Secondary key counter handling

Abstract

Example embodiments of the present disclosure are directed to secondary key (SK) counter handling. A method comprises receiving, from a source master node (MN), a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility (LTM) preparation initiated from the source MN; and during the LTM handover, generating a secondary node (SN) key based on a certain SK counter in the SK counter list.

Description

SECONDARY KEY COUNTER HANDLINGFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for secondary key (SK) counter handling.BACKGROUND

[0002] For New radio- dual connectivity (NR-DC) handover., when master-key of a master node (MN) is changed due to inter MN Handover, network may generate new secondary node (SN) keys with new SK-counter-list.

[0003] Furthermore, whenever Master-key is changed, MN should regenerate the SN-Keys. Master-key update and SK-counter fields are independent parameters, user device does not store the SK-counter value it just uses it to generate the new SN-keys. Whenever master key is changed, network (NW) may signal SK-counter value to force the user device to generate new SN keys.SUMMARY

[0004] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: obtain a secondary key, SK, counter list from a configuration of source master node, MN, or from a configuration of target MN; and during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, in accordance with a determination that the SK counter list is to be restarted or a further SK counter list is indicated, use the further SK counter list or a SK counter from the beginning of the SK counter list for generating the secondary node, SN, key.

[0005] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at ileast to: after initiating an LTM preparation, transmit a SK counter list to a target MN via a handover request; and during an inter master node LTM handover from the second apparatus to the target MN, transmit a restart indication for SK counters associated with the SK counter list to the terminal device via a cell switch command for switching to the target MN and to the target MN via a cell switch notification.

[0006] In a third aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: after an initiation of an LTM preparation from a source MN, receive a SK counter list from the source MN via a handover request; and during an LTM handover from the source MN to the third apparatus, receive, from the source MN, a restart indication for SK counters associated with the SK counter list via a cell switch notification.

[0007] In a fourth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: obtain a secondary key, SK, counter list from a configuration of a target master node, MN; and during a layer 1 / layer 2 triggered mobility, LTM, handover from a source MN to a target MN, receive a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and generate a secondary node, SN, key by the SK counter list and the SK counter indication.

[0008] In a fifth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: after initiating an LTM preparation, transmit a SK counter list to a target MN associated with an LTM handover via a handover request; and during the LTM handover from the second apparatus to the target MN, transmit, to a terminal device, a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and transmit, to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device.

[0009] In a sixth aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the third apparatus at least to: afteran initiation of an LTM preparation from a source MN, receive a SK counter list from the source MN via a handover request; during an LTM handover from the source MN to the third apparatus, receive, from the source MN via a cell switch notification, an indication of a SK counter corresponding to a SK counter indication, indicated by the source MN to a terminal device, associated with at least one of a SK counter index or a SK counter; and generate, for a secondary node, SN, change, a new SN key based on the SK counter.

[0010] In a seventh aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: receive, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and during the LTM handover, generate a secondary node, SN, key based on a certain SK counter in the SK counter list.

[0011] In an eighth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: after initiating an LTM preparation, share a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and transmit, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

[0012] In a ninth aspect of the present disclosure, there is provided a method. The method comprises: obtaining a secondary key, SK, counter list from a configuration of source master node, MN, or from a configuration of target MN; and during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, in accordance with a determination that the SK counter list is to be restarted or a further SK counter list is indicated, using the further SK counter list or a SK counter from the beginning of the SK counter list for generating the secondary node, SN, key.

[0013] In a tenth aspect of the present disclosure, there is provided a method. The method comprises: after initiating an LTM preparation, transmit a SK counter list to a target MN via a handover request; and during an inter master node LTM handover from a source MN to the target MN, transmitting a restart indication for SK counters associated with the SK counter list to the terminal device via a cell switch command for switching to the target MN and tothe target MN via a cell switch notification.

[0014] In an eleventh aspect of the present disclosure, there is provided a method. The method comprises: after an initiation of an LTM preparation from a source MN, receive a SK counter list from the source MN via a handover request; and during an LTM handover from the source MN to a target MN, receiving, from the source MN, a restart indication for SK counters associated with the SK counter list via a cell switch notification.

[0015] In a twelfth aspect of the present disclosure, there is provided a method. The method comprises: obtaining a secondary key, SK, counter list from a configuration of a target master node, MN; and during a layer 1 / layer 2 triggered mobility, LTM, handover from a source MN to a target MN, receiving a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and generating a secondary node, SN, key by the SK counter list and the SK counter indication.

[0016] In a thirteenth aspect of the present disclosure, there is provided a method. The method comprises: after initiating an LTM preparation, transmit a SK counter list to a target MN associated with an LTM handover via a handover request; and during the LTM handover from the source MN to the target MN, transmitting, to a terminal device, a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and transmitting, to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device.

[0017] In a fourteenth aspect of the present disclosure, there is provided a method. The method comprises: after an initiation of an LTM preparation from a source MN, receiving a SK counter list from the source MN via a handover request; during an LTM handover from the source MN to the target MN, receiving, from the source MN via a cell switch notification, an indication of a SK counter corresponding to a SK counter indication, indicated by the source MN to a terminal device, associated with at least one of a SK counter index or a SK counter; and generating, for a secondary node, SN, change, a new SN key based on the SK counter.

[0018] In a fifteenth aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and during the LTM handover, generating a secondary node, SN, key based on a certain SK counter in theSK counter list.

[0019] In a sixteenth aspect of the present disclosure, there is provided a method. The method comprises: after initiating an LTM preparation, sharing a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and transmitting, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

[0020] In a seventeenth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for obtaining a secondary key, SK, counter list from a configuration of source master node, MN, or from a configuration of target MN; and means for, during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, in accordance with a determination that the SK counter list is to be restarted, using a SK counter from the beginning of the SK counter list.

[0021] In an eighteenth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for after initiating an LTM preparation, transmit a SK counter list to a target MN via a handover request; and means for, during an inter master node LTM handover from the second apparatus to the target MN, transmitting a restart indication for SK counters associated with the SK counter list to the terminal device via a cell switch command for switching to the target MN and to the target MN via a cell switch notification.

[0022] In a nineteenth aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for after an initiation of an LTM preparation from a source MN, receive a SK counter list from the source MN via a handover request; and means for, during an LTM handover from the source MN to the third apparatus, receiving, from the source MN, a restart indication for SK counters associated with the SK counter list via a cell switch notification.

[0023] In a twentieth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for obtaining a secondary key, SK, counter list from a configuration of a target master node, MN; and means for, during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, receiving a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and generating a secondary node, SN, key by the SK counter list and the SK counter indication .

[0024] In a twenty-first aspect of the present disclosure, there is provided a secondapparatus. The second apparatus comprises means for, after initiating an LTM preparation, transmitting a SK counter list to a target MN associated with an LTM handover via a handover request; and means for, during the LTM handover from the second apparatus to the target MN, transmitting, to a terminal device, a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and means for transmitting, to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device.

[0025] In a twenty-second aspect of the present disclosure, there is provided a third apparatus. The third apparatus comprises means for, after an initiation of an LTM preparation from a source MN, receiving a SK counter list from the source MN via a handover request; means for, during an LTM handover from the source MN to the third apparatus, receiving, from the source MN via a cell switch notification, an indication of a SK counter corresponding to a SK counter indication, indicated by the source MN to a terminal device, associated with at least one of a SK counter index or a SK counter; and means for generating, for a secondary node, SN, change, a new SN key based on the SK counter.

