Getting in step breaks all barriers

A new network can synchronise over 100 axes within less than a millisecond and with less than one microsecond jitter. Based on Ethernet, it uses exceptionally advanced ASICs to overcome problems previously considered impossible. While Ethernet is popular for moving large amounts of data, it has not been considered suitable for precise co-ordination of movements. This is because it sorts out data by collision. Data packets are sent onto the network randomly, but if two or more are launched at the same time, the senders pause and try again, but after different time delays. Ethernet does, however, form the basis of new Isochrone Realtime-Ethernet, or IRT, which Siemens is launching at the Hanover Fair in April. It is launching IRT jointly with the Profibus Trade Organisation, which will incorporate it into its new Profinet V3 standard. At a press conference prior to the Fair, Helmut Gierse, president of Siemens' Automation and Drives Group, announced that the protocol will allow synchronisation of over 100 driving axes, or several hundred axes in modular machine operations. He claimed that typical solutions using fieldbuses, special drive buses, conventional Ethernet and real-time Ethernet synchronise a maximum of 30 to 40 drives or take several milliseconds to do the job. Mr Gierse told Eureka that it overcame the collision problem by, "collecting the data into well defined time slots. Collision avoidance is exactly the difficulty and a very highly integrated and complex ASIC is required to solve the problem." All the company was prepared to reveal at the press conference was that it was based on 100 megabit/sec switched Ethernet and adds a "deterministic" channel to IEEE 802.3 Ethernet. The line capacity is chronologically split into two separate channels, the deterministic one and an open one. The deterministic channel carries only cyclical high speed messages, while the open channel carries standard communications such as those using TCP/IP. One of the big advantages is that real time extensions have no effect on standard Ethernet standard functions. Switches with IRT functions behave like normal Ethernet switches. The company expects the first hardware samples of products based on the technology to be ready in 2004 with an extension of the technology planned for 2005. Gierse justified the long timescale: "First of all, we are entering unknown territory with this technology, regarding its application in industry; secondly, we want no half-hearted steps – we want to ensure that our customers derive full benefit from the new Profinet solution; and thirdly, we are providing the Profinet Trade Organisation with basic technology and, as is customary with such joint projects, we will be collecting the application expertise of member companies and incorporating this into the new technology." Pointers * New switched Ethernet technology will allow the synchronisation of more than 100 drive axes or several hundred drive axes in modular machine operations * By time dividing the Ethernet bus, the new synchronisation signals and more traditonal data strings, such as TCP/IP, will be unable to interfere with each other Siemens