WO2018166633A1

WO2018166633A1 - Method and nodes for handling registration of a ue to a core network

Info

Publication number: WO2018166633A1
Application number: PCT/EP2017/056452
Authority: WO
Inventors: Gunnar Mildh; Paul Schliwa-Bertling; Mikael Wass; Peter Hedman
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2017-03-17
Filing date: 2017-03-17
Publication date: 2018-09-20

Abstract

The embodiments herein relate to a method performed by a UE (101). The UE (101) is capable of accessing both a NGCN (105) and an EPC network (108). The UE (101) receives a support indicator which indicates that the RAN node (103a) supports connectivity to NGCN (105) and the EPC network (108). The UE (101) sends a NGCN registration message for registering the UE (101) to the NGCN (105). The UE (101) receives a response indicating that the UE (101) does not have right to register to the NGCN (105) or receiving no response to the NGCN registration message. The UE (101) sends, when said response indicates that the UE (101) does not have right to register to the NGCN (105) or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE (101) to the EPC (108).

Description

METHOD AND NODES FOR HANDLING REGISTRATION OF A UE TO A CORE NETWORK

5 TECHNICAL FIELD

Embodiments herein relate generally to a User Equipment (UE), a method performed by the UE, a Radio Access Network (RAN) node, a method performed by the RAN node, a Next Generation Core Network (NGCN) node and a method performed by the NGCN 10 node. More particularly the embodiments herein relate to handling registration of the UE to a Core Network (CN) for a Public Land Mobile Network (PLMN), where the UE is capable of accessing both a NGCN and an Evolved Packet Core (EPC) network.

15 BACKGROUND

The standardization organization Third Generation Partnership Project (3GPP) is currently in the processes of specifying a new Radio Interface called New Radio (NR) or Fifth Generation (5G) or G-Universal Mobile Telecommunications System (UMTS) Terrestrial 20 Radio Access (G-UTRA) as well as a Next Generation (NG) Packet Core Network (NGCN or NGC).

Figure 1 a is a schematic block diagram illustrating a high level architecture for a Next Generation (NextGen) System. Figure 1 a illustrates a NextGen UE 101 , a

25 NextGen(R)AN 103, a NGCN 105, a data network 110 and their reference points.

According to chapter 3 in 3GPP TR 23.799 V14.0.0 (2016-12), the NextGen UE 101 can be described as a UE 101 connecting to a NextGen system. The term UE with the reference number 101 is used herein when referring to a NextGen UE. The NextGen UE

30 101 may also be referred to as a 5G compatible UE 101 . The NextGen UE 101 may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operators radio access network and core network provide access, e.g. access to the Internet. The NextGen UE 101 may be any device, mobile or stationary, enabled to communicate in the communications network, for

35 instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device, Device to Device (D2D) device, Internet of Things (ΙοΤ) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The NextGen UE 101 may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the NextGen (R)AN 103, with another entity, such as another NextGen UE 101 or a server.

The NextGen(R)AN 103 refers to either a NextGen RAN (NG RAN) or a NextGen Access Network (NG AN), or both. The NG RAN is according to 3GPP, a radio access network that supports one or more of the following four options:

1 ) Standalone New Radio,

2) Standalone New Radio is the anchor with Evolved E-UTRA extensions,

3) Evolved E-UTRA,

4) Evolved E-UTRA is the anchor with New Radio extensions, with the common characteristics that the RAN interfaces with the next generation core. The term NG AN refers to a NextGen RAN or a Non-3GPP access network and interfaces with the next generation core. The term NextGen(R)AN and the reference number 103 is used herein when referring to either of the NG RAN or the NG AN. The NextGen Core 105 is a core network specified that connects to the NextGen R(AN) 103. The NextGen Core 105 comprises one or more NextGen Core Network (NGCN) nodes 105a. The NGCN nodes 105 may also be referred to as NGCN functions. The NGCN node 105 may be for example an Access Management Function (AMF), a Session Management Function (SMF), a User Plane Function (UPF) or any other suitable NGCN function. The abbreviation NGCN is used herein to refer to any of the terms NextGen Core and NextGen Core Network, and the term NextGen Core is a short version of the term NextGen Core Network. The terms NextGen Core and NextGen Core Network are used interchangeably herein. The Data Network 110 may be an operator external public or private data network or an intra-operator data network, e.g. for provision of Internet Protocol (IP) Multimedia

Subsystem (IMS) services. The data network 1 10 may be for example an IP network, an Ethernet network and non-IP network etc. and provides services to the NextGen UE 101. As seen in figure 1 a, NG2 is the reference point for the Control Plane (CP) between NextGen (R)AN 103 and the NextGen Core 105. NG3 is the reference point for the User Plane (UP) between NextGen (R)AN 103 and NextGen Core 105. The Control Plane (CP) is illustrated with a dashed line. NG1 (not shown in Fig. 1 a) is the reference point for the control plane between NextGen UE 101 and the NGCN 105. NG6 is the reference point between the NGCN 105 and the data network 1 10. This reference point NG6 corresponds to SGi for 3GPP accesses.

The problem with 5G is that there is no solution described how to handle roaming

UEs/subscribers 101 that are directed to a NGCN 105 (e.g. based on that the NextGen UE 101 supports NextGen Core) but do not have a valid 5G subscription or no rights to access the NGCN 105.

SUMMARY

An objective of embodiments herein is therefore to obviate at least one of the above disadvantages and to improve registration of a UE to a CN. According to a first aspect, the object is achieved by a method performed by a UE for handling registration of the UE to a CN for a PLMN. The UE is capable of accessing both a NGCN and an EPC network. The UE receives, from a RAN node, a support indicator which indicates that the RAN node supports connectivity to NGCN and to the EPC network. The UE sends, via said RAN node, at least an NGCN registration message to a NGCN node in the NGCN for registering the UE to the NGCN. The UE receives, via said RAN node, a response from the NGCN node indicating that the UE does not have right to register to the NGCN or receiving no response to the NGCN registration message. The UE sends, via said RAN node to an EPC node in the EPC network when said response indicates that the UE does not have right to register to the NGCN or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE to the EPC for the PLMN.

According to a second aspect, the object is achieved by a RAN node for handling registration of a UE to a CN for a PLMN. The UE is capable of accessing both a NGCN and an EPC network. The RAN node sends, to the UE, a support indicator which indicates that the RAN node supports connectivity to NGCN and to the EPC network. The RAN node receives, from the UE, at least an NGCN registration message for registering the UE to the NGCN for the PLMN. The RAN node routes the NGCN registration message to the NGCN node. The RAN node receives, from the NGCN node, a response indicating that the UE does not have right to register to the NGCN or receiving no response to the NGCN registration message. The RAN node sends, to the UE, the response from the NGCN node or sending no response to the NGCN registration message. The RAN node receives, from the UE when said response indicates that the UE does not have right to register to the NGCN or when no response to the registration message or registration messages is sent, an EPC registration message for registering the UE to the EPC network for the PLMN. The RAN nodes routes the EPC registration message from the UE to the EPC node.

According to a third aspect, the object is achieved by a method performed by a NGCN node for handling registration of a UE to a CN for a PLMN. The UE is capable of accessing both NGCN and an EPC network. The NGCN node is comprised in a NGCN. The NGCN node receives at least a NGCN registration message from the UE via a RAN node for registering the UE to the NGCN for the PLMN. The NGCN node sends, via said RAN node, a response to the UE indicating that the UE does not have right to register to the NGCN or sending no response to the NGCN registration message.

