Miguel Rodelgo-Lacruz

Base technologies for vehicular networking applications: review and case studies

In this paper, we review the state of the art of two key hardware technologies that support vehicular applications: on-board embedded systems and wireless sensor networks (WSN). We focus on pre-competitive or state-of-the-art hardware, and illustrate its use with two case studies: on-line navigation assistance and data collection in a mobile WSN. In the first case (based on a joint collaboration within project FUNCMOV PGIDIT05TIC00501CT, Xunta de Galicia, Spain), we describe our development experience with automotive embedded systems. In the second case, we analyze the feasibility of wake-up schema to gather data from highly dispersed sensor nodes. The goal of the paper is to offer a perspective on the current possibilities of these hardware systems.

Practical Scalability of Wavelength Routing Switches

Packet switches with optical fabrics can potentially scale to higher capacities. It is also potentially possible to improve their reliability, and reduce both their footprint and power consumption. A well-known alternative for implementing hardwired switches is Arrayed Waveguide Grating (AWG). Ideally, AWG insertion losses do not depend on the number of input-output ports, meaning that scalability is theoretically infinite. However, accurate second-order assessment has demonstrated that in-band crosstalk exponentially increases the power penalty, limiting the realistic useful size of AWG commercial devices to about 10-15 ports (13-18 dB) [1]. On the other hand, the in-band crosstalk at AWG outputs depends on the connection pattern set by the scheduling algorithm and this port count limitation is calculated for worst-case scenarios. In this paper, we show that distributed schedulers with predetermined connection patterns can be used to avoid these harmful arrangements. We also show that the probability of worst-case patterns is very low, allowing us to set a more realistic port limit for general centralized schedulers and very small losses. With these results, we calculate more realistic port count limits for both scheduler types.

Enhanced parallel iterative schedulers for IBWR optical packet switches

In this paper we propose an enhanced parallel iterative scheduler for IBWR synchronous slotted OPS switches in SCWP mode. It obtains a maximal matching of packet demands without resource conflicts. The analytical and numerical results are highly competitive regarding previous work.

Decoupled parallel hierarchical matching schedulers

The load balanced Birkhoff–von Neumann switch is an elegant VOQ architecture with two outstanding characteristics: (i) it has a computational cost of O(1) iterations and (ii) input controllers do not exchange information (as a result, it allows decoupled implementations with a low power density). The load balancing stage guarantees stability under a broad class of traffic patterns. It may alter packet sequence, but this can be solved with appropriate packet selection strategies. The average packet delay caused by previous maximal size matching algorithms, such as iSLIP, RDSRR, or PHM is noticeably lower than that of a Birkhoff–von Neumann switch, especially for low and medium loads. However, they need tightly coupled VOQ controllers, which implies higher power density. For example, this makes difficult to apply those algorithms to optical switching architectures. Moreover, they require O(log2N) iterations to converge, and this computational cost may be unacceptable for the slot lengths in optical packet switches. In this paper, we propose a family of decoupled Parallel Hierarchical Matching (PHM) VOQ controllers (DPHM). They outperform the Birkhoff–von Neumann scheduler, which can be viewed as a member of the family (in fact, the simplest one). DPHM schedulers have a computational cost of O(1) iterations and, unlike last generation maximal size matching algorithms, they allow a low input controller interconnection complexity (low power density switch implementation). Copyright

Guaranteeing packet order in IBWR optical packet switches with parallel iterative schedulers

The input-buffered wavelength-routed (IBWR) switch is a scalable switch fabric for optical packet switching (OPS) networks. In synchronous operation, when optical packets are of a fixed duration and aligned at switch inputs, the scheduling of this architecture can be characterised by a type of bipartite graph matching problem. This challenges the design of feasible algorithms in terms of implementation complexity and response time. A previous work presented and evaluated the insistent parallel desynchronized block matching (I-PDBM) algorithm for the IBWR switch. I-PDBM is a parallel iterative scheduler with a good performance and a simple hardware implementation. However, the algorithm does not maintain the packet sequence. In this paper, we present the I-PDBM algorithm with packet ordering (OI-PDBM), which prevents mis-sequencing and behaves as I-PDBM in terms of delay, buffer requirements and convergence speed. Copyright

