Glossary of Terms and acronyms

T1:
The transmission bit rate of 1.544 million bits per second. This is also equivalent to the ISDN Primary Rate Interface for the U.S. The European T1 or E1 transmission rate is 2.048 million bits per second. T1 is also known as DS1.

T3 Channel (DS-3):
In North America, a digital channel that communicates at 45.304 MBit/s.

TDMA:
Time division multiple access. Refers to a form of multiple access where a single carrier is the shared by many users. Signals from earth stations reaching the satellite consecutively are processed in time segments without overlapping.

Tele-medicine:
Term used to describe the practice of medicine using interactive video, voice and data. Typically this involves one or more experts at one site consulting to a patient, usually through another expert, located at a different site.

TI - Terrestrial Interference:
Interference to satellite reception caused by ground based microwave transmitting stations.

Tier 1:
Term used to describe a US ISP which operates high speed transcontinental networks. There are about half a dozen such ISPs. There is no real equivalent in Europe but their roles have largely been taken by national PTTs.

Tier 2:
These are ISPs that buy and re-sell capacity from Tier 1 ISPs. They are also described as being downstream from Tier 1.

Transmitter:
An electronic device consisting of oscillator, modulator and other circuits that produce a radio or television electromagnetic wave signal for radiation into the atmosphere by an antenna.

Transponder:
A combination receiver, frequency converter, and transmitter package, physically part of a communications satellite. Transponders have a typical output of five to 250 watts and operate over a frequency band with a 27 to 72 megahertz bandwidth. Communications satellites typically have between 12 and 50 transponders.

TVRO:
Television Receive Only terminals that use antenna reflectors and associated electronic equipment to receive and process television and audio communications via satellite. Typically small home systems. In Europe the term DTH receiver is normally used. In the USA TVRO usually refers to C-band television receivers.

TWTA:
Travelling wave tube amplifier. An electronic gun which is used to increase the power of a radio signal. On-board a satellite a TWTA is part of an electronic subsystem called a transponder.