Non-access stratum synchronization

Abstract

Embodiments of the invention relate to a network node and a network access node for solving NAS mismatch between a network and a client device. The present solution considers all NAS procedures which are currently used for signaling change in parameters or state change in the client device. The NAS procedure may be network initiated or client device initiated. For solving NAS mismatch a DL NAS message or a UL NAS message terminates the NAS procedure. Furthermore, embodiments of the invention also relate to corresponding methods and a computer program.

Description

[0001] NON-ACCESS STRATUM SYNCHRONIZATION

[0002] TECHNICAL FIELD

[0003] Embodiments of the invention relate to a network node and a network access node for non- access stratum (NAS) synchronization. Furthermore, embodiments of the invention also relate to corresponding methods and a computer program.

[0004] BACKGROUND

[0005] In a conventional way of paging mechanism in 3GPP, a user equipment (UE) calculates paging occasion (PO) in a paging frame (PF). The PO calculation is based on the identity of the UE. The details of such PO calculations are specified in 3GPP TS 38.304.

[0006] As the paging channel has limited capacity, several UEs may be assigned to the same paging channel. UE receives paging downlink control information (DCI) and the paging message is scrambled by paging radio network temporary identifier (P-RNTI). The paging DCI and the paging message are always sent in the same time slot. There is only one P-RNTI defined and is shared by all UEs.

[0007] SUMMARY

[0008] An objective of embodiments of the invention is to provide a solution which mitigates or solves the drawbacks and problems of conventional solutions.

[0009] The above and further objectives are solved by the subject matter of the independent claims. Further embodiments of the invention can be found in the dependent claims.

[0010] According to a first aspect of the invention, the above mentioned and other objectives are achieved with a network node configured to: transmit a downlink non-access stratum, NAS, transport message to a network access node, wherein the downlink NAS transport message comprises a NAS message of a NAS procedure between the network node and a client device and an indication indicating a NAS delivery status request for the NAS message; and receive a NAS delivery report message from the network access node, the NAS delivery report message indicating a NAS delivery status for the NAS message.

[0011] An advantage of the network node according to the first aspect is that a generalized solution for NAS synchronization is provided that works for all network initiated and client device initiated NAS procedures and is not scenario specific. Furthermore, the generalized solution will work for all the previously released client devices since only the network needs to be upgraded to support the generalized solution which will not impact legacy client devices.

[0012] In an implementation form of the network node according to the first aspect, the network node is configured to: apply a NAS configuration of the NAS message when the NAS delivery status is positive.

[0013] An advantage with this implementation form is that the network node will apply the new NAS configuration for the client device only when the NAS delivery status is positive to ensure there is no state / configuration mismatch between the client device and the network node.

[0014] In an implementation form of the network node according to the first aspect, the network node is configured to: retransmit the downlink NAS transport message to the network access node when the NAS delivery status is negative.

[0015] An advantage with this implementation form is that the network node will know that the NAS message has not been delivered to the client device and will take appropriate action to retransmit the downlink NAS transport message.

[0016] In an implementation form of the network node according to the first aspect, the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

[0017] An advantage with this implementation form is that signaling overhead for the introduced information elements, i.e., the NAS delivery status request and the NAS delivery status, is minimal.

[0018] In an implementation form of the network node according to the first aspect, the network node is part of a core network.

[0019] An advantage with this implementation form is that a general mechanism is provided that can be used to increase signaling reliability between any two network nodes.

[0020] In an implementation form of the network node according to the first aspect, the network node is an AMF. According to a second aspect of the invention, the above mentioned and other objectives are achieved with a network access node configured to: receive a downlink NAS transport message from a network node, wherein the downlink NAS transport message comprises a NAS message of a NAS procedure between the network node and a client device and an indication indicating a NAS delivery status request for the NAS message; determine a NAS delivery status for the NAS message based on the NAS delivery status request; and transmit a NAS delivery report message to the network node, the NAS delivery report message indicating the determined NAS delivery status for the NAS message.

[0021] An advantage with the network access node according to the second aspect is that a generalized solution for NAS synchronization is provided that works for all network initiated and client device initiated NAS procedures and is not scenario specific. Furthermore, the generalized solution will work for all the previously released client devices since only the network needs to be upgraded to support the generalized solution which will not impact legacy client devices.

[0022] In an implementation form of the network access node according to the second aspect, the network access node is configured to: determine the NAS delivery status based on an acknowledgement at a PDCP / RLC layer or an RRC delivery report message.

[0023] PDCP is understood as Packet Data Convergence Protocol and RLC is understood as Radio Link Control.

[0024] An advantage with this implementation form is the network access node will ensure that the message is delivered to the client device based on the acknowledgement at a PDCP / RLC layer or based on an RRC delivery report message.

[0025] In an implementation form of the network access node according to the second aspect, the NAS delivery status is positive or negative.

[0026] In an implementation form of the network access node according to the second aspect, the network access node is configured to: receive the downlink NAS transport message from the network node an additional time when the NAS delivery status is negative. An advantage with this implementation form is that the network node will know that the NAS message has not been delivered to the client device and will take appropriate action to retransmit the downlink NAS transport message.

[0027] In an implementation form of the network access node according to the second aspect, the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

[0028] An advantage with this implementation form is that signaling overhead for the introduced information elements, i.e., the NAS delivery status request and the NAS delivery status, is minimal.

[0029] In an implementation form of the network access node according to the second aspect, the network access node is part of a radio access network.

[0030] In an implementation form of the network access node according to the second aspect, the network access node is a gNB.

