OFAR-CM: Efficient Dragonfly networks with simple congestion management

Dragonfly networks are appealing topologies for large-scale Data center and HPC networks, that provide high throughput with low diameter and moderate cost. However, they are prone to congestion under certain frequent traffic patterns that saturate specific network links. Adaptive non-minimal routing can be used to avoid such congestion. That kind of routing employs longer paths to circumvent local or global congested links. However, if a distance-based deadlock avoidance mechanism is employed, more Virtual Channels (VCs) are required, what increases design complexity and cost. OFAR (On-the-Fly Adaptive Routing) is a previously proposed routing that decouples VCs from deadlock avoidance, making local and global misrouting affordable. However, the severity of congestion with OFAR is higher, as it relies on an escape sub network with low bisection bandwidth. Additionally, OFAR allows for unlimited misroutings on the escape sub network, leading to unbounded paths in the network and long latencies. In this paper we propose and evaluate OFAR-CM, a variant of OFAR combined with a simple congestion management (CM) mechanism which only relies on local information, specifically the credit count of the output ports in the local router. With simple escape sub networks such as a Hamiltonian ring or a tree, OFAR outperforms former proposals with distance-based deadlock avoidance. Additionally, although long paths are allowed in theory, in practice packets arrive at their destination in a small number of hops. Altogether, OFAR-CM constitutes the first practicable mechanism to the date that supports both local and global misrouting in Dragonfly networks.The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. ERC-2012-Adg-321253- RoMoL, the Spanish Ministry of Science under contracts TIN2010-21291-C02-02, TIN2012-34557, and by the European HiPEAC Network of Excellence. M. García participated in this work while affiliated with the University of Cantabria.Peer ReviewedPostprint (author's final draft

Network unfairness in dragonfly topologies

Dragonfly networks arrange network routers in a two-level hierarchy, providing a competitive cost-performance solution for large systems. Non-minimal adaptive routing (adaptive misrouting) is employed to fully exploit the path diversity and increase the performance under adversarial traffic patterns. Network fairness issues arise in the dragonfly for several combinations of traffic pattern, global misrouting and traffic prioritization policy. Such unfairness prevents a balanced use of the resources across the network nodes and degrades severely the performance of any application running on an affected node. This paper reviews the main causes behind network unfairness in dragonflies, including a new adversarial traffic pattern which can easily occur in actual systems and congests all the global output links of a single router. A solution for the observed unfairness is evaluated using age-based arbitration. Results show that age-based arbitration mitigates fairness issues, especially when using in-transit adaptive routing. However, when using source adaptive routing, the saturation of the new traffic pattern interferes with the mechanisms employed to detect remote congestion, and the problem grows with the network size. This makes source adaptive routing in dragonflies based on remote notifications prone to reduced performance, even when using age-based arbitration.Peer ReviewedPostprint (author's final draft

Indoor Positioning Prediction System Based on Wireless Networks and Depth Sensing Cameras

[Abstract] This work presents a new system for predicting the movement of people in indoor user environments, based on an advanced Indoor Positioning System (IPS) developed previously by the authors. The mentioned IPS proposes the combination of WiFi Positioning System (WPS) and depth maps provided by RGB-D cameras to improve the efficiency of existing methods, based uniquely on wireless positioning techniques. In this approach, the prediction of movements is carried out by means of a proactive strategy, delivering the next estimated position of the person. This estimation provides a richer location and context information, which is useful for ubiquitous computing purposes. For example, energy consumption can be optimized if lighting or electronic devices are turned on/off by means of the user trajectory prediction. This paper shows how several techniques, applied for the developed IPS, offer different solutions to the indoor prediction problem, and it discusses about which of them gives better resultsThis work has been developed with the help of the research project DPI2013-44776-R of MICINN. It also belongs to the activities carried out within the framework of the research network CAM RoboCity2030 S2013/MIT-2748 of Comunidad de Madridhttps://doi.org/10.17979/spudc.978849749808

Interfícies directes sensor-microcontrolador basades en modulacions Sigma-Delta

L’objectiu d’aquest treball de final de carrera és l’estudi i disseny d’un modulador Sigma-Delta amb components discrets que actuï d’interfície entre un sensor (senyal analògic) i un microcontrolador (senyal digital). El fet d’utilitzar components discrets respon a la facilitat d’integrar aquest mòdul en qualsevol circuit on es disposi d’un microcontrolador, amplificadors operacionals i comparadors. Com que actualment hi ha models de microcontroladors que incorporen mòduls analògics d’aquest tipus, l’integració d’un modulador Sigma-Delta sembla interessant per tenir una interfície senzilla, barata i de gran resolució amb el món analògic de baixa freqüència. El fet de poder prescindir del bloc de condicionament del senyal analògic (ajust del marge dinàmic, amplificació, filtrat...) juntament amb l’alta resolució i estabilitat fa que l’ús de modulacions Sigma-Delta sigui una opció molt interessant en interfícies de sensors. L’estudi del model matemàtic ha permès fer una primera estimació de la exactitud (en número de bits) d’un modulador d’ordre n. A partir d’aquí s’ha dissenyat un convertidor analògico-digital basat en un modulador Sigma-Delta de primer ordre. Mitjançant una aplicació de Labview s’han efectuat les proves necessàries per caracteritzar el model i corroborar el model matemàtic. Les proves experimentals s’han dut a terme amb un generador de senyals i un multímetre de gran precisió, controlats a través de l’ordinador. El següent pas ha estat utilitzar aquest model caracteritzat de modulador Sigma-Delta per actuar d’interfície entre un sensor de temperatura (una termoresistència de platí) i un microcontrolador connectat a un ordinador. Per realitzar les proves experimentals s’ha utilitzat (a més dels instruments detallats anteriorment) un calibrador de temperatura. El resultat final ha estat un circuit sensor de temperatura que connectat a un ordinador permet obtenir lectures de temperatura amb una gran precisió