Name

AVP Code

Data Type

Vendor

Allowed-WAF-WWSF-Identities

656

Grouped

3GPP

Specifies the addresses of the WebRTC Authentication Functions (WAF) and WebRTC Web Server Functions (WWSF) permitted for a subscription. This AVP provides control over which WebRTC-related entities can interact with the subscriber's data or sessions. The AVP structure is defined as follows:

WebRTC-Authentication-Function-Name: Specifies the name or address of a WebRTC Authentication Function (WAF) that is allowed for the subscription.

WebRTC-Web-Server-Function-Name: Specifies the name or address of a WebRTC Web Server Function (WWSF) that is allowed for the subscription.

Alternate-Digest-Algorithm

662

UTF8String

3GPP

Specifies the hash algorithm used in HTTP Digest Authentication, as outlined in [RFC7616]. This AVP is utilized alongside Digest-HA1 and Alternate-Digest-HA1 to provide enhanced authentication mechanisms for SIP-based signaling within IMS networks. The AVP contains the name of the hashing algorithm, such as:

MD5 – 128-bit hash, supported only for backward compatibility.

SHA-256 – 256-bit hash, offering stronger security.

SHA-512-256 – 256-bit output from SHA-512 for optimized performance.

When the Alternate-Digest-Algorithm AVP is present, the Alternate-Digest-HA1 AVP must also be included to convey the hashed value using the specified algorithm. At the same time, the Digest-HA1 AVP provides the MD5 hash for backward compatibility.

Alternate-Digest-HA1

663

UTF8String

3GPP

Contains the H(A1) hash value as specified in [RFC7616]. This AVP is used for HTTP Digest Access Authentication, enhancing security in IMS and other Diameter-based systems by storing pre-computed hash values. When the Alternate-Digest-Algorithm AVP is present, the Alternate-Digest-HA1 AVP must also be included to convey the hashed value using the specified algorithm. At the same time, the Digest-HA1 AVP provides the MD5 hash for backward compatibility.

Associated-Identities

632

Grouped

3GPP

Contains the private user identities linked to an IMS subscription. This AVP enables efficient management and retrieval of private user identities associated with a subscriber. The AVP structure is defined as follows:

User-Name: Specifies the private user identities associated with the IMS subscription.
Other AVPs are optional.

Associated-Registered-Identities

647

Grouped

3GPP

Contains the private user identities registered with the public user identity received in the request command. This AVP facilitates the mapping and management of private identities linked to a specific public identity in IMS networks. The AVP structure is defined as follows:

User-Name: Specifies the private user identities registered with the public user identity.

Call-ID-SIP-Header

643

OctetString

3GPP

Contains the information in the Call-ID header as defined in [RFC3261]. The Call-ID serves as a globally unique identifier for SIP dialogs or registrations, enabling SIP servers to track and correlate session-specific requests and responses.

Charging-Information

618

Grouped

3GPP

Contains the addresses of the charging functions in IMS and other Diameter-based systems. It plays a critical role in supporting charging-related processes by specifying the event charging and collection function names for both primary and secondary configurations. The AVP structure is defined as follows:

Primary-Event-Charging-Function-Name: Specifies the address of the primary event charging function.

Secondary-Event-Charging-Function-Name: Specifies the address of the secondary event charging function, used as a backup to the primary function.

Primary-Charging-Collection-Function-Name: Specifies the address of the primary charging collection function.

Secondary-Charging-Collection-Function-Name: Specifies the address of the secondary charging collection function, used as a backup to the primary function.

Confidentiality-Key

625

OctetString

3GPP

Contains the Confidentiality Key (CK). This AVP is used in secure communication scenarios within IMS and other Diameter-based networks to ensure confidentiality by encrypting sensitive data during transmission.

Contact

641

OctetString

3GPP

Contains contact addresses and parameters specified in the Contact header, as defined in [RFC3261]. This AVP is essential for SIP communication within IMS networks, as it specifies the URI and related parameters used for addressing and routing SIP messages.

Deregistration-Reason

615

Grouped

3GPP

Used to indicate the reason for a de-registration operation in IMS or other Diameter-based networks. This AVP is typically included in messages to provide context about why a user or service has been deregistered, such as user-initiated actions, network errors, or administrative decisions. The AVP structure is defined as follows:

Reason-Code: Specifies the reason for de-registration.

