T

T3, E3
T3 is one of the T-carrier multiplexing standards. It operates at 44.736 Mbps, the equivalent of 672 voice circuits. E3 is the European equivalent of T3, operating at 34.368 Mbps.

T-carrier
T-carriers are one of several hierarchical systems for multiplexing digitized voice signals. The first T-carrier was installed in 1962 by the Bell system. The T-carrier family of systems now includes T1, T1C, T1D, T2, T3, and T4 (and their European counterparts E1, E2, etc.). T1 and its successors were designed to multiplex voice communications. Therefore, T1 was designed such that each channel carries a digitized representation of an analog signal that has a bandwidth of 4,000 Hz. It turns out that 64 Kbps is required to digitize a 4,000-Hz voice signal. Although current digitization technology has reduced the requirement to 32 Kbps or less, a T-carrier channel is still 64 Kbps.

Thicknet
Thicknet is also known as 10Base5 or Yellow Wire. Thicknet can carry a signal 500 m before a repeater is required. The maximum number of nodes allowed in a trunk segment is 100. The maximum number of trunk segments allowed in an Ethernet network is five, of which only three may be populated with nodes. Thicknet is no longer installed in computer networks.

Thinnet
Thinnet (or 10Base2) can carry a signal 185 m before a repeater is required. The maximum number of nodes that can be connected to a Thinnet trunk segment is 30.

time-division multiplexing (TDM)
TDM is multiplexing technology that guarantees each port a fixed amount of bandwidth on a rotating basis. TDM is suited to constant bit-rate traffic. See MUX and STDM.

topology
Topology refers to the specific physical configuration of a network or a portion of a network. Ring and star are examples of different network topologies.

total internal reflection
Total internal reflection occurs when a light ray traveling in one material hits another material and reflects back into the original material without any loss of light. In optical fiber, total internal reflection occurs for two reasons. First, the core has a higher index of refraction than the cladding; this difference causes the light to refract, or bend. Second, the light signals enter the cable at a shallow angle; an overly steep light angle will cause some or all of the light to enter the cladding instead of reflecting back into the core. See refraction and index of refraction.

traffic
Traffic refers to the amount of information traveling across a network. It includes both user data and network-related information.

transceiver
A device that can both transmit and receive optical signals is referred to as a transceiver.

Transmission Control Protocol (TCP)
TCP is a Transport Layer protocol used to send messages reliably across a network. It is usually paired with IP.

transparent bridging
Transparent bridges enable frames to move back and forth between two network segments running the same MAC-layer protocols. This type of bridging is referred to as "transparent" because the source station transmits a frame to the destination station as if it were on the same physical network segment, that is, the bridge is "invisible." Transparent bridges typically connect Ethernet network segments. However, transparent bridging may also be used with Token Ring and FDDI networks.

Transport Driver Interface (TDI)
TDI is the Windows NT interface layer between various transport protocols (SPX or TCP) and server or redirector software interfaces.

twisted pair
In twisted pair cabling, pairs of conductors are twisted together to randomize possible cross-talk from nearby wiring. Inadequate twisting is detectable using modern cable testing instruments.