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Appendix A.2. Sending SNMP TRAPS using the SNMP Server/Agent
There are two ways to send traps using the driver
•A rule based appoach – COV (Change of Value): Driver watches a data point. If the data changes and meets the condition of some rule then the trap is generated.
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Change of Value (COV) Traps
Rules determine when to send an SNMP Trap. These rules are configured in Server Side Map Descriptors, and are applied to the data whenever it changes. Traps are sent on a Change of State (COS) of the relevant Data Array value, as determined by the following configurable criteria:
COS_Hi_Alm | High Alarm threshold, applies to numerical values |
COS_Hi_Warning | High Warning threshold, applies to numerical values |
COS_Lo_Warning | Low Warning threshold, applies to numerical values |
COS_Lo_Alm | Low Alarm threshold, applies to numerical values |
COS_Deadband | Deadband value which must be crossed for Alarm or Warning states to toggle (prevents chatter) |
COS_Normal | Normal value for a digital point (1 or 0) – when the value changes to or from Normal, a Trap is sent. For an analog point set |
| the 'COS_Normal' parameter = 'COS_Server_Event' and then specify the dead band. Each time the the analog value |
| changes by at the deadband or more (absolute change) then a trap will be sent |
Each Trap Map Descriptor must specify the destination of the Trap by configuring a Remote_Client_Node_Descriptor, as shown in the example below. The OID to which the data value is to be bound in the Trap message is specified in the Map Descriptor.
First, the Trap destination Node is set up as follows:
Remote_Client_Node_Descriptors |
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Node_Name, | Node_ID, | Protocol, | Adapter, | IP_Address |
NM_1, | 1, | SNMP, | N1, | 192.168.1.174 |
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The Trap Map Descriptors are then configured as below, using the desired COS rule parameters:
// Server Side Map Descriptors |
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Map_Descriptors |
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Map_Descriptor_Name, | Data_Array_Name, | Data_Array_Offset, | Function, | Node_Name, | SNMP_OID, | COS_Hi_Alm, | COS_Lo_Alm, | COS_Deadband |
PSU_Voltage_Alarm, | DA_AI3, | 0, | SNMP_TRAP, | NM_1, | 1.3.6.1.4.1.6347.1.1.0.0, | 10.5, | 7.3, | 0.2 |
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