Reason-Info: Provides additional information about the reason for de-registration.

Failed-PCSCF

664

Grouped

3GPP

Used to indicate the Fully Qualified Domain Name (FQDN) or IP addresses of the Proxy-Call Session Control Function (P-CSCF) nodes that have experienced failures. This information is critical for debugging and failover mechanisms within IMS. The AVP structure is defined as follows:

PCSCF-FQDN: Specifies the FQDN of the failed P-CSCF.

PCSCF-IP-Address: Specifies one or more IP addresses of the failed P-CSCF.

Feature-List

630

Unsigned32

3GPP

Represents a bitmask indicating the features supported by an application. Each bit in the mask corresponds to a specific feature, with a value of 1 indicating support for that feature and 0 indicating its absence. The interpretation of the bitmask is context-dependent and varies based on the associated Feature-List-ID AVP. For example, in the Cx application, the meanings of the bits are defined in [TS 29.229], Section 7.1.1.

Feature-List-ID

629

Unsigned32

3GPP

Identifies the specific feature list to which the corresponding Feature-List AVP applies. This AVP enables multiple feature sets to be defined, with the Feature-List-ID providing context for the bitmask in the Feature-List AVP.

From-SIP-Header

644

OctetString

3GPP

Carries the contents of the SIP From header field as defined in [RFC3261]. This AVP is used to communicate the originating party's address and related information in a SIP session.

Identity-with-Emergency-Registration

651

Grouped

3GPP

Contains a pair of private and public user identities that are emergency registered. Emergency registration enables a user to initiate communication during an emergency even if they are not authenticated through conventional registration methods. The AVP structure is defined as follows:

User-Name: Contains the private user identity associated with the emergency registration.

Public-Identity: Contains the public user identity associated with the emergency registration.

Additional AVPs: Can include other relevant AVPs to support specific network requirements.

Initial-CSeq-Sequence-Number

654

Unsigned32

3GPP

Represents the sequence number of the CSeq header field from the initial successful SIP REGISTER request. This value is extracted as defined in [RFC3261] and serves as a critical identifier for maintaining session consistency.

Integrity-Key

626

OctetString

3GPP

Contains the Integrity Key (IK), which is used to ensure message integrity and prevent tampering during transmission. This key is a fundamental element of secure communications in IMS and other Diameter-based systems.

LIA-Flags

653

Unsigned32 (Bitmask)

3GPP

Representing a bitmask. Each bit in the mask has a specific meaning, as defined in [TS29.299]. For instance:

Bit 0: PSI Direct Routing Indication

When set, this bit indicates that the request corresponds to PSI Direct Routing, requiring the HSS to include an AS name in the Server-Name AVP.

Note: Bits not explicitly defined are set to 0 by the sender and ignored by the receiver.

Line-Identifier

500

OctetString

ETSI

Used to carry a unique and fixed broadband access line identifier associated with a user. It enables the association of a specific user session or registration with the physical broadband access line utilized for the connection.

Loose-Route-Indication

638

Enumerated

3GPP

Specifies whether the loose route mechanism is required for serving registered Public User Identities. Values:

LOOSE_ROUTE_NOT_REQUIRED (0): Indicates that the loose route mechanism is not required.

LOOSE_ROUTE_REQUIRED (1): Indicates that the loose route mechanism is required.

Mandatory-Capability

604

Unsigned32

Represents one or more mandatory capabilities of an S-CSCF. These capabilities help identify the functional attributes supported by the S-CSCF as specified in [TS29.228] (Clause 6.7).

Multiple-Registration-Indication

648

Enumerated

3GPP

Used to indicate whether a request relates to a multiple registration scenario. Values:

NOT_MULTIPLE_REGISTRATION (0): Indicates that the request is not associated with multiple registrations.

MULTIPLE_REGISTRATION (1): Indicates that the request is related to multiple registrations.

Optional-Capability

605

Unsigned32

3GPP

Represents optional capabilities supported by an S-CSCF. Each value corresponds to a single optional feature or a set of features as defined in 3GPP [TS29.228] (Clause 6.7).

Originating-Request

633

Enumerated

3GPP

Indicates that a request to the HSS is related to an Application Server (AS) originating a SIP request during a Location-Information-Request (LIR) operation. Values:

ORIGINATING (0): Indicates that the request is for an originating SIP request from the AS.

