Catalog Dynamics: Impact of Content Publishing and Perishing on the Performance of a LRU Cache

The Internet heavily relies on Content Distribution Networks and transparent caches to cope with the ever-increasing traffic demand of users. Content, however, is essentially versatile: once published at a given time, its popularity vanishes over time. All requests for a given document are then concentrated between the publishing time and an effective perishing time. In this paper, we propose a new model for the arrival of content requests, which takes into account the dynamical nature of the content catalog. Based on two large traffic traces collected on the Orange network, we use the semi-experimental method and determine invariants of the content request process. This allows us to define a simple mathematical model for content requests; by extending the so-called "Che approximation", we then compute the performance of a LRU cache fed with such a request process, expressed by its hit ratio. We numerically validate the good accuracy of our model by comparison to trace-based simulation.Comment: 13 Pages, 9 figures. Full version of the article submitted to the ITC 2014 conference. Small corrections in the appendix from the previous versio

Univariate Potential Output Estimations for Hungary

Potential output figures are important ingredients of many macroeconomic models and are routinely applied by policy makers and global agencies. Despite its widespread use, estimation of potential output is at best uncertain and depends heavily on the model. The task of estimating potential output is an even more dubious exercise for countries experiencing huge structural changes, such as transition countries. In this paper we apply univariate methods to estimate and evaluate Hungarian potential output, paying special attention to structural breaks. In addition to statistical evaluation, we also assess the appropriateness of various methods by expertise judgement of the results, since we argue that mechanical adoption of univariate techniques might led to erroneous interpretation of the business cycle. As all methods have strengths and weaknesses, we derive a single measure of potential output by weighting those methods that pass both the statistical and expertise criteria. As standard errors, which might be used for deriving weights, are not available for some of the methods, we base our weights on similar but computable statistics, namely on revisions of the output gap for all dates by recursively estimating the models. Finally, we compare our estimated gaps with the result of the only published Hungarian output gap measure of Darvas-Simon (2000b), which is based on an economic model.combination, detrending, output gap, revision.

Univariate Potential Output Estimations for Hungary

Potential output figures are important ingredients of many macroeconomic modelsand are routinely applied by policy makers and global agencies. Despite itswidespread use, estimation of potential output is at best uncertain and dependsheavily on the model. The task of estimating potential output is an even moredubious exercise for countries experiencing huge structural changes, such astransition countries. In this paper we apply univariate methods to estimate andevaluate Hungarian potential output, paying special attention to structural breaks.In addition to statistical evaluation, we also assess the appropriateness of variousmethods by expertise judgement of the results, since we argue that mechanicaladoption of univariate techniques might led to erroneous interpretation of thebusiness cycle. As all methods have strengths and weaknesses, we derive a singlemeasure of potential output by weighting those methods that pass both thestatistical and expertise criteria. As standard errors, which might be used forderiving weights, are not available for some of the methods, we base our weightson similar but computable statistics, namely on revisions of the output gap for alldates by recursively estimating the models. Finally, we compare our estimated gapswith the result of the only published Hungarian output gap measure of Darvas-Simon (2000b), which is based on an economic model.ombination, detrending, new EU members, OCA, output gap, revision