Patent Description:
In order to satisfy the increasing demands of radio data traffic after the commercialization of a <NUM> communication system, efforts have been made to develop an advanced <NUM> communication system or a pre-<NUM> communication system. For this reason, the <NUM> communication system or the pre-<NUM> communication system is also referred to as a beyond-<NUM> network communication system or a post-LTE system. In order to accomplish a higher data transfer rate, the implementation of the <NUM> communication system in a super-high frequency (mmWave) band (e.g., about a <NUM> band) is being considered. Also, in order to obviate a propagation loss of a radio wave and increase a delivery distance of a radio wave in the super-high frequency band, discussions for the <NUM> communication system are underway about various techniques such as a beamforming, a massive MIMO, a full dimensional MIMO (FD-MIMO), an array antenna, an analog beam-forming, and a large scale antenna. Additionally, for an improvement in network of the <NUM> communication system, technical developments are being made in an advanced small cell, a cloud radio access network (cloud RAN), an ultra-dense network, a device to device (D2D) communication, a wireless backhaul, a moving network, a cooperative communication, coordinated multi-points (CoMP), a reception-end interference cancellation, and the like. Also, in the <NUM> communication system, a hybrid FSK and QAM modulation (FQAM) and a sliding window superposition coding (SWSC) are developed as advanced coding modulation (ACM) schemes, and a filter bank multi carrier (FBMC), a non-orthogonal multiple access (NOMA), and a sparse code multiple access (SCMA) are also developed as advanced access techniques.

Meanwhile, one of new structural features of the <NUM> network is the introduction of network slicing technology for radio access network (RAN) and core network (CN) structures. The network slicing technology bundles network resources and network functions into one independent slice for each individual service. Using the network slicing technology makes it possible to apply attributes such as isolation, customization, or independent management and orchestration of network system functions and resources to a mobile communication network structure. Therefore, a network operator can independently allocate network resources specialized to each service and user, and can independently and flexibly provide services by selecting and combining network functions of the <NUM> system according to criteria such as service, user, and business model.

One of technical issues (work tasks) essential to the development of a network slicing structure is network slicing roaming support. The disclosure describes network functions required in a home network and a visited network in order to realize the network slicing roaming support, that is, in order to support roaming of a terminal (UE).

3GPP technical report <NUM>, V1. <NUM>, entitled "Technical Specification Group Services and System Aspects; Study on Architecture for Next Generation System (Release <NUM>), describes a possible design of a system architecture for the next generation mobile networks. The new architecture shall support at least the new RAT(s), the Evolved E-UTRA, non-3GPP accesses and minimize access dependencies.

The disclosure provides a method for a terminal to access an operator's network that supports a network slice.

The disclosure provides a method for connecting a terminal-subscribed mobile communication operator (i.e., a home network) and a mobile communication operator of a visited area (i.e., a visited network) when the terminal attaches to an operator's network supporting a network slice and receive a service in a mobile communication system.

The disclosure provides a method for generating a packet data unit (PDU) session for serving home-routed traffic to a roaming terminal.

According to an embodiment of the invention, provided is a method performed by a first network repository function, NRF, entity according to claim <NUM>.

According to another embodiment of the invention, a first network repository function, NRF, entity is provided according to claim <NUM>.

According to still another embodiment of the invention, provided is a method performed by a requesting session management network function, SM NF according to claim <NUM>.

According to still another embodiment of the invention, a requesting session management network function, SM NF, is provided according to claim <NUM>.

According to still another embodiment of the invention, provided is a method performed by a second network repository function, NRF, entity according to claim <NUM>.

According to still another embodiment of the invention, a second network repository function, NRF, entity is provided according to claim <NUM>.

When a terminal desires to attach to other operator's network and receive a service in a roaming environment, it is possible to allocate a network slice capable of supporting the service and, through this, provide the service to the terminal.

When home-routed traffic is to be served, it is possible to generate a packet data unit (PDU) session to support a quality of service (QoS) suitable for a terminal and also efficiently operate radio resources and network resources.

Among the above listed figures, only the embodiments of <FIG> and <FIG> pertain to the claimed solution, whereas the remaining figures pertain to background art examples.

