Preliminary Specification of Basic Services and Protocols

network layer network layer QoS assurance Functional abstractions middleware events with context and temporal properties, event channels with quality properties message classes, messages with temporal properties, network reliability properties network dependent best effort message transfer Figure 6: Architectural layers. munication services as e.g. som form of reli le broadcast or group communication and tempora guarante s for the m ssage transfer. As an example, Figure 7 presents the preliminary specification of protocols and services for a particular CAN (CAN-Bus [28]). It lists the basic abstractions, the methods to deal with these abstractions, the system services available, the components to realize the system services and specific protocols needed to support the abstractions in the distributed architecture. The P/S layer supports events and different classes of event channels with different quality properties. It should be noted that the QoS properties in general depend on what the abstract network layer can provide. Thus, it may not always be possible to e.g. support a hard real-time event channel because the abstract network layer can not provide the respective guarantees. Therefore, the event channel classes supported are dependent on the zones in which publishers and subscribers reside. Figure 7 covers the case of a single zone which is a CAN-Bus. A detailed description of these abstractions and the mechanisms to enforce them on a CAN-Bus[28] is provided in Section4 of this deliverable with the title: ”A RealTime Event Channel Mod l for the CAN-Bus”. The dynami binding protocol of th P/S layer and the configuration protocol of the AN-layer are described in [17, 44]. 2.6 Adaptable Timed Event Service (ATES) A proposed solution to handle some of the timeliness requirements of CORTEX system entities is by using a specialized architectural building block, the Timely Computing Base, which provides a set of fundamental services tailored for that purpose. However, since the services provided by the TCB are just the essential ones in order to keep the TCB small, simple and hence reliable, the interface supplied by the TCB is, in a certain way, a low level interface, which should be hidden from sentient objects in the programming model. The Adaptable Timed Event Service (ATES ) is a middleware event service that extends the CORTEX publish/subscribe programming model with constructors to deal with timeliness requirements. ATES hides from sentient objects the low level services provided by the TCB concerning timing failure detection, coverage stability and awareness, and timely execution, providing high level abstractions more suitable