A "Policy-driven" approach of SLA Management

Transcription

1 A "-driven" approach of SLA Management Olivier Poupel, Arnaud Gonguet ALCATEL Route de Nozay, F Marcoussis Cedex, France. RÉSUMÉ Depuis plusieurs années, le monde des réseaux connaît deux évolutions majeures. L une, technique, due à la convergence des réseaux voix et données et au développement des applications communicantes qui requièrent une capacité, une disponibilité et une qualité croissante pour la transmission des informations. La deuxième évolution marque un changement dans l utilisation des réseaux : les flux des services circulant sur les réseaux ont chacun des contraintes différentes. Les opérateurs orientent donc leur gestion de réseaux vers la gestion des services. Parallèlement, apparaissent différentes approches «-driven» de gestion de réseaux. Le but de cet article est de montrer en quoi une approche «-driven» peut aussi servir à gérer des services. ABSTRACT. Since several years, the network area is going through two main evolutions. The first, technical, due to the convergence of the voice and data networks, and to the new communicating applications which require increasing capacity, availability and quality for the transmission of information. The second evolution is a new usage of networks: service flows transmitted over the networks each have different and specific constraints. Operators are now turning the network management to the management of services. At the same time, several -driven approaches of network management are looming on. This article aims at showing how a -driven approach can also be used to manage services. MOTS-CLÉS : Contrat de Niveau de Service (SLA), Gestion de SLA,, Gestion "driven", Modèle informationel de KEYWORDS: SLA, Service Level Agreement, SLA Management,, -based management, information model.

2 2 GRES, Décembre 2001, Marrakech. Introduction Since several years, the network area is going through two main evolutions. The first, technical, due to the convergence of the voice and data networks, puts operators in front of new network management problem. Moreover, the new communicating applications, more and more appreciated by end users, require increasing capacity, availability and quality for the transmission of information. The second evolution is a new usage of networks: service flows transmitted over the networks each have different and specific constraints that have to be taken into account in order to ensure the quality of the services. Operators are now turning the network management to the management of services. At the same time, several -driven approaches of network management are looming on. Since several years, standardization bodies have launched actions in this way. This article, structured on fifth parts, aims at showing how a driven approach can also be used to manage services. The first part introduces principles of network management by policies, through the works done in different standardization bodies. A service can be described thanks to an SLA (Service Level Agreement), which is a contract linking a client and a service provider, precisely defining rights and duties of each concerned parties. Several types of SLA exist depending on the type of the client (end user, operator, ) and services. The second part of this article details the way to formalize the definition of a service with an SLA. Managing a service is equivalent to managing the associated SLA. Operators, end users and equipments vendors have expressed requirements for service management. These are summarized in the third part. The fourth part shows how the network management -driven approach can be worthwhile applied to SLA management inside an IP network, answering the expressed requirements. The last part looks at the policy-driven approach with a critical point of view. What are the pros and cons of this new managing method? A new way to manage network... Managing a network means at least configuring and controlling the equipments in order to gain the maximum from the available resources. The different approaches developed to ensure the communication with the network elements are now showing restrictions. Telnet and CLI (Command Line Interface) are dependent of the underlying platform, have a complex syntax and nearly no semantic. The use of SNMP (Simple Network Management Protocol) to browse network elements MIBs

3 A "-driven" approach of SLA Management 3 (Management Information Base) and PIBs ( Information Base) is subject to frequent errors. Moreover, the proliferation of private MIBs and PIBs defeats interoperability. These restrictions have motivated standardization bodies like the DMTF (Distributed Management Task Force) and the IETF (Internet Engineering Task Force) to lay the foundations of the policy-based management of networks. The main idea of the -driven approach is to describe the principles of the network management with rules that are then specialized and disseminated towards the network elements. The works at the IETF started by the creation of the Framework working group whose first meeting occurred in Orlando in December The first policy information model document (PCIM: Core Information Model) has been definitely published in February 2001 [1]. This document is mainly inspired by the work done by the DMTF on the CIM (Common Information Model) [2] [3]. Today, the interest for this technique is growing. An extension to PCIM is about to be standardized [4], and several other information models are under study: the quality of service (QPIM: QoS Information Model) [5], security for IP networks (ICIM: IPSec Configuration Model) are the most achieved but works on MPLS (Multi-Protocol Label Switching) and layer three virtual private networks are on progress. The TMF (TeleManagement Forum) is also very interested by the policy-based management and has created a working group on this subject during the TeleManagement World event in Nice (France) in May This work is planned to be used in Catalyst Projects (multi-technologies, multi-vendors). Policies are in general written by operators and have a more or less abstract level. For example, a policy could be written like this: The traffic generated by the Research and Development department has priority on the traffic generated by people surfing the web during lunch hours. Policies are written using rules: If <Condition> then <Do Actions>. The details of the conditions and actions are described in the policy information models. They precise how to represent a rule, how to group elementary conditions to make a more complex condition, and the links between conditions and actions. The simplified architecture related to network policy-based management (Figure 1) is made of four elements [6]: The Manager, user interface for editing rules, manager of the Repository, and responsible for the notification of the presence or update of new rules to the Decision Points The Repository, database where rules to be applied on the network are stored

