7.3 Operation and maintenance characteristics

Among these characteristics:

• time spent per subscriber — for example, 0.065 person-hours per year per subscriber number;
• the average frequency of replacement of TECs, for example, one TECs per month for 5000 subscribers;
• total station downtime, for example, 2 hours in 40 years;
• downtime of individual subscriber and connecting lines, for example, 30 minutes per year per line.

Telecommunications Management Network (TMN)

General provisions

The telecommunications management network (TMN - Telecommunications Management Network) ¹ is defined by the system of standards for this network [51,62, 70]. The term "network management" in the early 1980s meant maintaining proper operation and maintenance of telecommunications networks.

Maintaining proper operation is ensuring that the basic tasks assigned to the network are performed under normal conditions and in situations where the network characteristics change, for example, when the incoming user load (traffic) increases.

Maintenance involves the work of restoring the performance or characteristics of the network when the elements of the network itself fail (equipment or program failures).

At the same time, a set of measures is applied, including on-line diagnostics to identify the site of damage and work on troubleshooting.

However, the significant development of these functions in recent years has led to the expansion of the use of the term "network management".

Historically, the creation of the concept of a telecommunications telecommunications management network (TMN) is due to the fact that the development and expansion of networks has drastically increased the cost of their maintenance. The only way to reduce such costs is to centralize maintenance. However, this proved to be a difficult task. All the benefits of centralization were reduced to "zero" for the following reasons.

1. Heterogeneity of telecommunication networks. All sections and lectures of this course show how diverse the means used for receiving, transmitting, switching, and processing information are. For example, switching stations represent a system that is completely different from the system intended for transmitting signals and built in accordance with the recommendations of SDH. Very different among themselves are different alarm systems, principles of construction and implementation of stations. For example, fixed network switching stations differ in the properties listed above from mobile communication stations.

   Therefore, the network management system must be adaptable to various technical means and technologies for receiving, transmitting and switching.
2. A variety of used equipment and services. Many equipment supply companies and other companies providing various communication services are currently working on communication networks. They differ in the equipment supplied by the company and the types of services provided. For example, Siemens equipment differs from Alcatel equipment. (Often the network on which the equipment of multiple suppliers is used is called multivendor, in accordance with the American term multi-vendor).

   The long-distance and mobile services provided by the companies, data transmission services, broadband television, etc., differ from each other. The only way to reduce the costs of the operator and the supplier for the adaptation of equipment is standards, typical interfaces and recommendations for operation.

   Therefore, the network management system must be adapted to work in a network containing heterogeneous equipment and providing different services.
3. The importance of the consequences of a communication network failure. The means of transmitting and processing information have always been the "nerve arteries" of the state, corporations, defense and everyday life. Therefore, a break of communication for a few minutes, and even more so hours, leads to significant negative consequences for the listed groups of modern society.

   Therefore, it is very important to ensure network reliability, fault tolerance, flexible and efficient network resource management.
4. Internationalization of communication networks. Currently, the flow of information is increasingly becoming international.

   Therefore, the maintenance system should be standard internationally.

The main provisions of the TMN system were developed by many organizations, but the main rules and basic provisions used in networks are recommendations of the following organizations: International Organization of Standards (ISO - International Standards Organization, ISO), Telecommunication Standardization Sector of the International Telecommunication Union (ITU - International Telecommunications Union - Telecommunication) Standardization), American National Standards Institute (ANSI - American National Standards Institute), ETSI (European Telecommunication Standards Institute - European Telecommunication Standards Institute).

Basic principles of TMN

The TMN concept encompasses network elements (NEs) —computers, databases, terminals, communications networks, and maintenance systems (OSS). It links them into a structure, architecture, the organization of which provides the interconnection of various types of network elements and systems supporting the functioning of the network. TMN also describes the standardized interfaces and protocols used to exchange information between them, as well as the functionality necessary to manage the network.

The control objects in the TMN model are:

Network Element - NE (Network Element) and System Support ² - OSS (Operations Support Systems).

A network element is a hardware unit of network equipment that is managed in a TMN. It can be both simple, and very complex, and "intelligently advanced" network elements, such as, for example, program-controlled stations, with their own system of support for operation and maintenance. They provide continuous monitoring of their work, initiate hardware and software automatic processing of the alarm signal and contain redundant equipment, for example, in the form of duplication of important functional parts. When a fault occurs, diagnostics are automatically turned on, which can determine the nature of the error, block the defective module and the associated equipment.

