WO2025175429A1

WO2025175429A1 - Enhancements to support rrc_inactive state

Info

Publication number: WO2025175429A1
Application number: PCT/CN2024/077598
Authority: WO
Inventors: Ayaz AHMED; Philippe Godin; Xiang Xu; Suresh P Nair; Ahmad AWADA
Original assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Current assignee: Nokia Shanghai Bell Co Ltd; Nokia Solutions and Networks Oy; Nokia Technologies Oy
Priority date: 2024-02-19
Filing date: 2024-02-19
Publication date: 2025-08-28
Anticipated expiration: 2026-08-19

Abstract

Example embodiments of the present disclosure provide a solution to support inactive state user equipments (UEs) in communication networks. In an example method, a first network element updates, based on a new security key derived, the security context included in UE context of at least one UE in an inactive state in a cell, and transmits, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with the new security key, before the satellite switch. The second network element receives and stores the UE context including the updated security context with the new security key, before satellite switch. In this way, the proactive transfer of the UE context including the updated security context with new security key for UEs in the inactive state is enabled, for facilitating the connection resume.

Description

ENHANCEMENTS TO SUPPORT RRC_INACTIVE STATE

FIELD

Example embodiments of the present disclosure generally relate to the field of communication, and in particular, to network elements, methods, apparatuses, and non-transitory computer readable mediums for enhancements required to support RRC_INACTIVE state functionality when served by non-terrestrial network (NTN) regenerative non-geostationary (NGSO) satellite deployments.

BACKGROUND

3GPP has considered two architecture options for New Radio (NR) NTN i.e., transparent architecture in which the satellite payload performs frequency conversion, amplification and filtering, with the gNB located on the ground, and regenerative architecture in which part or full gNB shall be onboard the satellite.

The support of NTN for transparent architecture has been specified in 3GPP Release-17 and Release-18. NTN Enhancements in Release-19 are expected to introduce the support of regenerative payload for NR NTN. One of the expected enhancements under NTN mobility and service continuity is “Enhanced support in RRC_INACTIVE” . It must be noted that, basic support of RRC_INACTIVE state for NR NTN is available already in 3GPP Release-17.

SUMMARY

In general, example embodiments of the present disclosure provide a solution to support RRC_INACTIVE state UEs in NTN regenerative satellite deployments.

In a first aspect, there is provided a first network element. The first network element comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the first network element at least to: update, based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and transmit, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state. The satellite switch herein refers to as change of NGSO satellite hosting full or part of the gNB serving fixed NTN cell on earth; i.e. the outgoing satellite stops serving the cell and an incoming satellite starts serving. The network elements (the first and second network elements) may be hosted on to a NGSO satellite which continuously orbits the earth.

In a second aspect, there is provided a second network element. The second network element comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the second network element at least to: receive, from a first network element serving the cell, which is to be served by the second network element after satellite switch, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before the satellite switch, wherein the UE context includes updated security context with new security key; and store the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In a third aspect, there is provided a third network element. The third network element comprises at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the third network element at least to: receive, from a second network element which is to serve the cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and transmit, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In a fourth aspect, there is provided a method. The method comprises: updating, at a first network element and based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.

In a fifth aspect, there is provided a method. The method comprises: receiving, from a first network element serving the cell which is to be served by a second network element, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before satellite switch, wherein the UE context includes updated security context with new security key; and storing, at the second network element, the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In a sixth aspect, there is provided a method. The method comprises: receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In a seventh aspect, there is provided an apparatus. The apparatus comprises: means for updating, at a first network element and based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and means for transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.

In an eighth aspect, there is provided an apparatus. The apparatus comprises: means for receiving, from a first network element serving the cell which is to be served by a second network element, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before satellite switch; and means for storing, at the second network element, the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In a ninth aspect, there is provided an apparatus. The apparatus comprises: means for receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and means for transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In a tenth aspect, there is provided a non-transitory computer-readable storage medium comprising program instructions. The program instructions, when executed by an apparatus, cause the apparatus to perform at least the following: updating, at a first network element and based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.

In an eleventh aspect, there is provided a non-transitory computer-readable storage medium comprising program instructions. The program instructions, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a first network element serving the cell which is to be served by a second network element, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before satellite switch, wherein the UE context includes updated security context with new security key; and storing, at the second network element, the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In a twelfth aspect, there is provided a non-transitory computer-readable storage medium comprising program instructions. The program instructions, when executed by an apparatus, cause the apparatus to perform at least the following: receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In a thirteenth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: update, at a first network element and based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and transmit, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.

In a fourteenth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: receive, from a first network element serving the cell which is to be served by a second network element, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before satellite switch, wherein the UE context includes updated security context with new security key; and store, at the second network element, the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In a fifteenth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: receive, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and transmit, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In a sixteenth aspect, there is provided a first network element. The first network element comprises: updating circuitry configured to update, at a first network element and based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and transmitting circuitry configured to transmit, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch, wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.

In a seventeenth aspect, there is provided a second network element. The second network element comprises: receiving circuitry configured to receive, from a first network element serving the cell which is to be served by a second network element, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before satellite switch, wherein the UE context includes updated security context with new security key; and storing circuitry configured to store, at the second network element, the UE context including the updated security context with new security key, wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.

In an eighteenth aspect, there is provided a third network element. The third network element comprises: receiving circuitry configured to receive, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and transmitting circuitry configured to transmit, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1A illustrates an example communication network in which embodiments of the present disclosure may be implemented;

FIG. 1B illustrates an example connection resume scenario in case of regenerative

NTN NGSO satellite deployment;

FIG. 2 illustrates an example of a process flow of enhanced support for RRC_INACTIVE state functionality in NTN regenerative NGSO satellite deployments in accordance with some example embodiments of the present disclosure;

FIG. 3 illustrates a process flow for one example implementation in accordance with some example embodiments of the present disclosure;

FIG. 4 illustrates a process flow for another example implementation in accordance with some example embodiments of the present disclosure;

FIG. 5 illustrates a flowchart of an example method implemented at a first network element in accordance with some other embodiments of the present disclosure;

FIG. 6 illustrates a flowchart of an example method implemented at a second network element in accordance with some other embodiments of the present disclosure;

FIG. 7 illustrates a flowchart of an example method implemented at a third network element in accordance with some other embodiments of the present disclosure;

FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing some example embodiments of the present disclosure; and

FIG. 9 illustrates a block diagram of an example of a computer-readable medium in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar elements.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein can be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an embodiment, ” “an example embodiment, ” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. 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 example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or” , mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable) :

(i) a combination of analog and/or digital hardware circuit (s) with software/firmware and

(ii) any portions of hardware processor (s) with software (including digital signal processor (s) ) , software, and memory (ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit (s) and or processor (s) , such as a microprocessor (s) or a portion of a microprocessor (s) , that requires software (for example, firmware) for operation, but the software may not be present when it is not needed for operation.