[0031] According to a third aspect of the invention, the above mentioned and other objectives are achieved with a method for a network node, the method comprises: transmitting a downlink NAS transport message to a network access node, wherein the downlink NAS transport message comprises a NAS message of a NAS procedure between the network node and a client device and an indication indicating a NAS delivery status request for the NAS message; and receiving a NAS delivery report message from the network access node, the NAS delivery report message indicating a NAS delivery status for the NAS message.

[0032] The method according to the third aspect can be extended into implementation forms corresponding to the implementation forms of the network node according to the first aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network node.

[0033] The advantages of the methods according to the third aspect are the same as those for the corresponding implementation forms of the network node according to the first aspect. According to a fourth aspect of the invention, the above mentioned and other objectives are achieved with a method for a network access node, the method comprises: receiving a downlink NAS transport message from a network node, wherein the downlink NAS transport message comprises a NAS message of a NAS procedure between the network node and a client device and an indication indicating a NAS delivery status request for the NAS message; determining a NAS delivery status for the NAS message based on the NAS delivery status request; and transmitting a NAS delivery report message to the network node, the NAS delivery report message indicating the determined NAS delivery status for the NAS message.

[0034] The method according to the fourth aspect can be extended into implementation forms corresponding to the implementation forms of the network access node according to the second aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network access node.

[0035] The advantages of the methods according to the fourth aspect are the same as those for the corresponding implementation forms of the network access node according to the second aspect.

[0036] According to a fifth aspect of the invention, the above mentioned and other objectives are achieved with a network node configured to: transmit a downlink NAS transport message to a network access node, wherein the downlink NAS transport message indicates an expected NAS message for a NAS procedure between the network node and a client device; receive an uplink NAS transport message from the network access node, wherein the uplink NAS transport message comprises a NAS message from the client device and indicates a NAS delivery status request for the NAS message from the client device; and transmit a NAS delivery report message to the network access node based on the NAS delivery status request, the NAS delivery report message indicating a NAS delivery status for the NAS message from the client device.

[0037] An advantage of the network node according to the fifth aspect is that a generalized solution is provided that works for all network initiated and client device initiated NAS procedures and is not scenario specific. Furthermore, the generalized solution will work for all the previously released client devices since only the network needs to be upgraded to support the generalized solution which will not impact legacy client devices. In an implementation form of the network node according to the fifth aspect, the network node is configured to: apply a NAS configuration on receiving the NAS message from the client device when the NAS delivery status for the NAS message from the client device is positive.

[0038] An advantage with this implementation form is that the network node will apply the NAS configuration for the client device only when the NAS delivery status is positive to ensure there is no state / configuration mismatch between the client device and the network node.

[0039] In an implementation form of the network node according to the fifth aspect, the network node is configured to: receive an uplink NAS transport message from the network access node an additional time when NAS delivery status for the NAS message from the client device is negative.

[0040] An advantage with this implementation form is that the network node will know that the NAS message has not been delivered to the client device and will take appropriate action to retransmit the downlink NAS transport message.

[0041] In an implementation form of the network node according to the fifth aspect, the expected NAS message and / or the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

[0042] An advantage with this implementation form is that signaling overhead for the introduced information elements, i.e., the expected NAS message, the NAS delivery status request and the NAS delivery status, is minimal,

[0043] In an implementation form of the network node according to the fifth aspect, the network node is part of a core network.

[0044] An advantage with this implementation form is that a general mechanism is provided that can be used to increase signaling reliability between any two network nodes.

[0045] In an implementation form of the network node according to the fifth aspect, the network node is an AMF. According to a sixth aspect of the invention, the above mentioned and other objectives are achieved with a network access node configured to: receive a downlink NAS transport message from a network node, wherein the downlink NAS transport message indicates an expected NAS message for a NAS procedure between the network node and a client device; transmit an uplink NAS transport message to the network node based on the expected NAS message, wherein the uplink NAS transport message comprises a NAS message from the client device and indicates a NAS delivery status request for the NAS message from the client device; and receive a NAS delivery report message from the network node, the NAS delivery report message indicating a NAS delivery status for the NAS message from the client device.

[0046] An advantage with the network access node according to the sixth aspect is that a generalized solution is provided that works for all network initiated and client device initiated NAS procedures and is not scenario specific. Furthermore, the generalized solution will work for all the previously released client devices since only the network needs to be upgraded to support the generalized solution which will not impact legacy client devices.

[0047] In an implementation form of the network access node according to the sixth aspect, the NAS delivery status is positive.

[0048] In an implementation form of the network access node according to the sixth aspect, the network access node is configured to: retransmit the uplink NAS transport message to the network node when the NAS delivery status is negative.

[0049] An advantage with this implementation form is that the network node will know that the NAS message has not been delivered to the client device and will take appropriate action to retransmit the downlink NAS transport message.

[0050] In an implementation form of the network access node according to the sixth aspect, the expected NAS message and / or the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

[0051] An advantage with this implementation form is that signaling overhead for the introduced information elements, i.e., the expected NAS message, the NAS delivery status request and the NAS delivery status, is minimal. In an implementation form of the network access node according to the sixth aspect, the network access node is part of a radio access network.

[0052] In an implementation form of the network access node according to the sixth aspect, the network access node is a gNB.

[0053] According to a seventh aspect of the invention, the above mentioned and other objectives are achieved with a method for a network node, the method comprises: transmitting a downlink NAS transport message to a network access node, wherein the downlink NAS transport message indicates an expected NAS message for a NAS procedure between the network node and a client device; receiving an uplink NAS transport message from the network access node, wherein the uplink NAS transport message comprises a NAS message from the client device and indicates a NAS delivery status request for the NAS message from the client device; and transmitting a NAS delivery report message to the network access node based on the NAS delivery status request, the NAS delivery report message indicating a NAS delivery status for the NAS message from the client device.

