Active Adaptation in QoS Architecture Model

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1 Active Adaptation in QoS Architecture Model Drago agar and Snjeana Rimac -Drlje Faculty of Electrical Engineering University of Osijek Kneza Trpimira 2b, HR Osijek, CROATIA Abstract - A new complex applications and services, especially distributed multimedia and interactive applications, could during the communication demand different level of QoS. The network, also, could change its preferences that result in QoS variation, and also QoS degradation. Overall variations are not necessarily a result of the traffic load, but could also be the result of using different possibilities on user devices, on different networks, or on mobile. All QoS changes could be caused by user or by network. Therefore, the QoS architecture has to continuously supervise the actual quality of service and build in the correction mechanisms. The network QoS mechanisms can improve network ability to offer high quality of service while efficiently uses network resources. The end system has to compensate the QoS variations and insure acceptable quality of service. One of the important components that can improve quality of service is the application itself. In this paper we propose the architecture that performs active adaptation of local resources, and supports the user with the best possible service, while the network gives the certain level of QoS. Key-Words: - QoS, application, architecture, adaptation, variation, service, resources, network 1 Introduction One of the important questions for the development of global information and communication infrastructure is Quality of Service (QoS). Quality of service represents the set of those quantitative and qualitative characteristics of a distributed multimedia system necessary to achieve the required functionality of an application. The great increasing of network capacities probably would not resolve problems according to heavy traffic load because of simultaneous increasing the number of users and new applications that starving for resources. The increasing of capacity will only help that new services and applications become more interesting and their demands more complex. For all of that reasons quality of service will become more and more important. To allow efficiently management of the network resources it is necessary to enable traffic differentiation and also resource reservation for the traffic of higher priorities. The quality of service that will be offered in the next network generation must go beyond the "besteffort" service level. The user services are and will be very diverse not only from information and media point of view but also from quality of service demands. The actual Internet technology is not suitable for real-time applications and services because the Internet was primarily developed for data communication without hard time constraint and only offers best-effort service, without any quality guaranties. In base of all real-time applications are demands for some guaranteed services and that kind of services cannot be achieved without management of network resources and resource reservations. All of that extends the demands for network control mechanisms and increases complexity of communications infrastructure. In any case the user must be able to receive the service which quality is enough predictable so that application can be performed in way for the duration of time that user defines. Depending on required quality of service guarantees, the networks should support four types of QoS traffic: the high quality guarantees for quantitative signal applications, the middle quality guarantees for qualitative signal applications, the low quality guarantees for time unstable applications and best-effort service for all other applications. To achieve acceptable quality of service it is necessary to design architectures and protocols to allow the user applications and services to define its own QoS requirements, and to achieve SLA (Service Level Agreement) between application/service and the network. In this paper we present an application QoS management system, which could actively manage the system resources in sense to perform gracefully degradation of quality when the network or local system resources become critical. In this way the application could actively negotiate to achieve acceptable level of user satisfaction. By the appropriate human-machine

2 interface the user could express his wishes on QoS, depending on current needs or desired cost of service that is ready to pay. 2 Application QoS and Resource Management 2.1 Application QoS Demands The QoS from the user level could be represented by the set of objective (qualitative aspect of presentation) and subjective (quantitative aspect of presentation) parameters. While the subjective parameters we can change during the session, the objective parameters we have to maintain constant. The application process makes the demands on service quality and transforms them in a form of QoS parameters, and than transfers them to the other system components. The negotiation process between the system components should define if they together could satisfy the demanded quality of service. If the negotiation process ends successively by service agreement about requested values of service quality, the application can run. This simple model of service quality could become very complicated. For example, the QoS demands could be changed during the application session. Furthermore, the agreed parameters could