T1/FT1 This indicates that the equipment will accommodate a full T1 or a fractional portion thereof.

T3 A term for a digital carrier facility used to transmit a DS-3 formatted digital signal at 44.746 megabits per second.

TA Terminal Adaptor. A DCE that connects to the ISDN S-Interface and enables non-ISDN terminal equipment to communicate over the ISDN. (equipment information)

TAC Terminal Access Controller. Historically, a device, usually accessible via dialup modems, used to access hosts on the ARPANET and MILNET.

TAU Trunk Access Unit provides physical and electrical connection between workstations and a Token ring network.

TCM Trellis Coded Modulation

TCP Transmission Control Protocol. The major transport protocol in the Internet suite of protocols providing reliable, connection-oriented, full-duplex streams. Uses IP for delivery.

TDM Time division multiplexing. The multiplexing technique used with multi-channel muxed modems.

TDMoIP Time Division Multiplexing over IP. A technology that transparently extends circuits over IP networks. (more info)

TEl Terminal Equipment Type 1. ISDN-compatible terminals.

Telco Telephone Company

Telnet The virtual terminal protocol in the Internet suite of protocols. Allows users of one host to log into a remote host and interact as normal terminal users of that host.

TERENA Trans-European Research and Education Networking Association.

TFTP Trivial File Transfer Protocol, is a simple form of the File Transfer Protocol (FTP) often used by boot diskless workstations, X-terminals, and routers. TFTP uses the User Datagram Protocol (UDP)and provides no security features.

Three-Way Handshake The process whereby two protocol entities synchronize during connection establishment.

TIP Terminal Interface Message Processor. This historic term refers to the nodes in the original ARPANET that had the capability to service terminals directly, allowing users to gain access to ARPANET hosts. A TIP was basically an IMP with a special terminal interface. TIPs later evolved to TACs.

TLD Top Level Domain.

TPO OSI Transport Protocol Class 0 (Simple Class). This is the simplest OSI Transport Protocol, useful only on top of an X.25 network (or other network that does not lose or damage data).

TP4 OSI Transport Protocol Class 4 (Error Detection and Recovery Class). This is the most powerful OSI Transport Protocol, useful on top of any type of network. TP4 is the OSI equivalent to TCP.

topology A network topology shows the computers and the links between them. A network layer protocol must stay abreast of the current network topology to be able to route packets to their final destination.

TN3270 A variant of the Telnet program that allows one to attach to IBM mainframes and use the mainframe as if you had a 3270 or similar terminal.

traceroute A program available on many systems which traces the path a packet takes to a destination. It is mostly used to debug routing problems between hosts. There is also a traceroute protocol defined in RFC 1393.

transceiver Transmitter-receiver. The physical device that connects a host interface to a local area network, such as Ethernet. Ethernet transceivers contain electronics that apply signals to the cable and sense collisions.

transfer syntax A description on an instance of a data type that is expressed as a string of bits.

transit network A transit network passes traffic between networks in addition to carrying traffic for its own hosts. It must have paths to at least two other networks.

Transport Layer The OSI layer that is responsible for reliable end-to-end data transfer between end systems.

TSU A term used by Adtran for it's line of T1/FT1 CSU/DSUs.

TTL Time To Live A field in the IP header which indicates how long this packet should be allowed to survive before being discarded. It is primarily used as a hop count.

tunneling Tunneling is used to get data between administrative domains which use a protocol that is not supported by the internet connecting those domains.

twinax A type of cabling with 2 conductor wires, common with some IBM equipment.

twisted pair Two wires twisted around each other to reduce induction (interference) from one wire to the other. Several sets of twisted pair wires may be enclosed in a single cable. Twisted pair is the normal cabling from a central office to your home or office, or from your PBX to your office phone. Twisted pair wiring comes in various thickneses. As a general rule, the thicker the cable is, the better the quality of the conversation and the longer cable can be and still get acceptable conversation quality. However, the thicker it is, the more it costs.

two-wire circuit A transmission circuit composed of two wires, signal and ground, used to both send and receive information. In contrast, a 4-wire circuit consists of two pairs. One pair is used to send. One pair is used to receive. All trunk circuits (long distance) are 4-wire. A 4-wire circuit delivers better reception, but also costs more. All local loop circuits (those coming from a Class 5 central office to the subscriber’s phone system) are 2-wire, unless a 4-wire circuit is requested

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