e Manager can access the sub-agent's OID in the same way that it accesses the Master Agents' OIDs. That is, the Manager can access the sub-agent's OIDs through the Master Agent. Requests or queries are sent to the Master Agent by the Manager. Queries related to the sub-agents registered with the Master Agent are forwarded to the respective sub-agents. The sub-agents send their responses to the Master Agent, which in turn sends them on to the Manager. The varbind values processed by the Master Agent are also sent to the Manager. The Master-Agent/Sub-Agent functional relationship is illustrated in Figure 12.15. The management information corresponding to the Sub-Agent is exposed through a table called the SubAgent table. Any agent can be registered as a sub-agent to a Master Agent. Sub-agents can be registered for SNMP, RMI and CORBA. Similarly, any SNMP agent can be registered as a sub-agent to the JMX Agent. Details of the SNMP agent, such as sub-agent name, port, time out and community, must be entered. In RMI and CORBA protocols, the sub-agents can be registered to the JMX Agent using the "Cascader Service". 12.10.4.3 Fault Group While managing the EMS, the NMS may encounter events and alerts. These details are exposed to the Manager through the Fault Group of the Fault-MIB. The Fault Group can be classified as general, database, notification and configuration details. 12 Fault Management General details include number of events generated, number of alerts generated, size of event queue, size of alert queue, user-defined properties and so on with respect to the objects being managed by the EMS. General details are exposed to the NMS. Database details corresponding to alerts, events and severity of the alerts are exposed by the EMS as database records. There is a table devoted to each of alerts, events and web NMS severities. The Alert table exposes data about the Alert objects in the EMS, the event table exposes data about events in the EMS and the Alert Count table shows the number of alarms of a particular se