Overview of Management Layers


In this section, you learn about the layers of management functions that must exist in an OSS.

Network management is defined as a collective set of management functions that can be applied to a network, such as an MSPP interoffice (IOF) ring. These functions are commonly referred to as FCAPS:

  • Fault management

  • Configuration management

  • Accounting management

  • Performance management

  • Security management

These functions exist as part of the telecommunications management network (TMN) framework. The TMN layers are the framework that defines how management is logically separated in an OSS. Developed within the International Telecommunications Union (ITU), the TMN framework breaks down the management functions into different layers that represent a hierarchical structure. Figure 15-1 shows the TMN framework.

Figure 15-1. TMN Framework


The TMN framework has four layers:

  • Element Management Layer (EML) The bottom of the pyramid, referred to as the EML, is responsible for managing each individual element of the network. The EML communicates management data, such as alarms, collected from the network elements to the next-highest layer: Network Management.

  • Network Management Layer (NML) The NML has the responsibility of ensuring end-to-end connectivity, network reliability, and capacity planning. It carries out these responsibilities by having access to the management data that the EML provides.

    The NML has complete visibility of the entire network, which consists of different technologiesfor example, Asynchronous Transfer Mode (ATM), digital subscriber line (DSL), SONET, and so onor a subsection of the network, such as all the MSPPs. The NML is also responsible for collecting any failures or performance degradations in the network that violate an SLA or help to provide advance warning of an SLA violation. Failures can be reported as alarms, error rates, and performance levels. Thus, the NML has the responsibility to report service-affecting problems to the Service Management Layer (SML). For example, an OSS that supports NML must provide the appropriate performance-management and fault-management functions so it can provide information that applications at the SML require (for example, SLA-monitoring applications and customer network management applications).

  • Service Management Layer (SML) The SML is responsible for managing the services within MSPP networks, such as Ethernet over SONET. The SML normally includes the contractual aspects of services that are provided to the end customers. Customer network management and service-layer management are supported at this layer.

  • Business Management Layer (BML) The BML's responsibilities include billing and company policies. Policy-management applications reside at this layer.

It is important to realize that, in many implementations of the Telecommunications Management Network (TMN) framework, management data might not be passed from a layer to the layer directly above it in all cases. Management data might pass from one layer to any layer above it, or to another system within the same layer, if required. For example, an EMS that supports EML functions might pass MSPP alarms data to a customer network management application residing at the SML. Each service provider or large enterprise that deploys its own OSS defines where the TMN functions will reside, keeping in mind the importance of not duplicating functionality. Duplication increases the complexity and cost of integrating different OSS components.

Furthermore, in certain OSS deployments, an application might support functions that span multiple layers of the TMN model. For example, an EMS might support both EML and NML functions within the EMS system. This EMS might support the correlation and aggregation of statistics collected from the MSPP network, or it might not provide this correlation and might leave this function for a NMS. CTM can manage individual 15454s in an interoffice facility (IOF) ring, for example, but it can also provision and maintain end-to-end circuits traversing one or more 15454 rings.




Building Multiservice Transport Networks
Building Multiservice Transport Networks
ISBN: 1587052202
EAN: 2147483647
Year: 2004
Pages: 140

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