[0054] The method according to the seventh aspect can be extended into implementation forms corresponding to the implementation forms of the network node according to the fifth aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network node.

[0055] The advantages of the methods according to the seventh aspect are the same as those for the corresponding implementation forms of the network node according to the fifth aspect.

[0056] According to an eighth aspect of the invention, the above mentioned and other objectives are achieved with a method for a network access node, the method comprises: receiving a downlink NAS transport message from a network node, wherein the downlink NAS transport message indicates an expected NAS message for a NAS procedure between the network node and a client device; transmitting an uplink NAS transport message to the network node based on the expected NAS message, wherein the uplink NAS transport message comprises a NAS message from the client device and indicates a NAS delivery status request for the NAS message from the client device; and receiving a NAS delivery report message from the network node, the NAS delivery report message indicating a NAS delivery status for the NAS message from the client device.

[0057] The method according to the eight aspect can be extended into implementation forms corresponding to the implementation forms of the network access node according to the sixth aspect. Hence, an implementation form of the method comprises the feature(s) of the corresponding implementation form of the network access node.

[0058] The advantages of the methods according to the eight aspect are the same as those for the corresponding implementation forms of the network access node according to the sixth aspect.

[0059] Embodiments of the invention also relate to a computer program, characterized in program code, which when run by at least one processor causes the at least one processor to execute any method according to embodiments of the invention. Further, embodiments of the invention also relate to a computer program product comprising a computer readable medium and the mentioned computer program, wherein the computer program is included in the computer readable medium, and may comprises one or more from the group of: read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), flash memory, electrically erasable PROM (EEPROM), hard disk drive, etc.

[0060] Further applications and advantages of embodiments of the invention will be apparent from the following detailed description.

[0061] BRIEF DESCRIPTION OF THE DRAWINGS

[0062] The appended drawings are intended to clarify and explain different embodiments of the invention, in which:

[0063] - Fig. 1 shows a network node according to an embodiment of the invention;

[0064] - Fig. 2 shows a flow chart of a method for a network node according to an embodiment of the invention;

[0065] - Fig. 3 shows a flow chart of a method for a network node according to an embodiment of the invention;

[0066] - Fig. 4 shows a network access node according to an embodiment of the invention;

[0067] - Fig. 5 shows a flow chart of a method for a network access node according to an embodiment of the invention;

[0068] - Fig. 6 shows a flow chart of a method for a network access node according to an embodiment of the invention; - Fig. 7 shows a communication system according to an embodiment of the invention;

[0069] - Fig. 8 and 9 shows signaling diagrams illustrating aspects of the invention; and

[0070] - Fig. 10 and 11 shows signaling diagrams illustrating further aspects of the invention.

[0071] DETAILED DESCRIPTION

[0072] It has been observed that a UE sometimes misses paging occasionally in the 5G network. Initially it was considered as an issue in the discontinuous reception (DRX) cycle mismatch between the UE and the network, but later detailed analysis showed that it’s the mismatch in the PEI with paging subgrouping (PEIPS) information stored in the UE and used by the network.

[0073] In the more general perspective, missing paging is due to a state / configuration mismatch between the UE and the access and mobility management function (AMF). Although there are already mechanisms in place that involves configuring Radio Link Control (RLC) Layer in Acknowledgment (AM) mode for Signaling Radio Bearer (SRB) 2 on the air interface and "NAS Non Delivery Indication" procedure on NG interface to inform the AMF about the issue with of the delivery of NAS messages, but in reality the loss of NAS message do happen in the field which causes state / configuration mismatch between the UE and the AMF. The NAS layer is used to manage the establishment of communication sessions and for maintaining continuous communications with the UE as it moves.

[0074] Therefore, a solution is herein disclosed which aims at having a generalized network-based solution that will solve the issue of UE / AMF mismatch and also work for all previous releases of UEs.

[0075] Fig. 1 shows a network node 100 according to an embodiment of the invention. In the embodiment shown in Fig. 1 , the network node 100 comprises a processor 102, a transceiver 104 and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 by communication means 108 known in the art. The network node 100 may be configured for wired communications in a communication system. The wired communication capability may be provided with a wired communication interface 110 e.g., coupled to the transceiver 104.

[0076] The processor 102 may be referred to as one or more general-purpose central processing units (CPUs), one or more digital signal processors (DSPs), one or more application-specific integrated circuits (ASICs), one or more field programmable gate arrays (FPGAs), one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, or one or more chipsets. The memory 106 may be a read-only memory, a random access memory (RAM), or a non-volatile RAM (NVRAM). The transceiver 104 may be a transceiver circuit, a power controller, or an interface providing capability to communicate with other communication modules or communication devices, such as network nodes and network servers. The transceiver 104, memory 106 and / or processor 102 may be implemented in separate chipsets or may be implemented in a common chipset.

[0077] That the network node 100 is configured to perform certain actions can in this disclosure be understood to mean that the network node100 comprises suitable means, such as e.g., the processor 102 and the transceiver 104, configured to perform the actions.

[0078] According to embodiments of the invention the network node 100 according to the first aspect of the invention is configured to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; and receive a NAS delivery report message 520 from the network access node 300, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message.

[0079] Furthermore, in an embodiment of the invention, the network node 100 according to the first aspect of the invention comprises a transceiver configured to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; and receive a NAS delivery report message 520 from the network access node 300, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message.

