3Com 2928 User Guide - Page 122

RMON Groups Among the RMON groups defined by RMON specifications (RFC 2819), the realized public MIB of the device supports the statistics group, history group, alarm group, and event group. Statistics group The statistics group defines that the system collects statistics on various traffic information on an interface (at present, only Ethernet interfaces are supported) and saves the statistics in the Ethernet statistics table (ethernetStatsTable) for query convenience of the management device. It provides statistics about network collisions, CRC alignment errors, undersize/oversize packets, broadcasts, multicasts, bytes received, packets received, and so on. After the creation of a statistics entry on an interface, the statistics group starts to collect traffic statistics on the interface. The result of the statistics is a cumulative sum. History group The history group defines that the system periodically collects statistics on traffic information at an interface and saves the statistics in the history record table (ethernetHistoryTable) for query convenience of the management device. The statistics data includes bandwidth utilization, number of error packets, and total number of packets. A history group collects statistics on packets received on the interface during each period, which can be configured through the command line interface (CLI). Alarm group The RMON alarm group monitors specified alarm variables, such as total number of received packets (etherStatsPkts) on an interface. After you define an alarm entry the system gets the value of the monitored alarm variable at the specified interval, when the value of the monitored variable is greater than or equal to the upper threshold, an upper event is triggered; when the value of the monitored variable is smaller than or equal to the lower threshold, a lower event is triggered. The event is then handled as defined in the event group. If the value of a sampled alarm variable overpasses the same threshold multiple times, only the first one can cause an alarm event. That is, the rising alarm and falling alarm are alternate. Event group The event group defines event indexes and controls the generation and notifications of the events triggered by the alarms defined in the alarm group and the private alarm group. The events can be handled in one of the following ways: z Log: Logging event related information (the time of the event occurred, contents of the event, and so on) in the event log table of the RMON MIB of the device, and thus the management device can check the logs through the SNMP GET operation. z Trap: Sending a trap to notify the occurrence of this event to the network management station (NMS). 1-2