CN111034250B

CN111034250B - Method for processing locally offloaded anchor User Plane Function (UPF) in 5G cellular network

Info

Publication number: CN111034250B
Application number: CN201880053068.2A
Authority: CN
Inventors: 裵范植; 李珍盛; 李知彻; 权奇锡; 文相畯; 朴重信
Original assignee: Samsung Electronics Co Ltd
Current assignee: Samsung Electronics Co Ltd
Priority date: 2017-08-14
Filing date: 2018-08-13
Publication date: 2023-11-10
Anticipated expiration: 2038-08-13
Also published as: KR20190018376A; KR102434074B1; CN111034250A

Abstract

A communication scheme for merging IoT technologies and a 5G communication system for supporting high data transmission rates in excess of 4G systems and a system thereof are disclosed. The present disclosure may be applied to smart services (e.g., services related to smart homes, smart buildings, smart cities, smart cars, networked cars, healthcare, digital education, retail business, security, and security) based on 5G communication technologies and IoT-related technologies. The present disclosure relates to a method of handling anchor UPFs for local offloading when a UE moves in a 5G cellular wireless communication system.

Description

Method for processing locally offloaded anchor User Plane Function (UPF) in 5G cellular network

Technical Field

The present disclosure relates generally to a method and more particularly to a method of handling an anchor user plane function (user plane function, UPF) for local offloading when a User Equipment (UE) moves in a 5G cellular wireless communication system.

Background

The above information is presented merely as background information to aid in the understanding of the present disclosure. There is no determination, nor assertion, as to whether any of the above can be used as prior art with respect to the present disclosure.

In order to meet the increasing demand for wireless data traffic since the deployment of 4G communication systems, efforts have been made to develop improved 5G or pre-5G communication systems. Thus, a 5G or pre-5G communication system is also referred to as a "transcendental 4G network" or a "LTE-after-system". A 5G communication system is considered to be implemented in a higher frequency (mmWave) band (e.g., 60GHz band) to achieve a higher data rate. In order to reduce propagation loss of radio waves and increase transmission distance, beamforming, massive Multiple Input Multiple Output (MIMO), full-size MIMO (FD-MIMO), array antennas, analog beamforming, massive antenna techniques have been discussed in 5G communication systems. Further, in the 5G communication system, system network improvement developments based on advanced small cells, cloud Radio Access Networks (RANs), ultra dense networks, device-to-device (D2D) communication, wireless backhaul, mobile networks, cooperative communication, cooperative multipoint (CoMP), receiving-end interference cancellation, and the like are underway. In 5G systems, hybrid FSK and QAM modulation (FQAM) and Sliding Window Superposition Coding (SWSC) have been developed as Advanced Coding Modulation (ACM), filter Bank Multicarrier (FBMC), non-orthogonal multiple access (NOMA) and Sparse Code Multiple Access (SCMA) as advanced access techniques.

The internet is a person-centric connected network in which people can generate and consume information. Today, the internet is evolving into the internet of things (IoT) in which distributed entities such as things exchange and process information without human intervention. Internet of things (IoE) is a combination of internet of things technology and big data processing technology through connection with a cloud server. The internet of things implementation requires technical elements such as "sensing technology", "wired/wireless communication and network infrastructure", "service interface technology" and "security technology", sensor networks, machine-to-machine (M2M) communication, machine Type Communication (MTC) and the like have been recently studied. Such an internet of things environment may provide an intelligent internet technology service that creates new value for human life by collecting and analyzing data generated between connected things. The internet of things can be applied to various fields including smart homes, smart buildings, smart cities, smart cars or interconnected cars, smart grids, healthcare, smart home appliances and advanced medical services through fusion and combination between existing Information Technology (IT) and various industrial applications.

Accordingly, various attempts have been made to apply 5G communication systems to IoT networks. For example, techniques such as sensor networks, MTC, and M2M communication may be implemented by beamforming, MIMO, and array antennas. Application of the cloud RAN as the big data processing technology described above may also be considered as an example of a fusion between 5G technology and IoT technology.

In order to facilitate the evolution from the conventional 4G Long Term Evolution (LTE) system to the 5G system, the 3GPP responsible for the cellular mobile communication standard has named and standardized a new core network structure as a 5G core (5 GC).

Disclosure of Invention

Technical problem

The present disclosure has been made to address at least the above disadvantages and to provide at least the advantages below.

The present disclosure relates to a process that includes signaling between network entities within a 5G core network to add or remove an anchor UPF to or from a PDU session if a UE that establishes a PDU session for a particular Data Network Name (DNN), such as the internet, moves to or from that area when the 5G cellular network service provider installs the anchor UPF for local offloading at that area. Further, the present disclosure provides a method of informing a UE of the addition and removal of an anchor UPF.

The method of adding or removing the anchor UPF may be different depending on the presence or absence (split into CM-IDLE or CM-CONNECTED state) of a non-access stratum (NAS) signaling connection between the UE and the access and mobility management function (AMF) of the 5G network. When an N9 tunnel between an anchor UPF and a Branch Point (BP) or an Uplink (UL) classifier (UL CL) responsible for traffic routing is maintained for a UE in a CM-IDLE state, overhead (e.g., backhaul traffic forwarded from a local server) may be generated because data transmission with the anchor UPF should be maintained by adding an intermediate UPF to ensure continuity of a session even though the UE leaves a service area of the anchor UPF. In particular, as the UE is farther from the service area of the anchor UPF, the overhead from the addition of the intermediate UPF may be significant. This may be contrary to the goal of reducing backhaul traffic within a cellular network by placing an anchor UPF in close proximity to a UE for local offloading.

Solution to the problem

According to an aspect of the present disclosure, a method is provided. The method comprises the following steps: allocating a first PDU session anchor to a PDU session for establishing the PDU session at the UE; adding a second PDU session anchor for local offloading of PDU sessions; controlling a first PDU session anchor based on a Service and Session Continuity (SSC) mode of the PDU session; and controlling the second PDU session anchor independently of the SSC mode of the PDU session.

According to an aspect of the present disclosure, an apparatus is provided. The apparatus includes a transceiver and a controller coupled to the transceiver. The controller is configured to: allocating a first PDU session anchor to a PDU session for establishing the PDU session at the UE; adding a second PDU session anchor for local offloading of the PDU session; controlling a first PDU session anchor based on SSC mode of the PDU session; and controlling the second PDU session anchor independently of the SSC mode of the PDU session.

The beneficial effects of the invention are that

According to the present disclosure, when a local server (e.g., content/multimedia server) installed on a cache content for each region in a 5G cellular network and an anchor UPF that can communicate with the local server are arranged, even if a UE frequently moves by applying a UL CL solution or an IPv6 multihoming solution to some traffic of a conventionally established PDU session, overhead from using a local offload solution for each region can be reduced, and performance of traffic offload can be improved by controlling offload traffic in a corresponding actual region.

Drawings

The foregoing and other aspects, features, and advantages of certain embodiments of the present disclosure will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagram of the network architecture and interfaces of a 5G cellular system according to an embodiment;

FIG. 2 is a diagram of a network architecture according to an embodiment;

FIG. 3 is a diagram of a network architecture according to an embodiment;

fig. 4 is a diagram of a case in which a UE moves between areas according to an embodiment;

fig. 5A is a flowchart of the internal operation of a Session Management Function (SMF) according to an embodiment;

fig. 5B is a flowchart of the internal operation of the SMF according to an embodiment;

fig. 5C is a flowchart of an internal operation of a UE receiving a notification according to an embodiment;

fig. 6 is a flowchart of an internal operation of a UE receiving a notification according to an embodiment;

FIGS. 7A and 7B are diagrams of an Xn-based handoff process, according to an embodiment;

fig. 8A and 8B are diagrams of an N2-based handover procedure according to an embodiment;

fig. 9A and 9B are diagrams of an N2-based handover procedure according to an embodiment;

fig. 10A and 10B are diagrams of an N2-based handover procedure according to an embodiment;

FIGS. 11A and 11B are diagrams of a service request procedure according to an embodiment;

FIGS. 12A and 12B are diagrams of a service request procedure according to an embodiment;

fig. 13 is a diagram of an NW (network) triggered service request procedure in a 5G cellular network according to an embodiment;

fig. 14A and 14B are diagrams of a registration procedure in a 5G cellular network according to an embodiment;

FIG. 15 is a diagram of a registration process, according to an embodiment;

FIG. 16 is a diagram of registration, according to an embodiment;

FIG. 17 is a diagram of the operation of a UPF when a data packet having an invalid IPv6 prefix configured for leaving an IP address arrives at a UPF from which an IP header can be identified, in accordance with an embodiment;

fig. 18 is a flowchart of an operation of an SMF receiving a notification message from a UPF for use of an invalid IP address according to an embodiment;

fig. 19 is a block diagram of a UE according to an embodiment; and

fig. 20 is a block diagram of a Base Station (BS) according to an embodiment.

Detailed Description

Embodiments of the present disclosure will be described hereinafter with reference to the accompanying drawings. However, the embodiments of the present disclosure are not limited to the particular embodiments, and should be construed to include all modifications, variations, equivalent devices and methods, and/or alternative embodiments of the present disclosure. In the description of the drawings, like reference numerals are used for like elements.

The terms "having," "can have," "including," and "can include," as used herein, mean that there are corresponding features (e.g., elements such as numerical values, functions, operations, or components) and that the presence of other functions is not precluded.

The term "a or B", "at least one of a or/and B" or "one or more of a or/and B" as used herein includes all possible combinations with the items they recite. For example, "a or B", "at least one of a and B" or "at least one of a or B" means (1) including at least one a, (2) including at least one B, or (3) including at least one a and at least one B.

Terms such as "first" and "second" as used herein may use the corresponding components regardless of importance or order and are used to distinguish one component from another without limitation. These terms may be used for distinguishing one element from another. For example, the first user device and the second user device indicate different user devices, regardless of order or importance. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present disclosure.

It will be understood that when an element (e.g., a first element) is "coupled" or "connected" to another element (e.g., a second element), it can be directly coupled/coupled to the other element, and intervening elements (e.g., third elements) may be present between the element and the other element. In contrast, it will be understood that when an element (e.g., a first element) is "directly coupled/coupled to" or "directly connected to" another element (e.g., a second element), there are no intervening elements (e.g., third elements) between the element and the other element.

The expression "configured to (or arranged to)" as used herein may be used interchangeably with "adapted to", "having the capabilities of …", "designed to", "adapted to", "manufactured to" or "capable of being" depending on the context. The term "configured to (set to)" does not necessarily mean "specially designed at the hardware level. Instead, the expression "an apparatus configured to" may mean that the apparatus is "capable of" in a particular context along with other devices or components. For example, "a processor configured (arranged) to perform A, B and C" may represent a dedicated processor (e.g., an embedded processor) for performing corresponding operations, or a general-purpose processor (e.g., a Central Processing Unit (CPU) or an Application Processor (AP)) capable of performing corresponding operations by running one or more software programs stored in a storage device.

The terminology used in describing the various embodiments of the disclosure is for the purpose of describing particular embodiments and is not intended to be limiting of the disclosure. As used herein, the singular is also intended to include the plural unless the context clearly indicates otherwise. Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the relevant art. Terms defined in the general dictionary should be construed to have the same or similar meaning as the context of the related art and should not be construed to have ideal or exaggerated meanings unless explicitly defined herein. According to circumstances, even the terms defined in the present disclosure should not be interpreted as excluding the embodiments of the present disclosure.

The term "module" as used herein may refer, for example, to a unit comprising one of hardware, software, and firmware, or a combination of two or more thereof. "module" may be used interchangeably with, for example, the terms "unit," logic block, "" component, "or" circuit. A "module" may be the smallest unit of integrated constituent elements or a part thereof. A "module" may be the smallest unit for performing one or more functions or a part thereof. The "module" may be implemented mechanically or electronically. For example, a "module" according to the present disclosure may include at least one of an Application Specific Integrated Circuit (ASIC) chip, a Field Programmable Gate Array (FPGA), and a programmable logic device for performing operations that have been completed as known or as will be developed below.

