Session management entity discovery for network session

Abstract

A method for discovering a session management entity (SME) to use for a network session of a device is disclosed. The method is performed by a network function. The method comprises receiving from a first SME a request for managing the first SME, wherein the request includes a network function profile of the first SME. The method further comprises, based at least on receiving the request, managing the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers of public land mobile networks of devices that can be served by the first SME.

Description

SESSION MANAGEMENT ENTITY DISCOVERY FOR NETWORK SESSIONTECHNICAL FIELD

[0001] This disclosure relates to session management entity discovery for a network session.BACKGROUND

[0002] Local Break Out (“LBO”) enables a mobile network operator (MNO) to provide to inbound roaming devices with an ability to order data which is provided directly by a visited mobile network. More specifically, LBO allows the inbound roaming devices to receive data services directly from the visited mobile network, i.e., a visited public land mobile network (VPLMN) instead of tunnelling back to a home mobile network, i.e., a home PLMN (HPLMN). One advantage of LBO is that it provides lower network latency.

[0003] In the LBO roaming mode, the session management function (SMF) and all user plane function(s) (UPF(s)) involved by a packet data unit (PDU) session are under the control of the VPLMN. The HPLMN can control the PDU session via subscription data per data network name (DNN) and per single network slice selection assistance information (S-NSSAI) whether the PDU session is to be set-up in the home routed (HR) roaming mode or in the LBO roaming mode.

[0004] In the LBO roaming mode, the access and mobility management function (AMF) selects an SMF in the VPLMN as described in 3GPP Technical Specification (TS) 23.502 version 18.4.0 (hereinafter "3GPP TS 23.502”) and 3GPP TS 23.501 version 18.4.0 (hereinafter, "3GPP TS 23.501).

[0005] For example, an SMF may be selected for the LBO roaming mode based on the discovery request described in clause 4.3.2.2.3.2 of 3GPP TS 23.502. The clause 4.3.2.2.3.2 discloses that: "AMF queries the appropriate NRF in serving PLMN by issuing the Nnrf_NFDiscovery_Request including at least the S-NSSAI of the Serving PLMN for this PDU Session from the Allowed NSSAI or Partially Allowed NSSAI, PLMN ID of the SUPI, DNN and possibly NSI ID if the AMF has stored an NSI ID for the S-NSSAI of the Serving PLMN for this PDU Session from the Allowed NSSAI or Partially Allowed NSSAI.”

[0006] Regarding the SMF selection, clause 6.3.2 of 3GPP TS 23.501 discloses that:

[0007] As disclosed above, one of the factors considered in selecting an SMF is a selected DNN. This DNN may be identified by an information element (IE) disclosed in 3GPP TS 29.510 version 18.5.0 (hereinafter, "3GPP TS 29.510”) clause 6.2.3.2.3. The description of the IE is provided below.

[0008] Regarding the IE, the clause 6.2.3.2.3 also discloses that:SUMMARY

[0009] Certain challenges presently exist. For example, in the existing art, an MNO may provide an LBO- based roaming service to roaming devices within its network with all SMFs capable of handling LBO sessions. However, there may be a scenario where it is desirable to use only some dedicated SMFs for the LBO sessions instead of all SMFs. Therefore, there is a need for a method of selecting an SMF to use for a network session (e.g., an LBO- based roaming session) for a device (e.g., a roaming device).

[0010] Accordingly, in one aspect of the embodiments of this disclosure, there is provided a method for discovering a session management entity (SME) to use for a network session of a device. The method is performed by a network function. The method comprises receiving from a first SME a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME. The method also comprises, based at least on receiving the request, managing the first SME using the received NF profile of the first SME. The received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice.

[0011] In another aspect, there is provided a method for registering a session management entity (SME) to use for a network session of a device. The method is performed by the SME. The method comprises transmitting, to a network function, a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice. The method further comprises, after transmitting the request, receiving, from the network function, a message indicating that the SME has been managed as requested by the request.

[0012] In a different aspect, there is provided a method for discovering a session management entity to use for a network session of a device. The method is performed by a mobility management function entity (MMFE). The method comprises receiving, from the device, a request for the network session, wherein the request for the network session comprises (I) a subscription permanent identifier (SUPI) of the device and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device.The method further comprises, based on the device's SUPI, deriving a public land mobile network (PLMN) identifier identifying a PLMN of the device. The method further comprises, based at least on receiving the request, transmitting, to a network function, a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.

[0013] In a different aspect, there is provided a computer program comprising instructions which when executed by processing circuitry cause the processing circuitry to perform the method of any one of the above embodiments.

[0014] In a different aspect, there is provided a carrier containing the computer program of the above embodiment, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

[0015] In a different aspect, there is provided a network function for discovering a session management entity (SME) to use for a network session of a device. The network function is configured to: receive from a first SME a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME. The network function is further configured to, based at least on receiving the request, manage the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice.

[0016] In a different aspect, there is provided a session management entity (SME) to use for a network session of a device. The SME is configured to transmit, to a network function, a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice. The SME is further configured to, after transmitting the request, receive, from the network function, a message indicating that the SME has been managed as requested by the request.

[0017] In a different aspect, there is provided a mobility management function entity (MMFE) for discovering a session management entity (SME) to use for a network session of a device. The MMFE is configured to receive, from the device, a request for the network session, wherein the request for the network session comprises (I) a subscription permanent identifier (SUPI) of the device and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device. The MMFE is further configured to, based on the device's SUPI, derive a public land mobile network (PLMN) identifier identifying a PLMNof the device. The MMFE is further configured to, based at least on receiving the request, transmit, to a network function, a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.