In the following description of the disclosure, a description of known functions or configurations incorporated herein may be omitted to avoid unnecessary obscuration of the disclosure. Terms used herein are defined in consideration of disclosed functions and may vary based on a user's or operator's intention or custom. Therefore, the definitions of terms should be made on the basis of the entire content of this disclosure.

In this disclosure, terms for identifying access nodes, terms for indicating network entities, terms for indicating messages, terms for indicating interfaces between network entities, terms for indicating various types of identification information, and the like are exemplary for convenience of description.

Hereinafter, for convenience of description, the terms and names defined in the 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) standard will be used. However, the disclosure is not limited to such terms and names, and may be equally applied to systems that comply with other standards.

<FIG> illustrates an example of a core network architecture excluding a terminal and a base station in a network that supports roaming between wireless communication systems applying a network slice and also serves home-routed traffic.

Referring to <FIG>, a core network of a wireless communication system that supports a network slice is divided into a visited public land mobile network (PLMN) and a home PLMN.

The visited PLMN to which a roaming terminal will attach includes a common control plane network function (CCNF) <NUM> and a slice specific core network function <NUM> that collects network functions (NFs) related to a network slice. The slice specific core network function <NUM> includes slice specific control plane network functions (SSCNF) <NUM> including Slice CP NF_1,. , Slice CP NF_n which are control plane network functions defined to be used only within a network slice, and slice specific user plane network functions (SSUNF) <NUM> including Slice UP NF_1,. , Slice UP NF_n which are user plane network functions defined to be used only within a network slice.

The home PLMN includes a subscriber repository <NUM> that stores subscription information of a terminal, a home policy control function <NUM> that controls applying a policy in the home PLMN, an application function (AF) <NUM> that provides information about the policy to the home policy control function <NUM>, and a slice specific core network function <NUM> that collects network functions related to a network slice. The slice specific core network function <NUM> includes SSCNF <NUM> including Slice CP NF_1,. , Slice CP NF_n which are control plane network functions defined to be used only within a network slice, and SSUNF <NUM> including Slice UP NF_1,. , Slice UP NF_n which are user plane network functions defined to be used only within a network slice.

In addition, the core network may include a visited NF repository function <NUM> and a home NF repository function <NUM>, which find appropriate network functions from network functions of the visited PLMN and the home PLMN by request. The visited NF repository function <NUM> may be located within the CCNF <NUM>. Also, the home NF repository function <NUM> may operate as a network function instance (NFI) selector located within the CCNF <NUM> and performing a function of selecting an appropriate NF from a network slice instance. Although this disclosure uses the term "NF repository function" for convenience of description, this may refer to an NFI selector when a network slice is used. Also, the NF repository function may be referred to as "NF discovery device" or "NF storage device".

The CCNF <NUM> is connected to a terminal attaching to the visited PLMN and a base station accessed by the terminal, processes control messages for managing the terminal, and manages the mobility of the terminal. In addition, the CCNF <NUM> is connected to the subscriber repository <NUM> located in the home PLMN, receives subscriber related information from the subscriber repository <NUM>, and performs authentication of the terminal. Also, the CCNF <NUM> selects a network slice instance to be provided to the terminal by using information of the accessing terminal, and selects an appropriate slice CP NF (control plane network function) from the SSCNF <NUM> belonging to the corresponding network slice instance. The CCNF <NUM> may use the visited NF repository function <NUM> to select the appropriate slice CP NF. The slice CP NF selects an appropriate slice UP NF (user plane network function) from the SSUNF <NUM> belonging to the network slice instance. The slice CP NF may use the visited NF repository function <NUM> to select the appropriate slice UP NF.

Alternatively, the CCNF <NUM> may select a network slice instance to be provided to the corresponding terminal by using information of the terminal, select a slice CP NF from the SSCNF <NUM> belonging to the corresponding network slice instance, and select a slice UP NF from the SSUNF <NUM> belonging to the corresponding network slice instance. That is, the CCNF <NUM> may select both the slice CP NF and the slice UP NF. Also, the CCNF <NUM> may use the visited NF repository function <NUM> to select appropriate slice CP NF and slice UP NF.

The slice CP NF and the slice UP NF selected in the visited PLMN support a data service in a terminal-belonging network slice through connection with a slice CP NF and a slice UP NF selected from the SSCNF <NUM> and the SSUNF <NUM> belonging to the home PLMN.

