David Gómez

A Proof-of-Concept for Semantically Interoperable Federation of IoT Experimentation Facilities

The Internet-of-Things (IoT) is unanimously identified as one of the main pillars of future smart scenarios. The potential of IoT technologies and deployments has been already demonstrated in a number of different application areas, including transport, energy, safety and healthcare. However, despite the growing number of IoT deployments, the majority of IoT applications tend to be self-contained, thereby forming application silos. A lightweight data centric integration and combination of these silos presents several challenges that still need to be addressed. Indeed, the ability to combine and synthesize data streams and services from diverse IoT platforms and testbeds, holds the promise to increase the potentiality of smart applications in terms of size, scope and targeted business context. In this article, a proof-of-concept implementation that federates two different IoT experimentation facilities by means of semantic-based technologies will be described. The specification and design of the implemented system and information models will be described together with the practical details of the developments carried out and its integration with the existing IoT platforms supporting the aforementioned testbeds. Overall, the system described in this paper demonstrates that it is possible to open new horizons in the development of IoT applications and experiments at a global scale, that transcend the (silo) boundaries of individual deployments, based on the semantic interconnection and interoperability of diverse IoT platforms and testbeds.

Impact of network coding on TCP performance in wireless mesh networks

Since it was originally proposed by Ahlswede et al. (2000), network coding (NC) has been the focus of many research efforts and proposals. In particular, NC has been put forward as a means to increase the capacity of wireless mesh networks, by exploiting the broadcast nature of wireless links. However, in spite of the fairly large number of papers on the subject of network coding, the impact of NC on TCP performance in wireless mesh networks is still not fully understood. By means of a thorough simulation study, this paper aims thus at providing insights about the interaction between TCPs congestion control mechanisms and the underlying NC done by wireless relays. In particular, we focus on the influence of the main parameters related to the coding buffer used by such relays to encode packets. Our results suggest the feasibility of devising engineering rules for setting such parameters. Another main conclusion, in line with previous preliminary findings by the authors (Hassayoun et al., 2010) is that TCP performance can indeed be improved by the use of NC, but only as long as the wireless channel quality is above a certain level.

Reliable communications over lossy wireless channels by means of the combination of UDP and Random Linear Coding

It goes without saying that TCP is the de-facto transport protocol to ensure reliable communications (for instance, in file transfers). On the other hand, and despite the growing relevance of wireless networks, the behavior of TCP over such technologies is well-known to present clear limitations. Several approaches have been made so as to overcome these problems. In this work we propose a different approach to ensure reliable transmissions over wireless links, based on an Random Linear Coding (RLC) scheme, operating together with UDP. We provide a model of the expected performance of the new scheme. Furthermore, based on an extensive simulation campaign over the ns-3 simulation framework, we assess the validity of this model and we compare its performance with that exhibited by the legacy TCP. The results show that, in particular for lossy links, the proposed scheme clearly outperforms TCP.

Reliable communications over wireless mesh networks with inter and intra-flow network coding

In this work we present a flexible Network Coding (NC) module integrated within the ns-3 framework. We have exploited it to implement an inter-flow coding protocol, in which intermediate nodes (routers) combine packets belonging to different flows, as well as an intra-flow coding scheme, in which both the source and intermediate nodes linearly code packets of the same flow. We assess the performance of both approaches to provide reliable communication services over wireless mesh networks, considering that links are prone to cause packet drops, comparing their behavior with the one exhibited by legacy TCP.

Enhanced opportunistic random linear source/network coding with cross-layer techniques over wireless mesh networks

In this paper we thoroughly study, by means of simulation, the combination of source and network random linear coding to provide reliable communications over wireless mesh networks. We assume that intermediate nodes code the packets they have previously stored before forwarding them. We also analyze the possibilities that are brought about by opportunistic listening and forwarding, combining them with the use of cross-layer information. We study the performance of the proposed scheme by means of an extensive simulation campaign carried out over the ns-3 platform; the results show that the coding functionality at the intermediate nodes leads to additional performance enhancements. In addition, they also demonstrate the potential benefits of integrating cross-layer techniques.