4 4 GRES, Décembre 2001, Marrakech. The Decision Point (PDP), in charge of retrieving rules in the Repository, of managing the Enforcement Points and ensuring the application of the rules by taking the necessary decisions The Enforcement Points (), in charge of applying the rules and decisions received from the PDP and notifying the results to the PDP. Manager LDAP, SQL, COPS, Repository LDAP, SQL, PDP COPS, Telnet/CLI, SNMP, Figure 1: Architecture of network policy-based management The protocols recommended by the IETF for policy-based network management are COPS (Common Open Service) for the communications between the PDP and s, and LDAP (Lightweight Directory Access Protocol) for the communication with the Repository. Other protocols, like SNMP or SQL (Structured Query Language) that are widely used within the Internet can also be used for the communications between the components described above. And a new way to describe services. The deregulation of the telecommunications world has given rise to lots of changes in the market. The appearance of SLAs is one of the most important. By

5 A "-driven" approach of SLA Management 5 allowing the simple and strict description of a service, the SLA allows new service providers to assert the conscientiousness of their proposals and to win market shares by attracting new clients encouraged to use new technologies and new services they correctly understand and overcome [7]. Operators and service providers experience the need to present a unified portfolio of services. An operator whose services are laying on a common base, an SLA for example, presents a coherent offer to customers that will be able to better express the services they need. Quality, methods for measurement, events reporting and notifications in case of violation of the agreements will be better understood by the two parties. The SLA can be defined as a contractual document between a customer and a service provider, setting the terms and conditions in which a transport service has to be subscribed and delivered. It contains administrative and technical information. The latter, data about the concerned part of the network and the flows to be treated, parameters describing the quality of service to be delivered, schedule for the activation of the service, means used to ensure that the service will correctly work, and security considerations, are part of the SLS (Service Level Specification) [8] [9]. The administrative terms, names of the parties involved in the transaction, designation of the service, pricing and penalties in case of one of the two parties infringes the clauses of the contract, are used to clarify the legal aspects of the agreement. The part of the network over which the service has to be delivered is specified with the ingress and egress points of the network: input/output cards of routers for example. The number and location of the input and output interfaces of the network define the model of communication of the transport service: pipe for point to point communications, hose for point-multipoint communications and funnel for multipoint-point communications. The customer provides relevant information to identify the flows that are concerned by the service. In the case of IP networks which enable differentiation of services, this can be achieved by a combination of source and destination addresses, port numbers of the application, DSCP field (Differentiated Services Code Point) and protocol used. Not only identifying the flow corresponding to a specific service, the SLA also specifies the profile the flow will have to respect to take advantage of the planned quality of service: transmission delay, jitter, packets loss and throughput. This profile, also called envelop, may be characterized by data like mean rate, peak rate, minimal size of packets, or a mixed of this data. Some flows are said to be conform and others non-conform. By changing the parameters describing the traffic envelop, more than two conformance levels can be defined. The SLA also specifies the treatment of the packets belonging to each level. Some packets, in general those from the lower conformity level, may be dropped. In a differentiated services enabled

6 6 GRES, Décembre 2001, Marrakech. IP network, some packets could be remarked with a new DSCP field, and some could be shaped by limiting the bandwidth or by being delayed. But it is still possible to treat these packets as the conform level ones with degraded performances. The schedule indicates when the service has to be available. This can be done by specifying starting and ending moments (dates and hours), or by more complex forms like each Monday from 8:00AM to 8:00PM, or the last day of the each months between 0:00AM and 2:00AM. An operator has to be able to guarantee the availability of the service it delivers. The mean time between failures (MTBF), the mean downtime per year (MDT) and the mean time to repair (MTTR) are classical data. The maximum number of failures per year and per access point, for example, can be added. More than the availability, the means the operator makes use of to guarantee the service can be specified in the SLA. The provider has to offer the choice of measurement methods, periods of measure, points of measure and reporting modes used to monitor the network. Several kinds of SLAs can be contracted at different technological levels of description of the network, or different interfaces. [10] details this diversity depending on the customers, the providers and the technological differences between the networks. Some expectations Until recently, IP networks used to share the resources between concurrent flows without taking care of the expected services. It is turning out that this best effort behavior is no more sufficient regarding the increase and diversification of traffic and services. IP network operators are evolving toward the management of networks according to the carried flows. In order to be able to provide services personalized according to the customers needs, information have to be exchanged between equipment and operating centers of the network [9]: SLAs are one of the main part of this new management architecture. Time to market. Users are looking for new services, cheaper and more quickly available. Operators are looking for innovative services, which performances can be ensured, and which are profitable enough to seek after investments [7]. The requirements expressed by users and operators have participated in the development of SLA management. Optimizing service deployment. Nowadays, implementing a new service on a network can take several months. Operators are looking for solutions to optimize the deployment of services. This can be done by using a database including the method of implementation of the services, the current and future trends of network load, the topology, and the SLA describing the service, in order to quickly generate the implementation of a new service (Figure 2). This automation of the implementation has two main consequences. First of all, the reduction of human activities during the

