The Telecommunications Management Network (TMN) currently ... encompasses traffic engineering and network management aspects as they are developed in.
Traffic Engineering and Network Traffic Management in the TMN environment Michel Dao and Prosper Chemouil France Télécom - CNET PAA/ATR 38-40, rue du général Leclerc 92131 Issy-les-Moulineaux, France Tel: +33 1 4529 4610 +33 1 4529 4309 Fax: +33 1 4529 6069 Email: {michel.dao, prosper.chemouil}@issy.cnet.fr Abstract: As the Telecommunications Network Management (TMN) standardization is progressing within the ITU-T and other international bodies, traffic engineering and network traffic management should become more and more impacted by the results of such an evolution. The objective of this article is on the one hand, to give an overview of the current TMN standardization achievement, focusing on the traffic area, and on the other hand, to point out issues and perspectives that are likely to affect the teletraffic domain in the future.
1. Introduction The Telecommunications Management Network (TMN) currently recommended by the ITU-T is aimed at developing generic models which allow to represent different management and operations levels and tasks in a multi-vendor environment [1]. The TMN framework therefore encompasses traffic engineering and network management aspects as they are developed in teletraffic. This paper addresses the question of the TMN view of traffic engineering and network traffic management as they are currently elaborated. It should be noted that these domains are not clearly identified by the TMN experts which consider the traffic management activities within the more general aspect of network management. Therefore work on traffic domains is generally diluted in the many questions carrying work on TMN recommendations or limited to very restrictive functions of traffic activities. Our paper is organized as follows: first we present an overview of the TMN, including the standardization background. Then we focus our analysis of the TMN
achievement regarding teletraffic aspects. We finally conclude our contribution by mentioning some perspectives regarding TMN modelling and new teletraffic domains which are expected to be studied in the framework of the TMN.
2. Overview of the TMN One of the objectives for the development of the Telecommunications Management Network (TMN) is to offer a common architecture for the management of heterogeneous networks, services and equipment. It should therefore allow for inter working among the multiple management and operations systems supporting the multi-vendor network; it should also ease management interworking among separately managed networks, so that inter-networked and cross-domain services can be managed on an end-to-end basis. Though this is not yet achieved, TMN should eventually make feasible the provision of services that span multiple networks, which is nowadays a difficult, and often unreliable business. 2.1. Background The concept of the TMN has been developed within International Telecommunications UnionTelecommunications (ITU-T, formerly CCITT) in order to define a standard architecture for the management of telecommunications services. The TMN project was started by ITU-T by the fall of 1985. These activities have so far involved a significant number of different study groups (SGs) within ITU-T, among which: SG 2: routing, traffic engineering and network management. SG 4: TMN architecture definition; generic network model, … SG 11: Q3-interface protocols; switching and signalling system management; ISDN management; intelligent network management; UPT management. SG 15: transmission system management; transmission system modelling; SDH and PDH management, ATM management. SG 4 is the major provider of TMN specifications, and has the responsibility for all of the TMN architectural specifications. It has provided us with the TMN principles, methodology, generic information model and general listing of services and functions for the TMN. Below are listed the recommendations of general nature issued or under discussion [2-8]: M3000: Overview of TMN recommendations - Tutorial Introduction to TMN. M.3010: Principles of a TMN - General structure for TMNs. M.3020: TMN Interface Specification Methodology - Documents the procedure for specifying TMN. M.3100: Generic Network Information Model for TMN - Set of Managed Objects representing resources that are applicable to all types of telecommunications networks.
