Serving node security key mismatch prevention

Abstract

According to an aspect, there is provided a network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node The network node may receive from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node. The network node may determine whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use. The network node may transmit, based on the determination, a second message comprising an indication associated with the matching to the user equipment.

Description

[0001] SERVING NODE SECURITY KEY MISMATCH PREVENTION

[0002] TECHNICAL FIELD

[0003] Various example embodiments generally relate to the field of telecommunication systems . In particular, some example embodiments relate to a solution for preventing any failure due to a serving node security key mismatch in Subsequent Conditional PSCell Addition / Change ( SCPAC ) mobility .

[0004] BACKGROUND

[0005] A user equipment (UE ) may be configured to apply dual-connectivity in a wireless communication network, for example , in a network applying Subsequent Conditional PSCell Addition / Change ( SCPAC ) mobility . When the UE sets up a dual-connectivity, the UE needs the Serving Node ( SN) key, K_SN, to secure and encrypt its connection with the serving SN . The SN key is generated by the UE using the a SN counter that is provided by a Master Node (MN) , the length of the SN counter, and the MN key, K_gNB .

[0006] The MN shares the list of sk-counters that the UE should draw a counter and generate an SN key to access SN . The MN may also inform the candidate SN about the SN key that the UE will use based on the drawn sk-counter The serving SN should know the SN key that the UE wil l use to have end-to-end cyphering .

[0007] The MN may initiate the SCPAC preparation with SN1 and SN2 providing the candidate SCPAC configurations of a SN1 and SN2 . The MN provides a list of sk-counters per SN, i . e . , one l ist for the SN1 and another list for the SN2 . For executing the SCPAC towards a PSCell provided by the SN2 , the UE needs to use a new key that is di f ferent than that is in use with SN1 . For this purpose , the UE draws an sk-counter from the list of sk-counters of the SN2 and generate the SN2 key .

[0008] The UE decodes the candidate SCPAC configuration and sends an RRCReconf igurationComplete message to the MN to indicate that which candidate configuration is executed . Accordingly, the MN informs the SN2 about the SCPAC execution .

[0009] However, i f the UE selects a wrong sk-counter, di f ferent than what the MN and the target SN expects , a mismatch between the UE and the target SN security key happens . This means that the target SN cannot decode the encrypted message , and this which will lead to a handover failure between the UE and the target SN .

[0010] There can be several reasons for a wrong sk-counter selection by the UE . For example , an improper UE implementation may lead to an s k-counter index shi ft ( i . e . , to selecting a wrong sk-counter ) or a failure scenario may lead the network to lose track of used sk- counters . Further, i f the UE starts drawing the wrong sk-counter, the following sk-counter selections will also follow the same mistake as the sk-counter selection is sequential .

[0011] SUMMARY

[0012] This summary is provided to introduce a selection of concepts in a simpli fied form that are further described below in the detailed description . This summary is not intended to identi fy key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter .

[0013] Example embodiments of the present disclosure provides a solution that prevents any failure due to a serving node security key mismatch in Subsequent Conditional PSCell Addition / Change ( SCPAC ) mobility . This and other benefits may be achieved by the features of the independent claims . Further example embodiments are provided in the dependent claims , the description, and the drawings .

[0014] According to a first aspect , a network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node , may comprise at least one processor and at least one memory storing instructions which, when executed by the at least one processor, cause the network node at least to : receive from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; determine whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a second message comprising an indication associated with the matching to the user equipment .

[0015] In an example embodiment of the first aspect , the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment .

[0016] In an example embodiment of the first aspect , wherein the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment . In an example embodiment of the first aspect , the second message comprises an index of a correct counter to be used by the user equipment .

[0017] In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the network node at least to : receive from the user equipment a third message comprising a regenerated second secondary network node key or a newly used second secondary network node counter associated with the second secondary network node ; determine that the regenerated second secondary network node key or the newly used second secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment .

[0018] In an example embodiment of the first aspect , the instructions , when executed by the at least one processor, cause the network node at least to : prior to receiving the first message , transmit to the user equipment a fi fth message compri sing a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .

[0019] In an example embodiment of the first aspect , the first message comprises a radio resource control , RRC, reconfiguration complete message .

[0020] According to a second aspect , a user equipment configured to operate in a dual-connectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node , may comprise at least one processor and at least one memory storing instructions which, when executed by the at least one processor, cause the user equipment at least to : transmit to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; and receive from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .

[0021] In an example embodiment of the second aspect , the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : initiate a random access procedure towards the second secondary network node in response to the approval .

[0022] In an example embodiment of the second aspect , the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : adj ust a counter index ; and transmit to the network node a third message comprising a regenerated second secondary network node key associated with the adj usted counter index or a newly used second secondary network node counter associated with the second secondary network node , the newly used second secondary network node counter being associated with the adj usted counter index ; receive from the network node a fourth message compri sing an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment ; and initiate a random access procedure towards the second secondary network node in response to the approval .

[0023] In an example embodiment of the second aspect , the second message comprises an index of a correct counter to be used by the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : adj ust the counter index based on the index received from the network node .

[0024] In an example embodiment of the second aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to : prior to transmitting the first message , receive from the network node a fi fth message comprising a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .

[0025] In an example embodiment of the second aspect , the first message comprises a radio resource control , RRC, reconfiguration complete message .

