Why Is the TMN Model Still Useful in Network Management After All These Years?

TMN 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.

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.
  • Service Management: 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.
  • Network Management: A management layer responsible for the management, including coordination of activity, of a network view.
  • Element Management: A management layer which is responsible for management of network elements on an individual or collective basis
  • Network Elements: 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).

It is obvious that TMN focus is not business management. TMN instead focuses on defining technically and conceptually the role of the devices, their configuration and monitoring, the configuration and monitoring of the network as a whole and finally the configuration and monitoring of services. But how are these functions mapped on the above layers? Most beginners get confused, so here are a few words for the most important layers that will help clarify things for the beginners:.

Element Management 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.

Network Management 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, network management 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.

Finally, 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.

Concluding, although at first, the TMN reference model may seem complicated and out-dated, it helps defines the concepts and provides a well-defined dictionary for Operatos and Manufacturers and for this reason it is still widely used.