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1995-02-20
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OSMKCM02 - ASYNCHRONOUS COMMUNICATION AND PERFORMANCE ISSUES
11/01/94
================================================================
Asynchronous Communications and Performance Issues
================================================================
Please Read Entire Document for Full Explanation of Procedures
----------------------------------------------------------------
SYMPTOMS:
Modem is slow.
Modem looses data.
RESOLUTION:
1. Correct DOS setting for asynchronous communications.
COM_DIRECT_ACCESS = OFF
COM_SELECT=COMx (x = port # the application is using)
COM_HOLD=ON
COM_RECEIVE_BUFFER_FLUSH=NONE
HW_TIMER=ON
HW_ROM_TO_RAM=ON
IDLE_SECONDS=60
IDLE_SENSITVITY=100
DOS_HIGH=ON(optional)
DOS_UMB=ON(optional)
2. CONFIG.SYS settings that may effect performance.
MAXWAIT =1
DISK_IO_PRIORITY=OFF(may get system performance hit)
3. Application settings that may effect performance.
Most applications provide the capability to set hardware
handshaking. This setting may also be disguised as RTS / CTS
handshaking. With this setting, the application becomes aware
of hardware handshaking. This allows the application to stop and
start according to the modem's speed.
For higher speeds, lock the modem at a speed higher than the
expected connecting speed. Sometimes locking at too high of a
speed can cause problems. Turn on error correction and data
compression. On BBS connections ANSI graphics are compressed,
thus increasing performance. For file transfers use Zmodem
protocol when possible. Zmodem is a streaming protocol and can be
60% faster than earlier block protocols.
4. AT modem commands that may effect performance.
The Hayes compatible modem has a set of AT commands designed to
control the performance and various attributes of the modem.
Attributes such as Data Compression and Error Correction are
normally set as defaults on most modems. This is usually
indicated by a light on most external modems. AT&F&K3&Q5 are the
commands used by one modem manufacturer to turn on the previously
mentioned attributes. For a detailed list of these commands,
refer to the documentation shipped with the modem.
To send commands to the nonvolatile string in your modem use
the following string as an example:
echo "AT commands &Wn" > COMx
(commands = Hayes AT commands compatible with your modem)
(n = 0 or 1, x = com1 through com4)
If you have a question, refer to the modem's documentation or
contact modem manufacturer.
LIMITATIONS
DOS applications running at BAUD rates higher than 9600 may not
perform correctly due to the multi-tasking nature of OS/2.
There are two popular communications program design styles,
interrupt driven and polling driven. Interrupt driven
communications programs work fine with OS/2 for the most part.
However, polling driven programs are very timing dependent
and timing critical. OS/2 being a pre-emptive multi-tasking
operating system may be processing another task during a
particular time slice. During that time slice, a time critical
application may not get service. This can result in an
application going out of synch. The vendor of the application
should know the design style the application uses.
----------------------------------------------------------------
IBM disclaims all warranties, whether express or implied,
including without limitation, warranties of fitness and
merchantability with respect to the information in this document.
By furnishing this document, IBM grants no licenses to any
related patents or copyrights.