Achievable Throughput - US Robotics COURIER User Manual

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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