Virtual CAN Networks Over TTP - Integrating Legacy Systems Within the Time-Triggered Architecture 2004-01-1734

The next generation of cars will consist of a high number of networked electronic control units (ECUs) and significantly more complex software modules and control applications than today's models. Besides applications like engine control, air condition control and anti-theft systems, which are already available in today's cars, the first steps towards the introduction of safety-relevant steer-by-wire and brake-by-wire systems will be undertaken. Additionally, the demand for in-car entertainment and information systems (e.g. Internet terminals, video-streaming applications) will also increase. Since all these systems have conflicting requirements to the underlying network protocol (latency, predictability, throughput…), the straight-forward way would be to use autonomous busses and networks for every kind of distributed system within the car body (ultra-available safety-relevant systems, non-safety-relevant control systems, entertainment and media systems).

This adds extra unwanted complexity and cabling overhead (and therefore cost) to the overall car electronics. So it is legitimate to think about alternative architectures, e.g. a common backbone network which can be used by all ECUs. Nevertheless, the integration to a single in-car network must not impair nor compromise the service of any safety-relevant system.

This paper describes how a Time-Triggered Architecture (TTA), based on an underlying time-triggered communication protocol, can be employed to provide such an integration. In the first part the concept of virtual networks over the Time-Triggered Protocol (TTP) is presented and discussed. The idea is to provide “virtual” networks layers, like CAN or TCP/IP on top of a single TTP network. The advantage of these virtual networks is that existing legacy applications that rely on a certain network technology will be able to work almost unchanged. Most of today's in-car control systems are based on CAN. If these systems were reused in such an integrated scenario, this might open a migration path towards the introduction of next-generation electronic systems, largely reducing cost for the redevelopment of existing solutions.

In the second part, this paper presents an implementation for a CAN emulation over TTP in some detail and discusses characteristics and concepts of this solution.