Testing and modeling Ethernet switches and networks for use in ATLAS high-level triggers

The ATLAS second-level trigger will use a multilayered local-area network to transfer 5-Gbyte/s detector data from similar to 1500 buffers to a few hundred processors. A model of the network has been constructed to evaluate its performance. A key component of the network model is a model of an individual switch, reproducing the behavior measured in real devices. A small number of measurable parameters are used to model a variety of commercial Ethernet switches. Using parameters measured on real devices, the impact on the overall network performance is modeled. In the Atlas context, both 100-Mbit and gigabit Ethernet links are required. A system is described that is capable of characterizing the behavior of commercial switches with the required number of nodes under traffic conditions resembling those to be encountered in the Atlas experiment. Fast Ethernet traffic is provided by a high-density custom-built tester based on field-programmable gate arrays, programmed in Handel-C and VHDL, while the gigabit Ethernet traffic is generated using Alteon NICs with custom firmware. The system is currently being deployed with 32 100-Mbit ports and 16 gigabit ports, and will be expanded to similar to 256 nodes of 100 Mbit and similar to 50 GBE nodes.