M.3180: Catalogue of TMN Management Information - Catalogues all the TMN managed objects that are documented in the ITU-T recommendations. M.3200: TMN Management Services: Overview - Gives a description of some conceptual management capabilities that a TMN could be expected to support. M.3400: TMN Management Functions - Identifies the functions that need to be supported at TMN interfaces. For the time being, the coordination among the different Study Groups of the ITU-T working on the TMN is the responsibility of a group called Joint Rapporteurs Meeting (Joint Coordination Group) - JRM (JCG). For the next study period starting in 1997, the proposal has been made by the TSAG (Telecommunications Standardization Advisory Group) to create a unique Study Group that would be responsible for all TMN activities and to delete the JCG. In addition to the work carried out within ITU-T, the European Telecommunications Standardization Institute (ETSI), has initiated numerous working groups within the Network Aspects (NA) sub-technical committee dealing with network architecture, operation and maintenance principle and performance (NA4). Their work resulted in a series of technical requirements which complemented the recommendations issued by ITU-T or have been used as contributions to ITU-T work. 2.2. The TMN Architecture The basic TMN concept provides an architecture for achieving interconnection between various types of operations systems and/or telecommunications equipment for the exchange of management information. There are three distinct architectures defined within the general TMN architecture: Functional architecture describes the appropriate distribution of functionality within the TMN. Function blocks and reference points between function blocks defined here lead to the requirements for the TMN recommended interface specifications. Physical architecture describes realizable interfaces and examples of physical components that make up the TMN. Information architecture rationalizes the application of OSI systems management principles to the TMN by providing an object-oriented view of management and managed resources. We will not discuss here the physical architecture of the TMN, both because it is out of the scope of our article and because it is the less mature part of the TMN. The TMN Functional Architecture The activities of network management have been organized into different functional areas by standardization bodies:
Fault Management - alarm surveillance, fault localization, testing; Configuration Management - provisioning, status, installation, initialization, inventory, backup and restoration; Accounting Management - collect accounting (billing) data, process and modify account records; Performance Management - data collection and filtering, traffic and network management, QoS observation and optimization; Security Management - provide secure access to network elements functions/capabilities, provide secure access to TMN components. These Management Application Functions (MAF) actually implement TMN management services. The management services found within the TMN are presented in M.3200 and their supporting functions are listed in M.3400 (see 2.1). They may also be classified according to different management layers: Network Element layer (NEL), Network Element Management layer (NEML), Network Management layer (NML), Service Management layer (SML) and Business Management layer (BML), defining a layered architecture as shown in Table 1. Functional Areas Layer
Fault
Configuration
Accounting
Performance
Security
Business Management Service Management Network Management Element Management
Q.823 M.3211 M.4100
Q.822
Table 1 - TMN Layered Architecture This table cannot yet be completely filled, and will be completed as TMN standardization progresses. Other classifications exist such as that based on the lifecycle of the network management (realtime supervision, daily operations and maintenance, long-term planning) or based on the network management actors (telecommunications service providers, customers, etc.). Traffic management and engineering fall into the Performance Management functional area and may use data collected by Accounting Management activities. The position of network planning among network management activities, as determined within the TMN environment, is not clearly
defined: strictly speaking (according to ITU-T recommendations), network planning is not part of the TMN; but one can argue that, as short-term and mid-term configurations result from some network planning activity, part of it may fall into Configuration Management activities. As traffic engineering clearly impacts on network planning, in the latter case traffic management should be concerned with Configuration Management. Function Blocks The TMN functional architecture comprises six components called function blocks: Operations System Function (OSF): The operations system function block hosts the various telecommunication management functions; this is where the core of the TMN is located; Mediation Function (MF): The mediation function block acts on the information being exchanged between network elements and operations systems. It realizes such operations as transforming object representations and providing upper layer protocol interworking functions; Data Communications Function (DCF): The data communications function block is responsible for the transportation of telecommunications management information between function blocks; Network Element Function (NEF): The network element function block represents the management function that are proper to and deported in network element, and can be access through standard interfaces; Work Station Function (WSF): The work station function block provides the means of communication between TMN function blocks and the user; Q Adapter Function (QAF): The Q adapter function block is responsible for the exchange of information between TMN function blocks and non-TMN equivalents of OSF and NEF function blocks to perform mediation functions. NEF, WSF and QAF are not entirely part of the TMN and constitute the interfaces of the TMN functional environment with external entities. Function blocks are in turn decomposed into functional components, the two most important being the MAF (see above) and the Management Information Base (MIB) in which are represented all the managed object within a managed system. Those managed object must be specializations of classes defined in the Generic Network Information Model (see TMN Management Information Model). Reference Points At the service boundaries of TMN function blocks are TMN reference points. A reference point is a conceptual point of information exchange between nonoverlapping function blocks.
