the network.

twisted-pair

A type of cable that uses multiple twisted pairs of copper wire.