Connection recovery procedure

Abstract

Example embodiments of the present disclosure are directed to connection recovery procedure. In a method, a first apparatus receives, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery. A configuration of the set of configurations is indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid. The first apparatus performs the connection recovery based on the identifier and the set of configurations.

Description

CONNECTION RECOVERY PROCEDUREFIELD

[0001] Various example embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to methods, devices, apparatuses and computer readable storage medium for connection recovery procedure.BACKGROUND

[0002] A communication network may serve as a facility that enables communication between two or more communication devices or provides communication devices access to a data network. A mobile or wireless communication network is one example of a communication network. A communication device may be provided with a service by an application server.

[0003] The communication network may operate in accordance with standards such as those provided by Third Generation Partnership Project (3GPP) or European Telecommunications Standards Institute (ETSI). Examples of standards provided by 3GPP are the so-called 3GPP standards for cellular technology generations, such as 3GPP standards for 4G technology, 5G technology, 6G technology etc.SUMMARY

[0004] In a first aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and, perform the connection recovery based on the identifier and the set of configurations.

[0005] In a second aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to: transmit, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatusassociated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid.

[0006] In a third aspect of the present disclosure, there is provided a method. The method comprises: receiving, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and performing the connection recovery based on the identifier and the set of configurations.

[0007] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: transmitting, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid.

[0008] In a fifth aspect of the present disclosure, there is provided a first apparatus. The first apparatus comprises means for receiving, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and, means for performing the connection recovery based on the identifier and the set of configurations.

[0009] In a sixth aspect of the present disclosure, there is provided a second apparatus. The second apparatus comprises means for transmitting, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid.

[0010] In a seventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the third aspect.

[0011] In an eighth aspect of the present disclosure, there is provided a computer readablemedium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

[0012] In some or all example embodiments of the first to eighth aspects,, the set of configurations may further comprise a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

[0013] In some example embodiments, the first apparatus may, in response to receiving, from the second apparatus, an indication for at least one of: the connection recovery, or a connection release, perform the connection recovery based on the identifier and a target configuration of the set of configurations.

[0014] In some example embodiments, the indication may indicate at least one of: a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level; and the first apparatus may perform the connection recovery based on the identifier and the target configuration.

[0015] In some example embodiments, the first apparatus may, in response to receiving the indication, start at least one of: at least one timer for a time period for the validation of the context information, or at least one further timer for a further time period associated with the reconnection request.

[0016] In some example embodiments, the first apparatus may determine a procedure for the connection recovery based on at least one of: the at least one timer, the at least one further timer, the list of cells, or a further list of cells for a protection of a connection request; and perform the connection recovery based on the procedure.

[0017] In some example embodiments, the at least one timer may comprise a first timer and a second timer, and the connection recovery may be initiated after expiry of the first timer and before expiry of the second timer.

[0018] In some example embodiments, first context information associated with a first level of a first configuration may be different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information may be different from a second time period for a validation of the second context information.

[0019] In some example embodiments, the connection recovery may comprise a radio resource control (RRC) connection recovery, and the identifier related to the first apparatus may comprise an RRC identifier related to the first apparatus for RRC configuration.

[0020] In some example embodiments, the first apparatus may transmit, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations.

[0021] In some example embodiments, the first apparatus may receive, from the second apparatus, at least one updated configuration; and perform the connection recovery based on the identifier and the at least one updated configuration.

[0022] In some example embodiments, at least one updated configuration may comprise at least one offset of the time period for the validation of context information.

[0023] In some example embodiments, the second apparatus may transmit, to the first apparatus, an indication for at least one of: the connection recovery, or a connection release.

[0024] In some example embodiments, the second apparatus may receive, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus configuration, or a support of the RRC connection recovery based on the set of configurations; and transmit, to the first apparatus, context information of the first apparatus.

[0025] In some example embodiments, the second apparatus may transmit, to the first apparatus, at least one updated configuration comprising at least one offset of the time period for the validation of context information.

[0026] In some example embodiments, the second apparatus may comprise a central unit and a distributed unit, and the at least one updated configuration may be transmitted from the central unit to the first apparatus via the distributed unit.

[0027] In some example embodiments, the second apparatus may receive, from the first apparatus, an acknowledgement message to an indication for a connection release; and transmit, to a third apparatus, a release complete message, the release complete message comprising a third timer to indicate a time period during which the context information is stored in the second apparatus.

[0028] In some example embodiments, the first apparatus may comprise a terminal device and the second apparatus may comprise a network device.