Reference points identify the information that passes between function blocks and are categorized as following: q reference points exist between function blocks that contain a management application function: it connects OSF, MF, NEF and QAF function blocks with each other either directly or via the DCF; f reference points connect OSF and MF function blocks to the WSF function block; x reference points connect OSFs of different TMN or the OSF of a TMN and the equivalent functionality in a non-TMN environment; g reference points are not considered to be part of the TMN (though they are concerned with TMN information), and are situated outside the TMN between the WSF and the human endusers; m reference points are also located outside the TMN between the QAF and non-TMN managed entities such as network element either outside the TMN, or not that do not conform to TMN recommendations. TMN
x
f
OSF
q
MF
q QAF
q NEF
m
WSF
g
Figure 1 - TMN Functional Architecture Figure 1 summarizes the functional architecture of the TMN. TMN Management Information Model The information conveyed at the reference points of the TMN and used within the different function blocks (MIB) must conform to a common model: the TMN management information model. The object-oriented approach has been chosen jointly by ITU-T and ISO; using this approach, resources are represented as classes of managed objects. The rules of OSI Systems Management Information construction and representation are used to define object classes, capturing for each class the behavior, attributes, controls and notifications applicable to each class of managed resource. Classes of managed objects are specified using a notation defined in the international standard Guidelines for the Definition of Managed Objects (GDMO). Generic Network Information Model The objective of the Generic Network Information Model (GNIM) is to identify and standardize classes of managed objects that are common to every telecommunications network. It should allow to define management services independent of the technology and of the actual realization of the network. The GNIM only defines the basic classes very close to transmission means (it is in fact based on an SDH information model) such as: equipment, termination point, crossconnection, etc.
3. Traffic Engineering and Network Traffic Management ITU-T and ETSI have defined a number of TMN management services in which traffic activities are involved. The first services concern circuit-switched traffic but are increasingly interested in other traffic types such as IN traffic, B-ISDN traffic and UPT traffic. Most of the works deal with the object modelling of functions at the network element level but encompass also some network management levels since the OS/NE interface is analyzed. The difficulty in the outcome of the work that is being carried out by the standardization bodies results from the variety of actors which are involved in the development of recommendations: switching experts, OA&M experts, TMN experts and traffic engineers who have different backgrounds and concerns. Nevertheless, coordination of experts and reusability of concepts have led to TMN recommendations which mostly comply with the existing recommendations describing functional requirements.
3.1. Traffic Activities for Circuit-Switched Networks Routing Administration and Digit Analysis Modelling of routing administration and digit analysis of circuit-switched traffic has been the first work related to teletraffic completed in the TMN framework. It resulted in an ETSI standard which describes how the routing is performed within a switch [9]. The routing modelling has been developed using the general principles described in ITU-T recommendation E.170 [10] in such a way that the produced TMN standard encompasses classical routing methods but may be extended to more sophisticated routing methods such as load sharing and dynamic routing. Presently, ETSI is updating the traffic routing model in order to account for other routing mechanisms not yet considered such as the crankback capability. Network Traffic Management Traffic Management has been considered as one of the priority TMN management services to be developed. It deals with the real-time network operation and covers the traffic supervision and control activities defined as Network Management (NM) at the ITU-T SG2. The ITU-T recommendation and European standards have been the subject of numerous discussions between experts in switching, in network management and in OA&M and result from compromises between different views. The first stage of the work dealt only with alarm surveillance due to the experts involved in the modelling process, but was soon extended to network monitoring through the participation of traffic management experts to comply with the ITU-T Rec. E.411 [11]. The modelling of the monitoring functions has been based on ITU-T Rec. Q.822 which was primarily developed for the transmission network performance management [12]. This model describes performance data and status indicators which are collected. A second stage has been concerned with the modelling of network management controls as defined in Rec. E.412 in order to complete the real-time network management activity [13]. This part encompasses all the traffic controls which are familiar to teletraffic engineers such as routing controls (Skip, Temporary alternative routing, Dynamic routing), volume controls (Code blocking, Call gapping, Leaky bucket) and protective controls (Selective circuit reservation, Automatic congestion control). The modelling activity has been carried out in parallel by both the ITU-T SG11 and ETSI STC NA4, and resulted in two standards which are almost similar due to the strong coordination between the experts groups involved [14] and [15]. Quality of Service Quality of service (QoS) requires the collection of various indicators which are not fully network specific, but also depends on the subscriber behavior. Therefore QoS is presently being related to charging: it has been recently recognized that data collected for charging represent a privileged source of information for obtaining QoS parameters. In particular, there is a strong demand in getting call detailed records (CDRs) to evaluate the service quality in the telephone network: a CDRs list has been determined, at the ITU-T SG2, by the QoS experts in liaison with the NM