Electronic devices according to the present disclosure may include, for example, at least one of a smart phone, a tablet Personal Computer (PC), a mobile phone, a video phone, an electronic book reader (e-book reader), a desktop computer, a notebook computer, a netbook computer, a workstation, a server, a Personal Digital Assistant (PDA), a Portable Multimedia Player (PMP), an MPEG-1 audio layer 3 (MP 3) player, an ambulatory medical device, a camera, and a wearable device. The wearable device may include at least one of an accessory type (e.g., a watch, a ring, a bracelet, a chain of feet, a necklace, glasses, a contact lens, or a Head Mounted Device (HMD)), a fabric or garment integrated type (e.g., an electronic garment), a body mounted type (e.g., a skin panel or tattoo), and a bioimplantable type (e.g., an implantable circuit).

The electronic device may be a household appliance. Household appliances may include, for example, televisions, digital Video Disc (DVD) players, audio, refrigerator, air conditioner, vacuum cleaner, oven, microwave oven, washing machine, air cleaner, set top box, home automation control panel, security control panel, television box (e.g., samsung HomeSync) ^TM 、Apple TV ^TM Or Google TV ^TM ) Game machine (e.g. Xbox) ^TM PlayStation ^TM ) At least one of an electronic dictionary, an electronic key, a camcorder, and an electronic photo frame.

The electronic devices may include at least one of various medical devices (e.g., various portable medical measurement devices (blood glucose monitoring devices, heart rate monitoring devices, blood pressure measurement devices, body temperature measurement devices, etc.), magnetic Resonance Angiography (MRA), magnetic Resonance Imaging (MRI), computed Tomography (CT) machines, and ultrasound machines), navigation devices, global Positioning System (GPS) receivers, event Data Recorders (EDRs), flight Data Recorders (FDRs), vehicle infotainment devices, electronic devices for vessels (e.g., navigation devices and gyroscopic compasses for vessels), avionics, security devices, automotive hosts, home robots or industries, automated Teller Machines (ATMs) in banks, point of sale (POS) devices in stores, or internet of things (IoT) devices (e.g., light bulbs, various sensors, electric or gas meters, sprinkler devices, fire alarms, thermostats, street lamps, toasters, sporting goods, hot water tanks, heaters, boilers, etc.).

The electronic device may include at least one of furniture or a part of a building/structure, an electronic board, an electronic signature receiving device, a projector, and various measuring instruments (e.g., a water meter, an electric meter, a gas meter, and a radio wave meter). The electronic device may be a combination of one or more of the various devices described above. The electronic device may also be a flexible device. Further, the electronic device is not limited to the above-described device, and may include an electronic device according to the development of new technology.

Hereinafter, an electronic apparatus will be described with reference to the drawings. In this disclosure, the term "user" means a person using an electronic device or a device using an electronic device (e.g., an artificial intelligence electronic device).

Hereinafter, the BS is an entity that allocates resources to the UE, and may be one of an eNode B, a Node B, a BS, a RAN, a radio access unit, a base station controller, and a Node on a network. UEs may include UEs, mobile Stations (MSs), cellular telephones, smart phones, tablets, computers, and multimedia systems capable of performing communication functions. Here, DL refers to a wireless transmission path of a signal transmitted by the BS to the UE, and UL refers to a wireless transmission path of a signal transmitted by the UE to the BS.

In contrast to the Evolved Packet Core (EPC), which is a traditional 4G network core, 5GC supports differentiated functions.

One differentiating function is a network slicing function. In the requirements of 5G, 5GC should support various UE types and services (e.g., enhanced mobile broadband (eMBB), ultra-reliable low latency communication (URLLC), large machine type communication (mctc)). The UE/service has different requirements on the core network. For example, the emmbb service requires a high data rate, while the URLLC service requires high stability and low latency. One technique proposed to meet such various service requirements is a network slicing scheme. Network slicing is a method of virtualizing a physical network to generate multiple logical networks, and Network Slice Instances (NSIs) may have different characteristics. This is possible because each NSI has a Network Function (NF) that is tailored to its characteristics. By allocating NSI suitable for the service characteristics required for each UE, various 5G services can be efficiently supported.

By dividing the mobility management function and the session management function, the network virtualization paradigm can be easily supported. In conventional 4G LTE, all UEs may receive services via the network through signaling exchanges with a single core device of a Mobility Management Entity (MME) responsible for registration, authentication, mobility management, and session management functions. However, when a single device such as MME supports all functions as the number of UEs increases, and mobility and traffic/session characteristics that should be supported according to the UE type are subdivided in 5G, the scalability of adding an entity according to each required function cannot be not reduced. Accordingly, various functions are developed based on the structure dividing the mobility management function and the session management function in order to improve the function/implementation complexity and expandability of the core device serving the control plane according to the signaling load.

Fig. 1 is a diagram of the network architecture and interfaces of a 5G cellular system according to an embodiment.

Referring to fig. 1, an AMF for managing mobility and network registration of a UE and an SMF for managing an end-to-end session are separated and signaling may be exchanged through an N11 interface.

The SSC mode is introduced to support various continuity requirements of applications or services of the UE and the use of the PDU session specific SSC mode. The SSC mode includes three modes. SSC mode 1 is a mode in which an anchor UPF (or PDU Session Anchor (PSA)) that is a communication contact with an external Data Network (DN) is not changed while a corresponding session (including when a UE moves) is maintained, and session continuity can be ensured since an IP address/prefix allocated to the corresponding session is not changed. SSC patterns 2 and 3 allow for modification of the anchor UPF. However, SSC patterns 2 and 3 may differ in that an existing anchor UPF may be maintained when a connection with a new anchor UPF is established in SSC pattern 3, even though the connection with the anchor UPF should be immediately broken when the anchor UPF is changed, and then a connection with a new anchor UPF should be established in SSC pattern 2. Thus, in an SSC mode 3 session, data can be transmitted simultaneously through multiple anchor UPFs for the same external data network. However, since the SSC mode 2 session corresponds to a look-ahead interruption, signaling overhead between an entity and tunnel management is small in the core network, whereas if the anchor UPF is changed at a point of time of transmitting traffic of the UE, a service interruption may occur.

A policy control function (policy control function, PCF) is included that is a server that manages service provider policies for the UEs and may store policies for requesting and selecting sessions for each UE and provide the policies to the UEs so that the service provider can use them to route the traffic of the UE. This strategy is called UE routing strategy (UE route selection policy, urs). In particular, the urs may include a network slice selection policy (network slice selection policy, NSSP) for supporting network slice techniques, an SSC mode selection policy (SSC mode selection policy, sscmssp) for supporting SSC modes, and a DNN selection policy for selecting a DNN corresponding to an Access Point Name (APN) used by the EPC. The urs may be managed while they are paired with traffic filters to specify rules for specific traffic. To transfer the URSP from the PCF to the UE, the PCP may first send it to the AMF over a standard interface (e.g., N15), and the AMF may transfer the UE-specific URSP over a standard interface (e.g., N1) via a non-access stratum (NAS) signaling with the UE.

Fig. 2 is a diagram showing a network structure of an application example of a UL CL solution that provides the following functions: according to an embodiment, some traffic is offloaded locally to a location near the UE in a 5G cellular network by assigning an IPv4 address towards the same DNN to a PDU session.

Referring to fig. 2, another function is to provide a solution for local offloading. When a single IP address is allocated to a specific session of a UE, a function of dividing UL traffic of the UE by UPF as UL CL or adding DL traffic toward the UE may be provided. In particular, to offload some of the traffic of the session to a local server near the UE, the SMF may configure traffic rules (e.g., based on 5-tuple) in UL CL UPF. Based on the traffic rules, the UL CL UPF can reroute certain traffic to the local server to be transparent to the UE.

Fig. 3 is a diagram showing a network structure of an application example of a BP solution providing a function for locally offloading some traffic of a PDU session towards the same DNN to a place close to a UE by assigning different IPV6 prefixes to respective IP-anchored UPFs of the PDU session of IPV6 type, according to an embodiment.

Meanwhile, referring to fig. 3,5GC, a multi-homing (multi-homing) function may be provided to an IPv6 type PDU session, in which a plurality of IPv6 prefixes are allocated to one PDU session, and a UE may perform data communication using the appropriate IPv6 prefix. Similar to UL CL UPF, BP UPF may divide or add traffic based on traffic rules. However, the UE may determine the amount of traffic to be locally offloaded by selecting the IPv6 prefix assigned to the UE. To determine the routing of the UE, the SMF may add the routing information option set forth in the document IETF RFC 4191 to the IPv6 router advertisement message and send the IPv6 router advertisement message to the UE through the data path of the corresponding PDU session by UP signaling.

In 5G cellular networks, an edge computing technology is supported, namely a local area data network (local area data network, LADN). Specifically, the technology is a method by which a network provides data network information available in an area where a UE is currently located, and the UE generates a data network session usable in a corresponding area using the provided available data network information, and releases or temporarily stops (or disables) the generated session when the UE leaves an area where transmission/reception of the data session is possible. This is a technique implemented when the UE establishes a new PDU session for the LADN (different from the method described below). Furthermore, in LTE systems, all IP traffic from the UE ends with a PDN-GW. In addition, to improve latency in the backhaul network, local IP access (LIPA) and selected IP traffic offload (SIPTO) have been proposed to place the IP anchor close to the UE. Similarly, this differs from the method described below according to configuring a new PDN connection by the UE.

Fig. 4 is a diagram of a UE moving from zone A0 to zone A2 via A1 according to an embodiment when an anchor UPF (corresponding to PSA 1) covers a wide area for data communication with a particular DNN (e.g., the internet) and anchor UPF (corresponding to PSA2 and PSA 3) covers some zones where local servers belonging to the DNN are deployed.

Referring to fig. 4, a scheme for maintaining or releasing an anchor UPF (PSA 2 or PSA 3) for a PDU session when a UE moves into or out of a service area (A1 or A2) of the anchor UPF (installed for communication with a local server) is described, in which a data transmission path including the anchor UPF is configured, in a 5G cellular network. Even if the anchored UPF for local offload is released, the anchored UPF (PSA 1) that provides a wider service area (A0) should be continuously maintained for the data transmission path of the PDU session. The movement of the UE may refer to a change in the BS to which the UE accesses.

The service area away from the anchor UPF may be defined in detail as follows for local offloading to communicate with a local server. When the UE moves to the BS installed in the service area of the anchor UPF, there is connectivity between the UPF and the BS. When the UE moves to a BS that is not included in the service area of the UPF, there is no connectivity between the UPF and the BS. This method may be applied when an anchor UPF is coexistent with the BS. In addition, when the connection between the UPF and the BS is limited due to dynamic conditions such as a service provider policy or a load state anchoring the UPF, the internet can be included in a non-connected range even though the UPF and the BS can be physically connected. In addition, as mentioned in the handover procedure of document 3gpp ts23.401 defining the EPC standard, it may be included in the non-connected range when there is no direct IP connection between the two entities. The service area anchoring the UPF may be preset in the SMF by a service provider local policy or dynamically allocated by the PCF that controls the policy of the session after the PDU session is established.

The SMF may manage an additional anchor UPF for local offloading for each DNN and an original anchor UPF for connection with a specific DN (such as an internet network) that is not used for local offloading when initially conducting a PDU session, respectively. The original anchor UPF may operate to link with the SSC pattern. As the UE moves and leaves the service area of the original anchor UPF, an intermediate UPF may be added to achieve session continuity. Furthermore, for PDU sessions corresponding to SSC mode 2/3, the original anchor UPF can be changed to a new anchor UPF that can cover the current location of the UE. However, as the UE moves and leaves the service area of the additional anchor UPF, the additional anchor UPF may be released from the corresponding PDU session by the SMF and only the original anchor UPF may be retained. In other words, the additional anchor UPF may operate without regard to the SSC pattern. In addition, when the location to which the UE moves is included in the service area of another additional anchor UPF, a new additional anchor UPF may be added. The SMF may inform the UE of the classification when the SMF manages the two types of anchor UPFs, respectively. In particular, for a PDU session in which each anchor UPF is assigned an IP address (including an IPv6 prefix), information may be provided that indicates whether the anchor UPF associated with the IP address belongs to the original or additional anchor UPF when the IP address is assigned to the UE. Further, when an anchor UPF is added to or changed in a PDU session of the UE, information indicating where the corresponding anchor UPF belongs may be provided. When an anchor UPF is added, a notification may be provided by sending an indicator to the UE indicating whether the anchor UPF is the original anchor UPF or an additional anchor UPF.