[0026] In an example embodiment of the second aspect , the instructions , when executed by the at least one processor, cause the user equipment at least to : initiate a random access procedure towards the second secondary network node right after transmitting the first message to the network node .

[0027] According to a third aspect , a method performed by a network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node , may comprise receiving from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; determining whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmitting, based on the determination, a second message comprising an indication associated with the matching to the user equipment .

[0028] In an example embodiment of the third aspect , the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment .

[0029] In an example embodiment of the third aspect , wherein the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment .

[0030] In an example embodiment of the third aspect , the second message comprises an index of a correct counter to be used by the user equipment .

[0031] In an example embodiment of the third aspect , the method further comprises receiving from the user equipment a third message comprising a regenerated second secondary network node key or a newly used second secondary network node counter associated with the second secondary network node ; determining that the regenerated second secondary network node key or the newly used second secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmitting, based on the determination, a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment .

[0032] In an example embodiment of the third aspect , the method further comprises , prior to receiving the first message , transmitting to the user equipment a fi fth message comprising a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .

[0033] In an example embodiment of the third aspect , the first message comprises a radio resource control , RRC, reconfiguration complete message .

[0034] According to a fourth aspect , a method performed by user equipment configured to operate in a dualconnectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node , may comprise transmitting to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter as sociated with a second secondary network node ; and receiving from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .

[0035] In an example embodiment of the second aspect , the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment , and the method further comprises initiating a random access procedure towards the second secondary network node in response to the approval .

[0036] In an example embodiment of the fourth aspect , the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment , and the method further comprises adj usting a counter index ; transmitting to the network node a third message compri sing a regenerated second secondary network node key associated with the adj usted counter index or a newly used second secondary network node counter associated with the second secondary network node , the newly used second secondary network node counter being associated with the adj usted counter index ; receiving from the network node a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment ; and initiating a random access procedure towards the second secondary network node in response to the approval .

[0037] In an example embodiment of the fourth aspect , the second message comprises an index of a correct counter to be used by the user equipment , and the method further comprises adj usting the counter index based on the index received from the network node .

[0038] In an example embodiment of the fourth aspect , the method further comprises , prior to transmitting the first message , receiving from the network node a fi fth message comprising a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use . In an example embodiment of the fourth aspect , the first message comprises a radio resource control , RRC, reconfiguration complete message .

[0039] In an example embodiment of the fourth aspect , the method further comprises initiating a random access procedure towards the second secondary network node right after transmitting the first message to the network node .

[0040] According to a fi fth aspect , a computer program is disclosed . The comprise program may comprise instructions that , when executed by an apparatus , cause the apparatus to perform a method according to the third or fourth aspect , or any example embodiment thereof .

[0041] According to a sixth aspect , a (non-transitory ) computer readable medium is disclosed . The (non- transitory) computer readable medium may comprise program instructions that , when executed by an apparatus , cause the apparatus to perform a method according to the third or fourth aspect , or any example embodiment thereof .

[0042] According to a seventh aspect , a network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node , may comprise means for : receiving rom a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; determining whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmitting, based on the determination, a second message comprising an indication associated with the matching to the user equipment .

[0043] According to an eighth aspect , a user equipment configured to operate in a dual-connectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node , may comprise means for : transmitting to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; and receiving from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .

[0044] Many of the attendant features will be more readily appreciated as they become better understood by reference to the following detailed description considered in connection with the accompanying drawings .

[0045] DESCRIPTION OF THE DRAWINGS

[0046] The accompanying drawings , which are included to provide a further understanding of the example embodiments and constitute a part of this speci fication, illustrate example embodiments and together with the description help to understand the example embodiments . In the drawings :

[0047] FIG . 1 illustrates an example of a SN key mismatch situation for a UE operating in a dual-connectivity mode .

[0048] FIG . 2 illustrates an example of an apparatus configured to practice one or more example embodiments .

[0049] FIG . 3 illustrates an example of an apparatus configured to practice one or more example embodiments . FIG . 4A illustrates a signalling diagram according to an example embodiment .

[0050] FIG . 4B illustrates a signalling diagram according to an example embodiment .

[0051] FIG . 40 illustrates a signalling diagram according to an example embodiment .

[0052] FIG . 4D illustrates a signalling diagram according to an example embodiment .

[0053] FIG . 4E illustrates a signalling diagram according to an example embodiment .

[0054] FIG . 4F illustrates a signalling diagram according to an example embodiment .

[0055] FIG . 5 illustrates example of a method according to an example embodiment .

[0056] FIG . 6 illustrates example of a method according to another example embodiment .

[0057] Like references are used to designate like parts in the accompanying drawings .

[0058] DETAILED DESCRIPTION

[0059] Reference will now be made in detail to example embodiments , examples of which are illustrated in the accompanying drawings . The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms , in which the present example may be constructed or utili zed . The description sets forth the functions o f the example and the sequence of steps for constructing and operating the example . However, the same or equivalent functions and sequences may be accomplished by di f ferent examples .

[0060] FIG . 1 illustrates an example of a SN key mismatch situation for a UE operating in a dual-connectivity mode . At 108, the UE 100 is in dual-connectivity (DC) with a Master node (MN) 102 and a Serving Node 1 (SN1) 104.

[0061] At 110 and 112, the MN 102 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change (SCPAC) with the SN1 104 and the SN2 106. The MN 102 may share the SN key or list of SN keys that the UE 100 will use to access to SN1 and SN2.

