A billing mediation system for use within a communications network that correlates session records pertaining to usage of network resources is disclosed. The billing mediation system includes a record receiver, a record correlator, a look ahead cache, a set of buffers, and a session records database. The set of buffers includes a single segment insert buffer, a multi segment insert buffer, a multi segment update buffer and a billing finalization update buffer. A method for correlating session records is also provided. The method includes receiving a session record, placing the session record into a segment buffer based on the type of record, and updating a look ahead cache including providing a timestamp for the last update for a session. The transfer of correlated session records to a billing system is based on whether records for a session have been received based on session tracking within the look ahead cache.