Trunk Type One, a digital transmission channel that carries data at the 1.544 Mbps rate (DS-1 level); in a digital service it is used primarily for short-haul links. A dedicated T1 can support as many as (130) IP voice calls vs. 24 simultaneous calls as in today's carrier networks.

Digital WAN carrier facility. T3 transmits DS-3-formatted data at 44.736 Mbps through the telephone switching network.

Telemetry Asynchronous Block Serial

AT&T polled point-to-point or multipoint communication protocol that supports moderate data transfer rates over intra-office wire pairs.

Terminal Access Controller

Internet host that accepts terminal connections from dial-up lines.

Terminal Access Controller Access Control System

Authentication protocol, developed by the DDN community, that provides remote access authentication and related services, such as event logging. User passwords are administered in a central database rather than in individual routers, providing an easily scalable network security solution.

Total Access Communications System

An analogue cellular phone technology. Used in the United Kingdom and Italy.

High-performance, packet-forwarding technology that integrates network layer (Layer 3) routing and data link layer (Layer 2) switching and provides scalable, high-speed switching in the network core. Tag switching is based on the concept of label swapping, in which packets or cells are assigned short, fixed-length labels that tell switching nodes how data should be forwarded.

ATM cells that have their CLP bit set to 1. If the network is congested, tagged traffic can be dropped to ensure delivery of higher-priority traffic.

Dynamic switching of voice calls between VoFR, VoATM, or VoHDLC PVCs and subchannels; also called tandeming. Tandem switching is often encountered in multi-hop VoFR call connection paths.

A Trans-Atlantic undersea fibre optic cable system.

The first transoceanic fibre optic cable that was installed in 1988.

A Transatlantic fibre optic cable linking the United States with both the United Kingdom and France. Associated with TAT G-1. Both TAT-9 and TAT G-1 are mutually restoring, meaning they will serve as back-ups to each other.

The first high-speed Trans-Atlantic fibre optic cable to link the USA with Germany. Associated with TAT-9.

Transparent Asynchronous Transmitter/Receiver Interface 4-byte/5-byte

Encoding scheme used for FDDI LANs as well as for ATM. Supports speeds of up to 100 Mbps over multimode fibre. TAXI is the chipset that generates 4B/5B encoding on multimode fibre.

Tape-automated bonding Ball Grid Array package

Transmission Convergence

Sublayer of the ATM physical layer that transforms the flow of cells into a steady flow of bits for transmission over the physical medium. Part of layer 1 of B-ISDN

Transaction Capabilities Application Part

Terminating Call Control

Tool Command Line Interface

Transmission Control Protocol/Internet Protocol

A set of communications protocols developed by the U.S. Department of Defence, now considered a de facto standard for local area networks.

Time Division Code Division Multiple Access

Time Division Duplex

Time Division Multiplexing

A method of multiplexing in which multiple information streams "take turns" with a single communications channel. Each stream is allocated a specific percentage of the common channel.

Time Division Multiple Access

One of several technologies used to separate multiple conversation transmissions over a finite frequency allocation of through-the-air bandwidth. Allocates a discrete amount of frequency bandwidth to each user, to permit many simultaneous conversations. However, each caller is assigned a specific timeslot for transmission. See also Code Division Multiple Access (CDMA).

Time Domain Reflectometer

Device capable of sending signals through a network medium to check cable continuity and other attributes. TDRs are used to find physical layer network problems.

Terminal Equipment

Any ISDN-compatible device that can be attached to the network, such as a telephone, fax, or computer.

Terminal Endpoint Identifier

Field in the LAPD address that identifies a device on an ISDN interface.

Telephone Company

A wireless communications system designed for the collection and dissemination of data. Applications include vehicle-based electronic systems: mobile telephony, vehicle tracking and positioning, on-line navigation and information services and emergency assistance. Static applications include stock control (automatic ordering), and monitoring of utilities meters.

Capability of transmitting or retrieving data over long distance communication links, such as satellite or telephone.

Science of converting sound to electrical signals and transmitting it between widely removed points.

Intelligent agent technology developed by General Magic Inc.

Standard terminal emulation protocol in the TCP/IP protocol stack. Telnet is used for remote terminal connection, enabling users to log in to remote systems and use resources as if they were connected to a local system.

One trillion bits.