The slice CP NF manages a packet data unit (PDU) session so that the terminal can receive a service through a data network (NW). The slice CP NF may include a session management function for managing transmission of service data for the terminal by communicating with the selected slice UP NFs.

The slice UP NF may perform a user plane function of a packet data unit gateway (P-GW) in the Long Term Evolution (LTE) system, such as processing packets for user service data through connection with a terminal and a base station.

The above-mentioned functions, for example, the subscriber authentication function of the CCNF <NUM>, the terminal mobility management function, the network slice selection function, the function of selecting the SSCNFs <NUM> and <NUM> and the SSUNFs <NUM> and <NUM>, and the function of processing control message through connection with a terminal and a base station, may be defined as individual network functions or as a partly combined network function.

<FIG> illustrates a network initial attach and registration procedure of a terminal in a roaming environment to which a network slice is applied, according to an embodiment of the disclosure.

User equipment (UE) <NUM>, that is, a terminal, transmits at step <NUM>, to a radio access network (RAN) <NUM>, that is, a base station, an initial attach request for requesting registration to attach to a visited PLMN according to roaming. The initial attach request may contain UE identification information, e.g., an international mobile subscriber identity (IMSI), an international mobile equipment identity code (IMEI), or a temporary ID such as a globally unique temporary identifier (GUTI). In addition, the initial attach request may contain slice selection assistance information including information about a service registered in a home PLMN operator by the UE, a service type supporting the service, a network slice type, or an identifier (ID) indicating a network slice.

When the initial attach request is received from the UE <NUM>, the RAN <NUM> selects a default CCNF <NUM> to process the initial attach request, and transmits the received initial attach request at step <NUM>. Based on at least a part of the slice selection assistance information or preset information in the visited PLMN, the RAN <NUM> may select the default CCNF <NUM> to support a network slice or service subscribed by the UE.

When the initial attach request is received from the RAN <NUM>, the default CCNF <NUM> connects with a subscriber repository <NUM> existing in the home PLMN to which the UE <NUM> belongs, performs an authentication procedure for determining whether the UE <NUM> is true UE, and retrieves subscription information (i.e., subscription data) of the UE <NUM> at step <NUM>.

The subscription information of the UE <NUM> may include information of a network slice to which the UE <NUM> subscribes. Also, at the authentication and subscription data retrieval step <NUM>, the default CCNF <NUM> may receive, from the subscriber repository <NUM>, information of default data network name (DNN) and information of a DNN list allowed according to a service level agreement (SLA) between the visited PLMN and the home PLMN.

Based on the slice selection assistance information received from the RAN <NUM> at the initial attach request reception step <NUM> and the subscription information of the UE <NUM> received from the subscriber repository <NUM> at the authentication and subscription data retrieval step <NUM>, the default CCNF <NUM> selects at step <NUM> a network slice instance that can be provided in the visited PLMN.

However, if the default CCNF <NUM> has difficulty in finding an appropriate network slice instance or if there is a more appropriate CCNF, the default CCNF <NUM> may forward an attach message to the more appropriate CCNF so that the more appropriate CCNF will be used as a serving CCNF <NUM>. That is, if the default CCNF is suitable for use, it may select a network slice instance at step <NUM>. However, if not suitable or if there is a more appropriate CCNF, the attach message is forwarded to the CCNF at step <NUM>, and the CCNF selects a network slice instance at step <NUM>. Hereinafter, the more appropriate CCNF will be defined and described as CCNF_1 <NUM>.

When the default CCNF <NUM> forwards the attach request message to the CCNF_1 <NUM> at step <NUM>, the serving CCNF is changed. The forwarded attach request message may contain information included in the initial attach request <NUM>, e.g., the UE identification information and the slice selection assistance information. In addition, the forwarded attach request message may contain information acquired at the authentication and subscription data retrieval step <NUM>, e.g., a subscribed mobility management (MM) context and a subscribed service management (SM) context. The subscribed SM context may include information about a default DNN and information about an allowed DNN list.

Alternatively, the CCNF_1 <NUM> may acquire information such as the subscribed MM context and the subscribed SM context by retrieving subscription information via connection with the subscriber repository <NUM>. The subscribed SM context may include information about a default DNN and information about an allowed DNN list.

