Specifies how often trap(s) will be sent by the SNMP agent.
once - The trap is only sent once.
decay - The same trap is sent multiple times at
approximately exponential decaying rate.
e.g. 1st trap is sent immediately,
2nd trap is at 1 minute,
3rd trap is at 2 minutes,
4th trap is at 4 minutes,
and so on.
The rate is capped at about 32 minutes.
NOTE : Decaying rate is used to avoid
overflood the NMS.