[0018] In a different aspect, there is provided an apparatus comprising processing circuitry; and a memory, said memory containing instructions executable by said processing circuitry, whereby the apparatus is operative to perform the method of any one of the above embodiments.

[0019] Some embodiments of this disclosure allow selecting a dedicated SMF to establish an LBO PDU session for an inbound roaming device (i.e., a user equipment (UE)) from a specific PLMN, e.g., the PLMN associated with the PLMN identifier (ID) of the UE's subscription permanent identifier (SUPI).BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0021] FIG. 1 shows an exemplary scenario where some embodiments of this disclosure can be applied.

[0022] FIG. 2 shows a process according to some embodiments.

[0023] FIG. 3 shows an example of a message flow diagram according to some embodiments.

[0024] FIG. 4 shows a process according to some embodiments.

[0025] FIG. 5 shows a process according to some embodiments.

[0026] FIG. 6 shows a process according to some embodiments.

[0027] FIG. 7 shows an apparatus according to some embodiments.DETAILED DESCRIPTION

[0028] FIG. 1 shows an exemplary scenario 100 where some embodiments of this disclosure can be applied. In the scenario 100, there are PLMNs 102, 104, and 106 provided by MNOs 112, 114, and 116, respectively. The PLMN 104 is a HPLMN of a UE 124 and the PLMN 106 is a HPLMN of a UE 126. In the scenario 100, the UE 124 travelled from a geographical region covered by the PLMN 104 to a geographical region covered by the PLMN 102 and the UE 126 travelled from a geographical region covered by the PLMN 106 to the geographical region covered by the PLMN 102. Since the PLMN 102 is a VPLMN to the UEs 124 and 126, the UEs 124 and 126 are roaming devices in the PLMN 102.

[0029] In order to setup roaming LBO sessions for the UEs 124 and 126, an AMF in the PLMN 102 requests a network repository function (NRF) in the PLMN 102 to select, from a list of SMFs, an SMF to use for the LBO sessions of the UEs 124 and 126. More specifically, for each of the UEs 124 and 126, the NRF may select an SMF based on a DNN and / or a S-NSSAI associated with each of the UEs 124 and 126. In this selection, the NRF may select any SMF as long as the SMF is associated with the DNN and / or the S-NSSAI associated with a particular UE.

[0030] However, there may be a scenario where the MNO 112 wants to restrict as to which SMF(s) can be used for the LBO sessions of the UEs 124 and 126. For example, the MNOs 112 and 114 may have an agreement that only some SMFs of the MNO 112 can be used for LBO sessions for inbound roaming devices coming from the MNO 114. In this scenario, there is a need for a method for the MNO 112 to configure its network entities (e.g., SMF, NRF, AMF, etc.) such that only some specific SMFs can be used for handling LBO sessions of UEs coming from the MNO 114.

[0031] Thus, according to some embodiments, a process 200 shown in FIG. 2 is provided. The process 200 is for discovering a session management entity (SME) to use for a network session (e.g., an LBO session) of a device (e.g., the UE 124). The process 200 is performed by a UE 252, a mobility management function entity (MMFE) 254, a network function 256, and SMEs 258 and 260. Note that the number of each of the entities 252-260 shown in FIG. 2 is provided for simple explanation purpose only and does not limit the embodiments of this disclosure in any way.

[0032] Examples of the UE 252 include but are not limited to a mobile phone, an Internet of Things (loT) device, a computer, a tablet, a vehicle, a tracking device, a watch, an extended reality (XR) device, etc.

[0033] The MMFE 254 is defined as an entity capable of performing a mobility management. Examples of the MMFE 254 include but are not limited to an access mobility and management function (AMF) or a mobility management entity (MME).

[0034] The network function 256 is defined as an entity capable of allowing other network functions to register and / or discover each other. Examples of the network function 256 include but are not limited to a network repository function (NRF) or any entity capable of storing network function (NF) profiles of SMEs. The network function 256 may be implemented as a physical node or in the cloud environment. In some embodiments, the network function 256 may be a software entity.

[0035] Each of the SMEs 258 and 260 is defined as an entity capable of managing network sessions. Examples of SME include but are not limited to a session management function (SMF), a packet gateway (PGW-C), etc.

[0036] The process 200 may begin with step s202. The step s202 comprises the SME 258 transmitting, to the network function 256, a request for managing the SME 258. The request may include a NF profile of the SME 258. The NF profile of the SME 258 may include one or more ranges of identifiers (IDs) of PLMNs of UEs that can be served by the SME 258 for a particular DNN and / or for a particular S-NSSAI.

[0037] In one example, the NF profile of the SME 258 may include an information element (IE) indicating a DNN supported by the SME 258, and according to some embodiments, this IE may contain a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported DNN.

[0038] In another example, the NF profile of the SME 258 may include an information element (IE) indicating a S-NSSAI supported by the SME 258, and according to some embodiments, this IE may contain a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported S-NSSAI.

[0039] In a different example, the NF profile of the SME 258 may include an information element (IE) indicating a S-NSSAI supported by the SME 258, and according to some embodiments, this IE may contain a list of one or more lEs each indicating a DNN supported by the SME 258. Each of these one or more lEs indicating DNNs supported by the SME 258 may include a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported DNN.

[0040] In a different example, the NF profile of the SME 258 may include a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for any DNN and any S-NSSAI.

[0041] In some embodiments, the request for managing the SME 258 may correspond to a request to register the SME 258 at the network function 256 using the NF profile of the SME 258. Alternatively, the request may correspond to a request to update the NF profile of the SME 258 stored in the network function 256 using the new NF profile of the SME 258 included in the request.