LBWS : a load-balanced distributed scheduler for WASPNET optical packet switches

In this paper we propose a novel scheduling approach for optical packet switching (OPS) WASPNET nodes, LBWS. Unlike the original WASPNET description, our scheduler is fully distributed and its computational cost is independent from switch size. This allows shorter packets, improving network performance. Based on a deterministic evolution of the switch configuration, our scheduling algorithm predicts packet delays at packet ingress to guarantee switch stability, and assigns fibre delay lines (FDLs) accordingly. It is not necessary to emulate RAM memories, since we assign delay lines according to packet delay predictions. We demonstrate that LBWS outperforms WASPNET in the cases studied, for nonuniform input traffic. Copyright

Off-the-shelf transparent HomePlug range extension

HomePlug powerline communications networks link individual computers or network segments via low-voltage power lines. The powerline medium is a harsh channel, since it varies in time and has a high attenuation. This makes difficult to communicate different devices in distant places in a building. A possible solution is the HomePlug repeater we propose in this paper. We show that it is impossible to develop a repeater at the physical layer, so we have developed it at medium access control (MAC) level. Its main distinctive features are transparency (no planning is necessary) and availability (it is built from off-the-shelf hardware).

Distributed resource scheduling in not-aligned optical cell switching

Most all-optical switching paradigms assume that different wavelengths are switched independently, which limits scalability. In optical cell switching (OCS), time is divided into time slots of fixed size by time-division multiplexing, and the wavelengths in a time slot are all bundled. Thus, each OCS switch (OCX) has a single switching plane and performs mere time-space switching. In OCS, each OCX requires optical slot synchronizers (OSYNs) at all inputs for the arrival slots to be aligned, so that cells can be simultaneously forwarded. In a recent OCS paradigm -not-aligned OCS-, the OSYNs and the alignment process are no longer required. Cell shifting still takes place inside the OCXs for minimizing the gaps between cells, but it is not necessary to align them to a reference time. Not-aligned OCS has clear advantages over aligned OCS: the total number of fiber delay loops (FDLs) and the hardware cost are reduced, and the number of switching operations is also lower. Moreover, cell arrival time to the switch is not critical, and the network becomes simpler and more flexible. In this paper, we propose a new distributed resource scheduling algorithm for not-aligned OCS networks, which takes connection blocking probability to reasonable values for practical loads.

Practical early detection of performance degradation in aggregated traffic links

The growth of Internet traffic and the many different traffic classes that exist make network performance control extremely difficult for operators. The methods available rely on complex or costly hardware. However, recent research on bandwidth sharing has introduced methods that require only basic statistics of aggregated link utilization, such as mean and variance. This data can be easily obtained through SNMP calls, lowering the cost of monitoring systems. Unfortunately, to the best of our knowledge, no tools have yet been developed to implement these methods. This paper presents the implementation of a plugin for the monitoring environment Nagios and the validation of a degradation detection tool from link utilization traces. The plugin does not require complex or costly hardware for acquiring data. Instead, it employs basic SNMP data about link utilization.

Approximation to Nanosecond Optical Switching Based on Commercial Devices

Optical Packet Switching (OPS) has been proposed as the ultimate solution for Wavelength Division Multiplexing (WDM) core networks, but it has not achieved commercial status due to numerous technological requisites such as packet tunable wavelength conversions, switching times in the order of nanoseconds, and individual wavelength switching. Nevertheless, new OPS paradigms reduce technological complexity by eliminating wavelength conversions and performing joint wavelength switching. Moreover, new interferometric optical devices capable of switching two optical signals in sub-nanosecond times are already commercially available. In this paper, we propose an all-optical switch architecture based on these devices, which switch all wavelengths as a bundle. We also perform a preliminary analysis of this architecture with some simplifications that allow us to set an upper bound on the maximum bit rate attainable in an ideal network (relaxing the need for 3R regeneration and electro-optical conversions).