Vasos Vassiliou

M-MPLS: Micromobility-enabled multiprotocol label switching

This paper presents the integration of multiprotocol label switching with hierarchical mobile IPv6. The resulting micromobility-based MPLS (M-MPLS) is defined in two modes of operation: overlay and integrated. In an overlay framework MPLS and HMIP operate on their respective layers without having common processes, tables, or signaling. In an integrated framework, related functions are merged. The overall goal of an integrated framework is to facilitate efficient and reliable network operations while simultaneously optimizing network utilization and system performance.

The GINSENG system for wireless monitoring and control: Design and deployment experiences

Todays industrial facilities, such as oil refineries, chemical plants, and factories, rely on wired sensor systems to monitor and control the production processes. The deployment and maintenance of such cabled systems is expensive and inflexible. It is, therefore, desirable to replace or augment these systems using wireless technology, which requires us to overcome significant technical challenges. Process automation and control applications are mission-critical and require timely and reliable data delivery, which is difficult to provide in industrial environments with harsh radio environments. In this article, we present the GINSENG system which implements performance control to allow us to use wireless sensor networks for mission-critical applications in industrial environments. GINSENG is a complete system solution that comprises on-node system software, network protocols, and back-end systems with sophisticated data processing capability. GINSENG assumes that a deployment can be carefully planned. A TDMA-based MAC protocol, tailored to the deployment environment, is employed to provide reliable and timely data delivery. Performance debugging components are used to unintrusively monitor the system performance and identify problems as they occur. The article reports on a real-world deployment of GINSENG in an especially challenging environment of an operational oil refinery in Sines, Portugal. We provide experimental results from this deployment and share the experiences gained. These results demonstate the use of GINSENG for sensing and actuation and allow an assessment of its ability to operate within the required performance bounds. We also identify shortcomings that manifested during the evaluation phase, thus giving a useful perspective on the challenges that have to be overcome in these harsh application settings.

MARCH: a medium access control protocol for multihop wireless ad hoc networks

The multiple access with reduced handshake (MARCH) protocol utilizes the broadcast characteristics of an omnidirectional antenna to reduce the number of control messages required to transmit a data packet in multihop ad hoc networks. In MARCH, the RTS-CTS handshake is used only by the first hop of a route to forward data packets while for the rest it utilizes a new CTS-only handshake. Since fewer control packets are transmitted, the probability of packet collision is reduced and therefore the channel throughput is increased. Simulation results demonstrate that MARCH outperforms MAC protocols that employ only the RTS-CTS handshake.

A Comprehensive Survey of Congestion Control Protocols in Wireless Sensor Networks

Congestion control and reliable data delivery are two primary functions of the transport layer in wired and wireless networks. Wireless sensor networks (WSNs) are a special category of wireless ad hoc networks with unique characteristics and important limitations. Limitations concern their resources, such as energy, memory, and computational power, as well as their applications. Due to these limitations and characteristics, the Transmission Control Protocol (TCP), the legacy protocol that implements congestion control and reliable transmission in the Internet, cannot apply to WSNs in its traditional form. To deal with this unavailability of a standard solution, many efforts are taking place in this area. In this paper, we review, classify, and compare algorithms, protocols, and mechanisms that deal directly with congestion control and avoidance in WSNs.

Requirements for the transmission of streaming video in mobile wireless networks

The ability to transmit video and support related real-time multimedia applications is considered important in mobile networks. Video streaming, video conferencing, online interactive gaming, and mobile TV are only a few of the applications expected to support the viability, and survival, of next generation mobile wireless networks. It is, therefore, significant to analyze the interaction of the particular media and applications. This paper presents the characteristics of mobile wireless networks and relates these characteristics to the requirements of video transmission. The relationship derived is based not only on the objective QoS metrics measured in the network, but also on the subjective quality measures obtained by video viewers at end hosts. Through this work we establish guidelines for the transmission of video based on the limits of mobile and wireless networks. We believe that the results help researchers and professionals in the fields of video production and encoding to create videos of high efficiency, in terms of resource utilization, and of high performance, in terms of end-user satisfaction.

