1 Introduction

The ever-increasing complexity and heterogeneity of distributed systems represents a major challenge for the Operation, Administration, Maintenance and Provisioning (OAM&P) of large-scale public and corporate networks. Integrated management solutions based on standardized management architectures ([7]) support the network providers' efforts in maintaining a high degree of quality and availability of their services while decreasing the cost of running the information technology infrastructure.

Apart from the well-known OSI/TMN and Internet management architectures, a third alternative is gaining increasing attention: the Common Object Request Broker Architecture ([2]) which has been standardized by the Object Management Group (OMG). Initially developed for distributed object-oriented programming, the advantages of using CORBA in the domain of network and systems management are more and more recognized.

One reason for this is the fact that today the development of management systems is perceived as a special case of developing large-scale information technology applications. The successful application of new principles from the field of software engineering like object-oriented techniques for the analysis, design and programming of complex software systems leads to the development of modular, well-structured management applications built from "off-the-shelf" software components. This yields demand for techniques that protect developers, at least to a certain degree, from the heterogeneity of the underlying operating systems. This is particularly important for the development of powerful management software.

Management in open, heterogeneous environments, in turn, can only be effective on the basis of standardized architectures because these encompass not only the communications infrastructure, but also end-user systems and their software. It is easy to see that in large networks the amount of managed systems can become very high; on the other hand, often enough those networks are managed from a single point of control which is flooded with error messages if several managed systems encounter failures. For this reason (and others given in the second section), it is necessary to extract the functionality from the managing systems and distribute this "management intelligence" between the managing and the managed systems.

This distribution can be done in two ways:

• by transferring management functionality dynamically from managing systems to the managed systems. This approach is termed Management by Delegation ([17], [5]). It requires either the implementation of functionality in scripting languages like Java ([6]) or Tcl ([13]) or the use of extensible agents and the existence of a delegation protocol. The drawback of this approach is that implementations of already existing management functionality like the ISO-OSI Systems Management Functions ([9]) cannot be reused.
• by isolating the management functionality from the managing systems, packaging it in the form of objects and distributing it across a CORBA-based environment. This can be done by implementing the management functionality in terms of Management Services i.e., a Middleware for systems management that can be inherited either by managing systems or managed systems with respect to their needs; already existing implementations of object catalogues can be encapsulated and reused. A special delegation protocol is not required.
  The major difference to the former approach is that the functionality can not be altered during the runtime of the agent since "raw" CORBA does not support passing objects by value.

In contrast to papers focusing on the more technical aspects of Management by Delegation ([1], [4]), the work presented in this paper focuses primarily on the service-based approach. It presents arguments for using "yet another management architecture" and discusses design issues for establishing a middleware accessible for managing systems and managed systems in the form of management services. Finally, a methodology for bringing together the two approaches i.e. implementing intelligent agents on the basis of CORBA is also described. It is therefore important to bear in mind that the two approaches described above are not mutually exclusive.

The paper is organized as follows: section 2 analyses the needs for distributed management and management by delegation; section 3 introduces the concepts for using CORBA as an architecture for systems management. Section 4 discusses some of the more technical considerations to be made when building intelligent agents based on the paradigm of distributed objects. Finally, the last section of the paper concludes and presents issues for further research.