Bachelor-Seminar Connected and Mobile Systems

The mathematician Dietrich Braess described the paradox that adding an additional link in a traffic scenario can cause a decrease in network performance. This counter-intuitive result has been recently discussed for routing algorithms. Thus, the task for this work is to describe Braess's paradox and recent findings concerning Braess's paradox and routing algorithms. Moreover, a connection to multi-connectivity (MC) in routing shall be drawn. MC is a technique that intentionally creates multiple communication paths to improve network performance. However, works have also demonstrated performance degradation due to MC. Therefore, a possible connection between Braess's paradox and performance degradation due to MC shall be investigated based on a literature review.

• Brass's paradox explained by Veritasium (starting from 6:30)
• Über ein Paradoxon aus der Verkehrsplanung (German)
• On Braess's paradox and routing algorithms
• Wardrop equilibrium and Braess's paradox for varying demand
• Connected papers for related work

Most modern wireless communication infrastructure follows a similar design paradigm: User devices can connect to th infrastructure through an infrastructure devices, commonly referred to as the access point. These devices not only act as a bridge between the wireless and the wired world, but also manage the wireless properties of all connected user devices. While this paradigm brings many benefits, like spatial reuse of frequencies, it also has one major flaw: It introduces critical infrastructure.

Should the functionality of the access point be disrupted, e.g. due to natural catastrophes, human failure or cyber attacks, devices that were previously connect to the disrupted access point need to find another method to connect to the network. While in most cases the neighboring access points may provide sufficient coverage of the area, there is the risk that certain zones are unreachable by them. This results in areas, which are completly cut of from radio communication. This is especially cire in cases, wherein the radio communication is required for critical services like emergency calls. Therefore, a solution is required to circumvent this major design flaw.

Your task is to provide an overview of different approaches that try to reduce the impact of access point failures. For each approach you present, you should discuss the type of disruption the authors are targeting, e.g. hardware failure, natural catastrophe, cyber attacks, etc., and their approach to repairing the network. Afterwards you should compare the different works and outline the differences in their design philosophies.

• Multi-Hop D2D Framework for Disaster-Resilient Communication Network
• Always Connected Things: Building Disaster Resilience IoT Communications

Many networks require some sort of time synchronization in order to achieve efficient scheduling and conserve energy. Manipulating local time is usually not considered a security threat, as most applications use the system clock to acquire time, which is handled by the Operating System (OS). However, some security mechanism are based on accurate timing like Time based One-Time Passwords (TOTPs). Thus, changing the local time or announcing faulty clocks to specific network participants could result in Denial Of Service (DOS) attacks.

Your task consists of an extensive literature research on the development of time synchronization in traditional networks, ad-hoc low-power networks and similar. Afterwards you will have to compare your findings, put them in context and present the challenges and missing links for them. A special focus should also be put into the research on security mechanisms in these networks.

• Wireless Clock Synchronization: A Comprehensive Survey and Taxonomy
• Delay Measured Time Synchronization Protocol with Skew Detection in RIOT OS