This document specifies the identity management and authentication protocols needed to support Mission Critical Push To Talk (MCPTT). Identity management applies only to on-network operation. Mission critical communication services are services that require preferential handling compared to normal telecommunication services@ e.g. in support of police or fire brigade. The MCPTT service can be used for public safety applications and also for general commercial applications (e.g.@ utility companies and railways). This document is applicable to User Equipment (UE) supporting the identity management client functionality@ and to application servers supporting the identity management server functionality.