5.2 Nhss_imsUEContextManagement Service

29.5623GPP5G SystemHome Subscriber Server (HSS) servicesRelease 18Stage 3TS

Tools: ARFCN - Frequency Conversion for 5G NR/LTE/UMTS/GSM

5.2.1 Service Description

See 3GPP TS 23.228 [6], clause AA.2.1.2.

5.2.2 Service Operations

5.2.2.1 Introduction

For the Nhss_imsUEContextManagement service the following service operations are defined:

– Registration

– DeregistrationNotification

– Deregistration

– Authorize

– Update

– RestorationInfoGet

– RestorationInfoUpdate

– RestorationInfoDelete

IMS restoration procedures are specified in 3GPP TS 23.380 [37].

The Nhss_imsUEContextManagement Service is used by Consumer NFs (I-CSCF/S-CSCF) to:

– register at the HSS by means of the Registration service operation (S-CSCF)

– get notified by means of the DeregistrationNotification service operation when HSS decides to deregister the registered consumer NF (S-CSCF)

– deregister from the HSS by means of the Deregistration service operation (S-CSCF)

– request registration authorization from HSS by means of the Authorize service operation (I-CSCF)

– update registration information stored at the HSS by means of the Update service operation (S-CSCF)

– retrieve Restoration Information stored at the HSS by means of the RestorationInfoGet service operation (S-CSCF)

– update Restoration Information stored at the HSS by means of the RestorationInfoUpdate service operation (S-CSCF)

– delete Restoration Information stored at the HSS by means of the RestorationInfoDelete service operation (S-CSCF)

5.2.2.2 Registration

5.2.2.2.1 General

The Registration service operation is invoked by a NF that has been selected to provide service to the UE to store related IMS UE Context Management information in HSS.

NF Consumer is S-CSCF.

As part of this procedure, the HSS updates the registration state of the requested IMS Public Identity and IMS Private Identity. The state of the IMS Public Identities in the same Implicit Registration Set is also updated.

The following procedures using the Registration service operation are supported:

– S-CSCF registration

5.2.2.2.2 S-CSCF Registration

Figure 5.2.2.2.2-1 shows a scenario where the S-CSCF sends a request to register at the HSS (see also 3GPP TS 23.228 [6] clause 5.2). The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPU, the S-CSCF Registration Information and the Registration Type.

Figure 5.2.2.2.2-1: S-CSCF registration

1. The S-CSCF sends a PUT request to the resource representing the UE’s S-CSCF registration to update or create S-CSCF registration information. The S-CSCF shall check whether there is a reg-id parameter in the Contact header in the SIP REGISTER message. If a reg-id parameter exists, the S-CSCF shall indicate to the HSS that the registration is related to a multiple registration as specified in clause 4.2.3 of 3GPP TS 23.380 [37]. If the S-CSCF received a S-CSCF reselection indicator from the I-CSCF, the S-CSCF shall include that indicator to the HSS.

2a. If the resource already exists, and if the S-CSCF registered is the same or if another S-CSCF is registered and S-CSCF reselection indication is received, the HSS updates the scscfRegistration resource by replacing it with the received resource information (e.g. S-CSCF name, state of the related IMS public identity based on the imsRegistrationType received) and responds with "204 No Content" or "200 OK" with the updated resource information and HSS supported features.

Additionally, if the S-CSCF is reselected, the HSS shall invoke the Deregistration Notification service operation towards the old S-CSCF using the callback URI provided by the old S-CSCF with deregistration reason set to "NEW SERVER ASSIGNED".

When receiving the "200 OK" response and if a multiple registration indicator has indicated to the HSS, the S-CSCF shall retrieve and update the restoration information as specified in clause 5.2.2.6 and clause 5.2.2.7.

2b. If the resource does not exist (there is no previous S-CSCF information stored in HSS), HSS stores the received S-CSCF registration data and responds with HTTP Status Code "201 created". A response body is included with the created resource and the features supported by HSS.

2c. If the operation is not authorized due to e.g. received IMS identities do not exist or do not match, or a different S-CSCF is registered and S-CSCF reselection is not authorized, HTTP status code "403 Forbidden" should be returned including additional error information in the response body (in "ProblemDetails" element).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the PUT response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.

