Today, Ethernet is used primarily as an information network. However, there is a strong belief that some recent technological advances will enable its use in dependable applications with real-time requirements. One of the most common arguments that has been traditionally put forward against its use in real-time applications is that Ethernet has a non-deterministic access delay, leading to an unpredictable timing behaviour of the supported applications.
An important recent development concerning Ethernet technologies has been in the switching domain. Switches may provide a flexible and scalable solution to the problems and limitations inherent to traditional Ethernet networks. Mechanisms such as micro-segmentation, full-duplex operation (leading to a collision-free environment), traffic prioritisation, on-the-fly commutation, flow control or spanning-tree protocols are emerging features that create an eagerness to expand Ethernet responsibilities to support dependable applications with real-time requirements.
It is also foreseen that future real-time and dependable systems will be more evolutionary in nature, rather than the totally pre-designed ones, which are currently prevalent. Indeed, the design practices followed in current real-time systems are quite inadequate to address issues such as flexibility, adaptability, and reconfigurability.
Envisaging a communication infrastructure for flexible and reconfigurable computer systems, Ethernet switches may play a crucial role. Features such as dynamic switching, auto negotiation, automatic load balancing and Virtual LANs can be exploited to enable the dynamic behaviour of the computer system.
The CIDER (Communication Infrastructure for Dependable Evolvable Real-time systems) project will encompass two key objectives:
2. The use of Ethernet as an enabling technology for self-evolving dependable real-time systems (dynamic set of services and hosts).
For the support of self-evolving systems, extension of the schedulability analysis to encompass dynamic topologies and service migration will be performed. This will demand the evaluation of admission control and online scheduling techniques. Although results are available concerning on-line scheduling algorithms, these most times consider slot-shifting approaches (to have time-bounded online algorithms), which are inappropriate for Ethernet-based networks. The expected results will constitute a basis for addressing issues such as flexibility, adaptability and reconfigurability in self-evolving dependable real-time systems.
A prototype will be developed to experimentally validate the proposed methodologies.
1. The use of Ethernet technologies for supporting current dependable real-time systems (typically composed by a fixed set of services and hosts);
For the support of current systems, analytical models for the schedulability analysis of real-time communication will be developed. The expected results are foreseen to constitute an important contribution to the state of the art. Until now, most R&D work related to the use of Ethernet technologies in real-time applications has been focusing either on obtaining probabilistic guarantees, modifying the protocol itself and/or on imposing severe restrictions in bandwidth utilisation.