This paper evaluates the performance of the two ETSI non-area forwarding algorithms in the GeoNetworking specification: Greedy Forwarding and Non-Area Contention-Based Forwarding (CBF). Non-area forwarding occurs when a packet is sent to a geographical Destination Area from a node located outside of this area, e.g., when a vehicle wants to alert of hazardous events to other vehicles located in a distant geographical area. The evaluation has been carried out both in urban and highway scenarios and takes into account the complete ETSI Architecture, including the interaction with the Decentralized Congestion Control (DCC) mechanism. We have also compared ETSI-defined mechanisms with optimizations found in the literature. Our main findings are that Greedy Forwarding, when combined with DCC, is extremely ineffective even with optimizations, and Non-Area CBFs (both ETSI CBF and an optimized version called S-FoT+) outperform Greedy Forwarding both in highway and urban scenarios.

This paper evaluates the performance of ETSI ITS Contention-Based Forwarding (CBF) and ETSI Simple GeoBroadcast forwarding while disseminating warning messages over a Geographical Area in highway and urban scenarios. Our experimental evaluation considers the complete ETSI ITS architecture including the Decentralized Congestion Control (DCC) mechanism. We propose an enhanced CBF mechanism, named S-FOT+, which combines several improvements to the ETSI CBF algorithm. S-FoT+ has a similar or better performance than the ETSI forwarding algorithms regarding both reliability and end-to-end delay while requiring much fewer transmissions. The improvements are equally effective and efficient in both urban and highway scenarios with large Destination Areas. Finally, we evaluate the trade-offs that stem from using multi-hop broadcast mechanisms in urban settings with smaller Destination Areas when compared to single-hop broadcast. Results show that multi-hop mechanisms significantly improve coverage at the cost of an increased number of transmissions.

Multicast forwarding in the context of IP-MPLS networks for services like VPLS has important scalability issues. Alternatives to per-VPLS tree construction based on aggregation of multipoint requests onto shared trees have been studied. Other works have focused on stateless forwarding based on Bloom filters. Both suffer from some type of forwarding anomalies. This paper proposes the combination of both forwarding modes: shared multicast trees and an efficient variant of stateless switching based on Bloom filters. Simulations prove that constraining the forwarding to the shared tree is an effective mechanism to prevent most side effects of Bloom filter-based forwarding, making the combined technique a good trade-off in terms of forwarding state consumption, yielding best performance in terms of overhead with respect to each technique in isolation.

In order to carry out their duty to serve and protect, law enforcement agencies (LEAs) must deploy new tools and applications to keep up with the pace of evolving technologies. However, police information and communication technology (ICT) systems have stringent security requirements that may delay the deployment of these new applications, since necessary security measures must be implemented first. This paper presents an integrated security architecture for LEAs that is able to provide common security services to novel and legacy ICT applications, while fulfilling the high security requirements of police forces. By reusing the security services provided by this architecture, new systems do not have to implement custom security mechanisms themselves, and can be easily integrated into existing police ICT infrastructures. The proposed LEA security architecture features state-of-the-art technologies, such as encrypted communications at network and application levels, or multi-factor authentication based on certificates stored in smart cards.

This article presents a novel framework for data-centric storage (DCS) in a wireless sensor and actor network (WSAN) that employs a randomly selected set of data replication nodes, which also change over time. This enables reductions in the average network traffic and energy consumption by adapting the number of replicas to applications' traffic, while balancing energy burdens by varying their locations. To that end, we propose and validate a simple model to determine the optimal number of replicas, in terms of minimizing average traffic/energy consumption, based on measurements of applications' production and consumption traffic. Simple mechanisms are proposed to decide when the current set of replication nodes should be changed, to enable new applications and nodes to efficiently bootstrap into a working WSAN, to recover from failing nodes, and to adapt to changing conditions. Extensive simulations demonstrate that our approach can extend a WSAN's lifetime by at least 60%, and up to a factor of 10× depending on the lifetime criterion being considered. The feasibility of the proposed framework has been validated in a prototype with 20 resource-constrained motes, and the results obtained via simulation for large WSANs have been also corroborated in that prototype.