[0062] At 114 and 116, both the SN1 104 and the SN2 106 may respond to the MN 102 with an SCPAC preparation acknowledgment .

[0063] At 118, the MN 102 may provide the candidate SCPAC configurations of the SN1 104 and the SN2 106 to the UE 100 in an RRCReconf iguration message. The MN 102 may also provide the list of sk-counters per SN, i.e., one list for the SN1 102 and another list for the SN2 106.

[0064] At 120, the UE may decode the RRCReconf iguration received from MN 102 and send an RRCReconf igurationComplete message to the MN 102 to approve the reception of the configuration.

[0065] At 122, once the SCPAC condition for a Primary Secondary Cell 2 (PSCell-2) (under the SN2 106) is met, the UE 100 may execute the SCPAC towards the PSCell-2. Since a PSCell-2 handover is inter-SN handover (from the SN1 104 to the SN2 106) , the UE 100 needs to use a new key with the SN2 106 that is different than that is in use with the SN1 104. For this purpose, the UE 100 draws an sk-counter from the list of sk-counters of the SN2 106 and generates the SN2 key.

[0066] At 124, the UE 100 decodes the candidate SCPAC configuration and sends an RRCReconf igurationComplete message to the MN 102 to indicate which candidate configuration is executed.

[0067] At 126, the MN 102 informs the SN2 106 about the SCPAC execution. At this point, the MN 102 may also share the SN key that the UE 100 is expected to use to access the SN2 106 in this message .

[0068] At 128 , the UE 100 may initiate the random access channel (RACH) procedure towards the SN2 106 , and the UE 100 uses the generated SN2 key to access the SN2 106 .

[0069] I f the UE 100 draws at 122 an sk-counter that is di f ferent than what the MN 102 and the SN2 106 expect , this will lead to a mismatch between the UE 100 and the SN2 106 in terms of a security key . The result is that the SN2 106 cannot decode the encrypted message received from the UE 100 , and this leads to a handover failure between the UE 100 and the SN2 106 .

[0070] There can be several reasons for a wrong sk-counter selection, for example , an improper UE implementation that leads to sk-counter index shi ft , an sk-counter use scenario or a failure scenario that leads the network to lose track of used sk-counters .

[0071] FIG . 2 illustrates an example of an apparatus 200 configured to practice one or more example embodiments . The apparatus 200 may comprise a network node , a master node , or in general a network device configured to implement functionality described herein . The apparatus 200 may comprise at least one processor 202 . The at least one processor 202 may comprise , for example , one or more of various processing devices , such as for example a coprocessor, a microprocessor, a controller, a digital signal processor ( DSP ) , a processing circuitry with or without an accompanying DSP, or various other proces sing devices including integrated circuits such as , for example , an application specific integrated circuit (AS IC ) , a field programmable gate array ( FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, or the like . The apparatus 200 may further comprise at least one memory 204. The memory 204 may be configured to store, for example, computer program code or the like, for example operating system software and application software. The memory 204 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination thereof. For example, the memory may be embodied as magnetic storage devices (such as hard disk drives, magnetic tapes, etc.) , optical magnetic storage devices, or semiconductor memories (such as mask ROM, PROM (programmable ROM) , EPROM (erasable PROM) , flash ROM, RAM (random access memory) , etc.) . The memory 204 is provided as an example of a (non-transitory ) computer readable medium. 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) .

[0072] The apparatus 200 may further comprise a communication interface 208 configured to enable the apparatus 200 to transmit and / or receive information.

[0073] When the apparatus 200 is configured to implement some functionality, some component and / or components of the apparatus 200, such as for example the at least one processor 202 and / or the at least one memory 204, may be configured to implement this functionality. Furthermore, when the at least one processor 202 is configured to implement some functionality, this functionality may be implemented using program code 206 comprised, for example, in the at least one memory 204.

[0074] The functionality described herein may be performed, at least in part, by one or more computer program product components such as software components. According to an example embodiment, the apparatus 200 comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code 206, when executed, to execute the embodiments of the operations and functionality described herein. Program code 206 is provided as an example of instructions which, when executed by the at least one processor 202, cause performance of the apparatus 200.

[0075] Alternatively, or in addition, the functionality described herein can be performed, at least in part, by one or more hardware logic components. For example, and without limitation, illustrative types of hardware logic components that can be used include field-programmable gate arrays (FPGAs) , application-specific integrated circuits (ASICs) , application-specific standard products (ASSPs) , system-on-a-chip systems (SOCs) , complex programmable logic devices (CPLDs) , graphics processing units (GPUs) , or the like.

[0076] The apparatus 200 may be configured to perform method (s) described herein or comprise means for performing method (s) described herein. In one example, the means may comprise the at least one processor 202, the at least one memory 204 including program code 206 configured to, when executed by the at least one processor 202, cause the apparatus 200 to perform the method ( s ) .

[0077] Although the apparatus 200 is illustrated as a single device, it is appreciated that, wherever applicable, functions of the apparatus 200 may be distributed to a plurality of devices.

[0078] In an example embodiment, the apparatus 200 may be a network node or a master node configured to provide dual-connectivity to a user equipment.

[0079] The network node may be configured to receive from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter as sociated with a second secondary network node ; determine whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a second message comprising an indication associated with the matching to the user equipment .

[0080] The indication may comprise an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment .

[0081] The indication may comprise a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment .

[0082] The second message may comprise an index of a correct counter to be used by the user equipment .

[0083] The network node may be configured to receive from the user equipment a third message comprising a regenerated second secondary network node key or a newly used second secondary network node counter associated with the second secondary network node ; determine that the regenerated second secondary network node key or the newly used second secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment . The network node may be configured to, prior to receiving the first message, transmit to the user equipment a fifth message comprising a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use.

[0084] The first message may comprise a radio resource control, RRC, reconfiguration complete message.

[0085] FIG. 3 illustrates an example of an apparatus 300 configured to practice one or more example embodiments. The apparatus 300 may comprise a user node, a user equipment, or in general a user device configured to implement functionality described herein. The apparatus 300 may comprise at least one processor 302. The at least one processor 302 may comprise, for example, one or more of various processing devices, such as for example a coprocessor, a microprocessor, a controller, a digital signal processor (DSP) , a processing circuitry with or without an accompanying DSP, or various other processing devices including integrated circuits such as, for example, an application specific integrated circuit (ASIC) , a field programmable gate array (FPGA) , a microcontroller unit (MCU) , a hardware accelerator, a special-purpose computer chip, or the like.

[0086] The apparatus 300 may further comprise at least one memory 304. The memory 304 may be configured to store, for example, computer program code or the like, for example operating system software and application software. The memory 304 may comprise one or more volatile memory devices, one or more non-volatile memory devices, and / or a combination thereof. For example, the memory may be embodied as magnetic storage devices (such as hard disk drives, magnetic tapes, etc.) , optical magnetic storage devices, or semiconductor memories ( such as mask ROM, PROM (programmable ROM) , EPROM ( erasable PROM) , flash ROM, RAM ( random access memory) , etc . ) . The memory 304 is provided as an example of a (non-transitory ) computer readable medium . The term "non-transitory, " as used herein, is a limitation of the medium itsel f ( i . e . , tangible , not a signal ) as opposed to a limitation on data storage persistency ( e . g . , RAM vs . ROM) .

[0087] The apparatus 300 may further comprise a communication interface 308 configured to enable the apparatus 300 to transmit and / or receive information .

[0088] When the apparatus 300 is configured to implement some functionality, some component and / or components of the apparatus 300 , such as for example the at least one processor 302 and / or the at least one memory 304 , may be configured to implement this functionality . Furthermore , when the at least one processor 302 is configured to implement some functionality, this functionality may be implemented using program code 306 comprised, for example , in the at least one memory 304 .

[0089] The functionality described herein may be performed, at least in part , by one or more computer program product components such as software components . According to an example embodiment , the apparatus 200 comprises a processor or processor circuitry, such as for example a microcontroller, configured by the program code 306 , when executed, to execute the embodiments of the operations and functionality described herein . Program code 306 is provided as an example of instructions which, when executed by the at least one processor 302 , cause performance of the apparatus 300 .

[0090] Alternatively, or in addition, the functionality described herein can be performed, at least in part , by one or more hardware logic components . For example , and without limitation, illustrative types of hardware logic components that can be used include field-programmable gate arrays ( FPGAs ) , application-speci fic integrated circuits (AS ICs ) , application-speci fic standard products (ASSPs ) , system-on-a-chip systems ( SOCs ) , complex programmable logic devices ( CPLDs ) , graphics processing units ( GPUs ) , or the like .

[0091] The apparatus 300 may be configured to perform method ( s ) described herein or comprise means for performing method ( s ) described herein . In one example , the means may comprise the at least one processor 302 , the at least one memory 304 including program code 306 configured to , when executed by the at least one processor 302 , cause the apparatus 300 to perform the method ( s ) .

[0092] In an example embodiment , the apparatus 300 may be a user equipment (UE ) configured to operate in a dualconnectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node .

[0093] The UE may be configured to transmit to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; and receive from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .

[0094] The indication may comprise an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment , and the user equipment may be configured to initiate a random access procedure towards the second secondary network node in response to the approval .

[0095] The indication may comprise a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment , and the user equipment may be configured to adj ust a counter index ; and transmit to the network node a third message comprising a regenerated second secondary network node key associated with the adj usted counter index or a newly used second secondary network node counter associated with the second secondary network node , the newly used second secondary network node counter being associated with the adj usted counter index ; receive from the network node a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment ; and initiate a random access procedure towards the second secondary network node in response to the approval .

[0096] The second message may comprise an index of a correct counter to be used by the user equipment , and the user equipment may be configured to adj ust the counter index based on the index received from the network node .

[0097] The user equipment may be configured to , prior to transmitting the first message , receive from the network node a f i fth message comprising a conf iguration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .

[0098] The first message may comprise a radio resource control , RRC, reconfiguration complete message . The user equipment may be conf igured to initiate a random access procedure towards the second secondary network node right after transmitting the first message to the network node .

[0099] FIG . 4A illustrates a signalling diagram according to an example embodiment .

[0100] At 404 , a UE 300 is in dual-connectivity ( DC ) with a Master Node (MN) 200 and a Serving Node 1 ( SN1 ) 400 .

[0101] At 406 and 408 , the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change ( SCPAC ) with the SN1 400 and an SN2 402 . The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402 .

[0102] At 410 and 412 , both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment .

[0103] At 414 , the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message . The MN 200 also provides the list of sk-counters per SN, i . e . , one list for the SN1 400 and another list for the SN2 404 . In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and waits for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0104] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration .

