Service providers are under tremendous pressure to offer a broader range of services that meet subscriber demands, and they need to deliver these services in a timely, reliable, and cost-efficient manner. Crucial to this is their ability to effectively manage the network to achieve benefits such as faster service activation time and guaranteed quality of service levels. All this is possible with readily available, scalable and non-proprietary network management solutions, with multi-vendor, multi-technology systems interoperating in an open architecture environment.

Until now, some obstacles stood in the way of achieving full-featured, end-to-end network management. These challenges have become the minimum requirements for any viable solution. They are addressed in the open, standard Common Object Request Broker Architecture (CORBA) network management layer to element management layer (NML-EML) interface solution, which was developed by the integrated multi-vendor network management working group of the TeleManagement Forum. This solution enables service providers to successfully achieve end-to-end network management.

WHAT ARE THE CHALLENGES?

Existing solutions specified to date have fallen short in the ability to provide full-featured, end-to-end network management. While the ITU-T recommendations for the Telecommunications Management Network (TMN) have been in existence for more than a decade, wide-scale deployment has not occurred. The result has been a proliferation of various proprietary solutions. These vendor-specific solutions raise interoperability issues, since the typical service provider's network includes transport equipment and management systems from multiple vendors.

Technological advances associated with transport network elements have also contributed to the complexity of the network management issue. The emergence of hybrid network elements, which provide one piece of equipment for multiple technologies, offers service providers benefits such as increased bandwidth and maximum network resource utilization. For example, it is not uncommon to find a single network element that supports Synchronous Optical Network (SONET), Synchronous Digital Hierarchy, dense wavelength division multiplexing, Asynchronous Transfer Mode (ATM), and Internet Protocol technologies.

In the past, technology-specific NML-EML interface solution, such as the ATM Forum M4 interface and the SONET Interoperability Forum network model, only supported a single technology. Such solutions are based on an underlying premise that networks have clear, technology-specific lines of delineation. However, these current technology-specific solutions cannot manage networks composed of hybrid network elements.

As mergers, acquisitions, and joint ventures become increasingly prevalent throughout the industry, the boundaries of a service provider's network expand and can stretch across traditional geographical boundaries. As a result, the scope of the management domain increases. Many previous solutions have not been validated across large-scale systems, and they are quickly becoming inadequate due to scalability factors.

WHAT IS NEEDED?

These network management challenges directly translate into minimal requirements for a viable solution. To be successful, a solution must be:

• Non-proprietary, vendor-neutral, and applicable across multi-vendor networks

• Commonly applicable to multiple technologies, in order to address the hybrid network element challenges

• Future-proof and not strictly associated with a specific technology, protocol, or implementation

• Usable and commercially viable

• Scalable (to meet the demands of managing large networks)

• Open and freely available

THE BEST SOLUTION

The ideal interface solution for addressing the network management challenges is fundamentally based on the layered architecture of the TMN. The CORBA NML-EML interface solution leverages the separation of management concerns outlined at the layers. The EML is concerned with managing the individual network elements or a group of network elements, whereas the NML focuses on the network as a whole.

At the NML, a network management system (NMS)is responsible for managing the network from one end to the other. It provides an abstracted view of the underlying network, without much visibility of specific network elements.

This "network view" at the NMLEML reference point is the key to the CORBA NML-EML interface solution. It makes it possible to obtain commonality across multiple vendor-specific equipment at the NML, and to normalize managed objects across multiple technologies at this reference point. Scalability is achieved because the managed objects are the only objects visible across the NMLEML interface.

The NML-EML interface solution includes a set of functional requirements, an information model and use cases, all of which are protocol-neutral. This ensures that the requirements and modeling efforts are preserved as technology evolves. The interface solution also includes the CORBA interface definition language (IDL). The enabling technology, CORBA, was chosen to increase commercial viability and to meet time-to-market demands.

The functional requirements of the CORBA NML-EML interface include the system management functional areas required for an NMS to achieve end-to-end network management. Specifically, the interface supports configuration management, fault management and NML-EML interface versioning.

The NMS uses a network resource autodiscovery process to build an inventory of all the resources it is managing. During this process, the NMS queries the EMS for managed physical and logical resources, including elements, physical/connection termination points, physical links and subnetwork connections. The queries provide an up-to-date, EMS-synchronized view of the underlying network.

The NMS may also query the EMS to retrieve data about the version of the NML-EML interface that is currently supported by the EMS. The query ensures that both the NMS and EMS are communicating across a compatible version of the interface.

With the CORBA NML-EML interface solution, the NMS can provision various attributes of the resources it is managing. Attributes include transmission parameters of termination points, as well as labels and user-friendly identifiers of managed objects.

Notifications of autonomous events allow the EMS to send asynchronous events to the NMS as they occur. Such events include the creation and deletion of managed objects, attribute value change events, state change events, and alarms. A filter can be set to control which event notifications the NMS receives.

A filter can also be set to control which alarms are sent to the NMS. Alarms are sent from the EMS to the NMS as they occur. The NMS can receive only the alarms it needs based on the filtering criteria, or it can receive all active alarms from an EMS for synchronization purposes.

BUILDING AN INFORMATION MODEL

The NML-EML interface specifies an information model that provides an abstracted view of the underlying network. The information model includes the following:

• NetworkR1 Object: Represents the EMS and its management domain

• Managed Element Object: Represents the network elements

• Multilayer Subnetwork: Represents the abstraction offered by the EMS to the NMS to symbolize a subnetwork that is managed by the EMS

• Topological Links: Represent physical links

• Physical Termination Points (PTPs): Represent the end points of a physical link

• Connection Termination Points (CPTs): Represent the connectable termination points contained in PTPs

• Subnetwork Connection Object: Represents the connection between two CTPs

• Route Object: Represents the path of a subnetwork connection of an ordered set of CTPs

Use cases capture the behavior of the NMS and the EMS under specific scenarios. The use cases defined in conjunction with the CORBA NML-EML interface include scenarios such as discovery of the network, provisioning of termination point transmission parameters, setup/teardown of subnetwork connections, alarm propagation and craft-related use cases.

PUTTING IT TO WORK

While the functional requirements, information model, and use cases define the NML-EML interface in a protocol-neutral format, the CORBA IDL was specified to enable the implementation of the solution.

A coarse-grain approach was used to define the IDL for scalability reasons. This approach leads to the adoption of a Facade Pattern, where manager objects are defined as first-class CORBA objects and services across the manager objects are used to retrieve information about the individual object classes. As a result, the number of actual CORBA first-class objects is more manageable.

The CORBA IDL definition specifies the NetworkR1, Managed Element Manager and Multilayer Subnetwork Manager as CORBA first-class objects.

WHAT DOES IT ALL MEAN?

The CORBA NML-EML interface solution was specified to address the problems and complexities of end-to-end network management across networks using multi-vendor, multi-technology network elements. In specifying the interface, the key requirement was a usable solution that is scalable and future-proof.

The design decisions surrounding the specification of the CORBA NML-EML interface make this solution a viable one that will allow service providers to expand their service offerings to meet subscribers' growing demands. Best of all, they can provide these services quickly and reliably, without accumulating high network costs.

Managing hybrid network elements with multiple-technology interfaces

Managing hybrid network elements via a single, common transport interface

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By Jeffrey Ross and Lee Chow

Jeffrey Ross is director of product management at Fujitsu; Lee Chow is strategic product planner at Tellabs.