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)

T-1: The T-carrier system, introduced by the Bell System in the U.S. in the 1960s, was the first successful system that supported digitised voice transmission. The original transmission rate (1.544 Mbps) in the T-1 line is in common use today in Internet service provider (ISP) connections to the Internet. Another level, the T-3 line, providing 44.736 Mbps, is also commonly used by ISPs. Another commonly installed service is a fractional T-1 line, which is the rental of some portion of the 24 channels in a T-1 line, with the other channels going unused.
The T-carrier system is entirely digital, using pulse code modulation and time-division multiplexing. The system uses four wires and provides full-duplex capability (two wires for receiving and two for sending at the same time). The T-1 digital stream consists of 24 64-Kbps channels that are multiplexed. (The standardized 64 Kbps channel is based on the bandwidth required for a voice conversation.) The four wires were originally a pair of twisted-pair copper wires, but can now also include coaxial cable, optical fiber, digital microwave, and other media. A number of variations on the number and use of channels are possible.
In the T-1 system, voice signals are sampled 8,000 times a second and each sample is digitised into an 8-bit word. With 24 channels being digitised at the same time, a 192-bit frame (24 channels each with an 8-bit word) is thus being transmitted 8,000 times a second. Each frame is separated from the next by a single bit, making a 193-bit block. The 192 bit frame multiplied by 8,000 and the additional 8,000 framing bits make up the T-1s 1.544 Mbps data rate. The signalling bits are the least significant bits per frame.

T-3: A leased-line connection capable of carrying data at 44,736,000 bits-per-second. This is more than enough to do full-screen, full-motion video.

TA: A terminal adapter (TA) is a hardware interface between a computer and an ISDN line. It's what replaces a modem when you are using an ISDN connection. Unlike "plain old telephone service," which carries signals in analog (voice) form between your computer and the telephone company's office, ISDN carries signals in digital form so there is no need to modulate and demodulate between analog and digital signals. The terminal adapter is what you have to install on a computer so that data can be fed directly into the ISDN line in digital form. Since ISDN service is not available from telephone companies in all areas, the terminal adapter is not usually built into a computer. You purchase and install it when you sign up for ISDN service.

TAG: A tag is a generic term for a language element descriptor. The set of tags for a document or other unit of information is sometimes referred to as markup, a term that dates to pre-computer days when writers and copy editors marked up document elements with copy editing symbols or shorthand.

TCP/IP: TCP/IP (Transmission Control Protocol/Internet Protocol) is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in the private networks called intranets and in extranets. When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.
TCP/IP is a two-layered program. The higher layer, Transmission Control Protocol, manages the assembling of a message or file into smaller packets that are transmitted over the Internet and received by a TCP layer that reassembles the packets into the original message. The lower layer, Internet Protocol, handles the address part of each packet so that it gets to the right destination. Each gateway computer on the network checks this address to see where to forward the message. Even though some packets from the same message are routed differently than others, theyll be reassembled at the destination.
TCP/IP uses the client/server model of communication in which a computer user (a client) requests and is provided a service (such as sending a Web page) by another computer (a server) in the network. TCP/IP communication is primarily point-to-point, meaning each communication is from one point (or host computer) in the network to another point or host computer. TCP/IP and the higher-level applications that use it are collectively said to be "stateless" because each client request is considered a new request unrelated to any previous one (unlike ordinary phone conversations that require a dedicated connection for the call duration). Being stateless frees network paths so that everyone can use them continuously. (Note that the TCP layer itself is not stateless as far as any one message is concerned. Its connection remains in place until all packets in a message have been received.)
Many Internet users are familiar with the even higher layer application protocols that use TCP/IP to get to the Internet. These include the World Wide Webs Hypertext Transfer Protocol (HTTP), the File Transfer Protocol (FTP), Telnet (Telnet) which lets you logon to remote computers, and the Simple Mail Transfer Protocol (SMTP). These and other protocols are often packaged together with TCP/IP as a "suite."
Personal computer users usually get to the Internet through the Serial Line Internet Protocol (SLIP) or the Point-to-Point Protocol (PPP). These protocols encapsulate the IP packets so that they can be sent over a dial-up phone connection to an access providers modem.
Protocols related to TCP/IP include the User Datagram Protocol (UDP), which is used instead of TCP for special purposes. Other protocols are used by network host computers for exchanging router information. These include the Internet Control Message Protocol (ICMP), the Interior Gateway Protocol (IGP), the Exterior Gateway Protocol (EGP), and the Border Gateway Protocol (BGP).

TELCO: In the United States and possibly other countries, "telco" is a short form for telephone company. Sometimes it means a local telephone company, such as a Bell operating company (BOC) or an independent local telephone company. Sometimes it means any telephone company, including one offering long-distance services.