The anchor UPF may be named PDU session anchor or PDA. Further, the additional anchor UPF and the original anchor UPF may be named differently.

The IPv6 prefix corresponds to an IPv6 type PDU session. If an IPv4 type PDU session is used in a cellular system supporting IPv4 multi-homing, the IPv6 prefix may be replaced with an IPv4 address.

In fig. 5A, 5B, 5C, and 6, the internal operation of the SMF and the internal operation of the UE are described. The SMF may manage information about the service area of the locally offloaded additional anchor UPF for each DNN of the PDU session established for the UE.

Fig. 5A is a flowchart of internal operations of an SMF for adding an additional anchor UPF when a UE enters a service area for locally offloaded additional anchor UPF for a PDU session, according to an embodiment.

Referring to fig. 5A, when the UE moves and is informed of the UE entering an additional anchor UPF service area for local offloading from the AMF managed by the SMF in step 501, the SMF may determine whether a new location of the UE is an area in which the additional anchor UPF may provide service in step 503. When it is determined that the UE has not entered the service area of the additional anchor UPF, the smf maintains the PDU session through the original anchor UPF in step 505. When it is determined that the UE enters the service area of the additional anchor UPF, the smf may add the additional anchor UPF to the existing PDU session of the UE supporting the DNN, which is the same as supported by the additional anchor UPF, in step 507. When an additional anchor UPF is added to the PDU session, the SMF may newly register service area information for receiving notification of a change in UE location for the corresponding PDU session in the AMF. Service area information to be registered in the AMF may be acquired based on the service area of the additional anchor UPF. In step 509, the smf may inform the UE to add additional anchor UPFs to the PDU session. Thereafter, in step 511, the smf determines whether the original anchor UPF of the corresponding PDU session can serve the current location of the UE. I.e. to determine if an intermediate UPF is required. When the SMF determines that the original anchor UPF of the corresponding PDU session can serve the new location of the UE, the SMF may establish an N3 tunnel for connecting the BS to which the UE is currently accessing and the original anchor UPF in step 513. In addition, additional anchor UPFs can be used as the UL CL/BP UPFs. However, in step 515, when it is determined that the original anchor UPF cannot serve the new location of the UE, the SMF may add a new intermediate UPF between the original anchor UPF and the BS to which the UE accesses to ensure session continuity.

Fig. 5B is a flowchart of the internal operations of an SMF for releasing an additional anchor UPF when a UE leaves the service area of the additional anchor UPF for local offloading for a PDU session, according to an embodiment.

Referring to fig. 5B, when the UE moves and is informed from the AMF that the UE leaves the registration service area in step 521, the smf may determine whether the new location of the UE is an area in which the additional anchor UPF may provide service in step 523. In step 525, the SMF may allow the additional anchor UPF to remain locally offloaded for the PDU session when the new location is an area in which the additional anchor UPF may provide services. On the other hand, in step 527, when it is determined that the UE leaves the service area of the additional anchor UPF, the SMF may release the additional anchor UPF from the corresponding PDU session. In step 529, when there is an IP address linked to the released additional anchor UPF, the SMF may send a notification to prevent the UE from using the IP address. The BP or UL CL function may also be released when the additional anchor UPF performs the BP or UL CL function. Thereafter, at step 531, the smf may determine whether an intermediate UPF is still required. At step 533, the SMF may maintain an N9 tunnel between the intermediate UPF and the original anchor UPF for the PDU session while the intermediate UPF is still needed. In step 535, when the intermediate UPF is not needed, the SMF may remove the N9 tunnel between the intermediate UPF and the original anchor UPF for the PDU session and release the intermediate UPF.

In addition, when the BS to which the UE accesses changes due to the movement of the UE and thus the UE leaves the service area of the existing additional anchor UPF allocated within the specific PDU session and the UE enters the service area of the new additional anchor UPF belonging to the PDU session, the UE may release the existing additional anchor UPF in the PDU session and simultaneously add the new additional anchor UPF. The change (relocation) of the additional anchor UPF can also be applied to the following embodiments.

Fig. 5C is a flowchart of the internal operations of the UE receiving a notification when the SMF adds an additional anchor UPF for local offloading of PDU sessions and sends the notification to the UE, according to an embodiment.

In step 540, the ue may receive a notification message from the SMF regarding the addition of an additional anchor UPF for the PDU session. The notification message may include PDU session identification information (e.g., PDU session ID), additional anchor UPF identification information, and traffic rules (e.g., 5-tuple) for local offloading. In step 545, the UE that has received the notification message may update the IP address of the additional anchor UPF linked to the corresponding PDU session in its own routing table and send traffic through the IP address for the traffic matching the traffic rules for local offloading.

Fig. 6 is a flowchart of the internal operation of a UE receiving a notification when the SMF releases an additional anchor UPF for local offloading from a PDU session and sends the notification to the UE, according to an embodiment.

In step 600, the ue may receive a notification message from the SMF regarding the release of the additional anchor UPF for the PDU session. The notification message may include PDU session identification information (e.g., PDU session ID) and additional anchor UPF identification information. In step 605, the UE that has received the notification message may release the IP address of the additional anchor UPF linked to the corresponding PDU session and may no longer use the corresponding IP address for new traffic.

Fig. 7A and 7B are diagrams of an Xn-based handover procedure including a procedure of adding or releasing an additional anchor UPF to or from a PDU session when a UE performs a handover, according to an embodiment.

In fig. 7A-7B, an Xn based handover procedure is described that includes a procedure to add or release additional anchor UPF for local offloading to the PDU session when the UE in CM-CONNECTED state performs the handover. A UE in CM-CONNECTED state that may perform handshaking by establishing a NAS signaling connection with an AMF of a 5G core network may be in a state where the UE establishes at least one PDU session with at least one (original) anchor UPF including the PDU session.

Referring to fig. 7A and 7B, in step 701, when a UE in a CM-CONNECTED state performs handover from a source BS to a target BS through an Xn interface between BSs, the target BS may transmit an N2 path switching request message to the AMF. The AMF may be notified that the UE has successfully handed over to the target BS by an N2 path handover request message, and a list of PDU sessions (e.g., including PDU session IDs) successfully handed over to the target BS may be transmitted together. In addition, for a quality of service (QoS) flow handed over to the target BS, the N2 path handoff request message may also include a list of QoS flows allowed per PDU session.

Thereafter, in step 702, the amf may send an N11 message from the list of PDU sessions included in the N2 path switch request to the SMF responsible for each PDU session. The N11 message may include UE identification information, BS identification information (e.g., RAN ID or cell ID), PDU session identification information, UE location information (e.g., identification information in units of TA (tracking area) to which the target BS belongs), and access type information. When two or more PDU sessions are controlled by different SMFs, the AMFs may generate N11 messages, respectively, and transmit the generated messages to the respective SMFs. When a network entity of the 5G network provides a service interface, the N11 message may be replaced with an operation of a service provided from the AMF or the SMF.

When it is determined that there is no connectivity with the additional anchor UPF (e.g., PSA2 of fig. 7A) for local offloading with the target BS for the PDU session included in the N11 message, the SMF that has received the N11 message may release the additional anchor UPF. In particular, in an IPv6 multi-homing PDU session, the SMF may additionally generate a message for IPv6 prefix setting to invalidate the IPv6 prefix associated with the additional anchor UPF. In step 703, the smf may configure a lifetime (lifetime) of the IPv6 prefix to be invalidated to zero and send an IPv6 Router Advertisement (RA) message to the UE. The IPv6 RA message may be generated by the SMF at a point of time when DL data transmission is possible and transmitted to the UE.

In step 704a, to release the additional anchor UPF, the SMF may send an N4 session release request to the corresponding UPF. The N4 session release request may include information (e.g., N4 session ID) for identifying the PDU session of the UE and a release cause value. The release cause may indicate that the UE leaves the service area of the corresponding UPF. Information for releasing IP addresses/prefixes associated with the corresponding UPF may also be included. The UPF having received the N4 session release request may discard the remaining packets of the corresponding PDU session and delete the PDU session context, which includes all tunnel information related to the corresponding PDU session and IP address/prefix. At step 704b, when the anchor UPF successfully completes the release of the PDU session context, the anchor UPF may generate an N4 session release response to send to the SMF. The N4 session release response may include information identifying the PDU session of the UE, such as an N4 session ID like an N4 session release request message.

Meanwhile, when it is determined that a new additional anchor UPF for local offloading can be added at a new location to which the UE moves for a particular PDU session, the SMF may perform an N4 session establishment procedure with the new additional anchor UPF (e.g., PSA3 of fig. 7A). Specifically, at step 705a, the smf may send an N4 session setup request to the new additional anchor UPF. The N4 session establishment request may include information for identifying the PDU session and information about the N4 session context to be installed in the UPF. The N4 session context information may include: packet detection rules, including information about rules for identifying packets (arriving UPFs); forwarding action rules, including rules regarding packet handling (forwarding/dropping/buffering); a usage reporting rule for collecting information about packet charging and usage; and QoS enforcement rules including information about QoS requirements (e.g., maximum rate enforcement) for the corresponding PDU session. To identify the PDU session, the SMF may generate an N4 session ID and store a mapping of the PDU session and the N4 session ID. Such information may also be included when the SMF assigns a new IP address/prefix.

At step 705b, when the UPF having received the N4 session establishment request message establishes a tunnel for the corresponding PDU session and completes association establishment with the IP address/prefix, the UPF may send an N4 session establishment response to return the generated tunnel identification information (e.g., TEID (tunnel endpoint ID)) to the SMF. Identification information (e.g., N4 session ID) generated to identify the corresponding PDU session may be transmitted.

When the SMF manages a PDU session in which there are a plurality of anchor UPFs including a new additional anchor UPF, the SMF may additionally select an intermediate UPF (e.g., the target UPF of fig. 7A) that provides BP/UL CL functions for dividing or adding traffic between the BS and the anchor UPF. The intermediate UPF may be selected from the UPFs and all anchor UPFs that have connectivity with the target BS, and the selection of the UPF may be performed based on various parameters that the SMF may take into account, such as UE location information, UPF load status, UPF location information, and UPF capacity. When the SMF selects the intermediate UPF, the SMF may perform an N4 session setup procedure using the intermediate UPF and an N4 session modification procedure using the anchor UPF in order to update a data transmission path for the PDU session. In addition, the SMF may send traffic routing filtering rules (e.g., based on 5-tuple) for BP/UL CL functions to the intermediate UPF. The N4 session establishment procedure may include: step 706a, in which the SMF sends an N4 session setup request signaling to the intermediate UPF, the signaling including an identification address of the target BS, an identification address of the anchor UPF, and tunnel identification information required for N9 tunnel setup; and step 706b, wherein the intermediate UPF sends an N4 session setup response signaling to the SMF, the signaling including an identification address of the intermediate UPF and tunnel identification information required by the intermediate UPF for N9 tunnel setup with the anchor UPF and an identification address of the intermediate UPF and tunnel identification information required for N3 tunnel setup with the target BS. Thereafter, at steps 707A, 707b, 708a, and 708b, the smf may provide information for N9 tunnel establishment with an intermediate UPF (e.g., identification address and tunnel identification information of the intermediate UPF) to the anchor UPF (e.g., PSA1 and PSA3 of fig. 7A) through an N4 session modification procedure.

Next, in step 709, the smf may transmit an N2 path switch Acknowledgement (ACK) message including PDU session identification information and CN (core network) tunnel information for the N3 tunnel established between the intermediate UPF and the target BS to the AMF. In step 710, the amf may transmit N2 session information (CN tunnel identification information including a corresponding PDU session) included in the N11 message received from the target SMF to the target BS. When the AMF generates a plurality of N11 messages, the AMF may wait for a response message for a specific time in order to receive responses to all of the plurality of N11 messages and transmit the collected response message to the target BS at once.

