In the previous generations of High Energy Physics experiments, most of the compute intensive processing was done on site (e.g. CERN) and in a few dedicated large computing centers. It quickly became apparent that this model could not be scaled to the LHC experiments needs. A hierarchical model of large computing centers (Tier 1) surrounded by smaller centers (Tier 2) and lab/university level centers (Tier 3) was developped. The « fabric » of the system is both hardware (e.g. dedicated network connections) and software (tools to authenticate people or services, locate and move data and run jobs around the world). Nowadays the model is less hierarchical but the main « construction bricks » remain the same. A more comprehensive description of the
World-wide LHC Computing grid (WLCG) is available here.

A Tier 1 center is located at the IN2P3 computing center (CCIN2P3) in Lyon, with dedicated connections to a dozen Tier 2 and Tier 3 sites in France, as well as sites in Romania, China and Japan (the « French Cloud ») and of course CERN. The LCG-France organisation coordinates the activities in France.

Laurent Duflot is currently the scientific coordinator of LCG-France : see here an interview given to the Lettre Informatique de l’IN2P3.