5.1.7 GPSI-to-Subscription-Network resolution procedure

23.5403GPP5G System: Technical realization of Service Based Short Message ServiceRelease 17Stage 2TS

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

5.1.7.1 General

MT SMS delivery procedure requires routing based on the GPSI of the SMS recipient for interactions between the SMS-GMSC and the UDM, e.g., to retrieve the SMS routing information (e.g., the SMSF address) or report delivery status. In case that the SMS recipient belongs to a PLMN different from the PLMN of the SMS sender, the signaling takes place across PLMN borders.

When using service-based interface between the SMS-GMSC and the UDM, if the GPSI is the only known SMS recipient’s identifier, the SMS-GMSC needs to determine the target PLMN to be able to interact with the UDM in the home PLMN of the SMS recipient. The SMS-GMSC can determine the target PLMN using one of the following mechanisms:

– GPSI-to-Subscription-Network resolution triggered by the NF consumer, described in clause 5.1.7.2.

– GPSI-to-Subscription-Network resolution using NRF, described in clause 5.1.7.4.

– GPSI-to-Subscription-Network resolution delegated by SCP, described in clause 5.1.7.3

It is assumed that the domain part in an External Identifier identifies the home PLMN and hence it is not required to determine the target PLMN when the GPSI is an External Identifier. The procedures described in the present clause 5.1.7 apply only when the GPSI is an MSISDN.

NOTE: While these mechanisms are defined to determine the target PLMN for interactions between the SMS entities such as SMS-GMSC and the UDM requiring routing based on the GPSI of the SMS recipient, it can be applicable to any use case and procedure requiring selection of the target PLMN based on GPSI in 5GS.

When the recipient GPSI belongs to the same country as the originating network and MNPF is not implemented in the country, the SMS-GMSC may skip the procedure and may directly discover UDM profile for invoking UDM service operation for routing information retrieval. In this case the SMS-GMSC determines the target PLMN ID from the recipient’s GPSI Prefix (e.g. CC+NDC) while sending the discovery request to the NRF.

5.1.7.2 GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC

5.1.7.2.1 General

Figure 5.1.7.2-1: GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC

1a-1b. The MNPF registers in the NRF with a new NF Type (e.g. MNPF).

2. MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in 3GPP TS 23.040 [2].

3a-3b. The SMS-GMSC should query the NRF to find the MNPF instance that manages the PLMN ID of the recipients GPSI’s subscription network. The MNPF may belong to the same PLMN with SMS-GMSC or belong to the number range holder network which is different with the PLMN of SMS-GMSC. In latter case, the local NRF forwards the discovery request to the NRF of the number range holder PLMN.

4. SMS-GMSC invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF to get the target PLMN ID of the GPSI.

5. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

After step 5, the Mobile Terminated short message transfer procedures defined in clause 5.1 is performed from step 2a. The SMS-GMSC uses the target PLMN ID to discover the UDM NF profile via NRF for sending the routing information query to the UDM. If the target PLMN ID is not own network, the local NRF forwards the discovery request to the NRF of the target PLMN.

5.1.7.2.2 GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC for Direct routing

When MNPF is implemented in a country or number portability domain with direct routing mechanism, the originating network first does the number portability query to identify the recipient GPSI’s subscription PLMN before routing any messages based on GPSI.

Figure 5.1.7.2.2-1 GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC (Direct Routing)

1. If the MNPF is deployed, the MNPF registers in the NRF with a new NF Type (e.g. MNPF).

2-3. The SMS-GMSC should query the NRF to find the MNPF instance that manages the PLMN ID of the recipients GPSI’s subscription network.

4. SMS-GMSC invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF to get the target PLMN ID of the GPSI.

5. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

NOTE: When the recipient GPSI belongs to the same country as the originating network and MNPF is not implemented in the country, the steps 1-5 is skipped. In this case the SMS-GMSC determines the target PLMN ID from the recipient’s GPSI Prefix (e.g. CC+NDC) based on local configuration.6-7. SMS-GMSC shall query the NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6. For step 7b-8b, if the target PLMN ID is not the originating network, the local NRF forwards the discovery request to the NRF of the target PLMN.

8-9. SMS-GMSC invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM of the target PLMN to get the serving node instance for UE. The UDM shall check the registration/reachability flags to determine the potential target nodes and responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response, in this procedure the SMSF instance Id is included in the response message.

