TA (terminal adapter)
A protocol converter that connects a non-ISDN device to the ISDN network.

TACS (Total Access Communications System)
A standard for analog telephony that was deployed widely in Europe before GSM became the most popular approach.

T-carrier
The North American standard of the PDH, a time-division multiplexed, digital transmission system. T-carrier is a PCM system that uses 64Kbps per channel as the basis of the hierarchy. Higher levels reflect aggregation of the 64Kbps channels. T-1 is a 1.544Mbps 24-channel communications circuit; T-2 is a 6.312Mbps 96-channel communications circuit; T-3 is a 44.736Mbps 672-channel communications circuit; T-4 is a 274.176Mbps 4,032-channel communications circuit.

tandem
(1) The connection of networks or circuits in series (i.e., the connection of the output of one circuit to the input of another). (2) An intermediate switch used in a tandem network, which connects only to other switches instead of customers.

tandem data circuit
A data circuit that contains two or more pieces of DCE in series.

tandem switch
Also called a junction exchange or a tandem office, a switch that is used to connect local exchanges throughout the metropolitan area.

tap
An open point on a cable bundle that is left so that technicians can easily splice off a pair to bring additional service to a home or to bring service to a new home.

tariff
The published rate for the use of a specific unit of equipment, facility, or type of service provided by a communications common carrier; also, the vehicle by which the regulating agencies approve or disapprove such facilities or services.

TASI (Time-Assignment Speech Interpolation)
Specialized switching equipment that connects a party to an idle circuit while speech is taking place, but disconnects the party when speech stops, so that a different party can use the same circuit. During the periods of heavy traffic, TASI can improve line efficiency by 45% to 80%.

Tbps (terabits per second)
Trillions of bits per second.

TCAP (Transaction Capabilities Applications Part)
A system that supports intelligent network service by enabling the exchange of noncircuit-related information between different signaling points (that is, network nodes).

TCP/IP (Transmission Control Protocol/Internet Protocol)
The most widely used internetworking protocol. Ensures that packets of data are delivered to their destinations in sequence in which they were transmitted. TCP roughly corresponds to Layer 4 of the OSI model. It provides reliable transmission of data. IP corresponds to Layer 3 (the network layer) of the OSI model and provides connectionless datagram service.

TDD (Time Division Duplexing)
A half-duplex technique in which each end of the conversation makes use of the same frequency.

TDM (Time Division Multiplexing)
A means of obtaining a number of channels over a single path by dividing the path into a number of time slots and assigning each channel its own intermittently repeated time slot. At the receiving end, each time-separated channel is reassembled.

TDMA (Time Division Multiple Access)
A multiple-access technique in which you first divide the available or allocated frequency spectrum into a number of channels. Then, within each channel you apply TDM to carry multiple users interleaved in time.

telco
A telephone company.

telecommunication lines
Telephone and other communication pathways that are used to transmit information from one location to another.

telecommunications
Any process that permits the passage of information from a sender to one or more receivers in any usable form (printed copy, fixed or moving pictures, visible or audible signals, and so on) by means of any electromagnetic system (electrical transmission by wire, radio, optical transmission, waveguides, and so on).

Telecommunications Technology Committee
A body that creates telecommunications standards that are followed in Japan.

teledensity
The number of main telephone lines per 100 inhabitants.

telephone channel
A transmission path designed for the transmission of representing human speech or other telephone communication (e.g., fax) requiring the same bandwidth. The bandwidth of an analog telephone channel is 4,000Hz.

telephony
A generic term describing voice telecommunications.

Telnet
The TCP/IP site protocol that supports a remote login capability.

tera
One trillion.

Terabit switch router
An emerging class of backbone platform that supports Tbps capacity. This type of router is agnostic, and it involves short and predictable delay, robust QoS features, multicast support, and carrier class-availability.

terminal
(1) A point at which information can enter or leave a communication network. (2) Any device capable of sending and/or receiving information over a communication channel. (3) Same as work station.

terminal multiplexer
A device that permits two or more terminals to share one cable as a data transmission path.

terminal server
A device that connects terminals to a network that is typically running Ethernet.

ThickNet (thick Ethernet cable)
Coaxial cable with electrical characteristics that meet the 10Base5 specification for Ethernet networks. It enables a signal to be carried as far as 1,640 feet (500 meters) before requiring a repeater. Also called 10Base5 cable.

ThinNet (thin Ethernet cable)
Coaxial cable with electrical characteristics that meet the 10Base2 specification for Ethernet networks. It enables a signal to be carried as far as 607 feet (185 meters) before requiring a repeater. Also called 10Base2 cable or Cheapernet.

throughput
The useful information processed or communicated during a specific time period; expressed in bits per second or packets per second.