As opposed to the network element "station", we can cite another NE - the "regenerator", which is the smallest unit in a digital signaling network. The number of regenerators on the network is huge, but they do not contain a large number of elements and service subsystems. These simple modules can cause a serious failure in case of an error.

These two examples of network elements represent the two poles - the most controlled objects (telephone exchange) and the least managed (regenerator). The range between them includes many other types of network elements.

The second type of TMN management objects is OSS (Functional Support Systems).

This term defines procedures (not only automated, but also, possibly, performed manually), which are aimed at maintaining the functioning of the network. These can be systems:

• exchange with existing NE management equipment;
• establishing an order for handling alarm messages;
• initiating procedures in the NE;
• dispatching and processing queues;
• introducing financial calculations and other procedures.

The network elements (NEs) and the support systems for functioning are interconnected via a Q-interface, which is defined in two parts:

• information model and
• communication protocols.

Information model

The information model describes:

• functions that are controlled and monitored in the network element.
• rules for creating managed objects, which are determined using the operation algorithm and files for registering events.

From the point of view of the TMN, all physical and logical resources — such as terminal and network terminals, routes, event logs, signal reports, and subscriber data — are regarded as management objects (MO).

Managed objects (resources) of such a network are NE network elements and OSS procedures that are performed both on the network element itself and on its properties (adjustment of characteristics).

The managed object represents a real physical object or logical resource.

The information model also defines the relationship between managed objects. These relationships are represented in the form of a tree called the Information Information Tree (MIT).

In fig. 7.1a shows the relationship between the network element (Public Switched Telephone Network) and support systems.

Operators using workstations can manage the procedures laid down in the OSS, which, in turn, manage the NE network elements. In fig. 7.1b gives an example of an information tree for the PSTN network, which shows the hierarchy in the network. Objects of the first level - station, node and logical resource "route"; objects of the second level - the lines that make up the route.

Programs included in OSS have one control program (program manager). It interacts with the network element program, which provides the interface between the network element and the operation support procedures (OSS) of workstations (see Figure 7.1) —a friendly interface with the operator. This program is called an agent (intermediary program).

The manager is a part of the control programs of the distributed process, which sends commands to perform management operations and receives notifications.

Fig. 7.1. The connection between the network element and the support systems of operation: a) functional diagram; b) information tree (Public Telephone Network)

An agent is a part of a distributed process program that directly controls the relevant objects. She is "responsible" for the execution of commands sent to him by the manager, and for informing the manager about the behavior of the subordinate objects using notifications.

These programs contain the necessary TMN databases. During the exchange, they use messages of the type "event", which starts the process on one of the parties, and the response responses of the "operation". The transmission of such signals (but not processing) does not depend on their content, which is typical of the so-called object-oriented processes.

The provisions and definitions of the TMN network objects discussed above constitute the essence of the object-oriented approach to the work of TMN. Recall the main features of this approach.

1. Information exchange is described in terms of managed objects (NE — network elements), considered as some of the resources that are managed or that serve to support certain management functions.
2. The managed object is an abstraction of such a resource, which displays its properties from the point of view of management. The managed entity may represent a relationship between resources or a combination of resources (for example, a network).
3. Each managed object belongs to some class of objects, which may be a subclass of another class.
4. The subclass inherits all the properties of the class from which it is separated, and clarifies the definition of a class by adding new properties to those that underlie the selection of the higher class.
5. Different classes can be represented as a tree showing the hierarchy of inherited properties. For example, the class of equipment of transmission systems is divided into subclasses of analog and digital systems; digital networks can be divided into plesiochronous and synchronous, etc.
6. Managed object is characterized by:
   • attributes;
   • control operations that can be applied to it;
   • notifications that they generate;
   • Behavior as a response to control commands or other influences.

The structure of the system to be managed is distributed, so network management is a distributed process. This entails the need to organize the exchange of information between management procedures for the purpose of monitoring and controlling various physical and logical network resources (switching and transmission resources).

As a protocol for transmitting control messages, the usual data transmission system protocols are used, whose operation does not rely on specific data attributes: the Common Control Information Protocol (CMIP) and the Access File and Management File Transfer Protocol (FTAP). ).