Abstract -- Object Evaluator Management Function

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Abstract -- Object Evaluator Management Function Network and Application Engineering Track
N3: Network Management

Object Evaluator Management Function

Choi, Taesang ( choits@cstp.umkc.edu)
Choi, Deokjai ( dchoi@cctr.umkc.edu)
Tang, Adrian ( tang@cstp.umkc.edu)

Abstract

In service management, there is a need to evaluate the quality of service of a service type object or the performance of a server object. This management function provides the capability for a manager to evaluate such managed objects. It introduces a managed object class called the objectEvaluator. An object evaluator (i.e., an instance of the objectEvaluator managed object class) encapsulates the evaluation function which is used to evaluate a given managed object in a periodic basis. After the managed object is evaluated at the end of each evaluation period, the result is stored in the object evaluator. By polling the result attribute of the object evaluator, the manager can find out the latest evaluation of the managed object.

A number of object evaluators can be associated with the same managed object. This is not surprising since a managed object can be evaluated in a number of ways. For example, the performance of an Ethernet network can be measured in terms of the performance of the MAC level, such as the number of the Ethernet frames sent and the number of the Ethernet frames dropped. It can be also measured in terms of the performance of the application servers (such as files servers or database servers) running in the network. In this simple example, we can thus associate at least two object evaluators with a managed object representing some Ethernet network. Each object evaluators encapsulates a particular evaluation function to evaluate the given managed object.

By storing the evaluation function and the evaluation period in an object evaluator, the manager essentially instructs its agent to apply the evaluation function at the end of each evaluation period. The following lists the advantages of having the evaluation performed by the agent instead of the manager:

Since the agent has more up-to-date informaion of the managed object and its environment, its evaluation would be more accurate than one performed by the manager.
If the manager has to perform the evaluation, it has to retrieve from the agent all the environmental information which is needed by the evaluation function; this will increase the network traffic load.
If the manager (e.g., an enterprise manager) happens to manage quite a number of managed resources, it would be computationally intensive for the manager to carry out all the evaluations. It would be better for the manager to delegate the evaluation responsibility to its agent(s).

To give an example of how an evaluation function can be used, let us consider the performance of a router managed object. Imagine that the router object has a number of performance attributes including the number of packets processed and the number of packets dropped. A high level manager, when polling for the performance of this router,may not care about specific values of these performance attributes; instead, it may be interested in only an aggregate health index which is evaluated by some evaluation function (e.g., one taking a weighted linear sum) on only those performance attributes which the manager is interested in. Used in this manner, an evaluation function can be viewed as an aggregation function deriving a composite value from simple values such as attribute values appearing in a managed object. Aggregation is not a new concept; the important point is that the aggregation is performed by the agent instead of the manager. Using an object evaluator, the manager instructs an agent how to perform the aggregation, turning a passive agent to be a smarter one. This technique of delegating resposibility to agents is extremely useful in an enterprise environment.

Section 2 describes the design of the objectEvalutor managed object class. We also examine two subcalsses of the objectEvaluator managed object class. These subclasses contain a constraint which is applied to the evaluated result at the end of each evaluation period. At the end of the section, we give a Health Monitoring Management model.

In Section 3, we show how to apply the Health Monitoring Management model to perform backup management in an enterprise environment. For our discussion, the less-than-threshold-objectEvaluator object in the Health Monitoring Management Model is called a "health monitor".

In Section 4, we conclude our work.