5.1.7.2.3 GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC for Indirect routing

When MNP is implemented in a country or number portability domain with indirect routing mechanism, the signalling messages are always routed to the number range holder network, the number range holder then performs a number portability check and forwards the request to the subscription network if the number is ported out. For the case of international SMS termination also indirect routing is applied. In the case of international SMS termination, the originating network is outside the number portability domain and may not have any knowledge of whether number portability is implemented in the country of the recipient GPSI.

Figure 5.1.7.2.3-1 GPSI-to-Subscription-Network resolution triggered by the SMS-GMSC (Indirect Routing)

1. If the MNP NF is deployed in the Number Range Holder PLMN, the MNP NF registers in the NRF of the number range holder PLMN with a new NF Type (e.g. MNP).

2-3. The SMS-GMSC should query the local NRF to find the MNP instance that manages the PLMN ID of the recipients GPSI’s subscription network, the local NRF forwards the discovery request to the NRF of the number range holder PLMN. 4. SMS-GMSC invokes Nmnp_NPStatus_Get (GPSI) to the MNP NF to get the target PLMN ID of the GPSI.

5. MNP NF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

NOTE: When the recipient GPSI belongs to the same country as the number range holder network and MNP is not implemented in the country, the steps 1-5 is skipped. In this case the SMS-GMSC determines the target PLMN ID from the recipient’s GPSI Prefix (e.g. CC+NDC) based on local configuration.

6-7. SMS-GMSC shall query the NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6.

– For step 7a-8a, if the target PLMN ID belongs to the number range holder PLMN, the local NRF forwards the discovery request to the NRF of the number range holder PLMN.

– For step 7b-8b, if the target PLMN ID belongs to the Subscription PLMN, the local NRF forwards the discovery request to the NRF of the Subscription PLMN.

5.1.7.3 SCP supports GPSI-to-Subscription-Network resolution procedure

5.1.7.3.1 General

This procedure is used to retrieve the PLMN ID of the recipients GPSI for further discovery of UDM NF profiles for invoking UDM service operation for routing information retrieval. In indirect Communication with Delegated Discovery, the SCP is the service consumer of the GPSI-to-Subscription-Network resolution service in MNPF and routes an SBI message based on GPSI when MNPF is implemented. The SCP shall use the discovery factors (see 3GPP TS 29.500 [11], clause 6.10) provided by the SMS-GMSC to determine when to invoke the MNPF resolution, and to obtain the identity (GPSI) of the recipient.

The SMS-GMSC sends routing information retrieval request to the SCP and the SCP uses the PLMN ID as the target PLMN ID in the discovery request towards NRF to discover the UDM NF profiles in the subscription network of the SMS recipient.

5.1.7.3.2 SCP supports GPSI-to-Subscription-Network resolution with MNPF

Figure 5.1.7.3.2-1: SCP supports GPSI-to-Subscription-Network resolution with MNPF

1a-1b. If the MNPF is deployed, the MNPF registers in the NRF with a new NF Type (e.g. MNPF).

2. MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in 3GPP TS 23.040 [2].

3. The SMS-GMSC sends Nudm_UECM_SendRoutingInfoForSM to the SCP to get the serving node instance for UE from the UDM. As specified in the Indirect Communication with Delegated Discovery model, the Nudm_UECM_SendRoutingInfoForSMt shall contain the discovery factors containing the GPSI (pointing to the Number Range Holder Network) and an indicator (i.e. "target-nw-resolution") that Subscription Network resolution is delegated to the SCP. The "target-nw-resolution" may also be sent by an SCP to the next hop SCP. The SCP receives the "target-nw-resolution" shall query the NF service consumer (MNPF) to obtain the PLMN ID of the recipient GPSI’s subscription network.

4a-4b. The SCP shall query the NRF to find the MNPF instance that manages the PLMN ID of the recipients GPSI’s subscription network. The MNPF may belong to the same PLMN with SMS-GMSC or belong to the number range holder network which is different with the PLMN of SMS-GMSC. In latter case, the local NRF forwards the discovery request to the NRF of the number range holder PLMN.

5. The SCP determines the target PLMN of the recipients GPSI’s subscription network using the SBI service of the MNPF i.e. the SCP invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF.

6. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

NOTE: If SCP is co-located with MNPF, steps between SCP and NRF to discover the MNPF, and steps between SCP and MNPF can be skipped.

7a-7b. SCP shall query the NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6.

8. SCP invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM to get the serving node instance for UE.

9. The UDM shall check the registration/reachability flags to determine the potential target nodes and responds to the SCP by sending Nudm_UECM_SendRoutingInfoForSM response, in this procedure the SMSF instance Id is included in the response message.

10. SCP forward the responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response (SMS Router address).

5.1.7.3.3 SCP supports GPSI-to-Subscription-Network resolution with NRF

Figure 5.1.7.3.3-1: SCP supports GPSI-to-Subscription-Network resolution with NRF

1a-1b. If the MNPF is deployed, the MNPF registers in the NRF with a new NF Type (e.g. MNPF).

2. MT SMS interaction between SC and SMS-GMSC follow the current procedure as defined in 3GPP TS 23.040 [2].

3. The SMS-GMSC sends Nudm_UECM_SendRoutingInfoForSM to the SCP to get the serving node instance for UE from the UDM. The Nudm_UECM_SendRoutingInfoForSM contains the NF service discovery factors with the GPSI (pointing to the Number Range Holder Network) and an indicator (i.e. "target-nw-resolution") indicating that Subscription Network resolution is delegated to the SCP. The "target-nw-resolution" may also be sent by an SCP to the next hop SCP.

4. The SCP should query the NRF to find the UDM instance that manages the user subscriptions using the GPSI. The NRF receives the "target-nw-resolution" shall query the NF service consumer (MNPF) to obtain the PLMN ID of the recipient GPSI’s subscription network.

5. The NRF determines the target PLMN of the recipients GPSI’s subscription network using the SBI service of the MNPF i.e. the NRF invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF. As an implementation choice the NRF may determine the target PLMN by other means, e.g. local configuration of ENUM query.

6. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

7. NRF returns the UDM instance related to the GPSI and target PLMN Id to the SCP. For inter-PLMN discovery, the local NRF shall query the NRF in the target PLMN to find the UDM instance. If there are not NF instances available that can serve the request, the local NRF provides the discovery response indicating the consumer NF to use a legacy interface for the next operation request in the procedure.

8. SCP invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM to get the serving node instance for UE.

10. SCP forward the responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response (SMS Router address).

5.1.7.3.4 SCP supports GPSI-to-Subscription-Network resolution with MNPF for Direct routing

Figure 5.1.7.3.4-1 shows the procedure for Direct Communication with Delegated Discovery, the SCP is the service consumer of the GPSI-to-Subscription-Network resolution service in MNPF and routes an SBI message based on GPSI when direct routing of MNPF is implemented.

Figure 5.1.7.3.4-1 SCP supports the GPSI-to-Subscription-Network resolution with MNPF for Direct Routing

1. If the MNPF is deployed, the MNPF registers in the NRF with a new NF Type (e.g. MNPF).

2. The SMS-GMSC sends Nudm_UECM_SendRoutingInfoForSM to the SCP to get the serving node instance for UE from the UDM. As specified in the Indirect Communication with Delegated Discovery model, the Nudm_UECM_SendRoutingInfoForSM shall contain the discovery factors containing the GPSI (pointing to the Number Range Holder Network) and an indicator that Subscription Network resolution is delegated to the SCP.

3-4. The SCP shall query the NRF to find the MNPF instance that manages the PLMN ID of the recipients GPSI’s subscription network.

5. The SCP determines the target PLMN of the recipients GPSI’s subscription network using the SBI service of the MNPF i.e. the SCP invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF.

6. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

NOTE 1: If SCP is co-located with MNPF, steps between SCP and NRF to discover the MNPF, and steps between SCP and MNPF can be skipped.

NOTE 2: When the recipient GPSI belongs to the same country as the originating network and MNPF is not implemented in the country, steps between SCP and MNPF can be skipped. In this case the SMS-GMSC or SCP determines the target PLMN ID from the recipient’s GPSI Prefix (e.g. CC+NDC) based on local configuration.

7-8. SCP shall query the NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6. For step 7b-8b, if the target PLMN ID is not the originating network, the local NRF forwards the discovery request to the NRF of the target PLMN.