become not maintainable because of network congestion that all together requires renegotiation. The primary source of QoS demands is a user and we need to allow the end user with appropriate interface to choose QoS parameters. The end system parameters could firmly impact on service quality from the user point of view. Depending on several criterion (using circumstances, user preferences, type of media, costs and resources availability, networks topology etc.) the applications must be able to get different level of presentational quality and quality of service. The levels of application performance depend and vary very widely on packet delivery time and on packet delay. Depending on different criteria (duration of session, reality of time, traffic directions and fidelity) we can divide the applications in several classes. The class of applications that needs a data from each packet in exactly limited period of time is called real-time applications. The classes of applications that will always wait for data are called elastic applications. The very important class of real-time applications is playback applications. Similarly, the applications exhibit wide range of sensitivity to loss of fidelity. We can recognise two somewhat artificially classes: intolerant applications, which require absolutely faithful playback, and tolerant applications, which can tolerate some loss of fidelity. We can assume that new complex applications and services, would during the communication require different level of service quality and would be executed with different (accessible) level quality of service. The important role of every end system is to compensate the variations in quality of service that the network gives and provide the user with accessible quality of service. One important component that could influence to improve quality of service is the application. In sense to validate the applications, that are executed on and systems, we can distinguish three types of applications: common, adaptive and proactive applications. The common applications dont perform any action to adapt itself to current resource availability. The rather inflexible behaviour of common applications makes them not well suited for distributed communication scenarios where quality of network service may change rapidly over time [2, 3, 4]. The multimedia and mobile communication, especially in the Internet network, more and more attention dedicate to adaptive QoS systems. Compared to common applications, the behaviour of adaptive applications is more intelligent. These applications are characterised by the ability to react to changes in the quantity resources. Adaptive applications support the user with the best service that is possible under the current circumstances. In this way the application can provide the user by the improved QoS support. An environmental change doesnt necessary lead to degradation of application QoS support. Even though when the degradation is unavoidable, as a result of limited resources, the level of QoS support is improved in comparison to common applications. The end user could only notice "gracefully" degradation of service quality, and the user satisfaction would be grater that adaptive compensation wasnt performed. The adaptive application can decide when to terminate itself in the case that observed parameters, that represent quality of service, fall below the specified predetermined threshold. From the former we can conclude that adaptation is not only passive one but also reactive process. Unlike the adaptive applications, the proactive applications actively influence on resource management. This is especially great advantage by the mobile devices, which use multitasking, and where many applications attempt to use limited resources, as e.g. bandwidth and processing time. If resources became critical, the proactive application first tries to adapt on new situation, as does adaptive application. If the adaptation is not sufficient to satisfy QoS demands specified by application user, the proactive application, in the second step, actively influence on resource scheduling, to achieve a better QoS support. That could allow the application to achieve application specific parameters for a long-term period, even than more applications try to compete for available resources.

3 To achieve certain level of service quality, the new architectures and protocols were designed. They can enable users applications and services to specify its QoS demands and the negotiation between the network and the application. The actual level of service quality is result of the current network facilities. The QoS architectures and their control systems offer a possibility to serve a user with guaranteed service end-to-end. They usually offer a number of control functions for different situations that could happen as for example: QoS specification, mapping, negotiation, renegotiation, supervision and adaptation [1]. 