[0080] Moreover, in yet another embodiment of the invention, the network node 100 according to the first aspect of the invention comprises a processor and a memory having computer readable instructions stored thereon which, when executed by the processor, cause the processor to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; and receive a NAS delivery report message 520 from the network access node 300, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message. According to embodiments of the invention the network node 100 according to the fifth aspect of the invention is configured to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 indicates an expected NAS message for a NAS procedure between the network node 100 and a client device 600; receive an uplink NAS transport message 530 from the network access node 300, wherein the uplink NAS transport message 530 comprises a NAS message from the client device 600 and indicates a NAS delivery status request for the NAS message from the client device 600; and transmit a NAS delivery report message 520 to the network access node 300 based on the NAS delivery status request, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message from the client device 600.

[0081] Furthermore, in an embodiment of the invention, the network node 100 according to the fifth aspect of the invention comprises a transceiver configured to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 indicates an expected NAS message for a NAS procedure between the network node 100 and a client device 600; receive an uplink NAS transport message 530 from the network access node 300, wherein the uplink NAS transport message 530 comprises a NAS message from the client device 600 and indicates a NAS delivery status request for the NAS message from the client device 600; and transmit a NAS delivery report message 520 to the network access node 300 based on the NAS delivery status request, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message from the client device 600.

[0082] Moreover, in yet another embodiment of the invention, the network node 100 according to the fifth aspect of the invention comprises a processor and a memory having computer readable instructions stored thereon which, when executed by the processor, cause the processor to: transmit a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 indicates an expected NAS message for a NAS procedure between the network node 100 and a client device 600; receive an uplink NAS transport message 530 from the network access node 300, wherein the uplink NAS transport message 530 comprises a NAS message from the client device 600 and indicates a NAS delivery status request for the NAS message from the client device 600; and transmit a NAS delivery report message 520 to the network access node 300 based on the NAS delivery status request, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message from the client device 600. Fig. 2 shows a flow chart of a method 200 according to the third aspect of the invention which may be executed in a network node 100, such as the one shown in Fig. 1. The method 200 comprises transmitting 202 a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; and receiving 204 a NAS delivery report message 520 from the network access node 300, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message.

[0083] Fig. 3 shows a flow chart of a method 200' according to the seventh aspect of the invention which may be executed in a network node 100, such as the one shown in Fig. 1. The method 200' comprises transmitting 202' a downlink NAS transport message 510 to a network access node 300, wherein the downlink NAS transport message 510 indicates an expected NAS message for a NAS procedure between the network node 100 and a client device 600; receiving 204' an uplink NAS transport message 530 from the network access node 300, wherein the uplink NAS transport message 530 comprises a NAS message from the client device 600 and indicates a NAS delivery status request for the NAS message from the client device 600; and transmitting 206' a NAS delivery report message 520 to the network access node 300 based on the NAS delivery status request, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message from the client device 600.

[0084] Fig. 4 shows a network access node 300 according to an embodiment of the invention. In the embodiment shown in Fig. 4, the network access node 300 comprises a processor 302, a transceiver 304 and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 by communication means 308 known in the art. The network access node 300 further comprises a communication interface 310 coupled to the transceiver 304, which means that the network access node 300 is configured for communications in a communication system.

[0085] The processor 302 may be referred to as one or more general-purpose CPUs, one or more DSPs, one or more ASICs, one or more FPGAs, one or more programmable logic devices, one or more discrete gates, one or more transistor logic devices, one or more discrete hardware components, one or more chipsets. The memory 306 may be a read-only memory, a RAM, or a NVRAM. The transceiver 304 may be a transceiver circuit, a power controller, or an interface providing capability to communicate with other communication modules or communication devices. The transceiver 304, the memory 306 and / or the processor 302 may be implemented in separate chipsets or may be implemented in a common chipset. That the network access node 300 is configured to perform certain actions can in this disclosure be understood to mean that the network access node 300 comprises suitable means, such as e.g., the processor 302 and the transceiver 304, configured to perform the actions.

[0086] According to embodiments of the invention the network access node 300 according to the second aspect of the invention is configured to: receive a downlink NAS transport message 510 from a network node 100, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; determine a NAS delivery status for the NAS message based on the NAS delivery status request; and transmit a NAS delivery report message 520 to the network node 100, the NAS delivery report message 520 indicating the determined NAS delivery status for the NAS message.

[0087] Furthermore, in an embodiment of the invention, the network access node 300 according to the second aspect of the invention comprises a transceiver configured to receive a downlink NAS transport message 510 from a network node 100, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message. The network access node 300 comprises a processor configured to determine a NAS delivery status for the NAS message based on the NAS delivery status request. The transceiver is further configured to transmit a NAS delivery report message 520 to the network node 100, the NAS delivery report message 520 indicating the determined NAS delivery status for the NAS message.

[0088] Moreover, in yet another embodiment of the invention, the network access node 300 according to the second aspect of the invention comprises a processor and a memory having computer readable instructions stored thereon which, when executed by the processor, cause the processor to: receive a downlink NAS transport message 510 from a network node 100, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; determine a NAS delivery status for the NAS message based on the NAS delivery status request; and transmit a NAS delivery report message 520 to the network node 100, the NAS delivery report message 520 indicating the determined NAS delivery status for the NAS message. Fig. 5 shows a flow chart of a method 400 according to fourth aspect of the invention which may be executed in a network access node 300. The method 400 comprises receiving 402 a downlink NAS transport message 510 from a network node 100, wherein the downlink NAS transport message 510 comprises a NAS message of a NAS procedure between the network node 100 and a client device 600 and an indication indicating a NAS delivery status request for the NAS message; determining 404 a NAS delivery status for the NAS message based on the NAS delivery status request; and transmitting 406 a NAS delivery report message 520 to the network node 100, the NAS delivery report message 520 indicating the determined NAS delivery status for the NAS message.