Meanwhile, at the network slice instance selection step <NUM>, the CCNF_1 <NUM> may select a network slice that can be provided by the visited PLMN, based on the slice selection assistance information or the like delivered through the attach request step <NUM>. The CCNF_1 <NUM> allocates a temporary ID of the UE, inserts information about a service agreed in the network, e.g., agreed slice selection assistance information, in an attach accept message, and forwards it to the default CCNF <NUM> at step <NUM>. The default CCNF <NUM> transmits the attach accept message to the RAN <NUM> at step <NUM>, and the RAN <NUM> transmits the attach accept message to the UE <NUM> at step <NUM>.

The above-described attach procedure may be applied even to a non-roaming situation. If information of a default DNN or allowed DNN list is a DNN value used in the home PLMN when the default CCNF <NUM> or the CCNF_1 <NUM> selects a network slice instance in a roaming situation, a home-routed traffic dedicated network slice instance may be selected.

<FIG> illustrates a process in which a terminal generates a PDU session for home-routed traffic in a roaming environment to which a network slice is applied, according to another embodiment of the disclosure.

In order to generate the PDU session in a visited PLMN which is in roaming, the terminal (i.e., UE) <NUM> transmits a NAS_PDU session request message for access to a serving CCNF <NUM> at step <NUM>. The NAS_PDU session request message includes at least one of a temporary ID which is an identifier of the UE, requested slice assistance information indicating a characteristic of the PDU session to be generated by the UE or a characteristic of a service to be used by the UE, or all or some parameters of a DNN. Like an access point name (APN) in the LTE network, the DNN indicates information of a network from which the UE will receive an Internet protocol (IP) address to be used. When the DNN is not contained in the NAS_PDU session request message, a default DNN acquired from subscription information may be used as the DNN.

When the NAS_PDU session request message is received at step <NUM>, the serving CCNF <NUM> may check subscription information at step <NUM> in order to determine whether a service is available for the slice assistance information and DNN requested by the UE. For this, the serving CCNF may request and retrieve the subscription information from a subscriber repository <NUM> in a home PLMN. In addition, when a network slice instance that allows a service for the requested slice assistance information and DNN is not determined, the serving CCNF <NUM> may select an appropriate network slice instance by using a network slice instance (NSI) selector.

The serving CCNF <NUM> may select at step <NUM> an SM NF1 <NUM> which is an NF for session management, based on information about the network slice instance selected at the subscription information check step <NUM>. Specifically, the serving CCNF <NUM> may select the SM NF1 <NUM>, based on a network function of the serving CCNF <NUM> and information about a network slice. Alternatively, the serving CCNF <NUM> may select the SM NF1 <NUM> by requesting an entity, such as an NF repository function <NUM> capable of finding an appropriate network function, to find an appropriate SM NF on the basis of the selected network slice instance information. A method for the serving CCNF <NUM> to find the SM NF by using the NF repository function <NUM> will be described later with reference to <FIG>.

When the SM NF1 <NUM> is selected at the SM NF selection step <NUM>, the serving CCNF <NUM> may transmit a PDU session request message to the SM NF1 <NUM> at step <NUM> in order to set up a PDU session. The PDU session request message may contain at least one of a UE identifier such as an IMSI or a temporary ID, agreed slice assistance information, a DNN, a session ID, NSI_1 which is information about the selected network slice instance, or the NAS_PDU session request message.

The SM NF1 <NUM> may select at step <NUM> a UP NF1 <NUM> which is an NF for a user plane function, based on the NSI_1 received in the PDU session request message <NUM>. The SM NF1 <NUM> may select the UP NF1 <NUM>, based on its own network function and information about a network slice. Alternatively, the SM NF1 <NUM> may select the UP NF1 <NUM> by requesting an entity, such as the NF repository function <NUM> capable of finding an appropriate network function, to find an appropriate UP NF on the basis of the selected network slice instance information, i.e., the NSI_1. A method for the SM NF <NUM> to find the UP NF by using the NF repository function <NUM> will be described later with reference to <FIG>.

The SM NF1 <NUM> sets up a user plane for the selected UP NF1 <NUM> at step <NUM>.

