Abdelhakim Hafid

A QoS broker based architecture for efficient Web services selection

Quality of service (QoS) support in Web services plays a great role for the success of this emerging technology. In this paper, we present a QoS broker-based architecture for Web services. The main goal of the architecture is to support the client in selecting Web services based on his/her required QoS. To achieve this goal, we propose a two-phase verification technique that is performed by a third party broker. The first phase consists of syntactic and semantic verification of the service interface description including the QoS parameters description. The second phase consists of applying a measurement technique to compute the QoS metrics stated in the service interface and compares their values with the claimed one. This is used to verify the conformity of a Web service from the QoS point of view (QoS testing). A methodological approach to generate QoS test cases, as input to QoS verification is used. We have implemented a prototype that includes the verification and certification components of the broker. We performed experiments to evaluate the importance of verification and certification features in the selection process using real Web services.

Wireless Mesh Networks Design — A Survey

With the advances in wireless technologies and the explosive growth of the Internet, wireless networks, especially Wireless Mesh Networks (WMNs), are going through an important evolution. Designing efficient WMNs has become a major task for networks operators. Over the last few years, a plethora of studies has been carried out to improve the efficiency of wireless networks. However, only a few studies are related to WMNs design and are mainly concerned with protocol design and routing metrics optimization. In this paper, we survey different aspects of WMNs design and examine various methods that have been proposed either to improve the performance of an already deployed network or to improve its performance by a careful planning of its deployment.

Quality-of-service adaptation in distributed multimedia applications

Abstract. High-speed networks and powerful end-systems enable new types of applications, such as video-on-demand and teleconferencing. Such applications are very demanding on quality of service (QoS) because of the isochronous nature of the media they are using. To support these applications, QoS guarantees are required. However, even with service guarantees, violations may occur because of resources shortage, e.g., network congestion. In this paper we propose new adaptation approaches, which allow the system to recover automatically, if possible, from QoS violations (1) by identifying a new configuration of system components that might support the initially agreed QoS and by performing a user-transparent transition from the original configuration to the new one, (2) by redistributing the levels of QoS that should be supported, in the future, by the components, or (3) by redistributing the levels of QoS that should be supported immediately to meet end-to-end requirements based on the principle that (local) QoS violation at one component may be recovered immediately by the other components participating in the support of the requested service. The proposed approaches, together with suitable negotiation mechanisms, allow us (1) to reduce the probability of QoS violations which may be noticed by the user, and thus, to increase the user confidence in the service provider, and (2) to improve the utilization of the system resources, and thus to increase the system availability.

Some principles for quality of service management

Distributed multimedia applications require a variety of levels of quality of service (QoS) from communication networks and end-systems which realize the multimedia interface with the human users or provide remotely accessed multimedia information. The management of these services has to take into account the available resources and the users wishes concerning the desired quality and costs. Based on our experience with the construction of a News-on-Demand prototype, we present in this paper a few simple principles applying to QoS management for distributed multimedia applications. We discuss in particular ways in which an application can adapt to reduced network performance related to throughput, loss, delay or jitter, and we consider the situation where the configuration of the distributed application can be selected dynamically and be revised during the running of the application. We also comment on the handling of QoS in a layered system architecture and the use of performance models for QoS management.

High accuracy localization method using AoA in sensor networks

In sensor networks, several applications such as habitat monitoring and moving objects tracking, require the knowledge of nodes positions. Position estimation most often includes errors due to the measurements of distance and incoming angles between neighbors. Erroneous positions are propagated from a node to other nodes exacerbating the degree of errors in the estimation of the positions of these nodes. In this paper, we propose a new localization method, called HA-A2L (High Accuracy localization based on Angle to Landmark); it consists of (a) a new protocol that allows nodes to exchange information pertinent to the localization process; and (b) a localization algorithm that uses estimation of distances and incoming angles to locate nodes in sensors networks. Compared, via simulations, to previous methods, such as APS and A2L, HA-A2L considerably increases the number of located nodes with far better accuracy.

