Audi's move is seen as likely to ignite the TTP volume-silicon market and to nudge other automakers in TTP's direction. A rigorously specified safety-critical bus is considered necessary for steer- and brake-by-wire systems within next-generation automobiles.

Since Audi (Ingolstadt, Germany) is a subsidiary of Volkswagen AG, industry watchers expect over a few years that other larger-volume car manufacturers will migrate to TTP, too. "Our background is to force and push standardization," said Walter Streit, senior engineer responsible for bus systems and airbags at Audi. "If Audi-VW goes in this direction, we believe other companies will follow us."

Indeed, observers said Audi's decision might cause BMW and Daimler-Chrysler to rethink their plans to devise an alternative safety-critical bus. An announcement from BMW and Daimler-Chrysler on a jointly developed solution is expected this week at the VDI Kongress on vehicular electronics in Baden-Baden, Germany.

"I am in discussions with engineers and executives at BMW and Daimler-Chrysler on the bus issue," said Audi's Sreit. "The choice is whether to do something new or use something that already exists. We all agree we want to reach one standard for the industry."

Coming on the heels of Honeywell's August decision to use TTP in the aerospace sector, Audi's embrace of the protocol should provide a big boost for TTTech AG (Vienna), the company created to commercialize the TTP technology after many years in development by Herman Kopetz, a professor at the Technical University.

The lack of OEM backing has held up TTP's march into systems and dampened chip makers' enthusiasm for the protocol. Earlier this year, executives from Motorola Inc., the leading supplier of chips to the automotive sector, said it could not continue pursuing solutions based on the protocol without an OEM customer declaring in favor of it.

"This move by Audi is a very important step for TTTech — we are happy to work with this leading OEM," said Stefan Poledna, chief executive officer of TTTech. "We expect other automotive companies to follow the direction of Audi and will continue to work hard to make TTP a standard."

Willibert Schleuter, head of electrical engineering at Audi, called TTP "by far the most mature solution on the market. It fulfills all requirements we have for our in-car communication networks and provides the means to handle the complexity and advanced functions of future systems. In addition, TTP gives us improved data throughput and further enhances overall system dependability."

Schleuter said that Audi will use TTP "as a standard platform for reliable information exchange between different electronic systems. This includes all aspects ranging from control strategies over sensor information exchange to diagnostics data. As an integration platform TTP links ECUs electronic control units and ECUs together with smart sensors and actuators."

Schleuter does not expect Audi to have problems finding silicon to implement TTP. Work has been going forward with ARM Ltd. (Cambridge, England) and Austria Mikro Systeme (Graz, Austria) to develop TTP-capable microcontrollers for use in automotive ECUs.

"Several leading silicon suppliers have expressed their interest to supply TTP-based silicon," Schleuter said. With intellectual property from TTTech, "it will be easy for Audi to get TTP silicon solutions in time on a variety of different CPU platforms. Based on our experience, the demand for silicon will be driven not only by the OEMs like Audi, but also by the tier-one suppliers."

Audi's Streit said that TTP would first appear in Audi automobiles toward the end of 2004 or the beginning of 2005. The delay stems from the automobile industry's long design-in cycle.

One reason for selecting TTP was the difficult nature of safety-critical theory, he said. "Very few people can judge what is 'safe.' Professor Kopetz's work is of a very high standard. TTTech is the right cooperative partner for us."

In TTP, safety is provided by means of an architecture based on time-division multiple-access (TDMA) time slots. The clock synchronization for controlling the slots at all nodes is a distributed correction scheme. A hardware "bus guardian" can prevent a node from trying to grab the bus due to a software error — keeping the so-called "babbling idiot" problem at bay.

Typically the bus is run at 2 Mbits/second over copper, although fiber-optic versions are possible.

Audi's decision follows an announcement that Honeywell will use TTP in aerospace applications. Honeywell's Engine and Systems division and TTTech agreed in late summer to collaborate in the manufacture of electronic control systems based on TTP for aircraft engines. The protocol is to be the base communications architecture for a number of Honeywell modular aerospace control products, including military and commercial APU and main-engine electronic fuel-control units.