Emulating opportunistic networks with KauNet Triggers

In opportunistic networks the availability of an end-to-end path is no longer required. Instead opportunistic networks may take advantage of temporary connectivity opportunities. Opportunistic networks present a demanding environment for network emulation as the traditional emulation setup, where application/transport endpoints only send and receive packets from the network following a black box approach, is no longer applicable. Opportunistic networking protocols and applications additionally need to react to the dynamics of the underlying network beyond what is conveyed through the exchange of packets. In order to support IP-level emulation evaluations of applications and protocols that react to lower layer events, we have proposed the use of emulation triggers. Emulation triggers can emulate arbitrary cross-layer feedback and can be synchronized with other emulation effects. After introducing the design and implementation of triggers in the KauNet emulator, we describe the integration of triggers with the DTN2 reference implementation and illustrate how the functionality can be used to emulate a classical DTN data-mule scenario

Autonomous Algorithms for Centralized and Distributed Interference Coordination: A Virtual Layer Based Approach

Interference mitigation techniques are essential for improving the performance of interference limited wireless networks. In this paper, we introduce novel interference mitigation schemes for wireless cellular networks with space division multiple access (SDMA). The schemes are based on a virtual layer that captures and simplifies the complicated interference situation in the network and that is used for power control. We show how optimization in this virtual layer generates gradually adapting power control settings that lead to autonomous interference minimization. Thereby, the granularity of control ranges from controlling frequency sub-band power via controlling the power on a per-beam basis, to a granularity of only enforcing average power constraints per beam. In conjunction with suitable short-term scheduling, our algorithms gradually steer the network towards a higher utility. We use extensive system-level simulations to compare three distributed algorithms and evaluate their applicability for different user mobility assumptions. In particular, it turns out that larger gains can be achieved by imposing average power constraints and allowing opportunistic scheduling instantaneously, rather than controlling the power in a strict way. Furthermore, we introduce a centralized algorithm, which directly solves the underlying optimization and shows fast convergence, as a performance benchmark for the distributed solutions. Moreover, we investigate the deviation from global optimality by comparing to a branch-and-bound-based solution.Comment: revised versio

Code of Best Practices in Fair Use for the Visual Arts

This Code of Best Practices provides visual-arts professionals with a set of principles addressing best practices in the fair use of copyrighted materials. It describes how fair use can be invoked and implemented when using copyrighted materials in scholarship, teaching, museums, archives, and in the creation of art.The Code addresses the following five questions:Analytic Writing: When may scholars and other writers about art invoke fair use to quote, excerpt, or reproduce copyrighted works?Teaching about Art: When may teachers invoke fair use in using copyrighted works to support formal instruction in a range of settings, including online and distance teaching?Making Art: Under what circumstances may artists invoke fair use to incorporate copyrighted material into new artworks in any medium?Museum Uses: When may museums and their staffs invoke fair use in using copyrighted works -- including images and text as well as time-based and born-digital material -- when organizing exhibitions, developing educational materials (within the museum and online), publishing catalogues, and other related activities?Online Access to Archival and Special Collections: When may such institutions and their staffs invoke fair use to create digital preservation copies and/or enable digital access to copyrighted materials in their collections