Performance Study of Node Placement for Congestion Control in Wireless Sensor Networks

Performance of Wireless Sensor Networks (WSNs) can be affected when the network is deployed under different topologies. In this paper we present a performance study of congestion control algorithms in WSNs when nodes are deployed under different topologies. To perform our research we have employed algorithms SenTCP, Directed Diffusion, and HT AP. The choice of these algorithms is based on the fact that they cover two major methods used for congestion mitigation. These are: a) decreasing the load by source rate reduction (used in SenTCP) and b) increasing resources as these would help in emptying the buffers of intermediate sensor node though the creation of alternative paths (used in HTAP) or creation of multiple paths used in Directed Diffusion). We have examined the performance of these algorithms with respect to their ability to maintain low delays, to support the required data rates and to minimize packet losses under four different topologies. The topologies we have used are Simple Diffusion, Constant Placement, R-random placement and Grid placement. Results indicate that congestion control performance in sensor networks can significantly be improved, in algorithms that use multiple or alternative paths to forward their data in case of congestion (Directed Diffusion and HT AP). Performance of rate-controlled algorithms like SenTCP exhibit improvement in terms of packet latency.

Congestion control in Wireless Sensor Networks through dynamic alternative path selection

Recent applications on Wireless Sensor Networks (WSNs) demand networks with high and consistent data load. Due to the limited resources of wireless sensor nodes, high data loads can easily lead to congestion conditions. Congestion is a highly undesirable situation since its appearance creates additional overhead to the already heavily loaded environment, which, eventually leads to resource depletion. Thus, congestion control algorithms need to be applied in order to mitigate congestion. In this paper, we present a lightweight congestion control and avoidance scheme, called Dynamic Alternative Path Selection Scheme (DAlPaS). DAlPaS is a very simple but effective scheme that controls congestion while it keeps overhead to the minimum. The operation of this scheme is based on the control of resources instead of controlling the sending rate at the source. The performance of DAlPaS has been evaluated against comparable schemes with promising results.

Mobility in WSNs for critical applications

Recent critical application sectors of sensor networks like military, health care, and industry require the use of mobile sensor nodes, something that poses unique challenges in aspects like handoff delay, packet loss, and reliability. In this paper we propose a novel mobility model that handles those challenges effectively by providing on-time mobility detection and handoff triggering. In that way soft handoffs and controlled disconnections are assured. The proposed solution uses cross-layer information from the MAC and Network layers. Our solution was implemented and evaluated in an experimental testbed, in the context of the European FP7 GINSENG project.

Inter-mobility support in controlled 6LoWPAN networks

The research and industrial community started to think of more complex application scenarios for wireless sensor networks, where the use of mobile sensor nodes is essential. The support of mobile sensor nodes in such applications requires the existence of a suitable mobility management protocol. However, existing mobility protocols, like MIPv6, can not be directly applied on mobile sensor nodes, since they are inefficient in terms of energy, communication, and computation cost, and fail to meet the stringent operational requirements of a mobile sensor node. In this paper we propose a new mobility management protocol for 6LoWPAN which uses the technology of Proxy Agents and aims to enhance the handoff time by predicting or rapidly responding to a handover event. The proposed protocol lessens the involvement of the mobile node in mobility-related message exchange.

Mobility solutions for wireless sensor and actuator networks with performance guarantees

Wireless sensor and actuator networks (WSANs) have been studied for about ten years now. However, a gap between research and real applications and implementations remains. The lack of an integrated solution, capable of providing the reliability levels of monitoring and actuation required by critical applications, have postponed the replacement and extension of the existing inflexible and expensive wired solutions with the low-cost, easy-to-deploy, and portable wireless options. In order to assist this transition this paper presents a new method for supporting mobility in WSANs specifically designed for time-critical scenarios. The method is being targeted for a critical application located in a real oil refinery, in which a WSAN has been implemented in the scope of a European research project.