What is IOI (Inter-operator identifier)?

Inter Operator Identifier (IOI) is a globally unique identifier. It is used to share between operator networks, content suppliers, and administrator organizations, to associate billing data created inside the IMS (IP Multimedia Subsystem). The Originating-IOI AVP holds the Inter Operator Identifier (IOI) for the beginning network as produced by the IMS network component which assumes liability for populating this boundary in a SIP request. The Terminating-IOI AVP holds the Inter Operator Identifier (IOI) for the ending network as produced by the IMS network component which assumes liability for populating this boundary in a SIP reaction.