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In order to expand the applicable range of in-vehicle LANs down to popular cars, drastic cost reduction is essential. In addition, an in-vehicle LAN with high transmission rate and advanced functioning is extremely important for the further spreading of vehicle electronics intended to enhance vehicle intelligence. We developed the Protocol for Automotive Low and Medium Speed Network (PALMNET) as an in-vehicle LAN system and put it into practical use in 1990. Based on this, we developed a new communication protocol and three ICs for an in-vehicle LAN called the Advanced Protocol for Automotive Local Area Multiplexing Network (Advanced PALMNET), which satisfies the above-mentioned requirements and covers the medium-to-low transmission rate (up to 125kbps) to high rate (up to 1Mbps).

The latency time of class C in-vehicle LAN systems was evaluated in order to analyze the difference in latency time between the non-destructive CSMA/CD (CSMA/CD+NDA) and the token passing selected as the high speed LAN protocols. The evaluating method was constructed by combining simulation and an analysis equation. As a result, the limits of traffic volume available for vehicle application were approximately 80 to 90 % for the CSMA/CD+NDA and 30 to 40 % for the token passing at a transmission rate of 1 Mbps.

Currently both the SAE and ISO are working on the standardization of distributed multiplex transmission protocols, and the Japanese Society of Automotive Engineers (JSAE) is in the process of evaluating the performance and reliability of a number of communication protocols with a view to contributing to this work of standardization.(1) This paper summarizes that aspect of the JSAE's communication protocol evaluation program that concerns response. CSMA /CD with non-destructive arbitration systems that are used in motor vehicles resemble ordinary CSMA/CD systems in that transmission delay times vary in accordance with traffic. Thus when there is a stringent need for response, it is essential to make judgments on the basis of the probability in terms of delay time. It is, however, impossible to determine delay probabilities experimentally due to the problem of the number of test runs, and this creates a need for methods using simulation and analysis.

At present, various communication protocols for an automotive distributed control multiplex system that aims at solving wire complexity and meeting the requirements of high reliability and open system flexibility have been proposed and installed in production cars. The requirements for an automotive distributed multiplex system, especially reliability, flexibility, and economy have been analyzed in detail, and as a result a new communication protocol based on SAE J-1850 has been developed. This paper describes the design philosophy and technical features of the protocol, named PALNET (Protocol for Automotive Local area Network) and the result of evaluation with the experimental system. PALNET covers moderate speed signals in vehicle electrical and electronic system. Main technical features of PALNET are as follows. Introduction of a new acknowledgement method named ANC (Acknowledgement for Network Control) secures high reliability of data communication.