Telecommunications Management Networks (TMN)

OSI Network Management Services for the Telecommunications Industry

TMN is becoming an important topic in the telecommunication service provider’s world. With the size and sophistication of the networks rapidly expanding, a clear need has been
established to provide convenient services to manage the telecommunications enterprise. Fault, Configuration, Accounting, Performance, and Security services are all important
elements of managing critical resources within large distributed telecommunications networks. The TMN concepts have been widely adopted to manage networks ranging from
high-speed fiber-optic networks to distributed cellular and satellite based wireless communication systems. With a significant amount of the fielded equipment providing heterogeneous
interfaces, a push has been on to encourage the development of a single set of protocols and service specifications to manage these networks. Requirements have been levied by the
ITU to encourage the integration of TMN capable services into network equipment. For example, new protocols must now include a General Description of Managed Objects
(GDMO) based Management Information Base.

This document highlights some of the differences between OSI network management and SNMP,
the major concepts involved in TMN and CMIP based management
architectures, and start into some of the specific areas.

CMIP/CMISE, on which TMN is based represents the
major alternative to using SNMP. If you enjoy starting arguments, go into a room of network management folks and indicate a strong opinion on the great advantages of using either
CMIP or SNMP to the exclusion of the other. It doesn’t matter which protocol suite that you advocate, someone will be convinced that you must be from somewhere on the wrong side
of the tracks to have espoused such an opinion. Fortunately, there will probably also be several people within the room that recognize that each of the approaches have there merits,
you just need to understand the pros and cons of each. SNMP is simple, that’s what the S stands for. CMIP is more complicated, (the C doesn’t stand for complicated, but it certainly
would have served the purposes here).

Why then are there these two popular but vastly different standards? The CMIP approach has been to provide a feature-rich set of services in which sophisticated services can be
provided by the agents. SNMP is based on a simpler interface, in which sophisticated management services fall to either out-of-band mechanisms or to the management system.

SNMP, by virtue of being connectionless with lower overhead is a good choice for managing networks where in-bound transport mechanisms are the primary means of
management traffic transport. Requests are issued once, if network problems or congestion impede their flow, re-transmissions are avoided, thereby avoiding situations in which the
management protocols become part of a problem rather than part of the solution. However, SNMP is not without its limitations, operations are all atomic, often requiring several
interactions between the management system and the managed agents to achieve meaningful results. Event notifications from the agents are sent in the form of unacknowledged traps,
that can result in critical network problems going unnoticed should the trap be discarded. While strategies for resolving these issues can be addressed through clever constructs in the
Managed Information Base (MIB), they aren’t always available.

CMIP, on the other hand, sacrifices a good bit of the simplicity of SNMP in return for more sophisticated services provided by the agents. Managers can make simple requests of
agents that can cause the agent to execute sophisticated sequences. Event management is managed through a set of accepted standards for event notification, discrimination, and
forwarding. Relationships between Managers and Agents can operate in either connection-oriented or connectionless modes (SNMP is connectionless only). Frameworks have been
specified for Alarm Management, Security Management, Fault Management, and Configuration Management. Advanced sets of services include scoping and filtering which permit
managers to issue requests that involve a larger set of components of the managed system.

TMN leverages the OSI management standards, and has included provisions for the use of SNMP where necessary. Important areas include:

• TMN Service Layers – specify every thing from managing the end-equipment to managing the enterprise business service model.
• TMN Object Architecture – specifies several generic managed object classes that can (and should) be used when defining a MIB for new equipment and protocols. In
  particular, the M.3100 provides a framework for the definition of network equipment MIBs. Fragments of network management objects are provided for items including circuits,
  termination points, and communication fabric.
• Object-Oriented Concepts – the OSI management standards are largely based on the concept of treating the enterprise as a large collection of objects. Concepts such as
  containment, class definition, instantiation, inheritance, and allomorphism (a redefinition of polymorphism for those of you already familiar with other types of object-oriented
  design).
• The Guidelines for Definition of Managed Objects (GDMO) – provide a paradigm and specification language for definition of the managed objects. The GDMO specification
  language, as accompanied by ASN.1 to describe the formats for information transit is an important element in understanding and developing MIBs.
• OSI Network Management Architecture – includes the Common Management Information Protocol (CMIP), Common Management Information Service Element (CMISE),
  and Common Management Information Services. It also doesn’t hurt to have an understanding of the underlying Remote Operations Service Element (ROSE) and Association
  Control Service Element (ACSE) services that support CMIS.
• OSI based MIB standard objects. Event Forwarding Discriminators (EFDs), Security, Alarm, and Logging objects have been specified in the open standards. Integrating
  services through these standards can greatly aid in limiting the complexity of equipment specific MIBs. Further, if you are using an off-the-shelf TMN management or agent
  product, many of these services and interfaces have already been incorporated.