experts in order to define a preliminary set of data. This list has the advantage to include the call failure records (CFRs) which have been specified by NTM experts to improve the network management activity in the detection of the source of abnormal situations. Presently, ITU-T SG 11 is developing a TMN model for CDR in accordance with ETSI STC NA4. This model should be based on the X.742 recommendation, and is provisionally referenced as Draft Rec. Q.82CDR [16], [17]. Traffic Measurements Traffic measurements, like traffic management, has been considered since the beginning as a crucial issue to study in the TMN framework. Nevertheless, no work has been specifically carried out on this TMN management service. It is obvious however that this item has been considered through the specification of NTM, QoS and more general performance parameters and indicators. In such a perspective, the X.72x (Management information), X.73y (Management functions) series and Q.822 provide good references for defining a recommendation on Traffic Measurements modelling. It is expected that this should be developed in the next study period. 3.2. Traffic activities for other networks For networks other than the circuit-switched network, the TMN approach related to the teletraffic domain is not clearly separated from the general OA&M services. Moreover, the specific traffic considerations within performance management must be viewed as a very first step where a few parameters only are defined. Recently, work has been initiated on SS No7 networks for which an information model has been described, and on intelligent networks (IN) which have a architecture similar to TMN. However, to our knowledge, no standards regarding the traffic management or performance management using the TMN approach for these networks exist for now. As regards broadband networks, studies are progressing slowly; lately, a recommendation has been approved by the ITU-T which deals with the principles of applying TMN concepts to the management of B-ISDN [18]. For the same functional areas as for circuit-switched networks, it describes the application of the TMN approach to B-ISDN networks. In addition, ETSI has developed a provisional ETS which describes the management architecture of an ATM cross-connected network based on Rec. M.3010, as well as a management information model which includes some performance management aspects, mainly based on Rec. Q.822 for the reuse of the data collection mechanisms [19]. Presently, this standard allows one to measure ATM performance at the cell level: number of incoming and outgoing cells in a node, number of discarded cells due to unallocation of VP/VC (virtual path/virtual circuit).
4. Issues and Perspectives 4.1. New traffic Issues New management services derived from upcoming technologies are expected to be developed in the near future. Workplans in the international bodies comprise the performance management of UPT (Universal Personal Telecommunications) and FPLMTS (Future Public Land Mobile Telecommunications Systems). In addition, present modelling work on must be expanded for IN and B-ISDN networks along with the development of traffic engineering and network management methods. It is also questionable to expand the TMN approach in order to encompass other traffic engineering activities like network design or traffic measurements for circuitswitched networks. One can expect however that the work which has been carried out in the TMN will extend more on the network level rather than the network element level. 4.2. Towards a Layered Model One of the topics of the recent work within SG 4 Question 23/4 of the ITU-T has been the definition of the requirements for the management of a simple leased line service, and the information model needed for these requirements. This subject has emerged because after the definition of the GNIM (see Generic Network Information Model above), the objective was to produce a generic model for the interface between the network layer and the service layer, the GNIM being relevant to the interface between the element layer and the network layer. Given the lack of contributions to define such a model, it was decided to tackle the problem from the service side with a simple example that should be extended in the future. In fact, this reveals one of the key issues regarding TMN standardization: the network element level can be standardized because it defines the management interface that should offer commercial equipment. At the other end, service level information that will be exchanged between telecommunication administrations or operators, or that will be delivered to customers can also be standardized. Between these two ends, concurrence will impose a much less open work in standardization. This is an important issue because in order to manage network traffic at a service level, one need to have a clear model of the stream of information that comes, for instance, from traffic performance at a network element level all the way to the performance of the service. And this cannot be achieved without a layered model of the network that would include a modelling of the traffic routing. Such models exist for traffic engineering[20], and also for other network operation activities such as network forecasting or network servicing for dimensioning; if it is desirable to standardize such models, and this is still a debatable issue, one should consider both unifying those models and studying their representation using object-oriented concepts that are (besides their intrinsic qualities) those adopted by the TMN area.
