Directory-Enabled Networking (DEN)

One of the most time-consuming aspects of NMS development is producing the information model. This is the way in which the managed objects, such as nodes, interfaces, links, virtual connections, network clouds, routes, and resource blocks (bandwidth and other traffic parameters), are represented inside the NMS. Rather than reinventing the wheel every time a new set of managed objects is needed (as occurs when an NE feature set is extended), another approach is to use an existing standard information model. DEN provides this and is not a product: It is more of a philosophy. Technically, DEN is a specification of an object-oriented information model. This is a set of:

• Classes, such as generic nodes (e.g., IP routers, FR switches)

• Class attributes, such as location, owner/operator

• Class methods , such as delete a specified node or monitor a specified node for notifications

• Class relationships ”for example, a node that owns connections that originate on it and terminate on other nodes

This models NEs and services as part of a managed environment in a repository-independent fashion. The purpose of DEN is to bind users and services to NEs, network paths, bandwidth, and other network parameters. To really leverage the concepts of PBNM, it is necessary to combine it with DEN. Central to DEN is the deployment of a strong directory technology product, from organizations such as Novell, Netscape, and Microsoft. Both the information model instantiation and the policies are stored in the directory.

The focus of DEN lies in providing a type of single system image for a managed network by combining the disparate elements of:

• A technology-independent information model

• A directory system for storing policies, the object model, and its instantiation (the network, its devices, users, services, etc.)

• A policy system as discussed earlier

• A traditional SNMP-based NMS

This is an ambitious undertaking combining products from a range of vendors . We now briefly discuss the principal elements.

The Information Model

There are currently two important standard information models:

• The Common Information Model (CIM)

• An extension to CIM called Directory-Enabled Networking (DEN)

CIM is an object-oriented model that describes how a system and its components may be managed. A central tenet of CIM is the presentation of a consistent view of the managed network, independent of any protocols (such as SNMP) and data formats supported by NEs. CIM is a layered model that starts with generic classes. These classes can be built upon and refined (e.g., starting with devices at the top level, a router is a refinement of the basic device type, as is a switch). Some CIM model components are:

• System

• Device

• Application

• Network

By describing these objects in a standard fashion, NMS designers can leverage existing work. This avoids the task of inventing a vendor-specific information model. The use of a standard model can also assist in interworking with other products.

DEN is an extension of CIM. It describes the physical and logical characteristics of NEs, service, and the policies used for their management. DEN provides a mapping of the information to a format that can be stored in an LDAP-based directory system.