Service quality measurements for IPv6 inter-networks

Measurement-based performance evaluation of network traffic is becoming very important, especially for networks trying to provide differentiated levels of service quality to the different application flows. The non-identical response of flows to the different types of network-imposed performance degradation raises the need for ubiquitous measurement mechanisms, able to measure numerous performance properties, and being equally applicable to different applications and transports. This paper presents a new measurement mechanism, facilitated by the steady introduction of IPv6 in network nodes and hosts, which exploits native features of the protocol to provide support for performance measurements at the network (IP) layer. IPv6 Extension Headers have been used to carry the triggers involving the measurement activity and the measurement data in-line with the payload data itself, providing a high level of probability that the behaviour of the real user traffic flows is observed. End-to-end one-way delay, jitter, loss, and throughput have been measured for applications operating on top of both reliable and unreliable transports, over different-capacity IPv6 network configurations. We conclude that this technique could form the basis for future Internet measurements that can be dynamically deployed where and when required in a multi-service IP environment

A Reaction Plane Detector for PHENIX at RHIC

A plastic scintillator paddle detector with embedded fiber light guides and photomultiplier tube readout, referred to as the Reaction Plane Detector (RXNP), was designed and installed in the PHENIX experiment prior to the 2007 run of the Relativistic Heavy Ion Collider (RHIC). The RXNP's design is optimized to accurately measure the reaction plane (RP) angle of heavy-ion collisions, where, for mid-central $\sqrt{s_{NN}}$ = 200 GeV Au+Au collisions, it achieved a $2^{nd}$ harmonic RP resolution of $\sim$0.75, which is a factor of $\sim$2 greater than PHENIX's previous capabilities. This improvement was accomplished by locating the RXNP in the central region of the PHENIX experiment, where, due to its large coverage in pseudorapidity ($1.0<|\eta|<2.8$) and $\phi$ (2$\pi$), it is exposed to the high particle multiplicities needed for an accurate RP measurement. To enhance the observed signal, a 2-cm Pb converter is located between the nominal collision region and the scintillator paddles, allowing neutral particles produced in the heavy-ion collisions to contribute to the signal through conversion electrons. This paper discusses the design, operation and performance of the RXNP during the 2007 RHIC run.Comment: 28 authors from 10 institutions, 24 pages, 16 figures and 3 tables. Published in Nuclear Instruments and Methods in Physics Research Section

The Historical Perspective of the Problem of Interpersonal Comparisons of Utility

The starting-point of the article is the inconsistency between the established practice of acceptance in many cases, of economic policy (i.e. progressive taxation, national insurance policies) and the theoretical rejection of interpersonal comparisons of utility who see it as an unscientific value judgement. The inconsistency is explained by identifying three groups of theorists: (1) those who thought of comparability as a value judgement and unacceptable for economic policy considerations (positivists), (2) those who agreed with the positivists, on the normative nature of comparability but accepted it as a basis for economic policy, and (3) those who thought of it as part of a scientific economics. The implication was that, despite the dominance of positivist methodology in other sub-fields, the historical experience points to the difficulty of applying positivist methodology to the issue of comparability. If the inconsistency is thus due to the inappropriateness of the positivist approach, the only possible solution is the explicit abandonment of this approach at least in matters related to the collective aspects of economics

Space Telescope and Optical Reverberation Mapping Project. VII. Understanding the Ultraviolet Anomaly in NGC 5548 with X-Ray Spectroscopy

During the Space Telescope and Optical Reverberation Mapping Project observations of NGC 5548, the continuum and emission-line variability became decorrelated during the second half of the six-month-long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with the Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all three observations: the UV emission-line flux decrease, the soft-excess increase, and the emission-line anomaly

Space Telescope and Optical Reverberation Mapping Project. III. Optical Continuum Emission and Broad-band Time Delays in NGC 5548

Galaxie

An IPv6-based measurement infrastructure for assessing internet traffic behaviour

The ability to measure the service experienced by network traffic is becoming of major importance due to the widespread IP connectivity and hence the increased need for service management, as well as due to the candidacy of the Internet to provide a global telecommunications infrastructure, supporting a range of different services and traffic. New measurement paradigms are being urged by the need for IP to deliver for time critical applications and at the same time, they are facilitated by latest protocol deployments. In this manuscript we present a novel way of conducting network measurements for the Next Generation (IPv6-based) Internet, enabled by the universal network transport and systems programmability. We raise the extreme importance of making measurements in-line with the actual network traffic and henceforth revealing its actual properties. We are presenting our experiences after building a prototype implementation of one-way, end-to-end measurements on top of an IPv6 network setup. We describe the overall design of our solution, as well as some early results in measuring properties of real TCP applications, over both wired and wireless topologies. Using in-line measurements, we compute the absolute application goodput of different TCP services, and also model the packet sequence distribution of two FTP streams