Path

640

OctetString

3GPP

Contains a comma-separated list of SIP proxies included in the Path header. This is defined in [RFC3327], facilitating SIP signaling in IMS networks.

PCSCF-FQDN

665

DiameterIdentity

3GPP

Contains the Fully Qualified Domain Name (FQDN) of the Proxy-Call Session Control Function (P-CSCF) in an IMS network. It is used to uniquely identify the P-CSCF node handling SIP signaling for a user.

PCSCF-IP-Address

666

DiameterAddress

3GPP

Contains the IPv4 or IPv6 address of the P-CSCF in the IMS network. It complements the PCSCF-FQDN AVP by providing the transport-layer address for the P-CSCF.

P-CSCF-Subscription-Info

660

Grouped

3GPP

Encapsulates subscription information related to the Proxy-Call Session Control Function (P-CSCF). It includes critical details such as SIP headers and contact information used during subscription requests in IMS networks. The AVP structure is defined as follows:

Call-ID-SIP-Header: Contains the Call-ID header as per SIP signaling.

From-SIP-Header: Represents the From header in SIP.

To-SIP-Header: Represents the To header in SIP.

Contact: Contains the Contact header with address and parameters.

Additional AVPs: Allows extensibility for further IMS use cases.

Primary-Charging-Collection-Function-Name

621

DiameterURI

3GPP

Provides the URI of the Primary Charging Collection Function (P-CCF) responsible for collecting charging data. It helps route Diameter accounting requests to the appropriate charging system.

Primary-Event-Charging-Function-Name

619

DiameterURI

3GPP

Specifies the URI of the Primary Online Charging Function (P-OCF). This AVP is integral to Diameter accounting processes in IMS, ensuring proper routing of accounting requests to the designated charging function.

Priviledged-Sender-Indication

652

Enumerated

3GPP

Informs the Serving-Call Session Control Function (S-CSCF) whether the Private User Identity is considered a privileged sender. Values:

NOT_PRIVILEDGED_SENDER (0): The sender is not considered privileged.

PRIVILEDGED_SENDER (1): The sender is considered privileged.

Public-Identity

601

UTF8String

3GPP

Contains the public identity of a user in the IMS. The identity is represented in either:

SIP URL: Follows the format defined in IETF RFC 3261 and RFC 2396, e.g., sip:user@example.com.

TEL URL: Adheres to the format in IETF RFC 3966, e.g., tel:+123456789.

Both formats must be in canonical form, as described in [TS23.003].

Reason-Code

616

Enumerated

3GPP

Defines the reason for network-initiated de-registration in IMS. It is an enumerated type with the following values: Values:

PERMANENT_TERMINATION (0): The registration is permanently terminated.

NEW_SERVER_ASSIGNED (1): A new server has been assigned.

SERVER_CHANGE (2): A change of server is required.

REMOVE_S-CSCF (3): The Serving-Call Session Control Function (S-CSCF) is being removed.

Reason-Info

617

UTF8String

3GPP

Provides textual information explaining the reason for a de-registration event in IMS. It is typically used to inform the user or system about why the de-registration occurred.

Record-Route

646

OctetString

3GPP

Contains a comma-separated list of Record Route headers, as defined in [RFC3261]. It is used to store the route taken by a SIP request for routing subsequent requests.

Registration-Time-Out

661

Time

3GPP

Specifies the time when the User Equipment's (UE's) registration expires in the IMS. It uses the Time data type as defined in [RFC6733].

Restoration-Info

649

Grouped

3GPP

Grouped AVP containing the information needed by the S-CSCF to handle requests for a user during restoration. It includes SIP-related details like the Path and Contact AVPs, among others. The AVP structure is defined as follows:

Path: Routing path of SIP requests.

Contact: Contact header details from the registration request.

Initial-CSeq-Sequence-Number: Initial CSeq sequence number.

Call-ID-SIP-Header: Call ID from the SIP header.

Subscription-Info: Information about the subscription.

P-CSCF-Subscription-Info: Subscription information related to the P-CSCF.

Additional AVPs as required.

RTR-Flags

659

Unsigned32 (Bitmask)

3GPP

Conveys flags indicating specific triggers or conditions related to the request. It contains a bitmask where each bit represents a specific condition. Bitmask Definition:

0: Reference Location Information Change - Indicates the request is triggered due to a change in Reference Location Information.

