电信专业英英词典T-3（在线收听）

　　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.

　　T-1 - A leased line connection that can carry 1,544,000 bits per second.

　　T-3 - A leased line connection that can carry 44,736,000 bits per second.

　　Tariff - Documents filed by a telephone company with a state public utility commission and the FCC describing its services and the payments to be charged for the services.

　　TCP/IP - See Transmission Control Protocol/Internet Protocol

　　Telecommunications Relay Center Fee/Charge/Surcharge - This state fee helps pay for the relay center that transmits and translates calls for people who are deaf, hard-of-hearing or speech disabled. Mandated nationally by Congress with the passage of the Americans with Disabilities Act, it may also be called “Telecommunication Devices for the Deaf Tax.”

　　Telephone Network - The system of wires, fiber-optic cables, satellites and transmission towers that transmit telephone messages from caller to receiver.

　　Telnet - A program that allows Internet users to login to computers other than their host. Telnet also refers to the act of doing so.

　　Text Format vs. HTML Format - Some Web applications, such as e-mail or Web pages, can either be viewed in Text or HTML formats. Text formats generally display only the words (text) in an e-mail or on a Web page and not graphics, such as artwork or photos. HTML format allows display of both text and graphics.

　　Toll Call - A call to any location outside the local service area. Otherwise known as a long distance call.

　　Transmission Control Protocol/Internet Protocol (TCP/IP) - A set of communications protocols or software necessary to access the Internet.

　　Trunk - A communication line between two switching systems. In other words, a telephone line.

　　TTY/TDD - Telephone Typewriter and Telephone Device for the Deaf. A telecommunication device for the hearing impaired using teletypewriter principals. The users call a special operator number and third-party translation.