Investigation of the networking performance of remote real-time computing farms for ATLAS trigger DAQ

To test the feasibility of using remote farms to perform real-time event selection in the trigger/data acquisition system for the ATLAS experiment at CERN, a proof of concept was set up during 2004. The behaviour of the request-response protocol to move application data has been measured for remote farms connected with different wide area networks including a dedicated lightpath, a virtual private network, and the standard production network. The dynamics and effect of using TCP/IP as the transport protocol has also been investigated for this realtime application. These data are compared with conventional bulk data transfers and used to validate the observed performance of the online farms and estimate the effect of this traffic pattern on the wide area network.