Texas Instruments 990 User Manual page 102
Dx10 hdlc communications package
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- Operation manual (276 pages) ,
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- Installation and operation manual (122 pages)
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Applications Programming
4.4
MANAGING THE FLOW OF COMMUNICATIONS
When
designing
applications
programs
that
use
the
network,
careful
consideration
should
be
given to managing the flow of
communications between programs.
Figure 4-4 shows an example
of
a
progr~m
in
a
secondary
station
that
is sending data to a
program in the primary station.
The data is to be formatted
and
printed
at
the
primary
station.
The communications line that
connects the stations operates at 9600 bits per second (bps).
A
rapid
succession of data sent from the secondary station arrives
at the primary station at 9600 bps
(about
1200
characters
per
second),
and
is
formatted
and
printed
at
300 bps (about 37
characters
per
second).
Traffic
is
regulated
on
the
communications
line~
therefore, the communications package soon
quits accepting the da ta
by
re turning
an
error
code
to
the
sender.
If this traffic were not regulated, the primary station
would quickly become congested with input
data
because
of
the
difference
in
the
line capacity of the communications line and
th e pr in te r •
PROGRAM IN
9600 BPS
PROGRAM IN
300 BPS
..
PRINT
...
DEVICE
SECONDARY
-
PRIMARY
STATION '
STATION
2280124
Figure 4-4
Managing the Flow of Communications
One possible solution to this problem
is
for
the
applications
programmer
to
put
some
constraints on the program sending the
data.
Another possible solution is to have the receiving program
write input data to a disk file
as
it
arrives
and
interleave
write
opera tions to the print device with read opera tions to the
conununications package.
This example illustrates that applications
programmers
must
be
familiar
with
the
configuration of the network, as well as the
environment in which the communications
package
operates.
The
flow
of
traffic
within
the
network
is a function of several
conditions, many of which are
dependent
upon
external
factors
that
influence
the operation of the communications package.
It
is suggested that careful
considera tion
be
given
to
ways
of
avoiding congestion, when designing applications programs.
4-16
2270526-9701
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