Configuring
the
Terminal
Choosing Buffer Sizes for Multipoint Configurations
When filling
in
either
of
the
two multipoint configuration
menus,
two
parameters
you
must
contend
with
are
BufSize
and
Numbufs.
HumBufs
specifies
the
desired
number
of datacomm buffers to be allocated for
use
by
the
terminal.
Bu
f 5 i ze specifies
the
size (in bytes) of each buffer used by
the
terminal.
The
same
buffers
are
used for
both
transmitting
and
receiving
data.
As a
result,
the
terminal
cannot
transmit
and
receive
data
at
the
same time.
If
transmit
data
is queued,
and
the
terminal
is
selected by
the
host
computer,
the
transmit
data
will be flushed.
If
this
occurs,
the
bell will
ring
to indicate
the
data
was flushed.
If
receive
data
is queued,
and
the
user
tries
to
enter
transmit
data,
the
transmit
data
will not be accepted
until
all
of
the
receive
data
has
been
processed.
The
memory space allocated to datacomm buffers is obtained from
the
terminal's
display
memory.
The
more space you allocate for datacomm buffers,
the
less space you
have
available
for display.
In
the
following discussion, procedures for selecting
the
values for
HumBu
f
sand
Bu
f S i ze
are
explained.
There
is no simple formula for selecting
the
most appropriate valuesfor
HumBuf
5
and
BufSize.
There
are, however,
three
primary
considerations:
1.
The overall buffersize
(Bu
f 5i ze x
HumBu
f s)
must
be
large
enoughto accomodate
the
largest
block
that
the
host
computer will
ever
send.
2.
Each
individual buffer
(Bu
f 5i z
e)
must
be less
than
or equal to
the
host
computer's receive
buffer size.
3.
BufSize
x
HumBufs
must
be less
than
or equal to 4096 bytes for
terminal
buffers.
If
you
are
merely configuring
the
terminal's datacomm buffers to
match
those of a
host
computer,
then
the
above guidelines will suffice. However, if you
are
responsible for configur-
ing
datacomm buffers
both
at
the
terminal
and
at
the
host computer,
the
situation
becomes
more complicated.
The
following
paragraphs
present
some of
the
things
you should consider.
Each
time
the
terminal
operator
presses
_,
a block of
data
is
transferred
from
the
cursor
active workspace to
the
datacomm
output
buffer(s) for
the
associated port.
If
this
block
of
data
is
larger
than
a single buffer,
then
it
will fill
as
many
buffers
as
necessary. When
the
data
is
transmitted
to
the
host
computer, each buffer is
transmitted
as
a block.
If
the
data
block
required more
than
one buffer,
it
will
require
a multiple block
transmission
(with
an
<ETB>
at
the
end
of
each except
the
final one, which is
terminated
by
an
<ETX
».
Such a
multiple
block
transmission
requires
considerably more line control activity (and physical
line
turnarounds
in
a
half
duplex configuration)
than
if
the
data
were
transmitted
as
a single block.
Therefore, you will
want
to consider
the
amount
of
data
to be
transmitted
in
response to a
typical _ key usage
and
tailor
your buffer sizes accordingly.
3-26
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