Note: Bits not defined in the specification must be cleared by the sender and ignored by the receiver.

SAR-Flags

655

Unsigned32 (Bitmask)

3GPP

Provides additional context in Server-Assignment-Request (SAR) messages. It contains a bitmask indicating specific behaviors or mechanisms to be executed. Bitmask Definition:

0: P-CSCF Restoration Indication - Indicates that the P-CSCF Restoration mechanism feature should be executed as per [TS23.380].

Note: Bits not defined in the specification must be cleared by the sender and ignored by the receiver.

SCSCF-Restoration-Info

639

Grouped

3GPP

Provides critical information to enable an S-CSCF (Serving Call Session Control Function) to restore or manage user requests efficiently. It encapsulates user-specific data and restoration details. The AVP structure is defined as follows:

User-Name: The username of the user whose restoration information is required.

Restoration-Info: Information related to restoring the user's session, present as a mandatory list.

Registration-Time-Out : The point in time when the user's registration will expire, if applicable.

SIP-Authentication-Scheme: The SIP authentication scheme applicable for the user.

Secondary-Charging-Collection-Function-Name

622

DiameterURI

3GPP

Provides the address of the Secondary Charging Data Function. It defines how to route Diameter accounting requests by extracting the Destination-Host and Destination-Realm from the provided URI.

Secondary-Event-Charging-Function-Name

620

DiameterURI

3GPP

Specifies the address of the Secondary Online Charging Function (OCF).

Server-Assignment-Type

614

Enumerated

3GPP

Defines the type of server update, request, or notification being performed during a Server-Assignment-Request (SAR) operation. Values:

0: NO_ASSIGNMENT - Requests user profiles without affecting registration state or retrieves restoration information.

1: REGISTRATION - Triggered by the initial registration of an identity.

2: RE_REGISTRATION - Indicates the re-registration of an identity or update of restoration information.

3: UNREGISTERED_USER - Generated when handling unregistered users, including failed P-CSCF scenarios.

4: TIMEOUT_DEREGISTRATION - Triggered when the SIP registration timer expires.

5: USER_DEREGISTRATION - Initiated by user-initiated deregistration requests.

6: TIMEOUT_DEREGISTRATION_STORE_SERVER_NAME - Similar to TIMEOUT_DEREGISTRATION but requests HSS to store the S-CSCF name.

7: USER_DEREGISTRATION_STORE_SERVER_NAME - Similar to USER_DEREGISTRATION but stores the S-CSCF name in HSS.

8: ADMINISTRATIVE_DEREGISTRATION - Triggered by administrative actions or network issues leading to deregistration.

9: AUTHENTICATION_FAILURE - Triggered by a failed user authentication.

10: AUTHENTICATION_TIMEOUT - Indicates an authentication timeout.

11: DEREGISTRATION_TOO_MUCH_DATA: Indicates data overflow during a user profile request.

12: AAA_USER_DATA_REQUEST: Used in the SWx protocol for accessing user data in non-Cx contexts.

13: PGW_UPDATE: Specific to the SWx protocol for packet gateway updates.

14: RESTORATION: Used in the SWx protocol for restoration scenarios.

Server-Capabilities

603

Grouped

3GPP

Grouped AVP that provides essential information to the I-CSCF for selecting an appropriate S-CSCF in an IMS network. It includes details about the mandatory and optional capabilities of the server and a list of server names. The AVP structure is defined as follows:

Mandatory-Capability: A list of mandatory capabilities (Unsigned32), indicating features the S-CSCF must support.

Optional-Capability: A list of optional capabilities (Unsigned32), representing features the S-CSCF may optionally support.

Server-Name: A list of server names (UTF8String), typically SIP-URLs identifying candidate S-CSCFs.

Server-Name

602

UTF8String

3GPP

Specifies the SIP-URL of a SIP server, such as the name of an S-CSCF, used in various IMS network scenarios. It plays a vital role in routing and identifying SIP elements in the IMS architecture.

