  The identification of b jets is a crucial issue to study and characterize
various channels like top quark events and many new physics scenarios.
Different b-tagging techniques are defined in CMS which benefit from the long
life time, high mass and large momentum fraction of the b-hadron produced in
b-quark jet. Effcient algorithms have been developed based on the measure of
b-hadron secondary vertex or on tracks with a large impact parameter. Data
collected in pp collisions at 7TeV in 2011 are used to estimate both the
b-tagging effciency and the mistag rate from light flavor jets.