5.2.2.3 DeregistrationNotification

5.2.2.3.1 General

The following procedure using the DeregistrationNotification service operation is supported:

– HSS initiated Deregistration

5.2.2.3.2 HSS initiated Deregistration

Figure 5.2.2.3.2-1 shows a scenario where the HSS notifies the registered NF about the deregistration of one or more IMS Public Identities (see also 3GPP TS 23.228 [6] clause 5.3.2.2.1). The request contains the callback URI for deregistration notification as received by the HSS during registration, and Deregistration Data.

Figure 5.2.2.3.2-1: HSS initiated NF Deregistration

1. The HSS determines the need to deregister one or more public identities and sends a POST request to the callbackReference as provided by the NF service consumer (S-CSCF) during the registration.

NOTE: The callbackReference identifies a public identity or an IRS or a Wildcarded PSI that shall be deregistered.

HSS includes DeregistrationData with the Deregistration Reason that triggered the notification and additional information about the public identities that shall be deregistered such as:

– Private Identity of the public identity to be deregistered,

– if several Private Identities with all associated Public Identities need to be deregistered, the Associated Private Identities.

2a. On success, the NF service consumer responds with "204 No Content" or with "200 OK" including additional information about the deregistration result such as:

– Associated Private Identities: it contains all Private Identities that have been deregistered together with the one in the Private User Identity received in the request,

– Identities with Emergency Registration: This information element indicates a list of pairs of private and public user identities which have not been de-registered due to emergency registration.

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the POST response body.

In the case of redirection, the NF Service Consumer shall return 3xx status code, which shall contain a Location header with an URI pointing to an alternative notification endpoint.

5.2.2.4 Deregistration

5.2.2.4.1 General

The following procedures using the Deregistration service operation are supported:

– S-CSCF deregistration

5.2.2.4.2 S-CSCF deregistration

Figure 5.2.2.4.2-1 shows a scenario where the S-CSCF sends a request to the HSS to deregister a user (see also 3GPP TS 23.228 [6] clause 5.3.1). The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPI or an IMPU and the deregistration information.

Figure 5.2.2.4.2-1: S-CSCF deregistering

1. The S-CSCF sends a PUT request to the resource representing the UE’s CSCF registration.

2a. The HSS shall check whether the received S-CSCF name matches the stored S-CSCF. If the S-CSCF name is different, the HSS shall check whether the S-CSCF reassignment is allowed (i.e. S-CSCF reassignment pending flag is set).

If an IMPI is received as ImsUeId, HSS shall deregister all IMPUs associated to that IMPI.

If an IMPU is received as ImsUeId, HSS shall deregister the IMPU and related IMPUs in the Implicit Registration Set for the related IMPI.

On success, HSS shall respond "204 No Content" or "200 OK".

2b. Otherwise the HSS responds with "403 Forbidden" (e.g. S-CSCF is not the current S-CSCF assigned) or "404 Not Found" (e.g. IMPU or IMPI do not exist).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the PUT response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.

5.2.2.5 Authorize

5.2.2.5.1 General

The Authorize service operation is invoked by a NF to request UE authorization to register or establish terminating /originating sessions in the IMS network.

NF Consumer is I-CSCF for IMS service.

As part of this procedure, the HSS authorizes or rejects the subscriber to use the IMS service based on the authorization information provided in the request and subscription data (e.g. roaming restrictions, barrings).

The following procedures using the Authorize service operation are supported:

– Authorization request

5.2.2.5.2 Authorization request

Figure 5.2.2.5.2-1 shows a scenario where the I-CSCF sends a request to the HSS to authorize the UE to register in a given PLMN’s P-CSCF or initiate a session for unregistered services (see also 3GPP TS 23.228 [6] clause 5.2.2.3 or 5.12.2). The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPU, and the AuthorizationRequest.

Figure 5.2.2.5.2-1: Authorization

1. The I-CSCF sends a POST request (custom method: authorize) to request for UE’s authorization to register or establish an originating/terminating session.

2a. If the operation cannot be authorized due to e.g. UE does not have required subscription data, HTTP status code "403 Forbidden" should be returned including additional error information in the response body (in "ProblemDetails" element).

2b. If successful, HSS responds with HTTP Status Code "200 OK" and may provide the S-CSCF identity which is serving the user, if any.

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the POST response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.

5.2.2.6 RestorationInfoGet

5.2.2.6.1 General

The RestorationInfoGet service operation is invoked by a NF to retrieve restoration information in HSS.

NF Consumer is S-CSCF.

