The TMN reference model refers to a set of standards by the International Telecommunications Union (ITU-T) for the specification of a Telecommunications Management Network (hence, the acronym TMN). TMN covers a wide range of topics related to the principles for how to manage telecommunication networks. The topics are formally described in standards that vendors should adhere to.

The commercial importance of TMN is limited and is, in fact, decreasing. Nevertheless, TMN is widely established as a reference framework that provides a clear and widely accepted terminology for management related topics.

What is the TMN reference model?

The TMN hierarchy, is a reference model that specifies a set of management layers that build on top of each other and address different abstractions of the management space. In practice, those layers are not always clearly separated in the systems that implement the corresponding functionality. However, as a reference, the layer concept is invaluable.
According to the TMN reference model, management systems are categorized to the following layers that perform specific functions and have a specific scope:

Business Management

A management layer responsible for the total enterprise and not subject to standardization.

A management layer that is concerned with, and responsible for, the contractual aspects, including service order handling, complaint handling and invoicing, of services that are being provided to customers or available to potential new customers.

A management layer responsible for the management, including coordination of activity, of a network view.

A management layer which is responsible for management of network elements on an individual or collective basis

An architectural concept that represents telecommunication equipment (or groups/parts of telecommunication equipment) and supports equipment or any item or groups of items considered belonging to the telecommunications environment that performs network element functions (NEFs).

A few words for the most important layers that are always confusing beginners, are following.

TMN – Element Management Layer (EMS)

The element management layer is concerned with managing the individual devices in the network and keeping them running.

This includes functions to view and change a network element’s configuration, to monitor alarms and events send from elements, and instructing network elements to run self-tests. Note, that the element management layer does not cover functions that deal with ensuring overall network integrity.

TMN – Network Management Layer (NMS)

The network management layer involves managing relationships and dependencies between network elements, generally required to maintain end-to-end connectivity of the network. This layer is concerned with keeping the network running as a whole.

For example, we may have a network with individual element configurations that are perfectly valid but that do not match up properly. As a consequence, the network will not work as intended. Such examples include static paths across the network, timer values that need to be tuned to avoid excessive timeouts and re-transmissions, etc. In this cases, the network management layer involves ensuring that data flows across the network and reaches its destination with acceptable throughput and delay.

Another example of a network management task is the management of a network connection as a whole—for instance, setting it up and monitoring it.

TMN – Service Management Layer

Service management is concerned with managing the services that the network provides and ensuring that those services are running and functioning as intended.

For example, when a customer orders a phone service, the service needs to be activated and be managed. For activating a phone service, this may require a number of operations that need to be carried out across the network so that the service is activated: A phone number must be allocated. The company directory must be updated etc. Later, the user might call the service help desk and complain that the service is not working properly.  Troubleshooting the service will then be required to identify the root cause of the problem and solve it.

These service-related tasks build on the functionality that is provided by the network management layer.

Summary

Although at first, the boundaries between network management and service management are blurred, at least conceptually, the difference between service and network management is significant. All this has been defined by the TMN reference model, still used to define monitoring and management functions.

“Network Management is technology dependent and driven by the implementation of the network. “
Chris Rizos
“Service Management is concerned with concepts that end users and customers relate to and the value that they derive from a network—namely, the service.”
Chris Rizos

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