Giovanni Di Stasi

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.

Combining multi-path forwarding and packet aggregation for improved network performance in wireless mesh networks

Combining Multi-Path Forwarding and Packet Aggregation for Improved Network Performance in Wireless Mesh Networks

An experimental study of the channel switching cost in multi-radio wireless mesh networks

A large body of research has recently addressed the channel assignment problem in multi-radio wireless mesh networks. In order to reduce interference, many proposals require radio interfaces to (more or less frequently) switch channels to exploit the availability of multiple orthogonal channels. However, such proposals have been almost exclusively evaluated by means of simulations and the impact of switching channels on the network performance has not been experimentally evaluated so far. In this article, we aim to fill such a gap and present the results of a thorough experimental campaign we conducted on the ORBIT wireless testbed to study the effects of switching channels in a multiradio wireless mesh network. Our experiments show that in common scenarios a channel switch causes a non-negligible interruption in the connectivity among nodes, which is on the order of 10 seconds. Also, our tests reveal that a rapid recovery from link failures caused by channel switches is prevented by a rather slow update of the advertised link quality. Inspired by the analysis of the experiments we conducted, we also propose and evaluate a preliminary technique to reduce the interruption in the delivery of packets caused by a channel switch.

Experimenting with P2P traffic optimization for wireless mesh networks in a federated OMF-PlanetLab environment

The ultimate success of the Wireless Mesh Network paradigm (WMN) in large scale deployments depends on the ability to test it in real world scenarios. A typical application scenario which is worth to be investigated in such a context is peer-to-peer traffic management. The creation of large scale testbeds for evaluating wireless mesh technologies and protocols, and for testing their ability to support real world applications in realistic environments, is then a crucial step. OMF (cOntrol and Management Framework) is a well-established control, measurement, and management framework for wireless testbeds. In this paper we present how we integrated an OMF-based wireless testbed in the planetary-scale PlanetLab testbed, making it possible for PlanetLab users to run experiments spanning on both PlanetLab and an OMF-based wireless testbed. In order to demonstrate the usefulness of such an integrated scenario, we tested on it an innovative peer-to-peer traffic optimization technique for the BitTorrent file sharing application. The possibility of running this kind of experiments highlighted several real-world issues which could be investigated thanks to our hybrid experimental scenario.

Bittorrent traffic optimization in Wireless Mesh Networks with ALTO service

Wireless Mesh Networks (WMNs) have recently gained wide attention as a way to provide Internet connectivity in hard-to-reach areas as well as in big cities. The main problem of such networks is their limited bandwidth availability compared to wired networks. Hence, efficient usage of available communication resources is of crucial importance for WMNs. Peer-to-peer applications, these days, produce a considerable amount of traffic over the Internet. Such applications build their own overlay network by not taking into account the topology and the status of the underlying infrastructure, so causing an inefficient utilization of physical communication resources. This problem is particularly severe for Wireless Mesh Networks. In this paper we propose a cross-layer solution for P2P Bittorrent traffic optimization in WMNs, based on the ALTO (Application Layer Traffic Optimization) Service recently defined by the IETF. Our solution is able to significantly optimize Bittorrent traffic and it does not require any modification to the Bittorrent application. The tests we performed show a reduction of about 27% of download time and a reduction of about 66% of traffic crossing the WMN borders.

Virtual network embedding in wireless mesh networks through reconfiguration of channels

Network virtualization is gaining a lot of interest from the research community thanks to its ability to support new networking paradigms and experimental scenarios. Virtual network embedding (VNE) is a key step for enabling network virtualization and its efficiency allows to maximize the profits of the physical network (also called substrate network) provider. In this paper we focus on the cases where the substrate network consists of a multi-radio IEEE 802.11 wireless mesh network. In such kind of network, bandwidth of a wireless link depends on the rate used to transmit but also on the number of wireless links that use the same channel, because of interference. Exploiting such a property, we propose a heuristic for the online, i.e. requests are not known in advance, VNE problem that is able to increase the profit of the substrate network provider by fictitiously augmenting the network resources and then reconfiguring the channels to avoid congestion.

WiMesh: A Tool for the Performance Evaluation of Multi-Radio Wireless Mesh Networks

In this paper we present WiMesh, a software tool we developed during the last ten years of research conducted in the field of multi-radio wireless mesh networks. WiMesh serves two main purposes: (i) to run different algorithms for the assignment of channels, transmission rate and power to the available network radios; (ii) to automatically setup and run ns-3 simulations based on the network configuration returned by such algorithms. WiMesh basically consists of three libraries and three corresponding utilities that allow to easily conduct experiments. All such utilities accept as input an XML configuration file where a number of options can be specified. WiMesh is freely available to the research community, with the purpose of easing the development of new algorithms and the verification of their performances.

A Load Balancing Algorithm against DDoS attacks in beyond 3G wireless networks

A Distributed Denial of Service (DDoS) attack aims at exhausting the resources of a communication system. A large amount of requests is sent to the targeted system by malicious users: the overload compromises the correct working of the structure. If the attack is successful, the system stops working. The assault does not provide the hacker with any sensitive information; so it does not appear as dangerous as it really is. Nevertheless, the denial of service is a huge security risk for Long Term Evolution (LTE) networks. In order to avoid this kind of risk, we present a mechanism that relocates the resources requested by the users, both voice and data. It is able to transfer the overload from congested eNodeBs to eNodeBs with free capacities. The mechanism is a Load Balancing Algorithm, fully integrated in the architecture of LTE networks. We simulated the attack scenario through Network Simulator 3 (ns-3). If the proposed algorithm is active, in case of a DDoS attack, communication services are always available for users.

Impact of multi-path routing on TCP performance

Routing packets over multiple disjoint paths towards a destination can increase network utilization by load-balancing the traffic over the network. The drawback of load-balancing is that different paths might have different delay properties, causing packets to be reordered. This can reduce TCP performance significantly, as reordering is interpreted as a sign of congestion. Packet reordering can be avoided by letting the network layer route strictly on flow-level. This will, however, also limit the ability to achieve optimal network throughput. There are also several proposals that try to mitigate the effects of reordering at the transport layer. In this paper, we perform an initial evaluation of such TCP reordering mitigations in multi-radio multi-channel wireless mesh networks when using multi-path routing. We evaluate two TCP reordering mitigation techniques implemented in the Linux kernel. The transport layer mitigations are compared using different multi-path routing strategies. Our findings show that, in general, flow-level routing gives the best TCP performance and that transport layer reordering mitigations only marginally can improve performance.

Integration of 3G connectivity in PlanetLab Europe: a step of an evolutionary path towards heterogeneous large scale network testbeds

Distributed research testbeds play a fundamental role in the evaluation of disruptive innovations for the Future Internet. In recent years, the main research funding agencies have promoted several initiatives aimed at designing and building open, large scale, realistic experimental facilities that could be used to evaluate innovative networking architectures, paradigms and services. In this paper, after discussing the main challenges in building such infrastructures, we present how, by leveraging the concept of federation, we managed to introduce a first degree of heterogeneity into PlanetLab Europe, a European testbed federated with PlanetLab, by providing UMTS connectivity to PlanetLab Europe nodes. Our contribution is just a first step of an evolutionary path whose further developments will lead to next generation large-scale heterogeneous testbeds for supporting experimentally-driven research on the Network of the Future (Preliminary results within the same framework of this work have been recently published in Canonico et al. (2007) and Botta et al. (2008)).