[0042] After receiving the request in the step s202, the process 200 may proceed to step s204. The step s204 comprises the SMF 260 transmitting, to the network function 256, a request for managing the SME 260. The request may include a NF profile of the SME 260. The NF profile of the SME 260 does not include one or more ranges of IDs of PLMNs of UEs that can be served by the SME 260 for a particular DNN and / or for a particular S-NSSAI. In other words, the NF profile of the SME 260 does not limit the use of the SME 260 to serving UEs having particular PLMN IDs.

[0043] In some embodiments, the request for managing the SME 260 may correspond to a request to register the SME 260 at the network function 256 using the NF profile of the SME 260. Alternatively, the request may correspond to a request to update the NF profile of the SME 260 stored in the network function 256 using the new NF profile of the SME 260 included in the request.

[0044] Even though FIG. 2 shows that the step s204 is performed after performing the step s202, in some embodiments, the steps s202 and s204 can be performed simultaneously. Alternatively, in some embodiments, the step s202 can be performed after performing the step s204.

[0045] After performing the steps s202 and s204, the process 200 may proceed to step s206. The step s206 comprises the network function 256 managing the SMEs 258 and 260 using the NF profiles of the SMEs 258 and 260 received in the requests. For example, the network function 256 may register the SMEs 258 and 260 using the received NF profiles. In another example, the network function 256 may update the existing NF profiles of the SMEs 258 and 260 stored in the network function 256 using the received NF profiles.

[0046] Even though FIG. 2 shows that the step s206 is performed after performing the steps s202 and s204, in some embodiments, the steps s202-s206 can be performed simultaneously. Alternatively, in some embodiments, the step s206 can be performed before performing any of the steps s202 and s204.

[0047] After the network function 256 managing the SMEs 258 and 260, the process 200 may proceed to step s208. The step s208 comprises the MMFE 254 receiving a request, from the UE 252, a request for a network session, e.g., a packet data unit (PDU) session. The request may include i) a subscription permanent identifier (SUPI) of the UE 252 and / or ii) a DNN requested by the UE for the network session (hereinafter, "UE-DNN”) and / or a S-NSSAI requested by the UE for the network session (hereinafter, "UE-S-NSSAI”).

[0048] After receiving the request in the step s208, the MMFE 254 may derive a PLMN ID identifying a PLMN of the UE 252 based on the received SUPI of the UE 252. Then the process 200 may proceed to step s210. The step s210 comprises the MMFE 254 determining to select an SME for the network session of the UE 252. Then the process 200 may proceed to step s212.

[0049] The step s212 comprises the MMFE 254 transmitting to the network function 256 a discovery request for discovering an SME to use for the network session of the UE 252. The discovery request may include i) a PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI. After the network function 256 receiving the discovery request, the process 200 may proceed to step s214.

[0050] The step s214 comprises the network function 256 performing an SME discovery - i.e., selecting an SME to use for the network session of the UE 252 based on i) the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI.

[0051] In selecting an SME to use for the network session of the UE 252, the network function 256 may check the NF profile of the SMEs registered at the network function 256. More specifically, in the example shown in FIG. 2, the network function 256 checks the NF profiles of the SMEs 258 and 260 and select an SME having the NF profile that matches i) the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI.

[0052] For example, as mentioned above, the NF profile of the SME 258 may include an IE indicating the DNN supported by the SME 258, and this DNN IE may also contain a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported DNN. In this example, the network function 256 may check if the DNN supported by the SME 258 is same as the UE-DNN. In case they are not the same, the SME 258 may not be selected in the step s214. On the other hand, in case they are the same, the network function 256 may also check if the PLMN ID of the UE 252 is within any of the ranges of the PLMN IDs of UEs indicated in the NF profile of the SME 258. If it is, then the SME 258 may be selected in the step s214.

[0053] In another example, as mentioned above, the NF profile of the SME 258 may include an IE indicating the S-NSSAI supported by the SME 258, and this S-NSSAI IE may also contain a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported DNN. In this example, the network function 256 may check if the S-NSSAI supported by the SME 258 is same as the UE-S-NSSAI. In case they are not the same, the SME 258 may not be selected in the step s214. On the other hand, in case they are the same, the network function 256 may also check if the PLMN ID of the UE 252 is within any of the ranges of the PLMN IDs indicated in the NF profile of the SME 258. If it is, then the SME 258 may be selected in the step s214.

[0054] Note that in case the process 200 is applied to an LBO roaming session, the process of selecting an SME in the step s214 may be little different. For example, in the scenario 100 shown in FIG. 1 , the inbound roaming device 124 travelled to the PLMN 102. In this case, in the step s208 of the process 200, the roaming device 124 (i.e., the UE 252) transmits, to the MMFE 254 (e.g., AMF 254), a request for a roaming session. This request may include a DNN requested by the device 124 and a S-NSSAI requested by the device 124. Here, the S-NSSAI included in the request is an S-NSSAI of the roaming device 124's HPLMN (i.e., the PLMN 104). Upon receiving the request, in the step s210, the MMFE 254 may convert the S-NSSAI of the roaming device 124's HPLMN included in the request to an S-NSSAI of the PLMN 102 (i.e., VPLMN) and, in the step s212, the MMFE 254 may transmit, to the NN 256 (e.g., NRF 256), a request for discovering an SMF, which may include the DNN requested by the device 124 and the S-NSSAI of the VPLMN which is mapped to the S-NSSAI include in the roaming request transmitted by the device 124. Note that, in this scenario, the S-NSSAI indicated in the NF profile of the SME 258 is also an S-NSSAI of the VPLMN, which is mapped to the S-NSSAI of the device 124's HPLMN. The rest of the process of selecting an SMF is identical to the process described in the preceding paragraph.

