The group chose Ethernet rather than an existing field bus because it offered lower cost and higher performance than the field busses available today. With IDA-compliant components in place, programmers won't have to write to low level device protocols, component manufacturers will have just one protocol to support and maintain, and end users will be able to freely mix components from different vendors. In addition, the IDA group wanted a product that was commercially available so that vendors could start developing immediately. NDDS has been on the market for several years and is used today in real-time systems for discrete control, large ship controls, and semiconductor manufacturing, among others. Rather than addressing a packet for all interested nodes and calling the network stack to send each packet, for example, a publisher simply defines a topic and then calls NDDS to send the data.
Subscribers simply register their interest in that topic.
NDDS takes care of all the network addressing and data delivery chores for the programmer, eliminating thousands of lines of code. NDDS automatically detects when nodes have left and joined the network. The RTPS model extends the publish-subscribe model by defining a set of object properties that give developers control over message flow, data delivery deadlines, fault tolerance, and issue validity. Distributed control applications use these properties to optimize available bandwidth, ensure real-time operations complete in time, and transparently filter issues from redundant publications. In addition, a paper and spreadsheet for calculating the probability of a collision causing, non-deterministic delay on Ethernet are available on the RTI Web site.