When the SM NF1 <NUM> recognizes from the DNN that the PDU session request of the UE is for home-routed traffic, the SM NF1 <NUM> selects an appropriate SM NF in the home PLMN at step <NUM> in order to transmit the PDU session request message. The SM NF1 <NUM> of the visited PLMN may select the SM NF of the home PLMN by requesting an entity, such as the NF repository function <NUM> of the visited PLMN capable of finding an appropriate network function, to find an appropriate SM NF on the basis of at least a part of the DNN or agreed slice assistance information. Also, when the home PLMN supports a network slice, the SM NF1 <NUM> may acquire together information about a network slice instance to which the selected SM NF of the home PLMN belongs. The NF repository function <NUM> of the visited PLMN may find an appropriate SM NF and a network slice instance of the home PLMN to which the SM NF belongs, in the home PLMN through an NF repository function <NUM> of the home PLMN. This method will be described later with reference to <FIG>. Meanwhile, the SM NF selection step <NUM> of the home PLMN may be performed by the SM NF1 <NUM> of the visited PLMN as described above, or may be performed by the serving CCNF <NUM>. Hereinafter, the SM NF selected in the home PLMN will be defined and described as an SM NF2 <NUM>.

The SM NF1 <NUM> transmits at step <NUM> an HR_PDU session request message to the SM NF2 <NUM> selected in the home PLMN in order to set up a PDU session. The HR_PDU session request message may contain at least one of a UE identifier such as an IMSI, agreed slice assistance information, a session ID, an address of the UP NF1 <NUM> of the visited PLMN, or information of network slice instance including the SM NF2 <NUM> of the home PLMN acquired at the SM NF selection step <NUM> of the home PLMN.

When the HR_PDU session request message is received at step <NUM>, the SM NF2 performs authorization based on an operator's policy through a policy function <NUM> at step <NUM>.

After the authorization, the SM NF2 <NUM> assigns an IP address of the UE <NUM> and selects an appropriate UP NF for setting up a user plane in the home PLMN at step <NUM>. The SM NF2 <NUM> may send a request to an entity such as the NF repository function <NUM> of the home PLMN capable of finding an appropriate network function and retrieve the appropriate UP NF in the home PLMN, based on at least a part of the DNN or agreed slice assistance information. Alternatively, when there is information of a network slice instance to which the SM NF2 <NUM> belongs, the SM NF2 <NUM> may send a request to an entity such as the NF repository function <NUM> of the home PLMN capable of finding an appropriate network function and retrieve the appropriate UP NF in the home PLMN, based on the network slice instance information. A method for the SM NF2 <NUM> to retrieve the UP NF in the home PLMN by using the NF repository function <NUM> of the home PLMN will be described later with reference to <FIG>. Hereinafter, the UP NF selected in the home PLMN will be defined and described as a UP NF2 <NUM>.

After assigning the UE IP address and selecting the UP NF in the home PLMN at step <NUM>, the SM NF2 <NUM> sets up a user plane for the selected UP NF2 <NUM> at step <NUM>. In addition, the SM NF2 <NUM> transmits an HR_PDU session response message containing a setup result of a PDU session to the SM NF1 <NUM> of the visited PLMN at step <NUM>. The HR_PDU session response message may contain at least one of the UE IP address acquired at the step <NUM>, a session ID, or address information of the selected UP NF2 <NUM>.

The SM NF1 <NUM> forwards the PDU session setup result to the UE <NUM> via the serving CCNF <NUM>. Specifically, at step <NUM>, the SM NF1 <NUM> generates a NAS_PDU session response message and transmits, to the serving CCNF <NUM>, a PDU session response containing the NAS_PDU session response message together with a UE temporary ID and the session ID. The NAS_PDU session response message may contain at least one of the agreed slice assistance information, the DNN, the UE IP address, or the session ID. At step <NUM>, the serving CCNF <NUM> forwards the NAS_PDU session response message to the UE to inform that the PDU session is generated.

<FIG> illustrates a process in which a serving CCNF finds an appropriate SM NF through an NF repository function at the SM NF selection step <NUM> of <FIG>.

The serving CCNF <NUM> sends at step 313a an NF discovery request message to the NF repository function <NUM> of the visited PLMN to request finding an appropriate SM NF. The NF discovery request message may contain at least one of SM NF information which is information about a type of NF to be found, serving CCFN information which is information about a requesting NF, a visited PLMN ID which is information about a PLMN from which a requested NF will be found, or previously allocated network slice instance information. In addition, the NF discovery request message may further contain at least one of an IMSI or a temporary ID as identification information of the UE.

