Deutsche Telekom

About: Deutsche Telekom is a company organization based out in Welwyn Garden City, United Kingdom. It is known for research contribution in the topics: Telecommunications network & Signal. The organization has 3473 authors who have published 5208 publications receiving 65429 citations. The organization is also known as: DTAG & German Telecom.

Laterally tapered InP-InGaAsP waveguides for low-loss chip-to-fiber butt coupling: a comparison of different configurations

Abstract: Low-loss chip to-fiber coupling can be achieved by on-chip spot-size transformers. Two simple versions using laterally tapered InP-InGaAsP waveguides at the 1.55 /spl mu/m wavelength have been fabricated: one consisting of two differently tapered layers, the other with only one taper. The influence of the taper shape and of fabrication tolerances on their performance is compared both experimentally and theoretically. The optimum insertion loss for a single transformer without antireflection coating, including Fresnel losses, amounts to 1.1 dB. >

Bigfoot, sasquatch, the yeti and other missing links: what we don't know about the as graph

Abstract: Study of the Internet's high-level structure has for some time intrigued scientists. The AS-graph (showing interconnections between Autonomous Systems) has been measured, studied, modelled and discussed in many papers over the last decade. However, the quality of the measurement data has always been in question. It is by now well known that most measurements of the AS-graph are missing some set of links. Many efforts have been undertaken to correct this, primarily by increasing the set of measurements, but the issue remains: how much is enough? When will we know that we have enough measurements to be sure we can see all (or almost all) of the links. This paper aims to address the problem of estimating how many links are missing from our measurements. We use techniques pioneered in biostatistics and epidemiology for estimating the size of populations (for instance of fish or disease carriers). It is rarely possible to observe entire populations, and so sampling techniques are used. We extend those techniques to the domain of the AS-graph. The key difference between our work and the biological literature is that all links are not the same, and so we build a stratified model and specify an EM algorithm for estimating its parameters. Our estimates suggest that a very significant number of links (many of thousands) are missing from standard route monitor measurements of the AS-graph. Finally, we use the model to derive the number of monitors that would be needed to see a complete AS-graph with high-probability. We estimate that 700 route monitors would see 99.9% of links.

Reputation Systems for Self-Organized Networks

Abstract: Self-organized networks such as mobile ad-hoc, Internet-based peer-to-peer, wireless mesh and Fourth generation (4G) wireless networks depend on cooperation of nodes. Reputation systems help nodes decide with whom to cooperate and which nodes to avoid. They have been studied and applied almost separately in diverse disciplines such as economics, computer science, and social science, resulting in effort duplication and inconsistent terminology. We aim to bring together these efforts by outlining features and fundamental questions common to reputation systems in general. We derive methodologies to address these questions for both reputation system design and research from our own experiences and evaluations by simulation and analytical modeling. We argue for using deviation tests, discounting, passing on only first-hand information, introducing secondary response, and stressing the importance of identity.

Low-Complexity Iris Coding and Recognition Based on Directionlets

Abstract: A novel iris recognition method is presented. In the method, the iris features are extracted using the oriented separable wavelet transforms (directionlets) and they are compared in terms of a weighted Hamming distance. The feature extraction and comparison are shift-, size-, and rotation-invariant to the location of iris in the acquired image. The generated iris code is binary, whose length is fixed (and therefore commensurable), independent of the iris image, and comparatively short. The novel method shows a good performance when applied to a large database of irises and provides reliable identification and verification. At the same time, it preserves conceptual and computational simplicity and allows for a quick analysis and comparison of iris samples.

Method of determining toll charges for vehicles using a traffic route

Abstract: In the proposed method of determining toll charges for vehicles using a traffic route, a radiolocation system is used to compare a vehicle's geographical location continuously with the geographical location of virtual collection points The virtual collection points are formed by data acquisition sectors extending over predetermined distances in the direction of each route