Glossary - T

T1 (network)

A TDM physical transmission standard consisting of two twisted wire pairs and related equipment capable of carrying a 1.544 Mbps DS-1 signal. Term often used interchangeably with DS-1.

T3 (network)

A TDM digital channel carrier that operates at 44.736 Mbps. It can multiplex 28 T1 signals and it is often used to refer to DS-3.
An informal term generally applied to any transmission system capable of carrying a 44.736 Mbps DWS-3 signal (coax, fiber optic, digital microwave, etc.). There is no transmission standard called "T-3.".

TA

Terminal Adapter/Adaptator (network, ISDN)
Equipment used to adapt Integrated Services Digital Network (ISDN) Basic Rate Interface (BRI) channels to existing terminal equipment standards such as RS-232 and V.35. A Terminal Adaptor is typically packaged like a modem, either as a standalone unit or as an interface card that plugs into a computer or other communications equipment (such as a router or PBX). A Terminal Adaptor does not interoperate with a modem; it replaces it.

Tag (World-Wide Web)

A formatting command included an HTML (or other markup language) document.

TASI

Time Assignment Speech Interpolation (communications)
TASI systems represent an example of an ANALOG Statistical Time Division Multiplexing scheme. These systems enjoyed limited use in the 1980s, and were particularly adept at sharing voice circuits; specifically PBX trunks. A TASI multiplexer is interconnected between the PBX and the trunk facilities. Usually, one analog trunk circuit is used for signaling purposes between TASI units at each end of the link. The remaining voice trunks support analog TASI TDM voice conversations. In normal telephone conversations, a majority of time is spent in a latent (idle) state. TASI trunks will allocate "snippets" of voice from another channel during this idle time. If an individual were to monitor these TASI trunks, they would hear bits and pieces of various conversations. The signaling channel is used for the signaling conversion between End-Point PBX (Private Branch Exchange) units and also for the allocation of bandwidth once incoming speech energy has been detected.
As digital speech processing became more common, TASI systems were created that had analog inputs, and digital outputs. This type of multiplexing technique is more commonly known as "Digital Speech Interpolation" (DSI).
Unfortunately, TASI and DSI systems suffer from a few drawbacks. First, there can be a lot of voice "clipping" noticed by users. This occurs when a little bit of speech is lost while waiting for the TASI mux to detect valid speech and allocate bandwidth. Clipping also occurs when there just isn't bandwidth present at the moment. Also, TASI and DSI units are very susceptible to audio input levels and may have problems with the transport of voiceband data (e.g. VF modem) signals.

TAXI

Transparent Asynchronous Transmitter/receiver Interface (network)
Physical layer specifications for the transmission of bit streams over multi-mode optic fiber at 100 Mbps using 4B/5B encoding. Same specifications as in FDDI. See PHY.

TC

Transmission Convergence (ATM)
One of the two PHY sublayers that is responsible for adapting the ATM cells into a stream of bits to be carried over the physical medium. See also PM.

TCP

Transmission Control Protocol (network, Internet)
Originally developed by the Department of Defense to support the interworking of dissimilar computers across a network. Provides end-to-end, connection-oriented, reliable transport layer (layer 4) functions over IP-controlled networks. Operating on top of IP (combined known as TCP/IP), it is responsible for multiplexing sessions, error recovery, end-to-end reliable delivery and flow control.

TCP/IP

Transmission Control Protocol/Internet Protocol (network, Internet)
Set of protocols developed by the Department of Defense to develop ways to connect dissimilar computers across a network. Protocol family of the Internet network, that combines both TCP and IP. Widely used applications, such as Telnet, FTP and SMTP interface to TCP/IP.

TCR

Tagged Cell Rate (ATM)

TCS

Transmission Convergence Sublayer (ATM)

TCU

Transmission Control Unit (communications)

TDJ

Transfer Delay Jitter (ATM)
See CDV.

TDM

Time-Division Multiplexing (network)
A technique for splitting the total bandwidth (link capacity) into several channels to allow bit streams to be combined (multiplexed). The bandwidth allocation is done by dividing the time axis into fixed-length slots and a particular channel can then transmit only during a specific time slot. The transmission rate of the high-speed circuit must be equal to, or greater than, the aggregate speed of all of the channels.

