Ideas for Troubleshooting and Fine-tuning Throughput (99154)

SUMMARY

Transmission rates across a WAN can sometimes be increased by making configuration adjustments. Before you can improve a throughput rate, though, you need to understand why it is slow, and what you can or cannot change to fix it. This article discusses these points using an example of a configuration with a throughput problem.

MORE INFORMATION

In one reported instance, two LAN Manager 2.2 networks were connected through remote bridges (64kbits/s), and a 380K file took more than 4 minutes to transfer. Configuring LAN Manager didn't help, nor did adjusting T1 = 3500 or 4500.

The theoretical throughput on the WAN link was 64Kbps; that rate might not seem slow, but there are other factors to consider. For one thing, divide by 8 bits/byte and this yields a not particularly fast 8Kbytes/sec. But there is some overhead for headers and so on, so the true data rate is closer to 6Kbytes/sec total between the two networks.

Also remember that the machine in question is never the only machine on the net. Broadcasts and traffic from other stations also are being passed.

To isolate the cause of a slow transmission rate, try a file copy to a local system. If that works much better, analyze traffic over the bridge.

The most likely culprit is high broadcast traffic. It doesn't take much to saturate a link as small as 8Kbytes/sec. TCP/IP, NetBEUI, and IPX create a lot of broadcast traffic over the bridges.

There are ways to reduce broadcast traffic, but be careful when trying them. Try reducing the frequency of server announcements (LAN Manager 2.1a and later versions default to 3 minutes, 2.1 and earlier to 1 minute). You can also shut off NET WHO if it's not being used, by setting "netwho=no" in the netlogon section of LANMAN.INI.

If these measures don't help, it may be necessary to study the traffic using a network analyzer to see if more traffic reduction is possible.