[0055] In a different example, as mentioned above, the NF profile of the SME 258 may include an IE indicating the S-NSSAI supported by the SME 258, and this S-NSSAI IE may also contain an IE indicating the DNN supported by the SME 258. This DNN IE may also contain a list of one or more ranges of PLMN IDs identifying the PLMNs of UE, which can be served by the SME 258 for the supported DNN. In this example, the network function 256 may check if the S-NSSAI supported by the SME 258 is same as the UE- S-NSSAI. In case they are not the same,the SME 258 may not be selected in the step s214. On the other hand, in case they are the same, the network function 256 may check if the DNN supported by the SME 258 is same as the UE-DNN. In case they are not the same, the SME 258 may not be selected in the step s214. On the other hand, in case they are the same, the network function 256 may also check if the PLMN ID of the UE 252 is within any of the ranges of the PLMN IDs indicated in the NF profile of the SME 258. If it Is, then the SME 258 may be selected in the step s214. Like the example above, in case the process 200 is applied to an LBO roaming session, the S-NSSAI of the roaming device's HPLMN included in the roaming request may be converted to an S-NSSAI of the VPLMN by the MMFE 254, and this converted S-NSSAI may be used for selecting an SME for the roaming session.

[0056] In some embodiments, an SME having a NF profile which does not contain a list of one or more ranges of IDs of PLMNs supported by UEs may be selected as a second preferred candidate in case there is an SME matching the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI, and this matching SME is selected as a first preferred candidate. Additionally or alternatively, in some embodiments, in case there is no SME matching the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI, an SME having a NF profile which does not contain a list of one or more ranges of IDs of PLMNs supported by UEs may be selected instead.

[0057] For example, in FIG. 2, let's assume that the NF profile of the SME 258 matches the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI and the NF profile of the SME 260 matches the UE-DNN and / or the UE-S-NSSAI. In this example, the SME 258 may be selected as the first preferred candidate and the SME 260 may be selected as the second preferred candidate.

[0058] In another example, let's assume that the NF profile of the SME 258 does not match the PLMN ID of the UE 252 and ii) the UE-DNN and / or the UE-S-NSSAI and the NF profile of the SME 260 matches the UE-DNN and / or the UE-S-NSSAI. In this example, the SME 258 may not be selected but the SME 260 may be selected.

[0059] After selecting an SME to use for the network session of the UE 252, the process 200 may proceed to step s216. The step s216 comprises the network function 256 transmitting to the MMFE 254 a message identifying the selected SME.

[0060] FIG. 3 shows an example of how the embodiments of this disclosure can be applied to the existing 3GPP process. FIG. 3 shows a process 300 for discovering an SMF to use for a LBO roaming session for a roaming device (e.g., the UE 124). The process 300 may begin with step 0A. The step 0A is an example of the step s202 shown in FIG. 2.

[0061] The step 0A comprises SMF1 transmitting a request to register the SMF1 at NRF ("Nnrf_NFRegister” or "NFUpdate” request). This request may correspond to a PUT request as defined in 3GPP TS 29.510 at clause 5.2.2.2 or 5.2.2.3. The request includes an NF profile of the SMF1. The NF profile may optionally include roamingpartner information, e.g., at DNN level, so that DNN level roaming partner information can be registered at the NRF and AMF can select the correct SMF for the LBO session based on the DNN level roaming agreement. The roaming partner information can be provided in the NF profile as follows.

[0062] As disclosed in 3GPP TS 29.510 at clause 6.1.6.2.2, the NF profile may include an IE identifying specific data for the SMF (“smflnfo”). As disclosed in 3GPP TS 29.510 at clause 6.1 .6.2.12, this IE may contain another IE containing a list ("sNssaiSmflnfoList”) of parameters ("SnssaiSmflnfoltem”) supported by the SMF per S-NSSAI. As further disclosed in 3GPP TS 29.510 at clause 6.1.6.2.29, each of these parameters contains a supported S-NSSAI ("sNssai”) and a list ("dnnSmflnfoList”) of parameters (“DnnSmflnfoltem”) supported by the SMF per DNN. According to some embodiments, each of these parameters supported by the SMF per DNN may contain an IE called "uePImnRangeList” which contains a list of one or more ranges of IDs of PLMNs of roaming UEs supported by the SMF1. This list indicates that the SMF1 can serve roaming UEs belonging to the indicated PLMNs. Thus, this list may correspond to the roaming partner information. The roaming partner information can be configured at DNN level, at S- NSSAI level, or at SMF level.

[0063] After creating or updating the NF profile of the SMF1, the process 300 may proceed to step 0B which comprises transmitting to the SMF1 a response indicating that the profile was created or updated. After performing the step 0B, the process 300 may proceed to step 0C. The step 0C is an example of the step s204 shown in FIG. 2.

[0064] The step 0C comprises SMF2 transmitting a request to register the SMF2 at the NRF ("Nnrf_NFRegister” or "NFUpdate” request). This request may correspond to a PUT request as defined in 3GPP TS 29.510 at clause 5.2.2.2 or 5.2.2.3. The request includes an NF profile of the SMF2. Unlike the NF profile of the SMF1 , the NF profile of the SMF2 does not contain a list of one or more ranges of IDs of PLMNs of roaming UEs supported by the SMF2.

[0065] After creating or updating the NF profile of the SMF2, the process 300 may proceed to step 0D which comprises transmitting to the SMF2 a response indicating that the profile was created or updated.

[0066] In step 1 , the AMF receives a PDU session establishment request from the UE. The step 1 is an example of the step s208 shown in FIG. 2. The PDU session establishment request may comprise the S-NSSAI and the DNN associated with the UE. After the AMF receiving the PDU session establishment request, the AMF decides to select an SMF for the PDU session in step 4.

