Patent ID: 8855597

Claim:
A system comprising: a Serving-Call Session Control Function (S-CSCF) for an IP Multimedia Subsystem (IMS) core network that is configured to: receive a session-related message for user equipment (UE) from an access network that is serving the UE, wherein the session-related message includes an identifier for the access network that provides service to the UE for accessing the IMS core network; identify location information related to the access network identifier in the session-related message; determine a time zone where the UE is located based on the location information; identify a local time for the S-CSCF based on an internal clock; adjust the local time for the S-CSCF based on the time zone of the UE to determine a local time for the UE; generate a Diameter charging message for the session; insert a timestamp in an Attribute Value Pair (AVP) of the Diameter charging message based on the local time for the UE; and transmit the Diameter charging message to an offline charging function.