We Claim:
1. A visited Online Charging System, OCS, (124, 628) in a Long Term Evolution/Evolved Packet Core, LTE/EPC network, comprising an Online Function, OCF, (404), a Account Balance Management Function, ABMF, (406), and a Rating Function, RF, (408), the system being configured to: receive a credit request from a network element (122) in a visited network (120) that has been requested to provide a service to a roaming mobile device (130, 630), determine a rating for the service based on a both local tariff defined by the operator of the visited network (120) and a tariff provided by a home OCS (114,618), grant a quota of service units to the network element (122) based on the local rating, transmit a credit response to the network element (122) indicating the granted quota, transmit an online charging request to a home OCS (114, 618) of the mobile device (130, 630) requesting charging information for an end user of the mobile device (130, 630), and to receive an online charging response from the home OCS (114, 618) that includes the charging information; wherein the charging information includes an allotment of service units from an account balance of the end user that is granted by the home OCS (114, 618) for use in credit control by the visited OCS (124, 628); create a temporary account for the end user based on the allotment of service units, and monitor the temporary account of the end user as quotas are granted to network elements (122), wherein, if the temporary account becomes depleted, the visited OCS (124, 628) requests an additional credit reservation from the home OCS (114, 618).
2. The system as claimed in claim 1 wherein: the visited OCS (124, 628) is further operable to set a life-cycle for the temporary account.
3. The system as claimed in claim 2 wherein: the visited OCS (124, 628) is further operable to report an unused portion of the temporary account to the home OCS (114, 618) if the life-cycle expires or the service ends.
4. The system as claimed in claim 1 wherein the charging information includes a currency conversion rate between the home OCS (114, 618) and the visited OCS (124, 628).

5. The system as claimed in claim 5 wherein: the visited OCS (124, 628) is further operable to insert an indication in the online charging request that local roaming charging applies for the service.
6. The system as claimed in claim 5 wherein: the interface between the visited OCS (124, 628) and the home OCS (114, 618) comprises a Diameter Ro interface, and a new Attribute Value Pair, AVP, is designated for the indication that local roaming charging applies for the service.
7. A method as claimed in performing local roaming charging in a visited Online Charging System, OCS, (124, 628) of an LTE/EPC network, characterized in that the method comprises:
receiving, in a visited Online Charging System, OCS, (124, 628) a credit request from a network element (122) in a visited network (120) that has been requested to provide a service to a roaming mobile device (130, 630); determining, in the visited OCS (124, 628), a rating for the service based on both a local tariff defined by the operator of the visited network (120) and a tariff provided by a home OCS (114, 618); granting a quota of service units to the network element (122) based on the local rating; transmitting a credit response from the visited OCS (124, 628) to the network element (122) indicating the granted quota, transmitting an online charging request from the visited OCS (124, 628) to a home OCS (114, 618) of the mobile device (130, 630) requesting charging information for an end user of the mobile device (130, 630); receiving an online charging response from the home OCS (114, 618) that includes the charging information, wherein the charging information includes an allotment of service units from an account balance of the end user that is granted by the home OCS (114, 618) for use in credit control by the visited OCS (124, 628); creating a temporary account for the end user based on the allotment of service units, monitoring, at the visited OCS (124, 628), the temporary account of the end user as quotas are granted to network elements (122), wherein, if the temporary account becomes depleted, the visited OCS (124, 628) requests an additional credit reservation from the home OCS (114, 618).
8. The method as claimed in claim 7 further comprising: setting a life-cycle for the
temporary account.

9. The method as claimed in claim 8 further comprising: reporting an unused portion of the temporary account to the home OCS (114, 618) if the life-cycle expires or the service ends.
10. The method as claimed in claim 7 wherein the charging information includes a currency conversion rate between the home OCS (114, 618) and the visited OCS (124, 628).
11. The method as claimed in claim 7 further comprising: inserting an indication in the online charging request that local roaming charging applies for the service.
12. The method as claimed in claim 11 wherein: the interface between the visited OCS (124, 628) and the home OCS (114, 618) comprises a Diameter Ro interface, and a new A VP is designated for the indication that local roaming charging applies for the service.
13. An apparatus comprising a memory and a processor, the memory containing a program comprising instructions which, when executed by the processor, cause the processor to implement a visited online charging system, OCS, (124, 628)characterized in that the visited OCS (124, 628) comprises: a rating function (408) operable to store a local tariff defined by an operator of a visited network (120); and an online charging function, OCF, (404) operable to receive a credit request from a network element (122) in the visited network (120) that has been requested to provide a service to a roaming mobile device (130, 630); wherein: the rating function (408) is further operable to determine a local rating for the service based on the local tariff; the OCF (404) is further operable to grant a quota of service units to the network element (122) based on the local rating, and to transmit a credit response to the network element (122) indicating the granted quota, the OCF (404) is further operable to transmit an online charging request to a home OCS (114, 618) of the mobile device (130, 630) requesting charging information for an end user of the mobile device (130, 630), and to receive an online charging response from the home OCS (114, 618) that includes the charging information; the charging information includes an allotment of service units from an account balance of the end user that is

granted by the home OCS (114, 618) for use in credit control by the visited OCS (124, 628); the OCF (404) is further operable to create a temporary account for the end user based on the allotment of service units in an account balance management function, ABMF, and the ABMF (406) is operable to monitor the allotment of service units in the temporary account, wherein, if the allotment of service units becomes depleted, the OCF (404) is operable to transmit another online charging request to the home OCS (114, 618) that requests a new allotment of service units, wherein, if there is a sufficient account balance for the end user, the home OCS (114, 618) may grant another allotment of service units in response to the online charging request.
14. The apparatus as claimed in claim 13 wherein: the OCF (404) is further operable to set a life-cycle for the temporary account in the ABMF (406).
15. The apparatus as claimed in claim 14 wherein: the OCF (404) is further operable to report an unused portion of the temporary account to the home OCS (114, 618) if the life-cycle expires or the service ends.
16. The apparatus as claimed in claim 13 wherein: the OCF (404) is further operable to insert an indication in the online charging request that local roaming charging applies for the service.
17. The apparatus as claimed in claim 13 wherein: the interface between the visited OCS (124, 628) and the home OCS (114, 618) comprises a Diameter Ro interface, and a new A VP is designated for the indication that local roaming charging applies for the service.