@phdthesis{Stauffert2022,
  author    = {Stauffert, Jan-Philipp},
  title     = {Temporal Confounding Effects in Virtual and Extended Reality Systems},
  doi       = {10.25972/OPUS-29060},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-290609},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Latency is an inherent problem of computing systems. Each computation takes time until the result is available. Virtual reality systems use elaborated computer resources to create virtual experiences. The latency of those systems is often ignored or assumed as small enough to provide a good experience. This cumulative thesis is comprised of published peer reviewed research papers exploring the behaviour and effects of latency. Contrary to the common description of time invariant latency, latency is shown to fluctuate. Few other researchers have looked into this time variant behaviour. This thesis explores time variant latency with a focus on randomly occurring latency spikes. Latency spikes are observed both for small algorithms and as end to end latency in complete virtual reality systems. Most latency measurements gather close to the mean latency with potentially multiple smaller clusters of larger latency values and rare extreme outliers. The latency behaviour differs for different implementations of an algorithm. Operating system schedulers and programming language environments such as garbage collectors contribute to the overall latency behaviour. The thesis demonstrates these influences on the example of different implementations of message passing. The plethora of latency sources result in an unpredictable latency behaviour. Measuring and reporting it in scientific experiments is important. This thesis describes established approaches to measuring latency and proposes an enhanced setup to gather detailed information. The thesis proposes to dissect the measured data with a stacked z-outlier-test to separate the clusters of latency measurements for better reporting. Latency in virtual reality applications can degrade the experience in multiple ways. The thesis focuses on cybersickness as a major detrimental effect. An approach to simulate time variant latency is proposed to make latency available as an independent variable in experiments to understand latency's effects. An experiment with modified latency shows that latency spikes can contribute to cybersickness. A review of related research shows that different time invariant latency behaviour also contributes to cybersickness.},
  subject      = {Virtuelle Realit{\"a}t},
  language  = {en}
}
@techreport{GrigorjewMetzgerHossfeldetal.2020,
  author    = {Grigorjew, Alexej and Metzger, Florian and Hoßfeld, Tobias and Specht, Johannes and G{\"o}tz, Franz-Josef and Schmitt, J{\"u}rgen and Chen, Feng},
  title     = {Technical Report on Bridge-Local Guaranteed Latency with Strict Priority Scheduling},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-198310},
  year      = {2020},
  abstract  = {Bridge-local latency computation is often regarded with caution, as historic efforts with the Credit-Based Shaper (CBS) showed that CBS requires network wide information for tight bounds. Recently, new shaping mechanisms and timed gates were applied to achieve such guarantees nonetheless, but they require support for these new mechanisms in the forwarding devices. This document presents a per-hop latency bound for individual streams in a class-based network that applies the IEEE 802.1Q strict priority transmission selection algorithm. It is based on self-pacing talkers and uses the accumulated latency fields during the reservation process to provide upper bounds with bridge-local information. The presented delay bound is proven mathematically and then evaluated with respect to its accuracy. It indicates the required information that must be provided for admission control, e.g., implemented by a resource reservation protocol such as IEEE 802.1Qdd. Further, it hints at potential improvements regarding new mechanisms and higher accuracy given more information.},
  subject      = {Echtzeit},
  language  = {en}
}
@techreport{GrigorjewMetzgerHossfeldetal.2020,
  author    = {Grigorjew, Alexej and Metzger, Florian and Hoßfeld, Tobias and Specht, Johannes and G{\"o}tz, Franz-Josef and Chen, Feng and Schmitt, J{\"u}rgen},
  title     = {Asynchronous Traffic Shaping with Jitter Control},
  doi       = {10.25972/OPUS-20582},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-205824},
  pages     = {8},
  year      = {2020},
  abstract  = {Asynchronous Traffic Shaping enabled bounded latency with low complexity for time sensitive networking without the need for time synchronization. However, its main focus is the guaranteed maximum delay. Jitter-sensitive applications may still be forced towards synchronization. This work proposes traffic damping to reduce end-to-end delay jitter. It discusses its application and shows that both the prerequisites and the guaranteed delay of traffic damping and ATS are very similar. Finally, it presents a brief evaluation of delay jitter in an example topology by means of a simulation and worst case estimation.},
  subject      = {Echtzeit},
  language  = {en}
}