7 A "-driven" approach of SLA Management 7 configuration phase, lowering transcription errors possibilities. Then a better use of the physical resources of the network improves profitability thanks to the definition of priorities between customers. In case of problems coming up from the network or caused by a new service to provision, the service provider will prefer to favor the one whose penalties are the lowest. SLA Database of Services Trends of network usage SLA analysis Synchronisation with billing and accounting Assurance Analysis of the state of the network Provisioning of the network Tests Network Figure 2 : Deployment of new service Choice of an operator. The emergence of new operators and the specialization of some service providers do not simplify the end users choice upon a more and more significant and often vague offer. By improving both the transparency of the offer, the means operators use to implement the proposed services and their capabilities for monitoring and assuring them, SLA management is a way to ease the customers choice of a service provider. Moreover, it encourages concurrence. Service negotiation. The choice of an operator, also called negotiation phase, can be automated and occurs between two computers, at least for the definition of the service. The part dedicated to the pricing negotiation is still within the competence of the operator and the customer. But, it s possible to imagine that preliminary agreements between a service provider and an end user allow a simplified contract negotiation.

8 8 GRES, Décembre 2001, Marrakech. Detection of service degradation. A requirement, mainly expressed by the service providers, is to be able to detect when a service is deteriorating. To achieve that, they have to correlate data coming from the network, measurements and alarms, with the needs of the services to be delivered by the network. A graduated assessment of the impact of the data on services, more precise than a simple binary relation service available, service unavailable, is strongly requested. In some cases the network does not present any particular problems, but the quality of the service is deteriorating. It becomes necessary to manage SLAs, in parallel with the network, to be able to forecast the failures of the networks and to implement alternative solutions. The cost of such operations limits its use to high revenue services. End to end services. Nowadays most of the services are using the resources of several networks belonging to one or more operators and of different technologies. An appropriate management of SLAs and standard SLAs are then necessary to ensure that the quality required by an end user is applied over all the crossed networks. The authors refer the reader to [10] for more details on the management of end-to-end services. Finally, SLA management is a key differential for operators in their portfolio, and customers are more and more looking at the quality of this feature before choosing a service provider. Some solutions On one hand there are requirements on SLA management expressed by operators, service providers, end users and equipment vendors, and on the other hand the concept of policy-based network management. How does this concept could be extended to the management of services, hence SLAs, and answer the expectations expressed above? Policies are a mean to allocate resources according to business decisions. A service described by an SLA can itself be considered as a whole of resources reservation. The way to define policies with existing information models [1] [4] [5] allows to describe the service and networking management actions with a sufficient abstracted level. Moreover, works currently in progress in standardization bodies aim at defining new policy information models dedicated to the description of services, like IP virtual private networks for example. All the information models are more or less specialized for a given domain but are linked and expressed in similar ways. This feature allows the easy definition of specific rules by preserving interoperability. Here is the way to commonly express the way to manage areas which were previously separated and even incompatible. Here is also the mean for an operator to present a unified portfolio of services thanks to the different parts of the SLA which are each dedicated to specific areas: security,

9 A "-driven" approach of SLA Management 9 accounting, quality (Figure 3). This common definition meets the requirement of optimization and rapidity of service deployment. Each package showed in the Repository (Figure 3) considered as an area of rules, is a part of the SLA contracted between the customer and the service provider. These business rules are independent of the underlying network. It allows to adapt them as close as possible to the needs of the users. The first step is the translation of the business rules in order to conform to the transmission technology. The second step is the adaptation of the result to the specificity of the network elements: functionality, version, protocol supported are taken into account at this stage (Figure 3). Repository Accounting Authentic. Security Routing Quality LDAP / SNMP Negotiation High Level Status PDP Provisioning Decisions Element-independent Level Packets Flow Network element Packets Flow Network Figure 3 : Levels of abstraction of policies This high level specification can be extended to lower levels. At the beginning, the spirit of policy-based management was that a PDP had to be able to take all kind of decisions. Now, it seems that PDP are developed inside more restricted areas. Among a single network, several PDPs can co-exist: one for security, and an other for activating differentiated services principles for example. Of course, the operator has to implement the co-existence and co-operation of several PDPs within its own domain.

