The CMS experiment at LHC started using the Resource Broker (by the EDG and LCG projects) to submit Monte Carlo production and analysis jobs to distributed computing resources of the WLCG infrastructure over 6 years ago. Since 2006 the gLite Workload Management System (WMS) and Logging & Bookkeeping (LB) are used. The interaction with the gLite-WMS/LB happens through the CMS production and analysis frameworks, respectively ProdAgent and CRAB, through a common component, BOSSLite. The important improvements recently made in the gLite-WMS/LB as well as in the CMS tools and the intrinsic independence of different WMS/LB instances allow CMS to reach the stability and scalability needed for LHC operations. In particular the use of a multi-threaded approach in BOSSLite allowed to increase the scalability of the systems significantly. In this work we present the operational set up of CMS production and analysis based on the gLite-WMS and the performances obtained in the past data challenges and in the daily Monte Carlo productions and user analysis usage in the experiment.

This paper studies the interaction of a forward error correction (FEC) code with queue management schemes like Drop Tail (DT) and RED. Since RED spreads randomly packet drops, it reduces consecutive losses. This property makes RED compatible a priori with the use of FEC at the packet level. We show, through simulations, that FEC combined with RED may indeed be more efficient than FEC combined with DT. This however depends on several parameters like the burstiness of the background traffic, the FEC block size and the amount of redundancy in a FEC block. We conclude generally that using FEC is more efficient with RED than with DT when the loss rate is small, a relatively important amount of redundancy and at most a moderate FEC block size is used. We complement these observations with a simple model, which is able to capture the tradeoff between the locality and the frequency of losses.

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