TDM

Time Division Multiplexing (communications)
A type of multiplexing where two or more channels of information are transmitted over the same link by allocating a different time interval ("slot" or "slice") for the transmission of each channel, i.e. the channels take turns to use the link. Some kind of periodic synchronising signal or distinguishing identifier is usually required so that the receiver can tell which channel is which.
TDM becomes inefficient when traffic is intermittent because the time slot is still allocated even when the channel has no data to transmit. Statistical time division multiplexing was developed to overcome this problem. See also TDMA.

TDMA

Time Division Multiple Access (communications)
Data multiplexing scheme used as the basis for all digital switching networks and Central Office switches. Each 8 kHz sample of an analog signal from a given phone line or channel is coded into 8 bits of digital information. These are then time multiplexed into successive bytes of data within a digital bus or channel of data. See also TDM.

TE

Terminal Equipment (network)

Telco (general)

TELephone COmpany (network)
Typically the regulated operating company. See also PTT, common carrier.

Teletel

French telecommunication service using the minitel terminal and the videotex protocol.

Telnet

An asynchronous, virtual terminal protocolt hat allows for remote access.

TERENA

Trans-European Research and Education Networking Association (network)
TERENA was formed in October 1994 by the merger of RARE and EARN to promote and participate in the development of a high quality international information and telecommunications infrastructure for the benefit of research and education.

Terminal (general)

A general device that allows you to send commands to a computer somewhere else. At a minimum, this usually means a keyboard and a display screen and some simple circuitry.
Usually you will use terminal software in a personal computer. the software pretends to be (emulates) a physical terminal and allows you to type commands to a remote computer.

TFTP

Trivial File Transfert Protocol/B> (network, Internet, unix)
Protocol used on a local network to transfer files. It uses UDP.

Throughput (communications)

Amount of information processed or communicated during a specified period of time; usually expressed in terms of bits-per-second (bps) or packets-per-second.

Time-Out - Timeout (general)

The expiration of a pre-defined interval which then triggers some action.
A common example is sending a message. If the receiver does not acknowledge the message within some preset timeout period, a transmission error is assumed to have occured. The resulting time-out usually results in a retransmission of information.

Time Sharing - Timesharing (operating system)

An operating system feature allowing several users to run several tasks concurrently on one processor, or in parallel on many processors, usually providing each user with his own terminal for input and output. time-sharing is multitasking for multiple users.

TM

Traffic Management
Means for providing connection admission (CAC), congestion and flow control (i.e. UPC, traffic shaping). See also Congestion control.

Token (network)

1. A basic, grammatically indivisible unit of a language such as a keyword, operator or identifier.
2. An abstact concept passed between cooperating agents to ensure synchronised access to a shared resource. Such a token is never duplicated or destroyed (unless the resource is) and whoever has the token has exclusive access to the resource it controls. See for example token-ring. If several programmers are working on a program, one programmer will "have the token" at any time, meaning that only he can change the program whereas others can only read it. If someone else wants to modify it he must first obtain the token.

Token Ring (network)

A computer local area network arbitration scheme in which conflicts in the transmission of messages are avoided by the granting of "tokens" which give permission to send. A station keeps the token while transmitting a message, if it has a message to transmit, and then passes it on to the next station.
Often, "Token Ring" is used to refer to the IBM's IEEE 802.5 token ring standard, which is the most common type of token ring and that generally runs at 4 Mbps or 16 Mbps; this is a shared medium whereby each user contends for the available bandwidth and the actual throughput for each user is a fraction of the LAN speed.

Traffic Contract (ATM)

An agreement between the user and the network management agent regarding the expected QoS provided by the network and the user's compliance with the pre-determined traffic parameters (i.e. PCR, MBS, burstiness, average cell rate).

Traffic Descriptors (ATM)

A set of parameters that characterize the source traffic. These are the PCR, MBS, CDV and SCR.

Traffic shaping (ATM)

A method for regulating non-complying traffic (i.e. violates the traffic parameters, such as PCR, CDV, MBS as specified by the traffic contract). See also GCRA. Usually this is a worst case or worst case plus average rate.

Trailer

Protocol control information located at the end of a PDU.

Transceiver

Device that broadcasts signals towards several other devices but in a passive way (it does not change the signals).

Transpac

French network service using X.25 standard.

TTP

Trusted Third Party (security, cryptography)
A security authority or its agent, trusted by other entities with respect to security-related activities.

Twisted Pair (Cable) (hardware)

A type of cable in which pairs conductors are twisted together to produce certain electrical properties.

Tx

Transmitter (network)
A terminal device that includes signal driving electronics.

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