This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

As used herein, the term “network” , “communication network” or “data network” refers to a network following any suitable communication standards, such as long term evolution (LTE) , LTE-advanced (LTE-A) , wideband code division multiple access (WCDMA) , high-speed packet access (HSPA) , narrow band Internet of things (NB-IoT) , wireless fidelity (Wi-Fi) and so on. Furthermore, the communications between a terminal device and a network device/element in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the fourth generation (4G) , 4.5G, the future fifth generation (5G) , IEEE 802.11 communication protocols, and/or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network device” refers to a node in a communication network via which a terminal device receives services (e.g., positioning services) therefrom. The network device may refer to a core network device or access network device, such as base station (BS) or an access point (AP) or a transmission and reception point (TRP) , for example, a node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a NR NB (also referred to as a gNB) , a remote radio unit (RRU) , a radio header (RH) , a remote radio head (RRH) , a WiFi device, a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology. In the following description, the terms “network device” , “AP device” , “AP” and “access point” may be used interchangeably.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE) , a Subscriber Station (SS) , a Portable Subscriber Station, a Mobile Station (MS) , a station (STA) or station device, or an Access Terminal (AT) . The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA) , portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE) , laptop-mounted equipment (LME) , USB dongles, smart devices, wireless customer-premises equipment (CPE) , an Internet of Things (IoT) device, a watch or other wearable, a head-mounted display (HMD) , a vehicle, a drone, a medical device and applications (for example, remote surgery) , an industrial device and applications (for example, a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts) , a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. In the following description, the terms “station” , “station device” , “STA” , “terminal device” , “communication device” , “terminal” , “user equipment” and “UE” may be used interchangeably.

As discussed above, “enhanced support in RRC_INACTIVE state” is one of the expected enhancements to be supported. Support for RRC_INACTIVE state for regenerative NGSO satellite deployments is seen as one of the key priorities, and brings in new challenges that are unique to NTN regenerative NGSO satellite scenarios.

An example of NGSO is Low Earth Orbit (LEO) satellite. By way of example of regenerative Low Earth Orbit (LEO) deployment with full gNB on satellite, a LEO beam footprint may range between 50 to 1000kms (with 20 to 40kms beam diameter) and the LEO satellite constantly orbits the earth with a relative speed of 7.56Km/sec. It means the serving satellite (serving gNB) changes at every fixed time interval even for a stationary UE on earth. For connected mode UEs, this shall be handled by triggering handover. However, for RRC_INACTIVE state UEs, when connection needs to be resumed (e.g., due to uplink (UL) or downlink (DL) data) , the UE may be served by a different satellite (therefore gNB) , (as constellation of NGSO satellites continuously orbits the earth) and that the satellite (therefore gNB) that holds the UE context might be multiple hops away.

In the handling of RRC_INACTIVE state UEs, upon connection resume e.g. due to MO data, the new serving gNB fetches the UE context from the last serving gNB via direct Xn link and the path switch is triggered by the new serving gNB after successful context fetch. Alternatively, if the connection resume is due to UE movement to a new radio access network (RAN) notification area (RNA) , upon cell re-selection, UE initiates RNAU, which in turn does the UE context fetch from last serving gNB and then triggers patch switch.

However, in the regenerative NGSO satellite deployments, at the time of connection resume, the satellite gNB that holds the UE context might be multiple hops away due to continuous satellite movement. Furthermore, the UE context retrieval over multiple Xn connectivity hops is not supported.

In NTN regenerative NGSO satellite deployment scenarios, the satellite gNB that has transitioned the UE to RRC_INACTIVE state, and the node that hosts the UE context and a next generation (NG) user plane (NG-U) downlink (DL) termination point might be multiple hops away from the current serving gNB, due to continuous movement of constellation of NGSO satellites in fixed orbits in the sky. When a connection has to be resumed either due to UL/DL data or cell re-selection outside the configured RNA, the current serving satellite gNB must fetch (or retrieve) the UE context from the last serving satellite gNB (that hosts the UE context and the NG-U DL termination point) which may be multiple hops away from the current serving satellite gNB. A multi-hop UE context fetch without direct Xn interface connectivity is not feasible with the Xn specifications.

Moreover, it must also be ensured that the data forwarding path is set up between new serving satellite gNB and the last serving satellite gNB which hosts the UE context and the NG-U DL termination point, because the last serving satellite gNB drifts multiple hops away with time (due to NGSO satellite movement) , till the connection is resumed (from RRC_INACTIVE state to RRC_CONNECTED state) and the DL NG-U path is switched to new serving gNB. However, this is not possible without enhancements.

In an example scenario for connection resume in NTN regenerative NGSO satellite deployment, the RRC resume is initiated due to UL data at UE when the last serving satellite gNB that holds the UE context is one hop away. However, the last serving satellite gNB might be ‘N or multiple’ hops away from the current serving satellite.

As per the current Xn interface specifications, UE context retrieval is possible only with the gNB that has direct Xn interface connectivity. It means that such retrieval or fetch is not feasible with the current standards without enhancements. That is, RRCResume cannot be initiated by the current serving gNB, without successful UE context fetch from the last serving gNB that hosts the UE context. Thus, with the current Xn Specifications, a UE in RRC_INACTIVE state cannot be resumed by the current serving satellite gNB in case of regenerative NTN NGSO satellite deployment scenarios, if the last serving satellite gNB is multiple hops aways.

Furthermore, data forwarding address indication including data forwarding address (es) from new serving satellite gNB to the last serving satellite gNB can only be initiated with direct Xn interface connectivity. It means that the data forwarding path between the last serving node that hosts the UE context and the NG-U DL termination point, and the current serving satellite gNB which may be multiple hops away, has to be setup at the time of satellite switch as a nested tunnel, which may require enhancements to the Xn Interface specification.

Embodiments of the present disclosure provide a solution to support RRC_INACTIVE state UEs, particularly, to support RRC_INACTIVE state in NTN regenerative satellite deployments. The proactive transfer of UE context including updated security context with new security key for RRC_INACTIVE state UEs before satellite switch is depicted in FIG. 2. Furthermore, the path switch and the NG-U DL termination point change for RRC_INACTIVE state UEs are discussed. For illustrative purposes, principles and example embodiments of the present disclosure will be described below with reference to FIG. 1A to FIG. 9. However, it is to be noted that these embodiments are given to enable the skilled in the art to understand inventive concepts of the present disclosure and implement the solution as proposed herein, and not intended to limit scope of the present application in any way.

FIG. 1A illustrates an example of an application scenario 100A in which some example embodiments of the present disclosure may be implemented. The application scenario 100A, which is a part of a communication network, includes terminal devices, network elements and core network entities, etc.

