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On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks

Published: 08 June 2020 Publication History

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, ATS). The former use one FIFO queue per flow, whereas the latter use one FIFO queue per input port. 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. Time-sensitive networks exist in two flavours: (1) in non-synchronized networks, local clocks run independently at every node and their deviations are not controlled and (2) in synchronized networks, the deviations of local clocks are kept within very small bounds using for example a synchronization protocol (such as PTP) or a satellite based geo-positioning system (such as GPS). We revisit the properties of regulators in both cases. 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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MP4 File (3393691.3394206.mp4)
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 traffic regulators. 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. We revisit the properties of regulators in synchronized and non-synchronized networks. We show that, in most situations, ignoring the timing inaccuracies can lead to network instability. We propose and analyze two methods (rate and burst cascade, and ADAM) for avoiding this problem. To establish these results, we develop a new framework that captures industrial requirements on clocks, and we develop a toolbox that extends network calculus to account for clock imperfections.

References

[1]
IEEE. 2019. Draft Standard for Local and Metropolitan Area Networks textemdashBridges and Bridged Networks textemdashAmendment: Asynchronous Traffic Shaping. IEEE P802.1Qcr/D2.0, Vol. In IEEE802.1 private repository. To obtain the access credentials, visit https://www.ietf.org/proceedings/52/slides/bridge-0/tsld003.htm or contact the IEEE802.1 chair. (Dec. 2019). http://www.ieee802.org/1/files/private/cr-drafts/d2/802-1Qcr-d2-0.pdf.
[2]
ITU. 1996. Definitions and Terminology for Synchronization Networks. ITU G.810 (1996). https://www.itu.int/rec/T-REC-G.810-199608-I/en.
[3]
Jean-Yves Le Boudec and Patrick Thiran. 2001. Network Calculus: A Theory of Deterministic Queuing Systems for the Internet. Springer-Verlag, Berlin Heidelberg. https://www.springer.com/us/book/9783540421849.

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cover image ACM Conferences
SIGMETRICS '20: Abstracts of the 2020 SIGMETRICS/Performance Joint International Conference on Measurement and Modeling of Computer Systems
June 2020
124 pages
ISBN:9781450379854
DOI:10.1145/3393691
Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for third-party components of this work must be honored. For all other uses, contact the Owner/Author.

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Publication History

Published: 08 June 2020

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Author Tags

  1. interleaved regulator
  2. network calculus
  3. per-flow regulator
  4. per-flow shaper
  5. time sensitive networks
  6. time synchronization

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  • Huawei Technologies

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  • (2022)Analysis of Dampers in Time-Sensitive Networks With Non-Ideal ClocksIEEE/ACM Transactions on Networking10.1109/TNET.2022.315217830:4(1780-1794)Online publication date: 1-Mar-2022
  • (2022)On Packet Reordering in Time-Sensitive NetworksIEEE/ACM Transactions on Networking10.1109/TNET.2021.312959030:3(1045-1057)Online publication date: Jun-2022
  • (2021)Enabling Heterogeneous Deterministic Networks with Smart Collaborative TheoryIEEE Network10.1109/MNET.011.200061335:3(64-71)Online publication date: May-2021
  • (2021)FactoRing: Asynchronous TSN-compliant Network with low bounded Jitters for Industry 4.02021 26th IEEE International Conference on Emerging Technologies and Factory Automation (ETFA )10.1109/ETFA45728.2021.9613631(1-8)Online publication date: 7-Sep-2021

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