Thereafter, the target BS may transmit release resource signaling to the source BS through the Xn interface to release the UE context in step 711. The source BS having received the release of resources may identify a successful handover to the target BS and release resources related to the UE.

When a new additional anchor UPF is added by an Xn based handover, the UE may be informed of the new IP address/prefix. At step 712, when an IPv6 multi-homing PDU session, the SMF may communicate the newly allocated IPv6 prefix to the UE over the UP path for local offload via generation of an IPv6 RA message and routing information (e.g., range information for a particular target IP address).

When the SMF changes the intermediate UFP from the source UPF to the target UFP, the SMF may generate signaling for releasing the N4 session with the source UPF at a point in time when the timer value set when the N4 session setup with the target UPF is completed at step 706b expires. At step 71a, the smf may send an N4 session release request message to the source UPF along with the release reason, and at step 713b, when the release is complete, the source UPF may generate an N4 session release response message to send it.

The names of the signal messages may be changed and the signal order may be changed or signaling may be integrated, depending on requirements such as handover performance optimization.

Fig. 8A and 8B are diagrams of an N2-based handover procedure including a procedure of adding or releasing an additional anchor UPF to or from a PDU session when a UE performs a handover, according to an embodiment.

In fig. 8A and 8B, an N2-based handover procedure is described, which includes a process of adding or releasing an additional anchor UPF to a PDU session when a UE in a CM-CONNECTED state performs handover. This process may be implemented when there is no Xn interface between the source BS and the target BS. A UE in CM-CONNECTED state with an AMF of the 5G core network maintaining a NAS signaling connection may have established a PDU session with at least one (original) anchor UPF.

Referring to fig. 8A and 8B, the source BS may select a target BS suitable for handover of the UE based on UE feedback (e.g., measurement report), and transmit a handover request message including identification information (e.g., RAN ID or cell ID) of the target BS and identification information (e.g., PDU session ID) of a PDU session currently used by the UE to the AMF in step 801. The PDU session used may be a session in which UL or DL data packets may be transmitted since a User Plane (UP) data transmission path has been established between the UE and the anchor UPF. In step 802, the amf may send a PDU session handover request message to the SMF for controlling a PDU session being used by the UE. When two or more PDU sessions are controlled by different SMFs, the AMFs may generate PDU session switching request messages and transmit the generated messages to the corresponding SMFs, respectively. When it is determined that the UE located in the target BS leaves the service area of the additional anchor UPF (PSA 2 of fig. 8A) for local offloading of the PDU session, the SMF having received the PDU session handover request message may release the additional anchor UPF. In particular, when an IPv6 multi-homing PDU session, the SMF may additionally generate a message for IPv6 prefix setting to invalidate the IPv6 prefix associated with the additional anchor UPF. The SMF may configure the lifetime of the IPv6 prefix to be invalidated to zero and send an IPv6 RA message to the UE. The SMF may generate and transmit an IPv6 RA message to the UE at a point of time when DL data transmission is possible.

To release the additional anchor UPF, the smf may send an N4 session release request to the corresponding UPF at step 803 a. The N4 session release request may include information (e.g., N4 session ID) for identifying the PDU session of the UE and a release cause value. The release cause may indicate that the UE leaves the service area of the corresponding UPF. Further, information for releasing the IP address/prefix associated with the corresponding UPF may also be included. The UPF having received the N4 session release request may discard the remaining packets of the corresponding PDU session and delete the PDU session context, which includes all tunnel information related to the corresponding PDU session and IP address/prefix. When the UPF successfully completes the release of the PDU session context, the UPF may generate an N4 session release response to send it to the SMF in step 803 b. The N4 session release response may include information identifying the PDU session of the UE, such as an N4 session ID.

Thereafter, an intermediate UPF (e.g., PSA1 of FIG. 8A) may be selected for establishing a connection between the target BS and the original anchor UPF at step 804. The intermediate UPF may be selected from the UPFs that have connectivity with both the target BS and the anchor UPF, and the selection of the UPF may be performed based on various parameters that the SMF may take into account, such as UE location information, UPF load status, UPF location information, and UPF capacity. When the intermediate UPF is selected, the smf may perform an N4 session setup procedure using the intermediate UPF in order to update the data transmission path for the PDU session in steps 805a and 805 b. The N4 session establishment procedure may include the steps of: the SMF sends an N4 session establishment request signaling to the intermediate UPF, wherein the signaling comprises an identification address of a target BS, an identification address of an anchoring UPF and tunnel identification information required by N9 tunnel establishment; and the intermediate UPF transmits an N4 session establishment response signaling to the SMF, wherein the signaling comprises an identification address of the intermediate UPF, tunnel identification information required by the intermediate UPF for establishing an N9 tunnel by using the anchor UPF, an identification address of the intermediate UMP and tunnel identification information required by establishing an N3 tunnel with the target BS.

Next, in step 806, the smf may transmit a PDU session handover response message including PDU session identification information and CN tunnel information for N3 tunnel establishment between the intermediate UPF and the target BS to the AMF.

In step 317 a, the amf may transmit a handover request message including the PDU session handover response message received from the SMF to the target BS. When a plurality of PDU session handover response messages are generated, the AMF may wait for the response messages for a specific time in order to receive all the response messages and transmit the collected response messages to the target BS at once. Upon receiving the handover request message, the target BS may perform an operation of allocating resources for an N3 tunnel established using an intermediate UPF for PDU sessions that may be allocated by the target BS. Further, the target BS may transmit a handover request ACK message including RAN tunnel information (e.g., identification address and tunnel identification information of the target BS) of the session and identification information (e.g., PDU session ID) of the corresponding session to the AMF in step 807 b. The handover request ACK message may include identification information of a corresponding session for the PDU session, which the target BS cannot allow, and a cause indicator.

Upon receiving the handover request ACK message, the amf generates and transmits a modify PDU session request message to the SMF for controlling a corresponding PDU session based on the identification information of the PDU session in step 808. The modify PDU session request message may include information, which varies depending on whether the target BS allows the PDU session. For PDU sessions allowed by the target BS, RAN tunnel information established by the target BS for the N3 tunnel may be included. Thereafter, in steps 809a and 809b, the smf may provide RAN tunnel information to the intermediate UPF through an N4 session modification procedure and complete the N3 tunnel establishment. In addition, when the N4 session establishment procedure is first performed in steps 805a and 805b, the SMF may perform the N4 session establishment procedure instead of the N4 session modification procedure. Meanwhile, for PDU sessions not allowed by the target BS, the SMF may perform a request for releasing the N3 and N9 tunnel resources set in steps 805a and 805b to the intermediate UPF. The SMF may additionally perform a PDU session release procedure for PDU sessions not allowed by the target BS.

Thereafter, the smf may send a modify PDU session response message to the AMF in step 810. The amf may then transmit a handover command message to the source BS in step 811. The handover command message may include session identification information allowed by the target BS and session identification information not allowed by the target BS, respectively. When it is determined that the handover to the target BS is to be performed, the source BS transmits a handover command message to the UE in step 812, and the UE performs synchronization with the target BS, and transmits a handover confirm message indicating a successful handover to the target BS in step 813.

Thereafter, in step 814, the target BS transmits a handover notification message including identification information (e.g., TAI (tracking area identifier)) and BS identification information (e.g., RAN ID or cell ID) in units of TAs to which the target BS belongs to the AMF. In step 815, when the AMF having received the handover notification message manages the active/inactive state according to the presence or absence of the UP connection of each PDU session of the UE, the AMF transmits a handover complete message to the SMF corresponding to the PDU session to the active PDU session. Meanwhile, when the AMF does not manage the UP connection state for each PDU session of the UE, the handover notification message may include identification information (e.g., PDU session ID) of the PDU session for which the target BS establishes the UP connection. The AMF may then transmit a handover complete message to the corresponding SMF through the PDU session identification information.

The SMF that has received the handover complete message may identify a successful handover. The SMF may then determine whether a new additional anchor UPF for local offloading may be added at the current location of the UE for each PDU session. When a new additional anchor UPF (e.g., PSA3 of fig. 8B) can be added, the SMF can perform an N4 session establishment procedure with the corresponding UPF. Specifically, at step 816a, the smf may send an N4 session setup request to the UPF. Such information may be included when the SMF assigns a new IP address/prefix. At step 816b, when the UPF having received the request message tunnels the corresponding PDU session and completes the establishment of the association with the IP address/prefix, the UPF may send an N4 session establishment response to the SMF to give an answer. Identification information (e.g., N4 session ID) generated to identify the corresponding PDU session may be transmitted. Alternatively, the N4 session ID may be first generated by the SMF and then sent to the UPF.

When the SMF manages a PDU session in which there are a plurality of anchor UPFs including a new additional anchor UPF, the SMF may additionally select an intermediate UPF that provides BP/UL CL functions for dividing or adding traffic between the BS and the anchor UPF. In steps 817a and 817B, when an intermediate UFP (e.g., the target UPF of fig. 8B) that has been included in the PDU session can perform the BP/UL CP function, the SMF can perform an N4 session modification procedure using the intermediate UPF. The SMF may transmit not only information required for N3 tunnel establishment with the target BS to the intermediate UPF, but also information required for N9 tunnel establishment with the new additional anchor UPF to the intermediate UPF. Similarly, the intermediate UPF may return information needed for N9 tunnel establishment to be sent to the new anchor UPF. In addition, the SMF may send routing filter rules (e.g., based on 5-tuple) for BP/UL CL functions to the intermediate UPF. Thereafter, at steps 818a and 81b, the smf may perform an N4 session modification procedure to send N9 tunnel setup information received from the intermediate UPF for the N9 tunnel established with the new additional anchor UPF.

In addition, when the SMF changes the intermediate UFP from the source UPF to the target UFP, the SMF may generate signaling for releasing the N4 session with the source UPF when the timer value set at the point of time of the N4 session establishment with the target UPF is completed in step 805b or 809 b. At step 820a, the smf may send an N4 session release request message to the source UPF along with the release reason, and at step 820b, when the release is complete, the source UPF may generate an N4 session release response message to give an answer.

In addition, the smf may send an ACK to the AMF in response to the handover complete message in step 819. In step 821a, the AMF having received the ACK may transmit a UE context release order message to the source BS in order to release the UE context in the source BS. In step 821b, after releasing the UE context, the source BS returns a UE context release complete message to the AMF.

When a new additional anchor UPF is added by an N2 based handover, the UE may be informed of the new IP address/prefix. In step 822, when an IPv6 Multi-homed PDU session (IPv 6 Multi-homed PDU session), the SMF may generate an IPv6 router advertisement and locally offloaded routing information for the newly allocated IPv6 prefix and send it to the UE through the UP path.

The names of the signaling messages used may be changed according to requirements such as handover performance optimization, and the order of some signaling or integrated signaling may be changed.

Fig. 9A and 9B are diagrams of an N2-based handover procedure including a procedure of adding or releasing an additional anchor UPF to or from a PDU session when a UE performs a handover, according to an embodiment.

In fig. 9A and 9B, an N2-based handover procedure is described, which includes a procedure of adding or releasing an additional anchor UPF to a PDU session when a UE in a CM-CONNECTED state performs handover. Referring to fig. 9A and 9B, the procedure is different in that after receiving a handover request ACK from the target BS in step 906B, the operation of releasing the additional anchor UPF in the PDU session established by the UE in steps 908a and 908B is performed. The detailed call flow is shown in fig. 9A and 9B. The operations from step 901 to step 922 are the same as those corresponding to fig. 8A and 8B, except that the point in time at which the operation of releasing the additional anchor UPF is performed is different.

Fig. 10A and 10B are diagrams of an N2-based handover procedure including a procedure of adding or releasing an additional anchor UPF to or from a PDU session when a UE performs a handover, according to an embodiment.

In fig. 10A and 10B, an N2-based handover procedure is described, which includes a procedure of adding or releasing an additional anchor UPF to a PDU session when a UE in a CM-CONNECTED state performs handover. Referring to fig. 10A and 10B, the procedure is different in that an existing additional anchor UPF is released and an additional anchor UPF is added for a PDU session successfully established by the BS at a point of time when the UE completes handover to the target BS in steps 1015a and 1015B. The detailed call flow is shown in fig. 10A and 10B. The operations from step 1001 to step 1022 are the same as those corresponding to the steps of fig. 8A and 8B or fig. 9A and 9B, except that the point in time at which the operation of releasing the additional anchor UPF is performed is different.