TELNET: Telnet is the way you can access someone elses computer, assuming they have given you permission. (Such a computer is frequently called a host computer.) More technically, Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. The Web or HTTP protocol and the FTP protocol allow you to request specific files from remote computers, but not to actually be logged on as a user of that computer. With Telnet, you log on as a regular user with whatever privileges you may have been granted to the specific applications and data on that computer.
A Telnet command request looks like this (the computer name is made-up):
telnet mail.plus.net 110
The result of this request would be an invitation to log on with a userid and a prompt for a password. If accepted, you would be logged on.
Telnet is most likely to be used by program developers and anyone who has a need to use specific applications or data located at a particular host computer.

TERABYTE: A terabyte is a measure of computer storage capacity and is 2 to the 40th power or, in decimal, approximately a thousand billion bytes (that is, a thousand gigabytes).

TERMINAL: 1) In data communications, a terminal is any device that terminates one end (sender or receiver) of a communicated signal. In practice, it is usually applied only to the extended end points in a network, not central or intermediate devices. In this usage, if you can send signals to it, its a terminal.
2) In telephony, the term Data Terminal Equipment (DTE) is used to describe the computer end of the DTE-to-DCE (Data Communications Equipment) communication between a computer and a modem.
3) In computers, a terminal (sometimes qualified as a "dumb" terminal) is an end-use device (usually with display monitor and keyboard) with little or no software of its own that relies on a mainframe or another computer (such as a PC server) for its "intelligence." IBMs 3270 Information Display System was a widely-installed system of such terminals in corporations. Many applications designed for the 3270 or other "dumb" terminals are still in use at PCs that emulate or act like a 3270. The VT-100 from DEC is another example of a widely-used so-called "dumb" terminal. A variation of this kind of terminal is being revived in the idea of the thin client or network computer.
4) The term is sometimes used to mean any personal computer or user workstation that is hooked up to a network.

TERMINAL EMULATOR: In computers, an emulator is a hardware device or a program that pretends to be another particular device or program that other components expect to interact with. For example, using a 3270 emulator, a program written to be used with the 3270 Display Terminal can communicate with and control a PC as though it were a 3270. Typically, an emulator is provided when a popular hardware device becomes outdated and no longer marketed but legacy programs exist that still need to communicate with the older device. The practice of using an emulator to make an older program work with a new end-use device is called terminal emulation.

TERMINAL SERVER: Generally in information technology, a terminal server is a hardware device or server that provides terminals (PCs, printers, and other devices) with a common connection point to a local or wide area network. The terminals connect to the terminal server from their RS-232 or RS-423 serial ports. The other side of the terminal server connects through network interface cards (NICs) to a local area network (LAN), usually an Ethernet or Token Ring LAN, through modems to the dial-in/out wide area network, or to an X.25 network or a 3270 gateway. (Different makes of terminal server offer different kinds of interconnection. Some can be ordered in different configurations based on customer need.) The use of a terminal server means that each terminal doesnt need its own network interface card or modem. The connection resources inside the terminal server are usually shared dynamically by all attached terminals.
Some terminal servers can be shared by up to 128 terminals. The terminals can be PCs, terminals that emulate 3270s, printers, or other devices with the RS-232/423 interface. In some terminal servers, the terminals can use TCP/IP for Telnet connection to a host, LAT to a DEC host, or TN3270 for Telnet connection to an IBM host with 3270 applications. With some terminal servers, a given terminal user can have multiple host connections to different kinds of host operating systems (UNIX, IBM, DEC).

THUMBNAIL: A graphic or image purposely made smaller in size in order to display multiple images on the same Web page at the same time. A popular practice on the Web because it gives the user the chance to choose the image they would like to see a larger version of. This is usually done by clicking your mouse on it.
The practice of using thumbnails is also used to display "samples" of images that are "free" thus, when a user click on it, they either need to enter in a password in order to get at it, or they are instructed on how to provide payment for the higher resolution larger version, before they can actually see it.

TIA: Abbreviations of Thanks In Advance, commonly used in newsgroup postings.

TIMEOUT: The facility whereby after a certain period of inactivity the connection or line is dropped.

TROJAN: A type of computer virus which comes disguised as a program. People download this program usually from the Internet because they think that the program is of some use, but once they start it up it could perhaps erase your hard drive or just wreak havoc all over your system. Recently there has been a discovery of a Trojan Horse type virus which comes in the form of a file called AOL4FREE.COM this file should NOT be downloaded to your system by any means. The name comes from the Greek legend of a horse that looks benevolent at first but really holds trouble.