In response to the request of the step 313a, the NF repository function <NUM> finds an appropriate SM NF by searching its database or other database and then forwards address information of the SM NF to the serving CCNF <NUM> at step 313b.

<FIG> illustrates a process in which an SM NF1 finds an appropriate UP NF through an NF repository function at the UP NF selection step <NUM> of <FIG>.

The SM NF1 <NUM> sends at step 315a an NF discovery request message to the NF repository function <NUM> of the visited PLMN to request finding an appropriate UP NF. The NF discovery request message may contain at least one of UP NF information which is information about a type of NF to be found, SM NF1 information which is information about a requesting NF, a visited PLMN ID which is information about a PLMN from which a requested NF will be found, or previously allocated network slice instance information. In addition, the NF discovery request message may further contain at least one of an IMSI or a temporary ID as identification information of the UE.

In response to the request of the step 315a, the NF repository function <NUM> finds an appropriate UP NF by searching its database or other database and then forwards address information of the UP NF to the SM NF1 <NUM> at step 315b.

<FIG> illustrates a process in which an SM NF1 of a visited PLMN finds an appropriate SM NF in a home PLMN through an NF repository function at the SM NF selection step <NUM> of the home PLMN of <FIG>.

The SM NF1 <NUM> sends at step 317a an NF discovery request message to the NF repository function <NUM> of the visited PLMN to request finding an appropriate SM NF in the home PLMN. The NF discovery request message may contain at least one of SM NF information which is information about a type of NF to be found, SM NF1 information which is information about a requesting NF, a home PLMN ID which is information about a PLMN from which a requested NF will be found, previously allocated network slice instance information if it exists, a DNN, or agreed slice assistance information. In addition, the NF discovery request message may further contain at least one of an IMSI or a temporary ID as identification information of the UE.

In response to the request of the step 317a, the NF repository function <NUM> of the visited PLMN sends the NF discovery request message to the NF repository function <NUM> of the home PLMN at step 317b. Then, the NF repository function <NUM> of the home PLMN finds an appropriate SM NF by searching its database or other database and forwards address information of the SM NF to the NF repository function <NUM> of the visited PLMN at step 317c. In case where the home PLMN supports a network slice, information about a network slice instance to which the found SM NF belongs may be forwarded together to the NF repository function <NUM> of the visited PLMN. Then, the NF repository function <NUM> of the visited PLMN forwards the received information to the SM NF1 <NUM> as response at step 317d.

<FIG> illustrates a process in which an SM NF2 finds an appropriate UP NF through an NF repository function at the UP NF selection step <NUM> of <FIG>.

The SM NF2 <NUM> sends at step 320a an NF discovery request message to the NF repository function <NUM> of the home PLMN to request finding an appropriate UP NF. The NF discovery request message may contain at least one of UP NF information which is information about a type of NF to be found, SM NF2 information which is information about a requesting NF, a home PLMN ID which is information about a PLMN from which a requested NF will be found, previously allocated network slice instance information if it exists, a DNN, or agreed slice assistance information. In addition, the NF discovery request message may further contain at least one of an IMSI or a temporary ID as identification information of the UE.

In response to the request of the step 320a, the NF repository function <NUM> finds an appropriate UP NF by searching its database or other database and then forwards address information of the UP NF to the SM NF2 <NUM> at step 320b.

<FIG> illustrates another example of a core network architecture excluding a terminal and a base station in a network that supports roaming between wireless communication systems applying a network slice and also serves home-routed traffic. According to the network architecture of <FIG>, contrary to the network architecture of <FIG>, a network slice instance for serving home-routed traffic is used through an NSI selector in a home PLMN.

Referring to <FIG>, a visited PLMN to which a roaming terminal will attach includes a CCNF <NUM> and a slice specific core network function <NUM> that collects network functions related to a network slice. The slice specific core network function <NUM> includes SSCNF <NUM> including Slice CP NF_1,. , Slice CP NF_n which are control plane network functions defined to be used only within a network slice, and SSUNF <NUM> including Slice UP NF_1,. , Slice UP NF_n which are user plane network functions defined to be used only within a network slice. The CCNF <NUM> may include a network slice instance (NSI) selector <NUM> in the visited PLMN.

