RFC 1021 (rfc1021) - Page 2 of 5
High-level Entity Management System (HEMS)
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RFC 1021 HEMS Overview October 1987 Note that the ability to control presupposes the ability to monitor. Changing the behavior of the network without being able to observe the effects of the changes is not useful. On the other hand, monitoring without control makes some sense. Simply understanding what is causing a network to misbehave can be useful. Control is also a more difficult functionality to define. Control operations other than the most generic, are usually device-specific. The problem is not just a matter of providing a mechanism for control, but also defining a set of control operations which are generally applicable across a diverse set of devices. Permitting remote applications to exercise control over an entity also implies the need for a suite of safeguards to ensure that unauthorized applications cannot harm the network. Because monitoring is the key first step, in this initial design of the system, the authors have concentrated more heavily on the problems of effective monitoring. Although the basic control mechanisms are defined, many components need for control, such as strong access control mechanisms, have not been fully defined. OVERVIEW OF THE HEMS The HEMS is made up of three parts: a query processor which can reside on any addressable entity, an event generator which also resides on entities, and applications which know how to send requests to the query processor and interpret the replies. The query processor and applications communicate using a message protocol which runs over a standard transport protocol. The Query Processor The query processor is the key to the management system. It interprets all monitoring and control requests. For optimal network management, we would like to see query processors on most network entities. To encourage the implementations of query processors, one of the primary goals in designing the query processor was to make it as small and simple as possible, consistent with management requirements. Defining the management requirements was no small task, since the networking community has not yet reached a consensus about what kinds of monitoring information should be available from network entities, nor what control functions are required to properly manage those entities. The standards for HEMS were developed through discussions with several interest groups, and represent the authors' best effort Partridge & Trewitt