[0029] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0031] FIG. 1A illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0032] FIG. 1 B illustrates a schematic diagram of connectivity options of a terminal device;

[0033] FIG. 2 illustrates a signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0034] FIG. 3 illustrates a signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0035] FIG. 4 illustrates an example signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0036] FIG. 5 illustrates another example signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0037] FIG. 6 illustrates another example signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0038] FIG. 7 illustrates another example signaling flow of a connection recovery procedure in accordance with some embodiments of the present disclosure;

[0039] FIG. 8 illustrates a flowchart of a method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0040] FIG. 9 illustrates a flowchart of a method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0041] FIG. 10 illustrates a flowchart of another method implemented at a first apparatus in accordance with some example embodiments of the present disclosure;

[0042] FIG. 11 illustrates a flowchart of another method implemented at a second apparatus in accordance with some example embodiments of the present disclosure;

[0043] FIG. 12 illustrates a flowchart of a method implemented at a third apparatus in accordance with some example embodiments of the present disclosure;

[0044] FIG. 13 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0045] FIG. 14 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0046] Throughout the drawings, the same or similar reference numerals represent the same or similar element.DETAILED DESCRIPTION

[0047] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0048] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0049] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0050] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0051] 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.

[0052] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included.

[0053] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0054] 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.

[0055] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0056] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE- Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-loT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1 G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communicationtechnologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0057] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0058] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0059] As used herein, the term “resource,” “transmission resource,” “resource block,” “physicalresource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0060] A core network function as described herein may be implemented as a core network entity that includes a combination of hardware processing circuit and software and / or firmware comprising machine-readable instructions, or software comprising machine-readable instructions that are executable by at least one processor of hardware processing circuit of an apparatus. A hardware processing circuit includes at least one processor and at least one memory storing machine- readable instructions that are executable by the at least one processor of the hardware processing circuit. A processor includes any or some combination of an accelerator, a microprocessor, a core of a multi-core microprocessor, a microcontroller, a programmable integrated circuit, a programmable gate array, a digital signal processor, a central processing unit, a graphic processing unit, a tensor processing unit. Memory includes any or some combination of volatile or non-volatile memory (e.g., a flash memory, cache, a random-access memory (RAM), and / or a read-only memory (ROM)). The memory stores the machine-readable instructions of the software and / or firmware for execution by the at least one processor of the hardware processing circuit. The machine-readable instructions are executable by the at least one processor of the hardware processing circuit cause the hardware processing circuit to perform the actions or operations of the methods described herein. For example, the session management function described herein may be implemented as a session management entity and the session management policy control function described herein may be implemented as a session management policy control entity, respectively.

[0061] FIG. 1A illustrates an example communication environment 100A in which example embodiments of the present disclosure can be implemented. The communication environment 100A involves a plurality of communication devices, including a first apparatus 110 and a second apparatus 120 communicating with each other. Additionally, the communication environment 100A may involve a third apparatus 130. The second apparatus 120 may communicate bidirectionally with the third apparatus 130.

[0062] In some example embodiments, if the first apparatus 110 is a terminal device and thesecond apparatus 120 is a network device in a RAN, a link from the first apparatus 110 to the second apparatus 120 is referred to as an uplink (UL), while a link from the second apparatus 120 to the first apparatus 110 is referred to as a downlink (DL). In UL, the first apparatus 110 is a transmitting (TX) device (or a transmitter) and the second apparatus 120 is a receiving (RX) device (or a receiver). In DL, the second apparatus 120 is a TX device (or a transmitter) and the first apparatus 110 is a RX device (or a receiver).

[0063] Moreover, the third apparatus 130 may be implemented as a core network (CN) device. In some example implementations, the third apparatus 130 may implement a mobility management (MM) network function (NF). Additionally, or alternatively, the third apparatus 130 or a further CN device in the communication environment 100A may implement a session management (SM) NF or any other suitable CN function.

[0064] The communication environment 100 may support a monolithic random access network (RAN) deployment and / or a disaggregated RAN deployment. The monolithic RAN deployment refers to a RAN deployed as a single, integrated unit. For example, the second apparatus 120 may be deployed as a single integrated unit. The disaggregated RAN deployment is an approach different from the monolithic RAN by separating the RAN into a plurality of functional components. This architecture may decouple hardware from software, allowing the RAN baseband software to be deployed as virtualized network functions on commercial-off-the-shelf (COTS) hardware. In a disaggregated RAN, the baseband unit's layer 1 , layer 2, and layer 3 functionalities may be split across distributed units (DU) that support layer 1 and layer 2, and centralized units (CU) that support layer 3. The second apparatus 120 may include at least one DU and at least one CU. This separation enables a more flexible and modular deployment of baseband software and hardware, which can be upgraded independently of each other.

