- T1 A committee belonging to the ANSI whose role is to establish US standards for digital telephony, particularly ISDN. The committee is in no way responsible for or involved with the Tl (1.5Mbit/s) circuit standards.
- T1 A US and Japanese standard for high-speed data transmission at 1.544Mbit/s - 24 64Kbit/s channels plus 8Kbit/s' control information are provided. Also called a DS1.
- T3 A US standard for high-speed data transmission at 44.736Mbit/s, providing the equivalent bandwidth of 28 T1 circuits. Also called a DS3.
- TA (Telecommunications Administration) A body, usually a company, that provides public telecommunications services.
- T-Carrier The US standards for digital transmission lines. The line types are of the form Tn or TIC, and the corresponding line signal standards of the form DSn or DSIC.
- Tap The connecting device on cable-based LANs like Ethernet, linking to the main transmission medium.
- TASE.2 Telecontrol Application Service Element Two
- TBI Ten Bit Interface
- TCP (Transmission Control Protocol) The standard transport level protocol that provides the full duplex, stream service on which many application protocols depend. TCP allows a process or one machine to send a stream of data to a process on another. Software implementing TCP usually resides in the operating system and uses the IP to transmit information across the network.
- TCP/IP (Transmission Control Protocol/Internet Protocol) The suite of protocols developed and used by DAR PA and the US DOD. They build up to Laye r Four of the ISO OSI model, but there is no direct correspondence layer for layer. Three main protocols sit above TCP/IP: Telnet, FTP and SMTP.
- TDM (Time Division Multiplexer/Multiplexing) Multiplexer which apportions the time available on its Composite link between its channels, interleaving data from successive channels. The method divides up digital channels to make maximum use of their bandwidth, by taking input from each source in turn. TDMs use one of two methods to achieve this, bit interleaving for synchronous protocols and character interleaving for asynchronous protocols.
- TDMA (Time Division Multiple Access) In LAN technology, a high-speed, burst mode of operation that can interconnect LANs. First used as a multiplexing technique on shared communications satellites.
- Teletex ITU-TS standard for text and message communications intended to replace telex-operating at 2,400bps, it accommodates upper and lower case characters and has a well-defined format for transmission and text presentation.
- Teletext Method of transmitting pages of information using broadcast transmission techniques. Embraces both standard broadcast transmission systems and in-house/cable systems using this format.
- Terminal emulation Software that allows a PC to mimic the attributes of a dumb terminal normally attached to a mainframe or mini-computer, giving the user with access to function keys and control sequences which the host applications normally use when communicating with one of their own dumb terminals. The most commonly emulated terminals are Dec's VT100 terminal and IBM's 3270.
- TFTP (Trivial File Transfer Protocol) The TCP/IP standard protocol for file transfer with minimal capability and minimal overhead. TFTP depends on the connectionless datagram delivery service, UDP.
- Thin Ethernet An 802.3 LAN that uses smaller than normal diameter coaxial cable; often used to link PCs together. It runs at the same frequency as Ethernet but at smaller distances. Colloquially called Cheapernet.
- TIA Telecommunications Industry Association
- Timeout The expiration of a pre-defined interval which then triggers some action. For example, in a 30-second, no activity timeout, disconnection occurs after 30 seconds of no data activity. Simple eh? Alternatively, the length or existence of such an interval.
- Token Unique information in a packet header which acknowledges that control of the network is to be relinquished upon receipt of the packet. An empty packet containing a token is forwarded by the recipient to the next node. The token packet passes round the LAN continuously and, as it goes by, give each workstation the all-clear to transmit data.
- Token Bus A LAN with a bus topology that uses token passing as its access method. The sequence of nodes is not governed by physical architecture, but is controlled by software. Arcnet and Map are examples.
- Token passing A technique for restricting access to a network, to a single node at a time. A token is passed from node to node, granting permission to transmit data. The sender attaches its message to the token which conveys it across the LAN to its destination, The message is ignored by all other nodes, and is acted upon by the addressee, When the recipient has accepted the message, it releases the token so that the next node wishing to send can use it.
- Token Ring A 4/16Mbit/s LAN architecture which uses a token passing access method to allow nodes on the network to transmit data. Defined in IEEE 802.5 with a ring architecture, a special data packet, called a token, is passed continuously from node to node (see Token passing, above). The sequence of nodes is governed by the physical order in which the nodes appear on the ring. Every node on the ring sees the data, but only the addressed receiving node will accept it.
- Top (Technical and Office Protocols) A Functional Profile originated by Boeing to separate networking in a non-shop floor environment. TOP was designed from the outset to be compliant with the ISO OSI seven-layer model. Development has beer merged with MAP, and the two functional profiles share a common integration strategy, and have a single (Map/Top) user group.
- TP-4/IP A term given to the ISO protocol suite that closely resembles TCP/IP. Transceiver - A communications device and software capable of transmitting and receiving (see also MAU). Transmission block - A sequence of continuous data characters or bytes transmitted as a unit, over which a coding procedure is usually applied for synchronous or error control purposes.
- Transparent Bridging So named because the intelligence necessary to make relaying decisions exists in the bridge itself and is thus "transparent" to the communicating workstations. It involves frame forwarding, learning workstation addresses and ensuring no topology loops exist (in conjunction with the Spanning Tree algorithm).
- Transport driver A network device driver that implements a protocol for communicating between LAN Manager and one or more media access control drivers. The transport driver transfers LAN Manager events between computers on the local area network.
- Transport Layer The Fourth Layer in the OSI model, drawn up by the ISO. The purpose of the transport layer is to act as an intermediary between the user and the network. All layers above the transport layer are network independent.
- Tree topology A graphic description of a network topology where there is only one route between any two nodes.
- Trellis coding An advanced method of modulation which combines coding of both amplitude and phase. This gives a greater throughput and lower error rate for speeds above 9.6Kbit/s.
- Trunk in token ring, a trunk is the cab e running between MSAUs and can be either fiber or shielded twisted pair cable. STP uses two positive transmit wires in normal mode, with no crossover, while fiber has one transmit fiber and one receiver fiber. In normal mode, the second pair of wires is not used it acts as backup and implements the Wrap feature.
- Twisted Pair Two insulated copper wires twisted together with the twists or lays varied in length to reduce potential signal interference between the pairs. Where cables comprise more than 25 pairs, they are usually bundled and wrapped in a cable sheath. Twisted pair is the most common medium for connecting phones, computers and terminals to PABXS. With the IEEE ratification of 10BaseT for networking 10Mbit/s Ethernet over UTP telephony wiring, twisted pair has become ubiquitous. As well as performance at Ethernet rates, it offers cost benefits to the end user through flexibility - ease of relocation. New data-grade and even voice-grade UTP methods support l00Mbit/s transmission, with 155Mbit/s ATM a probability.
- Type A Intelligent Network term describing IN services evoked by, and affecting, a single user. Most of them can only be invoked during call setup or teardown.
- Type B Intelligent Network term describing IN services invoked at any point by, and affecting directly, several users.