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This paper is an overview of the current state (calendar year 2010) of in-vehicle multiplexing and what pertinent technologies are emerging. Usage and trends of in-vehicle networking protocols will be presented and categorized. The past few years have seen a large growth in the number and type of communication buses used in automobiles, trucks, construction equipment, and military, among others. Development continues even into boating and recreation vehicles. Areas for discussion will include SAE Class A, B, C, Diagnostics, SafetyBus, Mobile Media, Wireless, and X-by-Wire. All existing mainstream vehicular multiplex protocols (approximately 40) are categorized using the SAE convention as well as categories previously proposed by this author. Top contenders will be pointed out along with a discussion of the protocol in the best position to become the industry standard in each category.

Multiplexing can be best discussed at three levels - vehicle, ECU or component, and IC. Within each level are partitions for software and hardware, and within each partition are divisions of functionality such as buffer size. The content in this book will help the reader to acquire a basic understanding of vehicle multiplexing systems, primarily from the passenger car and light truck viewpoint. Some discussion of heavy-duty and off-road vehicle multiplexing is presented, along with a look at industrial automation - a fast-growing multiplex field already eclipsing automotive usage.

A previous SAE 2001 Congress paper, “Multiplex Bus Progression” [1] introduced the idea of categorizing vehicle serial data protocols into additional areas beyond the traditional SAE Class A, B, and C. This paper will expand on that idea, and provide a 2003 update to the Diagnostics, SafetyBus, Mobile Media, and X-by-Wire categories. All existing mainstream vehicular multiplex protocols (approximately 40) are categorized using the SAE convention plus the new groupings. Top contenders will be pointed out along with a discussion of the protocol in the best position to become the industry standard in each category at this time.

The current SAE classification system for serial data communication protocols encompasses Class A, Class B, and Class C categories. Because of the proliferation of applications and new protocols these three groups are not enough. This paper will introduce and discuss several new categories which are Diagnostics, SafetyBus, Mobile Media, and X-by-Wire. The serial data protocols that fall under these categories are for the most part brand new and will serve distinct and unique tasks. All existing common vehicular multiplex protocols (approximately 40) will be categorized using the SAE convention plus the new groupings. Top contenders will be pointed out along with a discussion of the protocol in the best position to become the industry standard in each category. Future vehicle applications having up to seven different data networks will be presented.