According to a fourth aspect, the object is achieved by a UE for handling registration of the UE to a CN for a PLMN. The UE is capable of accessing both a NGCN and an EPC network. The UE is configured to receive a support indicator from a RAN node which indicates that the RAN node supports connectivity to NGCN and to the EPC network. The UE is configured to send, via said RAN node, at least an NGCN registration message to a NGCN node in the NGCN for registering the UE to the NGCN. The UE is also configured to receive, via said RAN node, a response from the NGCN node indicating that the UE does not have right to register to the NGCN or receiving no response to the NGCN registration message. The UE is configured to send, via said RAN node to an EPC node in the EPC network when said response indicates that the UE does not have right to register to the NGCN or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE to the EPC for the PLMN. According to a fifth aspect, the object is achieved by a RAN node for handling registration of a UE to a CN for a PLMN. The UE is capable of accessing both a NGCN and an EPC network. The RAN node is configured to send, to the UE, a support indicator which indicates that the RAN node supports connectivity to NGCN and to the EPC network. The RAN node is configured to receive, from the UE, at least an NGCN registration message for registering the UE to the NGCN for the PLMN, and to route the NGCN registration message to the NGCN node. The RAN node is configured to receive, from the NGCN node, a response indicating that the UE does not have right to register to the NGCN or receiving no response to the NGCN registration message. The RAN node is configured to send, to the UE the response from the NGCN node or sending no response to the NGCN registration message. The RAN node is further configured to receive, from the UE when said response indicates that the UE does not have right to register to the NGCN or when no response to the registration message or registration messages is sent, an EPC registration message for registering the UE to the EPC network for the PLMN. The RAN node is configured to route the EPC registration message from the UE to the EPC node.

According to a sixth aspect, the object is achieved by a NGCN node for handling registration of a UE to a CN for a PLMN. The UE is capable of accessing both NGCN and an EPC network. The NGCN node is comprised in a NGCN. The NGCN node is configured to receive at least a NGCN registration message from the UE via a RAN node for registering the UE to the NGCN for the PLMN. The NGCN node is configured to send, via said RAN node, a response to the UE indicating that the UE does not have right to register to the NGCN or sending no response to the NGCN registration message. Since the UE supporting both NGCN and EPC access via 5G constructs NGCN and EPC registration messages, and indicates NGCN and EPC to the RAN node for routing to the intended CN type, the UE will access EPC if it does not have any valid NGCN

subscription or no rights to access the NGCN. The UE will therefor always be registered to one CN, even if NGCN registration is not possible. Thus, the registration of the UE to a CN is improved.

Embodiments herein afford many advantages, of which a non-exhaustive list of examples follows: An advantage of the embodiments herein is an efficient handling of 5G capable UEs that have no valid 5G subscription when accessing a network that supports access to EPC and 5G/NGCN. The embodiments herein are not limited to the features and advantages mentioned above. A person skilled in the art will recognize additional features and advantages upon reading the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will now be further described in more detail in the following detailed description by reference to the appended drawings illustrating the embodiments and in which: Fig. 1 a is a schematic block diagram illustrating a NextGen communications system.

Fig. 1 b is a schematic block diagram illustrating embodiments of a NextGen

communications system. Fig. 2 is a signaling diagram illustrating embodiments of a method.

Fig. 3a is a flow chart illustrating embodiments of a method.

Fig. 3b is a flow chart illustrating embodiments of a method.

Fig. 4 is a flow chart illustrating embodiments of a method performed by a UE.

Fig. 5 is a schematic block diagram illustrating embodiments of a UE. Fig. 6 is a flow chart illustrating embodiments of a method performed by a RAN node.

Fig. 7 is a schematic block diagram illustrating embodiments of a RAN node. Fig. 8 is a flow chart illustrating embodiments of a method performed by a NGCN node.

Fig. 9 is a schematic block diagram illustrating embodiments of a NGCN node.

The drawings are not necessarily to scale and the dimensions of certain features may have been exaggerated for the sake of clarity. Emphasis is instead placed upon illustrating the principle of the embodiments herein.

DETAILED DESCRIPTION

One problem with 5G is that there is no solution described how to handle roaming UEs/subscribers 101 that are directed to a NextGen Core 105 (e.g. based on that the UE 101 supports NGCN 105) but do not have a valid 5G subscription or no rights to access the NGCN. These UEs/subscribers 101 can though have a valid LTE/EPC subscription.

Figure 1 b is a schematic block diagram illustrating a high level architecture for a Next Gen System. Figure 1 b illustrates a NextGen UE 101 , a NextGen (R)AN 103 comprising a RAN node 103a, a NGCN 105 comprising a NGCN node 105a, a data network 1 10 and corresponding reference points, as in figure 1 a described above. The description of these entities will not be repeated here for the sake of simplicity. In addition, figure 1 b illustrates an EPC 108 comprising at least one EPC node 108a. The EPC 108 may also be referred to as an EPC network 108. An example of the EPC node 108a may be for example a Mobility Management Entity (MME), a GateWay (GW) or any other suitable EPC node 108a.

A PLMN 120 comprises both an NGCN 105 and an EPC network 105, and it may be referred to as a multi-system network, where each of the NGCN and EPC network is seen as a system.

Figure 1 b shows that the NextGen (R)AN 103, the NGCN 105, the NGCN node 105a, the EPC network 108 and the EPC node 108a are comprised in the PLMN 120. Thus, the PLMN 120 comprises both CN nodes 105a, 108a and non-CN nodes, e.g. RAN node(s) 103a.

The PLMN 120 may be described as a mobile network owned (e.g. established and operated) by an operator for providing mobile communication services over an air interface to the UE 101. A PLMN 120 is identified by a PLMN Identity (ID). A PLMN area is a geographical area in which the PLMN 120 provides communication services to UEs 101. For example, a PLMN 120 may be restricted to one country.

The NextGen (R)AN 103 comprises one or more RAN nodes 103a supporting evolved Long Term Evolution (LTE) and/or New Radio (NR) radio access. Such RAN nodes 103a may also be referred to as base station, GNodeB, NodeB, evolved NodeB (eNB) etc., and the reference number 103a is also used when referring to such base stations. It is assumed that a RAN node 103a implementation will support connectivity to the EPC 108 using the S1 interface for the CP (S1AP) and for the UP (S1 -U), as well as to the NGCN 105 using the NG interface for the CP (NG2) and UP (NG3).

The RAN node 103a may also be referred to as a 5G RAN node, the NGCN node 105a may also be referred to as a 5G CN node, the UE 101 may be referred to as a 5G UE and the NGCN 105 may be referred to as 5GCN or 5G CN .

It should be noted that the communication links between the entities, nodes and functions in figure 1 b may be of any suitable kind including either a wired or wireless link. The links may use any suitable protocol depending on type and level of layer (e.g. as indicated by the Open Systems Interconnection (OSI) model) as understood by the person skilled in the art.

Furthermore, a given Evolved UTRAN (E-UTRAN) cell (e.g. RAN node 103a) supporting 3GPP Release 15 (Rel-15) will have the capability to serve legacy LTE UEs, e.g. Rel-8 LTE UEs, as well as new 5G compatible UEs 101 supporting E-UTRAN 3GPP Rel-15 and at least the Rel-15 Non-Access Stratum (NAS) protocol stack to connect and use the NextGen Core 105. UTRAN is short for UMTS Terrestrial Radio Access Network, and UMTS is short for Universal Mobile Telecommunications System . It is assumed that a cell (e.g. the RAN node 103a comprised in the NextGen (R)AN 103) that provides connectivity to NextGen Core 105 will indicate that connectivity support in the common control channel, e.g. in the broadcast channel in the system information. Based on the indication of the support of connectivity to the NGCN 105 in the given cell system information, a 5G compatible U E 101 will compile a NGCN NAS compliant registration message (e.g. NGCN Attach) and send it to the network (e.g. the RAN node 103a) in the system access procedure, e.g. at registration (Attach). Due to the aforementioned indication of support for connectivity to the NGCN 105 in the system information of the cell used by the UE 101 to access the CN 105, 108, the UE 101 provides the indication of its 5G capabilities to the RAN node 103a e.g. in the Radio Resource Control (RRC) protocol to the RAN node 103a e.g. in a RRC message carrying the NGCN Attach message. Based on the UE's 101 5G capabilities indication, the RAN node 103a will route that registration/NGCN Attach message over the NG2 interface to the NGCN 105.