Fig. 11A and 11B are diagrams of a service request procedure including a process of adding a new additional anchor UPF to an already established PDU session or releasing a conventionally added additional anchor UPF when a UE in a CM-IDLE state performs a service request, according to an embodiment.

In fig. 11A and 11B, a service request procedure is described, including a process of adding an additional anchor UPF for local offloading to a PDU session that the UE has established, or releasing the additional anchor UPF that has been conventionally added when the UE in the CM-IDLE state performs a service request.

Referring to fig. 11A and 11B, in step 1101, when the UE is required to activate an UP path of a specific PDU session due to generation of uplink data traffic, the UE transmits a service request message together with identification information (e.g., PDU session ID) of the corresponding PDU session through NAS signaling. In step 1102, NAS signaling is sent to the AMF via the RAN, and the RAN may send its location information and identification information (including cell ID, RAN ID, identification information in tracking area to which the BS belongs, and access type) together with NAS signaling through an N2 message. In step 1103, the AMF having received the N2 message may perform authentication and encryption procedures with the UE that has sent NAS signaling as needed.

Thereafter, in step 1104, the upf transmits an N11 message for activating an UP transmission path of the PDU session to the SMF managing the corresponding PDU session based on the PDU session identification information included in the service request message. Here, activation refers to re-establishing the UP transmission path that has been released (i.e., allocating resources for tunnel establishment and exchanging information). Further, when a network entity of the 5G network provides a service interface as shown in fig. 11A and 11B, an operation of a service provided by an AMF or an SMF may be utilized instead of the N11 message.

The SMF having received the N11 message may determine whether the UE enters a service area of an additional anchor UPF for local offloading or leaves the service area of the additional anchor UPF for a corresponding PDU session based on identification information and location information of the RAN to which the UE currently accesses. The additional anchor UPF may be added when it is determined that the location of the UE accessing the BS belongs to the service area of the additional anchor UPF. Further, the additional anchor UPF may be released when it is determined that the location of the UE accessing the BS leaves the service area of the additional anchor UPF.

In step 1105a, to add an additional anchor UPF, the SMF may send an N4 session setup request to the corresponding UPF. The N4 session establishment request may include PDU session identification information (e.g., N4 session ID) of the UE and information about the N4 session context to be installed in the UPF. The N4 session context information may include: packet detection rules, including information about rules for identifying packets arriving at the UPF; forwarding action rules, including rules regarding packet handling (forwarding/dropping/buffering); a usage reporting rule for collecting information about packet charging and usage; and QoS enforcement rules including information about QoS requirements (e.g., maximum rate enforcement) for the corresponding PDU session. Further, such information may be included together when the SMF assigns a new IP address/prefix. In step 1105b, when the UPF having received the N4 session establishment request message establishes a tunnel for the corresponding PDU session and completes the establishment of the association with the IP address/prefix, the UPF may send an N4 session establishment response to the SMF to return the generated tunnel identification information (e.g., TEID). At this time, identification information (e.g., N4 session ID) generated to identify the corresponding PDU session may be transmitted.

In step 1105a, to release the additional anchor UPF, the SMF may send an N4 session release request to the corresponding UPF. The N4 session release request may include information (e.g., N4 session ID) for identifying the PDU session of the UE and a release cause value. The release cause may indicate that the UE leaves the service area of the corresponding UPF. Further, information for releasing the IP address/prefix associated with the corresponding UPF may also be included. The UPF having received the N4 session release request may discard the remaining packets of the corresponding PDU session and delete the PDU session context, which includes all tunnel information related to the corresponding PDU session and IP address/prefix. Packet detection rules, forwarding action rules, usage reporting rules, and QoS enforcement rules associated with the PDU session may also be deleted. In step 1105b, when the UPF successfully completes the release of the PDU session context, the UPF may generate an N4 session release response to send to the SMF. The N4 session release response may include information identifying the PDU session of the UE, such as an N4 session ID.

Specifically, when an additional anchor UPF is added to the IPv6 multi-homing PUD session, the SMF may send an IPv6 prefix associated with the additional anchor UPF to the UE in addition to the PDU session, step 1105 c. The SMF generates an RA message to transmit an IPv6 prefix, and the UE may also transmit routing information (e.g., a destination address) for appropriately selecting the IPv6 allocated to the existing PDU session and the newly allocated IPv6 prefix. For example, the RA message may include domain information (e.g., FQDN (fully qualified domain name)) or IP address range (e.g., based on 5-tuple) corresponding thereto for content that a locally offloaded local server may download. The routing information may be provided to the SMF in advance or may be provided dynamically from the PCF that provides the session policy. An IPv6 RA message may be sent from the SMF to the UE via the additional anchor UPF.

Meanwhile, when the additional anchor UPF is released, the SMF may additionally generate a message for configuring the IPv6 prefix to invalidate the IPv6 prefix associated with the additional anchor UPF. In step 1105c, to configure the lifetime of the IPv6 prefix to be invalidated to zero and send an IPv6 RA message to the UE, the configuration of the IPv6 prefix may first be sent to the remaining anchor UPF (original PSA of fig. 11A and 11B). When the configuration of the invalid IPv6 prefix is not transmitted to the UE, the SMF may generate an RA message for reconfiguring the IPv6 prefix associated with the remaining anchor UPF (original PSA of fig. 11A and 11B) in the PDU session, and transmit the generated RA message to the UE. The IPv6 RA message may include routing information of the IPv6 prefix that may still be used and routing rules that preferentially use the IPv6 prefix. The default routing path may be configured or may be configured to have a higher priority than the IPv6 prefix determined to be invalid.

When an additional anchor UPF is added, a PIv RA message may be generated by the SMF and sent to the UE via the additional anchor UPF. However, when the additional anchor UPF is released, a PIv RA message may be generated by the SMF and sent to the UE via the additional anchor UPF or the existing original anchor UPF. When the data transmission path of the PDU session is not established, the IPv6 RA message may be buffered in the anchor UPF or may be forwarded to an intermediate UPF, which may perform buffering. Then, at a point in time when DL data can be transmitted to the UE, the IPv6 RA message may reach the UE from the UPF buffering the IPv6 RA message through a data transmission path of the corresponding PDU session. Further, when the additional anchor UPF is released, an IPv6 RA message may be first generated and transmitted to the UE before an N4 session release procedure with the additional anchor UPF. As described above, when the data transmission path of the PDU session is not established, the IPv6 RA message has been previously transmitted to the additional anchor UPF and buffered.

In step 1106, when the SMF manages a PDU session in which there are multiple anchor UPFs including a new additional anchor UPF, the SMF may additionally select an intermediate UPF (e.g., new I-UPF in fig. 11A and 11B) that provides BP/UL CL functions for dividing or adding traffic between the BS and the anchor UPF. Hereinafter, since the operations related to adding a new intermediate UPF are similar to the processes of steps 706a and 706b, a detailed description thereof will be omitted. In addition, when additional anchor UPFs added to the PDU session can directly provide BP or UL CL functionality, the process of selecting a new intermediate UPF can be omitted.

Meanwhile, when the additional anchor UPF is released, when the SMF determines that there is connectivity between the BS and the remaining anchor UPF (original PSA of fig. 11A and 11B) and there is an intermediate UPF (old I-UPF of fig. 11A and 11B) conventionally established for the PDU session, the SMF may configure a timer for performing a procedure of releasing it. In addition, when the SMF knows that DL data arrives at the corresponding PDU session including the IPv6 RA message (e.g., when the SMF receives a data notification from the UPF), the SMF can perform the N4 session modification procedure with the remaining anchor UPF. Through the N4 session modification procedure, a tunnel may be established through which the existing intermediate UPF (old I-UPF of fig. 11A and 11B) forwards buffered data to the anchor UPF (original PSA of fig. 11A and 11B). Thereafter, the SMF may provide tunnel information for forwarding the buffered data by performing an N4 session modification procedure using the existing intermediate UPF. Existing intermediate UPFs may send buffered data directly through a data forwarding tunnel established by the anchor UPF. The SMF may additionally configure a timer for releasing the data forwarding tunnel. Meanwhile, in step 1106, when the SMF determines that there is no connection between the BS for the PDU session and the remaining anchor UPF (original PSA of fig. 11A and 11B) (e.g., when a direct N3 tunnel cannot be established), the SMF may newly select an intermediate UPF for establishing a connection with the anchor UPF. When an intermediate UPF (old I-UPF of FIGS. 11A and 11B) is already included in the PDU session, a new intermediate UPF (new I-UPF in FIGS. 11A and 11B) can be selected only when connectivity exists between the BS and the intermediate UPF.

The new intermediate UPF may be selected from the UPFs that have connectivity with both the BS and the anchor UPF, and the selection of the UPF may be made based on various parameters that the SMF may take into account, such as UE location information, UPF load status, UPF location information, and UPF capacity. When the SMF selects an intermediate UPF, the SMF may perform an N4 session setup procedure using the intermediate UPF in steps 1107a and 1107b, and perform an N4 session modification procedure using the anchor UPF in steps 1108a and 1108b, so as to update the UP transmission path for the PDU session. When there are multiple anchor UPFs in the PDU session, including additional anchor UPFs, the SMF may use all of them to perform the N4 session modification procedure. The N4 session establishment procedure may include the steps of: the SMF sends an N4 session establishment request signaling comprising an identification address of the anchoring UPF and tunnel identification information required by the N9 tunnel establishment to the intermediate UPF; and the intermediate UPF sends an N4 session establishment response signaling to the SMF, the signaling including an identification address of the intermediate UPF and tunnel identification information required by the intermediate UPF for the N9 tunnel established with the anchor UPF. Further, when DL data is generated, the SMF may additionally request establishment of a tunnel to forward the buffered data. Thereafter, through the N4 session modification procedure, the SMF may provide information for the N9 tunnel established with the intermediate UPF (e.g., identification information of the intermediate UPF and tunnel identification information) and information about the buffered data forwarding tunnel to the anchor UPF. At step 1110, the anchor UPF that has received information about the data forwarding tunnel may forward the buffered data directly to the intermediate UPF.

When an intermediate UPF has been included in the PDU session, the SMF may perform operations related to N4 session modification using the existing intermediate UPF instead of the anchor UPF (i.e., steps 1108a and 1108b replace steps 1109a and 1109 b).

Next, in step 1111, the smf may transmit an N11 message including PDU session identification information and CN tunnel information for the N3 tunnel established between the intermediate UPF and the BS to the AMF. Further, when a network entity of the 5G network provides a service interface as shown in fig. 11A and 11B, the N11 message may be replaced with an operation of a service provided by the SMF.

Thereafter, the amf transmits an N2 request message including CN tunnel information and PDU session identification information received from the N11 message to the BS in step 1112. The AMF may also send NAS messages corresponding to service acceptance. The BS, having received the message, allocates resources for the N3 tunnel established for the corresponding session, and transmits the NAS message to the UE. In step 1113, the bs and the UE may perform RRC (radio resource control) connection reconfiguration to establish a Data Radio Bearer (DRB) conforming to the QoS rule of the corresponding session. When the DRB establishment is completed, the UE may transmit uplink data to the BS. In step 1114, the bs may transmit an N2 request ACK message including RAN tunnel identification information allocated for the N3 tunnel to the AMF.

Thereafter, in step 1115, the amf may transmit a Session Management (SM) request message including RAN tunnel information for N3 tunnel establishment included in the N2 request ACK message to the corresponding SMF. Further, when a network entity of the 5G network provides a service interface as shown in fig. 11A and 11B, an operation of a service provided by an AMF or an SMF may be used instead of the SM request message.

Thereafter, at step 1116, the smf may perform a signaling exchange with the PCF to apply dynamic policies to the PDU session and register the UE location as needed.

Next, at steps 1117a and 1117b, the smf may perform an N4 session modification procedure to send RAN tunnel information to the intermediate UPF. When there is no change in the intermediate UPF, the process can be performed with the old I-UPF. Transmission of buffered DL data including an IPv6 RA message may begin.