TIA (Telecommunications Industry Association)
An organization that recommends standards for telecommunication.

time-division switching
A switching method for a TDM channel that requires the shifting of data from one slot to another in the TDM frame. The slot question can carry a bit, byte, or, in principle, any other unit of data.

timeout
A set time period for waiting before a terminal system performs some action. Typical uses include a poll release (when a terminal is disconnected if the time-out period elapses before keying resumes), or in access timeout (when a terminal on a local area network using a CSMA/CD access method is prevented from transmitting for a specified time period after a collision occurs).

time-slot interchange
The interchange of time slots within a TDM frame.

Time to Live
A field in an IP datagram that is decremented by each router in order to guarantee that datagrams do not circulate on the Internet forever.

time transparency
The absence of delay and delay jitter through an ATM network thus allowing high-speed transportation of real-time services.

tip
The contacting part at the end of a telephone plug or the top spring of a jack. The conductors associated with these contracts. The other contact is called a ring.

token
A small, 8-bit word that is circulated in a unidirectional fashion among the devices on the network.

token passing
A network access method that uses a special bit pattern called a token that gives permission to nodes to transmit data, one node at a time. Each node is allowed to transmit a message only when it has the token. If a node has no messages to transmit when it receives the token, it passes the token to the next node.

Token Ring
A networked ring of devices that passes a special bit pattern called a token from node to node to determine which device can transmit data on the network. Operates at either 4Mbps or 16Mbps.

toll center
The exchange that is responsible for establishing and completing national, long-distance communications. Also called the Class 4 office, transit switch, toll office, or trunk exchange.

tone signaling
Transmission of supervisory, address, and alerting signals over a telephone circuit by means of tones.

tone-to-dial-pulse conversion
A system of converting DTMF signals to dial pulse signals when the trunks associated with outgoing trunk calls are not equipped to receive tone signals. Auxiliary dial pulse conversion equipment is not necessary.

topology
The connectivity among a group of nodes. Physical topology relates to how devices are cabled. Logical topology refers to how nodes actually interact.

trace packet
In packet switching, a packet that functions as a normal packet but causes a report of each stage of its process to be sent to the network control center.

traffic
(1) Messages sent and received over a communications channel. (2) A quantitative measurement of the total messages and their length, expressed in 100 call seconds or other units.

traffic flow
A measure of the density of traffic.

transaction
An item of business. The handling of customer orders and billing are examples of transactions.

transaction processing
In batch or remote batch processing, the processing of a job or job step-in interactive processing, an exchange between a terminal and another device that does a particular action; for example, the entry of a customer’s deposit and the updating of the customer’s balance.

transceiver
A device that connects a host interface to a local area network.

transducer
A device for converting signals from one form to another, such as a microphone or a receiver.

transmission line
A connection over which data devices communicate. There are five main types of transmission lines: circuits, channels, lines, trunks, and virtual circuits.

transmission medium
A physical pathway that connects computers, other devices, and people on a network. Transmission media can be either wireline (e.g., twisted-pair, fiber) or wireless (e.g., satellite, microwave).

transfer rate
The speed at which information can be sent across a bus or communications link.

translational bridge
A bridge that may connect two different MAC layers (e.g., 802.3 and FDDI).

transmission
Information that is sent in the form of electrical signals over electric wires, waveguides, or radio.

transmission speed
The rate at which information is passed through communications lines, generally measured in bits per second (bps).

transmit
To send information from one location to another.

transparent bridging
A system in which the bridge functions as a node on each of the connected networks, and its presence in the communications path between nodes is transparent. Communications proceeds as if the nodes were on the same network.

transponder
The receiver, transmitter, and antenna equipment that together forms a single repeater channel on a satellite.

transport layer
Layer 4 of the OSI model, providing reliable, transparent transfer of data between endpoints.

tree
A type of bus network topology in which the medium branches at certain points along its length to connect stations or clusters of stations; also called a branching bus.

troubleshooting
Monitoring and testing the performance of a network to detect and fix problems.

trunk
A circuit that is configured to support the calling loads generated by a group of users; the transmission facility that ties together switching systems.

tunneling
The encapsulation of one protocol within another. Tunneling is often used to transport a LAN protocol across a backbone network that does not support the LAN protocol.

turnkey system
A complete communications system, including hardware and software, assembled and installed by a vendor, and sold as a total package.

twisted-pair cable
A cable that consists of two insulated wires twisted around each other (and sometimes wrapped in additional insulation to help shield their signals from electromagnetic noise). Twisted-pair cable is often used in telephone wires; it also serves as the transmission medium in some LANs.

two-wire circuit
A circuit formed by two conductors insulated from each other that can be used as either a one-way transmission path, a half-duplex path, or a duplex path.

Twofish
A very strong encryption algorithm that was one of the five initial candidates for the AES.

type approval
An administrative procedure of technical tests and vetting applied to items of telecommunication equipment before they can be sold or interconnected with the public network. Also known as homologation.