User`s manual
EBCDIC
- Extended Binary
Coded-Decimal
Inter-
change
Code.
An 8-bit
character
code
used
primarily
in
I BM
equipment.
The
code
provides for 256 differ-
ent
bit
patterns.
Echo - A
portion
of
the
transmitted
signal
returned
from the
distant
point
to
the source with sufficient
magnitude
and
delay so as
to
cause
interference.
ENQ
(Enquiry) - (a.) Used in
BISYNC
as a
request
for response
to
obtain
identification
and/or
an
indication
of
station
status.
ENQ
is
transmitted
as
part
of
an
initialization sequence (line bid) in
point-
to-point
operation,
and
as
the
final
character
of
a
selection
or
polling sequence in
multipoint
operation.
(b.) Used in
DDCMP
to
signal a
control
message.
EDT
(End
of
Transmission) - Indicates
the
end
of
a
transmission, which
may
include
one
or
more
mes-
sages,
and
resets all
stations
on
the
line
to
control
mode
(unless it
erroneously
occurs within a
transmis-
sion block).
EOT
is
also
transmitted
as a negative
response
to
a polling sequence.
ETB
- End
of
Transmission
Block.
ETX
( End
of
Text) - Indicates the
end
of
a message.
If
multiple transmission blocks
are
contained
in a
message in BSC systems,
ETX
terminates
the
last
block
of
the
message.
(ETB
is used
to
terminate
pre-
ceding blocks.)
The
block check
character
is
sent
immediately following ETX.
ETX
requires a reply
indicating
the
receiving
station's
status.
Executive Routine - A
program
that
monitors
system
activity
and
transfers
control
to
subordinate
pro-
grams
for handling.
When
handling
is complete,
con-
trol is
returned
to
the
executive.
When
the
system is
inactive, the executive spins in
an
idle
mode.
Facility - See
Channel.
Full-Duplex - See Duplex.
H - High (positive).
Half-Duplex - Pertaining
to
an
alternate,
one-way-at-
a-time
independent
transmission.
(Contrast
with
duplex.)
Header -
The
control
information
prefixed in a mes-
sage text, e.g., source
or
destination
code, priority,
or
message type. Syn:
Heading,
Leader.
C-3
Idle Loop - See Executive
Routine.
ITB
(Intermediate
Text
In Binary Synchronous Com-
munications, Block) - A
control
character
used
to
ter-
minate
an
intermediate
block
of
characters.
The
block check
character
is sent immediately following
ITB,
but
no
line
turnaround
occurs.
The
response fol-
lowing ETB
or
ETX
also applies
to
all
of
the
lTD
checks immediately preceding
the
block
terminated
by ETB
or
ETX.
L - Low.
Line - See
Channel.
Link
- See
Channel.
Longitudinal Redundancy Check
(LRC)
- A system
of
error
control
based
on
the
transmission
of
a Block
Check
Character
(BCC)
based
on
preset rules.
The
check
formation
rule is applied in
the
same
manner
to
each
character.
LRC
-
Longitudinal
Redundancy
Check.
Mark - Presence
of
a signal. In telegraphy,
mark
rep-
resents the closed
condition
or
current
flowing.
Equivalent
to
a
binary
one
condition.
Modem -
Contraction
of
modulator-demodulator.
A
device
that
modulates
and
demodulates
signals
trans-
mitted
over
communication
facilities. (Same as
data
set.)
Modulation -
The
process by which
some
character-
istic
of
a high-frequency
carrier
signal is varied in
accordance
with
another
lower frequency
"informa-
tion"
signal.
This
technique
is used in
data
sets
to
make
business-machine signals
compatible
with
com-
munication
facilities.
Multiplexing -
The
division
of
a
transmission
facility
into two
or
more
channels.
Multipoint Circuit - A circuit
interconnecting
several
stations,
NAK
(Negative Acknowledgment) - Indicates
that
the
previous
transmission
block was in
error
and
the
receiver
is
ready
to
accept
a retransmission
of
the
erroneous
block.
NAK
is also
the
"not
ready"
reply
to
a
station
selection
(multipoint)
or
to
an
initialization sequence (line bid) in
point-to-point
operation.