OSMKCM02 - ASYNCHRONOUS COMMUNICATION AND PERFORMANCE ISSUES
01/30/96

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          Asynchronous Communication and Performance Issues
                      OS/2 2.1 and OS/2 2.11
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Please Read Entire Document for Full Explanation of Procedures
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DESCRIPTION

Modem is slow or loses data.

RESOLUTION

Correct DOS Settings for Asynchronous Communications
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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
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   MAXWAIT = 1
   DISK_IO_PRIORITY = OFF (might get system-performance hit)


Application Settings That Can Affect Performance
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* 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
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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
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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.

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