The communication system 100A may comprise at least one terminal device 111 (hereinafter may also be referred to as UE 111) in a cell 110. The communication network 100A may further comprise network elements which are onboard the satellites (hereinafter may also be referred to as satellite base stations or satellite gNBs) , e.g., the satellite gNBs 120 and 130. The satellite gNBs 120 and 130 may manage the cell 110. For example, the satellite gNB 120 serving the cell 110 may transition at least one UE 111 from RRC_CONNECTED state to the RRC_INACTIVE state. The at least one UE 111 and the satellite gNBs 120 and 130 may communicate data and control information to each other in the coverage of the cell 110. A link from the satellite gNBs 120 and 130 to the at least one UE 111 is referred to as a DL, while a link from the at least one UE 111 to the satellite gNBs 120 and 130 is referred to as an UL.

The core network 140 may support, for example, user authentication, access authorization, tracking, connectivity, and other access, routing, or mobility functions. The core network 140 may be an evolved packet core (EPC) , or a 5G core (5GC) , which may include a control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management functions (AMF) ) and a user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a packet data network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . For example, the AMF 141 may be coupled with the satellite gNBs 120 and 130 for access management, as shown in FIG. 1A. In some implementations, the control plane entity may manage non-access stratum (NAS) functions, such as mobility, authentication, and bearer management (e.g., data bearers, signal bearers, etc. ) for the one or more UEs 111 served by the one or more network entities associated with the core network 140.

In the descriptions of the example embodiments of the present disclosure, the network environment 100A may also be referred to as a communication system 100A (for example, a portion of a communication network) . For illustrative purposes only, various aspects of example embodiments will be described in the context of one or more terminal devices and network devices that communicate with one another. It should be appreciated, however, that the description herein may be applicable to other types of apparatus or other similar apparatuses that are referenced using other terminology.

Communications in the communication system 100A may be implemented according to any proper wireless or wired communication protocol (s) , comprising, but not limited to, cellular communication protocols and core network communication protocols of the fourth generation (4G) and the fifth generation (5G) and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA) , Frequency Division Multiple Access (FDMA) , Time Division Multiple Access (TDMA) , Frequency Division Duplex (FDD) , Time Division Duplex (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Division Multiple (OFDM) , Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

It is to be understood that the number of devices and their connection relationships and types shown in FIG. 1A are for illustrative purposes without suggesting any limitation. The communication system 100A may comprise any suitable number of devices adapted for implementing embodiments of the present disclosure.

FIG. 1B illustrates an example connection resume scenario in case of regenerative NTN NGSO satellite deployment. During the process flow 100B, the RRC resume is initiated due to UL data at UE side when the last serving satellite gNB (e.g., gNB1 as shown in FIG. 1B) that holds the UE context is one hop away. Practically, the last serving satellite gNB might be ‘N or multiple’ hops away from the current serving satellite (e.g., gNB3 as shown in FIG. 1B) . for example, In steps 12 and 13, the current serving satellite gNB (gNB3) initiates a ‘retrieval of UE context’ from the last serving satellite gNB (gNB1) that hosts the UE context and the NG-U DL termination point.

However, according to the current Xn interface specifications, UE context retrieval is possible only with the gNB that has direct Xn interface connectivity. It means that such retrieval or fetch for UE context (in steps 12, 13) are representative only and are not feasible with the current standards without enhancements. That is, RRCResume cannot be initiated by the current serving gNB, without successful UE context fetch from the last serving gNB that hosts the UE context. Thus, a UE in RRC_INACTIVE state cannot be resumed in case of regenerative NTN NGSO satellite deployment scenarios with Xn interface specifications.

Moreover, a data forwarding address indication including data forwarding address (es) in step 17 is also representative only and cannot be initiated without direct Xn interface connectivity (i.e. Xn connectivity between gNB3 and gNB1) . It means that the data forwarding path between the last serving node that hosts the UE context (gNB1) and the NG-U DL termination point, and the current serving satellite gNB (gNB3) cannot be set up without some enhancements to 3GPP Xn Interface specifications. Thus, the functional support of RRC_INACTIVE state that enables a connection to be resumed successfully from RRC_INACTIVE state to RRC_CONNECTED state in NTN regenerative NGSO satellite deployment scenarios is not feasible with existing specifications without enhancements to Xn interface.

FIG. 2 illustrates an example of a process flow 200 of enhanced support for RRC_INACTIVE UEs, for example, RRC_INACTIVE state functionality in NTN regenerative NGSO satellite deployments in accordance with some example embodiments of the present disclosure. For ease of understanding, the process flow 200 will be described with reference to FIG. 1A. It would be appreciated that although the process flow 200 has been described referring to the application scenario 100 of FIG. 1A, this process flow 200 may be likewise applied to other similar communication scenarios.

The first network element 220 updates (201) , based on a new security key derived, the security context included in user equipment (UE) context of at least one UE 111 in RRC_INACTIVE state in the cell 110 served by the first network element 220. The first network element 220 transmit (202) , to the second network element 230 which is to serve the cell 110 after satellite switch, the UE context 203 including the updated security context with new security key, before the satellite switch. The UE context 203 including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE 111 is resumed to a connected state.

The satellite switch herein refers to as change of NGSO satellite hosting full or part of the gNB serving fixed NTN cell on earth; i.e. the outgoing satellite stops serving the cell and an incoming satellite starts serving. The network elements (the first and second network elements) may be hosted on to a NGSO satellite which continuously orbits the earth. For example, the first network element 220 may correspond to satellite gNBs 120, and the second network element 130 may correspond to satellite gNBs 130, as shown in FIG. 1A. The network elements (the first network element 220 and second network element 230) may be hosted on to a NGSO satellite which continuously orbits the earth.

The second network element 230 receives (204) , from the first network element 220 serving the cell 110 which is to be served by the second network element 230 after satellite switch, the user equipment (UE) context 203 of at least one UE 111 in RRC_INACTIVE state in the cell 110, before the satellite switch. The UE context 203 including the updated security context with the new security key is received by a next serving network element till the at least one UE 111 is resumed to a connected state. For example, the UE context 203 includes updated security context with new security key. The second network element 230 stores (205) the UE context 203 including the updated security context with new security key.

The second network element 230 then transmits (206) , to the third network element 240, a path switch request 207 for a plurality of UEs to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element 220 to the second network element 230. The third network element 240 receives (208) , from the second network element 230 which is to serve the cell 110 served by the first network element 220, the path switch request 207 for a plurality of UEs to switch the NG-U DL termination point from the first network element 220 to the second network element 230. For example, the third network element 240 may correspond to the AMF 141 as shown in FIG. 1A.

The third network element 240 transmits (209) , to the second network element 230, a path switch response 210 indicating the NG-U DL termination point has been switched from the first network element 220 to the second network element 230. The second network element 230 then receives (211) , from the third network element 240, the path switch response 210 indicating the NG-U DL termination point has been switched to the second network element 230.