An approach for quality of service adaptation in service-oriented Grids

Some applications utilizing Grid computing infrastructure require the simultaneous allocation of resources, such as compute servers, networks, memory, disk storage and other specialized resources. Collaborative working and visualization is one example of such applications. In this context, quality of service (QoS) is related to Grid services, and not just to the network connecting these services. With the emerging interest in service‐oriented Grids, resources may be advertised and traded as services based on a service level agreement (SLA). Such a SLA must include both general and technical specifications, including pricing policy and properties of the resources required to execute the service, to ensure QoS requirements are satisfied. An approach for QoS adaptation is presented to enable the dynamic adjustment of behavior of an application based on changes in the pre‐defined SLA. The approach is particularly useful if workload or network traffic changes in unpredictable ways during an active session. Copyright

A quality of service negotiation approach with future reservations (NAFUR): a detailed study

Distributed multimedia (MM) applications such as video-on-demand and teleconferencing provide services with different quality of service (QoS) requirements. Hence, the user should be able to negotiate the desired QoS depending on his/her needs, the end-system characteristics and his/her financial capacity. In response to a service request with the desired QoS, most QoS negotiation approaches return an acceptance or a simple rejection of the request. More specifically, they provide the user only with the QoS that can be supported at the time the request is made and assume that the service is requested for indefinite duration. This paper describes work on a new QoS negotiation approach with future reservations (NAFUR) that decouples the starting time of the service from the time the service request is made and requires that the duration of the requested service must be specified. NAFUR allows to compute the QoS that can be supported for the time the service request is made, and at certain later times carefully chosen. As an example, if the requested QoS cannot be supported for the time the service request is made, the proposed approach allows to compute the earliest time, when the user can start the service with the desired QoS. NAFUR will help to increase (a) the flexibility of the system by providing the user with more choices, and (b) the system resource utilization, and the availability of the system, by encouraging the sharing of the resources, e.g. multicast for video-on-demand systems. Furthermore, it provides the flexibility to incorporate (a) a range of resource reservation schemes and scheduling policies, and (b) a range of new system component technologies.

Cooperative QoS management for multimedia applications

Quality of service (QoS) management is becoming more and more important, especially in networks where many applications are competing for a limited number of resources. As these applications become more complex (consider e.g. multiparty multimedia applications), the number of options for QoS management increases, leading to more complex decision processes. The authors propose an approach for cooperative QoS management, where application-oriented QoS agents are distributed throughout the network and the end systems, communicating with each other. This distributed management system tries to guarantee the QoS level negotiated with the users, at the same time optimizing resource usage. The advantages of distributing the management process are: (i) an easier and more precise localization of the cause of QoS problems, (ii) better knowledge of local situations, (iii) a lower complexity for a single QoS agent and (iv) an increase in possible actions. They describe management procedures for QoS negotiation, adaptation and renegotiation.

Establishing Strict Priorities in IEEE 802.11p WAVE Vehicular Networks

The WAVE (Wireless Access in Vehicular Environments) concept includes seven channels within the DSRC band. One of them, known as the Control Channel (CCH), is the one used to exchange all safety-related messages. Messages sent over the CCH have to be processed with different priorities depending on how critical they are for vehicle safety. However, the MAC protocol currently adopted for WAVE, namely EDCA, stops short of that requirement; it does not establish strict priorities, but only relative advantages for some types of messages over the others. Another problem is that, since messages are broadcasted on the CCH, there are no acknowledgments. This means that it is not possible to know whether a transmission was successful or not, which eliminates the possibility to use the binary exponential backoff technique to reduce congestion. In this paper, we propose a simple but effective solution to both of these problems. We use simulations to analyze the performance of the modified MAC protocol and compare it to that of the original EDCA. The results show that the proposed scheme outperforms EDCA. Our comparison focuses on the reduced probability of collision for high-priority frames (gain) and on the increased delays for lower-priority frames (price to pay).

Optimal Design of Broadband Wireless Mesh Networks

Design/planning of WMNs is the key phase before any deployment. Few proposals can be found in the open literature that deal with the design problem; moreover, they do not take into account all the parameters that have an impact on the outcome of the design and they assume the existence of a physical topology where the location and the characteristics of nodes (e.g., number of channels, number of radios) are fixed. In this paper, we define a generalized model for the WMNs design problem that takes into account all the parameters that have a significant impact on the network (interference, multi-channel, transmission power, etc.), the requirements of providers (expected amount of traffic/users), the constraints of the physical environment (potential locations of wireless routers, e.g., poles, and gateways, e.g., data centers), etc. The objective is to minimize the cost of the network and its operations while satisfying the requirements. The proposed model is shown to outperform considerably existing solutions.