The home PLMN includes a subscriber repository <NUM> that stores subscription information of a terminal, a home policy control function <NUM> that controls applying a policy in the home PLMN, an AF <NUM> that provides information about the policy to the home policy control function <NUM>, and a slice specific core network function <NUM> that collects network functions related to a network slice. The slice specific core network function <NUM> includes SSCNF <NUM> including Slice CP NF_1,. , Slice CP NF_n which are control plane network functions defined to be used only within a network slice, and SSUNF <NUM> including Slice UP NF_1,. , Slice UP NF_n which are user plane network functions defined to be used only within a network slice. The home PLMN may include a network slice instance (NSI) selector <NUM> that selects a network slice in the home PLMN.

In addition, the core network may include a visited NF repository function <NUM> and a home NF repository function <NUM>, which find appropriate network functions from network functions of the visited PLMN and the home PLMN by request. The visited NF repository function <NUM> may be located within the CCNF <NUM>. Also, the home NF repository function <NUM> may operate as an NFI selector located within the CCNF <NUM> and performing a function of selecting an appropriate NF from a network slice instance. Although this disclosure uses the term "NF repository function" for convenience of description, this may refer to an NFI selector when a network slice is used.

The CCNF <NUM> is connected to a terminal attaching to the visited PLMN and a base station accessed by the terminal, processes control messages for managing the terminal, and manages the mobility of the terminal. In addition, the CCNF <NUM> is connected to the subscriber repository <NUM> located in the home PLMN, receives subscriber related information from the subscriber repository <NUM>, and performs authentication of the terminal. Also, the CCNF <NUM> selects a network slice instance to be provided to the terminal by using information of the accessing terminal, and selects an appropriate slice CP NF from the SSCNF <NUM> belonging to the corresponding network slice instance. The CCNF <NUM> may use the visited NF repository function <NUM> to select the appropriate slice CP NF. The slice CP NF selects an appropriate slice UP NF from the SSUNF <NUM> belonging to the network slice instance. The slice CP NF may use the visited NF repository function <NUM> to select the appropriate slice UP NF.

Alternatively, the CCNF <NUM> may select, through the NSI selector <NUM>, a network slice instance to be provided to the corresponding terminal by using information of the terminal, select a slice CP NF from the SSCNF <NUM> belonging to the corresponding network slice instance, and select a slice UP NF from the SSUNF <NUM> belonging to the corresponding network slice instance. That is, the CCNF <NUM> may select both the slice CP NF and the slice UP NF. Also, the CCNF <NUM> may use the visited NF repository function <NUM> to select appropriate slice CP NF and slice UP NF.

The slice CP NF and the slice UP NF selected in the visited PLMN through the NSI selector <NUM> support a data service in a terminal-belonging network slice through connection with a slice CP NF and a slice UP NF selected from the SSCNF <NUM> and the SSUNF <NUM> selected through the NSI selector <NUM> belonging to the home PLMN.

In case of generating a PDU session for home-routed traffic in the network architecture of <FIG>, procedures similar to those of <FIG> are performed. However, at the subscription data check step <NUM>, the serving CCNF <NUM> transmits at least one of a home PLMN ID, DNN information, or agreed slice assistance information to the NSI selector of the visited PLMN in order to request an appropriate network slice instance value of the home PLMN. The NSI selector of the visited PLMN forwards information received from the serving CCNF <NUM> to the NSI selector of the home PLMN. The NSI selector of the home PLMN selects an appropriate network slice instance, based on the above information, and forwards the selected network slice instance to the serving CCNF <NUM>. In addition, the network slice instance information NSI_2 of the selected home PLMN is forwarded to the SM NF1 via the PDI session request <NUM> and may be used at step <NUM> of selecting the SM NF of the home PLMN.

<FIG> is a diagram illustrating a structure of a terminal according to an embodiment of the disclosure.

Referring to <FIG>, the terminal may include a transceiver <NUM>, a controller <NUM>, and a storage <NUM>. In the disclosure, the controller <NUM> may be defined as a circuit, an application specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit and receive signals to and from other network entities. For example, in a network initial connection and registration procedure of the terminal in a roaming environment to which a network slice is applied as shown in <FIG>, the transceiver <NUM> may transmit an initial attach request message to a base station (step <NUM>) or receive an initial attach accept message from the base station (step <NUM>). Also, in a process in which the terminal generates a PDU session for home-routed traffic in a roaming environment to which a network slice is applied as shown in <FIG>, the transceiver <NUM> may transmit a PDU session request message to a serving CCNF (step <NUM>) or receive a PDU session response message from the serving CCNF (step <NUM>).

