Prochain séminaire

STORE 14 - vendredi 15 Janvier 2021 (e-STORE organisé par le LAAS-CNRS)

Thématique : libre

Programme :

  • 10h00-10h10 - Accueil virtuel des participants
  • 10h10-10h40 - "On Resilience in Networks by Local Fast Failover Routing", Klaus-Tycho Foerster (University of Vienna, Austria)
  • 10h40-11h10 - "On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks", Ludovic Thomas (ISAE-Supaéro)


Résumé de l'exposé de Klaus-Tycho Foerster

  On Resilience in Networks by Local Fast Failover Routing
    Abstract:   In order to provide a high resilience and to react quickly to link failures, modern computer networks support fully decentralized flow rerouting, also known as local fast failover. In a nutshell, the task of a local fast failover algorithm is to pre-define fast failover rules for each node using locally available information only. In this talk I will give a brief introduction and overview to the topic, presenting a selection of our recent results in this area, mainly from the viewpoint of new algorithms, but also mentioning fundamental impossibility results (based on joint works with Gilles Tredan et al.)


Résumé de l'exposé de Ludovic Thomas

  On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks 
  Abstract:  Flow reshaping is used in time-sensitive networks (as in the context of IEEE TSN and IETF Detnet) in order to reduce burstiness inside the network and to support the 
computation of guaranteed latency bounds. This is performed using per-flow regulators (such as the Token Bucket Filter) or interleaved regulators (as with IEEE TSN Asynchronous Traffic Shaping). Both types of regulators are beneficial as they cancel the increase of burstiness due to multiplexing inside the network. It was demonstrated, by using network calculus, that they do not increase the worst-case latency. However, the properties of regulators were established assuming that time is perfect in all network nodes. In reality, nodes use local, imperfect clocks. In non-synchronized networks, we show that ignoring the timing inaccuracies can lead to network instability due to unbounded delay in per-flow or interleaved regulators. We propose and analyze two methods (rate and burst cascade, and asynchronous dual arrival-curve method) for avoiding this problem. In synchronized networks, we show that there is no instability with per-flow regulators but, surprisingly, interleaved regulators can lead to instability. To establish these results, we develop a new framework that captures industrial requirements on clocks in both non-synchronized and synchronized networks, and we develop a toolbox that extends network calculus to account for clock imperfections.

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