[0089] Fig. 6 shows a flow chart of a method 400' according to an eight aspect of the invention which may be executed in a network access node 300. The method 400' comprises receiving 402' a downlink NAS transport message 510 from a network node 100, wherein the downlink NAS transport message 510 indicates an expected NAS message for a NAS procedure between the network node 100 and a client device 600; transmitting 404' an uplink NAS transport message 530 to the network node 100 based on the expected NAS message, wherein the uplink NAS transport message 530 comprises a NAS message from the client device 600 and indicates a NAS delivery status request for the NAS message from the client device 600; and receiving 406' a NAS delivery report message 520 from the network node 300, the NAS delivery report message 520 indicating a NAS delivery status for the NAS message from the client device 600.

[0090] Fig. 7 shows a communication system 500 according to embodiments of the invention. The communication system 500 in the disclosed embodiment comprises a network node 100 and a network access node 300 configured to communicate and operate in the communication system 500. The network node 100 may be an AMF while the network access node 300 may be a base station of a RAN. The network node 100 and the network access node 300 may communicate with each other using suitable communication interfaces. The network access node 300 may also be configured to communicate with client devices 600 by e.g., using standardized air interfaces which may be denoted downlink (DL) and uplink (UL) communications.

[0091] Further details related to embodiments of the invention will be described in a 3GPP 5G context with reference to the signaling diagram of Figs. 8 to 11. Thus, 3GPP 5G terminology, definitions, expressions and system architecture may be used. Therefore, mentioned Figs, show signaling diagrams involving a network node 100 acting as an AMF 100 of a CN, a network access node 300 acting as a network node of a RAN and being denoted NG-RAN 300, and a client device 600 acting as a UE 600. It may however be noted that embodiments of the invention are not limited thereto.

[0092] A NAS procedure can in general be categorized as either network initiated or UE initiated and being based on whether a UL or a DL NAS message terminates the NAS procedure. The present solution considers all NAS procedures which are currently used for signaling change in parameters or state change in the UE 600. Fig. 8 illustrates a UE initiated NAS procedure with DL NAS message completing / terminating the NAS procedure and Fig. 9 illustrates a network initiated NAS procedure with DL NAS message completing / terminating the NAS procedure. Fig. 10 on the other hand illustrate a UE initiated NAS procedure with UL NAS message completing / terminating the NAS procedure and Fig. 11 illustrates a network initiated NAS procedure with UL NAS message completing / terminating the NAS procedure. Thus, based on which type of message carries the NAS configuration and which type of message completes / terminates the NAS procedure, a generalized solution can be provided for reliable delivery of these NAS messages for NAS synchronization.

[0093] Fig. 8 shows a UE initiated NAS procedure with DL NAS message completing / terminating the NAS procedure.

[0094] In step 1 in Fig. 8, the UE 600 transmits a UL information transfer message containing a UL NAS message to the NG-RAN 300. The UL NAS message is the initiating NAS message in the NAS procedure between the UE 600 and the AMF 100.

[0095] In step 2 in Fig. 8, the NG-RAN 300 transmits a UL NAS transport message to the AMF 100. The UL NAS transport message initiates the NAS procedure between the UE 600 and the AMF 100.

[0096] In step 3 in Fig. 8, the AMF 100 takes the decision to change NAS information / parameter and sends a DL NAS message to the UE 600 (not shown in the Fig.).

[0097] In step 4 in Fig. 8, the AMF 100 transmits a DL NAS transport message 510 to the NG-RAN 300. The DL NAS transport message 510 comprises a NAS message of the NAS procedure between the AMF 100 and the UE 600 and also comprises an indication which indicates a NAS delivery status request for the NAS message.

[0098] In step 5 in Fig. 8, the NG-RAN 300 transmits a DL information transfer message containing the DL NAS message to the UE 600. In step 6 in Fig. 8, the NG-RAN 300 determines a NAS delivery status based on an acknowledgement at a PDCP / RLC layer or an RRC delivery report message on the F1 interface in case of a split RAN architecture. For example, the NG-RAN receives a RLC acknowledgement (ACK) for the DL NAS message and determines if the NAS message has been delivered to the UE 600. Alternatively, in case of split RAN architecture the RRC delivery report message on the F1 interface from the distributed unit (DU) shall indicate the successful delivery of the NAS message to the centralized unit (CU) of the NG-RAN.

[0099] The NAS delivery status may be positive or negative where positive means that the DL NAS message has been successfully delivered to the UE 600.

[0100] In step 7 in Fig. 8, the UE 600 applies NAS information / parameter change and takes the new NAS configuration in the DL NAS message in use.

[0101] In step 8 in Fig. 8, the NG-RAN 300 transmits a NAS delivery report message 520 to the AMF 100. The NAS delivery report message 520 indicates a NAS delivery status for the NAS message.

[0102] In step 9 in Fig. 8, the AMF 100 applies a NAS configuration of the NAS message when the NAS delivery status is positive. The AMF 100 may also signal to the NG-RAN 300 any NAS configuration related information that is to be used by the NG RAN 300.

[0103] However, if the NAS delivery status is negative the AMF 100 retransmits the downlink NAS transport message 510 to the NG-RAN 300 (not shown in the Fig.). Hence, the NG-RAN 300 will receive the DL NAS transport message 510 from the AMF 100 an additional time when the NAS delivery status is negative.

[0104] The indication of the NAS delivery status request and / or the NAS delivery status may be indicated by a flag such as a bit-flag.

