Evaluation and simulation of event building techniques for a detector at the LHC

The main objectives of future experiments at the Large Hadron Collider are the search for the Higgs boson (or bosons), the verification of the Standard Model and the search beyond the Standard Model in a new energy range up to a few TeV. These experiments will have to cope with unprecedented high data rates and will need event building systems which can offer a bandwidth of 1 to 100GB/s and which can assemble events from 100 to 1000 readout memories at rates of 1 to 100kHz. This work investigates the feasibility of parallel event building sys- tems using commercially available high speed interconnects and switches. Studies are performed by building a small-scale prototype and by modelling this proto- type and realistic architectures with discrete-event simulations. The prototype is based on the HiPPI standard and uses commercially available VME-HiPPI interfaces and a HiPPI switch together with modular and scalable software. The setup operates successfully as a parallel event building system of limited size in different configurations, with different input data and different data flow management schemes. Realistic parameters of 40MB/s for the link speed and of 100us for the overhead have been measured and the total throughput is scalable with the number of destinations. The prototype measure- ments lead to a parametrized model of a parallel event building system which is implemented in a simulation program. This is used to simulate large-scale systems including a realistic model of the ATLAS event building system with realistic event size distributions from off-line simulations. The influence of different parameters and the scaling behaviour are investigated. Different data flow management schemes for destination assignment and traffic shaping are studied as well as a two-stage event building system.