Verification of the Fair Control System Using Deterministic Network Calculus

The FAIR control system (CS) is an alarm-based design and employs White Rabbit time synchronization over a GbE network to issue commands executed accurate to 1 ns. In such a network based CS, graphs of possible machine command sequences are specified in advance by physics frameworks. The actual traffic pattern, however, is determined at runtime, depending on interlocks and beam requests from experiments and accelerators. In ’unlucky’ combinations, large packet bursts can delay commands beyond their deadline, potentially causing emergency shutdowns. Thus, prior verification if any possible combination of given command sequences can be delivered on time is vital to guarantee deterministic behavior of the CS. Deterministic network calculus (DNC) can derive upper bounds on message delivery latencies. This paper presents an approach for calculating worst-case descriptors of runtime traffic patterns. These so-called arrival curves are deduced from specified partial traffic sequences and are used to calculate end-to-end traffic properties. With the arrival curves and a DNC model of the FAIR CS network, a worst-case latency for specific packet flows or the whole CS can be obtained.