Distributed real-time systems require predictable networks to exchange application data within bounded delays. Switched Ethernet is an attractive networking technology for distributed real-time systems. However, Ethernet devices require special coordination mechanisms to support real-time traffic because of their inherent competitive approach. Real-Time Ethernet (RTE) protocols aim at providing amendments to standard Ethernet to ensure latency guarantees and in-order delivery of real-time data, while keeping compatibility with Commercial-Off-The-Shelf (COTS) infrastructure tailored for high-bandwidth best-effort traffic.
This demonstrator highlights results from our work on Atacama, a comprehensive framework for mixed-criticality communication on multi-hop Ethernet networks. Atacama is the first solution for real-time Ethernet providing an open-source FPGA-based hardware implementation to enable rapid prototyping and experimental validation. Source code and documentation about the synthesizable modules and configuration tools are available for researchers to modify and build upon.
CPS Week 2013 Tutorial Description: Atacama: An Open Research Platform for Mixed-Criticality Real-time Switched Ethernet
The case study showcases a real-time video streaming application over a multi-hop network. Video lines travel from a video source to a remote display across multiple switches using a buffer-less communication scheme. Correct assembling and displaying of the video requires strict periodicity and tight synchronization between source and destination display. The latest prototypes of our enhanced NICs and switches deliver a highly predictable end-to-end latency for scheduled traffic over 1 Gbit/s links, reporting an unprecedented jitter of 8 ns per PHY in the path (close to the physical limit). Other demonstrated properties include robustness against unscheduled (best-effort) traffic, on-the-fly allocation of real-time bandwidth, and segmentation of real-time domains within large networks.
All the infrastructure used in the experiments below is available as an open-source package, making all results repeatable and verifiable.
A document summarizing the main properties of the framework and an intuitive description of the experimental setup used for the evaluations is available here.
The first experiment illustrates the low latency and jitter achieved with scheduled real-time frames, and the robustness against injection of unscheduled best-effort frames.
The second experiment illustrates the dynamic allocation of real-time bandwith depending on the content of the transmitted data: