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Modem
Contraction of modulator-demodulator.
Equipment required to lransfer data
over the telephone nelwork
Modem
The status of the modem when it is connected status to the telephone line and
is used to transfer data from the lerminal/compuler to a remote modem.
Modulation
Modulation is when an analogue carrier wave, e.g. tone of a given frequency, is
modified by a signal in such way that the modifying signal is "carried" by the
carrier wave. Data signals can lead to such modification according to
specifications given for such modulation.
P
Parity
An extra-bit code used to detect errors in transmission
R
RAM
Random Access Memory. A storage unit into which data may be both written
and read during operations.
Return channel
The data channel used for transmission at reduced speed.
Remote modem
The modem to which the call is made.
RTS
Request to Send.
The signal from the terminal/computer to the modem informing that the data is
now clear for transmission.
Ss
Startbit
The bit marking the commencement of a character with asynchronous
transmission.
Stopbit
The bit marking the end of a character with asynchronous transmission.
Synchronous
Data bits transmitted in synchronous format are transmitted one bit after
another.
No start/stop bits are transmitted but an additional clock signal serves
to synchronise the receiver and the transmitter. Usually certain sync characters
are needed to define the byte boundaries.
Tone signalling
A modern form of number transmission. A tastaphone (with keys instead of a
dialling template) normally uses tone signalling. This also requires a
contemporary telephone switch board
LZTR104006 R1.00
16-11
Zat 14.4/14.4-7 and 19.2/19.2-7
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