In this work we describe and analyze a new Quality of Service (QoS) architecture for wireless mesh networks. Such architecture is mainly composed of two components, i.e. a new admission control criteria for flows and a new link metric. The first allows to only admit flows whose required QoS (specified in terms of bandwidth) can be guaranteed, while the latter allows to maximize the number of accepted flows. In particular, the admission control criteria is designed to precisely evaluate the available bandwidth of the WMN links, which depends not only on the transmission rate of the link but also on the number and the transmission rates of the links in the neighboorhood working on the same channel. The new link metric, instead, is designed to select paths for flows so as to reduce the usage of resources. The proposed architecture relies on the ability of explicitly routing flows. To this purpose, we chose to employ MPLS (Multi Protocol Label Switching), which is able to finely control the path of each single flow. Such possibility further allows to increase the number of accepted flows by exploiting bandwidth where available.

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.

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.

Routing in multi-radio wireless mesh networks is a very challenging problem. In this paper, we propose a forwarding paradigm based on MPLS (Multi Protocol Label Switching) which makes use of a novel mechanism, denoted as MPLS splitting policy. Such mechanism allows to configure multiple next hops at an intermediate node, so that the incoming traffic is partitioned among the next hops according to predefined coefficients named split ratios. The MPLS splitting policy has been designed to allow for load balancing and fast local restoration. With such a mechanism, it is crucial to properly determine the set of split ratios, as they determine how the traffic is routed across the network. We present an approach to compute a set of split ratios that guarantee high performance under different traffic loads. To this end, we adopt the hose traffic model, according to which we only have knowledge of the maximum amount of traffic entering or leaving the network at each edge node. A thorough simulation study is conducted to show that our approach outperforms other routing protocols in terms of throughput and robustness against traffic load variations and single node failures.

Routing packets over multiple disjoint paths towards a destination can increase network utilization by load-balancing the traffic over the network. In wireless mesh networks, multi-radio multi-channel nodes are often used to create a larger set of interference-free paths thus increasing the chance of load-balancing. 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 forward traffic strictly on flow-level. This would avoid the negative drawbacks of packet reordering, but will also limit the ability to achieve optimal network throughput. On the other hand, there are several proposals that try to mitigate the effects of reordering at the transport layer. In this paper, we perform an in-depth evaluation of such TCP reordering mitigations in multi-radio multi-channel wireless mesh networks when using multi-path forwarding. We evaluate two TCP reordering mitigation techniques implemented in the Linux kernel. The transport layer mitigations are compared using different multi-path forwarding strategies. Our findings show that, in general, flow-level forwarding gives the best TCP performance and that transport layer reordering mitigations only marginally can improve 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.

In multi-radio wireless mesh networks, a network device simultaneously transmits packets over different channels by using multiple radios. Such frequency diversity not only in creases throughput but makes multi-path routing approaches extremely interesting. This is because the channel diversity reduces the risk for intra- and inter-flow interference. A fundamental problem to solve is the forwarding strategy which determines which packets to be sent over what multi-path segments at any given time. Ideally, the forwarding strategy should schedule flows according to the capacity constraints imposed by the channel assignment. However, the possibility to improve MAC layer efficiency by aggregating small packets into larger ones is reduced when packets are forwarded to different next-hops. In this paper, we develop a novel packet forwarding strategy for multi-radio mesh networks that combines the benefits of multi-path routing with packet aggregation. In our cross-layer approach, we effectively trade-off aggregation opportunities with channel diversity. Simulation results show that our approach can improve network throughput and delay by up to 15 percent and 25 percent, respectively, compared with aggregation unaware forwarding strategies.

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.

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.

Planetlab is widely recognized as being one of the most important Internet-scale testbeds. However, while allowing experimentations involving hundreds of hosts spread all over the world, PlanetLab still suffers of a few significant limitations. One of these limitations is the lack of heterogeneity, in particular in terms of access technologies. In this paper we describe the efforts we made, in the context of the OneLab European project, in order to mitigate this problem. In particular, we describe how we managed to integrate UMTS connectivity into a PlanetLab-based testbed. We illustrate the technical challenges we had to face, the final result we obtained, and present a case study meant to show the utility of having UMTS connectivity available in Planetlab.