*i want to know that what happen when validity time expire, some think that know is change state IDLE and remove from session, but what kind of request we send to client *
The Tcc timer supervises an ongoing credit-control session in the credit-control server. It is RECOMMENDED to use the Validity-Time as input to set the Tcc timer value. In case of transient failures in the network, the Diameter credit-control server might change to Idle state. To avoid this, the Tcc timer MAY be set so that Tcc equals to 2 x Validity-Time. in case of the timers expire diameter need to send a notification to connected devices that this session is no longer active so delete info about this session. Diameter send Session Termination Request and delete all related data if this session, also from the database.