Theoretical cutoff wavelength
The shortest wavelength at which a single mode can be propagated in a single mode fibre. Below the cutoff several modes will propagate and the fibre is no longer single, but multi-mode.

Tight buffered cable
Type of cable construction whereby each glass fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900 micrometers. Increased buffering provides ease of handling and connectorization.

Total reflection (TR)
The condition resulting in total reflection from a glass/glass, glass/air or a glass/metal interface in which all of the light is reflected. In optical fibre, it is the condition defined as

sin-1(n2/n1), where n2 is the lower index and n1 the higher index media.

For optical fibre to work, the cladding is n2 and the core is n1.

Triple-play/IP-TV
Ethernet based network structure that combines Voice, Data and Video

Twisted pair cable
A form of wiring in which a pair of copper wires are wrapped around one another again and again. Twisting two wires reduces their susceptibility to electrical interference.