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The following is a listing of the communications
term s used in this manual.
of communications term s refer to the manuaLIBM
Data Processing Techniques, Data Communications
Glossary, Form C20-1666.
Addressing.
The sending by a terminal (or multi
plexer) of a series of characters that specify the
remote terminal (or terminals) to receive the suc
ceeding message.
All Call. A method by which a transmitting terminal
or CPU sends a message that is received by all ter
minals on the communications line.
Bit. Contraction of "binary d igit," the sm allest
unit of information in a binary system. A bit may
be either a one or a zero.
B it R ate. The speed at which bits are transmitted,
usually expressed in bits-per-second.
Buffer. A storage device used to compensate for
a difference in rate of flow data, or time of occur
rence of events, when transmitting data from one
device to another.
Contention. A situation that exists on a communi
cations line when more than one terminal attempts
to use the line at the same time.
vents contention.
Data Set. A modulation/demodulation device de
signed to provide compatibility between input/output
equipment and communications facilities.
Demodulation. The conversion of frequency signals
from a communications line to signals for a busi
ness machine.
Half-Duplex. A communication channel capable of
transmitting in both directions, but in only one
direction at a time.
Line Control.
The system used by either the opera
tor or the machine controlling a communication
system to positively determine the transm it-receive
relations of the various term inals.
Master Terminal. A remote terminal on a multi
point line which is designated to perform all
For a complete listing
Line control pre
addressing or checking answer-back functions for
a group of term inals.
Modulation. The conversion of signals from a bus
iness machine to frequency signals for transmission
over communications lines.
Multiplexer. A device for collecting the input from
many communications lines and transferring it to
the CPU; also, for accepting information from the
CPU and transferring it to one of many communica
tions lines without forcing the CPU's timing to match
that of the connected terminal(s).
Non-Switched Line. A communications line devoted
to one user, not part of a switched network; a
leased private line or privately owned line.
On Line. Associated with a processor either directly
or through a transmission control unit.
sical connection can be accomplished by either
multi wire cable or a communications line.
Point-to-Point Transm ission. Transmission of
data directly between two points with no intermediate
term inal.
Polling.
The sending by a terminal (or multiplexer)
of a series of characters that allows a particular
remote terminal to transmit a message.
Subordinate Terminal. A remote terminal on a
multipoint line which has no answer-back capability
and depends on a m aster terminal to provide all
answer-back functions, in addressing or checking.
Switched Line. A communications line used by more
than one customer; part of a switched network.
Term inal. A machine or group of machines capable
of generating and/or receiving signals transmitted
and/or received from a communications line.
Time-Out. The time interval allotted for certain
operations before system operation is interrupted
and must be restarted.
Transmission Control Unit. A communications
multiplexer.
GLOSSARY
The phy
Glossary
47
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