Electronic Design

Multimedia Automotive Networks

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What network technologies are used in the automotive space?
Automotive networks typically consist of a hierarchy of networks, starting with local interconnect network (LIN), controller-area network (CAN), and FlexRay for system control and multimedia networks such as IDB-1394 and Media Oriented System Transport (MOST).

The differences in network speed are obvious (see the table). LIN supports a maximum of 20 kbits/s, and CAN supports a maximum of 1 Mbit/s. Yet FlexRay supports 10 Mbits/s. It's also more reliable and flexible. And, it provides enhanced payload support.

The multimedia support bus has a much higher bandwidth. MOST25 has 25 Mbits/s. MOST50 has 50 Mbits/s. IDB-1394 offers 400 Mbits/s. However, the 1394 technology provides a much higher bandwidth for consumer applications. It promises super-high bandwidth for automotive applications in the near future.

What are the advantages to a hierarchical approach?
A hierarchical approach helps optimize applications that have multiple application requirements. For instance, LIN suits low-cost implementations that typically require a driver to initiate functionality. These applications usually operate independently in a closed area and do not require the network to communicate with other functions. Examples include side-view mirrors, window control, and sunroofs.

The upper layer of the LIN, which is typically CAN, targets applications that need to communicate with other electronic control units (ECUs). A good example is a meter cluster, which gathers rapidly changing information about the car's operating conditions from multiple modules.

Highly reliable communication also is important between the ECUs that require CAN's solid network management system. Because of its high reliability, FlexRay is expected to become the upper layer of the CAN or to partly replace the CAN. FlexRay is 10 times faster than CAN and supplies a redundant network topology for increased reliability. Also, FlexRay provides the improved potential node counts on the network.

What services will multimedia networks typically provide?
The multimedia network requirements come mainly from personal entertainment applications, which resemble those in in-flight entertainment systems. A wide variety of devices will need to be supported, ranging from multiple audio (terrestrial radio, satellite radio, CDs) and video (DVDs, terrestrial TV, satellite TV navigation screen) devices to live video data from onboard cameras and personal equipment (games, MP3 players, media players).

The multimedia network also suits driver-assistance needs. Possible applications include live camera network data like parking assist, side and blindspot cameras, or vision-enhancement cameras for nighttime or low-visibility conditions like foggy days.

What are the differences between multimedia network technologies?
The IDB-1394 and MOST systems target similar applications. The most significant difference is the data rate. The IDB-1394 can support 400 Mbits/s and beyond, while MOST is limited to 50 Mbits/s. IDB-1394 is also very flexible and supports a variety of network topologies, including bus, tree, ring, or star. MOST primarily supports only the ring topology.

What is the relationship between IDB-1394 and IEEE 1394?
IDB-1394 and IEEE-1394 are transparent. The 1394TA and IDB Forum have jointly defined automotive requirements based on the IEEE-1394 standard.

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