9-10. SCP invokes Nudm_UECM_SendRoutingInfoForSM (GPSI) to the UDM of the target PLMN to get the serving node instance for UE. The UDM shall check the registration/reachability flags to determine the potential target nodes and responds to the SCP by sending Nudm_UECM_SendRoutingInfoForSM response, in this procedure the SMSF instance Id is included in the response message.

11. SCP forward the responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response (SMS Router address).

5.1.7.3.5 SCP supports GPSI-to-Subscription-Network resolution with MNPF for Indirect routing

Figure 5.1.7.3.5-1 shows the procedure for Indirect Communication with Delegated Discovery, the SCP is the service consumer of the GPSI-to-Subscription-Network resolution service in MNPF NF and routes an SBI message based on GPSI when indirect routing of MNPF is implemented.

Figure 5.1.7.3.5-1 SCP supports GPSI-to-Subscription-Network resolution with MNPF for Indirect routing

1. If the MNPF is deployed in the Number Range Holder PLMN, the MNPF registers in the NRF of the number range holder PLMN with a new NF Type (e.g. MNPF).

3-4. The SCP shall query the local NRF to find the MNPF instance that manages the PLMN ID of the recipients GPSI’s subscription network, the local NRF forwards the discovery request to the NRF of the number range holder PLMN.

5. The SCP determines the target PLMN of the recipients GPSI’s subscription network using the SBI service of the MNPF i.e. the SCP invokes Nmnpf_NPStatus_Get (GPSI) to the MNPF.

6. MNPF checks the portability status of the recipient GPSI and responds back with the target PLMN ID.

NOTE 1: If SCP is co-located with MNPF, steps between SCP and NRF to discover the MNPF, and steps between SCP and MNPF can be skipped.

NOTE 2: When the recipient GPSI belongs to the same country as the number range holder network and MNPF is not implemented in the country, the steps between SCP and MNPF can be skipped. In this case the SMS-GMSC or SCP determines the target PLMN ID from the recipient’s GPSI Prefix (e.g. CC+NDC) based on local configuration.

7-8. SCP shall query the local NRF to find the UDM instance serving the target PLMN based on target PLMN ID received in step 6.

– For step 7a-8a, if the target PLMN ID belongs to the number range holder PLMN, the local NRF forwards the discovery request to the NRF of the number range holder PLMN.

– For step 7b-8b, if the target PLMN ID belongs to the Subscription PLMN, the local NRF forwards the discovery request to the NRF of the Subscription PLMN.

11. SCP forwards the responds to the SMS-GMSC by sending Nudm_UECM_SendRoutingInfoForSM response (SMS Router address).

5.1.7.4 GPSI-to-Subscription-Network resolution using NRF

Figure 5.1.7.4-1 shows the procedure to determine the target PLMN based on the GPSI using the discovery and selection framework via the NRF as defined in 3GPP TS 23.501 [3] and 3GPP TS 23.502 [4].

Figure 5.1.7.4-1: Determination of target PLMN based on GPSI using NRF

1. The SMS-GMSC located in the PLMN of the SMS sender contacts the NRF in the source PLMN to perform NF/NF service discovery of the UDM instance(s). The discovery request is based on the GPSI of the SMS recipient and includes an indication for the NRF to determine the target PLMN and interface to be used (SBI or legacy interface).

2. Based on the indication to determine the target PLMN and interface to be used included in the discovery request, the NRF in the source PLMN retrieves the target PLMN ID by consuming the SBI services of the MNPF described in clause 6.7. The NRF performs an NP query to the MNPF using SBI for the GPSI of the SMS recipient.

3. The MNPF provides in the response the target PLMN information corresponding to the GPSI of the SMS recipient and the procedure continues in step 4.

2a-3a. The NRF may, as an alternative implementation option to steps 2-3, obtain the target PLMN information by other means, e.g., using DNS/ENUM resolution, local configuration in the NRF or direct access to Number Portability (NP) databases via non-SBI, if applicable.

NOTE 1: NP applies to GPSIs representing E.164 addresses (i.e., MSISDN). NP is subject to regional and regulatory requirements and is accomplished through the retrieval of ported data from NP databases. Support of ENUM or direct access to NP via non-SBI interfaces and the exact means to make the number portability data available to the NRF is subject to and configured per operator policy.