[0105] At 418 , when the SCRAG condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0106] At 420 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the sk-counter or the SN key that the UE 300 will use for accessing to the SN2 402 .

[0107] At 422 , the MN 200 determines whether the generated SN key or the sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use . In the case that the sk-counter or the SN key matches with the sk-counter or the SN key that the MN 200 expects the UE 300 to use, at 424 the MN 200 sends an approval for the sk-counter or the SN key to be used and grants an access to the SN2 402 .

[0108] At 426 , the MN 200 informs the SN2 404 about the SCPAC execution using a SN Reconf igurationComplete message . In an example embodiment , the MN 200 may share the SN key that the UE 300 is expected to use to access the SN2 402 in this message . At 428 , the UE 300 may initiate a random access channel (RACH) procedure towards the SN2 402 and use the generated SN2 key to access the SN2 402 .

[0109] Since the sk-counter and the SN key used for the SN access is controlled by the MN 200 and approved by the MN 200 , any mismatch between the UE 300 and the SN2 4402 will be prevented, and the UE 300 does not experience any failure due to a security key mismatch .

[0110] FIG . 4B illustrates a signalling diagram according to an example embodiment .

[0111] At 404 , a UE 300 is in dual-connectivity ( DC ) with a Master Node (MN) 200 and a Serving Node 1 ( SN1 ) 400 .

[0112] At 406 and 408 , the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change ( SCPAC ) with the SN1 400 and an SN2 402 . The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402 .

[0113] At 410 and 412 , both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment .

[0114] At 414 , the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message . The MN 200 also provides the list of sk-counters per SN, i . e . , one list for the SN1 400 and another list for the SN2 404 . In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and wait for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0115] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration .

[0116] At 418 , when the SCPAC condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0117] At 420 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the sk-counter or the SN key that the UE 300 will use for accessing to the SN2 402 .

[0118] At 430 , the MN 200 determines whether the generated SN key or the sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use . In this example embodiment , the generated SN key or the sk-counter received from the UE 300 does not match with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and the MN 200 rej ects the use of sk-counter or the SN key that was received from the UE 300 . At 432 , the MN 200 sends a message comprising a disapproval of the SN key or the sk-counter to the UE 300 . In an example embodiment , the message may al so comprise an index of a correct sk-counter to be used by the UE 300 to draw a new sk-counter .

[0119] At 434 , the UE 300 adj usts the counter index to obtain the new sk-counter and generate the new SN key . In an example embodiment , the UE 300 may use the new sk- counter index to draw the correct sk-counter and possibly also generate new SN key .

[0120] At 436 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the new sk-counter or the new SN key that the UE 300 will use for accessing to the SN2 402 .

[0121] At 438 , the MN 200 determines that the new SN key or the new sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and at 440 sends an approval for the sk-counter or the SN key to be used and grants 442 access to the SN2 402 .

[0122] At 442 , the MN 200 informs the SN2 404 about the SCPAC execution using a SN Reconfiguration Complete message . In an example embodiment , the MN 200 may share the SN key that the UE 300 is expected to use to access the SN2 402 in this message .

[0123] At 444 , the UE 300 may initiate a random access channel (RACH) procedure towards the SN2 402 and use the generated SN2 key to access the SN2 402 .

[0124] Since the sk-counter and the SN key used for the SN access is controlled by the MN 200 and approved by the MN 200 , any mismatch between the UE 300 and the SN2 4402 will be prevented, and the UE 300 does not experience any failure due to a security key mismatch .

[0125] FIG . 4C illustrates a signalling diagram according to an example embodiment .

[0126] At 404 , a UE 300 is in dual-connectivity ( DC ) with a Master Node (MN) 200 and a Serving Node 1 ( SN1 ) 400 .

[0127] At 406 and 408 , the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change ( SCPAC ) with the SN1 400 and an SN2 402 . The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402 .

[0128] At 410 and 412 , both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment .

[0129] At 414 , the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message . The MN 200 also provides the list of sk-counters per SN, i . e . , one list for the SN1 400 and another list for the SN2 404 . In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and wait for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0130] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration .

[0131] At 418 , when the SCRAG condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0132] At 420 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the sk-counter or the SN key that the UE 300 will use for accessing to the SN2 402 .

[0133] At 446 , instead of waiting an approval of the SN key or the sk-counter from the MN 200 , the UE 300 may initiate right after the step 420 a random access channel (RACH) procedure .

[0134] Meanwhile , after the RRCReconf igurationComplete message is sent by the UE 300 at 420 , at 448 the MN 200 determines whether the generated SN key or the sk-counter received from the UE 300 matches with a SN key or an sk- counter that the MN 200 expects the UE 300 to use . In this example embodiment , the generated SN key or the sk- counter received from the UE 300 does not match with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and the MN 200 rej ects the use of sk-counter or the SN key that was received from the UE 300 . At 450 , the MN 200 sends a message comprising a disapproval of the SN key or the sk-counter to the UE 300 . In an example embodiment , the message may al so comprise an index of a correct sk-counter to be used by the UE 300 to draw a new sk-counter .

[0135] At 452 , the UE 300 adj usts the counter index to obtain the new sk-counter and generate the new SN key . In an example embodiment , the UE 300 may use the new sk- counter index to draw the correct sk-counter and possibly also generate new SN key .

[0136] At 454 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the new sk-counter or the new SN key that the UE 300 will use for accessing to the SN2 402 .