[0065] It is to be understood that the number of devices and their connections shown in FIG. 1 A are only for the purpose of illustration without suggesting any limitation. The communication environment 100A may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the communication environment 100A. It is noted that although illustrated as a network device, the second apparatus 120 may be another device than a network device. Although illustrated as a terminal device, the first apparatus 110 may be another device than a terminal device.

[0066] In the following, for the purpose of illustration, some example embodiments are described with the first apparatus 110 operating as a UE and the second apparatus 120 operating as a base station. However, in some example embodiments, operations described in connection with aterminal device may be implemented at a network device or other device, and operations described in connection with a network device may be implemented at a terminal device or other device.

[0067] Communications in the communication environment 100A may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s- OFDM) and / or any other technologies currently known or to be developed in the future.

[0068] In some implementations, if the UE may be contacted any time, the RRC connection is on. Additionally, if the UE is not responding, a radio link failure and recovery procedure may be triggered. Reference is made to FIG. 1 B, which illustrates a schematic diagram 100B of connectivity options of a terminal device. As illustrated, if the UE is in the RRC_CONNECTED state, there are moments when the network device may lose the connection to the UE (denoted as “Break”). In these cases, the network device may wait for the UE to reconnect. For example, after a configuration change, UE and network need resynchronization (denoted as “Resync”).

[0069] In the communication between the UE and the network device, when the UE has the RRC connection on (that is, the UE is in the RRC_CONNECTED state) and all the data has been sent, a first power saving option is to start a discontinuous reception (DRX). In these cases, once the inactivity of the DRX takes longer, the UE may be moved to an RRCJNACTIVE state.

[0070] However, the network device may not know how fast the UE will need data connection again. It’s possible that UE would actually immediately need data connection again. An RRC procedure to move the UE to the RRCJNACTIVE state and then back to the RRC_CONNECTED state is rather heavy and slow compared to a scheduling request. It is to be studied to enhance definition of the UE states and how the network may start inactivation, but UE may still resume on lower layer.

[0071] For example, the gNB or the CU may fall in out of service due to, e.g., abnormal software behavior or platform / hardware problem. If the gNB or the CU recovers from the failure, the gNB or the CU may not keep storing all the contents in its cache before the failure occurred. If a UE context of the UE is lost, a connection to the UE may need to be established from scratch, which may take longer time. Furthermore, the UE may not be able to detect the failure of the gNB or the CU (alsoreferred to as “gNB / CU failure”) timely.

[0072] According to the current standard, a possible solution to detect the gNB / CU failure is to detect no response from the gNB or the CU / DU. For example, maximum UL retransmissions may be reached in the radio link control (RLC) layer or the random access problem may be detected. Therefore, tangible service interruption may be observed in case of the gNB / CU failure, according to the existing standard solutions.

[0073] Additionally, if the UE establishes a new non-access stratum (NAS)Zaccess stratum (AS) connection to the network device from the RRCJDLE state, the UE context may be produced from scratch based on AS / NAS capability of the UE. Protocol data unit (PDU) session(s), security activation, etc. may be established from scratch as well. Larger latency may be observed if the NAS / AS connection is established from the UE in the RRCJDLE state since all AS / NAS configurations may need to be built.

[0074] In accordance with some example embodiments of the present disclosure, there is provided several solutions for connection recovery. In a solution, an identifier of the UE and a set of configurations for connection recovery are configured for UE. The set of configurations is used to indicate a validation of context information associated with the identifier. In this way, the UE and / or the network device may stop data scheduling and release the connection timely using the set of configurations. Thus, the efficiency of the connection recovery procedure may be improved.

[0075] In another solution, a timer for the context information of the UE is proposed. The timer is used to determine whether the context information is valid upon a completion of the random access procedure. The UE releases the context information and initiates a connection establishment procedure, if the context information is invalid, i.e., the timer is expired. Additionally, the UE starts a reconnection procedure by transmitting a reconnection request to the network device if the context information is still valid, i.e., the timer is running. In this manner, the UE may perform the connection recovery in a flexible way. Thus, the efficiency of the connection recovery procedure is improved.

[0076] Several solutions of the present disclosure have been briefly described. Principle and implementations of the present disclosure will be described in detail below. Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0077] It is noted the order acts shown in FIG. 2-FIG. 12 are only an example but not limitation. Acts may be performed in any suitable manner. Example embodiments described with reference to FIG. 2 to FIG. 12 may be implemented separately or combined in any manner. For example, one or more example embodiments shown in a single drawing may be combined with one or more example embodiments shown in one or more other drawings.