Thereafter, the SMF may send an ACK of the SM request message of step 1115 to the AMF in step 1118. Further, when a network entity of the 5G network provides a service interface as shown in fig. 11A and 11B, an operation of a service provided by an AMF or an SMF may be used instead of a response to the SM request message.

In steps 1119a and 1119b, when a data forwarding tunnel is established by the SMF, an N4 session modification procedure for releasing the forwarding tunnel may be performed at a point of time when a timer configured at the time of establishing the tunnel expires.

In steps 1120a and 1120b, when the intermediate UPF is changed from the old I-UPF to the new I-UPF by the SMF, if a timer configured to release the old UPF expires at a point of time when the new I-UPF is set, the SMF may perform an N4 session release procedure using the old I-UPF in order to release the PDU session context of the old I-UPF.

Similarly, the names of the signaling messages used may be changed and the order of some of the signaling may be changed or signaling may be integrated, depending on requirements such as service request procedure performance optimization.

Fig. 12A and 12B are diagrams of a service request procedure including a procedure of adding a new additional anchor UPF to an inactive PDU session or releasing a conventionally added additional anchor UPF when a UE in a CM-CONNECTED state performs a service request for a PDU session without an UP connection, according to an embodiment.

In fig. 12A, 12B, and 13, the service request procedure includes the following processes: when a UE in the CM-CONNECTED state performs a service request for an invalid PDU session without an UP connection, a procedure of adding an additional anchor UPF for local offloading to the PDU session or releasing the conventionally added additional anchor UPF is added.

Referring to fig. 12A and 12B, when the UE is required to configure an UP path of a specific PDU session due to generation of uplink data traffic, the UE transmits a service request message together with identification information (e.g., PDU session ID) of the corresponding PDU session through NAS signaling in step 1201. In step 1202, NAS signaling is sent to the AMF via the RAN, and the RAN may send its location information together with identification information (including cell ID, RAN ID, identification information in units of tracking area to which the BS belongs, and access type) and NAS signaling through N2 message.

Then, in step 1203, the amf transmits an N11 message for activating the UP transmission path of the PDU session to the SMF managing the corresponding PDU session based on the PDU session identification information included in the service request message. Here, activation refers to re-establishing the UP transmission path that has been released (i.e., allocating resources and exchanging information for tunnel establishment). Further, when a network entity of the 5G network provides a service interface as shown in fig. 12A and 12B, an operation of a service provided by an AMF or an SMF may be used instead of the N11 message.

The SMF having received the N11 message may determine whether the UE enters a service area of an additional anchor UPF for local offloading or leaves the service area of the additional anchor UPF for a corresponding PDU session based on identification information and location information of the RAN to which the UE currently accesses. The additional anchor UPF may be added when it is determined that the location of the UE accessing the BS belongs to the service area of the additional anchor UPF. On the other hand, when it is determined that the location of the UE accessing the BS leaves the service area of the additional anchor UPF, the additional anchor UPF may be released.

To release the additional anchor UPF, the smf may send an N4 session setup request to the corresponding UPF at step 120a. The N4 session establishment request may include PDU session identification information (e.g., N4 session ID) of the UE and information about the N4 session context to be installed in the UPF. The N4 session context information may include: packet detection rules, including information about rules for identifying packets arriving at the UPF; forwarding action rules, including rules regarding packet handling (forwarding/dropping/buffering); a usage reporting rule for collecting information about packet charging and usage; and QoS enforcement rules including information about QoS requirements (e.g., maximum rate enforcement) for the corresponding PDU session. Further, such information may be included together when the SMF assigns a new IP address/prefix. At step 1204b, when the UPF having received the N4 session establishment request message establishes a tunnel for the corresponding PDU session and completes association establishment with the IP address/prefix, the UPF may send an N4 session establishment response to return the generated tunnel identification information (e.g., TEID). Identification information (e.g., N4 session ID) generated to identify the corresponding PDU session may be transmitted.

To release the additional anchor UPF, the smf may send an N4 session release request to the corresponding UPF at step 120a. The N4 session release request may include information (e.g., N4 session ID) for identifying the PDU session of the UE and a release cause value. The release cause may indicate that the UE leaves the service area of the corresponding UPF. Further, information for releasing the IP address/prefix associated with the corresponding UPF may also be included. The UPF receiving the N4 session release request may discard the remaining packets of the corresponding PDU session and delete the PDU session context, which includes all tunnel information related to the corresponding PDU session and IP address/prefix. Packet detection rules, forwarding action rules, usage reporting rules, and QoS enforcement rules associated with the PDU session may also be deleted. At step 1204b, when the UPF successfully completes the release of the PDU session context, the UPF may generate an N4 session release response to send to the SMF. The N4 session release response may include information identifying the PDU session of the UE, such as an N4 session ID.

In particular, when an additional anchor UPF is added to the IPv6 multi-homing PDU session, the SMF may send an IPv6 prefix associated with the additional anchor UPF to the UE in addition to the PDU session at step 1204 c. The SMF generates an RA message to transmit an IPv6 prefix, and the UE may also transmit routing information (e.g., a destination address) for appropriately selecting the IPv6 allocated to the existing PDU session and the newly allocated IPv6 prefix. The RA message may include domain information (e.g., FQDN) for content that the local server for local offload may download or an IP address range (e.g., based on 5-tuple) corresponding thereto. The routing information may be provided to the SMF in advance or may be provided dynamically from the PCF that provides the session policy. An IPv6 RA message may be sent from the SMF to the UE via the additional anchor UPF.

Meanwhile, when the additional anchor UPF is released, the SMF may additionally generate a message for establishing an IPv6 prefix to invalidate the IPv6 prefix associated with the additional anchor UPF. In step 1204c, to configure the lifetime of the IPv6 prefix to be invalidated to zero and send the IPv6 RA message to the UE, the configuration of the IPv6 prefix may first be sent to the remaining anchor UPF (original PSA of fig. 12A and 12B). In addition, when the configuration of the invalid IPv6 prefix is not transmitted to the UE, the SMF may generate an RA message for reconfiguring the IPv6 prefix associated with the remaining anchor UPF (original PSA of fig. 12A and 12B) in the PDU session, and transmit the generated RA message to the UE. The IPv6 RA message may include routing information of the IPv6 prefix that may still be used and routing rules that preferentially use the IPv6 prefix. The default routing path may be configured or may be configured to have a higher priority than the IPv6 prefix determined to be invalid.

When an additional anchor UPF is added, a PIv RA message may be generated by the SMF and sent to the UE via the additional anchor UPF. However, when the additional anchor UPF is released, a PIv RA message may be generated by the SMF and sent to the UE via the additional anchor UPF or the existing original anchor UPF. When the data transmission path of the PDU session is not established, the IPv6 RA message may be buffered in the anchor UPF or may be forwarded to the intermediate UPF performing the buffering. Then, at a point in time when DL data can be transmitted to the UE, the IPv6 RA message may arrive at the UE from the UPF, which buffers the IPv6 RA message through the data transmission path of the corresponding PUD session. The IPv6 RA message may be first sent to the UE before the N4 session release procedure with the additional anchor UPF. As described above, when the data transmission path of the PDU session is not established, the IPv6 RA message has been previously transmitted to the additional anchor UPF and buffered.

In step 1205, when the SMF manages a PDU session in which there are multiple anchor UPFs including a new additional anchor UPF, the SMF may additionally select an intermediate UPF (e.g., new I-UPF of fig. 12A and 12B) that provides BP/UL CL functions for dividing or adding traffic between the BS and the anchor UPF to which the UE accesses. Hereinafter, since the operations related to adding a new intermediate UPF are similar to the processes of steps 706a and 706b, a detailed description thereof will be omitted. In addition, when additional anchor UPFs added to the PDU session can directly provide BP or UL CL functionality, the process of selecting a new intermediate UPF can be omitted.

Meanwhile, when the additional anchor UPF is released, when the SMF determines that there is connectivity between the BS and the remaining anchor UPF (original PSA of fig. 12A and 12B) and there is an intermediate UPF (old I-UPF of fig. 12A and 12B) conventionally established for the PDU session, the SMF may configure a timer for performing a procedure of releasing it. In addition, when the SMF knows that DL data arrives at the corresponding PDU session including the IPv6 RA message (e.g., when the SMF receives a data notification from the UPF), the SMF can perform the N4 session modification procedure with the remaining anchor UPF. Through the N4 session modification procedure, a tunnel may be established through which the existing intermediate UPF (old I-UPF of fig. 12A and 12B) forwards buffered data to the anchor UPF (original PSA of fig. 11A and 11B). Thereafter, the SMF may provide tunnel information for forwarding the buffered data by performing an N4 session modification procedure using the existing intermediate UPF. Existing intermediate UPFs may send buffered data directly through a data forwarding tunnel established by the anchor UPF. The SMF may additionally configure a timer for releasing the data forwarding tunnel.

Meanwhile, when the SMF determines that there is no connection between the BS for the PDU session and the remaining anchor UPF (original PSA of fig. 12A and 12B) (e.g., when a direct N3 tunnel cannot be established), the SMF may newly select an intermediate UPF for establishing a connection between the BS and the anchor UPF in step 1205. When an intermediate UPF (the old I-UPF of FIGS. 11A and 11B) is already included in the PDU session, a new intermediate UPF (the new I-UPF of FIGS. 12A and 12B) can be selected only when there is no connection between the BS and the intermediate UPF.

The new intermediate UPF may be selected from the UPFs that have connectivity with both the BS and the anchor UPF, and the selection of the UPF may be made based on various parameters that the SMF may take into account, such as UE location information, UPF load status, UPF location information, and UPF capacity. When the SMF selects an intermediate UPF, the SMF may perform an N4 session setup procedure using the intermediate UPF in steps 1206a and 1206b, and perform an N4 session modification procedure using the anchor UPF in steps 1207a and 1207b, so as to update the UP transmission path for the PDU session. When there are multiple anchor UPFs in the PDU session, including additional anchor UPFs, the SMF may utilize all of them to perform the N4 session modification procedure. The N4 session establishment procedure may include the steps of: the SMF sends an N4 session establishment request signaling comprising an identification address of the anchoring UPF and tunnel identification information required by the N9 tunnel establishment to the intermediate UPF; and the intermediate UPF sends an N4 session establishment response signaling to the SMF, the signaling including an identification address of the intermediate UPF and tunnel identification information required by the intermediate UPF for the N9 tunnel established with the anchor UPF. Further, when DL data is generated, the SMF may additionally request establishment of a tunnel to forward the buffered data. Thereafter, through the N4 session modification procedure, the SMF may provide information for the N9 tunnel established with the intermediate UPF (e.g., identification information of the intermediate UPF and tunnel identification information) and information about the buffered data forwarding tunnel to the anchor UPF. In step 1209, the anchor UPF that has received information about the data forwarding tunnel may forward the buffered data directly to the intermediate UPF.

When an intermediate UPF has been included in the PDU session, the SMF may perform operations related to N4 session modification using the existing intermediate UPF instead of the anchor UPF (i.e., steps 1207a and 1207b replace steps 1208a and 1208 b).

Next, in step 1210, the smf may transmit an N11 message including PDU session identification information and CN tunnel information for the N3 tunnel established between the intermediate UPF and the BS to the AMF. Further, when a network entity of the 5G network provides a service interface as shown in fig. 12A and 12B, the N11 message may be replaced with an operation of a service provided by the SMF.

Thereafter, the amf transmits an N2 request message including CN tunnel information and PDU session identification information received from the N11 message to the BS in step 1211. The AMF may also send NAS messages corresponding to service acceptance. The BS, having received the message, allocates resources for the N3 tunnel established for the corresponding session, and transmits the NAS message to the UE. At this time, the bs and the UE may perform RRC connection reconfiguration to establish a DRB conforming to the QoS rule of the corresponding session in step 1212. When the DRB establishment is completed, the UE may transmit uplink data to the BS. In step 1213, the bs may transmit an N2 request ACK message including RAN tunnel identification information allocated for the N3 tunnel to the AMF.

Thereafter, the amf may transmit an SM request message including RAN tunnel information for N3 tunnel establishment included in the N2 request ACK message to the corresponding SMF in step 1214. Further, when a network entity of the 5G network provides a service interface as shown in fig. 12A and 12B, an operation of a service provided by the SMF may be used instead of the SM request message.