2.2 Network QoS Management In the base of real-time applications is request for some guaranteed services, and guaranteed services cannot be obtained without reservations. In any case the user must be able to receive a service which quality is enough predictable, so that application can be performed in acceptable way for the duration of time that user defines. Generally, stricter guarantees are more expensive because the shared resources became not available to other users. The consequence of above is that in communication networks exists invulnerable necessity for resources management, in order to give some guaranteed quality of service. An important consequence is that network elements must be able to maintain flow-specific state, what is fundamental change in Internet model. Depending on necessary quality of guarantees in network, QoS networks would support four types of QoS traffic: high quality guarantees for quantitative signal applications - these applications provide signalisation and can quantitative assign its resource requirements. Examples of these types of applications are IP telephony, video streams and other multimedia applications. middle quality guarantees for qualitative signal applications - recent adaptation of classical reservation model allowed an improved management of traffic resources for applications that can signal, but can not exactly quantify their resource requirements. Instead of quantitative parameters, a qualitative application simple identifies resource application and type of traffic flow and lets the network to give traffic handling priorities. low quality guarantees for unstable applications - the signalisation have sense only for applications that generate time stable sessions. For the applications as web browsing, the communication points can change so often that signalisation can not adapt. "best-effort" service for all other applications - it is obvious that many applications will continue to work very well without any guarantees offering standard service "best-effort". Data packets Signalisation Routing Classification Packet scheduler Flow specification Resource reservation Queue/Control Queue/Control Signalisation Admission control Backward processes Traffic control Data packets Figure 1. The network architecture QoS components In the last few years a much research was done in developing new network architectures and service models to fulfil the requirements of new applications. Although exist relatively fundamental differences between different proposed architectural models, the widely accepted agreement is that any new architecture, that supports multicasting and different quality of service, can be divided into five separated components (Figure 1.) [1]: Flow specification; the network and different data flows have to use a common language, so that data source can specify its traffic characteristics to the network, and to specify quality of service that will be attached to them. In some cases flow specification is the central component of the architecture, because it represents a service interface over which the application communicates with the network. Routing; the network must decide how to transport the packets from a source to destination or in multicast communication, to many destinations. Resource Reservation; to assign a quantitatively specific quality of service, it is usually necessary that network allocates some guaranteed resources, as bandwidth or the number of buffers. Admission Control; because the network resources are limited, all requests for resource reservation can not be accepted. In order to maintain the network load on satisfied level and to comply all requests for quality of service, the network architecture have to run an admission control algorithm. In this way the network load is maintained on acceptable level.

4 Packet scheduling; after every packet transmission the network element must decide which packet will go next. The packet-scheduling algorithm is present in all network architectures, and it determines which quality of service the network could provide. Before we can implement the QoS mechanisms its necessary to identify different traffic classes. The incoming traffic entering the network device is divided in different separated flows by the packet scheduler. Afterwards the traffic of each flow is directed in appropriate queue on the forwarding interface. The queues on every interface are served according to a particular algorithm. The queuing algorithm defines packet forwarding from the queue, and the resources that would be assigned to every queue and every flow [1]. A research on the IP networks with support for quality of service led to two distinct approaches: architecture of integrated services (Intserv) and architecture of differentiated services (Diffserv). The first provides guaranteed quality of service and second provides differentiated quality of service. The both concepts are developed under IETF (Internet Engineering Task Force). 3 QoS Adaptive Architecture The variations of QoS and also the QoS degradations are not necessary caused by overall traffic in the network but also can be a consequence of using on user devices with different possibilities, in different networks, or on mobile devices. The quality of service request will depend on several factors: application, service or problem that user tries to resolve, level of user devices and cost of service. 1 2 N INPUTS QoS NEGOTIATION OUTPUTS S DEMANDS LOCAL RESOURCES AVAILABLE NETWORK QoS QoS MANAGER PREDICTION MODEL ADAPTATION TASKS SPECIFIC QoS PARAMETERS LOCAL RESOURCES NETWORK QoS MANAGEMENT Figure 2. The proposed QoS adaptive architecture model The applications and services could during the communication: not respond to quality degradation, try to adapt to changes or actively participate to get better quality. Hence, we can assume that complex applications and services (for example multimedia, virtual reality, mobile applications etc.), would during the communication session request a variable level of quality of service or would be performed with variable (acceptable) quality of service. In the figure 2. we propose the adaptive architectural model for serving the applications with variable services demands. These type of applications can change the demands during the communication. Furthermore, the circumstances in which the application is performed (e.g. mobile network, roaming, multitasking, the user infrastructure etc.) could change during the session. However, we need a proactive model that can adapt to changes in application demands and in network changes. This adaptation is not passive one, it actively participate in managing of the local and global resources. The network architecture model is built on a set of well-defined building blocks (routing, reservation, scheduling, admission control, policy), and enables active influence of an

