The Inter Operator Identifier (IOI) is shared between sending and receiving networks, service providers, or content providers. The orig-IOI parameter is used by the originating network in the requests whereas the term-IOI parameter is used by the terminating network in the responses. 

As a P-CSCF, the SBC has the following abilities:

  • Use the orig-IOI in the REGISTER requests only. 
  • Include the orig-IOI in all the SIP requests and responses. While generating responses for any UE terminated requests, the SBC as a P-CSCF copies the orig-IOI parameter received in the P-Charging-Vector header of the request to the P-Charging-Vector header of the response, and also includes a term-IOI parameter. Both the orig-IOI and term-IOI parameters contain configured "Inter Operator ID" for the network.


The "Inter Operator ID" value associated with the Trunk Group towards the IMS core is used for the configuration.

Figure 1: Call Flow Depicting Insertion of Orig-IOI and Term-IOI at P=CSCF


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