Location3 (Allow grouping)

By default, PI Interface for SNMP sends a single request for each PI point to retrieve its corresponding OID value. To reduce the number of requests, the interface can group points so it can issue a single request for multiple points that have identical settings for the following attributes:

• SNMP device name (host = parameter in the instrumenttag attribute)

• Scan class (location4)

To enable grouping for a point, set its location3 attribute to 1. By default, PI Interface for SNMP groups points into sets of five. To configure the number of points in a group using PI ICU, go to the PISNMP tab, check Number of tags per set and specify the desired group size. The recommended maximum number of points per group is 100.

Note: When configuring points to be grouped, you must specify the network device (the host parameter) using identical network device names. Even if host= router and host= 192.168.100.10 refer to the same network device, the interface does not group them.

When PI Interface for SNMP first starts up, it logs a summary of the groups that it has allocated. For example,

PI SNMP- 1> There are 5 points/tags with Location3=1; Summary:
PI SNMP- 1> Set=1, Device=router, Scan class=2, Tags=4
PI SNMP- 1> Set=2, Device=router, Event tag=router_rx_Ethernet0/0, Tags=1

Using a single request to read multiple OIDs increases the efficiency of data collection. However, very large requests might be fragmented into multiple packets and might not reach their destination, or they might overwhelm the capability of the SNMP agent to respond.

If the SNMP agent does not recognize one or more of the OIDs in the group, all the points in the group are assigned the Configure error state. In this situation, the interface logs messages like the following:

To find out which point contains the unsupported OID, use the Getif program.

PI SNMP- 1> Device reports at least 1 unknown OID in the following set of 2 tags:
PI SNMP- 1> Tag: router_tx_Ethernet0/0, OID:
interfaces.ifTable.ifEntry.ifOutOctets.85
PI SNMP- 1> Tag: router_jab_4, OID:
rmon.statistics.etherStatsTable.EtherStatsEntry .etherStatsJabbers