Thereafter, at step 1215, the smf may perform a signaling exchange with the PCF to apply dynamic policies to the PDU session and register the UE location as needed.

Next, at steps 1216a and 1216b, the smf may perform an N4 session modification procedure to send the RAN tunnel information to the intermediate UPF. When there is no change in the intermediate UPF, the process can be performed with the old I-UPF. Transmission of buffered DL data including an IPv6 RA message may begin.

Thereafter, at step 1217, the smf may transmit an ACK of the SM request message at step 1214 to the AMF. Further, when a network entity of the 5G network provides a service interface as shown in fig. 12A and 12B, an operation of a service provided by the SMF may be used instead of a response to the SM request message.

In steps 1218a and 1218b, when a data forwarding tunnel is established by the SMF, an N4 session modification procedure for releasing the forwarding tunnel may be performed when a timer set when the tunnel is established expires.

In steps 1219a and 1219b, when the intermediate UPF is changed from the old I-UPF to the new I-UPF by the SMF, if a timer configured to release the old UPF expires at a point in time when the new I-UPF is set, the SMF may perform an N4 session release procedure using the old I-UPF in order to release the PDU session context of the old I-UPF.

Fig. 13 is a diagram of an NW-triggered service request procedure in a 5G cellular network according to an embodiment.

Additional anchor UPFs may be added to or released from an already established PDU session for local offloading based on NW-triggered service request procedures. As shown in fig. 13, when downlink data traffic arrives from a DN (e.g., the internet or a local server), a UE in a CM-IDLE state may transition to a CM-CONNECTED state, or may perform a procedure required to transmit DL traffic in a state in which the UE is in the CM-CONNECTED state, but an UP connection of a PDU session to which the DL traffic belongs is deactivated.

Specifically, the upf may receive DL traffic in step 1301, and in step 1302a, the upf may transmit DL data notification signaling indicating that DL data arrives at the SMF managing the corresponding PDU session. To manage multiple PDU sessions for the same UE, the SMF may also include the ID of the PDU session. In step 1302b, the upf may receive an ACK for DL data notification signaling from the SMF. In step 1303a, a DL data notification message may be forwarded from the SMF to the AMF that manages mobility of the UE through an N11 message. In step 1303b or 1306, the smf may receive an ACK for the N11 message from the AMF. Thereafter, the AMF may store the SMF transmitting the DL data notification and the PDU session identification information. In step 1303c, when the SMF receives information from the AMF indicating that the UE is not reachable or is reachable only for the UE that supervises the priority service, the SMF may send a failure indication to the UPF.

In steps 1304 and 1305, the amf may perform paging for the UE in the CM-IDLE state, and thus in step 1307, the UE may perform the service request described in the sixth embodiment in response to the paging. The SMF, having identified the location of the UE, may determine whether the UE enters or leaves the service area of the additional anchor UPF for the local offload. When it is determined that the location of the UE belongs to the service area of the additional anchor UPF, the additional anchor UPF may be added. On the other hand, when it is determined that the location of the UE leaves the service area of the additional anchor UPF, traffic received from the additional anchor UPF may be dropped, and a procedure for releasing the additional anchor UPF may be performed.

When the UE is in the CM-CONNECTED state, the AMF may transmit location information of the UE to the SMF without paging. The SMF, having identified the location of the UE, may determine whether the UE enters or leaves the service area of the additional anchor UPF for the local offload. When it is determined that the location of the UE belongs to the service area of the additional anchor UPF, the additional anchor UPF may be added. On the other hand, when it is determined that the location of the UE leaves the service area of the additional anchor UPF, traffic received from the additional anchor UPF may be dropped, and a procedure for releasing the corresponding UPF may be performed.

The procedure in which the SMF adds or releases an additional anchor UPF to or from the PDU session established by the UE may be performed based on the processing according to the sixth embodiment of the seventh embodiment.

Fig. 14A and 14B are diagrams of a registration procedure in a 5G cellular network according to an embodiment.

In fig. 14A and 14B, a registration procedure in a 5G cellular network is described. The UE may perform a registration procedure using the 5G network to acquire a right to use a service provided by the 5G cellular network, detect a location of the UE in the 5G network, or provide the service. Registration may be performed through a registration procedure shown in fig. 14A and 14B, in which initial registration may be performed when registration is initially performed in a 5G network, mobility registration may be performed when a UE in a CM-IDLE state leaves an allocated registration area (e.g., a list of areas in TA), and periodic registration may be performed when a periodic registration timer expires. To perform registration in the network, the UE transmits a registration request message to the network in step 1401, and the (R) AN selects a new AMF in step 1402, and transmits the registration request message to the AMF in step 1403. In steps 1404 to 1405, the AMF may receive information about the UE from an old AMF already in charge of the UE. When the new AMF does not receive a UE ID such as a subscriber permanent identifier (SUPI) from the old AMF, the new AMF may request the UE ID from the UE and receive it from the UE in steps 1406 to 1407. In steps 1408 to 1410, the new AMF selects AUSF (authentication server function) to authenticate the UE and generate a security key and perform authentication/security procedures. In steps 1411 to 1412, the new AMP may check the Permanent Equipment Identity (PEI) of the UE through an Equipment Identifier Repository (EIR). In steps 1413 to 1414c, the new AMF selects UDM (user data management) to load the subscription information of the UE and loads the UE subscription information from the UDM. Further, in steps 1415 to 1417, the new AMF selects the PCF to load network policy information of the UE and load network policy information of the UE. When the AMF changes and the old AMF has an association with a UE of the N3IWF (non-3 GPP interworking function), the new AMF informs the N3IWF about the change of AMF and releases the NGAP (NG application protocol) UE association with the old AMF in steps 1418 to 1419. At step 1420, the association between the old AMF and the PCF is deleted. When all the procedures are successfully performed, the ue transmits a registration accept message to inform that registration is successful in steps 1421 to 1422.

When mobility registration or periodic registration is performed, some of the procedures shown in fig. 14A and 14B may be omitted. Through the registration process, the UE may update its own capability information in the 5G network and negotiate various parameters with the 5G network.

Fig. 15 is a diagram of a registration procedure including a procedure of releasing a conventionally added additional anchor UPF from an already established PDU session when a UE in a CM-IDLE state performs the registration procedure, according to an embodiment.

In fig. 15, a registration procedure is described, which includes a process of releasing a PDU session conventionally added to an additional anchor UPF of an already established PDU session when a UE in a CM-IDLE state performs the registration procedure. As shown in fig. 15, a process may be additionally performed during the process (step 1501) of performing the registration process shown in fig. 12A, 12B, and 13.

First, the AMF may provide a service informing the UE of the location change. The SMF managing the PDU session of the UE may re-subscribe to the notification service when an additional anchor UPF is added to the PDU session, or the subscription information may be updated to receive the notification when the SMF has subscribed to and the location of the UE changes based on the service area of the additional anchor UPF. When the location of the UE leaves the service area of the additional anchor UPF, the AMF may notify the SMF of the event along with the new location information of the UE.

In step 1502, the amf may send a notification of the location change of the UE to the SMF via an N11 message. Further, when a network entity of the 5G network provides a service interface as shown in fig. 14A and 14B, an operation of a service provided by the AMF (e.g., step 1417 of fig. 14B) may be used instead of the N11 message.

The SMF having received the N11 message may determine whether the UE leaves a service area of an additional anchor UPF (e.g., PSA2 of fig. 15) of the corresponding PDU session based on the identification information and location information of the RAN to which the UE currently accesses. The additional anchor UPF may be released when it is determined that the location of the UE accessing the BS leaves the service area of the additional anchor UPF.

In step 1503a, to release the additional anchor UPF, the SMF may send an N4 session release request to the corresponding UPF. The N4 session release request may include information (e.g., N4 session ID) for identifying the PDU session of the UE and a release cause value. The release cause may indicate that the UE leaves the service area of the corresponding UPF. Further, information for releasing the IP address/prefix associated with the corresponding UPF may also be included. The UPF receiving the N4 session release request may discard the remaining packets of the corresponding PDU session and delete the PDU session context, which includes all tunnel information related to the corresponding PDU session and IP address/prefix. When the UPF successfully completes the release of the PDU session context, the UPF may generate an N4 session release response to send it to the SMF in step 1503 b. The N4 session release response may include information identifying the PDU session of the UE, such as an N4 session ID.

Thereafter, an intermediate UPF (e.g., the new I-UPF of FIG. 15) may be selected for establishing a connection between the target BS and the original anchor UPF (e.g., PSA1 of FIG. 15). The intermediate UPF (e.g., PSA1 of fig. 15) may be selected from the UPFs that have connectivity with both the target BS and the anchor UPF, and the selection of the UPF may be performed based on various parameters that the SMF may consider, such as UE location information, UPF load status, UPF location information, and UPF capacity.

When the SMF selects an intermediate UPF, the SMF may perform an N4 session setup procedure with the intermediate UPF in steps 1504a and 1504b and an N4 session modification procedure with the anchor UPF in steps 1505a and 1505b to update the UP transmission path for the PDU session. The N4 session establishment procedure may include the steps of: the SMF sends an N4 session establishment request signaling comprising an identification address of the anchoring UPF and tunnel identification information required by the N9 tunnel establishment to the intermediate UPF; and the intermediate UPF sends an N4 session establishment response signaling to the SMF, the signaling including an identification address of the intermediate UPF and tunnel identification information required by the intermediate UPF for the N9 tunnel established with the anchor UPF. Thereafter, in steps 1505a and 1505b, the SMF may provide information for the N9 tunnel established with the intermediate UPF (e.g., identification information of the intermediate UPF and tunnel identification information) to the anchor UPF through the N4 session modification procedure.

In steps 1506a and 1506b, when an intermediate UPF (e.g., the old I-UPF of FIG. 15) is already included in the PDU session, the SMF may perform an N4 session release procedure using the old I-UPF if the old I-UPF changes to the new I-UPF. If the intermediate UPF included in the PDU session has not changed, the SMF may perform an N4 session modification procedure using the intermediate UPF in steps 1506a and 1506 b. The SMF may remove (e.g., 5-tuple based) route filtering rules for BP/UL CL functions configured in the intermediate UPF.

Thereafter, at step 1507, the smf may respond to the N11 message sent at step 1502. When a network entity of the 5G network provides a service interface, the operation of the service provided by the SMF may be used instead of the N11 message transmitted by the SMF.

The N11 message may include not only identification information of the corresponding PDU session, but also information for invalidating the IPv6 prefix associated with the additional anchor UPF in the case of an IPv6 multi-homed PDU session. Information about the IPv6 prefix may be included in a registration accept message sent by the AMF to the UE.

Thereafter, the AMF may perform the remaining processes required to complete the registration at step 1508, which may correspond to steps 1418 through 1422 of fig. 14B, for example.

When the SMF releases the additional anchor UPF associated with the IPv6 prefix and then does not include information thereon in the N11 message (sent to the AMF), the release may not be notified to the UE, after which the following operations may be performed.

After releasing the additional anchor UPF, the UE may send uplink data using the invalid IPv6 prefix. The data arrives at the remaining (original) anchor UPF in the corresponding PDU session. The anchor UPF may determine that the source IP address of the corresponding data is invalid, and thus may generate and transmit an ICMPv6 error message with a code number 5 (source address failed ingress/egress policy) of the configuration message "destination unreachable" to the UE. The UE that has received the error message may identify an IP prefix that cannot be used and transmit data using another IP prefix. When there are a plurality of IP prefixes, an IP prefix matching the target address may be selected based on the IP routing table.

In addition, for an RA message including invalid information of an IP prefix, which the SMR transmits to the UE, an NW-triggered service request described in fig. 13 may be performed. The SMF may send a data notification to the AMF along with the identification information of the PDU session. When the UP connection for the PDU session is completed (i.e., activated), the SMF may send an IPv6 RA message to the UE via the remaining anchor UPF over the data transmission path.

In addition, the IPv6 prefix corresponds to an IPv6 type PDU session, however, when the procedure is applied to a cellular system supporting IPv4 multi-homing, if an IPv4 type PDU session is used, an IPv4 address may be used instead of the IPv6 prefix.

