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The Data Acquisition System of the Compact Muon Solenoid experiment at the Large Hadron Collider reads out event fragments of an average size of 2 kB from around 650 detector front- ends at a rate of up to 100 kHz. The first stage of event-building is performed by the Super-Fragment Builder employing custom-built electronics and a Myrinet optical network. It reduces the number of fragments by one order of magnitude, thereby greatly decreasing the requirements for the subsequent event-assembly stage. Back-pres- sure from the down-stream event-processing or variations in the size and rate of events may give rise to buffer overflows in the subdetector's front-end electronics, which would result in data corruption and would require a time-consuming re-sync procedure to recover. The Trigger-Throttling System protects against these buffer overflows. It provides fast feedback from any of the subdetector front-ends to the trigger so that the trigger can be throttled be- fore buffers overflow. This paper reports on new performance measurements and on the recent successful integration of a scaled-down setup of the described system with the trigger and with front-ends of all major subdetectors. The ongoing commissioning of the full-scale system is discussed. [ABSTRACT FROM AUTHOR]

The data acquisition system of the CMS experiment at the Large Hadron Collider features a two-stage event builder, which combines data from about 500 sources into full events at an aggregate throughput of 100 GB/s. To meet the requirements, several architectures and interconnect technologies have been quantitatively evaluated. Myrinet will be used for the communication from the underground frontend devices to the surface event building system. Gigabit Ethernet is deployed in the surface event building system. Nearly full hi-section throughput can be obtained using a custom software driver for Myrinet based on barrel shifter traffic shaping. This paper discusses the use of Myrinet dual-port network interface cards supporting channel bonding to achieve virtual 5 GBit/s links with adaptive routing to alleviate the throughput limitations associated with wormhole routing. Adaptive routing is not expected to be suitable for high-throughput event builder applications in high-energy physics. To corroborate this claim, results from the CMS event builder preseries installation at CERN are presented and the problems of wormhole routing networks are discussed. [ABSTRACT FROM AUTHOR]