[0137] At 456 , the MN 200 determines that the new SN key or the new sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and at 458 sends an approval for the sk-counter or the SN key to be used and grants 442 access to the SN2 402 .

[0138] At 460 , the MN 200 informs the SN2 404 about the SCPAC execution using a SN Reconfiguration Complete message . In an example embodiment , the MN 200 may share the SN key that the UE 300 is expected to use to access the SN2 402 in this message .

[0139] At 462 , the UE 300 may initiate a random access channel (RACH) procedure towards the SN2 402 and use the generated SN2 key to access the SN2 402 .

[0140] FIG . 4D illustrates a signalling diagram according to an example embodiment .

[0141] At 404 , a UE 300 is in dual-connectivity ( DC ) with a Master Node (MN) 200 and a Serving Node 1 ( SN1 ) 400 . At 406 and 408 , the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change ( SCPAC ) with the SN1 400 and an SN2 402 . The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402 .

[0142] At 410 and 412 , both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment .

[0143] At 414 , the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message . The MN 200 also provides the list of sk-counters per SN, i . e . , one list for the SN1 400 and another list for the SN2 404 . In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and waits for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0144] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration . At 418 , when the SCPAC condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0145] At 420 , the UE 300 decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed . The UE 300 also includes the sk-counter or the SN key that the UE 300 will use for accessing to the SN2 402 .

[0146] At 446 , instead of waiting an approval of the SN key or the sk-counter from the MN 200 , the UE 300 may initiate right after the step 420 a random access channel (RACH) procedure .

[0147] Meanwhile , after the RRCReconf igurationComplete message is sent by the UE 300 at 420 , at 464 the MN 200 determines whether the generated SN key or the sk-counter received from the UE 300 matches with a SN key or an sk- counter that the MN 200 expects the UE 300 to use . In this example embodiment , the generated SN key or the sk- counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and the MN 200 approves the use of sk-counter or the SN key that was received from the UE 300 .

[0148] At 466 , the MN 200 may send an approval for the sk- counter or the SN key to be used and grants an access to the SN2 402 . In case the UE 300 already started or completed the RACH procedure thi s information may be redundant to the UE 300 , and thus may be optionally to be sent by the MN 200 . Or, at 466, the MN 200 may send a determined sk-counter or a determined SN key to be used by the UE 300 and grants an access to the SN2 402.

[0149] At 468, the MN 200 may inform the SN2 404 about the SCPAC execution using a SN Reconf igurationComplete message. In an example embodiment, the MN 200 may share the SN key (or the sk-counter) that the UE 300 is expected to use to access the SN2 402 in this message, or the determined SN key (or the sk-counter) . The determined sk-counter or a determined SN key may, for example, be a newly determined one, a newly generated one, the expected one (in case the received one does not match the expected one) , or else.

[0150] A benefit with the solution disclosed above is that, in case the UE selects the correct sk-counter, the UE does not have to wait for the approval of the MN and proceed with access to the candidate SN.

[0151] FIG. 4E illustrates a signalling diagram according to an example embodiment.

[0152] At 404, a UE 300 is in dual-connectivity (DC) with a Master Node (MN) 200 and a Serving Node 1 (SN1) 400.

[0153] At 406 and 408, the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change (SCPAC) with the SN1 400 and an SN2 402. The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402.

[0154] At 410 and 412, both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment .

[0155] At 414, the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message. The MN 200 also provides the list of sk-counters per SN, i.e., one list for the SN1 400 and another list for the SN2 404. In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and waits for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0156] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration .

[0157] At 418 , when the SCPAC condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0158] At 470 , the UE 300 transmits the SN key or the sk- counter to the MN 200 along with the selected candidate SCPAC configuration before decoding the candidate SCPAC configuration and thus share such information with the MN 200 before sending a RRCReconf igurationComplete message . At 472 , the MN 200 determines whether the SN key or the sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use . In the case that the sk-counter or the SN key matches with the sk-counter or the SN key that the MN 200 expects the UE 300 to use, at 474 the MN 200 sends an approval for the sk-counter or the SN key to be used and grants an access to the SN2 402 .

[0159] At 476 , the UE decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed .

[0160] At 478 , the MN 200 informs the SN2 404 about the SCPAC execution using a SN Reconf igurationComplete message . In an example embodiment , the MN 200 may share the SN key that the UE 300 is expected to use to access the SN2 402 in this message .

[0161] At 480 , the UE 300 may initiate a random access channel (RACH) procedure towards the SN2 402 and use the generated SN2 key to access the SN2 402 .

[0162] FIG . 4 F illustrates a signalling diagram according to an example embodiment .

[0163] At 404 , a UE 300 is in dual-connectivity ( DC ) with a Master Node (MN) 200 and a Serving Node 1 ( SN1 ) 400 .

[0164] At 406 and 408 , the MN 200 may initiate a preparation of the Subsequent Conditional PSCell Addition / Change ( SCPAC ) with the SN1 400 and an SN2 402 . The MN 200 may share the SN key or list of SN keys that the UE 300 will use to access to the SN1 400 and SN2 402 .

