This Recommendation defines the stage 2 of the Integrated Services Digital Network (ISDN) as provided by telecommunications operators for the Malicious Call Identification (MCID) supplementary service. Stage 2 identifies the functional capabilities and the information flows needed to support the service description. The stage 2 description also identifies user operations not directly associated with a call. The malicious call identification supplementary service allows the served user to alert the service provider that a malicious call has been received and requests that the service provider retain the calling information for the purpose of identifying the caller. The MCID supplementary service is available to all telecommunications services.