EMS Manual

Introduction to EMS
EMS Manual—426909-005
1-5
EMS Capabilities and Features
sending command messages. For each command, the subsystem returns a
response message. The management application and the subsystem
communicate synchronously, in a one-command, one-response dialog.
The EMS interface is unidirectional and asynchronous. Operators and
management applications cannot use EMS to send information to subsystems, and
subsystems report event information regardless of whether or not an operator or
management application is interested in that information at the moment.

Variable urgency
In general, commands are treated as equally urgent, in that each must be
completed before the next one is issued. The operator or management application
determines what command to issue next. To the subsystem, a request for status
information is no less important or urgent than a request to stop all objects
immediately.
In EMS, although operators and management applications control the retrieval and
use of EMS information, subsystems can use certain EMS-defined conventions to
convey significance or urgency. These conventions are needed to emphasize
certain conditions that the operator or management application might otherwise not
recognize as significant in the continuous flow of event information.
Because of its unique characteristics, the EMS interface is a valuable complement to
the command-response interface. The two interfaces together can provide a wide
range of management services. For example, you can use EMS to monitor a large
array of subsystems. Then, when a significant situation arises, you can use the
command-response interface to initiate a dialog with the appropriate subsystem.
EMS Capabilities and Features
The primary function of EMS is to collect and distribute event messages. Event
messages are a special category of SPI messages used to convey information about
events, which are significant occurrences in the subsystem environment.
Event messages report many occurrences and conditions, such as:

Changes in the subsystem environment

Errors encountered during continuous operation (as opposed to errors
encountered during an interaction with a user or application, which are usually
reported directly to the user or application)

Conditions that might lead to a problem if not corrected

Situations requiring operator intervention

Significant losses of function or resources

Indications of why a process terminated