The following procedures using the RestorationInfoGet service operation are supported:

– Restoration Information Retrieval

5.2.2.6.2 Restoration Information Retrieval

Figure 5.2.2.6.2-1 shows a scenario where the NF service consumer (S-CSCF) sends a request to the HSS to retrieve the information related to a specific registration for a registered user (e.g. during a registration procedure, during an originating request procedure or during a terminating request procedure). The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPU.

Figure 5.2.2.6.2-1: Restoration Information Retrieval

1. The NF service consumer (S-CSCF) sends a GET request to the resource representing the UE’s S-CSCF restoration information.

2a. On success, the HSS responds with "200 OK" with the message body containing the UE’s S-CSCF restoration information. The S-CSCF shall send a request to the HSS to retrieve the UE’s IMS profile as specified in clause 5.3.2.2.4.

2b. If there is no valid restoration data for the UE, HTTP status code "404 Not Found" shall be returned and it should include additional error information in the response body (in the "ProblemDetails" element).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the GET response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.

5.2.2.7 RestorationInfoUpdate

5.2.2.7.1 General

The RestorationInfoUpdate service operation is invoked by a NF to update restoration information in HSS.

NF Consumer is S-CSCF.

The following procedures using the RestorationInfoUpdate service operation are supported:

– Restoration Information Update

5.2.2.7.2 Restoration Information Update

S-CSCF backup and update of S-CSCF restoration information in HSS is specified in clause 4.6 of 3GPP TS 23.380 [37].

Figure 5.2.2.7.2-1 shows a scenario where the S-CSCF sends a request to update restoration information at the HSS (see also 3GPP TS 23.228 [6] clause 4.24). The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPU.

Figure 5.2.2.7.2-1: Restoration Information Update

1. The S-CSCF sends a PUT request to the resource representing the UE’s S-CSCF restoration information to update or create S-CSCF restoration information.

2a. If there are S-CSCF restoration information related to the IMS Public Identity stored in the HSS, the HSS updates the Scscf Restoration Information resource by replacing it with the received restoration information and responds with "200 OK" or "204 No Content".

2b. If the resource does not exist (there is no previous S-CSCF restoration information stored in HSS for that user), HSS stores the received S-CSCF restoration data and responds with HTTP Status Code "201 created".

2c. If the request can’t be accepted (e.g. the S-CSCF is not allowed to create/update the restoration information), HTTP status code "403 Forbidden" should be returned including additional error information in the response body (in the "ProblemDetails" element).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the PUT response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.

5.2.2.8 RestorationInfoDelete

5.2.2.8.1 General

The RestorationInfoDelete service operation is invoked by a NF to delete restoration information in HSS.

NF Consumer is S-CSCF.

The S-CSCF consumes the RestorationInfoDelete service operation as a consequence of subscriber deregistration (TIMEOUT_DEREGISTRATION, USER_DEREGISTRATION, ADMINISTRATIVE_DEREGISTRATION). In restoration scenarios, the new S-CSCF after successful retrieval of restoration data, consumes the RestorationInfoDelete service operation to delete the restoration data stored by the old S-CSCF.

The following procedures using the RestorationInfoDelete service operation are supported:

– Restoration Information Delete

5.2.2.8.2 Restoration Information Delete

Figure 5.2.2.Z.2-1 shows a scenario where the S-CSCF sends a request to delete restoration information at the HSS. The request contains the IMS UE’s identity (/{imsUeId}) which shall be an IMPU.

Figure 5.2.2.8.2-1: Restoration Information Delete

1. The S-CSCF sends a DELETE request to the resource representing the UE’s S-CSCF restoration information to delete S-CSCF restoration information.

2a. If there are S-CSCF restoration information related to the IMS Public Identity stored in the HSS, the HSS deletes the Scscf Restoration Information resource by replacing it with the received restoration information and responds with "204 No Content".

2b. If the request can’t be accepted (e.g. the S-CSCF is not allowed to delete the restoration information), HTTP status code "403 Forbidden" should be returned including additional error information in the response body (in the "ProblemDetails" element).

2c. If there is no valid S-CSCF restoration information, HTTP status code "404 Not Found" should be returned including additional error information in the response body (in the "ProblemDetails" element).

On failure, the appropriate HTTP status code indicating the error shall be returned and appropriate additional error information should be returned in the DELETE response body.

In the case of redirection, the HSS shall return 3xx status code, which shall contain a Location header with an URI pointing to the endpoint of another HSS (service) instance.