Session-Priority

650

Enumerated

3GPP

Used to indicate the priority of a session to the HSS (Home Subscriber Server). It supports operator-specific mapping, where values received by the CSCF are mapped as described in [TS24.229], Table A.162. Values:

0: PRIORITY-0 (Highest Priority)

1: PRIORITY-1

2: PRIORITY-2

3: PRIORITY-3

4: PRIORITY-4

SIP-Auth-Data-Item

612

Grouped

3GPP

Contains authentication and/or authorization information required by a Diameter client for managing SIP sessions. It is a grouped AVP that includes various AVPs, such as authentication schemes, keys, and other context information. The AVP structure is defined as follows:

SIP-Item-Number: A sequence number identifying the SIP authentication data item.

SIP-Authentication-Scheme: Specifies the authentication scheme (e.g., Digest).

SIP-Authenticate: Authentication challenge data (e.g., nonce).

SIP-Authorization: Authorization data for the SIP client.

SIP-Authentication-Context: Context data for authentication.

Confidentiality-Key & Integrity-Key: Security keys used for encryption and integrity protection.

SIP-Digest-Authenticate: Contains SIP Digest-specific data.

Framed-IP-Address & Framed-IPv6-Prefix: IPv4 and IPv6 addressing information.

Framed-Interface-Id: Interface identifier for framed communications.

Line-Identifier: Identifiers for broadband access lines associated with the user.

SIP-Authenticate

609

OctetString

3GPP

Contains specific portions of the WWW-Authenticate or Proxy-Authenticate headers from SIP responses. It holds binary-encoded authentication challenge data (RAND) and authentication token (AUTN) necessary for SIP-based authentication. Length fixed at 32 octets.

The first 16 octets contain the RAND value.

The remaining 16 octets contain the AUTN value.

Additional details in [TS33.203].

SIP-Authentication-Context

611

OctetString

3GPP

Contains additional authentication-related context for SIP sessions.

SIP-Authentication-Scheme

608

UTF8String

3GPP

Specifies the authentication scheme used for authenticating SIP messages. It identifies the security mechanism required by the S-CSCF and HSS for SIP-based communications. Supported Authentication Schemes:
"Digest-AKAv1-MD5": Indicates the IMS-AKA authentication scheme. Used for backward compatibility. Requires RAND, AUTN, XRES, CK, and IK.

"SIP Digest": Denotes the SIP Digest authentication scheme.

"NASS-Bundled": Refers to the NASS Bundled authentication scheme.

"Early‑IMS‑Security": Refers to the GPRS-IMS-Bundled authentication scheme.

"Unknown": Indicates that the authentication scheme is currently undefined.

SIP-Authorization

610

OctetString

3GPP

Carries authorization data for SIP requests and is typically included in authentication-related Diameter operations. It contains binary-encoded information derived from SIP Authorization or Proxy-Authorization headers. Behavior in Different Scenarios:

Authentication Request: Contains the concatenation of fixed length of 30 octets.

RAND (16 octets): Random challenge sent to the terminal.

AUTS (14 octets): Authentication Synchronization Token received from the terminal.

Authentication Request Response: Contains XRES (Expected Response), binary-encoded, for validating the terminal's response.

SIP-Digest-Authenticate

635

Grouped

3GPP

Encapsulates information used for reconstructing the WWW-Authenticate or Proxy-Authentication SIP headers. These headers are required for implementing authentication mechanisms compliant with [RFC7616]. The AVP structure is defined as follows:

Digest-Realm: Specifies the authentication realm for the SIP Digest.

Digest-Algorithm: Indicates the algorithm used for hashing (e.g., MD5, SHA-256).

Digest-QoP: Quality of Protection (QoP) parameter defining the level of security. Common values include:

• "auth" (authentication only)

• "auth-int" (authentication with integrity protection).

Digest-HA1: A hash value computed using the SIP Digest algorithm and credentials.

Alternate-Digest-Algorithm: Provides a fallback algorithm for backward compatibility.

Alternate-Digest-HA1: Contains the hash value using the alternate digest algorithm.

Allows for additional AVPs for extensibility.

SIP-Item-Number

613

Unsigned32

3GPP

Indicates the sequence or index of a specific SIP-related item within a grouped AVP structure. It is used to uniquely identify an individual item when multiple instances of grouped AVPs are present in a message.

SIP-Number-Auth-Items

607

Unsigned32

3GPP

Indicates the number of SIP-Auth-Data-Item AVPs included in a request or response message.
In Requests: Specifies the number of authentication vectors requested by the S-CSCF.