[0026] In a twenty-third aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and means for, during the LTM handover, generating a secondary node, SN, key based on a certain SK counter in the SK counter list.

[0027] In a twenty-fourth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for, after initiating an LTM preparation, sharing a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and means for transmitting, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

[0028] In a twenty-fifth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the ninth aspect.

[0029] In a twenty-sixth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the tenth aspect.

[0030] In a twenty-seventh aspect of the present disclosure, there is provided a computerreadable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the eleventh aspect.

[0031] In a twenty-eighth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the twelfth aspect.

[0032] In a twenty-ninth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the thirteenth aspect.

[0033] In a thirtieth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourteenth aspect.

[0034] In a thirty-first aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifteenth aspect.

[0035] In a thirty-second aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the sixteenth aspect.

[0036] 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

[0037] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0038] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0039] FIGS. 2-3 illustrate signaling charts of examples of SN Key change;

[0040] FIG. 4 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0041] FIG. 5 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0042] FIG. 6 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0043] FIG. 7 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0044] FIG. 8 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0045] FIG. 9 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0046] FIG. 10 illustrates a flowchart of a method implemented at a third apparatus in accordance with some example embodiments of the present disclosure;

[0047] FIG. 11 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0048] FIG. 12 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0049] FIG. 13 illustrates a flowchart of a method implemented at a third apparatus in accordance with some example embodiments of the present disclosure;

[0050] FIG. 14 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0051] FIG. 15 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0052] FIG. 16 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0053] FIG. 17 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0054] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0055] Principle 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. Embodiments described herein can be implemented in various manners other than the ones described below.

[0056] 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.

[0057] 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.

[0058] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like 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 and they do not limit the order of the noun(s). 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.

[0059] As used herein, “at least one of the following: ” and “at least one of ” 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.

[0060] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0061] 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.

[0062] 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 (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0063] 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.

[0064] As used herein, the term “communication network” refers to a network followingany suitable communication standards, such as New Radio (NR), 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) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) 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 types of 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.

[0065] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0066] 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), 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, imagecapture 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 (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., 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. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0067] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0068] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. The communication environment 100 may comprise a first apparatus 110, e.g., a UE, which may be referred to as a terminal device.

[0069] The communication environment 100 may comprise a second apparatus 120, e.g., a gNB, which may be referred to as a network device. The first apparatus 110 may be served by a cell 101 managed by the second apparatus 120. The first apparatus 110 may communicate with the second apparatus 120 within the cell 101.

[0070] In a scenario of an NR-DC, the second apparatus 120 may be considered as a master network node, e.g., a master node (MN). In this case, the second apparatus 120 may also bereferred to as a first MN, e.g., MN 1. The first apparatus 110 may connect to a secondary node 140, which may be referred to as a first secondary node (SN), e.g., SN 1.

[0071] An inter-MN handover may occur due to, e.g., the mobility of the first apparatus 110. For example, during an inter-MN LTM handover, the first apparatus 110 may switch from the first MN to a second MN (e.g., MN 2).

[0072] For example, the communication environment 100 may comprise a third apparatus 130, e.g., a gNB, which may be referred to as a network device. A cell 102 may be managed by the third apparatus 130. During the inter-MN handover, the first apparatus 110 may switch from the second apparatus (e.g., MN 1) the third apparatus 130 (e.g., MN 2). After the handover completes, the first apparatus 110 may be served by a cell 102 managed by the third apparatus 130. In this case, the first MN may be considered as a source MN and the second MN may be considered as a target MN.

[0073] In some scenarios, SN change may also occur, e.g., due to the inter-MN handover. For example, the first apparatus 110 may change the corresponding SN from the secondary node 140 to a secondary node 150, which may be considered a second SN, e.g., SN 2.

[0074] In some example embodiments, a link from the network node to the first apparatus 110 is referred to as a downlink (DL), while a link from the first apparatus 110 to the network node is referred to as an uplink (UL). In DL, the network node is a transmitting (TX) apparatus (or a transmitter) and the first apparatus 110 is a receiving (RX) apparatus (or a receiver). In UL, the first apparatus 110 is a TX apparatus (or a transmitter) and the network node is a RX apparatus (or a receiver).

[0075] It is to be understood that the number of devices and their connections shown in FIG.1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implement example embodiments of the present disclosure.

[0076] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), 5.5G, the sixth generation (6G), 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 butnot 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.

[0077] For New Radio Dual Connectivity (NR-DC) handover, when Master Node (MN) Master-key is changed due to inter MN Handover, network generates new Secondary Node (SN) keys with new Secondary Key (SK)-counter-list.

[0078] Regarding the UE behavior in some discussed schemes, it is unclear that how a new security configuration for the Secondary Cell Group (SCG) is to be provided to the UE when the UE performs the L1 / L2 Triggered Mobility (LTM) handover when Subsequent- Conditional Primary Secondary Cell Addition or Change (S-CPAC) is configured at the SN side.

[0079] When the S-CPAC is configured at the same time as an NR-DC handover, the UE has two parallel key methods running at the same time.1. The UE generates keys using the SK-counter list. (S-CPAC behavior)2. The UE generate the key using the SK-counter indicated in the target configuration. (NR-DC handover behavior)

[0080] In the scenario of some discussed schemes, the S-CPAC configuration can be at the same time as the LTM configuration. Thus, it is not clear if the UE will generate the key using the SK-counter list or SK-counter in the target configuration.

[0081] FIGS. 2-3 illustrate signaling charts of examples of SN Key change, where FIG. 2 shows SN Key change for inter-MN Master Cell Group (MCG) LTM due to MN change and FIG. 3 shows SN Key change for Inter-Secondary Cell Group SCG (SCPAC) due to inter MN handover.

[0082] Reference is now made to FIG. 2, which shows a signaling chart for the SN key change for the Inter-MN Master Cell Group (MCG) LTM due to MN change. At step 250 and 255 in FIG. 2, on Cell Switch Indication, the UE generates the new master key for the target MN. The UE need to know which SK-counter to be used to generate the new SN key.

[0083] When MN Master-key is changed due to inter MN Handover, the network generates new SN keys with new SK-counter-list. Regarding the UE behavior, it is unclear how a newsecurity configuration for the SCG is to be provided to the UE.

[0084] Reference is now made to FIG. 3, which shows a signaling chart for the SN key change fir Inter-SN SCG (S-CPAC) due to inter MN handover. As shown in FIG. 3, S-CPAC is configured or active. On the inter MN base handover from MN1 to MN2, master key gets changed and hence at step 355 shown in FIG. 3, target MN may generate new SN keys for SNs on receiving Handover Request. In step 390 to step 396 shown in FIG. 3, on receiving the Radio Resource Control (RRC) Reconfiguration (Handover Command), the UE generates the MN key but it’s not clear how to generate the SN key.

[0085] The problem is also applicable for the LTM in dual connectivity when the Inter-MN MCG LTM is executed, the SN keys need to be refreshed for the normal case and SK-counter list needs to be refreshed or new keys needs to be generated if the S-CPAC is configured for the SN.

[0086] The In accordance with some example embodiments of the present disclosure, there is provided a solution for SK counter. In this solution, UE obtains a SK counter list from a configuration of source MN, or from a configuration of target MN. During an inter MN LTM handover from the source MN to the target MN, if the SK counter list is to be restarted or a further SK counter list is indicated, use the further SK counter list or a SK counter from the beginning of the SK counter list for generating the SN key.

