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How do I find the parameter definitions for the formulas used in finding network utilization?

Regarding SNMP, how do I find the parameter definitions for the formulas used in finding network utilization? Also, how do I find the current bandwidth used? Finally, how do I convert those ASCII values of ASN on a Windows platform?
Utilization is tricky. There are two ways to look at these within SNMP statistics. One is through packets passed (inOctets, outOctets). The other is percent utilization which refers to the percentage of time the circuit is busy. You can't take a 20 Mb file and divide it by packet size and assume that that is all the time it will take to move across the network. Each packet gets framed with information which means that the payload (or part of the packet that contains the data) is a smaller portion of the packet. When you add retransmissions to the equation, it can become even greater. The switch will hold packets (octets) in buffers to move them to the network. If the buffer gets full, it will begin discarding packets to be retransmitted by the requesting station.

If you go to www.snmplink.org you will find a ASN decoder and additional information. I am not sure what you are trying to do with this data, so it is a bit harder to provide examples. Also, the statistics you get depend on the MIB (Management Information Base) of your electronics and what they store for your use. The best way to find what the statistics mean for your electronics would be to contact your electronics manufacturer. Most of the time, however, you are provided with a percent utilization statistic.

You will want to examine all causes of errors, even those you would not normally think of as a cause. For instance, poor cabling can cause a lot of retransmissions which would elevate your utilization. Faulty network cards can do the same.

I would suggest that you go to www.castlerock.com and download a 30 day demo of SNMPc. This software has excellent help logs and will also allow you to use RMON if your devices are capable. RMON is a better tool for speed/utilization, but your hardware must support it.

This was last published in July 2004

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