[0105] In step 10 in Fig. 8, the UE 600 and the AMF 100 are synchronized in state / configu ration and the possibility of mismatch in NAS state or configuration is thus minimized.

[0106] Fig. 9 shows a network initiated NAS procedure with DL NAS message completing / terminating the NAS procedure. Steps 2 to 8 in Fig. 9 are the same as steps 4 to 10 in Fig. 8. Thus, the difference to the scheme in Fig. 8 is in step 1 in Fig. 9, where the AMF 100 instead of the UE 600 initiates the NAS procedure between the UE 600 and the AMF 100 by taking the decision to change NAS information / parameters and send a DL NAS message to the UE 600.

[0107] Hence, in the solution shown in Fig. 8 and 9, the DL NAS message carries the critical NAS configuration which also completes / terminates the NAS procedure between the AMF 100 and the UE 600 which e.g., implies: i. A new information element (IE) defining a “NAS delivery status request” is proposed be added to the critical DL NAS transport message that changes the NAS state / configuration. ii. The AMF 100 can set this new IE “NAS delivery status request” to request the delivery report from the NG-RAN 300. iii. The NG-RAN 300 returns a new NAS delivery report message indicating a “NAS delivery status”. iv. Only after this will the AMF 100 apply the new configuration / state for the UE 600 in question to ensure there is no NAS state / configuration mismatch between the UE 600 and the AMF 100.

[0108] Fig. 10 shows a UE initiated NAS procedure with UL NAS message completing / terminating the NAS procedure.

[0109] In step 1 in Fig. 10, the UE 600 transmits a UL information transfer message containing a UL NAS message to the NG-RAN 300. The UL NAS message is the initiating NAS message in the NAS procedure between the UE 600 and the AMF 100.

[0110] In step 2 in Fig. 10, the NG-RAN 300 transmits a UL NAS transport message to the AMF 100. The UL NAS transport message initiates the NAS procedure between the UE 600 and the AMF 100.

[0111] In step 3 in Fig. 10, the AMF 100 takes the decision to change NAS information / parameter and therefore sends a DL NAS message to the UE 600 and determines that terminating UL NAS message is expected after which new NAS parameters / information will be applied.

[0112] In step 4 in Fig. 10, the AMF 100 transmits a DL NAS transport message 510 to the NG-RAN 300. The DL NAS transport message 510 indicates an expected NAS message for the NAS procedure between the AMF 100 and the UE 600. In step 5 in Fig. 10, the NG-RAN transmits a DL information transfer message containing the DL NAS message to the UE 600.

[0113] In step 6 in Fig. 10, the UE 600 transmits a UL information transfer message containing the UL NAS message back to the NG-RAN 300.

[0114] In step 7 in Fig. 10, the NG-RAN 300 transmits a UL NAS transport message 530 to the AMF 100. The UL NAS transport message 530 comprises a NAS message from the UE 600 and also indicates a NAS delivery status request for the NAS message from the UE 600.

[0115] If the NAS delivery status is positive no further action needs to be taken by the NG-RAN 300. However, if the NAS delivery status is negative the NG-RAN 300 retransmits the uplink NAS transport message 530 to the AMF 100 (not shown in the Fig.).

[0116] In step 8 in Fig. 10, the AMF 100 applies a NAS configuration of the downlink NAS transport message 510 upon receiving the NAS message from the UE 600 and when the NAS delivery status for the NAS message from the UE 600 is positive.

[0117] The AMF 100 may optionally check whether the NAS message from the UE 600 is the expected NAS message or not. This check is just to cover the abnormal condition where a new NAS procedure is initiated by the UE 600 when it cannot complete the current procedure by sending UL response message but sends a NAS message initiating another procedure.

[0118] The AMF 100 will receive the uplink NAS transport message 530 from the NG-RAN 300 an additional time when NAS delivery status for the NAS message from the UE 600 is negative as previously mentioned or if there is no response from the AMF 100 for a certain time period.

[0119] In step 9 in Fig. 10, the AMF 100 transmits a NAS delivery report message 520 to the NG-RAN 300 based on the NAS delivery status request received in the UL NAS transport message 530. The NAS delivery report message 520 indicates a NAS delivery status for the NAS message from the UE 600.

[0120] The expected NAS message and / or the NAS delivery status request and / or the NAS delivery status may be indicated by a flag such as a bit flag.

[0121] In step 10 in Fig. 10, the UE 600 applies critical NAS information / parameter and takes the new NAS configuration in use. In step 11 in Fig. 10, the AMF 100 applies NAS parameter / configuration of the NAS message and further signals to the NG-RAN 300 any NAS configuration related information that is to be used by the NG RAN 300.

[0122] In step 12 in Fig. 10, the UE 600 and the AMF 100 are synchronized in state / configuration and the possibility of mismatch in the NAS state or configuration is thus minimized.

[0123] Fig. 11 shows a network initiated NAS procedure with UL NAS message completing / terminating the NAS procedure. Steps 2 to 10 in Fig. 11 are the same as steps 4 to 12 in Fig. 10. Thus, the difference to the scheme in Fig. 10 is in step 1 in Fig. 11 , where AMF 100 takes the decision to initiate a NAS procedure and sends a DL NAS message and expects a UL NAS message in response or as a confirmation.