[0067] Then, in step 5, the AMF transmits to the NRF a service discovery request ("Nrf_NFDiscovery_GET”) for finding an appropriate SMF for the PDU session, i.e., the AMF performs a SMF discovery for the inbound roamer for the LBO session. One example of the service discovery request is the GET request defined in 3GPP TS 29.510 at clause 5.3.2.2. The step 5 is an example of the step s212 shown in FIG. 2.

[0068] The service discovery request may include one or more query parameters. One of the query parameters is roaming information. The roaming information may identify the PLMN of the UE's SUPI and other discovery parameters such as the DNN and / or S-NSSAI associated with the UE.

[0069] Then, the NRF selects an SMF as explained above with respect to the step s214 shown in FIG. 2, and, in step 6, the NRF transmits to the AMF, a service discovery response ("NF Service Discovery Response”). The step 6 is an example of the step s216 shown in FIG. 2.

[0070] FIG. 4 shows a process 400 for discovering a session management entity (SME) to use for a network session of a device, according to some embodiments. The process 400 is performed by a network function (256). The process 400 may begin with step s402. The step s402 comprises receiving from a first SME a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME. The step s404 comprises, based at least on receiving the request, managing the first SME using the received NF profile of the first SME._The received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice.

[0071] In some embodiments, the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the first SME belong.

[0072] In some embodiments, the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for I) the first DNN and / or for the first NS or ii) any DNN and any NS.

[0073] In some embodiments, the network function is a network repository function (NRF), and the first SME is a session management function (SMF) or a packet gateway (PGW).

[0074] In some embodiments, the request is either a registration request to register the first SME at the network function or an update request to update the first SME's NF profile stored at the network function; and managing the first SME using the received NF profile comprises either registering the first SME at the network function using the received NF profile based at least on receiving the registration request or updating the first SME's NF profile stored at the network function using the received NF profile based at least on receiving the update request.

[0075] In some embodiments, the received NF profile of the first SME includes an information element (IE) containing information about a DNN supported by the first SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first DNN.

[0076] In some embodiments, the received NF profile of the first SME includes an information element (IE) containing information about an NS (e.g., S-NSSAI) supported by the first SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first NS.

[0077] In some embodiments, the process 400 further comprises receiving from a mobility management function entity (MMFE) a discovery request for discovering an SME, and the discovery request comprises (i) a PLMN ID of the device and (ii) a DNN ID identifying a particular DNN and / or an NS ID (e.g., S-NSSAI) identifying a particular network slice.

[0078] In some embodiments, the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME).

[0079] In some embodiments, the PLMN ID identifies a PLMN associated with the device's subscription permanent identifier (SUPI).

[0080] In some embodiments, the process 400 further comprises, after receiving the discovery request, i) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the DNN ID included in the discovery request identifies the first DNN; and iii) determining that the NS ID (e.g., S-NSSAI) included in the discovery request identifies the first network slice. The process 400 further comprises, based at least on the determinations i)-iii), determining to use the first SME for the network session of the device.

[0081] In some embodiments, the process 400 further comprises, after receiving the discovery request, i) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the NS ID included in the discovery request identifies the first NS ID. The process 400 further comprises, based at least on the determinations i) and ii), determining to use the first SME for the network session of the device.

[0082] In some embodiments, the process 400 further comprises: receiving from a second SME a request for managing the second SME, wherein the request includes a NF profile of the second SME; and based at least on receiving the request, managing the second SME using the received NF profile of the second SME, wherein the received NF profile of the second SME does not include any range of IDs of remote PLMNs served by the second SME.

[0083] In some embodiments, the process 400 further comprises, after receiving the discovery request, determining that the PLMN ID included in the discovery request is not within any one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and.based at least on the determination, selecting the second SME.

[0084] FIG. 5 shows a process 500 for registering a session management entity (SME) to use for a network session of a device, according to some embodiments. The process 500 is performed by the SME (258) (e.g., SMF) and may begin with step s502. The step s502 comprises transmitting, to a network function (256) (e.g., NRF), a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME for i) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice. Step s504 comprises, after transmitting the request, receiving, from the network function, a message indicating that the SME has been managed as requested by the request.

[0085] In some embodiments, the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the SME belong.

[0086] In some embodiments, the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for i) the first DNN and / or for the first NS or ii) any DNN and any NS.

[0087] In some embodiments, the SME is a session management function (SMF) or a packet gateway (PGW), and the network function is a network repository function (NRF).

[0088] In some embodiments, the request is either a registration request to register the SME at the network function or an update request to update the SME's NF profile stored at the network function.

[0089] In some embodiments, the NF profile of the SME includes an information element (IE) containing information about a DNN supported by the SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first DNN.

[0090] In some embodiments, the NF profile of the SME includes an information element (IE) containing information about an NS (e.g., S-NSSAI) supported by the SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first NS.

[0091] FIG. 6 shows a process 600 for discovering a session management entity (SME) (e.g., SMF) to use for a network session of a device (252). The process 600 is performed by a mobility management function entity (MMFE) (254) (e.g., AMF). The process 600 may begin with step s602. The step s602 comprises receiving, from the device (e.g., UE), a request for the network session, wherein the request for the network session comprises (i) a subscription permanent identifier (SUPI) of the device and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device. Step s604 comprises, based on the device's SUPI, deriving a public land mobile network (PLMN) identifier identifying a PLMN ofthe device. Step s606 comprises, based at least on receiving the request, transmitting, to a network function (256) (e.g., NRF), a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.

[0092] In some embodiments, the network session includes a local break out (LBO) session for the device within a network to which the MMFE and the network function belong.

[0093] In some embodiments, the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME), and the network function is a network repository function (NRF).

