Proportional delay differentiation provision by bandwidth adaptation of class‐based queue scheduling

Supporting quality of service (QoS) over the Internet is a very important issue and many mechanisms have already been devised or are under way towards achieving this goal. One of the most important approaches is the so‐called Differentiated Services (DiffServ) architecture, which provides a scalable mechanism for QoS support in a TCP/IP network. The main concept underlying DiffServ is the aggregation of traffic flows at an ingress (or egress) point of a network and the marking of the IP packets of each traffic flow according to several classification criteria. Diffserv is classified under two taxonomies: the absolute and the relative. In absolute DiffServ architecture, an admission control scheme is utilized to provide QoS as absolute bounds of specific QoS parameters. The relative DiffServ model offers also QoS guarantees per class but in reference to the guarantees given to the other classes defined. In this paper, relative proportional delay differentiation is achieved based on class‐based queueing (CBQ) scheduler. Specifically, the service rates allocated to the classes of a CBQ scheduler are frequently adjusted in order to obtain relative delay spacing among them. The model presented can also be exploited in order to meet absolute delay constraints in conjunction with relative delay differentiation provision. Simulation experiments verify that our model can attain relative as well as absolute delay differentiation provided that the preconditions posed are satisfied. Copyright © 2004 John Wiley & Sons, Ltd.     

Analyzing the Mobile WiMAX System Resource Exploitation of the Downlink Direction

Worldwide interoperability for microwave access (WiMAX) constitutes a viable networking technology, providing wireless connectivity in an efficient manner. In this work, on the grounds of the defined frame structure, a novel performance analysis of the mobile WiMAX standard in terms of the downlink resource utilization is presented. The analysis is validated via simulation, the results of which are also provided along with numerical results, studying the effectiveness of the OFDMA-based downlink mapping. The results reveal the relationship among the frame dimensions, the mapped request size, and the number of unexploited OFDMA slots.     

Cost-Efficient Design of Future Broadband Fixed Wireless Access Systems

In future broadband fixed wireless access systems the overall design procedure is critical for their successful commercial deployment as well as their efficient operation and management. The problem addressed in this paper is twofold. Specifically, at a first phase the radio access network planning problem is addressed, which aims at finding the minimum-cost configuration of Access Point Transceivers (APTs) given thegeographical layout of the area to be covered. At the second phase, the interconnecting planning problem is addressed and aims at finding the minimum-cost configuration of the AccessPoint Controllers (APCs) and Inter-Working Units (IWUs) given the Access PointTransceivers layout. Both problems are formally defined, optimally formulated, and solved by computationally efficient heuristics. Finally, results are provided and subsequent conclusions are drawn.     

Exploring the intra-frame energy conservation capabilities of the horizontal simple packing algorithm in IEEE 802.16e networks: an analytical approach

The power saving capabilities of the mobile devices in broadband wireless networks constitute a challenging research topic that has attracted the attention of researchers recently, while it needs to be addressed at multiple layers. This work provides a novel analysis of the intra-frame energy conservation potentials of the IEEE 802.16e network. Specifically, the power saving capabilities of the worldwide interoperability for microwave access downlink sub-frame are thoroughly studied, employing the well-known simple packing algorithm as the mapping technique of the data requests. The accurate mathematical model, cross-validated via simulation, reveals the significant ability to conserve energy in this intra-frame fashion under different scenarios. To the best of our knowledge, this is the first work providing intra-frame power-saving potentials of IEEE 802.16 networks. Additionally, this is the first study following an analytic approach.     

An intelligent agent negotiation strategy in the electronic marketplace environment

E-commerce will strongly penetrate the market if coupled with appropriate technologies and mechanisms. Mobile agents may enhance the intelligence and improve the efficiency of systems in the e-marketplace. We propose a dynamic multi-lateral negotiation model and construct an efficient negotiation strategy based on a ranking mechanism that does not require a complicated rationale on behalf of the buyer agents. This strategy can be used to extend the functionality of autonomous intelligent agents, so that they quickly reach to an agreement aiming to maximise their owner’s utility. The framework proposed considers both contract and decision issues, is based on real market conditions, and has been empirically evaluated. Moreover, it is shown that in a linear framework like the one we employ, more elaborate ranking mechanisms do not necessarily improve efficiency.     

Trust management framework for intelligent agent negotiations in ubiquitous computing environments

In dynamic ubiquitous computing environments, system entities may be classified into two main categories that are, in principle, in conflict. These are the Service Resource Requestors (SRRs) wishing to use services and/or exploit resources offered by the other system entities and the Service Resource Providers (SRPs) that offer the services/resources requested. Seeking for the maximisation of their welfare, while achieving their own goals and aims, entities may misbehave (intentionally or unintentionally), thus, leading to a significant deterioration of system’s performance. In this study, a reputation mechanism is proposed which helps estimating SRPs trustworthiness and predicting their future behaviour, taking into account their past performance in consistently satisfying SRRs’ expectations. Thereafter, under the assumption that a number of SRPs may handle the SRRs requests, the SRRs may decide on the most appropriate SRP for the service/resource requested on the basis of a weighted combination of the evaluation of the quality of their offer (performance related factor) and of their reputation rating (reliability related factor). The proposed trust management framework is distributed, considers both first-hand information (acquired from the SRR’s direct past experiences with the SRPs) and second-hand information (disseminated from other SRRs’ past experiences with the SRPs), while it exhibits a robust behaviour against inaccurate reputation ratings. The designed mechanisms have been empirically evaluated simulating interactions among self-interested agents, exhibiting improved performance with respect to random SRP selection.