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1997-04-11
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OSMKCM02 - ASYNCHRONOUS COMMUNICATION AND PERFORMANCE ISSUES
01/30/96
=======================================================================
Asynchronous Communication and Performance Issues
OS/2 2.1 and OS/2 2.11
=======================================================================
Please Read Entire Document for Full Explanation of Procedures
--------------------------------------------------------------
DESCRIPTION
Modem is slow or loses data.
RESOLUTION
Correct DOS Settings for Asynchronous Communications
----------------------------------------------------
1. Open OS/2 System.
2. Open Command Prompts.
3. Click-on DOS Window or DOS Full Screen with mouse button 2.
4. Select Settings to open the Settings notebook.
5. Select the Session tab.
6. Select the DOS Settings... push button.
7. Select the All DOS Settings button.
8. Set the following settings as shown:
COM_DIRECT_ACCESS = OFF
COM_SELECT = COMx (x is the port number the application is using)
COM_HOLD = ON
COM_RECEIVE_BUFFER_FLUSH = NONE
HW_TIMER = ON
HW_ROM_TO_RAM = ON
IDLE_SECONDS = 60
IDLE_SENSITIVITY = 100
DOS_HIGH = ON (optional)
DOS_UMB = ON (optional)
CONFIG.SYS Settings That Can Affect Performance
-----------------------------------------------
MAXWAIT = 1
DISK_IO_PRIORITY = OFF (might get system-performance hit)
Application Settings That Can Affect Performance
------------------------------------------------
* Most applications provide the ability to set hardware handshaking.
This setting also can be disguised as RTS or 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. Locking at too high 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.
AT Modem Commands That Can Affect 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 usually is indicated by a light on most external
modems. AT&F&K3&Q5 are the commands used by one modem manufacturer to
turn on the attributes mentioned previously. For a detailed list of
these commands, refer to the documentation that came 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 are Hayes AT commands compatible with your modem; n is 0 or
1; x is 1 through 4.)
If you have a question, refer to the modem's documentation or contact
the modem manufacturer.
Limitations
-----------
DOS applications running at rates higher than 9600 baud might not
perform correctly because of the multitasking nature of OS/2.
Two popular communication-program design styles are interrupt-driven
and polling-driven. Interrupt-driven communications programs work fine
with OS/2, for the most part. Polling-driven programs, however, are
very timing-dependent and timing-critical. OS/2, a preemptive,
multitasking operating system, might be processing another task during
a particular time slice. During that time slice, a time-critical
application might not get service, and could go out of synchronization.
The application vendor 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.
Copyright (c) 1994, 1996 IBM Corporation. Any trademarks and product
or brand names referenced in this document are the property of their
respective owners. Consult your product manuals for complete trademark
information.