[0087] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0088] Reference is now made to FIG. 4, which shows a signaling chart 400 for communication according to some example embodiments of the present disclosure. As shown in FIG. 4, the signaling chart 400 involves a first apparatus 110, a second apparatus 120 and a third apparatus 130, a secondary node 140, a secondary node 150 and an AMF 160. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 400.

[0089] The scenario of FIG. 4 refers to MN LTM HO with LTM and SCPAC co-located. In this scenario, the second apparatus 120 acts as a source MN and the third apparatus 130 acts a target MN.

[0090] As shown in FIG. 4, the first apparatus 110 is connected (405) to second apparatus 120 (MN 1) and is in NR-DC with the secondary node 140 (SN 1). Then the second apparatus 120 may generate (410) the SN-keys for SNs by using the SK-counters.

[0091] The second apparatus 120 may initiate (415) the SN Addition Request procedure to prepare SCPAC configuration including the SN Key and SK-Counter pair list for all the SK- counters that the second apparatus 120 has used to generated SN keys. The secondary node 150 (i.e., the second SN) may share the SCPAC configuration and confirms the the SN Key and SK-Counter pair list by sending (420) SN Addition Request acknowledge message.

[0092] Then the the second apparatus 120 may share (430) the SCPAC configurations in RRC reconfiguration message to the first apparatus 110 including SK-counter list in a source MN configuration that to be used by the first apparatus 110 during inter MN handover. The first apparatus 110 may confirm the source MN configuration by sending (435) a RRC reconfiguration complete message.

[0093] The second apparatus 120, on receiving (440) L3 measurement report from the first apparatus 110, may initiate (445) LTM preparation. The second apparatus 120 may send (450) a Handover request to the third apparatus 130 (e.g., a target MN) including SK-counter list. After sending (455) a Handover request acknowledge message, the target MN configuration including the SK-counter list may be sent (460) from the second apparatus 120 to the first apparatus 110 via an RRC reconfiguration message.

[0094] The first apparatus 110 may use the SK-counter list from the target MN configuration to generate the SN key upon inter MN LTM handover to the third apparatus 130.

[0095] Optionally, if the third apparatus 130 does not include the SK-counter list in the target MN configuration, the first apparatus 110 may use (465) the SK-counter list from the source MN configuration. In this case, third apparatus 130 may indicate that it aims to reuse the SK-counter list in the source MN configuration.

[0096] Then the first apparatus 110 may confirm the SK-counter list by sending (470) a RRC reconfiguration complete message.

[0097] As an option (475), second apparatus 120 may generate (480) the new SN key by using the target MN keys and share (485) the new SN key and SK-counter pair list with SNs (e.g., the secondary node 140 (e.g., the first SN)) in SN Modification request procedure. This is done during the LTM preparation.

[0098] The first apparatus 110 may send (488) LI measurement reports to serving DU and DU in the second apparatus 120. Then the second apparatus 120 may take decision for LTM handover and send (489) a Cell Switch Command to the first apparatus 110. The CellSwitch Command may include a restart indication for SK-counters in the SK-counter list.

[0099] On receiving the Cell switch Command, the first apparatus 110 may generate (490) the SN keys by using the target MN key and SK-counter from start of the SK-counter list.

[0100] As another option (490a), for each Inter-CU MN LTM, the first apparatus 110 knows that if it is configured S-CPAC, it needs to do SK-counter reset. Hence, the first apparatus 110 start the use of SK-counters from the beginning from the list.

[0101] In this case, the second apparatus 120 may send (491) the Cell Switch Notification to the third apparatus 130, it includes a restart indication of SK-counter keys. The third apparatus 130 may generate (493) the new SN key using the first SK-counter from the list and send (494) the SN key with SK counter pair to secondary node 140 in SN Modification Request Procedure. Optionally, the restart indication may be included in the SN Modification Request to indicate that secondary node 140 shall use the first SN key from the SK-counter list.

[0102] In a case where the third apparatus 130 on successful of cell switch (496), optionally, the third apparatus 130 may indicate (497) SN key and SK-counter pairs to other SNs (e.g., the secondary node 150) and perform (499) the handover completion procedures.

[0103] In this case, during LTM preparation, the target MN may include SK-counter list in a target MN configuration.

[0104] Upon inter MN handover, the source MN sends the SK -counter list restart indication to UE in Cell Switch Command.

[0105] The target MN, on receiving cell switch notification, prepares the new SN keys for corresponding SK-counters and shares with DC- active and configured SNs

[0106] The UE, on receiving the restart indication in Cell Switch Command (or in MAC CE), shall restart the use of SK-counters shared in target MN configuration.

[0107] Alternately MAC CE / Cell Switch Command can contain a new list of SK-counters that UE shall start using.

[0108] Alternately, MN shall share the new SK-counter list to UE through RRC signalling.

[0109] Alternately, if target MN does not contain SK-counter list, UE shall use the SK- counter list from source MN configuration.

[0110] Reference is now made to FIG. 5, which shows a signaling chart 500 forcommunication according to some example embodiments of the present disclosure. As shown in FIG. 5, the signaling chart 500 involves a first apparatus 110, a second apparatus 120 and a third apparatus 130, a secondary node 140, a secondary node 150 and an AMF 160. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 500.[OHl] The scenario of FIG. 5 refers to_SK-counter index in Cell Switch Command during MN LTM HO with LTM and SCPAC co-located^ In the scenario shown in FIG. 5, the second apparatus 120 acts as a source MN and the third apparatus 130 acts a target MN.

[0112] . In the scheme shown in FIG. 5, during the LTM preparation, the second apparatus 120 shares the Sk-counter list with source DU. Upon inter MN LTM handover, the source DU includes the Sk-counter index in Cell Switch Command sent to the first apparatus 110. The second apparatus 120 then indicates Sk-counter that is used for the target MN, and the third apparatus 130 generates new SN keys and shares with SNs along with corresponding Sk-counters.

[0113] As shown in FIG. 5, the first apparatus 110 connects (505) to the second apparatus 120 (which may be referred to as MN1 as well) and is in NR-DC with the secondary node 140 (which may be referred to as SN1 as well).

[0114] In some embodiments, the second apparatus 120 generates (510) the SN-keys for SNs by using the SK-counters and shares the list with SNs.

[0115] After generating the SN-keys, the MN initiates the SN Addition Request procedure to prepare SCPAC configuration. The second apparatus 120 includes the SN Key and the SK-Counter pair list for all the SK-counters that the second apparatus 120 has used to generated SN keys in a SN addition request, and transmit (515) the SN addition request to the secondary node 150. Then the secondary node 150 transmit (520) a SN addition request acknowledge to the second apparatus 120. Then the second apparatus 120 may optionally transmit (525) an Xn-U address indication to the secondary node 150.

[0116] Then the second apparatus 120 may share (530) the S-CPAC configuration in RRC reconfiguration to the first apparatus 110 including SK-counter list in MN configuration that to be used by the first apparatus 110 during SCPAC execution. Moreover, the RRC configuration may comprise MN RRC reconfiguration and SN RRC reconfiguration. Upon finishing the reconfiguration, the first apparatus 110 may transmit (535) a message indicating the RRC reconfiguration is complete to the second apparatus 120.

[0117] In some embodiment, the second apparatus 120 may receive (540) the L3 measurement report from the first apparatus 110. Then, at 545, the second apparatus 120 initiates the LTM preparation.