[0078] In the following discussion, the first apparatus 110 may be implemented as a terminal apparatus, and the second apparatus 120 may be implemented as a next generation gNB serving the first apparatus 110, a DU connecting with the first apparatus 110, and / or a CU connecting with the DU.

[0079] As briefly described, in a solution of the present disclosure, the UE perform the connection recovery based on the identifier and the set of configurations. FIG. 2 illustrates a signaling flow 200 of a connection recovery procedure in accordance with some embodiments of the present disclosure. The signaling flow 200 involves the first apparatus 110 and the second apparatus 120 in FIG. 1 A. For the purposes of discussion, the signaling flow 200 will be discussed with reference to FIG. 1A.

[0080] In operation, the second apparatus 120 transmits (2010) to the first apparatus 110, an identifier (ID) related to the first apparatus 110 and a set of configurations for connection recovery (also referred to as connection recovery configurations or recovery configurations or recovery configuration options). Correspondingly, the first apparatus 110 receives (2020) from the second apparatus 120, the identifier and the set of connection recovery configurations. A connection recovery configuration indicates, for example, but not limited to, a level of the configuration, a time period for a validation of context information of the first apparatus 110 associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid. The set of connection recovery configurations may include one or more recovery connection configurations. For example, each connection recovery configuration may indicate a level of recovery, a time period for context information validation, at least one apparatus (such as network device) for the context information validation, and / or a list of cells for the context information validation. In this way, the second apparatus 120 may configure the connection recovery rules or parameters for the first apparatus 110.

[0081] Optionally, the first apparatus 110 may select a target connection recovery configuration from the set of connection recovery configurations. As an example, the first apparatus 110 may select a connection recovery configuration with a best recovery level that is still valid. In this way, the first apparatus 110 may be configured with a plurality of recovery options. The first apparatus 110 may select a proper recovery configuration for the connection recovery. As used herein, the set of connection recovery configurations may also be referred to “a set of candidate connection recovery configurations” or “a set of connection recovery configuration options”. The target connection recovery configuration may be referred to as a target or selected recovery connection configuration option. The connection recovery may be performed by the first apparatus 110 based on the target connection recovery configuration.

[0082] Optionally, a connection between the first apparatus 110 and the second apparatus 120 may be an RRC connection. That is, the connection recovery may be an RRC connection recovery. In such cases, the identifier related to the first apparatus 110 may include an RRC identifier related to the first apparatus 110 for RRC configuration. That is, the RRC identifier of the first apparatus 110 is an identifier to be used for RRC configuration for the first apparatus 110. If the RRC connection between the first apparatus 110 and the second apparatus 120 is established, the RRC identifier of the first apparatus 110 may be assigned by the second apparatus 120. The first apparatus 110 may thus be identified during the RRC connection by the RRC identifier. Information related to the first apparatus 110 such as context information may be stored associated with the RRC identifier of the first apparatus 110. In this way, the RRC connection recovery may be achieved based on the connection recovery configuration with the RRC identifier. The RRC identifier may be included in a reconnection request for the RRC connection recovery, With the RRC identifier, the second apparatus 120 may identify the context information of the first apparatus 110, It is to be understood that although some example embodiments here are described with the identifier being the RRC identifier, in some other embodiments, the identifier associated with the first apparatus 110 may be any other suitable UE identifier. Scope of the present disclosure is not limited here.

[0083] Specifically, the time period for the context information validation of the first apparatus 110 may indicate at least one timer of the validation of the context information. The at least one timer may include a timer indicating an ending time for the time period of context information validation. The at least one timer may also include a timer indicating a beginning time point of the validation. Additionally, the list of cells may be indicated by an area in which the context information may be considered valid. That is, the context information may be considered as valid for cells or gNBs within the area. Optionally, the list of cells may be indicated by an area code broadcasted in system information. Alternatively, the list of cells may be indicated by a list of cell identifiers.

[0084] Moreover, the at least one apparatus may include at least one network device that stores the context information. The level of the configuration may be used to indicate a set of parameters among sets of parameters for the connection recovery, for example, the length of the time period, the number of the at least one apparatus, or the number of cells in the list. In this way, the network can configure multiple recovery options (validity period, list of g NBs / cells that are expected to have access to the context) for the first apparatus 110 during RRC connection state.