Fig. 16 is a diagram of a registration procedure including a process of releasing a conventionally added additional anchor UPF from an already established PDU session and a process of transmitting a notification to a UE in a CM-IDLE state when the UE performs the registration procedure, according to an embodiment.

In fig. 16, a method is described in which when an SMF managing a particular PDU session removes the additional anchor UPF associated with the IP prefix in the PDU session, the SMF informs the UE of the associated IP prefix over a signaling connection. Fig. 16 includes a process in which the SMF releases the additional anchor UPF when performing the registration process (steps 1601 to 1608 may correspond to steps 1501 to 1508 of fig. 15). In step 1609, the SMF may send such fact to the AMF through an N11 message, and the AMF may notify the UE of the information received from the SMF through the N11 message. Further, the amf may receive a registration complete message from the UE in step 1610. Specifically, the N11 message may include N1 SM information to be transmitted to the UE.

The N1 SM information may be defined by the following message. First, information may be included indicating that the IP prefix associated with the released additional anchor UPF is no longer used.

Second, information indicating that an anchor UPF corresponding to the released additional anchor UPF is released may be included. Whenever a PDU session is established and an anchor UPF is added, the UE should manage mapping information of the newly allocated anchor UPF. When information is received from the SMF indicating release of a particular anchor UPF, the UE may release the corresponding anchor UPF and operate to no longer use the IP prefix associated therewith.

Both methods may be implemented by a method such as inter-process communication (IPC) between a control plane layer implemented in a modem of the UE and an IP routing layer implemented in an OS of the UE.

Third, information of the PDU session to which the additional anchor UPF requesting activation release belongs may be included. Upon receiving the N1 SM information, the UE may perform a procedure of establishing an UP connection of the corresponding PDU session by directly performing a service request. When the data transmission path of the PDU session is fully configured, the SMF may transmit information about the invalidation of the IPv6 prefix associated with the released anchor UPF to the UE through an IPv6RA message.

To invalidate the IPv6 prefix, the SMF may configure the IPv6 prefix to be invalid and the router lifetime field to be zero in the IPv6RA message and send the IPv6RA message. Upon receiving the IPv6RA message, the UE may configure the failure timer value with reference to the router lifetime field. If the router lifetime field is configured to zero, the UE may immediately change the corresponding IP prefix to invalid upon receipt of the RA message state, and may not use it.

To invalidate the IPv6 prefix, the SMF may configure the IPv6 prefix to be invalid and the valid lifetime value of the prefix information option to be zero in the IPv6RA message and send the IPv6RA message. Upon receiving the IPv6RA message, the UE may configure an invalid timer value with reference to the valid time-to-live value in the prefix information option. If the valid lifetime value is configured to be zero, the UE may change the corresponding IP prefix to an invalid state immediately after receiving the RA message, and may not use it.

To invalidate the IPv6 prefix, the SMF may configure the valid IPv6 prefix (i.e., the IP prefix associated with the remaining anchor UPFs in the corresponding PDU session) as a default router, and configure the priority high in the IPv6 RA message, and send the IPv6 RA message. Since the UE may preferentially use the valid IPv6 prefix when receiving the IPv6 RA message, the UE may not use the invalid IPv6 prefix.

To invalidate the IPv6 prefix, the SMF may use the following method. When an additional anchor UPF for local offload is additionally allocated to a particular PDU session, the SMF may generate an IPV6 RA message to allocate an IPV6 prefix associated with the additional anchor UPF to the UE. In an IPv6 RA message, a finite value greater than 0 and a newly allocated IPv6 prefix may be configured in the router lifetime field. The UE having received the IPv6 prefix may refer to the router lifetime field, and use the IPv6 prefix only at a specific time. In order to continuously use the IPv6 prefix over the time configured in the router lifetime field, the SMF should send an IPv6 RA message for extending the lifetime to the UE. Thus, by not sending IPv6 RA messages for extending the lifetime after releasing the additional anchor UPF, the SMF may prevent the UE from using the corresponding IPv6 prefix after the lifetime expires.

Fig. 17 is a diagram of the operation of a UPF when a data packet with an invalid IPv6 prefix configured for leaving an IP address arrives at the UPF from which the IP header can be marked, according to an embodiment.

In fig. 17, a scheme is described in which a UE receives an IPv6 prefix associated with an additional anchor UPF in a particular PDU session, but processes data generated in a cellular network through the (invalid) IPv6 prefix after the additional anchor UPF is released by the SMF. The UPF may be an IP anchored UPF or a UPF with BP or UL CL functions that perform traffic routing functions.

In step 1705, the upf can receive data having a predetermined IPv6 prefix configured for leaving the IP address. At step 1710, the upf may determine whether the packet uses a valid IP address. When the UPF uses a valid IP address, the UPF may forward the data packet to a next level UPF or router of an internet network located outside the cellular network in order to send the data packet to a destination specified in the destination IP address, step 1715. When the UPF uses an invalid IP address, the UPF can discard the data packet and send a notification including the invalid IP address and corresponding PDU session identification information to the SMF managing the corresponding PDU session at step 1720.

Fig. 18 is a diagram of an operation in which the SMF receives a notification message for using an invalid IP address from the UPF according to an embodiment.

In step 1805, the smf receives a notification message from the UPF for use of the invalid IP address. At step 1810, upon receiving the notification, the SMF may determine whether the corresponding IP prefix is an IP prefix that the SMF conventionally allocates for the respective PDU session of the UE. In step 1815, the SMF may ignore the announce message when the IP prefix is not a conventionally allocated IP prefix. However, when it is determined that the IP prefix has been conventionally allocated, the following steps may be additionally performed. In step 1820, it is determined whether the SMF releases the additional anchor UPF associated with the IP prefix and a notification thereon has been sent to the UE. When a notification has been sent to the UE, the corresponding message may be ignored as in step 1815. However, in step 1825, when the additional anchor UPF has been released, but the notification thereon has not yet been sent to the UE, the SMF may generate a notification message for invalidating the corresponding IP prefix and sending it to the UE via an IPv6 RA message.

Fig. 19 is a diagram of a structure of a UE according to an embodiment.

Referring to fig. 19, the ue may include a transceiver 1910, a controller 1920, and a storage unit 1930. A controller is a physical element and may be defined as a circuit, an application specific integrated circuit, or at least one processor.

The transceiver 1910 may transmit/receive signals to/from another network entity. The transceiver 1910 may receive system information from a BS and receive a synchronization signal or a reference signal.

A controller 1920 may control the overall operation of the UE. The controller 1920 may control the flow of signals between the blocks to perform the operations/steps described above. The controller 1920 may control the operation to receive the remaining system information (RMSI) in the multi-beam based system.

The storage unit 1930 may store at least one piece of information transmitted/received through the transceiver 1910 and information generated through the controller 1920. The storage unit 1930 may store scheduling information related to RMSI transmission, physical Downlink Control Channel (PDCCH) timeline location related to RMSI, and period information of RMSI.

Fig. 20 is a diagram of a structure of a BS according to an embodiment.

Referring to fig. 20, the bs may include a transceiver 2010, a controller 2020, and a storage unit 2030. A controller may be defined as a circuit, an application specific integrated circuit, or at least one processor.

The transceiver 2010 may transmit/receive signals to/from another network entity. The transceiver 2010 may transmit system information to the UE and transmit synchronization signals or reference signals.

The controller 2020 may control overall operation of the BS. The controller 2020 may control the signal flow between blocks to perform the operations/steps described above. The controller 2020 may control operations to transmit RMSI in a multi-beam based system.

The storage unit 2030 may store at least one piece of information transmitted/received through the transceiver 2010 and information generated through the controller 2020. The storage unit 2030 may store scheduling information related to RMSI transmission, PDCCH timeline location related to RMSI, and period information of RMSI.

Not only the UE and the BS, but also each device (e.g., AMF, SMF, or UPF) included in the network system may include a transceiver, a controller, and a storage unit.

Various embodiments of the present disclosure may be implemented by software comprising instructions stored in a machine-readable storage medium readable by a machine (e.g., a computer). The machine may be a device that invokes instructions from a machine-readable storage medium and operates according to the invoked instructions and may include an electronic device. When an instruction is executed by a processor, the processor may perform a function corresponding to the instruction directly or using other components under the control of the processor. The instructions may include code that is generated or executed by a compiler or an interpreter. The machine-readable storage medium may be provided in the form of a non-transitory storage medium. Here, the term "non-transitory" is a limitation on the medium itself (i.e., tangible, not signals), and not on the durability of data storage.

According to an embodiment, a method according to various embodiments disclosed in the present disclosure may be provided as part of a computer program product. The computer program product may be traded as a product between the buyer and the seller. The computer program product may be distributed in the form of a machine-readable storage medium, such as a compact disk read only memory (CD-ROM), or may be distributed only by an application program store (e.g.,) And (5) distributing. In the case of online distribution, at least a portion of the computer program product mayIs temporarily stored or generated in a storage medium such as a memory of a server of the manufacturer, a server of the application store, or a relay server.

Each component (e.g., a module or program) according to various embodiments may include at least one of the above-described components, and a portion of the above-described sub-components may be omitted, or other sub-components may be further included. Alternatively or additionally, some components may be integrated in one component, and the same or similar functions performed by each respective component may be performed prior to integration. Operations performed by modules, programs, or other components according to various embodiments of the present disclosure may be performed sequentially, in parallel, repeatedly, or in a heuristic manner. Moreover, at least some operations may be performed in a different order, omitted, or other operations may be added.

While the disclosure has been shown and described with reference to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the disclosure. Accordingly, the scope of the disclosure should not be defined as limited to the embodiments but should be defined by the appended claims and equivalents thereof.

Claims

1. A method performed by a session management function, SMF, entity in a communication system, the method comprising:

allocating a first PDU session anchor in a procedure for establishing a protocol data unit, PDU, session on a user equipment, UE;

allocating a second PDU session anchor for selectively routing traffic to the data network, the second PDU session anchor being associated with the PDU session;

adding an intermediate user plane function, UPF, entity for data forwarding between the first PDU session anchor and the UE, in case the UE is located outside the service coverage of the first PDU session anchor; and

in case the UE is located outside the service coverage of the second PDU session anchor, releasing the second PDU session anchor,

wherein the first PDU session anchor is associated with a service and session continuity SSC mode of the PDU session.

2. The method of claim 1, further comprising:

wherein in case the SSC mode of the PDU session is SSC mode 1, the first PDU session anchor is maintained regardless of the mobility of the UE.

3. The method of claim 1, wherein the second PDU session anchor is independent of SSC pattern of the PDU session.

4. The method of claim 1, further comprising:

establishing an uplink classifier for the PDU session; and

uplink data is sent to the uplink classifier for routing the uplink data to the first PDU session anchor or the second PDU session anchor.

5. The method of claim 4, wherein establishing the uplink classifier comprises:

providing a traffic filter to the uplink classifier, the traffic filter indicating what traffic to forward to the first and second PDU session anchors, respectively.

6. A session management function, SMF, entity in a communication system, the SMF entity comprising:

a transceiver; and

a controller coupled to the transceiver and configured to:

a first PDU session anchor is allocated in the process for establishing a protocol data unit PDU session at the user equipment UE,

Allocating a second PDU session anchor for selectively routing traffic to the data network, the second PDU session anchor being associated with said PDU session,

7. The SMF entity of claim 6, wherein the controller is further configured to:

in case the SSC mode of the PDU session is SSC mode 1, the first PDU session anchor is maintained regardless of the mobility of the UE.

8. The SMF entity of claim 6, wherein the second PDU session anchor is independent of an SSC pattern of the PDU session.

9. The SMF entity of claim 6, wherein the controller is further configured to:

establishing an uplink classifier for the PDU session; and

Uplink data is sent via the transceiver to the uplink classifier for routing the uplink data to the first PDU session anchor or the second PDU session anchor.

10. The SMF entity of claim 9, wherein the controller is further configured to: providing, via the transceiver, a traffic filter to the uplink classifier, the traffic filter indicating what traffic is to be forwarded to the first PDU session anchor and the second PDU session anchor, respectively.