Trans-European Research and Education Networking Association

Organization that promotes information and telecommunications technologies development in Europe. Formed by the merger of EARN and RARE.

Communications processor that connects asynchronous devices such as terminals, printers, hosts, and modems to any LAN or WAN that uses TCP/IP, X.25, or LAT protocols. Terminal servers provide the internetwork intelligence that is not available in the connected devices.

Trivial File Transfer Protocol

A simplified version of FTP that transfers files but does not provide password protection or user-directory capability. It is associated with the TCP/IP family of protocol. TFTP depends on the connectionless datagram delivery service, UDP.

Texas Higher Education Network

Regional network comprising over 60 academic and research institutions in the Texas (United States) area.

Term used to define a thinner, less expensive version of the cable specified in the IEEE 802.3 10Base2 standard.

The actual speed of a network.

Telecommunications Industries Association

The group responsible for setting telecommunications standards in the United States.

Token Ring Interface Coupler

Controller through which an FEP connects to a Token Ring.

Terminal Identifier

Event that occurs when one network device expects to hear from another network device within a specified period of time, but does not. The resulting timeout usually results in a retransmission of information or the dissolving of the session between the two devices.

Transpath Input and Output Subsystem

Trunk Information Record Keeping System

Bellcore OSS that provides record keeping for interoffice trunk facilities.

Transparent Local Area Network

Transport Level Security

TLS provides for mutual authentication, integrity-protected negotiation and key exchange between two endpoints.

Telecommunication Management Network

ITU-T generic model for transporting and processing OAM&P information for a telecommunications network.

Refers to a generic type of LAN architecture. The token-ring concept involves a data signal, or token, that passes around a ring configuration from station to station, with no central control element.

Technical Office Protocol

OSI-based architecture developed for office communications.

Describes how a network is structured.

Type of Service

Token Ring Virtual LAN

A superset of PING used to evaluate the hops taken from one end of a link to the other.

Set of CoS attribute values assigned to a given port on an ATM switch. The profile affects numerous parameters for data transmitted from the port including rate, cell drop eligibility, transmit priority, and inactivity timer.

Shaping of the cell stream to improve the load of an ATM line. (2) Use of queues to limit surges that can congest a network. Data is buffered and then sent into the network in regulated amounts to ensure that the traffic will fit within the promised traffic envelope for the particular connection. Traffic shaping is used in ATM, Frame Relay, and other types of networks. Also known as metering, shaping, and smoothing.

Specific to handsets, a tri-band cellular phone will operate on three different frequencies, depending on the available network. Outside America, the GSM frequencies used are 900MHz and 1800MHz. 'American GSM', or PCS, operates at 1900MHz. The introduction of tri-band phones is a further step towards true worldwide roaming.

Token Ring Inter-Switch Link

Transport facility connecting two switch entities (typically called long haul transport).

Telephony Services Applications Programming Interface.

Telephone Service Factor

Transmitting Subscriber Information

Frame that can be sent by the caller with the caller's telephone number that can be used to screen calls.

Trans-Soviet Line

Formerly Trans-Siberian Line.

Tag-Switched Path

Time-To-Live

An IETF specification that calls for a minimum default value of 64 hops before a data packet expires.

Trusted Third-Party Services

Tributary Unit

Tributary Unit, virtual container in SDH in combination with its pointer

Trunk Up-Down

Protocol used in ATM networks that monitors trunks and detects when one goes down or comes up. ATM switches send regular test messages from each trunk port to test trunk line quality. If a trunk misses a given number of these messages, TUD declares the trunk down. When a trunk comes back up, TUD recognizes that the trunk is up, declares the trunk up, and returns it to service.

Tributary Unit Group

Additional TU-1s

TCP and UDP over Lightweight IP

Proposed protocol for running TCP and UDP applications over ATM.

TCP and UDP over Nonexistent IP

Proposed protocol for running TCP and UPD applications over ATM.

Communications switchboards used by the financial community. They have phones, speed-dial buttons, and monitors.

Teletel Vitesse Rapide

A 9.6 Kbps videotex service to handle low-resolution photos.

Relatively low-speed transmission medium consisting of two insulated wires arranged in a regular spiral pattern. The wires can be shielded or unshielded. Twisted pair is common in telephony applications and is increasingly common in data networks.

Number Transceive Slots