[0094] In some embodiments, the NS ID included in the request for the network session is an NS ID identifying an NS of a first network, the process further comprises converting the NS ID included in the request for the network session into an NS ID identifying an NS of a second network which is different from the first network, and the NS ID included in the discovery request is the NS ID identifying the NS of the second network.

[0095] FIG. 7 is a block diagram of network node 700 which can be used to implement any one of the network function 256, the SME 258, or the MMFE 254, according to some embodiments. As shown in FIG. 7, network node 700 may comprise: processing circuitry (PC) 702, which comprises one or more processors (P) 755 (e.g., one or more general purpose microprocessors and / or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (e.g., network node 700 may be a distributed computing apparatus comprising two or more computers or a monolithic computing apparatus consisting of a single computer); at least one network interface 748 (e.g., a physical interface or air interface) comprising a transmitter (Tx) 745 and a receiver (Rx) 747 for enabling network node 700 to transmit data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network) to which network interface 748 is connected (physically or wirelessly) (e.g., network interface 748 may be coupled to an antenna arrangement comprising one or more antennas for enabling network node 700 to wirelessly transmit / receive data); and a storage unit (a.k.a., "data storage system”) 708, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments where PC 702 includes a programmable processor, a computer readable storage medium (CRSM) 742 may be provided. CRSM 742 may store a computer program (CP) 743 comprising computer readable instructions (CRI) 744. CRSM 742 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 744 of computer program 743 is configured such that when executed by PC 702, the CRI causes network node 700 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, network node 700 may be configured to perform steps described herein without the need for code.That is, for example, PC 702 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and / or software.

[0096] Summary of EmbodimentsA1 . A method (400) for discovering a session management entity (SME) to use for a network session of a device (252), the method being performed by a network function (256), the method comprising: receiving (s402) from a first SME (258) a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME; and based at least on receiving the request, managing (s404) the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice.A2. The method of embodiment A1, wherein the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the first SME belong.A3. The method of embodiment A2, wherein the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for I) the first DNN and / or for the first NS or ii) any DNN and any NS.A4. The method of embodiment A1 or A2, wherein the network function is a network repository function (NRF), and the first SME is a session management function (SMF) or a packet gateway (PGW).A5. The method of any one of embodiments A1-A4, wherein the request is either a registration request to register the first SME at the network function or an update request to update the first SME's NF profile stored at the network function; and managing the first SME using the received NF profile comprises either registering the first SME at the network function using the received NF profile based at least on receiving the registration request or updating the first SME's NF profile stored at the network function using the received NF profile based at least on receiving the update request.A6. The method of any one of embodiments A1-A5, wherein the received NF profile of the first SME includes an information element (IE) containing information about a DNN supported by the first SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first DNN.A7. The method of any one of embodiments A1-A5, wherein the received NF profile of the first SME includes an information element (IE) containing information about an NS (e.g., S-NSSAI) supported by the first SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first NS.A8. The method of any one of embodiments A1-A7, wherein the method further comprises receiving from a mobility management function entity (MMFE) a discovery request for discovering an SME, and the discovery request comprises (I) a PLMN ID of the device and (ii) a DNN ID identifying a particular DNN and / or an NS ID (e.g., S-NSSAI) identifying a particular network slice.A9. The method of embodiment A8, wherein the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME).A10. The method of embodiment A8 or A9, wherein the PLMN ID identifies a PLMN associated with the device's subscription permanent identifier (SUPI).A11 . The method of any one of embodiments A8-A10, wherein the method further comprises: after receiving the discovery request,I) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the DNN ID included in the discovery request identifies the first DNN; andiii) determining that the NS ID (e.g., S-NSSAI) included in the discovery request identifies the first network slice; based at least on the determinations i)-iii), determining to use the first SME for the network session of the device.A12. The method of any one of embodiments A8-A10, wherein the method further comprises: after receiving the discovery request,I) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the NS ID included in the discovery request identifies the first NS ID; and based at least on the determinations I) and ii), determining to use the first SME for the network session of the device.A13. The method of any one of the embodiments A8-A12, wherein the method further comprises: receiving from a second SME a request for managing the second SME, wherein the request includes a NF profile of the second SME; and based at least on receiving the request, managing the second SME using the received NF profile of the second SME, wherein the received NF profile of the second SME does not include any range of IDs of remote PLMNs served by the second SME.A14. The method of embodiment A13, wherein the method further comprises: after receiving the discovery request, determining that the PLMN ID included in the discovery request is not within any one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and based at least on the determination, selecting the second SME.B1. A method (500) for registering a session management entity (SME) to use for a network session of a device (252), the method being performed by the SME (258) (e.g., SMF), the method comprising: transmitting (s502), to a network function (256) (e.g., NRF), a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME for I) afirst data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice; and after transmitting the request, receiving (s504), from the network function, a message indicating that the SME has been managed as requested by the request.B2. The method of embodiment B1 , wherein the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the SME belong.B3. The method of embodiment B2, wherein the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for I) the first DNN and / or for the first NS or ii) any DNN and any NS.B4. The method of embodiment B1 or B2, wherein the SME is a session management function (SMF) or a packet gateway (PGW), and the network function is a network repository function (NRF).B5. The method of any one of embodiments B1-B4, wherein the request is either a registration request to register the SME at the network function or an update request to update the SME's NF profile stored at the network function.B6. The method of any one of embodiments B1-B5, wherein the NF profile of the SME includes an information element (IE) containing information about a DNN supported by the SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first DNN.B7. The method of any one of embodiments B1-B5, wherein the NF profile of the SME includes an information element (IE) containing information about an NS (e.g., S- NSSAI) supported by the SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first NS.C1. A method (600) for discovering a session management entity (SME) (e.g., SMF) to use for a network session of a device (252), the method being performed by a mobility management function entity (MMFE) (254) (e.g., AMF), the method comprising: receiving (s602), from the device (e.g., UE), a request for the network session, wherein the request for the network session comprises (i) a subscription permanent identifier (SUPI) of the device and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device; based on the device's SUPI, deriving (s604) a public land mobile network (PLMN) identifier identifying a PLMN of the device; based at least on receiving the request, transmitting (s606), to a network function (256) (e.g., NRF), a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.C2. The method of embodiment C1, wherein the network session includes a local break out (LBO) session for the device within a network to which the MMFE and the network function belong.C3. The method of embodiment C1 or C2, wherein the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME), and the network function is a network repository function (NRF).C4. The method of any one of embodiments C1-C3, wherein the NS ID included in the request for the network session is an NS ID identifying an NS of a first network, the method further comprises converting the NS ID included in the request for the network session into an NS ID identifying an NS of a second network which is different from the first network, and the NS ID included in the discovery request is the NS ID identifying the NS of the second network.D1. A computer program (700) comprising instructions (744) which when executed by processing circuitry (702) cause the processing circuitry to perform the method of any one of embodiments A1-C4.D2. A carrier containing the computer program of embodiment D1 , wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.E1. A network function (256) for discovering a session management entity (SME) to use for a network session of a device (252), the network function being configured to: receive (s402) from a first SME (258) a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME; and based at least on receiving the request, manage (s404) the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice.E2. The network function of embodiment E1, wherein the network function is configured to perform the method of any one of embodiments A2-A14.F1 . A session management entity (SME) (258) to use for a network session of a device (252), the SME being configured to: transmit (s502), to a network function (256) (e.g., NRF), a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME for I) a first data network name (DNN) and / or for a first network slice (NS) or ii) any data network name and any network slice; and after transmitting the request, receive (s504), from the network function, a message indicating that the SME has been managed as requested by the request.F2. The SME of embodiment F1, wherein the SME is configured to perform the method of any one of embodiments B2-B7.G1 . A mobility management function entity (MMFE) (254) (e.g., AMF) for discovering a session management entity (SME) (e.g., SMF) to use for a network session of a device (252), the MMFE being configured to: receive (s602), from the device (e.g., UE), a request for the network session, wherein the request for the network session comprises (I) a subscription permanent identifier (SUPI) of the device and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device;based on the device's SUPI, derive (s604) a public land mobile network (PLMN) identifier identifying a PLMN of the device; based at least on receiving the request, transmit (s606), to a network function (256) (e.g., NRF), a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (I) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.G2. The MMFE of embodiment G1 , wherein the MMFE is configured to perform the method of any one of embodiments C2-C4.H1. An apparatus (700) comprising: processing circuitry (702); and a memory (741), said memory containing instructions executable by said processing circuitry, whereby the apparatus is operative to perform the method of any one of embodiments A1-C4.