[0124] Hence, in the solution shown in Fig. 10 and 11 , the DL NAS message carries the critical NAS configuration and the UL NAS message completes / terminates the NAS procedure between the AMF 100 and the UE 600 which e.g., implies: i. While sending a DL NAS message, which is an intermediate or the initiating NAS message in the NAS procedure between the AMF 100 and the UE 600, to the NG-RAN 300 using a DL NAS transport message, the AMF 100 indicates that an UL NAS message, which terminates the NAS procedure, is expected through a new IE “UL NAS message expected”. ii. A new IE “NAS delivery status request” is proposed be added to the critical UL NAS transport message that changes the NAS state / configuration. iii. On receiving the critical UL NAS message the NG-RAN 300 sends the UL NAS message to the AMF 100 in UL NAS transport message and sets a new IE “NAS delivery status request” in the UL NAS message to request a delivery report from the AMF 100. iv. The AMF 100 checks the UL NAS message if it is the expected response and sends a new NAS delivery report message for the reception of UL NAS message to the NG- RAN 300. v. Only after this will the AMF 100 apply the new configuration / state for the UE 600 in question to ensure there is no state / configuration mismatch between the UE 600 and the AMF 100. vi. If the AMF 100 does not send a response to the NG-RAN 300, the NG-RAN 300 can resend the UL NAS message again to the AMF 100 with the NAS delivery status request set. A network node 100 herein may also be denoted as an AMF or any corresponding network function in a communication system.

[0125] A network access node 300 herein may also be denoted as a radio network access node, an access network access node, an access point (AP), or a base station (BS), e.g., a radio base station (RBS), which in some networks may be referred to as transmitter, “gNB”, “gNodeB”, “eNB”, “eNodeB”, “NodeB” or “B node”, depending on the standard, technology and terminology used. The radio network access node may be of different classes or types such as e.g., macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby the cell size. The radio network access node may further be a station, which is any device that contains an IEEE 802.11 -conformant media access control (MAC) and physical layer (PHY) interface to the wireless medium (WM). The radio network access node may be configured for communication in 3GPP related long term evolution (LTE), LTE-advanced, fifth generation (5G) wireless systems, such as new radio (NR) and their evolutions, as well as in IEEE related Wi-Fi, worldwide interoperability for microwave access (WiMAX) and their evolutions.

[0126] A client device 600 herein may be denoted as a user device, a user equipment (UE), a mobile station, an internet of things (loT) device, a sensor device, a wireless terminal and / or a mobile terminal, and is enabled to communicate wirelessly in a wireless communication system, sometimes also referred to as a cellular radio system. The UEs may further be referred to as mobile telephones, cellular telephones, computer tablets or laptops with wireless capability. The UEs in this context may be, for example, portable, pocket-storable, hand-held, computer- comprised, or vehicle-mounted mobile devices, enabled to communicate voice and / or data, via a radio access network (RAN), with another communication entity, such as another receiver or a server. The UE may further be a station, which is any device that contains an IEEE 802.11- conformant MAC and PHY interface to the WM. The UE may be configured for communication in 3GPP related LTE, LTE-advanced, 5G wireless systems, such as NR, and their evolutions, as well as in IEEE related Wi-Fi, WiMAX and their evolutions.

[0127] Furthermore, any method according to embodiments of the invention may be implemented in a computer program, having code means, which when run by processing means causes the processing means to execute the steps of the method. The computer program is included in a computer readable medium of a computer program product. The computer readable medium may comprise essentially any memory, such as previously mentioned a ROM, a PROM, an EPROM, a flash memory, an EEPROM, or a hard disk drive. Moreover, it should be realized that the network node 100 and the network access node 300 comprise the necessary communication capabilities in the form of e.g., functions, means, units, elements, etc., for performing or implementing embodiments of the invention. Examples of other such means, units, elements and functions are: processors, memory, buffers, control logic, encoders, decoders, rate matchers, de-rate matchers, mapping units, multipliers, decision units, selecting units, switches, interleavers, de-interleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, TCM encoder, TCM decoder, power supply units, power feeders, communication interfaces, communication protocols, etc. which are suitably arranged together for performing the solution.

[0128] Therefore, the processor(s) of the network node 100 and the network access node 300 may comprise, e.g., one or more instances of a CPU, a processing unit, a processing circuit, a processor, an ASIC, a microprocessor, or other processing logic that may interpret and execute instructions. The expression “processor” may thus represent a processing circuitry comprising a plurality of processing circuits, such as e.g., any, some or all of the ones mentioned above. The processing circuitry may further perform data processing functions for inputting, outputting, and processing of data comprising data buffering and device control functions, such as call processing control, user interface control, or the like.

[0129] Finally, it should be understood that the invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims

CLAIMS1. A network node (100) configured to: transmit a downlink non-access stratum, NAS, transport message (510) to a network access node (300), wherein the downlink NAS transport message (510) comprises a NAS message of a NAS procedure between the network node (100) and a client device (600) and an indication indicating a NAS delivery status request for the NAS message; and receive a NAS delivery report message (520) from the network access node (300), the NAS delivery report message (520) indicating a NAS delivery status for the NAS message.

2. The network node (100) according to claim 1 , configured to: apply a NAS configuration of the NAS message when the NAS delivery status is positive.

3. The network node (100) according to claim 1 or 2, configured to: retransmit the downlink NAS transport message (510) to the network access node (300) when the NAS delivery status is negative.

4. The network node (100) according to any one of the preceding claims, wherein the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

5. The network node (100) according to any one of the preceding claims, wherein the network node (100) is part of a core network.

6. The network node (100) according to claim 5, wherein the network node (100) is an AMF.

7. A network access node configured to: receive a downlink NAS transport message (510) from a network node (100), wherein the downlink NAS transport message (510) comprises a NAS message of a NAS procedure between the network node (100) and a client device (600) and an indication indicating a NAS delivery status request for the NAS message; determine a NAS delivery status for the NAS message based on the NAS delivery status request; and transmit a NAS delivery report message (520) to the network node (100), the NAS delivery report message (520) indicating the determined NAS delivery status for the NAS message.

