Section: 13.4 Public User Identity
Content: A Public User Identity is any identity used by a user within the IMS subsystem for requesting communication to another user. The Public User Identity shall take the form of either a SIP URI (see IETF RFC 3261 [26]) or a Tel URI (see IETF RFC 3966 [45]). The 3GPP specifications describing the interfaces over which Public User Identities are transferred specify the allowed Public User Identity formats, in particular 3GPP TS 24.229[ IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 ]  [81] for SIP signalling interfaces, 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [95] for Cx and Dx interfaces, 3GPP TS 29.329[ Sh interface based on the Diameter protocol; Protocol details ]  [96] for Sh interface, 3GPP TS 29.165[ Inter-IMS Network to Network Interface (NNI) ]  [97] for II-NNI interface. In the case the user identity is a telephone number, it shall be represented either by a Tel URI or by a SIP URI that includes a "user=phone" URI parameter and a "userinfo" part that shall follow the same format as the Tel URI. According to 3GPP TS 24.229[ IP multimedia call control protocol based on Session Initiation Protocol (SIP) and Session Description Protocol (SDP); Stage 3 ]  [81], the UE can use either: - a global number as defined in IETF RFC 3966 [45] and following E.164 format, as defined by ITU-T Recommendation E.164 [10] or - a local number, that shall include a "phone-context" parameter that identifies the scope of its validity, as per IETF RFC 3966 [45]. According to 3GPP TS 29.165[ Inter-IMS Network to Network Interface (NNI) ]  [97] a global number as defined in IETF RFC 3966 [45] shall be used in a tel-URI or in the user portion of a SIP URI with the user=phone parameter when conveyed via a non-roaming II-NNI except when agreement exists between the operators to also allow other kinds of numbers. According to 3GPP TS 29.229[ Cx and Dx interfaces based on the Diameter protocol; Protocol details ]  [95] and 3GPP TS 29.329[ Sh interface based on the Diameter protocol; Protocol details ]  [96] the canonical forms of SIP URI and Tel URI shall be used over the corresponding Diameter interfaces. The canonical form of a SIP URI for a Public User Identity shall take the form "sip:username@domain" as specified in IETF RFC 3261 [26], clause 10.3. SIP URI comparisons shall be performed as defined in IETF RFC 3261 [26], clause 19.1.4. The canonical form of a Tel URI for a Public User Identity shall take the form "tel:+<CC><NDC><SN>" (max number of digits is 15), that represents an E.164 number and shall contain a global number without parameters and visual separators (see IETF RFC 3966[45], clause 3). Tel URI comparisons shall be performed as defined in IETF RFC 3966[45], clause 4. Public User Identities are stored in the HSS either as a distinct Public User Identity or as a Wildcarded Public User Identity. A distinct Public User Identity contains the Public User Identity that is used in routing and it is explicitly provisioned in the HSS.