The challenge is also to be able to standardize successive levels of the management of networks, in order to enable the interconnection and the common management of different networks, and the traceability of (among others) the traffic information throughout the different layers. From a practical point of view, if one considers that object-oriented concepts have any chance to become widely used for telecommunications software at large, one question should be answered: is it of any interest to design a network model that could be used for many activities in the areas of traffic engineering and network traffic management? The potential interest is that such a model would allow to develop more rapidly more interoperable traffic engineering and network management applications. The main problem that may be faced is the adequacy of object-oriented techniques for the implementation of such applications. Ongoing work at France Télécom CNET is aimed at answering such questions.
5. Conclusion In this paper we have described the present status of the TMN standards regarding traffic engineering and network traffic management. To this aim, we have presented the general characteristics of the TMN based on ITU-T or ETSI standards. Although the modelling effort has been important for some activities like network management of circuit-switched networks, it must be emphasized that, in general, the modelling of teletraffic functionalities is very sparse and diluted in the global activity covered by operations and maintenance. In particular, the network view is not yet satisfactory. However, work is still progressing to include new services and new technologies. TMN is aimed at providing a general frame for all network management activities, including performance and configuration management which encompass the teletraffic domain. Consequently, there is a tendency in the TMN community to take the responsibility of the development of all management activities and to standardize what is felt necessary by TMN. To this respect, it has to be reminded that, for all the network management activities, experts are also developing methods and new features, in particular in teletraffic. Therefore, it must be clear to anyone that it is the responsibility of teletraffic experts to develop the traffic engineering functionalities and, as customers, to specify their needs to TMN experts for modelling and implementation. The gathering of all TMN activities in a single Study Group within ITU-T may not make this task easier.
References [1] M. Sloman editor, "Network and Distributed System Management", Addison-Wesley, 1994 [2] ITU-T Recommendation M.3000: Overview of TMN Recommendations. Geneva, 10/94. [3] ITU-T Recommendation M.3010: Principles for a Telecommunications Management Network (TMN). Geneva, 10/92. [4] ITU-T Recommendation M.3020: TMN Interface Specification Methodology. Geneva, 07/95. [5] ITU-T Recommendation M.3100: Generic Network Information Model. Geneva, 07/95. [6] ITU-T Recommendation M.3180: Catalogue of TMN Management Information. Geneva, 10/92. [7] ITU-T Recommendation M.3200: TMN Management Services: Overview. Geneva, 10/92. [8] ITU-T Recommendation M.3400: TMN Management Functions. Geneva, 10/92. [9] ETSI IETS 300 292: Functional Specification of Call Routeing Information Management on the Operations System/Network Element (OS/NE) Interface. Sophia Antipolis, 01/95. [10] ITU-T Recommendation E.170: Traffic Routing. Geneva, 10/92. [11] ITU-T Recommendation E.411: International Network Management Operational Guidance. Geneva, 05/96. [12] ITU-T Recommendation Q.822: Performance Management. Geneva, 04/94. [13] ITU-T Recommendation E.412: Network Management Controls. Geneva, 05/96. [14] ITU-T Draft Recommendation Q.823: Stage 2 and Stage 3 Functional Specifications for Traffic Management. Revised COM11-R 156, Geneva, 07/96. [15] ETSI IETS 300 637: Functional Specification of Traffic Management on the Network Element/Operations System (NE/OS) Interface. Sophia Antipolis, 05/96. [16] ITU-T Draft Recommendation Q.82CDR: Call detail recording. Geneva, 01/96. [17] ITU-T Recommendation X.742: OSI Systems Management: Usage Metering Functions for Accounting Purposes. Geneva, 04/95 [18] ITU-T Recommendation M.3610: Principles for Applying TMN Concepts to the Management of B-ISDN. Geneva, 10/95. [19] ETSI ETS 300 469: B-ISDN Management Architecture and Management Information Model for the ATM Crossconnect. Sophia Antipolis, 08/95. [20] M. Dao and M. Lebourges, "Integration of Object-Oriented Programming and Distributed Algorithms for Network Design", in Networks'94, 161-166, Hungary, Sept. 1994.