8. The network access node (300) according to claim 7, configured to: determine the NAS delivery status based on an acknowledgement at a PDCP / RLC layer or an RRC delivery report message.

9. The network access node (300) according to claim 7 or 8, wherein the NAS delivery status is positive or negative.

10. The network access node (300) according to claim 9, configured to: receive the downlink NAS transport message (510) from the network node (100) an additional time when the NAS delivery status is negative.

11. The network access node (300) according to any one of claims 7 to 10, wherein the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

12. The network access node (300) according to any one of claims 7 to 11 , wherein the network access node (300) is part of a radio access network.

13. The network access node (300) according to claim 12, wherein the network access node (300) is a gNB.

14. A method (200) for a network node (100), the method (200) comprising: transmitting (202) a downlink non-access stratum, NAS, transport message (510) to a network access node (300), wherein the downlink NAS transport message (510) comprises a NAS message of a NAS procedure between the network node (100) and a client device (600) and an indication indicating a NAS delivery status request for the NAS message; and receiving (204) a NAS delivery report message (520) from the network access node (300), the NAS delivery report message (520) indicating a NAS delivery status for the NAS message.

15. A method (400) for a network access node (300), the method (400) comprising: receiving (402) a downlink NAS transport message (510) from a network node (100), wherein the downlink NAS transport message (510) comprises a NAS message of a NAS procedure between the network node (100) and a client device (600) and an indication indicating a NAS delivery status request for the NAS message; determining (404) a NAS delivery status for the NAS message based on the NAS delivery status request; andtransmitting (406) a NAS delivery report message (520) to the network node (100), the NAS delivery report message (520) indicating the determined NAS delivery status for the NAS message.

16. A computer program with a program code for performing a method according to claim 14 or 15 when the computer program runs on a computer.

17. A network node (100) configured to: transmit a downlink NAS transport message (510) to a network access node (300), wherein the downlink NAS transport message (510) indicates an expected NAS message for a NAS procedure between the network node (100) and a client device (600); receive an uplink NAS transport message (530) from the network access node (300), wherein the uplink NAS transport message (530) comprises a NAS message from the client device (600) and indicates a NAS delivery status request for the NAS message from the client device (600); and transmit a NAS delivery report message (520) to the network access node (300) based on the NAS delivery status request, the NAS delivery report message (520) indicating a NAS delivery status for the NAS message from the client device (600).

18. The network node (100) according to claim 17, configured to: apply a NAS configuration on receiving the NAS message from the client device (600) when the NAS delivery status for the NAS message from the client device (600) is positive.

19. The network node (100) according to claim 17 or 18, configured to: receive an uplink NAS transport message (530) from the network access node (300) an additional time when NAS delivery status for the NAS message from the client device (600) is negative.

20. The network node (100) according to any one of claims 17 to 19, wherein the expected NAS message and / or the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

21. The network node (100) according to any one of claims 17 to 20, wherein the network node (100) is part of a core network.

22. The network node (100) according to claim 21 , wherein the network node (100) is an AMF.

23. A network access node (300) configured to: receive a downlink NAS transport message (510) from a network node (100), wherein the downlink NAS transport message (510) indicates an expected NAS message for a NAS procedure between the network node (100) and a client device (600); transmit an uplink NAS transport message (530) to the network node (100) based on the expected NAS message, wherein the uplink NAS transport message (530) comprises a NAS message from the client device (600) and indicates a NAS delivery status request for the NAS message from the client device (600); and receive a NAS delivery report message (520) from the network node (300), the NAS delivery report message (520) indicating a NAS delivery status for the NAS message from the client device (600).

24. The network access node (300) according to claim 23, wherein the NAS delivery status is positive.

25. The network access node (300) according to claim 23 or 24, configured to: retransmit the uplink NAS transport message (530) to the network node (100) when the NAS delivery status is negative.

26. The network access node (300) according to any one of claims 23 to 25, wherein the expected NAS message and / or the NAS delivery status request and / or the NAS delivery status is indicated by a flag.

27. The network access node (300) according to any one of claims 23 to 26, wherein the network access node (300) is part of a radio access network.

28. The network access node (300) according to claim 27, wherein the network access node (300) is a gNB.

29. A method (200') for a network node (100), the method (200') comprising: transmitting (202') a downlink NAS transport message (510) to a network access node (300), wherein the downlink NAS transport message (510) indicates an expected NAS message for a NAS procedure between the network node (100) and a client device (600); receiving (204') an uplink NAS transport message (530) from the network access node (300), wherein the uplink NAS transport message (530) comprises a NAS message from the client device (600) and indicates a NAS delivery status request for the NAS message from the client device (600); andtransmitting (206') a NAS delivery report message (520) to the network access node (300) based on the NAS delivery status request, the NAS delivery report message (520) indicating a NAS delivery status for the NAS message from the client device (600).

30. A method (400') for a network access node (300), the method (400') comprising: receiving (402') a downlink NAS transport message (510) from a network node (100), wherein the downlink NAS transport message (510) indicates an expected NAS message for a NAS procedure between the network node (100) and a client device (600); transmitting (404') an uplink NAS transport message (530) to the network node (100) based on the expected NAS message, wherein the uplink NAS transport message (530) comprises a NAS message from the client device (600) and indicates a NAS delivery status request for the NAS message from the client device (600); and receiving (406') a NAS delivery report message (520) from the network node (300), the NAS delivery report message (520) indicating a NAS delivery status for the NAS message from the client device (600).

31. A computer program with a program code for performing a method according to claim 29 or 30 when the computer program runs on a computer.

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