Replaceable middleware communication modules for distributed data acquisition systems

Modern detector systems for experimental physics or medical applications are making use of networks for data acquisition and experimental control. These can be made very complex using advanced FPGAs and embedded software. It is preferable to make the network nodes loosely coupled. This improves stability and simplifies maintenance. Developing software for each specific project is often costly in time and resources. For the communication middleware it helps to use off-the-shelf solutions like CORBA, web services, publish-subscribe or other standard interfaces. Using standardized modules can dramatically reduce the costs for development and increase performance. The different standards come with a cost however, while they are offering a solution to one problem, they may introduce others. Some of them, like CORBA, are purely object-oriented which is an advantage for development but CORBA is also fairly complex. Others offer a more service oriented architecture with loose coupling among the communicating nodes but increases the communication overhead. We have developed a package with a replaceable set of middleware for the above-mentioned standards. It has been applied to the control- and data acquisition system for a SPECT camera and other in-house projects.