Architectural and Framework Standards: The TMN/FCAPS Model (ITU-T)
The ITU-T introduced the term Telecommunications Management Network (TMN) to describe a separate network that has interfaces to the telecommunication network (or production network). TMN defines interconnection points between the two networks and specifies management functionalities. The best description of how to operate a TMN is defined by the ITU-T recommendations M.3010, M.3400, and X.700.
The purpose of a framework is to describe the big picture, illustrate different functional areas, and identify how they interoperate. The focus of ITU-T M.3400 and X.700 is the specification and classification of management functionalities only. For example, it does not define whether syslog or trap messages are mandatory for event notifications. Neither does it define specific formats for storing accounting records. These details are defined in the lower-level specifications standards. In addition to the framework of M.3400, another recommendation (M.3010) defines the principles for a TMN. It includes details of a Data Communications Network (DCN) as a transport vehicle between the management applications and network elements. A DCN is also known as out-of-band-management, which separates user traffic from management traffic. Figure 3-1 illustrates the relationship between the telecommunications network, also called the service infrastructure, and the TMN.
Figure 3-1. TMN and Telecommunications Networks
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Another relevant aspect of M.3010 is the concept of layers. Network management tasks are grouped into functional areas such as FCAPS. In addition, a logical layered architecture (LLA) consists of five management layers:
Network Element Layer (NEL) defines interfaces for the network elements, instantiating functions for device instrumentation, ideally covering all FCAPS areas.
Element Management Layer (EML) provides management functions for network elements on an individual or group basis. It also supports an abstraction of the functions provided by the network element layer. Examples include determining equipment errors, measuring device temperatures, collecting statistical data for accounting purposes, and logging event notifications and performance statistics.
Network Management Layer (NML) offers a holistic view of the network, between multiple pieces of equipment and independent of device types and vendors. It manages a network as supported by the element management layer. Examples include end-to-end network utilization reports, root cause analysis, and traffic engineering.
Service Management Layer (SML) is concerned with, and responsible for, the contractual aspects of services that are being provided to customers. The main functions of this layer are service creation, order handling, service implementation, service monitoring, complaint handling, and invoicing. Examples include QoS management (delay, loss, jitter), accounting per service (VPN), and SLA monitoring and notification.
Business Management Layer (BML) is responsible for the total enterprise. Business management can be considered a goal-setting approach: "What are the objectives, and how can the network (and network management specifically) help achieve them?"
Figure 3-2 shows the relationship between the different layers as well as the relationship with the FCAPS model. Each management layer is responsible for providing the appropriate FCAPS functionality according to the layer definition. Each layer communicates with the layers above and below it.
Now that the different layers of the TMN model have been identified, the functionality of each FCAPS area is described next. The TMN architecture has a strong relationship to Open Systems Interconnection (OSI) standards and frameworks. ISO 7498-4 defines the framework, concepts, and terminology of the OSI Management standards: "Information Processing Systems - OSI - Basic Reference Model - Part 4: Management Framework."
The ITU-T M.3400 recommendation is one document within the M series. It specifies five management functional areas (FCAPS):
Fault management— Detect, isolate, notify, and correct faults encountered in the network.
Configuration management— Configure aspects of network devices, such as configuration file management, inventory management, and software management.
Accounting management— Collect usage information of network resources.
Performance management— Monitor and measure various aspects of performance so that overall performance can be maintained at a defined level.
Security management— Secure access to network devices, network resources, and services to authorized individuals.
The following section provides more details about each area. This chapter covers the FCAPS model extensively, because it sets the foundation for network management in general and provides a good understanding of accounting and performance management and their potential relationship to each other. Therefore, not only the accounting and performance parts of FCAPS are addressed, but the full model. Afterwards, other standards are discussed solely based on their specific relationship to accounting and performance management. Also, note that there is not an exact match between the brief FCAPS summary in Chapter 1 and the extended details for accounting and performance in this chapter. Chapter 1 provides the authors' definitions from a network element perspective, and this chapter covers FCAPS functionality from all layers of the TMN model.
Fault management is a set of functions that enable the detection, isolation, and correction of abnormal operation of the telecommunication network. The quality assurance measurements for fault management include component measurements for Reliability, Availability, and Survivability (RAS). Fault management consists of the following functions:
RAS quality assurance establishes the reliability criteria that guide the design policy for redundant equipment (a responsibility of configuration management) and the policies of the other function groups in this area.
Alarm surveillance describes the capability to monitor network element failures in near-real time.
Fault localization describes where the initial failure information is insufficient for fault localization. It has to be augmented with information obtained by additional failure localization routines at the application level.
Fault correction transfers data concerning the repair of a fault and the control of procedures that use redundant resources to replace equipment or facilities that have failed.
Testing can be carried out in two ways. In one case, a network element analyzes equipment functions, where processing is executed entirely within the network element. Another method is active testing of external device components, such as circuits, links, and neighbor devices.
Trouble administration transfers trouble reports originated by customers and trouble tickets originated by proactive failure-detection checks. It supports action to investigate and clear the problem and provides access to the status of services and the progress in clearing each problem.