10 10 GRES, Décembre 2001, Marrakech. The negotiation of SLA between one or several administrative domains with the same technology can be handled by a single PDP, as PDPs have the knowledge of transport technology dependent rules. It is necessary to add an other PDP in charge of the authentication of the parties of the negotiation. In fact, the negotiation process can be described with rules and the usually used protocols known by PDPs, COPS for example, are suitable for such an activity. In case of a negotiation between domains of different technologies, or straight with the end user or the computer entity in charge of the negotiation, the Manager is more adapted to this operation because it is aware of each part of the SLA. Customers can make several negotiations in parallel to different service providers in an automatic way. Such a process permits to save time and money. With some pros and cons. -driven approach in service management is innovative. But, the question is to know if meeting the requirements expressed by the main actors of networks and services management is sufficient? -based management introduces new protocols. Interfaces and protocols stacks are not all developed and implemented in equipments. Moreover, there is no compatibility between legacy and new protocols. There are the same problems with the new functionalities of policy-based networking. For example, policy enabled routers not only forward the packets as configured in the routing table, they allow more sophisticated ways of structuring the flows: accept or reject packets depending on the moment for example. The process of translation of the rules from the most abstract level, business rules, to the provisioning of the s of the network is made of two main steps. The steps of translation are network technology dependent and network element dependent. This can be a source of errors, whatever the mean used to achieve the translation: automatic or human. Moreover, operators usually use several equipment vendors to build their networks. The last step of the translation is different for each vendor and can even be different within equipments of the same vendors. The sources of errors and wrong configurations increase accordingly. On the other hand, the description of behaviors with rules that can have a high level of abstraction allows non-specialists in networks and services management to understand the processes. A policy telling that top priority will be given to the traffic of customers which had subscribed the Video-conference service, is easier to understand than a rule like If <IP address = > then <DSCP field=25>. Moreover, thanks to the specificities of the different policy information models (quality of service, security, MPLS ), specific PDPs are developed. This allows the definition of complex and efficient functionalities, which will be able to meet all the needed requirements for the definition of services.

11 A "-driven" approach of SLA Management 11 Lastly, the independency of the policies regarding the transport technologies and the equipments of the network will permit to use a single management system whatever the underlying equipments are. All the translation activities will be transparent for the operator. Conclusion Service management is a growing area within the telecommunications world. In parallel, techniques based on policy are evolving in standardization bodies and among operators. The application of the -driven approach to the management of SLAs has a lot of advantages and offers operators a key differentiation in a portfolio of services. Customers can also use it to orientate their choices. As a young technology, policy-based management needs more studies and development to become a main actor in networks and services management. Even if policy-based management is a promising technology, some issues still have to be targeted: scalability, standardization of interfaces and capabilities of description available in the current and future policy information models. By leading research activities in SLA definition and SLA management, Alcatel actively contributes to the development of tomorrow tools which will allow to deliver next generation services requesting optimization and reliability of next generation networks. References [1] IETF-RFC 3060, Core Information Model -- Version 1 Specification, B. Moore, E. Ellesson, J. Strassner, A. Westerinen, February 2001 [2] DMTF, DMTF Technologies : CIM Standards << CIM Schema : Version 2.4, [3] DMTF, Common Information Model (CIM) Specification, version 2.2, June 1999, [4] IETF-draft, Core Information Model Extensions, draft-ietf-policy-pcim-ext- 04.txt, B. Moore, L. Rafalow, Y. Ramberg, Y. Snir, A. Westerinen, R. Chadha, M. Brunner, R. Cohen, J. Strassner, September 2001, work in progress, expire in March 2002 [5] IETF-draft, QoS Information Model, draft-ietf-policy-qos-info-model-03.txt, Y. Snir, Y. Ramberg, J. Strassner, R. Cohen, April 2001, work in progress, expire in November 2001

12 12 GRES, Décembre 2001, Marrakech. [6] IETF-RFC 2753, A Framework for -based Admission Control, R.Yavatkar, D. Pendarakis, R. Guerin, January 2000 [7] TeleManagement Forum, GB 917, SLA Management Handbook, June 2001 [8] IST TEQUILA, D1.1 : Functional Architecture Definition and Top Level Design, September 2000 [9] EURESCOM-P1008, Specification of Inter-domain Quality of Service Management Interfaces, May 2001 [10] GRES 01, Impact on Telecom research focus of business and industrial requirements for Service Level Agreement management, E. Marilly O. Martinot, S. Betgé-Brezetz, GRES 2001, Gestion de REseau et de Service, December st, 2001, Marrackech, Morocco