2,859 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
Statistical Delay Bound for WirelessHART Networks
In this paper we provide a performance analysis framework for wireless
industrial networks by deriving a service curve and a bound on the delay
violation probability. For this purpose we use the (min,x) stochastic network
calculus as well as a recently presented recursive formula for an end-to-end
delay bound of wireless heterogeneous networks. The derived results are mapped
to WirelessHART networks used in process automation and were validated via
simulations. In addition to WirelessHART, our results can be applied to any
wireless network whose physical layer conforms the IEEE 802.15.4 standard,
while its MAC protocol incorporates TDMA and channel hopping, like e.g.
ISA100.11a or TSCH-based networks. The provided delay analysis is especially
useful during the network design phase, offering further research potential
towards optimal routing and power management in QoS-constrained wireless
industrial networks.Comment: Accepted at PE-WASUN 201
On Cyclic Dependencies and Regulators in Time-Sensitive Networks
For time-sensitive networks, as in the context of
IEEE TSN and IETF Detnet, cyclic dependencies are associated
with certain fundamental properties such as improving availability
and decreasing reconfiguration effort. Nevertheless, the
existence of cyclic dependencies can cause very large latency
bounds or even global instability, thus making the proof of the
timing predictability of such networks a much more challenging
issue. Cyclic dependencies can be removed by reshaping
flows inside the network, by means of regulators. We consider
FIFO-per-class networks with two types of regulators: perflow
regulators and interleaved regulators (the latter reshape
entire flow aggregates). Such regulators come with a hardware
cost that is less for an interleaved regulator than for a perflow
regulator; both can affect the latency bounds in different
ways. We analyze the benefits of both types of regulators in
partial and full deployments in terms of latency. First, we
propose Low-Cost Acyclic Network (LCAN), a new algorithm
for finding the optimum number of regulators for breaking all
cyclic dependencies. Then, we provide another algorithm, Fixed-
Point Total Flow Analysis (FP-TFA), for computing end-to-end
delay bounds for general topologies, i.e., with and without cyclic
dependencies. An extensive analysis of these proposed algorithms
was conducted on generic grid topologies. For these test networks,
we find that FP-TFA computes small latency bounds; but, at
a medium to high utilization, the benefit of regulators becomes
apparent. At high utilization or for high line transmission-rates, a
small number of per-flow regulators has an effect on the latency
bound larger than a small number of interleaved regulators.
Moreover, interleaved regulators need to be placed everywhere
in the network to provide noticeable improvements. We validate
the applicability of our approaches on a realistic industrial timesensitive
network
Worst-case Delay Analysis of Time-Sensitive Networks with Deficit Round-Robin
In feed-forward time-sensitive networks with Deficit Round-Robin (DRR),
worst-case delay bounds were obtained by combining Total Flow Analysis (TFA)
with the strict service curve characterization of DRR by Tabatabaee et al. The
latter is the best-known single server analysis of DRR, however the former is
dominated by Polynomial-size Linear Programming (PLP), which improves the TFA
bounds and stability region, but was never applied to DRR networks. We first
perform the necessary adaptation of PLP to DRR by computing burstiness bounds
per-class and per-output aggregate and by enabling PLP to support non-convex
service curves. Second, we extend the methodology to support networks with
cyclic dependencies: This raises further dependency loops, as, on one hand, DRR
strict service curves rely on traffic characteristics inside the network, which
comes as output of the network analysis, and on the other hand, TFA or PLP
requires prior knowledge of the DRR service curves. This can be solved by
iterative methods, however PLP itself requires making cuts, which imposes other
levels of iteration, and it is not clear how to combine them. We propose a
generic method, called PLP-DRR, for combining all the iterations sequentially
or in parallel. We show that the obtained bounds are always valid even before
convergence; furthermore, at convergence, the bounds are the same regardless of
how the iterations are combined. This provides the best-known worst-case bounds
for time-sensitive networks, with general topology, with DRR. We apply the
method to an industrial network, where we find significant improvements
compared to the state-of-the-art
Worst-Case Timing Analysis of AeroRing- A Full Duplex Ethernet Ring for Safety-critical Avionics
Avionics implementation with less cables will clearly improve the efficiency of aircraft while reducing weight and maintenance costs. To fulfill these emerging needs, an innovative avionics communication architecture, based on Gigabit Full Duplex Ethernet ring, is proposed in this paper. To adapt this COTS technology to safety-critical avionics, an adequate tuning process of the communication protocol and the choice of reliability mechanisms to achieve timely and reliable communications are first detailed. Then, efficient timing analyses of such a proposal based on Network Calculus are conducted, accounting the impact of a ring topology and the specified reliability mechanisms. Third, these general analyses are illustrated in the case of a realistic avionic application, to replace the AFDX backup network with AeroRing, to reduce wires, while guaranteeing timely communications
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