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6.0 Chapter 6. Recommendations and Problem Solving
This chapter contains recommendations to help you prevent or handle
problems you may have while using the LAN Support Program Custom. It also
outlines guidelines for adjusting the NETBIOS parameter values when using
DXMT0MOD.SYS. Adjusting these parameters can improve the performance of a
token-ring network and its attached computers.
If you do not find the information you need in this chapter, you may want
to consult other sections of the book, as follows:
° For tips on using DOS 5.0 with the LAN Support Program Custom, see
Chapter 5, "Using DOS 5.0, Windows, and QEMM-386."
° See "List of Parameters" in topic 4.3.1 if you are having trouble
loading the LAN Support Program Custom and do not find help in this
chapter. This section describes some parameters that may be affecting
your configuration.
Figure 6-1 tells you where to find descriptions of the topics covered in
this chapter.
+------------------------------------------------------------------------+
| Figure 6-1. Where to Find Topics in This Chapter |
+------------------------------------+-----------------------------------+
| Topic | See: |
+------------------------------------+-----------------------------------+
| Provide service information | "Service Information" in |
| | topic 6.1 |
+------------------------------------+-----------------------------------+
| Change parameters if an | "Application Requests Too Much |
| application requests too much | Buffer" in topic 6.2 |
| buffer | |
+------------------------------------+-----------------------------------+
| Verify the operation of the | "Verifying Adapter Operation" in |
| adapter | topic 6.3 |
+------------------------------------+-----------------------------------+
| Change NETBIOS parameters to | "Tuning Performance When NETBIOS |
| improve the performance of a | (DXMT0MOD.SYS) Is Used" in |
| token-ring network that uses | topic 6.4 |
| NETBIOS | |
+------------------------------------+-----------------------------------+
6.1 Service Information
When you request service for the LAN Support Program Custom, gather the
following information before you contact service support. The following
facts enable your service representative to help you better:
1. Adapter name
2. Other adapters in the computer and interrupt level
3. LAN Support Program Custom (version number displayed when the LAN
Support Program Custom is loaded)
4. Adapter speed and interrupt level
5. PC type and model
6. Monitor type and display adapter
7. Version of DOS
8. Which application software you are using
9. A description of the problem
10. The contents of CONFIG.SYS and AUTOEXEC.BAT.
6.2 Application Requests Too Much Buffer
If the application that opens the adapter requests too many transmit
buffers, too many link stations, or transmit buffers that are too large,
the adapter fails to open. The error message displayed depends on the
application. For example, if you are using the NETBIOS device driver
DXMT0MOD.SYS, the adapter will fail to open if the DS, DN, ST, ES, or EST
parameters are set too high (see "NETBIOS Device Driver Keyword Parameter
Descriptions" in topic 4.4.3 for a description of these parameters). If
you are using Personal Communications/3270, the adapter will fail to open
if the path information unit (PIU) size or the number of network stations
to be supported by a gateway are too high.
6.3 Verifying Adapter Operation
If you receive any error messages when you activate the LAN Support
Program Custom, see Appendix A, "Messages." To verify adapter operation,
run the adapter diagnostics.
6.4 Tuning Performance When NETBIOS (DXMT0MOD.SYS) Is Used
This section describes changing the NETBIOS device driver parameters to
improve the performance of a token-ring network and its attached
computers. For a description of the parameters discussed in this section,
see "NETBIOS Device Driver Keyword Parameter Descriptions" in topic 4.4.3.
The current LAN Support Program Custom default parameters were designed to
support the original 4-Mbps token-ring adapters with 8 or 16 KB of memory.
The Token-Ring Network Adapter with which the LAN Support Program Custom
is shipped contains 64 KB of memory. Because of this additional memory
and the faster processing speeds of today's PCs, you can change some of
the default NETBIOS parameters in the LAN Support Program Custom for
better performance. To use the entire 64 KB of memory available on the
adapter, IBM recommends setting the shared RAM size to 16 KB. See the
adapter installation and testing instructions for more information.
