3,862 research outputs found
Stability and performance guarantees in networks with cyclic dependencies
With the development of real-time networks such as reactive embedded systems, there is a need to compute deterministic performance bounds. This paper focuses on the performance guarantees and stability conditions in networks with cyclic dependencies in the network calculus framework. We first propose an algorithm that computes tight backlog bounds in tree networks for any set of flows crossing a server. Then, we show how this algorithm can be applied to improve bounds from the literature fir any topology, including cyclic networks. In particular, we show that the ring is stable in the network calculus framework
Community Detection via Semi-Synchronous Label Propagation Algorithms
A recently introduced novel community detection strategy is based on a label
propagation algorithm (LPA) which uses the diffusion of information in the
network to identify communities. Studies of LPAs showed that the strategy is
effective in finding a good community structure. Label propagation step can be
performed in parallel on all nodes (synchronous model) or sequentially
(asynchronous model); both models present some drawback, e.g., algorithm
termination is nor granted in the first case, performances can be worst in the
second case. In this paper, we present a semi-synchronous version of LPA which
aims to combine the advantages of both synchronous and asynchronous models. We
prove that our models always converge to a stable labeling. Moreover, we
experimentally investigate the effectiveness of the proposed strategy comparing
its performance with the asynchronous model both in terms of quality,
efficiency and stability. Tests show that the proposed protocol does not harm
the quality of the partitioning. Moreover it is quite efficient; each
propagation step is extremely parallelizable and it is more stable than the
asynchronous model, thanks to the fact that only a small amount of
randomization is used by our proposal.Comment: In Proc. of The International Workshop on Business Applications of
Social Network Analysis (BASNA '10
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
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
Diffusion Adaptation Strategies for Distributed Estimation over Gaussian Markov Random Fields
The aim of this paper is to propose diffusion strategies for distributed
estimation over adaptive networks, assuming the presence of spatially
correlated measurements distributed according to a Gaussian Markov random field
(GMRF) model. The proposed methods incorporate prior information about the
statistical dependency among observations, while at the same time processing
data in real-time and in a fully decentralized manner. A detailed mean-square
analysis is carried out in order to prove stability and evaluate the
steady-state performance of the proposed strategies. Finally, we also
illustrate how the proposed techniques can be easily extended in order to
incorporate thresholding operators for sparsity recovery applications.
Numerical results show the potential advantages of using such techniques for
distributed learning in adaptive networks deployed over GMRF.Comment: Submitted to IEEE Transactions on Signal Processing. arXiv admin
note: text overlap with arXiv:1206.309
Collaborative Engineering Environments. Two Examples of Process Improvement
Companies are recognising that innovative processes are determining factors in competitiveness. Two examples from projects in aircraft development describe the introduction of collaborative engineering environments as a way to improve engineering processes. A multi-disciplinary simulation environment integrates models from all disciplines involved in a common functional structure. Quick configuration for specific design problems and powerful feedback / visualisation capabilities enable engineering teams to concentrate on the integrated behaviour of the design. An engineering process management system allows engineering teams to work concurrently in tasks, following a defined flow of activities, applying tools on a shared database. Automated management of workspaces including data consistency enables engineering teams to concentrate on the design activities. The huge amount of experience in companies must be transformed for effective application in engineering processes. Compatible concepts, notations and implementation platforms make tangible knowledge like models and algorithms accessible. Computer-based design management makes knowledge on engineering processes and methods explicit
- âŠ