[0165] At 410 and 412 , both the SN1 400 and the SN2 402 may respond to the MN 200 with an SCPAC preparation acknowledgment . At 414 , the MN 200 provides the candidate SCPAC configurations of the SN1 400 and the SN2 402 in an RRCReconf iguration message . The MN 200 also provides the list of sk-counters per SN, i . e . , one list for the SN1 400 and another list for the SN2 404 . In an example embodiment , the MN 200 may also provide a configuration for the UE 300 to wait for an approval of a SN node key or a SN counter before use . In other words , the ef fect of the configuration is that the UE 300 wil l send the drawn sk-counter to the MN 200 when a SCPAC condition is met and waits for the approval of the MN 200 before accessing to the candidate SN . In an example embodiment , the configuration may be transmitted to the UE 300 in the RRCReconf iguration message . In another example embodiment , instead of explicitly indicating the configuration to the UE 300 , the UE 300 may have to implement a default behaviour (without the explicit configuration by the MN 200 ) of indicate the sk-counter to be used to the MN 200 and waiting for the approval from the MN 200 before accessing to the candidate SN .

[0166] At 416 , the UE decodes the RRCReconf iguration message received from MN 200 and sends a RRCReconf igurationComplete message to the MN 200 to approve the reception of the configuration .

[0167] At 418 , when the SCPAC condition for a PSCell under the SN2 402 is met , the UE executes the SCPAC towards the PSCell . As the PSCell handover is an inter-SN handover from the SN1 400 to the SN2 402 , the UE 300 needs to use a new key di f ferent than that is in use with the SN1 400 . Therefore , the UE 300 draws an sk- counter from the list of sk-counters of the SN2 402 and generates the SN2 key .

[0168] At 470 , the UE 300 transmits the SN key or the sk- counter to the MN 200 along with the selected candidate SCPAC configuration before decoding the candidate SCPAC configuration and thus share such information with the MN 200 before sending a RRCReconf igurationComplete message .

[0169] At 482 , the MN 200 determines whether the generated SN key or the sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use . In this example embodiment , the generated SN key or the sk-counter received from the UE 300 does not match with a SN key or an sk-counter that the MN 200 expects the UE 300 to use , and the MN 200 rej ects the use of sk-counter or the SN key that was received from the UE 300 .

[0170] At 484 , the MN 200 sends a message comprising a disapproval of the SN key or the sk-counter to the UE 300 . In an example embodiment , the message may al so comprise an index of a correct sk-counter to be used by the UE 300 to draw a new sk-counter .

[0171] At 486 , the UE 300 adj usts the counter index to obtain the new sk-counter and generate the new SN key . In an example embodiment , the UE 300 may use the new sk- counter index to draw the correct sk-counter and possibly also generate new SN key .

[0172] At 488 , the UE 300 transmits the SN key or the sk- counter to the MN 200 along with the selected candidate SCPAC configuration before decoding the candidate SCPAC configuration and thus share such information with the MN 200 before sending a RRCReconf igurationComplete message .

[0173] At 490 , the MN 200 determines whether the SN key or the sk-counter received from the UE 300 matches with a SN key or an sk-counter that the MN 200 expects the UE 300 to use . In the case that the sk-counter or the SN key matches with the sk-counter or the SN key that the MN 200 expects the UE 300 to use, at 492 the MN 200 sends an approval for the sk-counter or the SN key to be used and grants an access to the SN2 402 .

[0174] At 494 , the UE decodes the candidate SCPAC configuration and sends a RRCReconf igurationComplete message to the MN 200 to indicate which candidate configuration is executed .

[0175] At 496 , the MN 200 informs the SN2 404 about the SCPAC execution using a SN Reconf igurationComplete message . In an example embodiment , the MN 200 may share the SN key that the UE 300 is expected to use to access the SN2 402 in this message .

[0176] At 498 , the UE 300 may initiate a random access channel (RACH) procedure towards the SN2 402 and use the generated SN2 key to access the SN2 402 . In another example embodiment , the UE 300 may alternatively initiate a RACHless access towards the SN 402 , for example , in case the UE 300 has already initiated early timing advance before , or other procedures , or based on information which do not require a RACH procedure to access the SN 402 .

[0177] FIG . 5 illustrates example of a method according to an example embodiment . The method may be performed by a network node configured support dual-connectivity of a user equipment to the network node and to a first secondary network node .

[0178] At 500 , the method may compri se receiving from the user equipment being served by the first secondary node a first message compris ing a generated second secondary node key or a second secondary node counter associated with a second secondary node .

[0179] At 502 , the method may comprise determining whether the generated second secondary node key or the secondary node counter matches with a second secondary node key or a second secondary node counter that the network node expects the user equipment to use .

[0180] At 504 , the method may comprise transmitting, based on the determination, a second message comprising an indication associated with the matching to the user equipment .

[0181] FIG . 6 illustrates example of a method according to another example embodiment . The method may be performed by a user equipment configured to operate in a dualconnectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node .

[0182] At 600 , the method may comprise transmitting to the network node a first message comprising a generated second secondary node key or a second secondary node counter associated with a second secondary node .

[0183] At 602 , the method may comprise receiving from the network node a second message comprising an indication whether the generated second secondary node key or the secondary node counter matches with a second secondary node key or a second secondary node counter that the network node expects the user equipment to use .

[0184] Further features of the methods directly result from the functionality of the network node or the user equipment , as described throughout the description, claims , and drawings , and are there fore not repeated here . An apparatus may be configured to perform or cause performance of any aspect of the method ( s ) described herein . Further, a computer program or a computer program product may comprise instructions for causing, when executed by an apparatus , the apparatus to perform any aspect of the method ( s ) described herein . Further, an apparatus may comprise means for performing any aspect of the method ( s ) described herein . According to an example embodiment , the means comprises at least one processor ; and at least one memory storing instructions that , when executed by the at least one processor, cause the apparatus at least to perform any aspect of the method ( s ) .