The method for handling registration of the UE 101 to a CN 105, 108 for a PLMN 120 according to some embodiments will now be described with reference to the signaling diagram depicted in Figure 2. Figure 2 illustrates embodiments of a method performed in a communications system, e.g. a communications system as exemplified in figure 1 b. The dashed arrows and boxes represent optional steps, and the continuous arrows and boxes represent mandatory steps. The method comprises at least some of the following steps, which steps may be performed in any suitable order than described below:

Step 201

The RAN node 103a sends an indication of RAN support for NGCN connectivity and preferably also for EPC connectivity to the UE 101 . In other words, the indication indicates that the RAN node 103a supports connectivity to NGCN and EPC. The UE 101 receives the indication from the RAN node 103a. The UE 101 may be a roaming UE which roams into the PLMN 120.

Step 202

The UE 101 creates a NAS registration message for NGCN 105, and optionally for the EPC 108. Step 203a

The UE 101 sends the NAS registration message for NGCN 105 to the RAN node 103a. The RAN node 103a receives the NAS registration message for NGCN 105 form the UE 5 101 .

Step 203b

The UE 101 may also send a NAS registration message for EPC 108 to the RAN node 103a. The RAN node 103a may receive the NAS registration message from the UE 101.

10

If the UE 101 sends a registration message for the EPC 108 to the RAN node 103a at this instance, then this message may be sent in a separate message to the RAN node 103a or in one common message together with the registration message for the NGCN 105 mentioned in the above step 203a.

15

Step 204

The RAN node 103a routes the registration of the UE 101 to NGCN 105, and optionally the registration of the UE 101 to the EPC 108.

20 Step 205

If the UE 101 is allowed to register in the NGCN 105, the NGCN node 105 sends a registration confirmation to the UE 101. If this happens, then the registration of the UE 101 according to the present method is completed.

25 Step 205a

If the UE 101 is not allowed to register in the NGCN 105, the NGCN node 105 may send a response to the UE 101 , via the RAN node 103a, indicating that the UE 101 has no right to register in NGCN 105, or the NGCN 105 does may not send any response at all to the UE 101 . Thus, there are two alternatives if the UE is not allowed to register in the NGCN 30 105:

1 ) The NGCN node 105 sends a response to the UE 101.

2) The NGCN 105 does not send any response to the UE 101 . It should be noted that whether the UE 101 doesn't receive any response to the registration message sent in step 203a may be determined in many well-known ways. For example, the UE 101 may repeat step 203a several and thus send several registration message without receiving any response before the jtermines that it receives no response to the registration messag nt in step 203a.

Step 206

If the UE 101 also sent the registration message for EPC 108 in step 203b and if the UE 101 is allowed to register in the EPC 108, then the EPC node 108a sends a registration confirmation to the UE 101 via the RAN node 103a. The UE 101 receives the registration confirmation from the EPC node 108a.

Step 207

If the UE 101 receives a response in step 205a indicating that the UE 101 has no right to register in the NGCN 105 or if the UE 101 doesn't receive any response to the registration message sent in step 203a, then the UE 101 creates a NAS registration message for the EPC 108.

Step 208

If the UE 101 receives a response in step 205a indicating that the UE 101 has no right to register in the NGCN 105 or if the UE 101 doesn't receive any response to the registration message sent in step 203a, then the UE 101 sends a NAS registration message for the EPC 108. The sending of the NAS registration message illustrated with step 208 is an alternative to step 203b. In other words, there are two alternatives for sending the NAS registration message: 1 ) In step 203b directly after or together with the transmission of the NGCN registration message in step 203a, or 2) in this step 208 after the UE 101 has received a response in step 205a indicating that the UE has no right to register in the NGCN 105 or if the UE has not received such response. Step 209

The RAN node 103a routes the registration request sent in step 208 to the EPC node 108a. Step 210

In response to receiving the registration request sent in step 208, the EPC node 108a registers the UE 101 in the EPC 108 and sends a registration confirmation to the UE 101 . The confirmation may be sent via at least one of the NGCN node 105 and the RAN node 5 103a.

The method described above will now be described with reference to figure 3a. The steps in figure 3a are performed by the UE 101 . Figure 3a illustrates embodiments of a method performed in a communications system, e.g. a communications system as

0 exemplified in figure 1 b. The dotted arrows and boxes represent optional steps, and the continuous arrows and boxes represent mandatory steps. The method comprises at least some of the following steps, which steps may be performed in any suitable order than described below: 5 Step 201

This step corresponds to step 201 in figure 2. The UE 101 receives from the RAN node 103a, an indication indicating support for connectivity to both NGCN 105 and EPC 108 networks. 0 Step 203a

This step corresponds to step 203a in figure 2. The UE 101 sends, via said RAN node 103a, a registration message to a NGCN node 105a in a NGCN 105 for registering to the PLMN 120. Sending the registration message implies the creation of the message as in step 202 above. Note that step 203b is not performed here, i.e. the UE doesn't5 send any registration message for the EPC 108 at this instance.

Step 205a

This step corresponds to step 205a in figure 2. The UE 101 receives, via said RAN node 103a, a response from the NGCN node 105a indicating that the UE 101 has no right to0 register in the NGCN 105, or receives no response from the NGCN node 105a. Note that step 206 is not performed here, i.e. the UE doesn't receive any registration confirmation from the EPC node 108a at this instance. Step 208

This step corresponds to step 208 in figure 2. The UE 101 sends, via said RAN node 103a, a registration message to an EPC node 108a in an EPC network 108 for registering to the EPC 108 for the PLMN 120. Sending the registration message implies the creation of the message as in step 207 above.

Step 210b

This step corresponds to step 210b in figure 2. The UE 101 receives, via said RAN node 103a, a registration confirmation message indicating a successful registration to the EPC network 108 for the PLMN 120.

Step 380

The UE 101 may store registration information indicating that the UE 101 has no right to register to the NGCN 105 for the PLMN 120 and/or indicating the CN 105, 108 the UE 101 has been successfully registered to for the PLMN 120.

The method described above will now be described with reference to figure 3b. The steps in figure 3b are performed by the UE 101 . Figure 3b illustrates embodiments of a method performed in a communications system, e.g. a communications system as exemplified in figure 1 b. One difference between figures 3a and 3b is that steps 208 and 210b are performed in figure 3a, but not in figure 3b. Another difference is that steps 203b and 206a are performed in figure 3b, but not in figure 3a. The dashed arrows and boxes represent optional steps, and the continuous arrows and boxes represent mandatory steps. The method comprises at least some of the following steps, which steps may be performed in any suitable order than described below:

Step 201

This step corresponds to step 201 in figure 2 and step 201 in figure 3a. The UE 101 receives from the RAN node 103a, an indication indicating support for connectivity to both NGCN 105 and EPC 108 networks. Step 203a

This step corresponds to step 203a in figure 2 and step 203a in figure 3a. The UE 101 sends, via said RAN node 103a, a registration message to a NGCN node 105a in a

NGCN 105 for registering to the PLMN 120. Sending the registration message implies the creation of the message as in step 202 above.

203b

This step corresponds to step 203b in figure 2. The UE 101 Send, via said RAN node 103a, a registration message to an EPC node 108a in an EPC network 108 for

registering to the PLMN 120. The PLMN 120 is the same PLMN as for the registration message to the NGCN 105.

Step 205a

This step corresponds to step 205a in figure 2 and step 205a in figure 3a. The UE 101 may receive, via said RAN node 103a, a response from the NGCN node 105a indicating that the UE 101 has no right to register in the NGCN 105, or receives no response from the NGCN node 105a.

Step 206a

The UE 101 receives, via said RAN node 103a, a registration confirmation message indicating a successful registration to the EPC network 108 for the PLMN 120.

Step 380

The method described above will now be described seen from the perspective of the UE 101. Figure 4 is a flowchart describing the present method performed by the UE 101 , for handling registration of the UE 101 to a CN 105, 108 for a PLMN. The UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be a NextGen UE and the RAN node 103a may be a NextGen RAN node. The method comprises at least some of the following steps to be performed by the UE 101 , which steps may be performed in any suitable order than described below: Step 401

This step corresponds to step 201 in figures 2, 3a and 3b. The UE 101 receives, from a RAN node 103a, a support indicator which indicates that the RAN node 103a supports connectivity to NGCN 105 and to the EPC network 108. The support indicator may be in the form of a flag where the presence of the flag indicates the support for connectivity to NGCN 105 and EPC 108.