[0118] In some embodiment, after initiating an LTM preparation, the second apparatus 120 may transmit (550) a SK counter list to a target MN (i.e., third apparatus 130) associated with an LTM handover via a handover request. For example, the second apparatus 120 may send Handover request to target MNs including SK-counter list. Upon receiving the Handover request, the third apparatus 130 may transmit (555) a handover request acknowledgement including the SK counter list to the second apparatus 120 as a response.

[0119] In some embodiments, if the second apparatus 120 determines that a handover request acknowledgment including the SK counter list is received from the target MN, the second apparatus 120 may share (560) the SK counter list to a source distributed unit at the source MN (i.e., the second apparatus 120). For example, the second apparatus 120 shall share the SK-counter list to source DU along with other security configurations.

[0120] In some embodiment, the first apparatus 110 may obtain (565) a SK counter list from a configuration of a target MN (i.e., the third apparatus 130). For example, the third apparatus 130 shall include the SK-counter list in target MN configuration, and the target MN configuration is transmitted to the first apparatus 110. The first apparatus 110 will use the SK-counter list from the target MN configuration to generate the SN key upon inter MN LTM handover to target MN.

[0121] In some embodiment, the first apparatus 110 may indicate (570) that the RRC configuration is complete to the second apparatus 120.

[0122] In some embodiments, at block 575, on receiving LI measurement reports from the first apparatus 110, the second apparatus 120 may take decision to perform inter CU LTM mobility.

[0123] In some embodiments, during an LTM handover from a source MN to a target MN, the first apparatus 110 may receive (580) a cell switch command including SK counter indication which may be associated with a SK counter index or a SK counter. For example, the Source DU may send cell switch command to UE. The cell switch command includes SK-counter index (index from the shared SK-counter list) or a SK counter from the SK counter list.

[0124] In some embodiments, the first apparatus 110 may generate (585) a SN key by usinga SK counter corresponding to the SK counter index from the SK counter list. For example, on receiving SK-counter index, the first apparatus 110 fetches the corresponding SK-counter and generates the new SN key by using the SK counter and the target MN master key. In some embodiments, the first apparatus 110 may generate (585) a SN key by using a SK counter received in cell switch command and the target MN key.

[0125] In some embodiments, the second apparatus 120 may transmit (590), to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device. For example, the second apparatus 120 may send a cell switch notification (it includes the SK-counter that is used from the SK- counter list in the cell switch command) to the third apparatus 130.

[0126] In some embodiment, the third apparatus 130 may generate (592), for a SN change, a new SN key based on the SK counter. For example, the third apparatus 130 may generate the SN key for corresponding SK-counters and shares with SN. Then the first apparatus 110 may transmit (595), to the third apparatus 130, an indication indicating that the RRC reconfiguration is complete.

[0127] In some embodiments, the third apparatus 130 may transmit (593 and 596), to a SN connected with the terminal device for a dual connectivity and a further SN associated with the LTM handover via a SN modification request, the new SN key and the SK counter used for generating the new SN key. For example, the third apparatus 130 may transmit the SN modification request to the secondary node 150, wherein the SN modification request may comprise the new SN key, SK-counter pair list.

[0128] Upon receiving the SN modification request, the secondary node 150 may transmit (594 and 597) a SN modification request acknowledgement to the third apparatus 130.

[0129] Finally, on successful of cell switch, the third apparatus 130 may optionally indicate (598) SN key and SK-counter pairs to other SNs and performs the handover completion procedures. Moreover, at this time, the data forwarding may be performed and the path switch and handover completion is completed.

[0130] In this solution, during LTM preparation, source MN in the source MN shares the SK-counter list with source DU. Upon inter MN LTM handover, source DU in the source MN includes SK-counter index in Cell Switch Command sent to UE. Source MN then may indicate SK-counter that’s used to target MN, and target MN generates new SN keys and shares with SNs along with corresponding SK-counters. Alternately upon inter MN LTM handover, source DU in the source MN includes SK-counter in Cell Switch Command sentto UE.

[0131] Reference is now made to FIG. 6, which shows a signaling chart 600 for communication according to some example embodiments of the present disclosure. As shown in FIG. 6, the signaling chart 600 involves a first apparatus 110, a second apparatus 120 and a third apparatus 130, a secondary node 140, a secondary node 150 and an AMF 160. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 600.

[0132] The scenario of FIG. 6 refers to SK Counter handling during inter MN basic handover and no SN change. In the scenario shown in FIG. 6, the first apparatus 110 may be referred to as a UE, the second apparatus 120 may be referred to as a source MN, the third apparatus 130 may be referred to as a target MN, and the secondary node 140 and the secondary node 150 may be the SNs that provide DC related functions.

[0133] In the scheme shown in FIG. 6, upon inter MN handover, the third apparatus 130 shall generate new SN keys by using target MN key and preconfigured SK-counters. The new SN key and SK-counter pair lists with configured SNs are shared. The first apparatus 110 is indicated to use the preconfigured SK-counter list from start.

[0134] As shown in FIG. 6, the second apparatus 120 generates (602) the SN-keys for SNs by using the SK-counters and shares the list with SNs.

[0135] For example, the first apparatus 120-1 generates SN keys for list of SK-counters to share with SNs.

[0136] The second apparatus 120 includes the SN Key and the SK-Counter pair list for all the SK-counters that the second apparatus 120 has used to generated SN keys in a SN addition request, and transmit (604) the SN addition request to the secondary node 150. Moreover, the second apparatus 120 may also transmit (606) the SN addition request to the AMF 140. For example, the second apparatus 120 may prepare the SN configuration. Then it shares the list of SN key and SK-Counter pairs with SNs in SN Addition Request.

[0137] Then the secondary node 150 transmit (608) a SN addition request acknowledge to the second apparatus 120. And the AMF 140 may also transmit (610) the SN addition request acknowledge to the second apparatus 120. Then the second apparatus 120 may optionally transmit (612) an Xn-U address indication to the secondary node 150. The second apparatus 120 may also optionally transmit (614) an Xn-U address indication to the AMF 140.

[0138] In some embodiments, on receiving SN configurations (in SN AdditionAcknowledge) the second apparatus 120 prepares RRC reconfiguration. It includes SN configuration. MN includes the SK-counter list in RRC Reconfiguration. Then the second apparatus 120 transmit (616) the indication of the RRC reconfiguration to the first apparatus 110. On receiving the SK-counter list, the first apparatus 110 stores (618) the SK-Counter list in a separate variable called refresh SK-counter list.

[0139] In some embodiments, the first apparatus 110 transmit (620), to the second apparatus 120, an indication indicating that the RRC reconfiguration is complete. Then the first apparatus 110 may transmit (622) a measurement report to the second apparatus 120. For example, on receiving the measurement report from the first apparatus 110, the second apparatus 120, i.e., the source MN(MNl), initiates inter MN handover towards the third apparatus 130, that is, the target MN (MN2).

[0140] The second apparatus 120 sends (624) the Handover Request including a preconfigured SK-counter list. On receiving Handover request, the third apparatus 130 may prepare (626) new SN keys for preconfigured SK-counters and shares with configured SNs at the following steps. Moreover, the third apparatus 130 may also include a restart indication towards SNs, such that SNs shall use SN keys and SK-counters from the start of the preconfigured list.

[0141] In some embodiments, the third apparatus 130 may transmit (628) a SN modification request to the secondary node 140, and the third apparatus 130 may also transmit (630) the SN modification request to the secondary node 150. Upon receiving the SN modification request, the secondary node 140 may transmit (632) a SN modification request acknowledgement to the third apparatus 130, and the secondary node 150 may also transmit (634) a SN modification request acknowledgement to the third apparatus 130.