In this way, the proactive transfer of the UE context including the updated security context with new security key for UEs in the RRC_INACTIVE state is enabled, for facilitating the connection resume. Meanwhile, the NG-U DL termination has been changed to the new serving satellite base station.

FIG. 3 illustrates a process flow 300 for one example implementation in accordance with some example embodiments of the present disclosure. As shown in FIG. 3, a UE is in RRC_CONNECTED state (step 1) , while consecutive satellite gNBs have Xn connectivity (step 3) , where satellite gNB1 receive DL data from UPF (step 2) . At step 4, NGSO satellite 1 (hosting gNB 1) moves the UE to RRC_INACTIVE state (step 5) , via a RRCRelease message with a suspend configuration. In step 6, a stationary UE may remain in the same NTN cell and a moving UE may re-select a new NTN cell. At time T, gNB 1 serve the cell (step 7) . At time ‘T+T1’ , a satellite switch is triggered, resulting into satellite 1 drifting away and satellite 2 (hosting gNB 2) starting to serve the UE.

In step 8, before satellite switch, successive serving gNBs, transfer the UE context of all the RRC_INACTIVE UEs to the next serving satellite gNB (without path switch) . The serving gNB that initiated RRC_CONNECTED state to RRC_INACTIVE state transition maintains the UE context till the NG-U DL termination points switched to the new serving satellite gNB after connection is resumed, and the UE context release at last serving gNB shall be triggered after successful connection resume and path switch.

In step 9, i.e., before the satellite switch, while satellite 1 (hosting gNB1) is still serving the cell, the serving gNB1 updates the AS security context in the UE context of all the RRC_INACTIVE state UEs with a computed security key. Furthermore, in step 10, i.e., before satellite 1 switches and satellite 2 starts to serve, satellite 1 (hosting gNB 1) proactively moves the UE context with the updated AS security context using the new computed security key of all the RRC_INACTIVE state UEs via a non-UE associated (or UE-associated) Xn interface message (s) with UE contexts, for example, included in a transparent container.

After step 10, the satellite 2 (hosting gNB 2) creates/stores UE context including the new security key for all the RRC_INACTIVE state UEs for which the context was transferred. In step 11, the satellite 2 triggers a data forwarding address indication including at least one data forwarding address for data transfer towards the last serving satellite (hosting gNB 1) to enable NG-U DL data transfer. In step 11, DL data is transmitted from UPF to the last serving gNB. In step 13, a data forwarding tunnel is set up between the last serving gNB1 and the current serving gNB2. In step 14, From time (T+Tl) , gNB2 serves cell. The subsequent steps 15 and 16 are similar to steps 9 and 10. Furthermore, the subsequent step 17 is similar to step 11, but triggers step 18 to set up a nested tunnel for NG-U DL data. In steps 19 and 20, DL data may be transmitted from UPF to the last serving gNB and from the last serving gNB to the current serving gNB.

In step 21, i.e., at time ‘T+2T1’ , the satellite 3 (hosting gNB 3) starts to serve the cell, and the UE has UL data to send (step 22) , hence it triggers a RRC resume request in step 23. In step 24, as the current serving satellite 3 (hosting gNB 3) has already received the UE context (including the updated security context with new security key) in step 16, it triggers the RRCResume message towards the UE (step 25) .

In step 26, UE shall decrypt the RRC resume message using the new security key. In step 27, the UE transitions from RRC_INACTIVE to RRC_CONNECTED state. In step 28, RRC resume complete message is transmitted from the UE. After step 26, a path switch request procedure for a plurality of UEs shall be triggered by the current serving satellite 3 (hosting gNB3) to switch the NG-U DL termination point from satellite 1 (hosting gNB1) . In step 27, gNB3 transmits a path switch request for the plurality of UEs to the AMF, and receives a path switch response from the AMF. In step 31, DL data may be transmitted from UPF to the current serving gNB (gNB) . In step 32, AMF releases the UE context of the plurality of UEs in last serving satellite gNB (e.g., via an indication) .

During the process flow 300, at the time of satellite switch, the serving satellite gNB proactively transfers the UE context of all the UEs in the RRC_INACTIVE state including the updated security context with new security key, to the next serving satellite gNB, while the path switch is triggered only upon successful connection resume. Successive serving satellite gNBs before satellite switch (or cell switch) , updates the security context by computing a security key and proactively transfers the UE context of all the UEs in the RRC_INACTIVE state to the next serving satellite gNB. This may be done in a non-UE associated Xn (or UE-associated) signaling message with UE contexts, for example, included in a transparent container.

The last serving satellite gNB that initiated RRC_CONNECTED state to RRC_INACTIVE state transition still maintains the UE contexts of the UEs in the RRC_INACTIVE state, as it still hosts the NG-U DL termination point till the connection is resumed successfully. Upon reception of new non-UE associated (or UE associated) Xn interface message, carrying UE contexts of UEs of last serving satellite gNB (as in previous step) , the new serving satellite gNB after satellite switch, creates and/or stores the UE context for all the UEs and initiates the data forwarding address indication via a Xn-U Address Indication including the data forwarding addresses for potential data transfer before NG-U DL termination point changes for all the UEs.

As the UE context including the updated AS security context with new security key of the UEs in the RRC_INACTIVE state is proactively moved to the next serving satellite gNB that serves the UEs in a given NTN cell, a connection resume shall be directly executed at the current serving satellite gNB without “UE context retrieval” over Xn interface. It enables fast RRC_INACTIVE state to RRC_CONNECTED state transition with no Xn signaling overhead and delay during connection resume. Upon successful connection resume of one or more UEs, the new serving satellite gNB triggers NG-U DL path switch via a path switch request procedure for one or more UEs.

Assuming the probability of several UEs resuming the connection at about the same time, a path switch request procedure may be enhanced to include the path switch request for multiple UEs which have resumed the connection at the same time. Upon successful path switch, the 5G Core (5GC) initiates the release of the contexts in the last serving gNBs.

FIG. 4 illustrates a process flow 400 for another example implementation in accordance with some example embodiments of the present disclosure. As shown in FIG. 4, a UE is in RRC_CONNECTED state (step 1) , while consecutive satellite gNBs have Xn connectivity (step 3) , where satellite gNB1 receive DL data from UPF (step 2) . At step 4, NGSO satellite 1 (hosting gNB 1) moves a UE to RRC_INACTIVE state (step 5) , via a RRC Release message with a suspend configuration. In step 6, a stationary UE may remain in the same NTN cell and a moving UE may re-select a new NTN cell. At time T, gNB 1 serve the cell (step 7) . At time ‘T+T1’ , a satellite switch is triggered, resulting into satellite 1 drifting away and satellite 2 (hosting gNB 2) starting to serve the UE.