Step 402

This step corresponds to step 203a in figures 2, 3a and 3b. The UE 101 sends, via said RAN node 103a, at least an NGCN registration message to a NGCN node 105a in the NGCN 105 for registering the UE 101 to the NGCN 105.

The NGCN registration message may be a NAS NGCN registration message. Step 403

This step corresponds to step 203b in figure 2 and step 203b in figure 3b. The UE 101 may send, via said RAN node 103a to the EPC node 108a before receiving a response from the NGCN node 105a (step 405 below), an EPC registration message corresponding to said EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN 120.

There are at least the following two alternatives for when the NGCN registration message and the EPC registration message are created:

1 ) The NGCN registration message may be created by the UE 101 after having

received the support indicator and the EPC registration message may be created after receiving a response from the NGCN node 105a indicating that the UE 101 does not have right to register to the NGCN 105.

2) The NGCN registration message and the EPC registration messages may be created, after receiving the support indicator and before receiving a response from the NGCN node 105a indicating that the UE 101 does not have right to register to the NGCN 10).

Step 404

This step corresponds to step 206a in figure 2 and step 206a in figure 3b. This step is performed after step 403. The UE 101 may receive, from the EPC node 108a in the EPC network 108, information indicating that the UE 101 has right to register in the EPC network 108.

Step 405

This step corresponds to step 205a in figures 2a, 3a and 3b. The UE 101 receives, via said RAN node 103a, a response from the NGCN node 108a indicating that the UE 101 does not have right to register to the NGCN 105 or receiving no response to the NGCN registration message. The received response may comprise at least one of:

a rejection of registering the UE 101 to the NGCN 105;

a request to re-register to the EPC network 108; and

a Register to EPC over the same cell/tracking area (RTEosC) indicator. Step 406

This step corresponds to step 203b and step 208 in figure 2, step 208 in figure 3a and step 203b in figure 3b. The UE 101 sends, via said RAN node 103a to an EPC node 108a in the EPC 108 network when said response indicates that the UE 101 does not have right to register to the NGCN 105 or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE 101 to the EPC 108 for the PLMN 120.

Information about the UEs 101 capability of accessing the NGCN 105 may be excluded in the EPC registration message, or the EPC registration message may comprises an EPC indicator which indicates that the UE 101 requests to register to the EPC network 108.

The EPC registration message may be a NAS EPC registration message.

Note that this step is only performed when a negative response is received from the NGCN node 105a or when no response is received at all with respect to the sent registration message or registration messages. In other words, if a response is received with respect to one of the sent registration message(s), e.g. with respect to an EPC registration message, then this step will not be executed. Step 407

This step corresponds to steps 380 in figures 3a and 3b. The UE 101 may store registration information which indicates that the UE 101 does not have right to register to the NGCN 105 for the PLMN, when receiving in step 405 a response from the NGCN node 105a indicating that the UE 101 does not have right to register to the NGCN 105 for the PLMN.

Step 408

This step corresponds to steps 205a, 206a and 210b in figure 2, step 205a and 210b in figure 3a and step 205a and 206a in figure 3b. The UE 101 may receive, via said RAN node 103a, a registration confirmation from the EPC node 108a indicating a successful registration to the EPC network 108 for the PLMN, or from the NGCN node 105a indicating a successful registration to the NGCN 105 for the PLMN. Step 409

This step corresponds to step 380 in figures 3a and 3b. The UE 101 may store

registration information which indicates which CN 105, 108 the UE 101 has been successfully registered to for the PLMN. The registration information is to be used for future registration of the UE 101 for the same PLMN.

A first computer program may comprise instructions which, when executed on at least one processor, cause the at least one processor to carry out the method steps 401 -409. A first carrier may comprise the first computer program, and the first carrier may be one of an electronic signal, optical signal, radio signal or computer readable storage medium.

To perform the method steps shown in figures 2, 3a, 3b and 4 for handling registration of a UE 101 to a, CN 105, 108 for a PLMN, the UE 101 may comprise an arrangement as shown in Figure 5. As mentioned above, the UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be NextGen UE, and the RAN node 103a may be a NextGen RAN node.

The UE 101 is configured to, e.g. by means of a receiving module 501 , to receive, from a RAN node 103a, a support indicator which indicates that the RAN node 103a supports connectivity to NGCN 105 and to the EPC network 108. The received response may comprise at least one of: • a rejection of registering the UE 101 to the NGCN 105;

• a request to re-register to the EPC network 108; and

• a RTEosC indicator.

5 The receiving module 501 may also be referred to as a receiving unit, a receiving means, a receiving circuit, means for receiving, input unit etc. The receiving module 501 may be a receiver, a transceiver etc. The receiving module 501 may be a wireless receiver of the UE 101 of a wireless or fixed communications system.

10 The UE 101 is configured to, e.g. by a sending module 503, send, via said RAN node 103a, at least an NGCN registration message to a NGCN node 105a in the NGCN 105 for registering the UE 101 to the NGCN 105. The sending module 503 may also be referred to as a sending unit, a sending means, a sending circuit, means for sending, output unit etc. The sending module 503 may be a transmitter, a transceiver etc. The sending module

15 503 may be a wireless transmitter of the UE 101 of a wireless or fixed communications system. The NGCN registration message may be a NAS NGCN registration message.

The UE 101 is configured to, e.g. by means of the receiving module 501 , receive, via said RAN node 103a, a response from the NGCN node 108a indicating that the UE 101 does 20 not have right to register to the NGCN 105 or receiving no response to the NGCN

registration message.

The UE 101 is configured to, e.g. by means of the sending module 503, send, via said RAN node 103a to an EPC node 108a in the EPC 108 network when said response

25 indicates that the UE 101 does not have right to register to the NGCN 105 or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE 101 to the EPC 108 for the PLMN. Information about the UEs 101 capability of accessing the NGCN 105 may be excluded in the EPC registration message, or the EPC registration message may comprise an EPC indicator

30 which indicates that the UE 101 requests to register to the EPC network 108. The EPC registration message may be a NAS EPC registration message.

The NGCN registration message may be created, e.g. by means of a creating module 505 comprised in the UE 101 , after having received the support indicator and the EPC 35 registration message may be created after receiving a response from the NGCN node 105a indicating that the UE 101 does not have right to register to the NGCN 105. The NGCN registration message and the EPC registration messages may be created, e.g. by means of the creating module 505, after receiving the support indicator and before receiving a response from the NGCN node 105a indicating that the UE 101 does not have 5 right to register to the NGCN 105. The creating module 505 may also be referred to as a creating unit, a creating means, a creating circuit, means for creating, etc. The creating module 505 may be a processor 508 of the UE 101.

The UE 101 may be further configured to, e.g. by means of the sending module 503, 10 send, via said RAN node 103a to the EPC node 108a before receiving a response from the NGCN node 105a, a EPC registration message corresponding to said EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN.

The UE 101 may be further configured to, e.g. by means of the receiving module 501 , 15 receive, from the EPC node 108a in the EPC network 108, information indicating that the UE 101 has right to register in the EPC network 108.

The UE 101 may be configured to, e.g. by means of a storing module 510, store registration information, e.g. in a memory 513, which indicates that the UE 101 does not 20 have right to register to the NGCN 105 for the PLMN, when receiving a response from the NGCN node 105a indicating that the UE 101 does not have right to register to the NGCN 105 for the PLMN. The storing module 510 may also be referred to as a storing unit, a storing means, a storing circuit, means for storing, etc. The storing module 510 may be the processor 508 of the UE 101.

25

The memory 513 which may be comprised in the UE 101 may comprise one or more memory units. The memory 513 may be arranged to be used to store data, received data streams, power level measurements, messages, indicators, confirmations, threshold values, time periods, configurations, schedulings, and applications to perform the

30 methods herein when being executed in the UE 101 .