In Responses: Indicates the actual number of authentication vectors provided by the Diameter server.

Subscription-Info

642

Grouped

3GPP

Contains subscription-related information for the User Equipment (UE) in the IMS network. It aggregates critical details such as SIP headers and routing information associated with a subscription request. The AVP structure is defined as follows:

Call-ID-SIP-Header: Contains the data from the Call-ID header of the SIP request.

From-SIP-Header: Includes the information from the "From" header of the SIP request.

To-SIP-Header: Contains the "To" header details of the SIP request.

Record-Route: Represents the Record-Route header, detailing the path through which SIP messages traverse.

Contact: Specifies the contact address and parameters of the subscription request.

Allows for additional AVPs for extensibility.

Supported-Applications

631

Grouped

3GPP

Lists the application identifiers supported by a Diameter node. This AVP enables nodes to communicate their capabilities in terms of supported authentication, accounting, or vendor-specific applications. The AVP structure is defined as follows:

Auth-Application-Id: Lists the identifiers of authentication applications supported by the node.

Acct-Application-Id: Lists the identifiers of accounting applications supported by the node.

Vendor-Specific-Application-Id: Specifies vendor-specific application IDs supported by the node.

Allows for additional AVPs for extensibility.

Supported-Features

628

Grouped

3GPP

Communicates the features supported by the origin host for a particular application. This AVP allows a destination host to interpret the capabilities or feature sets available to the origin host. The AVP structure is defined as follows:

Vendor-Id: Specifies the vendor ID associated with the feature list (e.g., 10415 for 3GPP or custom IDs for other vendors).

Feature-List-ID: Identifies the specific feature list for a given vendor and application.

Feature-List: Contains a bitmask that represents the features supported by the origin host.

Allows for additional AVPs for extensibility.

To-SIP-Header

645

OctetString

3GPP

Contains the information in the To header as defined in [RFC3261].

UAR-Flags

637

Unsigned32 (Bitmask)

3GPP

Contains a bitmask used for specific signaling scenarios in IMS. It provides additional context to the HSS or other Diameter peers by indicating the type of registration request or operation being performed. Bitmask Definition:

0: IMS Emergency Registration: Indicates that the request corresponds to an IMS Emergency Registration.

Bits not defined in the table must be cleared by the sending I-CSCF and ignored by the receiving HSS.

User-Authorization-Type

623

Enumerated

3GPP

Used in the User Authorization operation (UAR command) to indicate the type of user authorization being performed. The AVP provides context for processing user registration, de-registration, or capability requests. Values:

0: REGISTRATION: Used for initial registration or re-registration. Determined when the Expires field in SIP REGISTER is not zero.

1: DE_REGISTRATION: Used for de-registration when the Expires field in SIP REGISTER equals zero.

2: REGISTRATION_AND_CAPABILITIES: Used when requesting S-CSCF capability information from the HSS, typically when the stored S-CSCF is unavailable.

User-Data

606

OctetString

3GPP

Contains the user-specific data required to provide services. The exact structure and content of this AVP are defined in [TS29.228], where it is used to exchange user profiles and related information.

User-Data-Already-Available

624

Enumerated

3GPP

Indicates to the HSS whether the S-CSCF already possesses the user profile information required to serve the user. This allows the system to avoid redundant data exchanges. Values:

0: USER_DATA_NOT_AVAILABLE: The S-CSCF does not have the required user profile data.

1: USER_DATA_ALREADY_AVAILABLE: The S-CSCF already has the necessary user profile data.

Visited-Network-Identifier

600

OctetString

3GPP

Contains an identifier that helps the HSS to recognize the visited network. It is often used to map the P-Visited-Network-ID header in SIP messages into a format suitable for the Diameter protocol.

WebRTC-Authentication-Function-Name

657

UTF8String

3GPP

Specifies the address of a WebRTC Authentication Function (WAF) allowed for the subscription.

WebRTC-Web-Server-Function-Name

658

UTF8String

3GPP

Specifies the address of a WebRTC Web Server Function (WWSF) allowed for the subscription. This AVP assists in defining the WWSFs that can process web server operations for the user.

Wildcarded-IMPU

636

UTF8String

3GPP

Сontains a wildcarded Public User Identity (IMPU) stored in the HSS. The wildcarding mechanism is used to associate a set of public user identities with a single profile in the IMS domain.