[0142] In some embodiments, the third apparatus 130 may transmit (636) the Handover request acknowledgement to the second apparatus 120. For example, the third apparatus 130, i.e., the target MN(MN2), send the restart indication towards the first apparatus 110 in MN RRC Reconfiguration (Handover command).

[0143] In some embodiment, the second apparatus 120 may transmit (638) an indication of RRC reconfiguration to the first apparatus 110. Then the first apparatus 110 may transmit (640) an indication of the completion of the RRC reconfiguration to the third apparatus 130.

[0144] In some embodiments, the first apparatus 110 may generate (642) new MN keys, and the first apparatus 110 may restart the use of the SK-counter list using the refresh SK-counter list. For example, the first apparatus 110 may restart the preconfigured SK-counters list anduse from first to generate SN-key for SNs. The first apparatus 110 may also generate the new SN key by using the first SK-counter and use the new SN key to send data to the SN.

[0145] In some embodiments, the first apparatus 110 may transmit (644) an indication of RRC Reconfiguration complete to the third apparatus 130. Then the RRC Reconfiguration complete is transmitted (646) to the secondary node 150 by the third apparatus 130. For example, the first apparatus 110 may send the SN RRC Reconfiguration complete to the SN via the third apparatus 130.

[0146] Finally, the third apparatus 130 and the secondary node 140 perform (648) the path update or path switch procedure.

[0147] In this solution, upon inter MN handover target MN shall generate new SN keys by using target MN key and preconfigured SK-counters. The new SN key and SK-counter pair lists may be shared with configured SNs and the UE may be indicated to use the preconfigured SK-counter list from start

[0148] Reference is now made to FIG. 7, which shows a signaling chart 700 for communication according to some example embodiments of the present disclosure. As shown in FIG. 7, the signaling chart 700 involves a first apparatus 110, a second apparatus 120 and a third apparatus 130, a secondary node 140, a secondary node 150 and an AMF 160. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 700.

[0149] The scenario of FIG. 7 refers to SK Counter handling during inter MN basic handover and no SN change. In this scenario, the second apparatus 120 acts as a source MN and the third apparatus 130 acts a target MN. the secondary node 140 acts as a source SN and the secondary node 150 acts a target SN.

[0150] As shown in FIG. 7, the first apparatus 110 is connected (702) to second apparatus 120 (MN 1) and is in NR-DC with the secondary node 140 (SN 1).

[0151] The first apparatus 110 sends (704) L3 measurement report to the second apparatus 120 and the second apparatus 120 takes (706) decision to prepare LTM candidates.

[0152] The second apparatus 120, for every MN LTM targets CUs (not cells), shares (708) the SK-counter list with target MNs (such as the third apparatus 130).

[0153] For example, the second apparatus 120 may send (710) a Handover request to the third apparatus 130 (e.g., a target MN) including SK-counter or a SK-counter list. After that,the third apparatus 130 may send (712) a Handover request acknowledge message to the second apparatus 120, the target MN configuration including the SK-counter list may be sent (460) from the second apparatus 120 to the first apparatus 110 via Handover Request Acknowledge message. The second apparatus 120, after receiving the Handover Request Acknowledge, shares (714) the SK-counter list with source DU along with other security parameters. The the second apparatus 120 may include the SK-counter or SK-counter list in MN configuration and send (716) it in an RRC Reconfiguration message to the first apparatus 110.

[0154] Optionally (708a), the second apparatus 120 can generate SN keys by using target MN keys and SK-counters. The second apparatus 120 may share the new SN keys with SN for corresponding MNs.

[0155] The first apparatus 110 may report (720) LI measurement Reports to the second apparatus 120 and the second apparatus 120 may trigger LTM Cell Switch to third apparatus 130. The second apparatus 120 sends (722) a Cell Switch Command to the first apparatus 110. The Cell Switch Command includes SK-counter index. At the same time, the second apparatus 120 sends (726) a Cell Switch Notification containing SK-counter to the third apparatus 130.

[0156] Then the first apparatus 110 may generate (724) the SN Key by using the SK-counter (fetched by using the SK-counter index) from SK-counter list. As another option (724a), when no SK-counter is provided in the Cell Switch Command for inter CU LTM HO, the first apparatus 110 and the second apparatus 120 generate new SN-keys based on default SK- counter value 1. In this case explicit SK-counter signaling is avoided.

[0157] The third apparatus 130, on receiving the Cell Switch Notification, may generate (728) the new SN keys and share (730) with the secondary node by using SN Modification Request procedure. Then the third apparatus 130 may perform (734) the path switch and handover procedure completion.

[0158] In this solution, for every MN (not for every candidate) SK-counter or SK-counter- list is included. Towards UE, In the RRC-Reconfiguration message, the LTM-Config will include SK-counter value for every MN-cell-set-ID (Rel-19-ID).

[0159] On MCG cell-switch, source DU indicate the SK-Counter-index to UE. Source MN also indicate selected SK-counter and SN-key to SN after regenerating the SN keys. On receiving switching command for MCG, UE also regenerate SN keys based on the received SK-counter-index value.

[0160] Alternatively, it is possible that no SK-counter is provided in cell-switch command. In this case, UE and source MN generates new SN-keys based on default SK-counter value, e.g., with [ counter=l],

[0161] By using the solutions mentioned above, key derivation may be used and the SK- counter issue on inter MN handover (on MN key change) can be solved.

[0162] FIG. 8 shows a flowchart of an example method 800 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the first apparatus 110 in FIG. 1.

[0163] At block 810, the first apparatus 110 obtains a secondary key, SK, counter list from a configuration of source master node, MN, or from a configuration of target MN.

[0164] At block 820, during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, in accordance with a determination that the SK counter list is to be restarted or a further SK counter list is indicated, uses the further SK counter list or a SK counter from the beginning of the SK counter list for generating the secondary node, SN, key.

[0165] In some example embodiments, the method 800 further comprises: after an initiation of an LTM preparation from a source MN, receiving the configuration of the target MN via a radio resource control signaling; and determining whether the SK counter list is included in the configuration of the target MN; and in accordance with a determination that the SK counter list is included in the configuration of the target MN, obtaining the SK counter list from the configuration of the target MN.

[0166] In some example embodiments, the method 800 further comprises: in accordance with a determination that the SK counter list is not included in the configuration of the target MN, obtaining the SK counter list from the configuration of the source MN.

[0167] In some example embodiments, the method 800 further comprises: receiving an indication that the configuration of the source MN is to be reused by the target MN.

[0168] In some example embodiments, the method 800 further comprises: receiving, from the source MN, a cell switch command for switching to the target MN; in accordance with a determination that the cell switch command includes a restart indication for SK counters, using the SK counter from the beginning of the SK counter list.

[0169] In some example embodiments, the method 800 further comprises: in accordance with a determination that a cell switch command for switching to the target MN is received from the source MN and the first apparatus is configured with subsequent conditional primary secondary cell addition or change, S-CPAC use the SK counter from the beginning of the SK counter list.

[0170] In some example embodiments, the first apparatus comprises a terminal device.

[0171] FIG. 9 shows a flowchart of an example method 900 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0172] At block 910, after initiating an LTM preparation, the second apparatus 120 transmits a SK counter list to a target MN via a handover request.

[0173] At block 920, during an inter master node LTM handover from the second apparatus to the target MN, the second apparatus 120 transmits a restart indication for SK counters associated with the SK counter list to the terminal device via a cell switch command for switching to the target MN and to the target MN via a cell switch notification.

