The first generation of Media Oriented Systems Transport (MOST) runs at 25 Mbps and is now on the road around the world in over 50 vehicle models from many car manufacturers. It serves as the communication backbone of the infotainment systems of all these automobiles. MOST25 uses a fiber optic system to transport its data. Some of the largest car manufacturers in Asia are now gearing up to bring out vehicles with MOST. They are implementing a new MOST Technology that uses unshielded twisted pair (UTP) copper connections and double-density coding that increases the bandwidth to 50 Mbps. MOST has undergone extensive enhancements, not only technologically but also in the areas of robustness and ease of use, cost reduction, and bandwidth increase.

The infotainment systems in vehicles are constantly becoming more powerful. New functions are integrated that place higher requirements on the network. For example, hard disks are being introduced into the car, there's navigation in the rear seats, HD Video, DVB-T, etc. These require increased bandwidth from the backbone of the vehicle. MOST150 meets the requirements of next generation multimedia devices by offering a bandwidth of 150 Mbps and mechanisms to support cost effective video streaming. Beyond that, MOST150 provides an automotive-ready Ethernet channel conform to IEEE 802.3. This way, MOST becomes a fusion of Ethernet capabilities and high quality of service (QoS) audio and video streaming capabilities on an automotive grade physical layer.

Fig. 1. MOST150 supports multiple automotive-specific and multimedia signal sources and signal sinks.

Before the following article dives into the features of MOST150 though, it gives an overview of the general technical direction that MOST Cooperation has pursued over the past years.

Robustness and Ease-of-use

One focal point of MOST Cooperation's efforts was to optimize robustness and ease-of-use. In order to achieve that, many measures have been taken. For example, the cooperation has overhauled its MOST specifications and implemented an integrated compliance verification process in order to establish a stringent quality control of MOST implementations while reducing the cost at the same time. To further optimize robustness and user friendliness, the specifications have been refined to remove ambiguities and add clarity. Since its first volume implementation, the MOST specifications have continuously been amended and extended in order to narrow the possibility for different interpretations by implementers. For example the management of a MOST network has been described in a very detailed way. The definition of the Network Services have been optimized for seamless portability to different system architectures as they have to run on different platforms with a wide range of characteristics and performance capabilities.

Another example for increased robustness and ease-of-use is that MOST Cooperation has added descriptions of the dynamic behavior of functional entities such as various APIs. The necessary master functions to manage a MOST network like Network Master, Power Master etc have been described with Message Sequence Charts. These specifications have even been implemented in software that is available as standard code.

These important functions, that are usually located in a head unit and control the whole MOST network, no longer need to be developed again by each Tier 1 supplier. Furthermore, MOST Cooperation has triggered the development of a broad environment of infrastructure for MOST. While MOST Cooperation itself has for example developed a tool for XML based API modeling and offers it to members on its website, also the members have been encouraged to develop necessary products. Meanwhile powerful tools are available from different vendors for network analysis and compliance verification that cover all aspects of development, production and quality assurance of MOST components.

Less Cost of Optical Components

As the market has grown, the cost of a MOST node has been roughly cut in half. However, like with any new technology, there is still some room for further cost reductions. One area is the optical connector. Since the optical components account for about two thirds of the cost of a MOST interface, the MOST Cooperation invested the effort of restructuring the fiber optic transceiver (FOT) supply chain. So far the FOT is being delivered to the connector manufacturer who assembles FOT and connector into an optical header and then delivers it to the Tier 1. The margin multiplication and duplication of process steps that occur in this process is what makes the optics so expensive. With the new design, the supply chain is optimized, as FOT and connector will both be directly delivered to the Tier 1.

MOST150 Enables Transport of Video Streams and IP-Based Packet Data

Technologically MOST150 is a big step that addresses the requirements of high speed data and video transport. In addition to higher bandwidth of 150 Mbps, MOST150 features an isochronous transport mechanism to support extensive video applications, as well as an Ethernet channel for efficient transport of IP-based packet data. Using MOST, audio and video signals can be transported with high bandwidth efficiency and with almost no overhead for addressing, collision detection/recovery or broadcast. This way MOST150 offers capacity that packet-switched networks can only achieve with much higher gross bandwidth. Consequently multiple high-definition (HD) and single definition (SD) video streams and multi-channel surround sound with premium quality of service can be transported, while simultaneously moving high loads of packet data around.

Fig. 2. The optical MOST150 backbone addresses future telematics and infotainment applications as well as car-internal information functions.

MOST150 allows carmakers to continue to use POF as transport medium and LEDs as light sources. They can continue to use their established optical wire harness and assembly processes which makes the transition to higher bandwidth networking with MOST150 a smooth evolution.

Transparent Ethernet Channel

Like MOST25 and MOST50, MOST150 offers the well known channels for synchronous, packet and control data " but in addition it offers also two new channels: an Ethernet channel and an isochronous channel. The Ethernet channel can transport unmodified Ethernet frames. It also supports addressing using MAC addresses. This permits software stacks and applications from the consumer and IT domain, where the speed of innovation is much faster, to be seamlessly migrated into the car. TCP/IP stacks or protocols utilizing TCP/IP can communicate via MOST150 without any modification.

It presents itself to applications as if it were Ethernet. From a high-level view MOST150 is a multiplexed network that includes the current MOST with double bandwidth as well as 10/100 Ethernet (just that the bandwidth allocation can be configured in a flexible way). This way MOST150 is the automotive-ready physical layer for Ethernet in the car.

Digital Transmission Content Protection for Video over MOST

The majority of MOST systems on the road today do not transport video digitally. The main reason is that it was forbidden to send DVD content digitally over any network and hybrid systems with both analog and digital video were not economically feasible. With the integration of DVD Audio and DVD Video into digital networks, the requirement for content protection comes into place. DVD content on a digital network must be DTCP (Digital Transmission Content Protection) protected.

The vehicle architectures were already defined and being rolled out without digital video when, in 2003, MOST was the first network to be fully approved by the DVD Copy Control Association (DVD CCA) to carry DTCP protected content. This was made possible by adapting DTCP to the MOST standard. By doing so, also HD-DVD and Blu-ray content on MOST is supported since AACS (Advanced Access Content System) licensing allows digital outputs which are protected using DTCP. DTCP requires source and sink devices to authenticate each other. In addition, there is a need to encrypt multimedia streaming data before sending it over a digital network. A sink device therefore has to be able to decrypt protected digital content. DTCP on MOST also supports point-to-multipoint connections.

Fig. 3. For aftersales software updates, diagnosis functions and the integration of portable consumer devices, the system offers connectivity to Ethernet and USB.

Conclusion

MOST is already the de-facto standard of the automotive industry for distributing infotainment information around a vehicle. These latest developments make it an even more attractive solution for a variety of A/V applications both inside and outside the car. MOST provides a cost-effective and bandwidth efficient backbone with high data rates, a variety of physical layers and a simple architecture for scalability to different speed grades. It can transparently transport Ethernet and IP traffic with a robust infrastructure already proven under the stringent EMC, environmental, quality and robustness requirements of the automotive world.

Wolfgang Bott is Technical Coordinator for MOST Cooperation. He can be reached under contact@mostcooperation.com