gloss_T

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T.120

This ITU-T standard covers the data-sharing component of real-time multimedia over the network and is the basis for such applications as whiteboard sharing and file collaboration during a point-to-point or multipoint session. T.120 is included in video conferencing standards as H.320, H.323, and H.324. See H.320, H.323, H.324.

T1.

The ITU-T specifies a four-level, time-division multiplexing hierarchy for the telephone system in North America. T1 provides 24 channels of 64Kbit/sec bandwidth, for a total bandwidth of 1.544Mbits/sec. A T1 circuit can transport voice, video, data, and fax. T1 service sold in 64Kbit/sec increments is called fractional T1.

T2.

T2 is the equivalent of four T1s, and it offers 6.3Mbits/sec of bandwidth. Each T2 link can carry at least 96 64Kbit/sec circuits. T2 is not a commercially available service, but it is used within the telephone company's hierarchy.

T3.

A T3 circuit carries in one multiplexed signal stream the equivalent of 28 T1 circuits. It provides 44.736Mbits/sec of bandwidth. T3 is not widely used for LANs.

Technical Office Protocol (TOP).

TOP is the OSI protocol stack for office automation; it is not widely implemented.

Telnet.

Telnet is the TCP/IP protocol for terminal emulation.

terminal emulation.

A terminal emulator converts a perfectly capable computer into an enslaved screen and keyboard combination, capable only of raw input and output.

throughput.

Throughput is a measure, in bits per second or bytes per second, of the traffic carrying capacity of a channel. LAN and telephone throughput is generally expressed in bits/sec, while computer-based throughput, such as bus capacity and drive I/O rates, are generally expressed in bytes/sec. One byte/sec is usually equal to 8 bits/sec.Given a particular signaling scheme, a channel's throughput is proportional to its bandwidth ( expressed in Hz). Despite common usage, maintaining the distinction between bandwidth and throughput is essential to a full understanding of how networks function. (See bandwidth.)

time domain reflectometer (TDR).

A TDR is a troubleshooting device that is capable of sending radar-like signals through a cable to check continuity, length, and other attributes.

token passing.

Token passing is a network access method that requires nodes to possess an electronic token before transmitting frames onto the shared network medium. Token Ring, Token Bus, and FDDI use token-passing schemes.

Token Ring.

Token Ring is the IEEE 802.5 specification for a 4Mbit/sec or 16Mbit/sec network that uses a logical ring topology, a physical star topology, and a token-passing access method. It works with UTP, STP, and fiber- optic cable. Each ring can have up to 256 stations .

token.

A token is a pattern of bytes that mediates access on a Token Ring or Token Bus network.

transceiver.

A transceiver is a device for transmitting and receiving packets between the computer and the wire. The transceiver is usually integrated directly onto the network adapter card.

Transmission Control Protocol/Internet Protocol (TCP/IP).

TCP/IP is the protocol suite developed by the Advanced Research Projects Agency (ARPA), and is almost exclusively used on the Internet. It is also widely used in corporate internetworks because of its superior design for WANs. TCP governs how packets are sequenced for transmission on the network. IP provides a connectionless datagram service. The term "TCP/IP" is often used to generically refer to the entire suite of related protocols.

transparent bridging.

Transparent bridging connects similar LANs and is usually used with Ethernet. In transparent bridging, when the station transmits a frame, that frame does not know what path it will take. Instead, the bridges determine the best path at the time the frame is sent. In contrast, in source routing, the path is determined at the start of the transmission, rather than frame by frame.

Transport layer.

The Transport layer is the fourth layer of the OSI model, and it provides reliable end-to-end data transport, including error detection between two end user devices. Examples of transport protocols are the Transmission Control Protocol (TCP), Sequenced Packet Exchange (SPX), and Transport Protocol Class 0 (TP0).

Transport Protocol Class 0, Class 4 (TP0, TP4).

These protocols are OSI transport protocols. Transport Protocol Class 0 is a connectionless transport protocol for use over reliable networks. Transport Protocol Class 4 is a connection-based transport.

Trivial File Transfer Protocol (TFTP).

TFTP is a simplified version of FTP, the TCP/IP file transfer protocol.

tunneling.

The process of encasing one protocol in another's format is called tunneling. For example, AppleTalk packets are often enveloped in TCP/IP packet formats for transmission on an enterprise network. Tunneling is also called encapsulation.

twisted pair.

Twisted pair is a type of copper wiring in which two wires are twisted around one another to reduce noise absorbtion and signal loss. The Electronics Industry Association/Telecommunications Industry Association (EIA/TIA) specifies a five-level standard for commercial building telecommunications wiring. Category 1 wiring is old-style unshielded twisted-pair telephone cable and is not suitable for data transmission. Category 2 is for use up to 4Mbits/sec; it resembles IBM Cabling System Type 3 cable. Category 3 UTP is specified for speeds up to 10Mbits/sec, and it is the minimum cable required for 10BaseT Ethernet. Category 4 is the lowest grade UTP acceptable for 16Mbit/sec Token Ring. Category 5 is certified for speeds up to 100Mbits/sec, but it can handle speeds of up to 155Mbits/sec. Category 5 cable is suitable for FDDI and other high-speed networks.

two-phase commit.

In a distributed database, a two-phase commit ensures data integrity by confirming the successful completion of every step in a transaction before committing any of the steps.

Type 1.The

IBM Cabling System specifies different types of wire. Type 1 is a dual-pair, 22 American Wire Gauge (AWG) cable with solid conductors and a braided shield. It is a type of shielded twisted pair.

Type 2.

Type 2 is the IBM Cabling System's specification for a six-pair, shielded, 22 AWG wire used for voice transmission. It is the same wire as Type 1, but has an additional four-pair wire.

Type 3.

Type 3 is the IBM Cabling System's specification for a single-pair, 22 or 24 AWG, unshielded twisted-pair wire. It is common telephone wire.

Type 5.

Type 5 is 100/140 micron fiber; IBM now recommends 125 micron fiber.

Type 6.

Type 6 wire is two-pair, stranded 26 AWG wire used for patch cables.

Type 8.

Type 8 wire is a two-pair, 26 AWG, shielded cable without any twists ; it is commonly used under carpet.