The UE 101 may be configured to, e.g. by means of the receiving module 501 , receive, via said RAN node 103a, a registration confirmation from the EPC node 108a indicating a successful registration to the EPC network 108 for the PLMN, or from the NGCN node 35 105a indicating a successful registration to the NGCN 105 for the PLMN. The UE 101 may be configured to, e.g. by means of the storing module 510, store

registration information, e.g. in the memory 513, which indicates which CN 105, 108 the UE 101 has been successfully registered to for the PLMN. The registration information may be to be used for future registration of the UE 101 for the same PLMN.

Those skilled in the art will also appreciate that the receiving module 501 , the sending module 503, the creating module 505 and the storing module 510 described above may refer to a combination of analog and digital circuits, and/or one or more processors

configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processor 508 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether

individually packaged or assembled into a system-on-a-chip (SoC).

The method described above will now be described seen from the perspective of the UE 101. Figure 6 is a flowchart describing the present method performed by the RAN node 103a, for handling registration of the UE 101 to a CN 105, 108 for a PLMN. The UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be a NextGen UE and the RAN node 103a may be a NextGen RAN node. The method comprises at least some of the following steps to be performed by the RAN node 103a, which steps may be performed in any suitable order than described below:

Step 601

This step corresponds to step 201 in figure 2. The RAN node 103a sends, to the UE 101 , a support indicator which indicates that the RAN node 103a supports connectivity to NGCN 105 and to the EPC network 108.

Step 602

This step corresponds to step 203a in figure 2. The RAN node 103a receives, from the UE 101 , at least an NGCN registration message for registering the UE 101 to the NGCN 105 for the PLMN. Tthe NGCN registration message may be a NAS NGCN registration message. Step 603

This step corresponds to step 204 in figure 2. The RAN node 103a routes the NGCN registration message to the NGCN node 105a. Step 604

This step corresponds to step 203b in figure 2. The RAN node 103a may receive, from the UE 101 before receiving a response from the NGCN node 105a, an EPC registration message corresponding to said EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN. The EPC registration message may be a NAS EPC registration message.

Step 605

This step corresponds to step 204 in figure 2. The RAN node 103a may send the EPC registration message to the EPC node 108a. Step 606

This step corresponds to step 206a in figure 2. The RAN node 103a may receive, from the EPC node 108a in the EPC network 108, information indicating that the UE 101 has right to register in the EPC network 108. Step 607

This step corresponds to step 206a in figure 2. The RAN node 103a may send to the UE 101 the information from the EPC node 108a (the information received in step 606) indicating that the UE 101 has right to register in the EPC network 108. Step 608

This step corresponds to step 205a in figure 2. The RAN node 103a receives, from the NGCN node 105a, a response indicating that the UE 101 does not have right to register to the NGCN 105 or receiving no response to the NGCN registration message. The sent response may comprise at least one of:

• a rejection of registering the UE 101 to the NGCN 105,

• a request to re-register to the EPC network 108; and

• a RTEosC indicator. Step 609

This step corresponds to step 205a in figure 2. The RAN node 103a sends, to the UE 101 , the response from the NGCN node 108a or sending no response to the NGCN registration message.

Step 610

This step corresponds to step 208 in figure 2. The RAN node 103a receives, from the UE 101 when said response indicates that the UE 101 does not have right to register to the NGCN 105 or when no response to the registration message or registration messages is sent, an EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN.

Information about the UEs 101 capability of accessing NGCN 105 may be excluded in an EPC registration message, or the EPC registration message may comprise an EPC

indicator which indicates that the UE 101 requests to register to the EPC 108.

The EPC registration message may be a NAS EPC registration message. Step 61 1

This step corresponds to step 209 in figure 2. The RAN node 103a routes the EPC registration message from the UE 101 to the EPC node 108a.

Step 612

This step corresponds to steps 205a, 206a and 210b in figure 2. The RAN node 103a may receive a registration confirmation from the EPC node 108a indicating a successful registration to the EPC network for the PLMN, or from the NGCN node 105a indicating a successful registration to the NGCN for the PLMN.

Step 613

This step corresponds to steps 205a, 206a and 210b in figure 2. The RAN node 103a may send the registration confirmation to the UE 101 .

Step 614

If registration to the NGCN 105 was rejected, the RAN node 103a may store NGCN rejection information for a time period. The UE 101 may be prevented from further registration attempts to the NGCN 105 during the time period in which the NGCN rejection information is stored. A second computer program may comprise instructions which, when executed on at least one processor, cause the at least one processor to carry out the method steps 601 -614. A second carrier may comprise the second computer program, and the second carrier may be one of an electronic signal, optical signal, radio signal or computer readable storage medium.

To perform the method steps shown in figures 2, 3a, 3b and 6 for handling registration of a UE 101 to a CN 105, 108 for a PLMN, the RAN node 103a may comprise an

arrangement as shown in Figure 7. As mentioned above, the UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be NextGen UE, and the RAN node 103a may be a NextGen RAN node.

The RAN node 103a is configured to, e.g. by means of a sending module 701 , send, to the UE 101 , a support indicator which indicates that the RAN node 103a supports

connectivity to NGCN 105 and to the EPC network 108. The sending module 701 may also be referred to as a sending unit, a sending means, a sending circuit, means for sending, output unit etc. The sending module 701 may be a transmitter, a transceiver etc. The sending module 701 may be a wireless transmitter of the RAN node 103a of a wireless or fixed communications system.

The RAN node 103a is configured to, e.g. by means of a receiving module 703, receive, from the UE 101 , at least an NGCN registration message for registering the UE 101 to the NGCN 105 for the PLMN. The NGCN registration message may be a NAS NGCN

registration message. The receiving module 703 may also be referred to as a receiving unit, a receiving means, a receiving circuit, means for receiving, input unit etc. The receiving module 703 may be a receiver, a transceiver etc. The receiving module 703 may be a wireless receiver of the RAN node 103a of a wireless or fixed communications system. The RAN node 103a is configured to, e.g. by means of a routing module 705, route the NGCN registration message to the NGCN node 105a. The routing module 705 may also be referred to as a routing unit, a routing means, a routing circuit, means for routing, etc. The routing module 705 may be a processor 708 of the RAN node 103a. The RAN node 103a is configured to, e.g. by means of the receiving module 703, receive, from the NGCN node 105a, a response indicating that the UE 101 does not have right to register to the NGCN 105 or receiving no response to the NGCN registration message. The RAN node 103a is configured to, e.g. by means of the sending module 701 , send, to the UE 101 , the response from the NGCN node 108a or sending no response to the

NGCN registration message. The sent response may comprise at least one of:

• a rejection of registering the UE 101 to the NGCN 105;

• a request to re-register to the EPC network 108; and

· a RTEosC indicator.

The RAN node 013 is configured to, e.g. by means of the receiving module 703, receive, from the UE 101 when said response indicates that the UE 101 does not have right to register to the NGCN 105 or when no response to the registration message or registration messages is sent, an EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN. Information about the UEs 101 capability of accessing NGCN 105 may be excluded in an EPC registration message, or the EPC registration message may comprise an EPC indicator which indicates that the UE 101 requests to register to the EPC 108. The EPC registration message may be a NAS EPC registration message.

The RAN node 103a is configured to, e.g. by means of the routing module 705 route the EPC registration message from the UE 101 to the EPC node 108a.

The RAN node 103a may be configured to, e.g. by means of the receiving module 703, receive, from the UE 101 before receiving a response from the NGCN node 105a, an EPC registration message corresponding to said EPC registration message for registering the UE 101 to the EPC network 108 for the PLMN.

The RAN node 103a may be configured to, e.g. by means of the sending module 701 , send the EPC registration message to the EPC node 108a.

The RAN node 103a may be configured to, e.g. by means of the receiving module 703, receive from the EPC node 108a in the EPC network 108 information indicating that the UE 101 has right to register in the EPC network 108. The RAN node 103a may be configured to, e.g. by means of the sending module 701 , send, to the UE 101 the information from the EPC node 108a indicating that the UE 101 has right to register in the EPC network 108. The RAN node 103a may be configured to, e.g. by means of the receiving module 703, receive a registration confirmation from the EPC node 108a indicating a successful registration to the EPC network for the PLMN, or from the NGCN node 105a indicating a successful registration to the NGCN for the PLMN. The RAN node 103a may be configured to, e.g. by means of the sending module 701 , send the registration confirmation to the UE 101.