Optical Code Division Multiple Access (OCDMA) techniques have shown outstanding capabilities in the sharing of optical media, in particular in access networks. However, OCDMA systems may suffer from Multiple Access Interference (MAI) and other kinds of noise when many users access the shared media simultaneously, increasing the BER (Bit Error Rate) to unacceptable levels, that is, a situation at which all combined signals interfere and are lost. This work proposes a mixed OCDMA and Tunable Transmitter-Fixed Receiver (TT-FR) WDM and ring architecture at which the ring is split into small-size segments to limit the probability of MAI. Essentially, every segment in the ring has got two hub nodes (on the segment's head and tail) which forwards inter-segment traffic to other hub nodes on dedicated home wavelengths, thus making use of WDM. The access media inside the segment is shared between the nodes by means of OCDMA, and code reuse is possible on different segments. Our performance analysis shows how to split a given ring into segments in order to minimise the BER due to multiple users accessing the network and allow for high bit-rates for a given traffic load. In addition, we analyse the possibility of introducing Forward Error Correction (FEC) at a moderate overhead cost to improve performance.

This paper studies data-centric storage (DCS) as a suitable system to perform data aggregation on wireless sensor and actor networks (WSANs), in which sensor and actor nodes collaborate together in a fully distributed way without any central base station that manages the network or provides connectivity to the outside world. The authors compare different multi-replication DCS proposals and choose the best one to be applied when studying data aggregation. In addition, the authors provide mathematical models for the production, consumption and overall network traffic for different application profiles. Those application profiles are based on the ability of a particular application to perform data aggregation and on what type of traffic is dominant, either the consumption or the production one. Furthermore, the authors provide closed formulas for each application profile that defines the optimal number of replicas that minimise the overall network traffic. Finally, the authors validate the proposed models via simulation.

This paper presents a novel framework for Data Centric Storage in a wireless sensor and actor network that enables the use of a randomly-selected set of data replication nodes which also change over the time. This allows reducing the average network traffic and energy consumption by adapting the number of replicas to applications' traffic, while balancing energy burdens by varying their location. To that end we propose and validate a simple model to determine the optimal number of replicas, in terms of minimizing average traffic/energy consumption, from the measured applications' production/consumption traffic. Simple protocols/mechanisms are proposed to decide when the current set of replication nodes should be changed, to enable new applications and sensor nodes to efficiently bootstrap into a working sensor network, to recover from failing nodes, and to adapt to changing conditions. Extensive simulations demonstrate that our approach can extend a sensor network's lifetime by at least a 60%, and up to a factor of 10x depending on the lifetime criterion being considered.

In Peer-to-Peer (P2P) systems where stored objects are small, routing dominates the cost of publishing and retrieving an object. In such systems, the issue of fairly balancing the routing load among all nodes becomes critical. In this paper we address this issue for Chord-based P2P systems. We first present an analytical model to evaluate the routing fairness of Chord based on the well accepted Jain's Fairness Index (FI). Our model shows that Chord performs poorly, with a FI around 0.6, mainly due to the different sizes of the zones between nodes. Following this observation, we propose a simple enhancement to the Chord finger selection algorithm with the goal of mitigating this effect. The key advantage of our proposal as compared to previous approaches is that it does not add any overhead to the basic Chord algorithm. The proposed approach is evaluated analytically showing a very substantial improvement over Chord, with a FI around 0.9. We conduct an extensive large-scale simulation study to evaluate our proposal and validate the analysis. The simulation study includes, among other aspects, churn conditions, heterogeneous nodes and Zipf-like object popularity.

Access to Wireless Sensor Networks (WSNs) from external applications will become a key aspect in order to successfully deploy this technology. This paper presents the Light-Weight Exterior Sensornet Protocol (LWESP), to enable the communication between applications and WSNs. This protocol is a combination of the Sensor Communication Language (SENCOMLNG) and the eXtensible Binary Enconding (XBE32). SENCOMLNG is an XML-based language. XBE32 provides an efficient encoding of the SENCOMLNG in order to reduce the bandwidth utilization and the processing cost in the WSN gateways, that in many scenarios could also be resource-restricted devices. Finally, we present a test-bed based on JAVA as well as a comparison between our proposal and other solutions showing that LWESP outperforms all the previous proposals in terms of bandwidth utilization.

As stateful flow-aware services are becoming commonplace, distributed router architectures have to quickly assign packets being forwarded to service-specialized processors in order to balance flow processing and state among them. Moreover, packets belonging to the same flow must be always assigned to the same CPU, even if some of the service processors become unavailable. This paper presents two novel fast robust hashing algorithms for persistent flow-to-CPU mapping, that require less hashing operations per packet than previous robust hash algorithms, thus being able to fulfill all the above requirements to implement flow-aware services at wire-speed.