COUNTER values

Some OID values are given in terms of a COUNTER. A COUNTER is an unsigned 32-bit integer ranging from 0 to 4,294,967,295.When a COUNTER value reaches the maximum, it rolls over to 0. In particular, these OIDS are both COUNTERS:

interfaces.ifTable.ifEntry.ifInOctets
interfaces.ifTable.ifEntry.ifOutOctets

Therefore, if the PI SNMP points use the raw values for these OIDs, such values will continuously increase numbers up to the maximum.A graphical trend of these numbers will probably not be meaningful.

Alternatively, you can configure the PI SNMP Interface to retrieve COUNTER values per unit time. If Location2 is set to 1, the PI SNMP Interface retrieves the difference between two successive readings divided by the scan time. For example,

scanned value = 2000
previous value = 200
scan time = 1 minute
stored value = (2000 – 200)/60 = 30

A graphical trend of such values will be more meaningful because it provides the number of octets transferred per second.

Note: For more detailed information on SNMP, consult SNMP, SNMPv2, SNMPv3, and RMON 1 and 2, Third Edition, by William Stallings (Addison-Wesley, 1999, ISBN 0201485346), or your Windows help files.