Current Research Interests

J. Liebeherr

Large-Scale Environmental Sensing on a Budget: Environmental sensing factors plays an important role in sustainability efforts. For instance, by monitoring soil conditions and evaporation on their fields, farmers can precisely tailor watering schedules, thereby preserving scarce water resources. Making such efforts practicable in rural areas of developing nations requires low-cost communication subsystems that can collect sensor data across large areas with low power requirements. We are developing LoRa mesh networks that can be scaled to a hundred nodes, covering a hundred or more square kilometers, at a cost of less than US$15 per node. A low-power design enables nodes to operate for years on two AA batteries in many sensing applications. Our LoRa mesh networks are self-organizing, in the sense that sensor nodes can be dynamically added to an existing network and the network self-heals after node failures, without central control or management. Our work on LoRa mesh networks has spawned projects on smart irrigation system, greenhouse gas monitoring, and community ecology.

More Information:

  • D. Wu, A. Bogdan, J. Liebeherr, "Large-Scale Environmental Sensing of Remote Areas on a Budget," IEEE Internet of Things Magazine, 6(2):130-136, June 2023.
    (Paper)   (DOI: 10.1109/IOTM.001.2200185)
  • D. Wu, J. Liebeherr, "A low-cost low-power LoRa mesh network for large-scale environmental sensing," IEEE Internet of Things Journal, 10(19):16700-16714, October 2023.
    (Paper)   (DOI: 10.1109/JIOT.2023.3270237)

Designing traffic control algorithms with Network Calculus: Recently, there has been a new surge of interest in shaping and scheduling algorithms, for several reasons. The specification of an Ultra-Reliable Low-Latency Communication (URLLC) service category for 5G networks, with guaranteed latencies below 1 ms, has raised the ante on traffic control algorithms. New standardization efforts in the IEEE for Layer-2 networks and in the IETF for Layer-3 networks define a compatible framework for traffic control algorithms with assured latency bounds in local and wide area networks. Second, large content providers that manage traffic within and between servers, clusters, and data centers rely on fine-grain traffic control at multiple levels of aggregation, which creates a need for new hierarchical scheduling and shaping mechanisms. An additional factor for the current interest in scheduling are new architectures for line rate switches with programmable packet schedulers that permit a customization of scheduling algorithms to application requirements. The necessity to adapt traffic control to the demands of applications motivates the search for novel algorithms and methods for scheduling. We seek to develop new traffic control algorithms that are based on the sound mathematical principles of the network calculus and that allow an efficient implementation in deployed systems. Doing so we seek to develop theoretical underpinnings for scheduling and shaping algorithms in modern communication networks. By also implementations of the developed scheduling and shaping methods, we want to close the gap between theory and application of traffic control algorithms.

More Information:

  • J. Liebeherr, "Duality of the Max-Plus and Min-Plus Network Calculus," Foundations and Trends in Networking, Vol. 11, No. 3-4, pp. 139-282, 2017.
  • J. Liebeherr, "A Fluid-Flow Interpretation of SCED Scheduling," Proceedings of International Workshop on Network Calculus and Applications (NetCal 2018), ITC-30, Vienna, September 2018.

Application-layer Internetworking: The explosive increase of network-enabled sensors, actuators, and other cyber-physical systems, referred to as the Internet of Things (IoT), together with the proliferation of proprietary network infrastructures that largely bypass the public Internet, requires new solutions for interconnecting large numbers of heterogeneous networks. We seek to develop an internetworking architecture that is based on selforganizing application-layer networks. Self-organizing means that devices use all their communication modalities to detect and establish connectivity with other devices to form a network. All nodes of an application-layer network participate in relaying data between sources and destinations of information. Application-layer internetworking refers to the interconnection of devices with attachment points in different network infrastructures at the level of application programs. The long-term goal is to explore the foundations of application-layer internetworking and develop new protocol solutions that enable and facilitate such internetworking. We address challenges of integrating low-power IoT devices into the novel internetworking architecture, and addresses scalable routing, resilience to failures, and network policies.
A major vehicle for developing, evaluating, and deploying solutions is an overlay network system, called HyperCast, that we have developed in my research group. HyperCast is an open source software system (of about 100,000 lines of code) for self-organizing application-layer overlay networks. Initially conceived for the empirical evaluation of large-scale reliable multicasting, the software has evolved into a programming platform for application-layer internetworking networks that accommodates different types of substrate networks and permits a variety of message semantics.

More Information:

  • J. Liebeherr, M. Valipour, T. Y. Zhao, "Elements of Application-layer Internetworking for Adaptive Self-organizing Networks," Proceedings of the IEEE, April 2019.
    (DOI: 10.1109/JPROC.2019.2894291)