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COURIER HIGH SPEED MODEMS
The
above
protocols further
reduce
throughput
when
an
error
control connection is established. The accuracy of
the
data
is checked twice,
by
the
file transfer protocol
and
the
modern. To
avoid
redundancy,
use
the
above protocols
only
for non-ARQ connections,
and
only
at
speeds
of 2400
bps
and
below.
For
the
best
throughput,
but
on
error-controlled connections
only
and
with
hardware
flow control,
we
recommend
the
most
current
version of Zrnodern.
Overhead
is
minimal
with
this protocol,
with
throughput
almost
equal
to
that
obtained
with
no
file-transfer protocol. Leave
the
modern
at
its &M4
and
&Kl settings for
both
error control
and
data
com-
pression. Yrnodern-G is
another
good
choice,
but
never
without
both
the
local
and
remote
moderns
using
error
control: if Yrnodern-G detects
an
error,
it
aborts
the
connection. Do
not
use
either protocol
with
software flow
control (XON/XOFF signaling).
Achievable Throughput
The table
below
indicates
the
maximum
throughput,
in
charac-
ters
per
second (cps),
that
can
normally
be
expected
under
the
following conditions.
• Connection Oink)
rate
of 14.4K
bps
• DTE rate set
at
57.6K bps;
modem
set to
&Bl
• V.42
bis
compression negotiated for
the
call,
and
the
default size 11-bit, 2048-entry dictionary
• Straight
data
(e.g.,
not
already
compressed,
no
file-
transfer protocol)
• Transmission from a fast (e.g., 286)
computer
Throughput
(cps)
when
set
to
14.4K
bps
File
Type
Assembler
or
Compiler listing
Text file
Binary file:
.EXE
Binary file: .COM
.ARC files (common
on
BBS's)*
Random
binary
8-bit*
MNP5
V.42 bis
2880
2325-2625
2175-2400
2100-2250
1500-1650
1460-1575
3840
3400-5760
2030-2600
2050-2300
1700
1700
*These
files
are
already
compressed
or
appear
to the
modem
to
be
com-
pressed. Additional MNP5 compression causes
throughput
lower
than
what
can
be expected
using
MNP
without
compression. We
recommend
setting
the
modem
to &K3
when
transferring these files, to allow V.42
bis
but
disable MNP5.
Link Negotiation and Error Control A-9
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