Simulation of the ALICE DAQ System with GALSIM

We present some of the simulation results for the DAQ system of the ALICE Abstract:experiment at the Large Hadron Collider (LHC) at CERN. The simulation is performed by the ALICE DAQ Simulation Program GALSIM. Abstract:GALSIM comprises two software packages; 1)the basic ALICE DAQ simulation Abstract:program ALSIM and 2) a graphic user interface which dynamically displays Abstract:the data transport and synchronization messages in the DAQ system. GALSIM Abstract:is written in MODSIM II and has been developed by the ALICE DAQ group at Abstract:the Department of Physics, University of Oslo, Norway. In the paper, we will first introduce the basic ALICE DAQ system and the sAbstract:imulator GALSIM. We will then concentrate on the simulation of the ALICE Abstract:DAQ topology with various parameters. The results we present can be viewed Abstract:as an extension of the DAQ simulation shown in the ALICE Technical Abstract:Proposal. Among the important results, we emphasize on the following issues, 1. The effect of message latency. Messages are used by the Event Abstract:Destination Manager to signal to a number of Local Data Concentrators Abstract:(LDCs) to send sub-events to Global Data Collectors via switch. Messages Abstract:with long latency will tremendously slow down the system. The simulation Abstract:results under different experimental latencies are illustrated. 2. Balancing the traffic in the Event Building system. For the event Abstract:building in a large DAQ system, all the data that belong to the same event will have to be sent to the same data processor from LDCs. Tokens can be Abstract:used to coordinate the data transmission among the LDCs in the system. However, tokens may influence the system balance in term of buffer usage Abstract:and traffic pattern. By GALSIM, the simulator results affected by the Abstract:tokens can be monitored and analyzed. 3, The size of the DAQ system versus link speed. The cost of a DAQ system will depend not only on the price of each device but on the size of the Abstract:whole system. However, due to the complexity of DAQ systems, one needs to Abstract:investigate the trade-offs between link bandwidth/delay and the number of Abstract:data links. We will in our paper explore this issue.