5 application process to negotiate acceptable level of QoS. The specific QoS parameters the network needs for further packet handling and resource management are mapped to specific network (IPv4, IPv6, RSVP), which is performed on specific physical layer (ATM, SONET, etc.). The QoS specification defines QoS parameters and estimates their syntax and semantics. The cost of service, which the user is ready to pay for defined level of QoS, is very important by considering the QoS specification. If the cost of service will not be included in specification, the user will always choose the highest level of QoS. The QoS mapping transforms the QoS parameters from one level to another. By the QoS negotiation we can achieve an agreement about the QoS parameters between the user and the system. The agreement between the network and the application that defines the QoS level is defined by SLA (Service Level Agreement). The second mechanism we have introduced to improve user satisfaction is application itself. The adaptive applications actively react to changes in resource quantity. They support the user with the best possible service within the given circumstances. Such behaviour has many advantages in mobile surrounding with variable network characteristics. The improved adaptive application represents proactive applications, which we use in this model. The proactive applications actively influence on resource management. This is especially important by mobile devices that use multitasking, where many applications attempt to use the limited resources (e.g. bandwidth, processing time). If a resources become critical, the proactive application first attempts to adapt to new situation, similarly as the adaptive application. If this adaptation is not satisfactory to meet the users application QoS requests, the proactive application, in the second step, influences on resource sharing to achieve a better QoS support. The influence to resource sharing can be realised in two ways: first, by influencing on resource sharing that affect to degradation of the quality of service, and second, in some cases the resource management would not be possible because of limited and engaged resources, in that cases we must investigate the other resources to achieve the desired QoS (more processing time, better compression algorithms etc.). All these situations are incorporated in our adaptation model by appropriate adaptation tasks. In the proposed architectural model some of the improvements are: it provides end-to-end QoS guarantee; it uses adaptive network QoS management to guarantee QoS requirements; it allows proactive attempt to application and local system resources. 4 Conclusion The network s and application s QoS variations could degrade the level of user satisfaction. Therefore the applications are desired to actively adapt themselves and to adjust their resources demands dynamically, in response to fluctuations in either and system or network resources. The user must be able to receive the service which quality is sufficiently predictable, and the application should be executed in accessible manner, for the duration of time that user determinates. The network must be able to manage its resources, to offer particular level of service quality. The main goal of QoS control is to maximise the user satisfaction by the best use of limited resources. By adopting highly sophisticated QoS mechanisms we can improve application/network ability to offer the high quality of service, while efficiently uses a raw system resources. However, these mechanisms have their price in terms of increased costs, and we have to estimate them in contrast the benefits they offer. In the proposed architecture it is achieved high degree of system availability by the maximal adaptation of the application and the network. The variations, that are comprised, could be caused by the limited system resources or by the variations in application demands. This adaptive architectural model insures the best level of service, through the network, while efficiently manages the available resources. References: [1] Aurrecoechea C., A. T. Campbell, L. Hauw, A survey of QoS architectures. Multimedia Systems (1998) 6: [2] M. Bechler, H. Ritter, J.H. Schiller, Quality of Service in Mobile and Wireless Networks: The Need for Proactive and Adaptive Applications. Proceedings of the 33 rd Hawaii Int. Conference on System Sciences , [3] Y. Matsui, et.al., An Extensible Object Model for QoS Specification in Adaptive QoS Systems. Proceedings of the Second IEEE International Symposium on Object-Oriented Real-Time Distributed Computing, [4] B. Li, W. Kalter, K. Nahrstedt, A Hierarchical Quality of Service Control Architecture for Configurable Multimedia Applications, Journal of High Speed Networks, Special Issue on Management of Multimedia Networking, IOS Press, 2001.