TCP Performance Enhancement over Wireless Mesh Networks by means of the Combination of Multi-RAT Devices and the MPTCP Protocol

The last trends at communications realms, in particular, wireless technologies, where it is more and more usual that devices carry more than one interface (i.e. multi-RAT, Radio Access Technology), to get access to the Internet, question the classic single-path paradigm, imposed by the mainstream transport protocol, TCP. In this work we assess the behavior of Multipath TCP (MPTCP), which allows the transparent breakdown of a single TCP session into multiple simultaneous subflows. This straightforward feature might lead to remarkable performance enhancements, yielding as well a stronger resilience against failures within any of the routes. Moreover, we evaluate three different routing algorithms (link, node and zone disjoint) that aim to discover the optimal route configuration of disjoint paths over a Wireless Mesh Network (WMN), exploiting the possibilities arisen by this brand new protocol. We use the obtained results to evaluate, by means of simulation, the behavior of the MPTCP protocol, showing that the aggregated performance is significatively higher than that of achieved by the traditional single-path and single-flow TCP.

On the use of Hidden Markov Processes and auto-regressive filters to incorporate indoor bursty wireless channels into network simulation platforms

AbstractIn this paper we thoroughly analyze two alternatives to replicate the bursty behavior that characterizes real indoor wireless channels within Network Simulation platforms. First, we study the performance of an improved Hidden Markov Process model, based on a time-wise configuration so as to decouple its operation from any particular traffic pattern. We compare it with the behavior of Bursty Error Model Based on an Auto-Regressive Filter, a previous proposal of ours that emulates the received Signal to Noise Ratio by means of an auto-regressive filter that captures the “memory” assessed in real measurements. We also study the performance of one of the legacy approaches intrinsically offered by most network simulation frameworks. By means of a thorough simulation campaign, we demonstrate that our two models are able to offer a much more realistic behavior, yet maintaining an affordable response in terms of computational complexity.

On the modeling of a realistic wireless channel by means of a Hidden Markov Process

In this work we deal with the analysis of different channel models, which aim to replicate the bursty characteristic of real indoor wireless channels within a network simulation framework. In particular, we focus on the performance of Hidden Markov Processes, comparing it with other alternatives, such as the legacy models which the ns-3 network simulator implements by default and another one whose operation is based on the estimation of the received signal strength by means of an auto-regressive filter.

Semantic Registration and Discovery System of Subsystems and Services within an Interoperable Coordination Platform in Smart Cities

Smart subsystems like traffic, Smart Homes, the Smart Grid, outdoor lighting, etc. are built in many urban areas, each with a set of services that are offered to citizens. These subsystems are managed by self-contained embedded systems. However, coordination and cooperation between them are scarce. An integration of these systems which truly represents a “system of systems” could introduce more benefits, such as allowing the development of new applications and collective optimization. The integration should allow maximum reusability of available services provided by entities (e.g., sensors or Wireless Sensor Networks). Thus, it is of major importance to facilitate the discovery and registration of available services and subsystems in an integrated way. Therefore, an ontology-based and automatic system for subsystem and service registration and discovery is presented. Using this proposed system, heterogeneous subsystems and services could be registered and discovered in a dynamic manner with additional semantic annotations. In this way, users are able to build customized applications across different subsystems by using available services. The proposed system has been fully implemented and a case study is presented to show the usefulness of the proposed method.

Performance of Random Linear Coding Over Multiple Error-Prone Wireless Links

In this letter we derive an exact formulation for the performance of Random Linear Coding (RLC) when applied over multiple wireless links. We combine this technique with UDP so as to offer a reliable communication service . We extend a previous result, which only considered one single link, to embrace both multiple sources as well as varying quality of wireless links. We establish the number of excess packets that are required to successfully accomplish the communication and, based on the Bianchi model, we calculate the achieved throughput. We also propose a context-aware probabilistic transmission scheme that leads to a relevant performance gain. We use a thorough simulation-based study over the ns-3 framework to assess the validity of the proposed model and to broaden the corresponding analysis.