465 research outputs found
An Optimal Trade-off between Content Freshness and Refresh Cost
Caching is an effective mechanism for reducing bandwidth usage and
alleviating server load. However, the use of caching entails a compromise
between content freshness and refresh cost. An excessive refresh allows a high
degree of content freshness at a greater cost of system resource. Conversely, a
deficient refresh inhibits content freshness but saves the cost of resource
usages. To address the freshness-cost problem, we formulate the refresh
scheduling problem with a generic cost model and use this cost model to
determine an optimal refresh frequency that gives the best tradeoff between
refresh cost and content freshness. We prove the existence and uniqueness of an
optimal refresh frequency under the assumptions that the arrival of content
update is Poisson and the age-related cost monotonically increases with
decreasing freshness. In addition, we provide an analytic comparison of system
performance under fixed refresh scheduling and random refresh scheduling,
showing that with the same average refresh frequency two refresh schedulings
are mathematically equivalent in terms of the long-run average cost
Age-Optimal Information Updates in Multihop Networks
The problem of reducing the age-of-information has been extensively studied
in the single-hop networks. In this paper, we minimize the age-of-information
in general multihop networks. If the packet transmission times over the network
links are exponentially distributed, we prove that a preemptive Last Generated
First Served (LGFS) policy results in smaller age processes at all nodes of the
network (in a stochastic ordering sense) than any other causal policy. In
addition, for arbitrary general distributions of packet transmission times, the
non-preemptive LGFS policy is shown to minimize the age processes at all nodes
of the network among all non-preemptive work-conserving policies (again in a
stochastic ordering sense). It is surprising that such simple policies can
achieve optimality of the joint distribution of the age processes at all nodes
even under arbitrary network topologies, as well as arbitrary packet generation
and arrival times. These optimality results not only hold for the age
processes, but also for any non-decreasing functional of the age processes.Comment: arXiv admin note: text overlap with arXiv:1603.0618
Blockchain technology into the logistics supply chain implementation effectiveness
Technologies currently have a tremendous impact on all spheres of economy, business and a state. They integrally change people’s conception of trade, property, and market entities interaction.
Artificial intelligence, additive, informationommunication, green technologies, biotechnologies, and blockchain technologies development and implementation confirm their leadership importance and inevitability in relation to the activities traditional approaches. In the modern world only the companies with flexible vision, equipment and technologies able to instantly reform, adapt to new conditions and challenges, will benefit. The point at issue is Industry 4.0 as a new technological mode emergence
Update or Wait: How to Keep Your Data Fresh
In this work, we study how to optimally manage the freshness of information
updates sent from a source node to a destination via a channel. A proper metric
for data freshness at the destination is the age-of-information, or simply age,
which is defined as how old the freshest received update is since the moment
that this update was generated at the source node (e.g., a sensor). A
reasonable update policy is the zero-wait policy, i.e., the source node submits
a fresh update once the previous update is delivered and the channel becomes
free, which achieves the maximum throughput and the minimum delay.
Surprisingly, this zero-wait policy does not always minimize the age. This
counter-intuitive phenomenon motivates us to study how to optimally control
information updates to keep the data fresh and to understand when the zero-wait
policy is optimal. We introduce a general age penalty function to characterize
the level of dissatisfaction on data staleness and formulate the average age
penalty minimization problem as a constrained semi-Markov decision problem
(SMDP) with an uncountable state space. We develop efficient algorithms to find
the optimal update policy among all causal policies, and establish sufficient
and necessary conditions for the optimality of the zero-wait policy. Our
investigation shows that the zero-wait policy is far from the optimum if (i)
the age penalty function grows quickly with respect to the age, (ii) the packet
transmission times over the channel are positively correlated over time, or
(iii) the packet transmission times are highly random (e.g., following a
heavy-tail distribution)
Change Rate Estimation and Optimal Freshness in Web Page Crawling
For providing quick and accurate results, a search engine maintains a local
snapshot of the entire web. And, to keep this local cache fresh, it employs a
crawler for tracking changes across various web pages. However, finite
bandwidth availability and server restrictions impose some constraints on the
crawling frequency. Consequently, the ideal crawling rates are the ones that
maximise the freshness of the local cache and also respect the above
constraints. Azar et al. 2018 recently proposed a tractable algorithm to solve
this optimisation problem. However, they assume the knowledge of the exact page
change rates, which is unrealistic in practice. We address this issue here.
Specifically, we provide two novel schemes for online estimation of page change
rates. Both schemes only need partial information about the page change
process, i.e., they only need to know if the page has changed or not since the
last crawled instance. For both these schemes, we prove convergence and, also,
derive their convergence rates. Finally, we provide some numerical experiments
to compare the performance of our proposed estimators with the existing ones
(e.g., MLE).Comment: This paper has been accepted to the 13th EAI International Conference
on Performance Evaluation Methodologies and Tools, VALUETOOLS'20, May 18--20,
2020, Tsukuba, Japan. This is the author version of the pape
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