Mechanism for PTT users to change the type of the call in SIP based PoC networks

Currently the users register to services and once the registration is successful; the service starts running for the user. The users have no option to switch between services based on their need. Deregistering is not the preferred option when users want to temporarily stop the service execution or if they want to switch over to another service from the existing one. Usually in SIP based IMS networks, the IMS Application Server hosts the services and the serving proxy i.e. the S-CSCF triggers the required service for a user based on "Initial Filter Criteria (iFC) or Shared filter criteria (SiFC)".