In step 8, before satellite switch, successive serving gNBs, transfer the UE context of all the RRC_INACTIVE UEs to the next serving satellite gNB (followed by a path switch) . In step 9, i.e., before the satellite switch, while satellite 1 (hosting gNB1) is still serving the cell, the serving gNB1 updates the AS security context in the UE context of all the RRC_INACTIVE state UEs with a computed security key. Furthermore, in step 10, i.e., just before satellite 1 switches and satellite 2 starts to serve, satellite 1 (hosting gNB 1) proactively moves the UE context with the updated AS security context of all the RRC_INACTIVE state UEs via a non-UE associated (or UE-associated) Xn interface message (s) with UE contexts, for example, included in a transparent container. It also includes the computed security key.

After step 9, the satellite 2 (hosting gNB 2) creates/stores UE context including the new security key for all the RRC_INACTIVE state UEs for which the context was transferred (step 10) . In step 11, From time (T+t1) , gNB2 serves the cell. In step 12, the satellite 2 triggers a data forwarding address indication including at least one data forwarding address for data transfer towards the last serving satellite (hosting gNB 1) to enable NG-U DL data transfer. In step 13, a data forwarding tunnel is set up between the last serving gNB1 and the current serving gNB2. In step 13, the new serving satellite 2 (hosting gNB 2) , triggers a path switch request procedure. Particularly, gNB2 transmits a path switch request to the AMF (step 13) , and receives a path switch response from the AMF (step 14) , where DL data may be transmitted from UPF to gNB2 (step 15) . In step 16, after the path switch request procedure successfully completed, UE context at last serving satellite 1 (hosting gNB 1) shall be released. The subsequent steps 17 and 19 are similar to the steps 9 and 10. Furthermore, the subsequent steps 21 to 25 are similar to the steps 12 to 16.

In step 26, i.e., at time ‘T+2T1’ , the satellite 3 (hosting gNB 3) starts to serve the cell. UE has UL data to send (step 27) , hence it triggers a RRCResumeRequest in step 28 is initiated. In step 29, as the current serving satellite 3 (hosting gNB 3) has already received the UE context (including the updated security context with new security key) in step 19, it triggers the RRCResume message towards the UE and the UE successfully resumes the connection with step 30.

In step 31, UE shall decrypt the RRC resume message using new key. In step 32, the UE transitions from RRC_INACTIVE to RRC_CONNECTED state. In step 33, RRC resume complete message is transmitted from the UE. As the NG-U DL termination point has been already switched with satellite switch also for RRC_INACTIVE state UEs, the data transmission shall happen in this implementation without NG signaling delay due to the path switch request procedure.

During the process flow 400, at the time of satellite switch, the serving satellite gNB, proactively transfers the UE context of all the UEs in the RRC_INACTIVE state including updated AS security context with a new security key, to the next serving satellite gNB, while the NG-U DL termination (for all the UEs in the RRC_INACTIVE state) is also changed to the new serving gNB at the time of satellite switch. Successive serving satellite gNBs before satellite switch (or cell switch) , updates the security context by computing a security key and proactively transfers the UE context of all the UEs in the RRC_INACTIVE state to the next serving satellite gNB. This may be done in a non-UE associated Xn (or UE-associated) signaling message with UE contexts, for example, included in a transparent container.

Upon reception of new non-UE associated (or UE associated) Xn interface message, carrying UE contexts of RRC_INACTIVE state UEs (as in previous step) , after satellite switch, the new serving satellite gNB shall create the UE context for all the UEs in the RRC_INACTIVE state, initiate the data forwarding address indication via a Xn-U Address Indication including the data forwarding addresses for potential data transfer before NG-U DL termination point changes for all the UEs in the RRC_INACTIVE state, and triggers NG-U DL path switch via a path switch request procedure.

Assuming the probability of several UEs resuming the connection at about the same time, a path switch request procedure may be enhanced to include the path switch requests for multiple UEs which have resumed the connection at the same time, in a single message.

As the UE context including the updated security context with new security key of RRC_INACTIVE state UEs is proactively moved to the next serving satellite gNB that serves the UEs in a given NTN cell, a connection resume shall be directly executed at the current serving satellite gNB without “UE context retrieval” over Xn interface. It enables fast RRC_INACTIVE state to RRC_CONNECTED state transition with no Xn signaling overhead during connection resume. As the NG-U DL termination is also switching to the new serving satellite gNB with the satellite switch, the data transfer after connection resume happens without the delay involved in triggering the path switch request procedure after successful RRC resume. The UE context release shall be triggered by 5GC after the path switch request has been completed successfully.

According to embodiments of the present disclosure, it provides a workable and optimal solution to support RRC_INACTIVE state in NTN regenerative NGSO scenarios. It does the proactive transfer of the UE context including the updated security context with new security key for RRC_INACTIVE state UEs, which is vital for the RRC connection resume to work successfully.

The Xn signaling for UE context retrieval upon a RRCResumeRequest is not required, due to proactive UE context transfer including the updated security context with new security key for RRC_INACTIVE state UEs at the time of satellite switch. Alternatively, both the Xn signaling for UE context retrieval upon the RRC resume request, and the NG signaling for a path switch request after connection resume is not required, due to proactive UE context transfer including the updated security context with new security key for RRC_INACTIVE state UEs at the time of satellite switch and the NG-U DL path switch after each satellite switch.

FIG. 5 illustrates a flowchart of an example method 500 implemented at a first network element in accordance with some other embodiments of the present disclosure. It is to be understood that the method 500 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard. For ease of understanding, the method 500 will be described from the perspective of the first network element 120 with reference to FIG. 1A.

At block 510, the first network element 120 updates, based on a new security key derived, the security context included in user equipment (UE) context of at least one UE 111 in RRC_INACTIVE state in a cell 110 served by the first network element 120. At block 520, the first network element 120 transmits, to a second network element 130 which is to serve the cell 110 after satellite switch, the UE context including the updated security context with new security key, before the satellite switch. The UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE 111 is resumed to a connected state. The satellite switch herein refers to as change of NGSO satellite hosting full or part of the gNB serving fixed NTN cell on earth; i.e. the outgoing satellite stops serving the cell and an incoming satellite starts serving. The network elements (the first and second network elements) may be hosted on to a NGSO satellite which continuously orbits the earth. The network elements may be hosted on to a NGSO satellite which continuously orbits the earth.

In some embodiments, the UE context may be transmitted via a non-UE associated Xn interface message or a UE-associated message, and may be included in a transparent container.

In some embodiments, the first network element 120 may receive, from the second network element 130, a data forwarding address indication including at least one data forwarding address for data transfer, before switching of the cell 110 from the first network element 120 to the second network element 130, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element 120 and the second network element 130 is established, and wherein before switching of the cell 110 from the second network element 130 to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element 130 from the next serving network element, such that the second network element 130 forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element 120 to forward data received from a next generation (NG) user plane (NG-U) at the first network element 120 to the next serving network element in a nested tunnel.

