Message size

For PI tags whose Location3 field is zero, PI SNMP does not group multiple requests for information into a single SNMP GetRequest message. In other words, the PDU (Protocol Data Unit) that PI SNMP sends to a network device contains a GetRequest for only a single OID. The size of such a message is of the order of 80 octets.

The size of a GetResponse PDU from the network device depends on the OID value requested, and can vary greatly. For example, the value for system.sysDescr.0 returned by the network device may be a descriptor such as:

IOS I 3600 Software (C3660-DS-M), Version 12.0(5)T1, RELEASE SOFTWARE (fc1) Copyright I 1986-1999 by cisco Systems, Inc. Compiled Thu 19-Aug-99 18:15 by cmong

The above returned value by itself consists of 213 octets. With the addition of the various headers (SNMP, UDP, IP), the size of the complete message is about 280 octets.

When PI SNMP retrieves numeric values, the size of the returned message is also about 80 octets. For comparison, a single PING message from a Windows machine contains about 64 octets.