6.4.1 Performance Tuning
No single set of parameters can be optimum for all configurations. You
need to experiment with the parameters to find the best ones for your
configuration. Performance tuning is the process of selecting parameter
values to maximize the performance of your token-ring network. The
following guidelines offer some suggestions to assist you.
6.4.2 Taking Advantage of Large Frame Sizes
Transmitting a frame requires a certain overhead that is fairly constant,
independent of the frame size. Therefore, using larger frame sizes
increases the efficiency of the computer using the LAN Support Program
Custom.
For applications that can take advantage of large frame sizes, you can
improve the performance of the computer by increasing the DHB.SIZE (DS)
parameter. Increasing this parameter increases the size of the transmit
frame. Final determination of the NETBIOS session transmit frame size is
a function of the value of DHB.SIZE, the number of receive buffers in the
receiver, and the maximum frame size that can pass through a bridge in the
path. See the IBM Local Area Network Technical Reference for a
description of NETBIOS frame size determination.
When you increase the DS parameter, you reduce the amount of memory that
can be used for receive buffers. However, reducing the memory for receive
buffers may not cause any performance problems if you have set your shared
RAM size to 16 or 64 KB.
6.4.3 Increasing the Number of Outstanding Frames
The DLC.MAXOUT (MO) parameter allows you to influence the number of
outstanding frames in the network. You can increase the efficiency of the
network by allowing more data to be in transit in the network.
Setting MO to 4 increases the number of outstanding frames per NETBIOS
interface link station from 2 to 4. Increasing MO can improve the
efficiency of your network, especially if bridges are in the link station
traffic path. However, in some rare cases, increasing MO may cause
congestion at these bridges. You may also have congestion problems when
communicating with 8- or 16-KB token-ring network adapters.
6.4.4 Decreasing the Number of Acknowledgment Frames
The DLC.MAXIN (MI) parameter allows you to influence the number of LLC
acknowledgment frames on the network. Increasing MI increases the number
of frames that are received before an acknowledgment is sent. It is very
important that the MI value of the receiving station be less than the MO
value of the sending station. If the MI value of the receiving station is
greater then the MO value of the sending station, the performance of the
network is significantly degraded. It is recommended that you increase MO
and MI in all the stations in the network (for example, set MO to 4 and MI
to 2), or else allow the MI value to default to 1.
6.4.5 Reducing the Amount of Broadcast Traffic
Reducing the amount of broadcast traffic is especially valuable in
networks with bridges. The REMOTE.NAME.DIRECTORY (RND) parameter can help
reduce broadcast traffic. Setting RND to 17 is suggested. Using this
value for RND requires about 1 KB of memory in the computer.
You can also change the values of the TRANSMIT.TIMEOUT (TT) and
TRANSMIT.COUNT (TC) parameters to reduce network traffic. For example, at
the default value of TC = 6, queries will be transmitted 6 times. If you
change TC to equal 3, queries will only be sent 3 times. Since queries
are sent less frequently, the traffic generated when setting up a NETBIOS
session is decreased.
Similarly, if you increase TT, you can spread the traffic load. If you
set TT = 6, queries will only be generated at 3-second intervals. A
combination of TT = 6 and TC = 3 causes only 3 NETBIOS call queries to be
generated at 3-second intervals, instead of the default of 6 call queries
at 1/2 second intervals.
6.4.6 Examples of NETBIOS Parameter Configurations
As an example, the following device driver command line for DXMT0MOD.SYS
may improve performance for configurations where the adapter is configured
for 64 KB shared RAM and using applications that can take advantage of
large frames (in this case, 4096-byte frames).
DEVICE=\LSP\DXMT0MOD.SYS DS=4096 MO=4 RND=17
For applications that do not use large frames, the following configuration
may improve performance:
DEVICE=\LSP\DXMT0MOD.SYS MO=4 RND=17
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