[0185] Any range or device value given herein may be extended or altered without losing the ef fect sought . Also , any embodiment may be combined with another embodiment unless explicitly disallowed .

[0186] Although the subj ect matter has been described in language speci fic to structural features and / or acts , it is to be understood that the subj ect matter defined in the appended claims is not necessarily limited to the speci fic features or acts described above . Rather, the speci fic features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims .

[0187] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or al l of the stated benefits and advantages . It will further be understood that reference to ' an ' item may refer to one or more of those items .

[0188] The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate . Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subj ect matter described herein . Aspects of any of the example embodiments described above may be combined with aspects of any of the other example embodiments described to form further example embodiments without losing the effect sought.

[0189] The term 'comprising' is used herein to mean including the method, blocks, or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0190] 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 .

[0191] Although subjects may be referred to as 'first' or 'second' subjects, this does not necessarily indicate any order or importance of the subjects. Instead, such attributes may be used solely for the purpose of making a difference between subjects.

[0192] 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 . This definition of circuitry applies to all uses of this term in this application, including in any claims .

[0193] As a further example , as used in this appl ication, 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 i f applicable to the particular claim element , a baseband integrated circuit or processor integrated circuit for a mobi le device or a similar integrated circuit in server, a cellular network device , or other computing or network device .

[0194] It will be understood that the above description is given by way of example only and that various modi fications may be made by those skilled in the art . The above speci fication, examples and data provide a complete description of the structure and use of exemplary embodiments . Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments , those skilled in the art could make numerous alterations to the disclosed embodiments without departing from scope of this speci fication .

Claims

CLAIMS1 . A network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node , comprising : at least one processor ; and at least one memory storing instructions which, when executed by the at least one processor, cause the network node to at least to : receive from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; determine whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a second message comprising an indication associated with the matching to the user equipment .2 . The network node according to claim 1 , wherein the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment .3 . The network node according to claim 1 , wherein the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counter to the user equipment .4 . The network node according to claim 3 , wherein the second message comprises an index of a correct counter to be used by the user equipment .5 . The network node according to claim 3 or 4 , wherein the instructions , when executed by the at least one processor, cause the network node at least to : receive from the user equipment a third message comprising a regenerated second secondary network node key or a newly used second secondary network node counter associated with the second secondary network node ; determine that the regenerated second secondary network node key or the newly used second secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmit , based on the determination, a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment .6 . The network node according to any one of claims 1 - 5 , wherein the instructions , when executed by the at least one processor, cause the network node at least to : prior to receiving the first message , transmit to the user equipment a fi fth message comprising a configuration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .7 . The network node according to any one of claims 1 - 6 , wherein the first message comprises a radio resource control , RRC, reconfiguration complete message .8 . A user equipment configured to operate in a dualconnectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node , the user equipment comprising : at least one processor ; and at least one memory storing instructions which, when executed by the at least one processor, cause the user equipment at least to : transmit to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; and receive from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .9 . The user equipment according to claim 8 , the indication comprises an approval of the generated second secondary network node key or the second secondary network node counter to the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : initiate a random access procedure towards the second secondary network node in response to the approval .10 . The user equipment according to claim 8 , the indication comprises a disapproval of the generated second secondary network node key or the second secondary network node counter and an index of a correct counterto the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : adj ust a counter index ; transmit to the network node a third message comprising a regenerated second secondary network node key associated with the adj usted counter index or a newly used second secondary network node counter associated with the second secondary network node , the newly used second secondary network node counter being associated with the adj usted counter index ; receive from the network node a fourth message comprising an approval of the regenerated second secondary network node key or the newly used second secondary network node counter to the user equipment ; and initiate a random access procedure towards the second secondary network node in response to the approval .11 . The user equipment according to claim 9 or 10 , wherein the second message comprises an index of a correct counter to be used by the user equipment , and wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : adj ust the counter index based on the index received from the network node .12 . The user equipment according to any one of claims 8 - 11 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : prior to transmitting the first message , receive from the network node a fi fth message comprising aconfiguration for the user equipment to wait for an approval of a second secondary network node key or a second secondary network node counter before use .13 . The user equipment according to claim 8 , wherein the instructions , when executed by the at least one processor, cause the user equipment at least to : initiate a random access procedure towards the second secondary network node right after transmitting the first message to the network node .14 . The user equipment according to any one of claims 8 - 13 , wherein the first message comprises a radio resource control , RRC, reconfiguration complete message .15 . A method performed by a network node that supports dual-connectivity of a user equipment to the network node and to a secondary network node , the method comprising : receiving from a user equipment being served by a first secondary network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; determining whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use ; and transmitting, based on the determination, a second message comprising an indication associated with the matching to the user equipment .16 . A method performed by a user equipment configured to operate in a dual-connectivity mode with a network node and a secondary network node , the user equipment being served by a first secondary network node , the method comprising : transmitting to the network node a first message comprising a generated second secondary network node key or a second secondary network node counter associated with a second secondary network node ; and receiving from the network node a second message comprising an indication whether the generated second secondary network node key or the secondary network node counter matches with a second secondary network node key or a second secondary network node counter that the network node expects the user equipment to use .17 . A computer program compri sing instructions for causing an apparatus to carry out the method of any of claims 15 - 16 .

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