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Dynamic Hierarchical Bandwidth Reservations for Switched Ethernet
Ref: CISTER-TR-181004       Publication Date: 5, May, 2018

Abstract:
Meeting system wide timeliness requirements within Cyber-Physical Systems (CPS) is a challenging task due to their typically complex networking infrastructure among other factors. Current communication technologies do not overcome this challenge, particularly when allowing adaptation of the system for efficient bandwidth usage. A component-based design approach can help coping with the network complexity by allowing composition of complex applications through the integration of independently developed adaptive components while maintaining their individual properties. In this context, network reservations are an important design element that favors composability in the time domain with online adaptation by providing temporal isolation. Based on these principles, we propose in this work a framework for supporting composability in Ethernet networks using ordinary COTS switches and the FTT-SE protocol. We dedicate particular attention to the worst-case response time analysis of messages transmitted within reservations. This analysis is a key element for guaranteed timeliness in an adaptive framework. In the first part of our work, we develop a new worst-case network delay analysis for sporadic reservations associated with asynchronous messages, which we call flat reservations, and assess its efficiency through extensive simulation. Our results show that our analysis is accurate, with an exact match for a significant percentage of messages in the message sets (up to 60% on average). Moreover, we were able to identify the regions in the system configuration where our analysis is accurate, thus providing a system designer with an indication of confidence in our analysis. When multiple applications co-exist in the system, flat reservations are not adequate to provide the desired level of isolation between different applications and to meet their timing requirements. For this reason, we resort to the Hierarchical Scheduling Framework (HSF), an important technique to achieve composability, particularly in the time domain as it allows reserving and partitioning the resources in multiple levels. Hence, in the second part of our work, we implement an HSF that enforces temporal properties of the partitions, using different reservation scheduling policies, namely polling and sporadic servers. Our results highlight the strong partitioning capabilities of our approach, with full temporal isolation across different hierarchical partitions. Finally, in the third part of our work, we provide a novel method to generate server interfaces that minimizes the servers bandwidth requirement. We validate the approach with extensive simulations using random message sets and hierarchies.

Zahid Iqbal

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