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1. Recorp: Receiver-Oriented Policies for Industrial Wireless Networks

   https://doi.org/10.1109/IoTDI49375.2020.00020  

   Brummet, Ryan; Chipara, Octav; Herman, Ted (April 2020, 2020 IEEE/ACM Fifth International Conference on Internet-of-Things Design and Implementation (IoTDI))

   The next generation of Industrial Internet-of-Things (IIoT) systems will require wireless solutions to connect sensors, actuators, and controllers as part of feedback-control loops over real-time flows. A key challenge in such networks is to provide predictable performance and adaptability to variations in link quality. We address this challenge by developing Receiver Oriented Policies (RECORP), which leverages the stability of IIoT workloads to build a solution that combines offline policy synthesis and run-time adaptation. Compared to schedules that service a single flow in a slot, RECORP policies share slots among multiple flows by assigning a coordinator and a set of candidate flows in the same slot. At run-time, the coordinator will dynamically execute one of the flows depending on what flows the coordinator has already received. The net effect of this strategy is that a node can dynamically repurpose the retransmissions remaining after receiving the data of an incoming flow to service other incoming flows opportunistically. Therefore, the flows that are executed in a slot can be adapted in response to the variable link conditions observed at run-time. Furthermore, RECORP also provides predictable performance: a policy meets the end-to-end reliability and deadline constraints of flows given probabilistic link qualities. When RECORP policies and schedules are configured to meet the same end-to-end reliability target of 99%, larger-scale multihop simulations show that across typical IIoT workloads, policies provided a median improvement of 1.63 to 2.44 times in real-time capacity as well as a median reduction of 1.45 to 2.43 times in worst-case latency. 

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2. A Flexible Retransmission Policy for Industrial Wireless Sensor Actuator Networks

   https://doi.org/10.1109/ICII.2018.00017  

   Brummet, Ryan; Gunatilaka, Dolvara; Vyas, Dhruv; Chipara, Octav; Lu, Chenyang (October 2018, 2018 IEEE International Conference on Industrial Internet (ICII))

   Real-time and reliable communication is essential for industrial wireless sensor-actuator networks. To this end, researchers have proposed a wide range of transmission scheduling techniques. However, these methods usually employ a link-centric policy which allocates a fixed number of retransmissions for each link of a flow. The lack of flexibility of this approach is problematic because failures do not occur uniformly across links and link quality changes over time. In this paper, we propose a flow-centric policy to flexibly and dynamically reallocate retransmissions among the links of a multi-hop flow at runtime. This contribution is complemented by a method for determining the number of retransmissions necessary to achieve a user-specified reliability level under two failures models that capture the common wireless properties of industrial environments. We demonstrate the effectiveness of flow centric policies using empirical evaluations and trace-driven simulations. Testbed experiments indicate a flow-centric policy can provide higher reliability than a link-centric policy because of its flexibility. Trace-driven experiments compare link-centric and flow-centric policies under the two reliability models. Results indicate that when the two approaches are configured to achieve the same reliability level, a flow-centric approach increases the median real-time capacity by as much as 1.42 times and reduces the end-to-end response times by as much as 2.63 times. 

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3. WARP: On-the-fly Program Synthesis for Agile, Real-time, and Reliable Wireless Networks

   https://doi.org/10.1145/3412382.3458270  

   Brummet, Ryan; Hossain, Md Kowsar; Chipara, Octav; Herman, Ted; Goddard, Steve (May 2021, Proceedings of the 20th International Conference on Information Processing in Sensor Networks)

   null (Ed.)

   Emerging Industrial Internet-of-Things systems require wireless solutions to connect sensors, actuators, and controllers as part of high data rate feedback-control loops over real-time flows. A key challenge is to provide predictable performance and agility in response to fluctuations in link quality, variable workloads, and topology changes. We propose WARP to address this challenge. WARP uses programs to specify a network’s behavior and includes a synthesis procedure to automatically generate such programs from a high-level specification of the system’s workload and topology. WARP has three unique features: (1) WARP uses a domain-specific language to specify stateful programs that include conditional statements to control when a flow’s packets are transmitted. The execution paths of programs depend on the pattern of packet losses observed at runtime, thereby enabling WARP to readily adapt to packet losses due to short-term variations in link quality. (2) Our synthesis technique uses heuristics to improve network performance by considering multiple packet loss patterns and associated execution paths when determining the transmissions performed by nodes. Furthermore, the generated programs ensure that the likelihood of a flow delivering its packets by its deadline exceeds a user-specified threshold. (3) WARP can adapt to workload and topology changes without explicitly reconstructing a network’s program based on the observation that nodes can independently synthesize the same program when they share the same workload and topology information. Simulations show that WARP improves network throughput for data collection, dissemination, and mixed workloads on two realistic topologies. Testbed experiments show that WARP reduces the time to add new flows by 5 times over a state-of-the-art centralized control plane and guarantees the real-time and reliability of all flows. 

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4. From Schedules to Programs — Reimagining Networking Infrastructure for Future Cyber-Physical Systems

   https://doi.org/10.1145/3491371.3491387  

   Hossain, Md Kowsar; Brummet, Ryan; Chipara, Octav; Herman, Ted; Goddard, Steve (December 2021, 8th NSysS 2021: 8th International Conference on Networking, Systems and Security)

   Future cyber-physical systems will require higher capacity, meet more stringent real-time requirements, and adapt quickly to a broader range of network dynamics. However, the traditional approach of using fixed schedules to drive the operation of wireless networks has inherent limitations that make it unsuitable for these systems. As an alternative, we propose to replace schedules with domain-specific programs that coordinate the operation of the network. Our idea is that nodes in the network will run automatically generated programs that make informed decisions about flows at run time rather than using an a priori fixed schedule. We will sketch a domain-specific language that uses this additional flexibility to increase network capacity significantly. Furthermore, the constructed programs are also sufficiently simple to efficiently analyze key performance metrics such as flow response time and reliability. We conclude with future research directions. 

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5. APaS: An Adaptive Partition-Based Scheduling Framework for 6TiSCH Networks

   https://doi.org/10.1109/RTAS52030.2021.00033  

   Wang, Jiachen; Zhang, Tianyu; Shen, Dawei; Hu, Xiaobo Sharon; Han, Song (May 2021, the 27th IEEE Real-Time and Embedded Technology and Applications Symposium (RTAS))

   null (Ed.)

   The past decade has witnessed the rapid development of real-time wireless technologies and their wide adoption in various industrial Internet-of-Things (IIoT) applications. Among those wireless technologies, 6TiSCH is a promising candidate as the de facto standard due to its nice feature of gluing a real-time link-layer standard (802.15.4e, for offering deterministic communication performance) together with an IP-enabled upper-layer stack (for seamlessly supporting Internet services). 6TiSCH's built-in random slot selection scheduling algorithm, however, often leads to large and unbounded transmission latency, thus can hardly meet the real-time requirements of IIoT applications. This paper proposes an adaptive partition based scheduling framework, APaS, for 6TiSCH networks. APaS introduces the concept of resource partitioning into 6TiSCH network management. Instead of allocating network resources to individual devices, APaS partitions and assigns network resources to different groups of devices based on their layers in the network so as to guarantee that the transmission latency of any end-toend flow is within one slotframe length. APaS also employs a novel online partition adjustment method to further improve its adaptability to dynamic network topology changes. The effectiveness of APaS is validated through both simulation and testbed experiments on a 122-node multi-hop 6TiSCH network. 

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