Stefano Avallone

Research challenges in QoS routing

Quality of Service Routing is at present an active and remarkable research area, since most emerging network services require specialized Quality of Service (QoS) functionalities that cannot be provided by the current QoS-unaware routing protocols. The provisioning of QoS based network services is in general terms an extremely complex problem, and a significant part of this complexity lies in the routing layer. Indeed, the problem of QoS Routing with multiple additive constraints is known to be NP-hard. Thus, a successful and wide deployment of the most novel network services demands that we thoroughly understand the essence of QoS Routing dynamics, and also that the proposed solutions to this complex problem should be indeed feasible and affordable. This article surveys the most important open issues in terms of QoS Routing, and also briefly presents some of the most compelling proposals and ongoing research efforts done both inside and outside the E-Next Community to address some of those issues.

A channel and rate assignment algorithm and a layer-2.5 forwarding paradigm for multi-radio wireless mesh networks

The availability of cost-effective wireless network interface cards makes it practical to design network devices with multiple radios which can be exploited to simultaneously transmit/receive over different frequency channels. It has been shown that using multiple radios per node increases the throughput of multi-hop wireless mesh networks. However, multi-radios create several research challenges. A fundamental problem is the joint channel assignment and routing problem, i.e., how the channels can be assigned to radios and how a set of flow rates can be determined for every network link in order to achieve an anticipated objective. This joint problem is NP-complete. Thus, an approximate solution is developed by solving the channel assignment and the routing problems separately. The channel assignment problem turns out to be the problem to assign channels such that a given set of flow rates are schedulable and itself is shown to be also NP-complete. This paper shows that not only the channels but also the transmission rates of the links have to be properly selected to make a given set of flow rates schedulable. Thus, a greedy heuristic for the channel and rate assignment problem is developed. Algorithms to schedule the resulting set of flow rates have been proposed in the literature, which require synchronization among nodes and hence modified coordination functions. Unlike previous work, in this paper a forwarding paradigm is developed to achieve the resulting set of flow rates while using a standard MAC. A bi-dimensional Markov chain model of the proposed forwarding paradigm is presented to analyze its behavior. Thorough performance studies are conducted to: a) compare the proposed greedy heuristic to other channel assignment algorithms; b) analyze the behavior of the forwarding paradigm through numerical simulations based on the Markov chain model; c) simulate the operations of the forwarding paradigm and evaluate the achieved network throughput.

A channel assignment algorithm for multi-radio wireless mesh networks

Wireless mesh networks (WMNs) are receiving increasing attention as an effective means to deploy ISPs wireless last mile access, wireless enterprise backbone networks and several other applications. The focus of this paper is on multi-radio wireless mesh networks, given the considerable improvement in network throughput that multiple radios allow to achieve and the availability of cost-effective wireless devices. Interesting research problems are still unsolved in this field. Due to the scarcity of non-overlapped frequency channels and available radios per node, interference is still present, which limits the bandwidth available on network links and eventually cuts the achievable throughput down. As interference depends on how channels are bound to radio interfaces, a proper channel assignment scheme is needed to reduce the interference. In this paper we identify some key requirements of a channel assignment scheme and show the interdependence between the channel assignment and the routing problems. Accordingly, a centralized channel assignment and routing algorithm is developed for multi-radio wireless mesh networks aiming to maximize the network throughput. An integer linear programming (ILP) model is presented to evaluate the performance of our heuristic. Finally, a performance study is carried out to assess the effectiveness of our proposed algorithm.

Energy efficient online routing of flows with additive constraints

A number of studies report that ICT sectors are responsible for up to 10% of the worldwide power consumption and that a substantial share of such amount is due to the Internet infrastructure. To accommodate the traffic in the peak hours, Internet Service Providers (ISP) have overprovisioned their networks, with the result that most of the links and devices are under-utilized most of the time. Thus, under-utilized links and devices may be put in a sleep state in order to save power and that might be achieved by properly routing traffic flows. In this paper, we address the design of a joint admission control and routing scheme aiming at maximizing the number of admitted flow requests while minimizing the number of nodes and links that need to stay active. We assume an online routing paradigm, where flow requests are processed one-by-one, with no knowledge of future flow requests. Each flow request has requirements in terms of bandwidth and m additive measures (e.g., delay, jitter). We develop a new routing algorithm, E2-MCRA, which searches for a feasible path for a given flow request that requires the least number of nodes and links to be turned on. The basic concepts of E2-MCRA are look-ahead, the depth-first search approach and a path length definition as a function of the available bandwidth, the additive QoS constraints and the current status (on/off) of the nodes and links along the path. Finally, we present the results of the simulation studies we conducted to evaluate the performance of the proposed algorithm.