[0097] Conclusion

[0098] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above-described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[0099] As used herein transmitting a message "to” or "toward” an intended recipient encompasses transmitting the message directly to the intended recipient or transmitting the message indirectly to the intended recipient (i.e., one or more other nodes are used to relay the message from the source node to the intended recipient). Likewise, as used herein receiving a message "from” a sender encompasses receiving the message directly from the sender or indirectly from the sender (i.e., one or more nodes are used to relay the message from the sender to the receiving node). Further, as used herein "a” means "at least one” or "one or more.”

[0100] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[0101] Appendix

[0102] Appendix begins here.

[0103] Appendix ends here.

Claims

CLAIMS1. A method (400) for discovering a session management entity (SME) to use for a network session of a device (252), the method being performed by a network function (256), the method comprising: receiving (s402) from a first SME (258) a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME; and based at least on receiving the request, managing (s404) the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the first SME.

2. The method of claim 1 , wherein the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the first SME belong.

3. The method of claim 2, wherein the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for i) a first data network name (DNN) and / or for a first network slice (NS) or ii) any DNN and any NS.

4. The method of any one of claims 1-3, wherein the network function is a network repository function (NRF), and the first SME is a session management function (SMF) or a packet gateway (PGW).

5. The method of any one of claims 1 -4, wherein the request is either a registration request to register the first SME at the network function or an update request to update the first SME's NF profile stored at the network function; and managing the first SME using the received NF profile comprises either registering the first SME at the network function using the received NF profile based at least on receiving the registration request or updating the first SME's NF profile stored at the network function using the received NF profile based at least on receiving the update request.

6. The method of any one of claims 1-5, wherein the received NF profile of the first SME includes an information element (IE) containing information about a DNN supported by the first SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first DNN.

7. The method of any one of claims 1-5, wherein the received NF profile of the first SME includes an information element (IE) containing information about an NS supported by the first SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the first SME for the first NS.

8. The method of any one of claims 1-7, wherein the method further comprises receiving from a mobility management function entity (MMFE) a discovery request for discovering an SME, and the discovery request comprises (I) a PLMN ID of the device and (ii) a DNN ID identifying a particular DNN and / or an NS ID identifying a particular network slice.

9. The method of claim 8, wherein the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME); wherein the PLMN ID identifies a PLMN associated with the device's subscription permanent identifier (SUPI).

10. The method of any one of claims 8-9, wherein the method further comprises: after receiving the discovery request,i) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the DNN ID included in the discovery request identifies the first DNN; and ill) determining that the NS ID included in the discovery request identifies the first network slice; based at least on the determinations i)-iii), determining to use the first SME for the network session of the device.11 . The method of any one of claims 8-9, wherein the method further comprises: after receiving the discovery request,I) determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and ii) determining that the NS ID included in the discovery request identifies the first NS ID; and based at least on the determinations I) and ii), determining to use the first SME for the network session of the device.