The controller <NUM> may control the overall operation of the terminal according to embodiments of the disclosure. For example, the controller <NUM> may control signal flows between respective blocks to perform operations according to flowcharts described above. In particular, the controller <NUM> may control operations disclosed herein for attachment and home-routed PDU session generation of the terminal according to embodiments of the disclosure. In an embodiment, the controller <NUM> may be configured to control the transceiver <NUM> to transmit a PDU session request message, which contains slice assistance information indicating the characteristics of a service that the terminal desires to use, to a CCNF of a visited PLMN, and also control the transceiver <NUM> to receive a PDU session response message containing an IP address of the terminal from the CCNF of the visited PLMN.

The storage <NUM> may store at least one of information transmitted/received through the transceiver <NUM> and information generated through the controller <NUM>. For example, the storage <NUM> may store information for identifying the terminal, slice selection assistance information, and the like.

<FIG> is a diagram illustrating a structure of a CCNF according to an embodiment of the disclosure.

Referring to <FIG>, the CCNF may include a transceiver <NUM>, a controller <NUM>, and a storage <NUM>. In the disclosure, the controller <NUM> may be defined as a circuit, an application specific integrated circuit, or at least one processor.

The transceiver <NUM> may transmit and receive signals to and from other network entities. For example, in a network initial connection and registration procedure of a terminal in a roaming environment to which a network slice is applied as shown in <FIG>, the transceiver <NUM> may receive an initial attach request message from a base station (step <NUM>) or transmit an initial attach accept message to the base station (step <NUM>). Also, in a process in which the terminal generates a PDU session for home-routed traffic in a roaming environment to which a network slice is applied as shown in <FIG> and <FIG>, the transceiver <NUM> may receive a PDU session request message from the terminal (step <NUM>), transmit the PDU session request message to an SM NF1 (step <NUM>), receive a PDU session response message from the SM NF1 (step <NUM>), transmit the PDU session response message to the terminal (step <NUM>), transmit an NF discovery request message to an NF repository function (step 313a), or receive an NF discovery response message from the NF repository function (step 313b).

The controller <NUM> may control the overall operation of the CCNF according to embodiments of the disclosure. For example, the controller <NUM> may control signal flows between respective blocks to perform operations according to flowcharts described above. In particular, the controller <NUM> may control operations disclosed herein for attachment and home-routed PDU session generation of the terminal according to embodiments of the disclosure. In an embodiment, the controller <NUM> may be configured to control the transceiver <NUM> to receive a PDU session request message, which contains slice assistance information indicating the characteristic of a service that the terminal desires to use, from the terminal, to transmit a first discovery request message containing a home PLMN ID of the terminal and the slice assistance information to an NF repository function, and to receive a first discovery response message containing an address of an SF NF of the home PLMN from the NF repository function.

The storage <NUM> may store at least one of information transmitted/received through the transceiver <NUM> and information generated through the controller <NUM>. For example, the storage <NUM> may store an ID of a terminal, a home PLMN ID of the terminal, slice selection assistance information, an IP address of the terminal, and the like.

In the above-described embodiments of the disclosure, various elements are expressed in singular or plural forms. However, such singular or plural forms are merely selected for the sake of convenience of description and not intended to limit the disclosure. Any element expressed in a plural form may refer to a singular element, and vice versa.

Claim 1:
A method performed by a first network repository function, NRF, entity (<NUM>) in a serving public land mobile network, PLMN, the method comprising:
receiving (317a), from a requesting session management network function, SM NF (<NUM>), in the serving PLMN, a first NF discovery request message including an identifier of a home PLMN, agreed network slice assistance information, and a data network name;
transmitting (317b), to a second NRF entity (<NUM>) in the home PLMN, a second NF discovery request message including the agreed network slice assistance information, and the data network name based on the identifier of the home PLMN;
as a response to the second NF discovery request message, receiving (317c), from the second NRF entity (<NUM>), an address of a target SM NF (<NUM>) in the home PLMN; and
transmitting (317d), to the requesting SM NF (<NUM>), the address of the target SM NF (<NUM>).