A Channel Assignment Algorithm for Multi-Radio Wireless Mesh Networks

The focus of this paper is on wireless mesh networks. In particular, we study the multi-radio case, given the considerable improvement in network throughput that multiple radios allow to achieve and the availability of cost-effective wireless devices. Interesting research problems are still unsolved in this field. Due to the scarcity of non-overlapped frequency channels and available radios per node, interference is still present, which cuts the achievable throughput down. As interference depends on how channels are bound to radio interfaces, a proper channel assignment scheme is needed to reduce the interference. In this paper we identify some key requirements of a channel assignment scheme. Accordingly, a centralized channel assignment algorithm is developed for multi-radio wireless mesh networks in order to maximize the throughput and address the interference problems. Finally, a performance study is presented to assess the effectiveness of our proposed algorithm.

An energy efficient channel assignment and routing algorithm for multi-radio wireless mesh networks

Endowing mesh routers with multiple radios is a recent solution to improve the performance of wireless mesh networks. The approaches proposed in the literature to solve the problem how to assign channels to radio have mainly focused so far on reducing interference or maximizing the throughput. To the best of our knowledge, none of such approaches attempted to save network resources for the purpose of reducing energy consumption and RF emissions. In this paper, a channel assignment and routing algorithm is presented aiming to turn off as many radio interfaces as possible while providing a required level of performance. Simulation studies show that the proposed algorithm enables to achieve nearly the same performance of traditional algorithms while considerably reducing the number of radio interfaces turned on.

A Traffic-Aware Channel and Rate Reassignment Algorithm for Wireless Mesh Networks

Channel assignment is among the most challenging issues for multiradio wireless mesh networks, given the variety of objectives that can be pursued and the computational complexity of the resulting problems. The channel assignment problem has been also shown to be interdependent with the routing problem, i.e., the problem to determine the amount of traffic flow to be routed on every link. Such a relationship raises the need to recompute the channel assignment every time the traffic pattern changes. However, channel assignment algorithms designed to assign channels from scratch will likely return a completely different configuration of radios, which would disrupt the network operation for the time required to switch to using the links established on the new channels. As shown by the experiments that we conducted, such a time may not be negligible, due to the resistance of routing protocols designed for wireless ad hoc and mesh networks to rapidly flagging a link as established/lost. Such a consideration, along with the observation that channel assignment algorithms may be suboptimal, led us to the design of a channel reassignment algorithm that takes the current channel assignment into account and attempts to cope with the new traffic pattern in the best manner possible while modifying the channel on a limited number of radios. In this paper, we illustrate such a channel reassignment algorithm and evaluate its performance by means of both simulations and experiments with real hardware.

MAM-UML: an UML profile for the modeling of mobile-agent applications

This paper introduces an approach for the modeling of mobile-agent applications. It aims to deal with the lack of appropriate concepts and notations, in the standard UML, to capture relevant abstractions for the modeling of mobile-agent features. The approach is materialized by an UML profile, which includes views to model organizational, life cycle, interaction and mobility aspects of mobile-agent applications contributing to the analysis, design and implementation phases of their development.

A Simulated Annealing Based Approach for Power Efficient Virtual Machines Consolidation

In the Cloud Computing paradigm there is an emerging Green Computing awareness, aimed at increasing the cost-efficiency of the underlying infrastructure. The pursued objective is to find the right compromise between the energy consumption and the perceived quality of service of the applications running in the cloud. Big data centers, along with the adoption of the virtualization technology, are increasingly experiencing the need to reduce consumption, because of both the environmental pollution and the economic concern. Among the novel techniques used to minimize the energy consumption wastefulness there is the Virtual Machines Consolidation, which leverages the VM live migration. The goal is to increase the overall cost-efficiency by reducing the number of active nodes. The main contributions of this paper are the proposal of a novel model for the consolidation problem and a Simulated Annealing based algorithm which solves it by evaluating the attractiveness of the possible VM migrations.

A Channel Assignment and Routing Algorithm for Energy Harvesting Multiradio Wireless Mesh Networks

Wireless mesh networks are being deployed all around the world both to provide ubiquitous connection to the Internet and to carry data generated by several services (video surveillance, smart grids, earthquake early warning systems, etc.). In those cases where fixed power connections are not available, mesh nodes operate by harvesting ambient energy (e.g., solar or wind power) and hence they can count on a limited and time-varying amount of power to accomplish their functions. Since we consider mesh nodes equipped with multiple radios, power savings and network performance can be maximized by properly routing flows, assigning channels to radios and identifying nodes/radios that can be turned off. Thus, the problem we address is a joint channel assignment and routing problem with additional constraints on the node power consumption, which is NP-complete. In this paper, we propose a heuristic, named minimum power channel assignment and routing algorithm (MP-CARA), which is guaranteed to return a local optimum for this problem. Based on a theoretical analysis that we present in the paper, which gives an upper bound on the outage probability as a function of the constraint on power consumption, we can guarantee that the probability that a node runs out of power with MP-CARA falls below a desired threshold. The performance of MP-CARA is assessed by means of an extensive simulation study aiming to compare the solutions returned by MP-CARA to those found by other heuristics proposed in the literature.