Communications Systems Glossary

Telegraphy.  Literally, telegraphy means "writing at a distance".

Telephony.  Literally, telephony means "speaking at a distance".

Ter.  Ter is a postscript used to note the third version of an ITU standard (ter is French for three).

Ternary.  Ternary means having three states.

Throughput.  Throughput is the amount of information carried by a communication system. Data rate equals information rate plus overhead.

Time-division duplex (TDD).  Time-division duplex (TDD) refers to duplexs communications links where the uplink is separated from the downlink by the allocation of different time slots in the same frequency band.

Time-division multiple access (TDMA).  Time-division multiple access is a mechanism for sharing a channel, whereby a number of users have access to the whole channel bandwidth for a small period of time (a time slot).

Time division multiplexing (TDM).  Time division multiplexing (TDM) is a technique that shares a transmission channel between users by dividing transmission time by allotting to each device a time slot during which it can send or receive data.

Token bus.  Token bus is a medium access technique using token passing on a logical bus local area network (LAN) topology.

Token-passing.  Token-passing is a media access technique in which a small set of bits called the token is passed between network devices.

Token ring.  Token ring is a medium access technique using token passing on a logical ring local area network (LAN) topology.

Topology.  The topology describes the way in which the devices on a LAN are connected together.

Transceiver.  Transceiver is a contraction of transmitter/receiver-a device that is able to act as both a transmitter and a receiver.

Transmission Control Protocol/Internet Protocol (TCP/IP).  The Transmission Control Protocol/Internet Protocol is the most common suite of internetwork protocols.

Transmission medium.  The transmission medium is the physical path between transmitters and receivers in a communications system.

Transponder.  In satellite communications, a transponder receives the transmission from earth (uplink), amplifies the signal, changes frequency and retransmits the data to a receiving earth station (downlink).

Transport layer (Layer 4).  The transport layer is layer 4 of the 0SI model, which provides reliable, transparent transfer of data between endpoints. The transport layer is responsible for generating the end user’s address and for the integrity of the receipt of message blocks. Among the most complex of protocols.

Twisted pair.  A copper transmission line consisting of two insulated wires twisted together. Its two forms are shielded twisted pair (STP) and unshielded twisted pair (UTP)

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