[0174] In some example embodiments, the method 900 further comprises: in accordance with a determination that a handover request acknowledgment including the SK counter list is received from the target MN, forwarding a configuration of the target MN including the SK counter list to the terminal device via an RRC reconfiguration message.

[0175] In some example embodiments, the method 900 further comprises: in accordance with a determination of a secondary node, SN key change due to the inter master node LTM handover, generating new SN keys by using target MN keys and SK counter in the configured SK counter list; and transmitting, to a SN connected with the terminal device for a dual connectivity, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0176] In some example embodiments, the second apparatus comprises a source MN for the inter master node LTM handover.

[0177] FIG. 10 shows a flowchart of an example method 1000 implemented at a third apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0178] At block 1010, after an initiation of an LTM preparation from a source MN, the third apparatus receives a SK counter list from the source MN via a handover request.

[0179] At block 1020, during an LTM handover from the source MN to the third apparatus, the third apparatus receives, from the source MN, a restart indication for SK counters associated with the SK counter list via a cell switch notification.

[0180] In some example embodiments, the method 1000 further comprises: transmitting, to the source MN, a handover request acknowledgment including the SK counter list.

[0181] In some example embodiments, the method 1000 further comprises: in accordance with a determination of a secondary node, SN key change due to the inter master node LTM handover, based on the restart indication for SK counters, generating new SN keys by using the SK counters from the beginning of the SK counter list; and transmitting, to a SN connected with the terminal device for a dual connectivity via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0182] In some example embodiments, the method 1000 further comprises: in accordance with a determination of a secondary node, SN key change due to the inter master node LTM handover, based on the restart indication for SK counters, generating new SN keys by using the SK counters from a further SK counter list configured by the third apparatus; and transmitting, to a SN connected with the terminal device for a dual connectivity via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0183] In some example embodiments, the method 1000 further comprises: transmitting, via the SN modification request to the SN, restart indication for SK counters associated with the SK counter list.

[0184] In some example embodiments, the method 1000 further comprises: in accordance with a determination of a completion of the inter master node LTM handover, transmitting to a further SN via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0185] In some example embodiments, the third apparatus comprises a target MN for the inter master node LTM handover.

[0186] FIG. 11 shows a flowchart of an example method 1100 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the firstapparatus 110 in FIG. 1.

[0187] At block 1110, the first apparatus 110 obtains a secondary key, SK, counter list from a configuration of a target master node, MN. and

[0188] At block 1120, during a layer 1 / layer 2 triggered mobility, LTM, handover from a source MN to a target MN, the first apparatus 110 receives a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter.

[0189] At block 1130, the first apparatus 110 generates a secondary node, SN, key by the SK counter list and the SK counter indication.

[0190] In some example embodiments, the method 1100 further comprises: after an initiation of an LTM preparation from the source MN, receiving the configuration of the target MN via a radio resource control signaling.

[0191] In some example embodiments, the method 1100 further comprises: obtaining an association between a set of SK counter indices and a plurality of SK counters in the SK counter list; and in accordance with a determination that the SK counter indication associated with the SK counter index, determining a target SK counter to be used based on the SK counter index and the association.

[0192] In some example embodiments, the first apparatus comprises a terminal device.

[0193] FIG. 12 shows a flowchart of an example method 1200 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1200 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0194] At block 1210, after initiating an LTM preparation, the second apparatus transmits a SK counter list to a target MN associated with an LTM handover via a handover request, and

[0195] At block 1220, during the LTM handover from the second apparatus to the target MN, the second apparatus transmits, to a terminal device, a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter.

[0196] At block 1230, the second apparatus transmits, to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device.

[0197] In some example embodiments, the method 1200 further comprises: in accordancewith a determination that a handover request acknowledgment including the SK counter list is received from the target MN, sharing the SK counter list to a source distributed unit at the source MN.

[0198] In some example embodiments, the second apparatus comprises a source MN for the LTM handover.

[0199] FIG. 13 shows a flowchart of an example method 1300 implemented at a third apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1300 will be described from the perspective of the third apparatus 130 in FIG. 1.

[0200] At block 1310, after an initiation of an LTM preparation from a source MN, the third apparatus receives a SK counter list from the source MN via a handover request.

[0201] At block 1320, during an LTM handover from the source MN to the third apparatus, the third apparatus receives from the source MN via a cell switch notification, an indication of a SK counter corresponding to a SK counter indication, indicated by the source MN to a terminal device, associated with at least one of a SK counter index or a SK counter.

[0202] At block 1330, the third apparatus generates, for a secondary node, SN, change, a new SN key based on the SK counter.

[0203] In some example embodiments, the method 1300 further comprises: transmitting, to the source MN, a handover request acknowledgment including the SK counter list.

[0204] In some example embodiments, the method 1300 further comprises: in accordance with a determination of a secondary node, SN key change due to the LTM handover, generating the new SN key; and transmitting, to a SN connected with the terminal device for a dual connectivity and a further SN associated with the LTM handover via a SN modification request, the new SN key and the SK counter used for generating the new SN key.

[0205] In some example embodiments, the third apparatus comprises a target MN for the LTM handover.

[0206] FIG. 14 shows a flowchart of an example method 1400 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1400 will be described from the perspective of the first apparatus 110 in FIG. 1.

[0207] At block 1410, the first apparatus receives, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN.

[0208] At block 1420, during the LTM handover, the first apparatus generates a secondary node, SN, key based on a certain SK counter in the SK counter list.

[0209] In some example embodiments, the method 1400 further comprises: receiving the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

[0210] In some example embodiments, the method 1400 further comprises: in accordance with a determination that a SK counter index is received from the source MN via a cell switch command, determining the certain SK counter based on the SK counter index.

[0211] In some example embodiments, the method 1400 further comprises: obtaining an association between a set of SK counter indices and a plurality of SK counters in the SK counter list; and determining the SK counter to be used based on the received SK counter index and the association.

[0212] In some example embodiments, the method 1400 further comprises: in accordance with a determination that there is no SK counter indicated by a cell switch command, using the default SK counter as the certain SK counter.

[0213] In some example embodiments, the cell switch command is a command for mater cell group switch without a SN change.

[0214] In some example embodiments, the first apparatus comprises a terminal device.

[0215] FIG. 15 shows a flowchart of an example method 1500 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1500 will be described from the perspective of the second apparatus 120 in FIG. 1.

[0216] At block 1510, after initiating an LTM preparation, the second apparatus shares a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation.

[0217] At block 1520, the second apparatus transmits, to a terminal device, the SK counterlist or SK counters for generating a secondary node, SN, key.

[0218] In some example embodiments, the method 1500 further comprises: transmitting the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

[0219] In some example embodiments, the method 1500 further comprises: transmitting a SK counter list to a target MN via a handover request; and in accordance with a handover request acknowledgment is received from the target MN, sharing the SK-counter list with a source distributed unit along with other security parameters.

[0220] In some example embodiments, the method 1500 further comprises: generating SN keys by using target MN keys of the set of target MN and corresponding SK-counters; and sharing the SN keys with SNs of corresponding target MNs.

[0221] In some example embodiments, the method 1500 further comprises: transmitting, a SK counter index to a terminal device via a cell switch command to indicate a certain SK counter in the SK counter list.

[0222] In some example embodiments, the cell switch command is a command for mater cell group switch without a SN change.

[0223] In some example embodiments, the method 1500 further comprises: transmitting, to a target MN, a cell switch notification indicating the certain SK counter.

