6,125 research outputs found
On Time Synchronization Issues in Time-Sensitive Networks with Regulators and Nonideal Clocks
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. 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.Comment: ACM SIGMETRICS 2020 Boston, Massachusetts, USA June 8-12, 202
Differentiable Programming & Network Calculus: Configuration Synthesis under Delay Constraints
With the advent of standards for deterministic network behavior, synthesizing
network designs under delay constraints becomes the natural next task to
tackle. Network Calculus (NC) has become a key method for validating industrial
networks, as it computes formally verified end-to-end delay bounds. However,
analyses from the NC framework have been designed to bound the delay of one
flow at a time. Attempts to use classical analyses to derive a network
configuration have shown that this approach is poorly suited to practical use
cases. Consider finding a delay-optimal routing configuration: one model had to
be created for each routing alternative, then each flow delay had to be
bounded, and then the bounds had to be compared to the given constraints. To
overcome this three-step process, we introduce Differential Network Calculus.
We extend NC to allow the differentiation of delay bounds w.r.t. to a wide
range of network parameters - such as flow paths or priority. This opens up NC
to a class of efficient nonlinear optimization techniques that exploit the
gradient of the delay bound. Our numerical evaluation on the routing and
priority assignment problem shows that our novel method can synthesize flow
paths and priorities in a matter of seconds, outperforming existing methods by
several orders of magnitude
Real-Time Performance of Industrial IoT Communication Technologies: A Review
With the growing need for automation and the ongoing merge of OT and IT,
industrial networks have to transport a high amount of heterogeneous data with
mixed criticality such as control traffic, sensor data, and configuration
messages. Current advances in IT technologies furthermore enable a new set of
automation scenarios under the roof of Industry 4.0 and IIoT where industrial
networks now have to meet new requirements in flexibility and reliability. The
necessary real-time guarantees will place significant demands on the networks.
In this paper, we identify IIoT use cases and infer real-time requirements
along several axes before bridging the gap between real-time network
technologies and the identified scenarios. We review real-time networking
technologies and present peer-reviewed works from the past 5 years for
industrial environments. We investigate how these can be applied to
controllers, systems, and embedded devices. Finally, we discuss open challenges
for real-time communication technologies to enable the identified scenarios.
The review shows academic interest in the field of real-time communication
technologies but also highlights a lack of a fixed set of standards important
for trust in safety and reliability, especially where wireless technologies are
concerned.Comment: IEEE Internet of Things Journal 2023 | Journal article DOI:
10.1109/JIOT.2023.333250
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