Telecom Dictionary

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T1 Carrier
A T1 carrier is a time-division multiplexed digital transmission facility capable of supporting 24 
voice channels, (each encoded as a 64 kbps PCM DS0 signal), producing an aggregate 
multiplexer output signal at the 1.544 Mbps DS1 rate. Developed in the 1960s, the T1 carrier is 
designed to operate full duplex over two pairs in unshielded twisted pair (UTP) cable.

Tandem Switching System
A tandem switching system is a broad functional category describing systems that connect trunks 
to trunks, and route traffic through a network.

Tariff
A tariff is a published rate for a specific telecommunications service, equipment, or facility that 
constitutes a public contract between the user and the telecommunications supplier (i.e., carrier); 
tariff services and rates are established by and for telecommunications common carriers in a 
formal process in which carriers submit filings for federal or state government regulatory review, 
public comments, possible amendment, and approval.

TA 
terminal adapter

TCP/IP
Transmission control protocol/internet protocol. TCP/IP is the transport layer and Internet layer, 
respectively, of the Internet suite of protocols. TCP corresponds to layer 4 of the OSI protocol 
stack: IP performs some of the functions of layer 3. It is a connectionless protocol used primarily 
to connect dissimilar networks to each other.

TCP 
transmission control protocol

TDMA 
time division multiple access

TDM 
time division multiplexing

Telecommunications
Telecommunications is any process that enables one or more users to pass to one or more other 
users information of any nature delivered in any usable form, by wire, radio, visual, or other 
electrical, electromagnetic, optical means. The word is derived from the Greek tele, "far off," and 
the Latin communicare "to share."

Telecommunications Closet
In a premises distribution system, a telecommunications closet is an area for connecting the 
horizontal and backbone wiring and for containing active or passive PDS equipment.

Telecommunications Network
A telecommunications network is a system of interconnected facilities designed to carry traffic 
from a variety of telecommunications services. The network has two different but related 
aspects. In terms of its physical components, it is a facilities network. In terms of the variety of 
telecommunications services that it provides, it can support a set of many traffic networks, each 
representing a particular interconnection of facilities.

Telecommunications Service
Telecommunications service is a specified set of information transfer capabilities provided to a 
group of users by a telecommunications system.

Terrestrial Microwave Radio
Terrestrial microwave radio is a transmission systems consisting of at least two radio 
transmitter/receivers (transceivers) connected to high gain antennas (directional antennas which 
concentrate electromagnetic or radiowave energy in narrow beams) focused in pairs on each 
other. The operation is point-to-point, that is, communications are established between two and 
only two antennas (installations) with line-of-sight visibility. This can be contrasted to point-to-
multipoint systems like broadcast radio or television.

TIA 
Telecommunications Industry Association

Time Division Multiplexing (TDM)
Time Division Multiplexing is a transmission facility shared in time (rather than frequency), i.e., 
signals from several sources share a single channel or bus by using the channel or bus in 
successive time slots. A discrete time slot or interval is assigned to each signal source.

Time Division Switch
A time division switch is a switch that implements the switch matrix using the TDM process, in a 
time-slot interchange (TSI) arrangement (usually denoted by T in combined time and space 
division switches).

Token Passing Bus LAN (IEEE 802.4)
A token passing bus LAN is a LAN using a deterministic access mechanism and topology in which 
all stations actively attached to the bus "listen" for a broadcast token or supervisory frame. 
Stations wishing to transmit must receive the token before doing so; however the next logical 
station to transmit may not be the next physical station on the bus. Access is controlled by pre-
assigned priority algorithms.

Token Passing Ring LAN (IEEE 802.5)
A token passing ring LAN is a LAN using a deterministic access mechanism and topology, in 
which a supervisory frame (or token) is passed from station to adjacent station sequentially. 
Stations wishing to transmit must wait for the "free" token to arrive before transmitting data. In a 
token ring LAN the start and end points of the medium are physically connected, leading to a ring 
topology.

TP 
transaction processing

Tracking
Tracking features user-defined approval levels and project milestone tables to generate project 
cost and status information, which is tracked for reporting and review. As assigned tasks are 
completed, supervisors make daily entries identifying the number of hours worked on a task, 
materials used, and the number of work units completed. This information is then available for 
project jeopardy tracking, cost tracking, and determination of contractor payments due.

Traffic
Traffic is the flow of information within a telecommunications network.

Transceiver
A transceiver is a generic term describing a device that can both transmit and receive. In IEEE 
802 local area network (LAN) standards, a transceiver consists of a transmitter, receiver, power 
converter, and, for CSMA/CD LANs, collision detector and jabber detector capabilities. The 
transmitter receives signals from an attached terminal's network interface card (NIC) and 
transmits them to the coaxial cable or other LAN medium. The receiver receives signals from the 
medium and transmits them via the transceiver cable and NIC to the attached terminal. The 
jabber detector is a timer circuit that protects the LAN from a continuously transmitting terminal.

Transfer Mode
Transfer mode is a generic term for switching and multiplexing aspects of broadband integrated 
services digital networks (BISDN), adopted by CCITT Study Group XVIII.

Transmission control protocol/internet protocol (TCP/IP)
See "Internet suite of protocols" and "TCP/IP".

Transmission Facilities
Transmission facilities provide the communication paths that carry user and network control 
information between nodes in a network. In general, transmission facilities consist of a medium 
(e.g., free space, the atmosphere, copper or fiber optic cable) and electronic equipment located 
at points along the medium. This equipment amplifies (analog systems) or regenerates (digital 
systems) signals, provides termination functions at points where transmission facilities connect to 
switching systems, and may provide the means to combine many separate sets of call 
information into a single "multiplexed" signal to enhance the transmission efficiency.

Transmission Impairments
Transmission impairments is the degradation caused by practical limitations of channels (e.g., 
signal level loss due to attenuation, echo, various types of signal distortion, etc.), or interference 
induced from outside the channel (such as power-line hum or interference from heavy electrical 
machinery).

Transmission Medium
Transmission medium is any material substance or "free space" (i.e., a vacuum) that can be, or 
is, used for the propagation of suitable signals, usually in the form of electromagnetic (including 
light waves), or acoustic waves, from one point to another; unguided in the case of free space or 
gaseous media or guided by a boundary of material substance.

Transport Services
Transporrt Services are network switching, transmission and related services that support 
information transfer capabilities between originating and terminating access service facilities.

Trunk
In a network, a trunk is a communications path connecting two switching systems used to 
establish end-to-end connections between customers.

Twisted Pair
Twisted pair is the most common type of transmission medium, consisting of two insulated 
copper wires twisted together. The twists or lays are varied in length to reduce the potential for 
interference between pairs. In cables greater than 25 pair, the twisted pairs are grouped and 
bound together in a common cable sheath. See unshielded twisted pair.