The Evolved Packet Core (EPC) uses Diameter for access to the HSS, EIR and OCS. If the EPC has not been deployed in a PLMN and a subscriber roams into a network where an EPC has been deployed, then queries from the V-PLMN will use Diameter and the H-PLMN has existing legacy elements like the HLR, EIR and Prepaid SCP that use SS7. This use case describes Diameter Interworking between LTE and Legacy Elements Inter-PLMN (Roaming).
