The input stage consists of only one process. This single process combines the input stage pipeline functionality and the overall control of the compute node backend system, creating the superficial appearance of a single backend processing pipeline. This section of the document will describe how the input stage pipeline is designed, and how the input stage manages the processes in the lag processing stage. The control interface of the compute node backend system is described later in the section called “Application interface”.

The input stage pipeline is fixed with regard to the pipeline elements and their connections. Of course, the pipeline responds to the creation, activation and destruction of backend configurations dynamically, on demand. One other feature of the input stage pipeline that may be controlled dynamically is the generation of lag frame dump files (see the section called “wcbe_framedump”). Other input stage parameters are provided at start-up and cannot be changed in a running system.