The RAN node 103a may be configured to, e.g. by means of a storing module 710, if registration to the NGCN 105 was rejected, store, e.g. in a memory 713, NGCN rejection information for a time period. The UE 101 may be prevented from further registration attempts to the NGCN 105 during the time period in which the NGCN rejection information is stored. The storing module 710 may also be referred to as a storing unit, a storing means, a storing circuit, means for storing, etc. The storing module 710 may be the processor 708 of the RAN node 103a.

The memory 713 which may be comprised in the RAN node 103a may comprise one or more memory units. The memory 713 may be arranged to be used to store data, received data streams, power level measurements, messages, indicators, confirmations, threshold values, time periods, configurations, schedulings, and applications to perform the

methods herein when being executed in the RAN node 103a.

Those skilled in the art will also appreciate that the sending module 701 , receiving module 703, routing module 705 and the storing module 710 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processor 708 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single ASIC, or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a SoC. The method described above will now be described seen from the perspective of the NGCN node 105a. Figure 8 is a flowchart describing the present method performed by the NGCN node 105a, for handling registration of the UE 101 to a CN 105, 108 for a PLMN. The UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be a NextGen UE and the RAN node 103a may be a NextGen RAN node. The method comprises at least some of the following steps to be performed by the NGCN node 105a, which steps may be performed in any suitable order than described below:

Step 801

This step corresponds to step 204 in figure 2. The NGCN node 105a receives at least a NGCN registration message from the UE 101 via a RAN node 103a for registering the UE 101 to the NGCN 105 for the PLMN. The NGCN registration message may be a NAS,

NGCN registration message. Step 802

This step corresponds to step 205a in figure 2. The NGCN node 105a sends, via said

RAN node 103a, a response to the UE 101 indicating that the UE 101 does not have right to register to the NGCN 105 or sending no response to the NGCN registration message. The response may comprise at least one of:

• a rejection of registering the UE 101 to the NGCN 105;

• a request to re-register to the EPC network 108; and

• a RTEosC indicator. Step 803

This step corresponds to steps 205a, 206a, 210b in figure 2. The NGCN node 105 may send, via said RAN node 103a, a registration confirmation to the UE 101 indicating a successful registration to the EPC network for the PLMN, or directly to the UE 101 indicating a successful registration to the NGCN for the PLMN.

A third computer program may comprise instructions which, when executed on at least one processor, cause the at least one processor to carry out the method steps 801 -803. A third carrier may comprise the third computer program, and the third carrier may be one of an electronic signal, optical signal, radio signal or computer readable storage medium. To perform the method steps shown in figures 2, 3a 3b and 8 for handling registration of a UE 101 to a, CN 105, 108 for a PLMN, the NGCN node 105a may comprise an

arrangement as shown in Figure 9. As mentioned above, the UE 101 is capable of accessing both a NGCN 105 and an EPC network 108. The UE 101 may be NextGen UE, and the RAN node 103a may be a NextGen RAN node.

The NGCN node 105a is configured to, e.g. by means of a receiving module 901 ,

receive at least a NGCN registration message from the UE 101 via a RAN node 103a for registering the UE 101 to the NGCN 105 for the PLMN. The NGCN registration message may be a NAS NGCN registration message. The receiving module 901 may also be referred to as a receiving unit, a receiving means, a receiving circuit, means for receiving, input unit etc. The receiving module 901 may be a receiver, a transceiver etc. The

receiving module 901 may be a wireless receiver of the NGCN node 105a of a wireless or fixed communications system.

The NGCN node 105a is configured to, e.g. by means of a sending module 903, send, via said RAN node 103a, a response to the UE 101 indicating that the UE 101 does not have right to register to the NGCN 105 or sending no response to the NGCN registration message. The response may comprise at least one of:

· a rejection of registering the UE 101 to the NGCN 105

• a request to re-register to the EPC network 108; and

• a RTEosC indicator.

The sending module 903 may also be referred to as a sending unit, a sending means, a sending circuit, means for sending, output unit etc. The sending module 903 may be a transmitter, a transceiver etc. The sending module 903 may be a wireless transmitter of the NGCN node 105a of a wireless or fixed communications system.

The NGCN node 105a may be configured to, e.g. by means of the sending module 903, send, via said RAN node 103a, a registration confirmation to the UE 101 indicating a successful registration to the EPC network for the PLMN, or directly to the UE 101 indicating a successful registration to the NGCN 105 for the PLMN.

The NGCN node 105 may comprise comprises a processor 905 and a memory 908. The memory 908 comprises instructions executable by the processor 905. The memory 905 which may be comprised in the NGCN node 105a may comprise one or more memory units. The memory 905 may be arranged to be used to store data, received data streams, power level measurements, messages, indicators, confirmations, threshold values, time periods, configurations, schedulings, and applications to perform the methods herein when being executed in the NGCN node 105a.

Those skilled in the art will also appreciate that the receiving module 901 and the sending module 903 described above may refer to a combination of analog and digital circuits, and/or one or more processors configured with software and/or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processor 905 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single ASIC, or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a SoC.

The present mechanism for handling registration of the UE 101 to a CN 105, 108 for a PLMN may be implemented through one or more processors, such as a processor 508 in the UE arrangement depicted in Figure 5, a processor 708 in the RAN node arrangement depicted in figure 7 and a processor 905 in the NGCN node arrangement depicted in Figure 9, together with computer program code for performing the functions of the embodiments herein. The processors may each be for example a Digital Signal Processor (DSP), ASIC processor, Field-programmable gate array (FPGA) processor or

microprocessor. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into at least one of the UE 101 , the RAN node 103a and the NGCN node 105a. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code can furthermore be provided as pure program code on a server and downloaded to at least one of the UE 101 , the RAN node 103a and the NGCN node 105a.

Some embodiments described herein may be summarised in the following manner: The UE 101 supporting EPC and NGCN access via 5G constructs EPC or NGCN NAS registration message, and indicates EPC or NGCN to a 5G RAN node 103a for routing to the intended CN type, when support for both types are indicated by the 5G RAN node 193. A NGCN 105 being aware, e.g. by means of configuration, that a given cell/RAN node 103a that it provides connectivity to also provides connectivity to EPC 108.

A NGCN node 105a providing information, designated as e.g. RTEosC to a 5G capable UE 101 that has no right to use it, e.g. due to subscription information indicating to the NGCN 105 that the subscriber associated with the UE 101 has no rights to be registered and served by that CN 105, 108 about the need to re-register.

As an alternative to an explicit indication from the NGCN node 105a, the UE 101 may have a feature where it will upon rejection from the NGCN 105, performs a re-registration attempt towards the EPC 108.

As an alternative to an RTEosC from the NGCN node 105, the UE 101 may indicate "EPC" to the RAN node 103a in e.g. a RRC message when the UE 101 has not been successfully registered in NGCN 105 in the selected PLMN 120, and also indicates the UE 101 capability of NGCN to the RAN node 103a e.g. in a RRC message and/or CN in a NAS message. If EPC is available for the selected PLMN, the RAN node 103a routes the UE 101 to the EPC 108. If the EPC node 108a decides that the UE 101 shall be served by NGCN 105, the EPC 108 may redirect the UE 101 to the NGCN 105 (via the RAN or directly within the CN). When the UE 101 has been successfully registered in the NGCN 105 for the selected PLMN 120, the UE 101 may store this information and may indicate the UE 101 preference to register towards the NGCN 105 in a later communication for this PLMN.

