ocesses NE performance information enable configuration of the NE carry out remote operations on the NE. The need for both NMS and EMS in management is appreciated when many nodes, networks and NEs must be managed. The EMS can be used to manage a spe- cific group which can be separated logically. Groups may be assigned to an EMS so that it manages a specific node, network or a number of specific devices. The advantages of using an EMS to manage devices are: management of specific devices connected to different networks management of all devices in a particular network reduce the load on the NMS through sharing and balancing. Hence the involvement of both NMS and EMS in the management hierarchy helps to manage the managed objects more effectively. 12.10.1 Interface Between NMS and EMS The NMS and EMS are used for effectively managing a large number of NEs. A single NMS can manage a number of EMS. This hierarchy can be extended so that a num- ber of higher level managers are used to manage a number of low-level managers. OSS for Telecom Networks High Level Manager (NMS) Low Level Manager Low Level Manager Low Level Manager (EMS) (EMS) (EMS) Group of NEs Group of NEs Group of NEs Figure 12.10 Relationship between NEs, EMS and NMS. SECURITY JMX Agent JMX Agent JMX Agent AdventNet Vendor Figure 12.11 Position of AdventNet EMS and JMX agents relative to NEs and NMS. 12 Fault Management A management structure benefits from a defined communication channel between the high-level and low-level managers. Communication between an EMS and its NMS is called northbound or upward communication. This communication is carried out using protocols such as SNMP, HTTP/HTML, RMI, CORBA and TL1, and through a northbound interface. An interface between the NMS and the EMS should be able to: send independent notifications to the NMS when a managed object is added to or deleted from the management domain, that is, the managed network send autonomous notifications to the NMS when an event or alert is generated forward notification to specif