Content for  TS 33.127  Word version:  18.8.0

Annex E provides detailed description of STIR SHAKEN and RCD/eCNAM procedures.

The IMS Signalling Function that interacts with the AS for verification or the LMISF-IRI (inbound roaming with HR) or P-CSCF (inbound roaming with LBO) shall provide the IRI-POI functions for STIR/SHAKEN and RCDeCNAM. In addition, at the originating side of the session, the IMS Signalling Function that interacts with the AS for signing shall provide the IRI-POI functions for STIR/SHAKEN and RCD. In some redirection cases, the IMS Signalling Function, even if not interacting with the AS of verification, may have to provide the IRI-POI functions for STIR/SHAKEN and RCD/eCNAM (see clause 7.11.2.3 of TS 33.128). Depending on the deployment, the IMS Signalling Function that interacts with the AS for signing is either the Telephony AS or the Egress IBCF (see Figure E.2.1-1). Similarly, depending on the deployment, the IMS Signalling Function that interacts with the AS for verification is either the Telephony AS or the Ingress IBCF (see Figure E.2.1-1). Accordingly, Table 7.14.2-1 identifies the IRI-POIs for STIR/SHAKEN and RCD while Table 7.14.2-2 identifies the IRI-POIs for eCNAM. In Tables below, option 1 and option 2, indicate the deployment options of IMS Signalling Function that interacts with the AS for signing or AS for verification. Such deployment options can be mutually independent in the originating CSP or the terminating CSP. For emergency sessions, Egress IBCF interacts with the AS for signing.

The IRI-POI present in the IMS network functions listed in Table 7.14.2-1 and Table 7.14.2-2 shall generate xIRI when it detects the following specific events or information:

• Signature generation.
• Signature validation.

The Signature generation xIRI is generated when the IRI-POI present in the Telephony AS for non-roaming UE or outbound roaming UE (HR) or in the egress IBCF detects that the Telephony AS or egress IBCF has sent a signing request (HTTP POST request) to the AS for signing and received a signing response (HTTP 200 OK) containing the Identity header. This interaction occurs when the Telephony AS or egress IBCF has received a SIP INVITE request from a UE. The xIRI shall contain the identity token which also includes the signed RCD information if RCD is supported, and the initial caller number if changes occur on that number. The Signature validation xIRI is generated when:

• The IRI-POI present in the Telephony AS or ingress IBCF has sent a verification request (HTTP POST request) containing the Identity token to the AS for verification and received a verification response (200 OK) containing the verification outcome (validation passed / validation failed / no validation). The xIRI shall contain the calling party identity, the identity token, the verification outcome, and the RCD or eCNAM related information if RCD or eCNAM is supported.
• The IRI-POI present in the P-CSCF for inbound roaming UE (LBO) or LMISF-IRI for inbound roaming UE (HR) receives a SIP INVITE request including appropriate SIP headers containing the verification outcome and RCS or eCNAM related information if RCS or eCNAM is supported.

These xIRIs should be correlated by MDF2 with the xIRIs related to IMS session establishment. The correlation identifier found in the STIR/SHAKEN xIRIs and IMS xIRIs should help the MDF2 performing the correlation procedure and generated IRIs with both sets of data for delivery to LEMF.