As an alternative to an RTEosC from the NGCN 105, when the UE 101 has not been registered in the PLMN 120 using the NGCN 105, the UE 101 may add both EPC and NGCN NAS registration messages (e.g. in an Attach message for EPC 108 and e.g. a Registration message for NGCN 105, or in any other suitable message). The RAN node 103a may route to the preferred CN 105, 108 which then redirects to the other CN in case the UE 101 is not allowed in selected CN. The UE 101 then stores the decision for the PLMN 120 and uses the NAS message according to the CN where the UE 101 was previously registered to. As another alternative to an RTEosC from the NGCN 105, the UE 101 may be provisioned per PLMN 120 whether EPC 108 or NGCN 105 is preferred. The provisioning information may be contained in the UE 101 as part of subscription information and/or user credentials e.g. in the Universal Integrated Circuit Card (UlCC), Universal Subscriber Identity Module (USIM) or a part of other secured storage in the UE 101.

The RTEosC may be sent by the NGCN node 105a to the UE 101 as a response to the registration request indicating to that UE 101 that a re-registration attempt to the EPC 105 is possible in the same cell as used to attempt registration to the 5G CN.

As an alternative to the RTEosC, the NGCN node 105 may include in the response to the UE 191 that registration to the NGCN 105 is not allowed, and optionally whether this indication applies to cell/RAN node, Tracking Area (TA) or PLMN. The UE 101 at reception of the RTEosC may compile a registration message compliant with the EPC NAS protocol. As an alternative, the UE 101 may evaluate the indication of NGCN not allowed and its scope limitation combined with other information to decide whether to attempt registration with EPC 108 in the same cell/RAN node/TA/RAT/PLMN. The UE 101 may send the registration message, e.g. EPC Attach to the RAN node 103a excluding the information about its 5G capability or alternatively includes a specific

indication that the UE 101 wants to connect to the EPC 108. This will ensure that RAN node 103a selects the EPC 108 when routing the registration message to the CN 105,

108. The UE 101 may send the message using same cell as when used for the initial

NGCN registration.

The embodiments herein relate to UE connectivity to NGCN 105 and EPC 108. The UE

101 knows that the RAN node 103a supports both EPC and NGCN. If the UE 101 has no access to NGCN 105, then the UE 101 should try the EPC 108 with the same radio node.

NGCN is prioritized. The EPC 105 is used only if UE 101 is not allowed to access NGCN 105. The UE 101 may create two NSA messages at the same time, for EPC and NGCN or at separate times. Then RAN node 103a may select (NGCN is priority) one of the

messages. The NGCN 105 does not perform any selection of messages or CN. If NGCN is not allowed, then the RAN node 103a selects the message for the EPC 108, i.e. the other registration message. At successful registration, the UE 101 may store information about access to NGCN or EPC. The UE 101 may use the same access the next time it visits the cell.

One type of reject cause (e.g. rejection of registration to NGCN 105) may lead to re- registration. At reject of the NGCN registration, there is no need to change cell or RAN node 103a since the RAN node 103a supports both EPC and NGCN. There may also be a timer for validity of rejection. The reject message may be for specific geographical area, e.g. PLMN. Thus, the methods herein are performed in the same radio layer. The embodiments herein are not limited to the above described embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above

embodiments should not be taken as limiting the scope of the embodiments, which is defined by the appending claims. It should be emphasized that the term "comprises/comprising" when used in this specification is taken to specify the presence of stated features, integers, steps or components, but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof. It should also be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements. The terms "consisting of" or "consisting essentially of" may be used instead of the term comprising.

The term "configured to" used herein may also be referred to as "arranged to", "adapted to", "capable of" or "operative to".

It should also be emphasised that the steps of the methods defined in the appended claims may, without departing from the embodiments herein, be performed in another order than the order in which they appear in the claims.

Claims

1. A method performed by a User Equipment, UE, (101 ) for handling registration of the UE (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile Network, PLMN, wherein the UE (101 ) is capable of accessing both a Next Generation Core Network, NGCN, (105) and an Evolved Packet Core, EPC, network (108), the method comprising:

receiving (201 , 401 ), from a Radio Access Network, RAN, node (103a), a support indicator which indicates that the RAN node (103a) supports connectivity to NGCN (105) and to the EPC network (108);

sending (203a, 402), via said RAN node (103a), at least an NGCN registration message to a NGCN node (105a) in the NGCN (105) for registering the UE (101 ) to the NGCN (105);

receiving (205a, 405), via said RAN node (103a), a response from the NGCN node (108a) indicating that the UE (101 ) does not have right to register to the NGCN (105) or receiving no response to the NGCN registration message; and

sending (208, 406), via said RAN node (103a) to an EPC node (108a) in the EPC (108) network when said response indicates that the UE (101 ) does not have right to register to the NGCN (105) or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE (101 ) to the EPC (108) for the PLMN.

2. The method according to claim 1 , wherein the received response comprises at least one of:

a rejection of registering the UE (101 ) to the NGCN (105);

a request to re-register to the EPC network (108); and

a Register to EPC over the same cell/tracking area, RTEosC, indicator.

3. The method according to any one of claim 1 -2, further comprising:

sending (203b, 403), via said RAN node (103a) to the EPC node (108a) before receiving a response from the NGCN node (105a), a EPC registration message corresponding to said EPC registration message for registering the UE (101 ) to the EPC network (108) for the PLMN; and

receiving (206a, 404), from the EPC node (108a) in the EPC network (108), information indicating that the UE (101 ) has right to register in the EPC network (108).

4. The method according to any one of claims 1 -3, wherein the NGCN registration message is created after having received the support indicator and the EPC registration message is created after receiving a response from the NGCN node (105a) indicating that the UE (101 ) does not have right to register to the NGCN (105).

5. The method according to any one of claims 1 -3, wherein the NGCN registration message and the EPC registration messages are created, after receiving the support indicator and before receiving a response from the NGCN node (105a) indicating that the UE (101 ) does not have right to register to the NGCN (105).

6. The method according to any one of claims 1 -5, further comprising:

storing (380, 407) registration information which indicates that the UE (101 ) does not have right to register to the NGCN (105) for the PLMN, when receiving (205a, 380) a response from the NGCN node (105a) indicating that the UE (101 ) does not have right to register to the NGCN (105) for the PLMN.

7. The method according to any one of claims 1 -6, further comprising:

receiving (205a, 206a, 210b, 408), via said RAN node (103a), a registration confirmation from the EPC node (108a) indicating a successful registration to the EPC network (108) for the PLMN, or from the NGCN node (105a) indicating a successful registration to the NGCN (105) for the PLMN; and

storing (380, 409) registration information which indicates which CN (105, 108) the UE (101 ) has been successfully registered to for the PLMN, wherein the registration information is to be used for future registration of the UE (101 ) for the same PLMN.

8. The method according to any one of claims 1 -7, wherein information about the UEs (101 ) capability of accessing the NGCN (105) is excluded in the EPC registration message; or

wherein the EPC registration message comprises an EPC indicator which indicates that the UE (101 ) requests to register to the EPC network (108).

9. The method according to any one of claims 1 -8, wherein the EPC registration message is a Non Access Stratum, NAS, EPC registration message.

10. The method according to any one of claims 1 -9, wherein the NGCN registration message is a Non Access Stratum, NAS, NGCN registration message.

1 1 . The method according to any one of claims 1 -10, wherein the UE (101 ) is a Next 5 Generation UE, NextGen UE, and the, RAN node (103a) is a NextGen RAN node.

12. A method performed by a Radio Access Network, RAN, node (103a) for handling registration of a User Equipment, UE, (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile Network, PLMN, wherein the UE (101 ) is capable of accessing both a

10 Next Generation Core Network, NGCN, (105) and an Evolved Packet Core, EPC, network (108), the method comprising:

sending (201 , 601 ), to the UE (101 ), a support indicator which indicates that the RAN node (103a) supports connectivity to NGCN (105) and to the EPC network (108);

receiving (203a, 602), from the UE (101 ), at least an NGCN registration

15 message for registering the UE (101 ) to the NGCN (105) for the PLMN;

routing (204, 603) the NGCN registration message to the NGCN node

(105a);

receiving (205a, 608), from the NGCN node (105a), a response indicating that the UE (101 ) does not have right to register to the NGCN (105) or receiving no

20 response to the NGCN registration message;

sending (205a, 609), to the UE (101 ), the response from the NGCN node (108a) or sending no response to the NGCN registration message;

receiving (208, 610), from the UE (101 ) when said response indicates that the UE (101 ) does not have right to register to the NGCN (105) or when no response to 25 the registration message or registration messages is sent, an EPC registration message for registering the UE (101 ) to the EPC network (108) for the PLMN; and

routing (209, 61 1 ) the EPC registration message from the UE (101 ) to the EPC node (108a).