TMN Components and Their Interfaces

Within TMN, the management system consists of several types of components. Shown in Figure 1,
these components include Operations Systems (OS),
a Data Communications Network (DCN),
Workstations, Network Elements, Mediation Devices, and Q Adapters. Operations Systems provide
management services that provide for the surveillance, monitoring
and control of the managed network, interacting with components within the network
to gather information and issue commands that may affect the behavior of the network.
These are roughly equivalent to the manager components of SNMP managed networks.
Workstations provide network management staff an ability to monitor and interact with the network
management system. The data communications network can take several form ranging from a
dedicated OSI network using CLNP routing to in-band communications services. The
Network Elements (NE) and Q-Adapters (QA) provide agent services in which the actual MIB
objects are contained. The primary distinction between the NE and QA are that typically
the NE are used to represent network communications equipment that has an embedded CMIP
agent, where the QA are typically equipment that act as proxy agents between the TMN
CMIP interface and legacy equipment supporting either proprietary or other interface
standards. The Mediation Devices (MD) can be used to provide mid-level management services
that represent aggregate behaviors of groupings of the network elements supported by the NE
and QAs.

Figure 1 – TMN Functional / Interface Architecture

As in many telecommunications systems, the interconnections between the major elements of the system are represented by additional alphabet soup. Interfaces include:

• Q3 – Interface protocol suite defined in Q.811 and Q.812.
  It represents the CMISE interface between the participating elements of the network.
  This is the mechanism used by the OS to collect and disseminate management
  information. It is also the most mature interface within the TMN architecture.
• Qx – is a lighter weight interface, intended to facilitate the development of agents in
  situations where the complexity of providing a complete CMIS based MIB isn’t feasible.
  This interface is typically found between the MD and supporting NE and QA.
  An example protocol suite is defined in G.773
• F – provides a conduit for information between the OS and WS components.
• X – interconnects TMNs. It supports the interface between the OS and external systems
  and provides security features for access control.
• OS – Operations System; monitor, coordinate and control telecommunication functions
• WS – Work Station; translates information into displayable format
• DCN – Data Communications Network (Layer1-3)
• MD – Mediation Device; may block, store, adapt, filter, threshold and condense information;
• QA – Q Adaptor ; connects equipment with non-TMN compatible interfaces to a TMN
• NE – Network Element

Of these interfaces, much of the current system developers are focused on development of
equipment that supports the Q3 interface.

TMN Layers

Following the lead of the OSI layered protocol model, TMN provides an organization of management services in the form of a five layer hierarchy of services. The services provided
by the TMN layers include:

• Business Management – handling items including billing, account management and administration. This layer relies on inputs from both the Service and Element
  Management layers for input
• Service Management
• Network Management – provides oversight services to aid in managing major sections of the network
• Element Management – provides oversight and coordination of the services provided by groups of network elements
• Network Element – provides agent services, mapping the physical aspects of the equipment into the TMN framework

If you are involved in development of communications equipment such as switches, hubs and the like, you are most likely to need to focus on the Network Element layer, with
occasional forays into element management. Much of the focus of developers has been on the areas of Network Element and Element Management services, building a framework on
which the higher layer services can be incorporated into management systems for deployment.

Standards Galore

The standards that define TMN span a large number of ITU-T documents. The X.700 series of standards define the baseline CMIP/CMIS services as well as defining the major
management functions. The X.700 series of standards were developed to support generic OSI network management services and include:

• X.700 Management Framework
• X.701 System Management Overview
• X.710 Common Management Information Service (CMIS) Definition
• X.711 Common Management Information Protocol (CMIP) Specification
• X.712 CMIP Protocol Implementation Conformance Statement (PICS)
• X.720 Management Information Model
• X.721 Definition of Management Information
• X.722 Guidelines for the Definition of Managed Objects (GDMO)
• X.730 Object Management Function
• X.731 State Management Function
• X.732 Attributes for Representing Relationships
• X.733 Alarm Reporting Function
• X.734 Event Report Management Function
• X.735 Log Control Function
• X.736 Security Alarm Reporting Function
• X.738 Summarization Function
• X.739 Workload Monitoring Function
• X.740 Security Audit Trail Function
• X.745 Test Management Function

Light reading if you have a week or two to spare. Not to mention the fact that these protocols and services also make fairly extensive use of external OSI application and
presentation layer services including the Remote Operations Service Element (ROSE) as a request transport mechanism and the Association Control Service Element (ACSE) to establish
bindings between the participating management elements. Naming and directory services can also come into play when correlating network element information to the CMIP object
naming model.

Extending this information into a framework that is useful for the TMN services, the M.3000 series of standards have been developed. The TMN M.3000 series includes the
following recommendations:

• M.3000 Tutorial Introduction to TMN
• M.3010 Principles for a TMN
• M.3020 TMN Interface Specification Methodology
• M.3100 Generic Network Information Model for TMN
• M.3200 TMN Management Services Overview
• M.3300 TMN Management Capabilities at the F Interface

Additional information describing the Q interface can be found in recommendations Q.811, Q.812, and G.773. Additional information and guidance can be found from the Network
Management Forum.