RFC 1021 (rfc1021) - Page 2 of 5

High-level Entity Management System (HEMS)

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