30 13. The method according to claim 12, wherein the sent response comprises at least one of:

a rejection of registering the UE (101 ) to the NGCN (105);

a request to re-register to the EPC network (108); and

a Register to EPC over the same cell/tracking area, RTEosC, indicator.

14. The method according to any one of claim 12-13, further comprising:

receiving (203b, 604), from the UE (101 ) before receiving a response from the NGCN node (105a), an EPC registration message corresponding to said EPC registration message for registering the UE (101 ) to the EPC network (108) for the PLMN; 5 sending (204, 605) the EPC registration message to the EPC node (108a):

receiving (206a, 606) from the EPC node (108a) in the EPC network (108) information indicating that the UE (101 ) has right to register in the EPC network (108); and sending (206a, 607), to the UE (101 ) the information from the EPC node (108a) indicating that the UE (101 ) has right to register in the EPC network (108).

10

15. The method according to any one of claims 12-14, further comprising:

receiving (205a, 206a, 210b, 612) a registration confirmation from the EPC node (108a) indicating a successful registration to the EPC network for the PLMN, or from the NGCN node (105a) indicating a successful registration to the NGCN for the PLMN; 15 and

sending (205a, 206a, 210b, 613) the registration confirmation to the UE

(101 ).

16. The method according to any one of claims 12-15, further comprising:

20 if registration to the NGCN (105) was rejected, storing (614) NGCN rejection information for a time period, and wherein the UE (101 ) is prevented from further registration attempts to the NGCN (105) during the time period in which the NGCN rejection information is stored.

25 17. The method according to any one of claims 12-16, wherein information about the UEs (101 ) capability of accessing both NGCN (105) is excluded in an EPC registration message; or

wherein the EPC registration message comprises an EPC indicator which indicates that the UE (101 ) requests to register to the EPC (108).

30

18. The method according to any one of claims 12-17, wherein the EPC registration message is a Non Access Stratum, NAS, EPC registration message.

19. The method according to any one of claims 12-18, wherein the NGCN registration 35 message is a Non Access Stratum, NAS, NGCN registration message.

20. The method according to any one of claims 14-19, wherein the UE (101 ) is a Next Generation UE, NextGen UE and the RAN node (103a) is a NextGen RAN node. 21 . A method performed by a Next Generation Core Network, NGCN, node (105a), for handling registration of a User Equipment, UE, (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile Network, PLMN, wherein the UE (101 ) is capable of accessing both NGCN (105) and an Evolved Packet Core, EPC, network (108), wherein the NGCN node (105a) is comprised in a NGCN (105), the method comprising:

receiving (204, 801 ) at least a NGCN registration message from the UE

(101 ) via a Radio Access Network, RAN, node (103a) for registering the UE (101 ) to the NGCN (105) for the PLMN; and

sending (205a, 802), via said RAN node (103a), a response to the UE (101 ) indicating that the UE (101 ) does not have right to register to the NGCN (105) or sending no response to the NGCN registration message.

22. The method according to claim 21 , wherein the response comprises at least one of:

a rejection of registering the UE (101 ) to the NGCN (105);

a request to re-register to the EPC network (108); and

a Register to EPC over the same cell/tracking area, RTEosC, indicator.

23. The method according to any one of claims 21-22, further comprising:

sending (205a, 206a, 210b, 803), via said RAN node (103a), a registration confirmation to the UE (101 ) indicating a successful registration to the EPC network for the PLMN, or directly to the UE (101 ) indicating a successful registration to the NGCN (105) for the PLMN.

24. The method according to any one of claims 21-23, wherein the NGCN registration message is a Non Access Stratum, NAS, NGCN registration message.

25. The method according to any one of claims 21-24, wherein the UE (101 ) is a Next Generation UE, NextGen UE and the RAN node (103a) is a NextGen RAN node.

26. A User Equipment, UE, (101 ) for handling registration of the UE (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile Network, PLMN, wherein the UE (101 ) is capable of accessing both a Next Generation Core Network, NGCN, (105) and an Evolved Packet Core, EPC, network (108), the UE (101 ) being configured to:

receive, from a Radio Access Network, RAN, node (103a), a support indicator which indicates that the RAN node (103) supports connectivity to NGCN (105) and to the EPC network (108);

send, via said RAN node (103a), at least an NGCN registration message to a NGCN node (105a) in the NGCN (105) for registering the UE (101 ) to the NGCN (105);

receive, via said RAN node (103a), a response from the NGCN node (108a) indicating that the UE (101 ) does not have right to register to the NGCN (105) or receiving no response to the NGCN registration message; and to

send, via said RAN node (103a) to an EPC node (108a) in the EPC (108) network when said response indicates that the UE (101 ) does not have right to register to the NGCN (105) or when no response to the sent registration message or registration messages is received, an EPC registration message for registering the UE (101 ) to the EPC (108) for the PLMN.

27. A Radio Access Network, RAN, node (103a) for handling registration of a User Equipment, UE, (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile Network, PLMN, wherein the UE (101 ) is capable of accessing both a Next Generation Core Network, NGCN, (105) and an Evolved Packet Core, EPC, network (108), the RAN node (103a) being configured to:

send, to the UE (101 ), a support indicator which indicates that the RAN node (103a) supports connectivity to NGCN (105) and to the EPC network (108), wherein;

receive, from the UE (101 ), at least an NGCN registration message for registering the UE (101 ) to the NGCN (105) for the PLMN;

route the NGCN registration message to the NGCN node (105a);

receive, from the NGCN node (105a), a response indicating that the UE (101 ) does not have right to register to the NGCN (105) or receiving no response to the NGCN registration message;

send, to the UE (101 ), the response from the NGCN node (108a) or sending no response to the NGCN registration message;

receive, from the UE (101 ) when said response indicates that the UE (101 ) does not have right to register to the NGCN (105) or when no response to the registration message or registration messages is sent, an EPC registration message for registering the UE (101 ) to the EPC network (108) for the PLMN; and to route the EPC registration message from the UE (101 ) to the EPC node

(108a).

28. A Next Generation Core Network, NGCN, node (105a), for handling registration of a 5 User Equipment, UE, (101 ) to a Core Network, CN, (105, 108) for a Public Land Mobile

Network, PLMN, wherein the UE (101 ) is capable of accessing both NGCN (105) and an Evolved Packet Core, EPC, network (108), wherein the NGCN node (105a) is comprised in a NGCN (105), the NGCN node (105a) being configured to:

receive at least a NGCN registration message from the UE (101 ) via a Radio 10 Access Network, RAN, node (103a) for registering the UE (101 ) to the NGCN (105) for the PLMN; and to

send, via said RAN node (103a), a response to the UE (101 ) indicating that the UE (101 ) does not have right to register to the NGCN (105) or sending no response to the NGCN registration message.

15

29. A first computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 1-1 1 .

20 30. A first carrier comprising the first computer program of claim 29, wherein the first carrier is one of an electronic signal, optical signal, radio signal or computer readable storage medium.

31 . A second computer program comprising instructions which, when executed on at least 25 one processor, cause the at least one processor to carry out the method according to any one of claims 12-20.

32. A second carrier comprising the second computer program of claim 31 , wherein the second carrier is one of an electronic signal, optical signal, radio signal or computer

30 readable storage medium.

33. A third computer program comprising instructions which, when executed on at least one processor, cause the at least one processor to carry out the method according to any one of claims 21-25.

35

34. A third carrier comprising the third computer program of claim 33, wherein the third carrier is one of an electronic signal, optical signal, radio signal or computer readable storage medium.