In some embodiments, the first network element 120 may transition, via a radio resource control (RRC) release message with a suspend configuration, the at least one UE 111 from RRC_CONNECTED state to the RRC_INACTIVE state.

In some embodiments, the first network element 120 may maintain the UE context including the updated security context until a NG-U downlink (DL) termination point hosted by the first network element 120 is switch to the second network element 130 after the at least one UE 111 is resumed to the RRC_CONNECTED state.

In some embodiments, the first network element 120 may receive, from the second network element 130, a data forwarding address indication including at least one data forwarding address for data transfer, after switching of the cell 110 from the first network element 120 to the second network element 130, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and wherein after switching of the cell from the second network element 130 to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element 130 from the next serving network element, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element 130 to the first network element 120 for establishing a data forwarding nested tunnel between the first network element 120 and the next serving network element, till a NG-U DL termination point hosted by the first network element 120 is switched to a network element where the at least one UE 111 resumes connection from the inactive state to the connected state.

In some embodiments, the first network element 120 may release the UE context including the updated security context, after a data forwarding tunnel between the first network element 120 and the second network element 130 is established based on the data forwarding address indication.

In some embodiments, at least one of the following: the first network element 120 is a last serving network element, and the second network element 130 is a current serving network element; the first network element 120 and the second network element 130 may be satellite base stations; or the third network element 141 may be an access and mobility management function (AMF) .

FIG. 6 illustrates a flowchart of an example method 600 implemented at a second network element in accordance with some other embodiments of the present disclosure. It is to be understood that the method 600 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard. For ease of understanding, the method 600 will be described from the perspective of the second network element 130 with reference to FIG. 1A.

At block 610, the second network element 130 receives, from a first network element 120 serving a cell 110 which is to be served by the second network element 130 after satellite switch, user equipment (UE) context of at least one UE 111 in RRC_INACTIVE state in the cell 110, before the satellite switch, wherein the UE context includes updated security context with new security key. At block 620, the second network element 130 stores the UE context including the updated security context with new security key. The UE context including the updated security context with new security key is received by a next serving network element till the at least one UE 111 is resumed to a connected state.

In some embodiments, the UE context is received via a non-UE associated Xn interface message or a UE-associated message, and may be included in a transparent container.

In some embodiments, the second network element 130 may transmit a data forwarding address indication including at least one data forwarding address for data transfer, before switching of the cell 110 from the first network element 120 to the second network element 130, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element 120 and the second network element 130 is established, and wherein before switching of the cell 110 from the second network element 130 to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is transmitted by the next serving network element to the second network element 130, such that the second network element 130 forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element 120 to forward data received from a next generation (NG) user plane (NG-U) at the first network element 120 to the next serving network element in a nested tunnel.

In some embodiments, the second network element 130 may receive a RRC resume request triggered by the at least one UE 111, before switching a NG-U downlink (DL) termination point hosted by the first network element to the second network element, and may transmit a RRC resume message to the at least one UE 111 based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.

In some embodiments, the second network element 130 may transmit, to a third network element 141, a path switch request for a plurality of user equipments (UEs) to switch the NG-U DL termination point from the first network element 120 to the second network element 130, after the at least one UE 111 is resumed to the RRC_CONNECTED state, and may receive, from the third network element 141, a path switch request response indicating the NG-U DL termination point has been switched to the second network element 130.

In some embodiments, the second network element 130 may transmit, to the first network element 120, a data forwarding address indication including at least one data forwarding address for data transfer, after switching of the cell 110 from the first network element 120 to the second network element 130, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element 120 and the second network element 130 is established, wherein after switching of the cell from the second network element 130 to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element 130 from the next serving network element, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element 130 to the first network element 120 for establishing a data forwarding nested tunnel between the first network element 120 and the next serving network element, till a NG-U DL termination point hosted by the first network element 120 is switched to a network element where the at least one UE 111 resumes connection from the inactive state to the connected state.

In some embodiments, the second network element 130 may receive a RRC resume request triggered by the at least one UE 111, after switching a NG-U downlink (DL) termination point hosted by the first network element 120 to the second network element 130, and may transmit a RRC resume message to the at least one UE 111 based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.

In some embodiments, the second network element 130 may transmit, to a third network element 141, a path switch request for a plurality of user equipments (UEs) to switch the NG-U DL termination point from the first network element 120 to the second network element 130, after the UE context including the updated security context with the new security key is received by the second network element 130 while the plurality of UEs is still in the inactive state, and may receive, from the third network element 141, a path switch request response indicating the NG-U DL termination point has been switched to the second network element 130.

FIG. 7 illustrates a flowchart of an example method 700 implemented at a second network element in accordance with some other embodiments of the present disclosure. It is to be understood that the method 700 may include additional blocks not shown and/or may omit some blocks as shown, and the scope of the present disclosure is not limited in this regard. For ease of understanding, the method 700 will be described from the perspective of the third network element 141 with reference to FIG. 1A.

At block 710, the third network element 141 receives, from a second network element 130 which is to serve a cell 110 served by a first network element 120, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element 120 to the second network element 130. At block 720, the third network element 141 transmits, to the second network element 130, a path switch response indicating the NG-U DL termination point has been switched to the second network element 130.

In some embodiments, the path switch request response may be received after the plurality of UEs are resumed to the RRC_CONNECTED state.

In some embodiments, the third network element 141 may transmit, to the first network element 120, an indication to release UE context of the plurality of UE.

In some embodiments, the path switch request response may be received after UE context of the plurality of UEs is transfer from the first network element 120 to the second network element 130 while the plurality of UEs are still in the inactive state.

In some embodiments, an apparatus capable of performing the method 500 (for example, the first network element 120) may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for updating, based on a new security key derived, the security context included in user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell served by the first network element; and means for transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch.

The satellite switch herein refers to as change of NGSO satellite hosting full or part of the gNB serving fixed NTN cell on earth; i.e. the outgoing satellite stops serving the cell and an incoming satellite starts serving. The network elements (the first and second network elements) may be hosted on to a NGSO satellite which continuously orbits the earth. The network elements may be hosted on to a NGSO satellite which continuously orbits the earth.

In some example embodiments, the UE context may be transmitted via a non-UE associated Xn interface message or a UE-associated message, and may be included in a transparent container.

In some example embodiments, the apparatus may comprise: means for receiving, from the second network element, a data forwarding address indication including at least one data forwarding address for data transfer, before switching of the cell from the first network element to the second network element, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and wherein before switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element from the next serving network element, such that the second network element forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element to forward data received from a next generation (NG) user plane (NG-U) at the first network element to the next serving network element in a nested tunnel.