[0224] In some example embodiments, the second apparatus comprises a source MN for the LTM handover.

[0225] In some example embodiments, a first apparatus capable of performing any of the method 800 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 800. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG.1.

[0226] In some example embodiments, the first apparatus comprises means for obtaining a secondary key, SK, counter list from a configuration of source master node, MN, or from a configuration of target MN; and means for during an inter master node layer 1 / layer 2 triggered mobility, LTM, handover from the source MN to the target MN, in accordance witha determination that the SK counter list is to be restarted, using a SK counter from the beginning of the SK counter list.

[0227] In some example embodiments, the first apparatus further comprises: means for after an initiation of an LTM preparation from a source MN, receiving the configuration of the target MN via a radio resource control signaling; and means for determining whether the SK counter list is included in the configuration of the target MN; and means for in accordance with a determination that the SK counter list is included in the configuration of the target MN, obtaining the SK counter list from the configuration of the target MN.

[0228] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that the SK counter list is not included in the configuration of the target MN, obtaining the SK counter list from the configuration of the source MN.

[0229] In some example embodiments, the first apparatus further comprises: means for receiving an indication that the configuration of the source MN is to be reused by the target MN.

[0230] In some example embodiments, the first apparatus further comprises: means for receiving, from the source MN, a cell switch command for switching to the target MN; means for in accordance with a determination that the cell switch command includes a restart indication for SK counters, using the SK counter from the beginning of the SK counter list.

[0231] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that a cell switch command for switching to the target MN is received from the source MN and the first apparatus is configured with subsequent conditional primary secondary cell addition or change, S-CPAC use the SK counter from the beginning of the SK counter list.

[0232] In some example embodiments, the first apparatus comprises a terminal device.

[0233] In some example embodiments, a second apparatus capable of performing any of the method 900 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations of the method 900. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1.

[0234] In some example embodiments, the second apparatus comprises means for after initiating an LTM preparation, transmitting a SK counter list to a target MN via a handoverrequest; and means for during an inter master node LTM handover from the second apparatus to the target MN, transmitting a restart indication for SK counters associated with the SK counter list to the terminal device via a cell switch command for switching to the target MN and to the target MN via a cell switch notification.

[0235] In some example embodiments, the second apparatus further comprises: means for in accordance with a determination that a handover request acknowledgment including the SK counter list is received from the target MN, forwarding a configuration of the target MN including the SK counter list to the terminal device via an RRC reconfiguration message.

[0236] In some example embodiments, the second apparatus further comprises: means for in accordance with a determination of a secondary node, SN key change due to the inter master node LTM handover, generate new SN keys by using target MN keys and SK counter in the configured SK counter list; and means for transmitting, to a SN connected with the terminal device for a dual connectivity, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0237] In some example embodiments, the second apparatus comprises a source MN for the inter master node LTM handover.

[0238] In some example embodiments, a third apparatus capable of performing any of the method 1000 (for example, the third apparatus 130 in FIG. 1) may comprise means for performing the respective operations of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the third apparatus 130 in FIG. 1.

[0239] In some example embodiments, the third apparatus comprises means for after an initiation of an LTM preparation from a source MN, receiving a SK counter list from the source MN via a handover request; and means for during an LTM handover from the source MN to the third apparatus, receiving, from the source MN, a restart indication for SK counters associated with the SK counter list via a cell switch notification.

[0240] In some example embodiments, the third apparatus further comprises: means for transmitting, to the source MN, a handover request acknowledgment including the SK counter list.

[0241] In some example embodiments, the third apparatus further comprises: means for in accordance with a determination of a secondary node, SN key change due to the inter masternode LTM handover, based on the restart indication for SK counters, generating new SN keys by using the SK counters from the beginning of the SK counter list; and means for transmitting, to a SN connected with the terminal device for a dual connectivity via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0242] In some example embodiments, the third apparatus further comprises: means for in accordance with a determination of a secondary node, SN key change due to the inter master node LTM handover, based on the restart indication for SK counters, generating new SN keys by using the SK counters from a further SK counter list configured by the third apparatus; and means for transmitting, to a SN connected with the terminal device for a dual connectivity via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0243] In some example embodiments, the third apparatus further comprises: means for transmitting, via the SN modification request to the SN, restart indication for SK counters associated with the SK counter list.

[0244] In some example embodiments, the third apparatus further comprises: means for in accordance with a determination of a completion of the inter master node LTM handover, transmitting to a further SN via a SN modification request, a list of the new SN keys and corresponding SK counters used for generating the new SN keys.

[0245] In some example embodiments, the third apparatus comprises a target MN for the inter master node LTM handover.

[0246] In some example embodiments, a first apparatus capable of performing any of the method 1100 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 1100. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1.

[0247] In some example embodiments, the first apparatus comprises means for obtaining a secondary key, SK, counter list from a configuration of a target master node, MN; and means for during a layer 1 / layer 2 triggered mobility, LTM, handover from a source MN to a target MN, receiving a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and means for generating a secondary node, SN, key by the SK counter list and the SK counter indication.

[0248] In some example embodiments, the first apparatus further comprises: means for after an initiation of an LTM preparation from the source MN, receiving the configuration of the target MN via a radio resource control signaling.

[0249] In some example embodiments, the first apparatus further comprises: means for obtaining an association between a set of SK counter indices and a plurality of SK counters in the SK counter list; and means for in accordance with a determination that the SK counter indication associated with the SK counter index, determining a target SK counter to be used based on the SK counter index and the association..

[0250] In some example embodiments, the first apparatus comprises a terminal device.

[0251] In some example embodiments, a second apparatus capable of performing any of the method 1200 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1.

[0252] In some example embodiments, the second apparatus comprises means for after initiating an LTM preparation, transmitting a SK counter list to a target MN associated with an LTM handover via a handover request; and means for during the LTM handover from the second apparatus to the target MN, transmitting, to a terminal device, a cell switch command including a SK counter indication associated with at least one of a SK counter index or a SK counter; and means for transmitting, to the target MN via a cell switch notification, a SK counter corresponding to a SK counter indication indicated by the second apparatus to a terminal device.

[0253] In some example embodiments, the second apparatus further comprises: means for in accordance with a determination that a handover request acknowledgment including the SK counter list is received from the target MN, sharing the SK counter list to a source distributed unit at the source MN.

[0254] In some example embodiments, the second apparatus comprises a source MN for the LTM handover.

[0255] In some example embodiments, a third apparatus capable of performing any of the method 1300 (for example, the third apparatus 130 in FIG. 1) may comprise means for performing the respective operations of the method 1300. The means may be implementedin any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the third apparatus 130 in FIG. 1.

[0256] In some example embodiments, the third apparatus comprises means for after an initiation of an LTM preparation from a source MN, receive a SK counter list from the source MN via a handover request; means for during an LTM handover from the second apparatus to the target MN, receive, from the source MN via a cell switch notification, an indication of a SK counter corresponding to a SK counter indication, indicated by the source MN to a terminal device, associated with at least one of a SK counter index or a SK counter; and means for generating, for a secondary node, SN, change, a new SN key based on the SK counter.

[0257] In some example embodiments, the third apparatus further comprises: means for transmitting, to the source MN, a handover request acknowledgment including the SK counter list.

[0258] In some example embodiments, the third apparatus further comprises: means for in accordance with a determination of a secondary node, SN key change due to the LTM handover, generate the new SN key; and means for transmitting, to a SN connected with the terminal device for a dual connectivity and a further SN associated with the LTM handover via a SN modification request, the new SN key and the SK counter used for generating the new SN key.

