Hot Billing refers to the real time Usage charge calculation and transfer of Call Detail records (CDR’s). This processing is happened within a short period of time. This is basically used for prepaid billing. Hot billing performs credential & balance check and after then it performs transfer and cost calculation of CDRs. Typical for Hot Billing CDR’s are processed outside the switch. The transfer and processing is done within a defined time window. An exact value of this time window is not given, but a common understanding is that the transfer and processing has to be done within a few seconds in case of Hot Billing.
Warm Billing refers to the near real time cost calculation of CDRs( Call Detail Records). Only difference between hot and warm billing is that time window for warm billing is within in few minutes whereas in hot billing time window for CDRs processing is within few seconds.
This is basically used for postpaid billing. Swtich sends CDRs to Rating system and In Rating system , periodically batch runs to calculate the usage charges. This rated usage charge is used by Billing system to bill postpaid customer during billing period.