2-2about the total traffic, error statistics and performance statistics of the network segments to which theports of the managed network devices are connected. Thus, the NMS can further manage the networks.Commonly Used RMON GroupsEvent groupEvent group is used to define the indexes of events and the processing methods of the events. Theevents defined in an event group are mainly used by entries in the alarm group and extended alarmgroup to trigger alarms.You can specify a network device to act in one of the following ways in response to an event:z Logging the eventz Sending traps to the NMSz Logging the event and sending traps to the NMSz No processingAlarm groupRMON alarm management enables monitoring on specific alarm variables (such as the statistics of aport). When the value of a monitored variable exceeds the threshold, an alarm event is generated,which then triggers the network device to act in the way defined in the events. Events are defined inevent groups.With an alarm entry defined in an alarm group, a network device performs the following operationsaccordingly:z Sampling the defined alarm variables periodicallyz Comparing the samples with the threshold and triggering the corresponding events if the formerexceed the latterExtended alarm groupWith extended alarm entry, you can perform operations on the samples of alarm variables and thencompare the operation results with the thresholds, thus implement more flexible alarm functions.With an extended alarm entry defined in an extended alarm group, the network devices perform thefollowing operations accordingly:z Sampling the alarm variables referenced in the defined extended alarm expressions periodicallyz Performing operations on the samples according to the defined expressionsz Comparing the operation results with the thresholds and triggering corresponding events if theoperation result exceeds the thresholds.History groupAfter a history group is configured, the Ethernet switch collects network statistics informationperiodically and stores the statistics information temporarily for later use. A history group can providethe history data of the statistics on network segment traffic, error packets, broadcast packets, andbandwidth utilization.With the history data management function, you can configure network devices to collect history data,sample and store data of a specific port periodically.