[0259] In some example embodiments, the third apparatus comprises a target MN for the LTM handover.

[0260] In some example embodiments, a first apparatus capable of performing any of the method 1400 (for example, the first apparatus 110 in FIG. 1) may comprise means for performing the respective operations of the method 1400. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1.

[0261] In some example embodiments, the first apparatus comprises means for receiving, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and means for during the LTM handover, generating a secondary node, SN, key based on a certain SK counter in the SK counter list.

[0262] In some example embodiments, the first apparatus further comprises: means for receiving the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

[0263] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that a SK counter index is received from the source MN via a cell switch command, determining the certain SK counter based on the SK counter index.

[0264] In some example embodiments, the first apparatus further comprises: means for obtaining an association between a set of SK counter indices and a plurality of SK counters in the SK counter list; and means for determining the SK counter to be used based on the received SK counter index and the association.

[0265] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that there is no SK counter indicated by a cell switch command, using the default SK counter as the certain SK counter.

[0266] In some example embodiments, the cell switch command is a command for mater cell group switch without a SN change.

[0267] In some example embodiments, the first apparatus comprises a terminal device.

[0268] In some example embodiments, a second apparatus capable of performing any of the method 1500 (for example, the second apparatus 120 in FIG. 1) may comprise means for performing the respective operations of the method 1500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1.

[0269] In some example embodiments, the second apparatus comprises means for after initiating an LTM preparation, sharing a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and means for transmitting, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

[0270] In some example embodiments, the second apparatus further comprises: means for transmitting the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

[0271] In some example embodiments, the second apparatus further comprises: means for transmitting a SK counter list to a target MN via a handover request; and means for in accordance with a handover request acknowledgment is received from the target MN, sharing the SK-counter list with a source distributed unit along with other security parameters.

[0272] In some example embodiments, the second apparatus further comprises: means for generating SN keys by using target MN keys of the set of target MN and corresponding SK- counters; and means for sharing the SN keys with SNs of corresponding target MNs.

[0273] In some example embodiments, the second apparatus further comprises: means for transmitting, a SK counter index to a terminal device via a cell switch command to indicate a certain SK counter in the SK counter list.

[0274] In some example embodiments, the cell switch command is a command for mater cell group switch without a SN change.

[0275] In some example embodiments, the second apparatus further comprises: means for transmitting, to a target MN, a cell switch notification indicating the certain SK counter.

[0276] In some example embodiments, the second apparatus comprises a source MN for the LTM handover.

[0277] FIG. 16 is a simplified block diagram of a device 1600 that is suitable for implementing example embodiments of the present disclosure. The device 1600 may be provided to implement a communication device, for example, the first apparatus 110 or the second apparatus 120 or the third apparatus 130 as shown in FIG. 1. As shown, the device 1600 includes one or more processors 1610, one or more memories 1620 coupled to the processor 1610, and one or more communication modules 1640 coupled to the processor 1610.

[0278] The communication module 1640 is for bidirectional communications. The communication module 1640 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1640 may include at least one antenna.

[0279] The processor 1610 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 onmulticore processor architecture, as non-limiting examples. The device 1600 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.

[0280] The memory 1620 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) 1624, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 1622 and other volatile memories that will not last in the power-down duration.

[0281] A computer program 1630 includes computer executable instructions that are executed by the associated processor 1610. The instructions of the program 1630 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1630 may be stored in the memory, e.g., the ROM 1624. The processor 1610 may perform any suitable actions and processing by loading the program 1630 into the RAM 1622.

[0282] The example embodiments of the present disclosure may be implemented by means of the program 1630 so that the device 1600 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 15. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0283] In some example embodiments, the program 1630 may be tangibly contained in a computer readable medium which may be included in the device 1600 (such as in the memory 1620) or other storage devices that are accessible by the device 1600. The device 1600 may load the program 1630 from the computer readable medium to the RAM 1622 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. 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).

[0284] FIG. 17 shows an example of the computer readable medium 1700 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 1700 has the program 1630 stored thereon.

[0285] 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, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although 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.

[0286] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non- transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. 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.

[0287] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code 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 code, 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.

[0288] In the context of the present disclosure, the computer program code 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.

[0289] 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.

[0290] Further, although 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, although 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. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0291] 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

WHAT IS CLAIMED IS:

1. A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus at least to: receive, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and during the LTM handover, generate a secondary node, SN, key based on a certain SK counter in the SK counter list.

2. The first apparatus of claim 1, wherein the first apparatus is caused to: receive the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

3. The first apparatus of claim 1 or 2, wherein the first apparatus is caused to: in accordance with a determination that a SK counter index is received from the source MN via a cell switch command, determine the certain SK counter based on the SK counter index or the SK counter received from the source MN via a cell switch command.

4. The first apparatus of claim 3, wherein the first apparatus is caused to: obtain an association between a set of SK counter indices and a plurality of SK counters in the SK counter list; and determine the SK counter to be used based on the received SK counter index and the association.

5. The first apparatus of claim 1 or 2, wherein the first apparatus is caused to: in accordance with a determination that there is no SK counter indicated by a cell switch command, use the default SK counter as the certain SK counter.

6. The first apparatus of claim 3 or 5, wherein the cell switch command is a command for mater cell group switch without a SN change.

427. The first apparatus of any of claims 1-5, wherein the first apparatus comprises a terminal device.

8. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus at least to: after initiating an LTM preparation, share a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and transmit, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

9. The second apparatus of claim 8, wherein the second apparatus is caused to: transmit the SK counter list or the SK counters in an LTM configuration via radio resource control reconfiguration message, wherein LTM configuration includes respective SK counter for each identifier of the set of target MNs.

10. The second apparatus of claim 8, wherein the second apparatus is caused to: transmit a SK counter list to a target MN via a handover request; and in accordance with a handover request acknowledgment is received from the target MN, shares the SK-counter list with a source distributed unit along with other security parameters.

11. The second apparatus of claim 8, wherein the second apparatus is caused to: generate SN keys by using target MN keys of the set of target MN and corresponding SK- counters; and share the SN keys with SNs of corresponding target MNs.

12. The second apparatus of claim 8, wherein the second apparatus is caused to: transmit, a SK counter index to a terminal device via a cell switch command to indicate a certain SK counter in the SK counter list.

13. The second apparatus of claim 12, wherein the cell switch command is a command for mater cell group switch without a SN change.4314. The second apparatus of claim 12, wherein the second apparatus is caused to: transmit, to a target MN, a cell switch notification indicating the certain SK counter.

15. The first apparatus of any of claims 8-14, wherein the second apparatus comprises a source MN for the LTM handover.

16. A method comprising: receiving, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and during the LTM handover, generating a secondary node, SN, key based on a certain SK counter in the SK counter list.

17. A method comprising: after initiating an LTM preparation, sharing a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and transmitting, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

18. A first apparatus comprising: means for receiving, from a source master node, MN, a secondary key, SK, counter list or SK counters for a set of target MNs having a centralized unit associated with a layer 1 / layer 2 triggered mobility, LTM, preparation initiated from the source MN; and means for, during the LTM handover, generating a secondary node, SN, key based on a certain SK counter in the SK counter list.

19. A second apparatus comprising: means for, after initiating an LTM preparation, sharing a secondary key, SK, counter list or SK counters with a set of target MNs having a centralized unit associated with the preparation; and means for transmitting, to a terminal device, the SK counter list or SK counters for generating a secondary node, SN, key.

20. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 16 or the method of claim 17.

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