Section: 5.3.4.3 Inter-network correlation
Content: To enable the different operators involved in IMS sessions to identify each other, the Inter Operator Identification concept (IOI) is introduced. IOI allows operators involved with session signalling to identify each other by exchanging operator identification information within the SIP signalling. The IOI is composed of one pair of originating IOI and terminating IOI. Additionally, one or more transit IOI values may occur. The IOI concept may help to support inter operator charging. The following requirements relate to the IOI concept: a) The IOI concept shall allow operators to uniquely identify each other for the SIP based requests; for example between A's Home PLMN and B's Home PLMN or between an A's Home PLMN and a A's Visited PLMN. b) The IOI concept can be used for inter operator accounting identification purposes. c) It shall be possible to prevent the information used for IOI from being passed to the UE. d) It shall be possible to apply the IOI concept on a peer to peer basis between operators. It shall be possible to use different identity values for operator identification between operators involved in IMS session related procedures and session unrelated procedures. e) IOI identities shall be included within SIP signalling: 1) When a SIP request is passed out of an IMS network the IOI identity of that IMS network (referred as originating IOI) shall be included in the SIP signalling. 2) When a SIP response is returned the IOI identity of that responding IMS network (referred as terminating IOI) shall be included in the SIP signalling. 3) For interconnection scenarios where one or more transit operators are between the originating and terminating operator, the identities of involved transit operators (referred as transit IOI) may be included in the SIP signalling. It should be noted that transit operators can be selected independently for each SIP method and direction of request. Due to operator policy, a transit operator may also hide his identity by adding a void value. Addition and deletion of transit IOI values are operator configurable. Details are described in the TS 24.229[ IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 ]  [211]. 3a) The transit operator may provide IMS application servers to an operator network. The set of transit IOI values received in any SIP request or SIP response may be delivered to the IMS application server as per operator policy. 4) The set of originating IOI, transit IOI(s), and terminating IOI is applicable to a single inter IMS network signaling exchange (e.g., A’s Visited PLMN and A’s Home PLMN or A’s Home PLMN to B’s Home PLMN). When the SIP signaling progresses to another PLMN a new set of originating IOI, transit IOI(s), and terminating IOI is generated. The set of IOI values generated for one inter-operator signaling exchange should not be passed to the operators involved in a subsequent inter-operator signaling exchange. For example, the set of IOIs for the path from A’s Visited PLMN to A’s Home PLMN is different than for the path from A’s Home PLMN to B’s Home PLMN and the set of IOI values for one should not be transmitted across the other. 5) The path between an S-CSCF and an application server is an independent signaling exchange from those signaling exchanges between PLMNs. As such, the set of originating and terminating IOIs exchanged on those paths should not be transmitted on the path toward the application server. In addition, any set of originating and terminating IOIs for the path from the S-CSCF to an application server should not be transmitted on any other path from the S-CSCF. The set of transit IOI values received in any SIP request or SIP response may be delivered to the IMS application server as per operator policy. This set of transit IOI values delivered to the IMS application server do not reflect inter operator path between the S-CSCF and the application server, but rather the path either inbound to the S-CSCF or outbound from the S-CSCF and may be useful for operator-specific application processing in the application server. NOTE 0: No transit networks are expected between the S-CSCF and a 3rd party application server. f) Each IMS network is responsible for including its own unique IOI Identity into the SIP signalling. The IOI Identity shall be unique for each IMS operator (for example the IOI Identity of Home Operator A is different from Home Operator B). g) Three types of IOI shall be defined: 1) Type 1 IOI: between the Home PLMN and a Visited PLMN for an end user in roaming situation (case when the P-CSCF is located in a visited network); 2) Type 2 IOI: between the IMS network operator which holds the subscription of the originating end user and the IMS network operator which holds the subscription of the terminating end user. In case of redirection, Type 2 IOI can be used between IMS network operators which hold a subscription of the terminating end user, i.e. between the terminating party's IMS network operator from which the session is redirected to the terminating party's IMS network operator to which the session is redirected. In case Visited PLMN loopback is applied for Roaming Architecture for Voice over IMS with Local Breakout, Type 2 IOI can be used between A’s Visited PLMN and B’s Home PLMN. 3) Type 3 IOI: between the home IMS network operator and a service provider; h) For Type 1 IOI, the P-CSCF is responsible for generating the originating IOI and the S-CSCF in the Home PLMN is responsible for generating the terminating IOI; For Type 1 IOI, the "enhanced MSC for ISC" is responsible for generating the originating IOI. In case Visited PLMN loopback is applied for Roaming Architecture for Voice over IMS with Local Breakout, Type 1 IOI is also used between A’s Home PLMN and Visited PLMN on the loopback path in which the S-CSCF is responsible for generating the originating IOI and the TRF is responsible for generating the terminating IOI. i) For Type 2 IOI, the S-CSCF in the originating party's home IMS network or the E-CSCF in the originating party's local network or the originating MGCF is responsible for generating the originating IOI and the S-CSCF in the terminating party's IMS home network or the terminating MGCF is responsible for generating the terminating IOI. In case of redirection by the S-CSCF, the S-CSCF-in the terminating party's IMS network operator from which the session is redirected- is responsible for generating the originating IOI and the S-CSCF in the terminating party's IMS network operator or the terminating MGCF- to which the session is redirected- is responsible for generating the terminating IOI. In case of Visited PLMN loopback is applied for Roaming Architecture for Voice over IMS with Local Breakout, the TRF in A’s Visited PLMN is responsible for generating the originating IOI, and the S-CSCF in the B’s Home PLMN is responsible for generating the terminating IOI. NOTE 1: The originating IOI generated by the MGCF may not be reliable depending on Operators’ network configuration. j) For Type 3 IOI, when forwarding a request to an AS, the S-CSCF in the Home PLMN is responsible for generating the originating IOI and the AS contacted by this S-CSCF is responsible for generating the terminating IOI. For a Type 3 IOI, when an AS initiates a request, the AS is responsible for generating the originating IOI and the S-CSCF or I-CSCF contacted by this AS is responsible for generating the terminating IOI. For Type 3 IOI, when the E-CSCF forwards a request to the EATF or to the LRF, the E-CSCF is responsible for generating the originating IOI, and the EATF and LRF are responsible for generating the terminating IOI. For Type 3 IOI, when the LRF initiates a request to the E-CSCF, the LRF is responsible for generating the originating IOI, and the E-CSCF is responsible for generating the terminating IOI. k) IOI Identities received in the session signalling shall be incorporated into the CDRs produced by the IMS network elements. The operator identification information may be used for inter operator accounting purposes. l) The allocation of the IOI values for the operators is outside the scope of 3GPP standardization. NOTE 2: The relationship of the IOI concept with security aspects between operators is not specified in this document.