Configuration management provides functions to identify, collect configuration data from, exercise control over, and provide configuration data to network elements. Configuration management supports the following functions:
Installing the physical equipment and logical configurations.
Service planning and negotiation, which addresses planning for the introduction of new services, changing deployed service features, and disconnecting existing services.
Provisioning, which consists of necessary procedures to bring equipment into service but does not include installation. As soon as the unit is ready for service, the supporting programs are initialized via the TMN. The state of the unit (in service, out of service, standby, or reserved) and selected parameters may also be controlled by provisioning functions.
Status and control where the TMN provides the capability to monitor and control certain aspects of the network element (NE) on demand. Examples include checking or changing an NE's service state (in service, out of service, or standby) or the state of one of its subparts and initiating diagnostic tests within the NE. Normally, a status check is provided in conjunction with each control function to verify that the resulting action has taken place. When associated with failure conditions, these functions are corrective in nature (such as service restoration).
Network planning and engineering deals with functions associated with determining the need for growth in capacity and the introduction of new technologies. Planning and engineering are examples of functions across multiple areas, because they relate to the performance section from a monitoring perspective and to the configuration section from an enforcement perspective.
Accounting management lets you measure the use of network services and determine costs to the service provider and charges to the customer for such use. It also supports the determination of charges for services. Accounting management includes the following functions:
Usage measurement— Consists of the following subfunctions:
- Planning and management of the usage measurement process
- Network and service usage aggregation, correlation, and validation
- Usage distribution
- Usage surveillance
- Usage testing and error correction
- Measurement rules identification
- Usage short-term and long-term storage
- Usage accumulation and validation
- Administration of usage data collection
- Usage generation
Tariffing and pricing— A tariff is used to determine the amount of payment for services usage.
Collections and finance— Functionality for administering customer accounts, informing customers of balances and payment dates, and receiving payments.
Enterprise control— This group supports the enterprise's financial responsibilities, such as budgeting, auditing, and profitability analysis.
Performance management provides functions to evaluate and report on the behavior of telecommunication equipment and the effectiveness of the network or network element. Its role is to gather and analyze statistical data for the purpose of monitoring and correcting the behavior and effectiveness of the network, network elements, or other equipment, and to aid in planning, provisioning, maintenance, and quality measurement. Performance management includes the following functions:
Performance quality assurance— Includes quality measurements, such as performance goals and assessment functions.
Performance monitoring— This component involves the continuous collection of data concerning the performance of the network element. Acute fault conditions are detected by alarm surveillance methods. Very low rate or intermittent error conditions in multiple equipment units may interact, resulting in poor service quality, and may not be detected by alarm surveillance. Performance monitoring is designed to measure the overall quality, using monitored parameters to detect such degradation. It may also be designed to detect characteristic patterns of impairment before the quality has dropped below an acceptable level. Performance monitoring includes the following functions:
- Performance monitoring policy
- Network performance monitoring event correlation and filtering
- Data aggregation and trending
- Circuit-specific data collection
- Traffic status
- Threshold crossing alert processing
- Trend analysis
- Performance monitoring data accumulation
- Detection, counting, storage, and reporting
Performance management control— This group includes the setting of thresholds and data analysis algorithms and the collection of performance data. It has no direct effect on the managed network. For network traffic management and engineering, this includes functions that affect the routing and processing of traffic.
Performance analysis— The collected performance records may require additional processing and analysis to evaluate the entity's performance level. Therefore, performance analysis includes the following functions:
- Recommendations for performance improvement
- Exception threshold policy
- Traffic forecasting (trending)
- Performance summaries (per network and service, and traffic-specific)
- Exception analysis (per network and service, and traffic-specific)
- Capacity analysis (per network and service, and traffic-specific)
- Performance characterization
Security is required for all functional areas. Security management consists of two main functions:
Security services for communications provide authentication, access control, data confidentiality, data integrity, and nonrepudiation. These may be exercised in the course of any communications between systems and between users or customers and systems. In addition, a set of pervasive security mechanisms are defined that are applicable to any communication, such as event detection, security audit-trail management, and security recovery.
Security event detection and reporting reports activities that may be construed as a security violation (unauthorized user, physical tampering with equipment) on higher layers of security applications.
Security management includes the following functions:
Containment and recovery
The TMN Framework
The framework shown in Figure 3-3 brings it all together. The different logical layers sit on top of each other; each layer is responsible for implementing the FCAPS functionality and passes the collected information to the next layer. From a customer's applicability perspective, after identifying and prioritizing the requirements, you can map various network management products to this matrix and identify what is required to meet your needs.
Figure 3-3. TMN Management Layers and FCAPS
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From the perspective of this book, relevant layers of the TMN architecture are the Network Element Layer (NEL); the Element Management Layer (EML), related to similar device types; the Network Management Layer (NML), related to mediation; and the Service Management Layer (SML), related to service monitoring and accounting. The Business Management Layer (BML) is outside the scope of this book. If you're interested, you're encouraged to study the ITU-T M series for more details.
Note that the FCAPS model describes the conceptual model of functional areas; it does not define accounting and performance standards for data collection. Therefore, a second level of standards is required for data collection. At the network element layer, it can be SNMP or IPFIX. IPDR is appropriate at the Element Management Layer.