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When comparing vehicle communication architectures, the passive star network has been shown to be the highest fault tolerant system. Despite this trait, the passive star architecture has not been widely implemented due to its potential application limitations: insufficient node count and relatively short node lengths. These constraints arise from the basic function of the star, i.e. to evenly distribute a given amount of optical power to all nodes connected to the star without amplification or retransmission. This paper provides a solution to overcome the limitations of the passive star through the introduction of a new communication component, the Active Distribution Node (ADN). The ADN enables a passive star network to support larger node counts and significantly longer node lengths, without sacrificing fault tolerance or the low cost nature of the basic passive star architecture.

The evolution of vehicle electronics has resulted in corresponding changes in how vehicle communications networks are being used. Initially used for diagnostic and low speed data sharing applications, networks are increasingly being used for real time control applications that require significantly higher data rates. While high speed networking technology has been primarily developed for office LAN and telecommunications applications, the requirements of in-vehicle communication networks differ significantly from their office and factory counterparts. This paper will examine the issues involved in choosing a physical layer for a vehicle network including: media bandwidth, electromagnetic compatibility (EMC) requirements, fault tolerance, serviceability requirements, ability to meet vehicle environmental requirements, network architecture limitations, and cost.