A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
T Carrier - T1 or T3 transmissions systems.
T1 - (1) T-carrier one signal; 1.544 Mbps circuit; the equivalent of 24 analog lines. (2) Basic 24-channel 1.544 Mbps pulse code modulation system used in the United States. Aka DS1 (but DS1 lines do not have a -135-V carrier).
T3 - Transmission at 44.376 Mbps. Commonly referred to as 45 Mbps or DS3. Capable of handling 672 voice conversations.
Tandem - Telephone company node / central office classification, containing a switch where all outer and inner area code traffic is handled, in an area code where the handoff for long distance service happens. A central office that carries a call, but only switches the call to the central office where the called customer is served - it does not actually connect the call with the end customer.
Tandem Switch - see Tandem.
Tandem Trunks - Trunk lines connecting central offices / switching equipment.
Tariff - Published rates, regulations and descriptions governing the provisions of telecommunications services.
Telco - Local telephone company; local exchange carrier.
Telecommunications - The exchange of information across a distance.
Telecommunications Common Carrier (TCC) - Person, firm, or corporation that owns or operates telecommunications facilities for the purpose of providing either the facilities or services for profit.
Telecommunications Device for the Deaf (TDD) - A device, attached to a telephone handset, allowing deaf people to communicate by typing messages to each other.
Ten/One Hundred - Ethernet reference. 10BaseT is 10Mbps, 100BaseT is 100 Mbps, aka 802, 10/100. As 10BaseT and 100BaseT can interconnect, the network as a whole is commonly called ten/one hundred network.
Tera - Prefix for Trillion. Example - 1 THz equals 1,000,000,000,000 hertz.
Terabyte - 1 Trillion bytes.
Terrestrial Data Service - Data signal transport service over terrestrial microwave.
Terrestrial Facilities - Transmitters, telephone lines, telephone poles, central offices - communication facilities that are based on the ground. Pretty much anything but satellites.
Terrestrial Microwave - Aka eyeball shot, 38 Gig, or radio. Used to bypass construction costs of broadband private line services. Usually in the 33-39 Ghz range, available in T1, DS3, and STS-1, with range dependent on antenna size (usually 1 or 2 feet in diameter; 1 ft dish had a 1-3 mile range, 2 ft dish of 2-7 miles), depending on weather (range is reduced due to rain, snow, and fog).
THz - Short for Terahertz - 1 THz equals 1,000,000,000,000 Hz.
Tie Line - Private line communications channel provided by communications carriers that link two or more points together.
Time Division Multiplex (TDM) - See Multiplex
Time Slot - On a time-division multiplexed circuit; a channel is also called a time slot.
Time Division Multiple Access (TDMA) - Aka Frequency Division Multiple Access (FDMA) - Another name for time division multiplexing; only TDMA or FDMA can multiplex signals together over a transmission frequency, used in spread spectrum cellular radios/transmitters by the cellular telephone industry.
Toll Call - Any transmission on the public switched network to a point outside the local service area.
Toll Office - Switching center where intercity circuits terminate; usually one switching center in a city is designated as the toll office and is also used for mileage rate measurements.
Topology - Two types; physical and logical. Logical topology defines the way a LAN communicates. Physical topology defines the way a LAN is physically wired.
Traffic Overflow - Condition that occurs when the number of calls to be processed exceeds the capacity of a particular trunk group; calls are redirected automatically or manually to another trunk group.
Transducer - Device that converts signals from one form to another.
Transmission - Analog, digital, or light-wave signals, sent across a media.
Transmission Control Protocol (TCP) - Part of the TCP/IP protocol, ensuring data gets deliverd in the proper sequence to the upper application layer without duplication, errors, or missing data; the TCP layer sections data into segments, giving each segment a sequence number and header, to which an IP header is added prior to handoff to lower layers and remote host connections.
Transmission Control Protocol/Internet Protocol (TCP/IP) - The two best know internet protocols, often erroneously thought of as one protocol. TCP which corresponds to layer 4 (the transport layer)of the OSI reference model, provides reliable transmission of data. IP which corresponds to layer 3 of the network layer of the OSI reference model, provides connectionless datagram service. TCP/IP was developed by the Department of Defense in the 1970's to support construction of internetworks worldwide.
Transport Layer - Communications protocol layer that performs error correction and the controls the direction of data flow (receive/transmit).
Transport Medium - Physical component (fiber optic, coax, copper twisted pair, or air) that a signal is transported over.
Transport Protocol - Refers to how data should be presented to a layer or device in a transmission protocol; examples are SONET, T1, STS-1 and OC-N.
Trunk - (1) Group of circuits that carry call traffic in and out of the switch. (2) Circuit or channel connecting two exchanges or two switching devices. (3) Circuit capable of being switched at both ends. [Trunk differs from a line or circuit; one end does not terminate on a switching machine.]
Trunk Group - Group of telephone lines that connect a key telephone system or PBX to the phone company. Used in applications such as incoming customer service lines, information lines, or sales lines.
Tunneling - Encapsulating data from one application/protocol to another - used for transporting multiple protocols over single connections, also used in network security applications.
Twisted Pair - Communications wiring; 19 to 26 AWG solid and insulated, color-coded wire pairs. Common sizes include 2 pair, 3 pair, 4 pair, 25 pair, 50 pair, and 100 pair, used in computer networks. Ratings include CAT 3 (voice), CAT4 (voice and 10baseT) an CAT5 (100baseT and token ring).
Two-Way Calling - Inbound and outbound traffic on the same switched service trunk group.
Two Wire Circuit - Circuit that uses two wires to work, such as the phone line in your house. Aka subscriber loop.