The Private User Identity is applicable to IMS subscribers only. The Private User Identity is in the form of a Network Access Identifier (NAI), which is defined in RFC 4282. If the GAA bootstrapping is based on authentication data from the IM domain, the corresponding Private User Identity from the IM d omain (IMPI) is used as it is. If the GAA bootstrapping is based on the authentication data from the CS/PS domain, a Private User Identity is derived from user's IMSI according TS 23.003 is used. The Private User Identity is permanent subscriber data and is stored in HSS and in S-CSCF.

The Public User Identities of an IMS subscriber contain one or several instances of Public User Identity or Wildcarded Public User Identity, which are defined in TS 23.003. The Public User Identities are permanent subscriber data and are stored in HSS, S-CSCF and BSF.

The Private Service Identity is applicable to a PSI user and is similar to a private user identity in the form of a Network Access Identifier (NAI), which is defined in RFC 4282. The Private Service Identity is operator defined. The Private Service Identity is permanent data and is stored in HSS and S-CSCF.

The Public Service Identity hosted by an application server may match either to a distinct PSI or a wilcarded PSI that is stored in the HSS. The PSI is defined in TS 23.003. The relationship between Wildcarded Public Service Identities and Private Service Identities is one-to-one. A Public Service Identity (distinct PSI or Wildcarded PSI) cannot be shared by more than one Private Service Identity. The Public Service Identity is permanent data and is stored in HSS and S-CSCF.

Flag associated to each Public User Identity to indicate that the identity is barred from any IMS communication. A Public User Identity that is barred is allowed to register with the IMS. The Barring indication is permanent subscriber data and is stored in the HSS and in the S-CSCF.

The list of authorized visited network identifiers is associated with the Public User Identity to indicate which visited network identifiers are allowed for roaming. If the Public User Identity is part of a set of implicitly registered Public User Identities, the list of authorized visited network identifiers shall be the same for the whole set. The list of authorized visited network identifiers is permanent subscriber data and is stored in the HSS. This list can be a linear list of visited network identifiers or a compound list of network identifier types e.g. home PLMN or home country; however the exact structure of the list is an implementation option.

The Services related to Unregistered State is a parameter associated to each Public User Identity and Public Service Identity and it indicates whether the identity has services related to unregistered state or not. For a Public Service Identity the parameter shall always be set to value indicating that the identity has services related to unregistered state. The Services related to Unregistered State is permanent subscriber data stored in the HSS.

The Implicitly Registered Public User Identity Set contains one or several instances of Public User Identity of an IMS subscriber, and is defined in TS 29.228 following the described concept in TS 23.228. Several Implicitly Registered Public User Identity Sets can be configured for a given user. Each Public User Identity shall be included in no more than one Implicitly Registered Public User Identity Set. The Implicitly Registered Public User Identity Sets are permanent subscriber data and are conditionally stored in HSS and in S-CSCF.

The Default Public User Identity indicator marks the Public User Identity to be used as default Public User Identity in each Implicitly Registered Public User Identity Set, and is defined in TS 29.228. There shall be one Default Public User Identity per Implicitly Registered Public User Identity Set. The Default Public User Identity indicator is permanent subscriber data and is conditionally stored in the HSS.

The PSI Activation State is specific for Public Service Identities and is defined in TS 29.328. The PSI Activation State indicator for distinct PSIs is temporary subscriber data and is stored in the HSS. The PSI Activation State indicator for wildcarded PSIs is permanent subscriber data and is stored in the HSS. A wildcarded PSI or a distinct PSI that matches a wildcarded PSI shall not be activated/deactivated via the Sh interface.

The Display Name is a string associated with a Public Identity The Display Name is permanent subscriber data and is conditionally stored in the HSS and in the S-CSCF.

The Alias Public User Identity Set contains two or more Public User Identities of an IMS subscriber, and these Public User Identities in the set are aliases of each other and their treatment is identical. Several Alias Public User Identity Sets can be configured for a given user. Each Public User Identity shall be included in no more than one Alias Public User Identity Set. All the Public User Identities in every Alias Public User Identity Set shall be included in the same Implicitly Registered Public User Identity Set, and shall be linked to the same Service Profile and share the same service data for each and every service, but there can be more than one Alias Public User Identity Set per Implicitly Registered Public User Identity Set and Service Profile. The Alias Public User Identity Sets are permanent subscriber data and are conditionally stored in the HSS and in the S-CSCF.

The Loose-Route Indication indicates if the loose-route mechanism is required for all the Public User Identities belonging to a Private User Identity. It is defined in TS 29.228 following the described concept in TS 24.229. The Loose-Route Indication shall have the same value for all the Private Identities of the IMS subscription if at least one Public User Identity is shared by the multiple Private Identities; otherwise, each Private User Identity may have a different Loose-Route Indication value. The Loose-Route Indication is permanent subscriber data and is conditionally stored in the HSS and in the S-CSCF.

The Service Priority Level indicates the Priority Level allowed for the Public Identity. It is defined in TS 29.228 following the described concept in TS 24.229. The Service Priority Level is permanent subscriber data and is conditionally stored in the HSS and the S-CSCF.

The Extended Priority provides priority information for the Public Identity. It provides support for more than one subscribed namespaces in an operator's network, as included in priority mechanisms described in TS 24.229 and it is defined in TS 29.228. The Extended Priority is permanent subscriber data and is conditionally stored in the HSS and the S-CSCF.

The Reference Location Information contains the reference location for the Private User Identity (e.g. line identification in the case of fixed line access). It is defined in TS 29.228 following the described concept in TS 23.167. The Reference Location Information is permanent subscriber data and is conditionally stored in the HSS and the S-CSCF.

The Priviledged-Sender Indication indicates if the corresponding Private User Identity shall be considered a priviledged sender. It is defined in TS 29.228 following the described concept in TS 24.229. If for an IMS subscription at least one Public User Identity is shared by more than one Private Identity, then all these Private Identities shall have the same value for the Priviledged-Sender Indication; otherwise, each Private User Identity may have a different Priviledged-Sender Indication value. The Priviledged-Sender Indication is permanent subscriber data and is conditionally stored in the HSS and in the S-CSCF.

An Additional MSISDN (A-MSISDN) is an MSISDN optionally assigned in addition to the already assigned MSISDN(s) to a user with PS subscription. For the definition of A-MSISDN see TS 23.003. It is a permanent subscriber data stored in the HSS/HLR. It is temporarily stored in the MME, SGSN and AS.