This day we have an idea about the balling system. This system process the accounts, balance of all the postpaid customers, this system get the data feeds from the smart network system or what called CDR. the CDR after each call has to do the following tasks: a- generate the calls time b-generate the ph.number of calling c- generate the ph.number of customer d- generate the calling time by seconds e- the real duration f- the calls cost So. as it explained the billing system gets the data "calls time, number of calls, calls cost...etc from the CDR then the system of billing process this data in order to manage the balance of the customers as well generates the bills