Influence of Switch Queue Length on Data Acquisition System using DCB

A Data Acquisition (DAQ) system has become to be used in the field of large-scale scientific experiments with the advance of information technology. Especially, in DAQ System for a high energy physics experiment such as ATLAS experiment at CERN, parallel processing using a large number of network switches enhances the efficiency of acquiring and analyzing experimental data. Additionally, a DAQ system has many-to-one simultaneous communication that gathers data generated by a large number of detectors into one computer for analysis. Properties of such communication can cause network traffic congestions and packet losses, thereby decreasing throughput. One solution for such problem is Data Center Bridging (DCB) technology used to establish lossless Ethernet networks. In addition, since event fragments in a large-scale DAQ system are transmitted using many network switches, the buffer size of a network switch is critical. This study focuses on the queue of the network switch of a DAQ system using DCB and the effects on system performance. The fairness and throughput of each flow in many-to-one simultaneous communication system were measured. We confirmed maximum performance was achieved when an average queue length in the network switch was small.