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MKCM02.FAX
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1994-12-10
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Async Communications and Performance 8/12/94
file name
OSMKCM02.FAX
TITLE
Asynchronous Communications and Performance Issues
DESCRIPTION OF SYMPTOMS
My modem is slow.
My modem looses data.
SUMMARY OF RESOLUTION
1. The correct DOS setting for asynchronous communications.
2. Config.sys settings that may effect performance.
3. Application settings that may effect performance.
4. AT modem commands that may effect performance.
DETAILS OF RESOLUTION
1. 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. MAXWAIT = 1
DISK_IO_PRIORITY = OFF (may get system performance hit)
3. Most applications provide the capability to set hardware
handshaking. This setting may also be disguised as RTS / CTS
handshaking. When 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 will be
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. The Hayes compatible modem has a rich 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. Usually
this will be indicated by an indicator light on most external
modems. AT&F&K3&Q5 are the commands used by one popular modem
manufacturer to turn on the fore mentioned attributes. For a
detailed list of these commands look in the reference manual
shipped with your 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)
* when in doubt see the modem's owner manual 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 highly 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 which design style the application adheres to.
12/31/99