12. The method of any one of claims 8-9, wherein the method further comprises: after receiving the discovery request, determining that the PLMN ID included in the discovery request is within one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and based at least on the determinations, determining to use the first SME for the network session of the device.

13. The method of any one of the claims 8-12, wherein the method further comprises: receiving from a second SME a request for managing the second SME, wherein the request includes a NF profile of the second SME; andbased at least on receiving the request, managing the second SME using the received NF profile of the second SME, wherein the received NF profile of the second SME does not include any range of IDs of remote PLMNs served by the second SME.

14. The method of claim 13, wherein the method further comprises: after receiving the discovery request, determining that the PLMN ID included in the discovery request is not within any one of said one or more ranges of the IDs of the remote PLMNs served by the first SME; and based at least on the determination, selecting the second SME.

15. A method (500) for registering a session management entity (SME) to use for a network session of a device (252), the method being performed by the SME (258), the method comprising: transmitting (s502), to a network function (256), a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME; and after transmitting the request, receiving (s504), from the network function, a message indicating that the SME has been managed as requested by the request.

16. The method of claim 15, wherein the network session includes a local break out (LBO) session for a roaming device within a network to which the network function and the SME belong.

17. The method of claim 16, wherein the PLMNs of the devices are PLMNs of roaming devices that can be served by the first SME for i) a first data network name (DNN) and / or for the first network slice (NS) or ii) any DNN and any NS.

18. The method of claim 15 or 17, wherein the SME is a session management function (SMF) or a packet gateway (PGW), and the network function is a network repository function (NRF).

19. The method of any one of claims 15-18, wherein the request is either a registration request to register the SME at the network function or an update request to update the SME's NF profile stored at the network function.

20. The method of any one of claims 15-19, wherein the NF profile of the SME includes an information element (IE) containing information about a DNN supported by the SME, and the IE containing the information about the supported DNN includes a first DNN identifier (ID) identifying the first DNN and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first DNN.21 . The method of any one of claims 15-19, wherein the NF profile of the SME includes an information element (IE) containing information about an NS supported by the SME, and the IE containing information about the supported NS includes a first NS ID identifying the first NS and said one or more ranges of the IDs of the PLMNs of devices that can be served by the SME for the first NS.

22. A method (600) for discovering a session management entity (SME) to use for a network session of a device (252), the method being performed by a mobility management function entity (MMFE) (254), the method comprising: receiving (s602), from the device, a request for the network session, wherein the request for the network session comprises (I) a public land mobile network (PLMN) identifier identifying a PLMN of the device, and (ii)a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device; based at least on receiving the request, transmitting (s606), to a network function (256), a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.

23. The method of claim 22, wherein the network session includes a local break out (LBO) session for the device within a network to which the MMFE and the network function belong.

24. The method of claim 22 or 23, wherein the MMFE is an access and mobility management function (AMF) or a mobility management entity (MME), and the network function is a network repository function (NRF).

25. The method of any one of claims 22-24, wherein the NS ID included in the request for the network session is an NS ID identifying an NS of a first network, the method further comprises converting the NS ID included in the request for the network session into an NS ID identifying an NS of a second network which is different from the first network, and the NS ID included in the discovery request is the NS ID identifying the NS of the second network.

26. The method of any one of claims 22-25, wherein the PLMN identifier is derived based on a subscription permanent identifier (SUPI) of the device and the SUPI is included in the request.

27. A computer program (700) comprising instructions (744) which when executed by processing circuitry (702) cause the processing circuitry to perform the method of any one of claims 1-26.

28. A carrier containing the computer program of embodiment 27, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium.

29. A network function (256) for discovering a session management entity (SME) to use for a network session of a device (252), the network function being configured to: receive (s402) from a first SME (258) a request for managing the first SME, wherein the request includes a network function (NF) profile of the first SME; and based at least on receiving the request, manage (s404) the first SME using the received NF profile of the first SME, wherein the received NF profile of the first SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that that can be served by the first SME.

30. The network function of claim 29, wherein the network function is configured to perform the method of any one of claims 2-14.

31. A session management entity (SME) (258) to use for a network session of a device (252), the SME being configured to: transmit (s502), to a network function (256), a request for managing the SME, wherein the request includes a network function (NF) profile of the SME, wherein the NF profile of the SME includes one or more ranges of identifiers (IDs) of public land mobile networks (PLMNs) of devices that can be served by the SME; and after transmitting the request, receive (s504), from the network function, a message indicating that the SME has been managed as requested by the request.

32. The SME of claim 31 , wherein the SME is configured to perform the method of any one of claim 16- 21.

33. A mobility management function entity (MMFE) (254) for discovering a session management entity (SME) to use for a network session of a device (252), the MMFE being configured to: receive (s602), from the device (e.g., UE), a request for the network session, wherein the request for the network session comprises (i) a public land mobile network (PLMN) identifier identifying a PLMN of the device, and (ii) a data network name (DNN) ID identifying a DNN requested by the device and / or a network slice (NS) ID identifying an NS requested by the device; based at least on receiving the request, transmit (s606), to a network function (256) , a discovery request for discovering the SME to use for the network session, wherein the discovery request comprises (i) the PLMN ID identifying the PLMN of the device and (ii) the DNN ID identifying the DNN requested by the device and / or an NS ID corresponding to the NS requested by the device.

34. The MMFE of claim 33, wherein the MMFE is configured to perform the method of any one of claims 22-26.

35. An apparatus (700) comprising: processing circuitry (702); and a memory (741), said memory containing instructions executable by said processing circuitry, whereby the apparatus is operative to perform the method of any one of claims 1-26.

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