Description: This is a short introduction in order to help you understand how the A.I.M.O.S. SNMP Agent realises SNMP alarm forwarding. When the A.I.M.O.S. SNMP Agent is informed about a failure in the monitored system, it must find out which SNMP Managers will have to get an alarm message. Each SNMP Manager who is to get the alarm message, requires an entry in the aimosPhoneBookTable. This entry contains the IP address used for alarm forwarding.

Prior to the explanation on how the A.I.M.O.S. SNMP Agent determines the list of phone book entries which have to be informed about an active alarm, the three aspects with a decisive influence on this determination will be explained in the following:

. Alarms with similar characteristics will be put together in alarm groups. The alarm groups defined in the system are listed in the table aimosAlarmGroupTable. Via aimosAlarmAlarmGroupID each alarm is assigned to exactly one alarm group.

. The Provider can create work shifts and determine various alarm distribution rules in dependence of each work shift. The work shifts defined in the system are listed in the table aimosWorkShiftTable. The currently active work shift is set by each Organisation itself using the object aimosOrgActiveWorkShiftID in the aimosOrgTable.

. The third point of influence are the alarm recipient lists. Each Organisation defines its own alarm recipient lists by adding the according entries to the table aimosAlarmRecipientListTable. For each alarm recipient list the phone book entries assigned to it are listed in the aimosAlarmRecipientListMemberTable. One phone book entry (i.e. one SNMP Manager) can be assigned to several alarm recipient lists simultaneously.

In order to get the list of SNMP Managers that have to be informed, the A.I.M.O.S. SNMP Agent proceeds as follows:

. The A.I.M.O.S. SNMP Agent checks the aimosAlarmConfigTable, and uses the object aimosAlarmAlarmGroupID in order to find out to which alarm group the alarm belongs.

. Next, it determines which Organisations are authorised to receive alarms of this alarm group. This information is laid down in the table aimosAlarmGroupAllowedOrgTable.

. The A.I.M.O.S. SNMP Agent checks the value of aimosAlarmForwardingType of each affected organisation in order to determine the organisations having alarm forwarding enabled as well as the kind of alarm forwarding to be used (SNMPv1 trap or SNMPv2c notification).

. For each Organisation that is allowed (allowed org) and enabled (alarm forwarding enabled) to receive alarms, the current work shift is identified via the object aimosOrgActiveWorkShiftID.

. The table aimosAlarmDistributionPlanTable now shows which alarm recipient lists have to be used. The table provides one alarm recipient list per Organisation, AlarmGroup and work shift. If there is no entry for a certain combination, no alarm will be sent. If there is an entry, each member of the alarm recipient list (aimosAlarmRecipientListMemberTable) will receive an alarm notification, unless a phone book entry was deactivated via aimosPhoneBookActive.

After the alarm recipients have been identified, the various counters required for sending traps must be identified:

. The aimosAlarmListAlarmEventID identifies the cause leading to the dispatch of a aimosAlarmNew or a aimosAlarmChanged notification to one or more SNMP Managers. Here, the counter will be increased by one for each cause. If the cause leads to sending a aimosAlarmCleared notification, the counter will not be increased. Instead, the count of the according aimosAlarmNew or (if present) the latest aimosAlarmChanged notification will be used.

. The aimosAlarmListID is identical to the aimosAlarmListAlarmEventID, as long as the aimosAlarmChanged alarm has not been implemented.

. The aimosAlarmTrapID uniquely identifies each notification that was not sent to an SNMP Manager.

. Each SNMP Manager can rely on the aimosAlarmTrapNotificationID to have a continuous numeration. If not, one notification got lost.

At long last the A.I.M.O.S. SNMP Agent have to collect some information required to provide the notifications:

. The A.I.M.O.S. SNMP Agent have to inspect the aimosAlarmConfigTable (and in a future version of the A.I.M.O.S. SNMP Agent the aimosAlarmSeverityRangeTable) to determine the alarms severity (in the future version for each organisation).

. The A.I.M.O.S. SNMP Agent collects the organisation specific customer device information to be provided with the notification by means of the values of aimosMasterTrapInfo, aimosSubRackTrapInfo, aimosRemoteTrapInfo and aimosCableTrapInfo.

Now the A.I.M.O.S. SNMP Agent has collected all information required for SNMP alarm forwarding. The A.I.M.O.S. SNMP Agent will now perform the following actions:

. Create one entry per organisation in the alarm list (aimosAlarmListTable) using the organisations ID (aimosOrgID) and the alarm List ID (aimosAlarmListID) as index.

. Send one SNMP notification to each manager discovered by the steps mentioned above and create for each notification one entry in the trap list (aimosAlarmTrapTable) using the organisations ID (aimosOrgID), the alarm List ID (aimosAlarmListID) and the trap ID (aimosAlarmTrapID) as index.

Each manager have to acknowledge the received notifications by means of setting aimosAlarmTrapAcknowledgementState using its organisation ID (aimosOrgID), the alarm list ID (aimosAlarmListID) and the alarm trap ID (aimosAlarmTrapID) to acknowledged(2).

After having emitted the alarm notification, the A.I.M.O.S. SNMP Agent expects an acknowledgement within a certain interval, that can be specified (in seconds) in aimosAlarmAckExpectInterval. If there is no such acknowledgement, the A.I.M.O.S. SNMP Agent will continue to emit the alarm until the acknowledgement is received.

The notification remains in the alarm list . as long as the based alarm event is active or . if at least one notification related to the alarm event is not yet acknowledged by at least one of the involved SNMP Managers.

The entries in the trap table (aimosAlarmTrapTable) are earlier removed: If a manager has performed the required acknowledgements, its entries in the trap table are removed. After remove from the trap and alarm list table, the removed entries are available in the alarm log (aimosAlarmLogTable). The specific alarm event ID will not be used again unless an alarm list rebuild resets the counter to zero or the wrap value (2^32-1) is reached. If a similar or even the same alarm event occurs again (after the old one gets cleared), than the notification will not contain the formerly used alarm event ID but a new one.