The CMS RPC system - detector performance and upgrade

The Resistive Plate Chambers are used in CMS as dedicated muon trigger detector both in the barrel and in the two endcap regions. They also contribute to the identification of the muons, together with Drift Tube in the barrel and Cathode Strip Chambers in the endcaps. About 4000 square meter of double gap RPCs have been produced and have been installed in the experiment since 2007. We will present the performance study and operational experience after three years of successful data taking at LHC. The upgrade program foreseen for the next two years also will be outlined.