In some example embodiments, the apparatus may comprise: means for transitioning, via a radio resource control (RRC) release message with a suspend configuration, the at least one UE from RRC_CONNECTED state to the RRC_INACTIVE state.

In some example embodiments, the apparatus may comprise: means for maintaining the UE context including the updated security context until a NG-U downlink (DL) termination point hosted by the first network element is switch to the second network element after the plurality of UEs are resumed to the RRC_CONNECTED state.

In some example embodiments, the apparatus may comprise: means for receiving, from the second network element, a data forwarding address indication including at least one data forwarding address for data transfer, after switching of the cell from the first network element to the second network element, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, wherein after switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element from the next serving network element, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element to the first network element for establishing a data forwarding nested tunnel between the first network element and the next serving network element, till a NG-U DL termination point hosted by the first network element is switched to a network element where the at least one UE resumes connection from the inactive state to the connected state.

In some example embodiments, the apparatus may comprise: means for releasing the UE context including the updated security context, after a data forwarding tunnel between the first network element and the second network element is established based on the data forwarding address indication.

In some example embodiments, at least one of the following: the first network element is a last serving network element, and the second network element is a current serving network element; the first network element and the second network element may be satellite base stations; or the third network element may be an access and mobility management function (AMF) .

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 500. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some embodiments, an apparatus capable of performing the method 600 (for example, the second network element 130) may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving, from a first network element serving the cell which is to be served by the second network element after satellite switch, user equipment (UE) context of at least one UE in RRC_INACTIVE state in the cell, before the satellite switch, wherein the UE context includes updated security context wih new security key; and means for storing the UE context including the updated security context with new security key. The UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE has resumed to a connected state.

In some example embodiments, the UE context may be received via a non-UE associated Xn interface message or a UE-associated message, and may be included in a transparent container.

In some example embodiments, the apparatus may comprise means for transmit, a data forwarding address indication including at least one data forwarding address for data transfer, before switching of the cell from the first network element to the second network element, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and wherein before switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is transmitted by the next serving network element to the second network element, such that the second network element forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element to forward data received from a next generation (NG) user plane (NG-U) at the first network element to the next serving network element in a nested tunnel.

In some example embodiments, the apparatus may comprise means for receiving a RRC resume request triggered by the at least one UE, before switching a NG-U downlink (DL) termination point hosted by the first network element to the second network element; and means for transmitting a RRC resume message to the at least one UE based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.

In some example embodiments, the apparatus may comprise means for transmitting, to a third network element, a path switch request for a plurality of user equipments (UEs) to switch the NG-U DL termination point from the first network element to the second network element, after the plurality of UEs are resumed to the RRC_CONNECTED state; and means for receiving, from the third network element, a path switch request response indicating the NG-U DL termination point has been switched to the second network element.

In some example embodiments, the apparatus may comprise means for transmitting, to the first network element, a data forwarding address indication including at least one data forwarding address for data transfer, after switching of the cell from the first network element to the second network element, wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and wherein after switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element from the next serving network element, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element to the first network element for establishing a data forwarding nested tunnel between the first network element and the next serving network element, till a NG-U DL termination point hosted by the first network element is switched to a network element where the at least one UE is resumes connection from the inactive state to the connected state.

In some example embodiments, the apparatus may comprise means for receiving a RRC resume request triggered by the at least one UE, after switching a NG-U downlink (DL) termination point hosted by the first network element to the second network element; and means for transmitting a RRC resume message to the at least one UE based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.

In some example embodiments, the apparatus may comprise means for transmitting, to a third network element, a path switch request for a plurality of user equipments (UEs) to switch the NG-U DL termination point from the first network element to the second network element, after the UE context including the updated security context with the new security key is received by the second network element while the plurality of UEs is still in the inactive state; and means for receiving, from the third network element, a path switch request response indicating the NG-U DL termination point has been switched to the second network element.

In some embodiments, the apparatus further comprises means for performing other steps in some embodiments of the method 600. In some embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some embodiments, an apparatus capable of performing the method 700 (for example, the third network element 141) may comprise means for performing the respective steps of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus comprises: means for receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and means for transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.

In some example embodiments, the path switch request response may be received after the plurality of UEs are resumed to the RRC_CONNECTED state.

In some example embodiments, the apparatus comprises: means for transmitting, to the first network element, an indication to release UE context of the plurality of UEs.

In some example embodiments, the path switch request response may be received after UE context of the plurality of UEs is transfer from the first network element to the second network element while the plurality of UEs are still in the inactive state.

FIG. 8 illustrates a simplified block diagram of a device 800 that is suitable for implementing some example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the first network element 120 or the second network element 130 or the third network element 141 as shown in FIG. 1A. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

The communication module 840 is for bidirectional communications. The communication module 840 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements.

The processor 810 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 820 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 824, an electrically programmable read only memory (EPROM) , a flash memory, a hard disk, a compact disc (CD) , a digital video disk (DVD) , and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The program 830 may be stored in the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

The embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIGS. 2-7. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 830 may be tangibly contained in a computer-readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer-readable medium to the RAM 822 for execution. The computer-readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like.

FIG. 9 illustrates a block diagram of an example of a computer-readable medium 900 in accordance with some example embodiments of the present disclosure. The computer-readable medium 900 has the program 830 stored thereon. It is noted that although the computer-readable medium 900 is depicted in form of CD or DVD in FIG. 1A1, the computer-readable medium 900 may be in any other form suitable for carry or hold the program 830.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer-readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the method 500, 600 and 700 as described above with reference to FIG. 5, FIG 6 or FIG 7. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer-readable medium, and the like.

The computer-readable medium may be a computer-readable signal medium or a computer-readable storage medium. A computer-readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer-readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non-transitory, ” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM) .

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A first network element comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the first network element at least to:

update, based on a new security key derived, security context included in user equipment (UE) context of at least one UE in an inactive state in a cell served by the first network element; and

transmit, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with the new security key, before the satellite switch,

wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.
The first network element of claim 1, wherein the UE context is transmitted via a non-UE associated Xn interface message or a UE-associated message, and is included in a transparent container.
The first network element of claim 1 or 2, wherein the first network element is further caused to:

before switching of the cell from the first network element to the second network element, receive, from the second network element, a data forwarding address indication including at least one data forwarding address for data transfer,

wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and

wherein before switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element from the next serving network element, such that the second network element forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element to forward data received from a next generation (NG) user plane (NG-U) at the first network element to the next serving network element in a nested tunnel.
The first network element of any of claims 1-3, wherein the first network element is further caused to:

transition, via a radio resource control (RRC) release message with a suspend configuration, the at least one UE from a connected state to the inactive state.
The first network element of claim 4, wherein the first network element is further caused to:

maintain the UE context including the updated security context until a NG-U downlink (DL) termination point hosted by the first network element is switch to the second network element after the at least one UE is resumed to the connected state.
The first network element of claim 1 or 2, wherein the first network element is further caused to:

after switching of the cell from the first network element to the second network element, receive, from the second network element, a data forwarding address indication including at least one data forwarding address for data transfer,

wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and

wherein after switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is received by the second network element from the next serving network element, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element to the first network element for establishing a data forwarding nested tunnel between the first network element and the next serving network element, till a NG-U DL termination point hosted by the first network element is switched to a network element where the at least one UE is resumes connection from the inactive state to the connected state.
The first network element of any of claims 1-6, wherein at least one of the following:

the first network element is a last serving network element, and the second network element is a current serving network element; or

the first network element, the second network element and the next serving network element are satellite base stations.
A second network element comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the second network element at least to:

receive, from a first network element serving a cell which is to be served by the second network element after satellite switch, user equipment (UE) context of at least one UE in an inactive state in the cell, before the satellite switch, wherein the UE context includes updated security context with a new security key; and

store the UE context including the updated security context with the new security key,

wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.
The second network element of claim 8, wherein the UE context is received via a non-UE associated Xn interface message or a UE-associated message, and is included in a transparent container.
The second network element of claim 8 or 9, wherein the second network element is further caused to:

before switching of the cell from the first network element to the second network element, transmit, a data forwarding address indication including at least one data forwarding address for data transfer,

wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and

wherein before switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is transmitted by the next serving network element to the second network element, such that the second network element forwards the data forwarding address indication including at least one data forwarding address of the next serving network element to the first network element to forward data received from a next generation (NG) user plane (NG-U) at the first network element to the next serving network element in a nested tunnel.
The second network element of claim 10, wherein the second network element is further caused to:

before switching a NG-U downlink (DL) termination point hosted by the first network element to the second network element, receive a RRC resume request triggered by the at least one UE; and

transmit a RRC resume message to the at least one UE based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.
The second network element of claim 11, wherein the second network element is further caused to:

transmit, to a third network element, a path switch request for a plurality of UEs to switch the NG-U DL termination point from the first network element to the second network element, after the plurality of UEs are resumed to the connected state; and

receive, from the third network element, a path switch request response indicating the NG-U DL termination point has been switched to the second network element.
The second network element of claim 8 or 9, wherein the second network element is further caused to:

after switching of the cell from the first network element to the second network element, transmit, to the first network element, a data forwarding address indication including at least one data forwarding address for data transfer,

wherein based on the data forwarding address indication, a data forwarding tunnel between the first network element and the second network element is established, and

wherein after switching of the cell from the second network element to a next serving network element, a data forwarding address indication including at least one data forwarding address of the next serving network element is transmitted by the next serving network element to the second device, such that the data forwarding address indication including at least one data forwarding address of the next serving network element is forwarded by the second network element to the first network element for establishing a data forwarding nested tunnel between the first network element and the next serving network element, till a NG-U DL termination point hosted by the first network element is switched to a network element where the at least one UE is resumes connection from the inactive state to the connected state.
The second network element of claim 13, wherein the second network element is further caused to:

after switching a NG-U downlink (DL) termination point hosted by the first network element to the second network element, receive a RRC resume request triggered by the at least one UE; and

transmit a RRC resume message to the at least one UE based on the UE context including the updated security context, wherein the RRC resume message is encrypted using the new security key.
The second network element of claim 14, wherein the second network element is further caused to:

transmit, to a third network element, a path switch request for a plurality of UEs to switch the NG-U DL termination point from the first network element to the second network element, after the UE context including the updated security context with the new security key is received by the second network element while the plurality of UEs is still in the inactive state; and

receive, from the third network element, a path switch request response indicating the NG-U DL termination point has been switched to the second network element.
The second network element of any of claims 8-15, wherein at least one of the following:

the first network element is a last serving network element, and the second network element is a current serving network element;

the first network element and the second network element are satellite base stations; or

the third network element is an access and mobility management function (AMF) .
A third network element comprising:

at least one processor; and

at least one memory storing instructions that, when executed by the at least one processor, cause the third network element at least to:

receive, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and

transmit, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.
The third network element of claim 17, wherein the path switch request response is received after the plurality of UEs are resumed to the connected state.
The third network element of claim 18, wherein the third network element is further caused to:

transmit, to the first network element, an indication to release UE context of the plurality of UEs.
The third network element of claim 17, wherein the path switch request response is received after UE context of the plurality of UEs is transfer from the first network element to the second network element while the plurality of UEs are still in the inactive state.
The third network element of any of claims 17-20, wherein at least one of the following:

the first network element is a last serving network element, and the second network element is a current serving network element;

the first network element and the second network element are satellite base stations; or

the third network element is an access and mobility management function (AMF) .
A method comprising:

updating, at a first network element and based on a new security key derived, security context included in user equipment (UE) context of at least one UE in an inactive state in a cell served by the first network element; and

transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch,

wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.
A method comprising:

receiving, from a first network element serving a cell which is to be served by a second network element, user equipment (UE) context of at least one UE in an inactive state in the cell, before satellite switch, wherein the UE context includes updated security context and a new security key; and

storing, at the second network element, the UE context including the updated security context with new security key,

wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.
A method comprising:

receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and

transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.
An apparatus comprising:

means for updating, at a first network element and based on a new security key derived, security context included in user equipment (UE) context of at least one UE in an inactive state in a cell served by the first network element; and

means for transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch,

wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.
An apparatus comprising:

means for receiving, from a first network element serving a cell which is to be served by a second network element, user equipment (UE) context of at least one UE in an inactive state in the cell, before satellite switch, wherein the UE context includes updated security context and a new security key; and

means for storing, at the second network element, the UE context including the updated security context with new security key,

wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.
An apparatus comprising:

means for receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and

means for transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

updating, at a first network element and based on a new security key derived, security context included in user equipment (UE) context of at least one UE in an inactive state in a cell served by the first network element; and

transmitting, to a second network element which is to serve the cell after satellite switch, the UE context including the updated security context with new security key, before the satellite switch,

wherein the UE context including the updated security context with the new security key is transmitted to a next serving network element till the at least one UE is resumed to a connected state.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

receiving, from a first network element serving a cell which is to be served by a second network element, user equipment (UE) context of at least one UE in an inactive state in the cell, before satellite switch, wherein the UE context includes updated security context and a new security key; and

storing, at the second network element, the UE context including the updated security context with new security key,

wherein the UE context including the updated security context with the new security key is received by a next serving network element till the at least one UE is resumed to a connected state.
A non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least:

receiving, from a second network element which is to serve a cell served by a first network element, a path switch request for a plurality of user equipments (UEs) to switch a next generation (NG) user plane (NG-U) downlink (DL) termination point hosted by the first network element to the second network element; and

transmitting, to the second network element, a path switch response indicating the NG-U DL termination point has been switched to the second network element.