The NRF may use the DNS/ENUM translation mechanism to resolve the GPSI of the SMS recipient in E.164 format to a URI as specified in IETF RFC 6116 [12]. The NRF performs an ENUM query for the GPSI of the SMS recipient in step 2a. The output of the lookup process in the DNS/ENUM server is a URI that is provided in the ENUM response and points to the source PLMN or the NRF in the target PLMN with which the source PLMN has an interconnection agreement using SBI, so that the NRF in the source PLMN can send an inter-PLMN service discovery request to the NRF in the target PLMN.

NOTE 2: The DNS/ENUM server searches for an ENUM record matching the GPSI of the SMS recipient. An ENUM record for the individual GPSI or number series provisioned in the DNS/ENUM server can be used to indicate whether the user belongs to the same PLMN or another PLMN in the same or different country. A URI as a result of the lookup process in the DNS/ENUM server can be provided by provisioning an ENUM service using the http or https scheme URI as defined in IETF RFC 4002 [13] and IETF RFC 6118 [14].

4. Based on the response from the MNPF, the NRF in the source PLMN determines the target PLMN where to search for UDM instances.

If the NRF has obtained the target PLMN information by other means in steps 2a-3a, the NRF determines the target PLMN based on the information from ENUM response, NP databases via non-SBI and/or local configuration.

If the GPSI belongs to the source PLMN, the source NRF searches for UDM instances matching the discovery criteria that can serve the request in the source PLMN using SBI services and provides the discovery response in step 7.

If the GPSI belongs to a different PLMN, the NRF in the source PLMN checks whether the source PLMN has an interconnection agreement using SBI with the target PLMN and, in that case, sends an inter-PLMN discovery request to the NRF in the target PLMN to retrieve the UDM instances that can serve the SMS recipient, as defined in clause 4.17.5 of 3GPP TS 23.502 [4] and 3GPP TS 29.510 [10]. The discovery request across PLMNs shall include the GPSI of the SMS recipient, the indication to determine the target PLMN and interface to be used and may include an indication that NP information has been already obtained, if applicable.

5. Based on the indication to determine the target PLMN and interface to be used included in the discovery request from the source NRF, the NRF in the target PLMN applies the behaviour described for the source NRF in steps 2-3 (or alternatively, steps 2a-3a).

The target NRF may perform a query to the MNPF using SBI if NP is required and NP information has not been retrieved previously (e.g., if source and target PLMNs belong to different countries or portability domains and NP is required in the target PLMN). The target NRF obtains the PLMN ID of the new target PLMN in the response from the MNPF.

6. The target NRF provides the inter-PLMN discovery response including one of the following:

– UDM instance(s) matching the discovery criteria in the target PLMN.

– Information about a new target PLMN as a result of an NP query performed in the target PLMN selected first by the source PLMN, if applicable. The source NRF may then send an inter-PLMN discovery request to the NRF in the new target PLMN if there is an interconnection agreement based on SBI.

– No UDM instance(s) found in the target PLMN, implying that SBI interactions should not be used.

7. If the source NRF finds UDM instances matching the filter criteria in the source PLMN or receives UDM instances from the target NRF in the response to a discovery request across PLMNs in step 6, the source NRF provides the UDM instances in the discovery response to the SMS-GMSC.

If the source NRF receives information about a new target PLMN in the discovery response from the target NRF as a result of an NP query performed in the target PLMN, the source NRF checks whether the source PLMN has an interconnection agreement using SBI with the new target PLMN and, in that case, sends a discovery request across PLMNs to the new target NRF as described in step 4.

If no UDM instances can serve the request using SBI, the source NRF provides the discovery response indicating the SMS-GMSC to use a non-SBI interface for the next operation request in the procedure.

8a. If the discovery response includes UDM instances that can serve the SMS recipient, the SMS-GMSC sends the operation request using SBI to e.g., retrieve the SMS routing information from the UDM, and the SBI-based MT SMS procedure can be executed as described in clause 5.1.

8b. If no UDM instances are provided in the discovery response, the SMS-GMSC sends the operation request via legacy interface using MAP/Diameter to e.g., retrieve the SMS routing information from the HLR/HSS/UDM.