Dataflow in the DZero level3 Trigger/DAQ system

The Level3 Trigger / Data Acquisition system (L3DAQ) for the DZero detector was redesigned from scratch for the Fermilab Tevatron's Run II. The L3DAQ moves data at a rate of 250 MB/sec from 63 readout crates to one of 82 trigger farm nodes. The L3DAQ system is built around a CISCO 6509 Ethernet switch and uses TCP/IP for all communication and dataflow. This poster will detail the dataflow in the system, which includes the event building in each Level 3 Trigger node, the TCP/IP settings used to maximize throughput, the trigger node advertisement scheme used, and means used to restrict peak dataflow through the switch and avoid dropped packets. Other data paths and the physical layout of the entire system will also be described.