On the Necessity for High-availability Data Center Backends in a Distributed Wireless System

When business processes depend on the processing capabilities within a data center, the typical system architecture use a high-availability setup to maintain a high level of service. Faced with a specific machine-to-machine system consisting of many endpoints that collect and forward data to the data center we argue that the dependability of the overall system does not necessitate a high level of service for the data center components. Taking an existing discrete event simulation model of a distributed technical system we investigate and discuss the effects of prolonged outages of the data center on the major business processes of the system

Modeling the GPRS Network Latency with a Double Pareto-lognormal or a Generalized Beta Distribution

Taking a newly collected large data set on the TCP connection termination latency in GPRS networks we try to identify the underlying statistical distribution. The data extends the observed latencies to large time scales necessitating a heavy-tail distribution. Many distributions work well for the main body of the data. However, the heavy tail of the distribution benefits from mixing different statistical distributions. We compare several distributions and find that the double Pareto-lognormal distribution and the generalized Beta distribution of the second kind fit the data equally well

Network-wide Measurement of TCP RTT in 2G Networks

We analyze existing server-side log data of a large scale automatic toll system to measure the TCP round-trip-time (RTT) as experienced by the communication between the central system and the on-board units (OBUs) deployed for tolling heavy-goods vehicles. The RTT is estimated from passive monitoring by parsing server-side log files and aggregating fleet-wide statistics over time. Using this data we compare the characteristics of the four different types of OBU and the three GPRS (2G) networks used. We find the RTT data to be consistent with existing, smaller samples and extend the observed RTT range by an order of magnitude. The OBU types exhibit a markedly different behavior, most notably for long RTTs, and we find one of the 2G networks to -˜hum’ at 50 Hz and harmonics

Network-Wide Measurement of GPRS Bandwidth and Latency

Complementing a recently collected large data set on the TCP connection termination latency in GPRS networks we analyze server-side log data generated in a large scale automatic toll system to observe the network bandwidth. After a recent architectural change the on-board units (OBUs) record GPS tracks and transmit track data to the central system for processing rather than transmitting the toll data after local processing. The bandwidth in upload direction is estimated from the server-side log entries and corrected for the network latency. The data collected allows comparing the performance of seven types of OBUs in three GPRS networks over time. While the three networks differ in the average bandwidth offered, the biggest performance impact is the OBU type where modems with the same specification yield different upload rates. In addition we update the GPRS network latency data by fitting two statistical distributions, improving markedly on the prior results

Implementation funktionaler Programmiersprachen durch Quelltexttransformation

Die Dissertation liefert einen Beitrag zur Entwicklung von Compilern funktionaler Sprachen zur Erzeugung von Zielcode in einer höheren prozeduralen Programmiersprache. In der Dissertation werden mehrere Implementationstechniken funktionaler Sprachen analysiert, wobei für jede Technik ein Verfahren zur Realisierung eines auf der Übersetzung in eine prozedurale Sprache basierenden Compilers angegeben wird. Durch die verschiedenen Implementationsverfahren, die in der Arbeit analysiert bzw. definiert wurden, sind die beiden großen Klassen funktionaler Sprachen abgedeckt worden: strikte und nicht-strikte funktionale Programmiersprachen. Die Dissertation kann in drei größere Teile gegliedert werden, die sich mit folgenden Bereichen beschäftigen: Direkte übersetzungen funktionaler in prozedurale Programmiersprachen Übersetzung des Codes der abstrakten SECD-Maschine in eine prozedurale Sprache Erzeugung des Zielcodes in einer prozeduralen Programmiersprache bei Graph-Reduktion-basierten Implementationstechniken. Im ersten Teil, dem Schwerpunkt der Arbeit, wird eine über existierende Ansätze hinausgehende Transformation einer einfachen strikten funktionalen Programmiersprache (erweiterter Lambda-Kalkül) in den Code einer prozeduralen Zielsprache eingeführt und durch ein formales System von Transformationsregeln beschrieben. Die Transformation zeichnet sich durch Transparenz und Einfachheit (Erzeugung minimalen Codes) aus. Im zweiten und dritten Teil werden die aus der Literatur bekannten Implementationstechniken modifiziert bzw. optimiert, um Zielprogramme in einer höheren prozeduralen Programmiersprache erzeugen zu können.This work contributes methods for the design and implementation of translation schemes for functional programming languages with procedural programming languages as a target. The dissertation analyzes different implementation techniques of functional languages. For each technique an approach is defined for the implementation of a compiler that translates the functional source language into a procedural target language. The analyzed techniques cover both classes of functional languages, strict and non-strict ones. The work is structured into three parts with the following topics: direct translation of functional programming languages into procedural programming languages; translation of the code of the SECD-abstract machine into a procedural language; emission of a target code in a procedural language by graph-reduction-based implementation techniques. In the first part, we give a formal definition for translating a simple functional language (syntacticly sugared lambda calculus) into the code of a procedural programming language. The defined transformation is simple and transparent. In the second and the third part, existing translation schemes are modified, i. e. two known implementation techniques are optimized to emit target code in an procedural language

The Rendezvous is Dead -- Long Live the Protected Object

This paper outlines the short-comings of rendezvous and the advantages of protected objects as a means of synchronization in Ada 95. A common Ada benchmark suite, ACES, gives the misleading impression that protected objects are cheaper per se. This work shows that the main benefit of protected objects stems from the potential to reduce the number of context switches. Based on the latter observation, a general model to translate rendezvous into protected objects is developed. This model is further refined to replace entire server tasks that make calls to or accept rendezvous. A quantitative evaluation shows the benefits of protected objects for each approach and illustrates that the number of context switches can be reduced at least by 50% when tasks with rendezvous are replaced by protected objects resulting in significant execution time savings for applications requiring many synchronizations. 1 Introduction In a concurrent language entities for threaded execution (tasks) and method..

A Study of Evaluation Order Semantics in Expressions with Side Effects

The presence of side effects in even a very simple language of expressions gives rise to a number of semantic questions. The issue of evaluation order becomes a crucial one and, unless a specific order is enforced, the language becomes non-deterministic. In this paper we study the denotational semantics of such a language under a variety of possible evaluation strategies, from simpler to more complex, concluding with unspecified evaluation order, unspecified order of side effects and the mechanism of sequence points that is particular to the ANSI C programming language. In doing so, we adopt a dialect of Haskell as a metalanguage, instead of mathematical notation, and use monads and monad transformers to improve modularity. In this way, only small modifications are required for each transition. The result is a better understanding of different evaluation strategies and a unified way of specifying their semantics. Furthermore, a significant step is achieved towards a complete and accurate semant..