Event Building in the ATLAS DAQ/EF Prototype "-1

In the framework of the ATLAS DAQ/EF prototype "-1" a stand-alone small- scale event building prototype has been developed in order to study the issues of switch-based parallel event building as needed for experiments at LHC. The event building prototype is designed in two layers: the technology-independent layer defines a high-level event building model, while the technology dependent layer uses commercially available interfaces and switches for a choice of three technologies: ATM, Fast Ethernet and Fibre Channel. The decoupling of the two layers is achieved by the means of a connection-oriented message passing li- brary. The prototype has been implemented using PowerPC-based VME proces- sors running a real-time UNIX operating system and works successfully with emulated input and output. The performance in terms of total throughput and protocol overhead for all three technologies has been measured.