Marcel Cavalcanti de Castro

Peer-to-Peer Overlay in Mobile Ad-hoc Networks

Wireless multi-hop networks such as mobile ad-hoc (MANET) or wireless mesh networks (WMN) have attracted big research efforts during the last years as they have huge potential in several areas such as military communications, fast infrastructure replacement during emergency operations, extension of hotspots or as an alternative communication system. Due to various reasons, such as characteristics of wireless links, multi-hop forwarding operation, and mobility of nodes, performance of traditional peer-to-peer applications is rather low in such networks. In this book chapter, we provide a comprehensive and in-depth survey on recent research on various approaches to provide peer-to-peer services in wireless multi-hop networks. The causes and problems for low performance of traditional approaches are discussed. Various representative alternative approaches to couple interactions between the peer-to-peer overlay and the network layer are examined and compared. Some open questions are discussed to stimulate further research in this area.

Capacity Increase for Voice over IP Traffic through Packet Aggregation in Wireless Multihop Mesh Networks

Recently, voice over IP (VoIP) has become an important service for the future internet. However, for ubiquitous wireless VoIP services, greater coverage will be necessary as promised by the advent of e.g. 802.11 WLAN based wireless meshed networks. Unfortunately, the transmission of small (voice) packets imposes high overhead which leads to low capacity for VoIP over 802.11 based multihop meshed networks. In this work, we present a novel packet aggregation mechanism that significantly enhances capacity of VoIP in wireless meshed networks while still maintaining satisfactory voice quality. Extensive experiments using network simulation ns-2 confirm that our packet aggregation algorithm can lead to a significantly increase in the number of supported concurrent VoIP flows over a variety of different hop numbers while reducing the MAC layer contention.

Performance Evaluation of Structured P2P over Wireless Multi-hop Networks

Internet connected wireless multi-hop networks are an interesting alternative for providing broadband wireless access. In order for the network to be transparent, the same services need to be available as in standard infrastructure wireless deployments. However, there is a significant challenge in providing services such as authentication, name resolution, VoIP over multi-hop mesh networks as dedicated servers implementing those services might be not available. Therefore, deploying overlay networks in the mesh to decentralize those services and move towards a Peer-to-Peer paradigm is an interesting approach. However, the multi-hop nature of wireless mesh networks and the restrictions in resource availability might cause problems when deploying overlay networks on top of such environments. In this paper, we investigate the overhead and trade-offs when deploying a structured overlay solution such as the Bamboo DHT over wireless multi-hop mesh networks. We provide various simulation results characterizing the overhead of management and control traffic and give recommendations for performance improvement.

Qos-aware channel scheduling for multi-radio/multi-channel wireless mesh networks

In non-static multi-radio/multi-channel wireless mesh networks architectures such as Net-X, mesh nodes need to switch channels in order to communicate with different neighbors. Present channel schedulers do not consider the requirements of real time traffic such as voice over IP. Thus the resulting quality is low. We propose a novel channel scheduler for the Net-X platform that takes into account packet priorities. We evaluate the algorithm on the KAUMesh testbed. Our algorithm outperforms the standard round-robin scheduler both in terms of average delay and jitter.

Practical considerations for channel assignment in wireless mesh networks

In multi-radio wireless mesh networks (WMNs) several radios can operate within one node simultaneously on different channels. Due to frequency selective fading and varying output powers of WLAN cards the received signal strength on channels in the U-NII band can differ by several dB. Furthermore, power leakage from neighboring channels in the frequency spectrum can cause adjacent channel interference (ACI). Using a IEEE 802.11a testbed, we experimentally evaluate the achievable throughput of a multi-radio mesh network in a string topology under the impact of ACI and channel heterogeneity. Our results show that for low PHY rates the channel separation is a good indicator for throughput. However, for high PHY rates the propagation properties of a specific channel also need to be considered. Based on the results we provide recommendations for designing channel assignment algorithms for IEEE 802.11-based WMNs.

Optimizing SIP Service Provisioning in Internet Connected MANETs

Recently, mobile ad-hoc networks (MANETs) have gained a lot of attraction because they are flexible, self-configurable and fast to deploy. Systems beyond 4G are likely to consist of a combination of heterogeneous wireless technologies and naturally might comprise MANETs as one component. In order to provide multimedia services such as voice over IP in such environment, support for session initiation protocol (SIP) is essential. A MANET is a decentralized collection of autonomous nodes but a SIP infrastructure requires centralized proxies and registrar servers. In this paper, we first study the implications of using standard SIP architecture in Internet connected MANETs. We analyze limitations of SIP service scalability when centralized proxies/registrars located in the access network are used by MANET nodes. Finally, we present alternative approaches to provide SIP services in such environment to avoid current limitations

OLSR and Net-X as a framework for channel assignment experiments: extended abstract

We present a software framework for channel assingment and routing experiments in multi-channel/multi-radio wireless mesh networks. Based on a plug-in architecture we develop a traffic demand-aware channel assignment algorithm. The evaluation in KAUMesh -- an experimental multi-radio mesh network -- shows around 30% throughput improvement with respect to a traffic un-aware channel assignment scheme.

Measuring the Impact of ACI in Cognitive Multi-Radio Mesh Networks

In this paper we address the impact of ACI on dynamic spectrum allocation in multi-radio systems. In particular, we present the benefits of dynamic spectrum allocation by adapting channel bandwidth and distance in order to mitigate ACI in multi-radio mesh networks. Based on our measurement campaign in an indoor mesh testbed, which we extended in order to use adaptive channel width, we evaluate the performance in terms of network throughput. We show that by using channel bandwidth adaptation and antenna separation, the impact of ACI can be significantly reduced. The performed experiments give important insights into ACI in multi-radio cognitive systems which help to develop e.g. better channel assignment algorithms or capacity estimation methods.

Opportunistic P2P communications in delay-tolerant rural scenarios

Opportunistic networking represents a promising paradigm for support of communications, specifically in infrastructureless scenarios such as remote areas communications. In principle in opportunistic environments, we would like to make available all the applications thought for traditional wired and wireless networks like file-sharing and content distribution. In this paper, we present a delay-tolerant scenario for file sharing applications in rural areas, where an opportunistic approach is exploited. In order to support communications, we compare two peer-to-peer (P2P) schemes initially conceived for wireless networks and prove their applicability and usefulness to a DTN scenario, where replication of resources can be used to improve the lookup performance and the network can be occasionally connected by means of a data mule. Simulation results show the suitability of the schemes and allow to derive interesting design guidelines on the convenience and applicability of such approaches.

Policy-based dynamic reconfiguration of mobile ad hoc networks

Ad hoc networks are intrinsically dynamic with respect to mobility, traffic patterns, node density, number of nodes, physical topology, and others. This scenario imposes several challenges to the ad hoc routing protocols, and there is no single solution for all scenarios. This paper proposes the application of Policy-Based Network Management (PBNM) for dynamic reconfiguration of ad hoc networks. PBNM uses the concept of policies formed by events, conditions and actions. The occurrence of an event triggers conditions evaluation, and if evaluated to true, a set of actions should be performed. The paper contribution comprises the proposal of an ad hoc policy information model based on DEN-ng policy model for the implementation of a policy manager prototype to be integrated in the NS-2 simulator allowing dynamic reconfiguration of routing protocol parameters in simulation time; and the proposal of policies for dynamically adjusting the ad hoc routing protocol behavior.