[0085] Optionally, first context information associated with a first level of a first configuration may be different from a second context of the first apparatus 110 associated with a second level of a second configuration. That is, for different recovery level, different context information may be valid. Additionally, a first time period for a validation of the first context information may be different from asecond time period for a validation of the second context information. That is, for different recovery level, the timer for context information validation may be different. In these cases, the level of the configuration may indicate one of the first level or the second level instead of the corresponding parameters. By way of example, in case of radio link failure (RLF), the network may keep complete previous configuration for 5 seconds. That is, for a first level of recovery corresponding to the RLF, for a time duration being 5 seconds, the valid context information may be complete previous configuration. After 5 seconds, the recovery configuration in the RRC setup is valid. Further example embodiments may include but not be limited to in a cell level, context (that is, valid context information) may be kept for 10 second (that is, another recovery level with another time duration), higher UP resources like in RRC inactive may be kept for one minute and after that minimum UE context with RRC ID may be kept for up to 10 minutes, or the like. The first apparatus 110 may be informed about how long different recovery options are valid, also the first apparatus 110 may learn in which cell / gNB where the recovery options are valid. In this way, various recovery options with different levels may be configured for the first apparatus. These options may correspond to different valid context information and / or different validation durations. With these recovery configurations or options, UE may flexibly select a proper configuration or option for the connection recovery. It is to be understood that these time durations and contents of context are only for the purpose of illustration, without suggesting any limitation. Embodiments of the present disclosure are not limited here.

[0086] Moreover, optionally, the set of configurations may further include a configuration for a reconnection request. In these cases, the configuration may include, for example, but not limited to, a next hop chaining count, a configuration of a signaling radio bearer 1 (SRB1 ) delivering the reconnection request, a list of cells for the reconnection request, or a second time period associated with the reconnection request. The second time period associated with the reconnection request may be a time duration for a protection of the reconnection request. With this time duration, the reconnection request may be encrypted. In this way, further parameters such as next hop chaining count, SRB1 for the reconnection request, cells or protection duration for the reconnection request may be configured for the first apparatus 110.

[0087] By transmitting the recovery configuration(s) to the first apparatus 110, such as UE, both UE and network know the recovery configuration(s). It thus allows to use secured RRC reconnection request message for the connection recovery.

[0088] Furthermore, the first apparatus 110 performs (2030) the connection recovery based on the identifier and the set of configurations.

[0089] Optionally, the second apparatus 120 may transmit an indication to the first apparatus 110.The indication may indicate the connection recovery and / or a connection release. Moreover, in response to receiving the indication, the first apparatus 110 may perform the connection recovery based on the identifier and a target configuration of the set of configurations. Alternatively, the first apparatus 110 may transmit an acknowledgement (ACK) of the indication to the second apparatus 120, In response to transmitting the acknowledgement, the first apparatus 110 may perform the connection recovery. As used herein, performing an operation in response to receiving a message may refer to performing the operation in response to receiving the message or in response to transmitting an ACK of the message. In this way, the connection recovery may be triggered by the connection recovery indication and / or the connection release indication.

[0090] Optionally, the second apparatus 120 may transmit, to the third apparatus 130, a release complete message. Additionally, the release complete message may include a third timer to indicate a time period during which the context information is stored in the second apparatus 120.Specifically, the third apparatus 130 may be a device implementing the core network function. In this way, the third apparatus 130 such as a core network function may be informed about the release completion and also be informed about the validation time duration of the context information of the first apparatus 110.

[0091] Moreover, optionally, the indication may indicate at least one of a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level. In these cases, the first apparatus 110 may perform (2030) the connection recovery based on the identifier and the target configuration. In this way, the second apparatus 120 may choose the target recovery configuration for the first apparatus 110.

[0092] Furthermore, optionally, in response to receiving the indication or responding an ACK of the indication, the first apparatus 110 may start at least one timer and / or at least one further timer. Specifically, the at least one timer may be for a time period for the validation of the context information. The at least one timer may include a first timer and a second timer with a time duration longer than the first timer, if the first timer expiries, the connection recovery may be performed. If the second timer expiries, the context information is invalid, the first apparatus 110 may not perform the connection recovery based on the target configuration. That is, the connection recovery may be initiated after expiry of the first timer and before expiry of the second timer. For example, the first timer may be related to a minimum length of time of the validation of the context information. The second timer may be related to a maximum length of time of the validation of the context information. In some embodiments, the first timer and the second timer may be started simultaneously. Alternatively, the second timer may be started in response to expiry of the first timer. As used herein, the first and / or second timer may be referred to as “connection recoverytimer” or “context information validation timer”. In this way, the first apparatus 110 may be configured about when to perform the connection recovery. For example, the first apparatus 110 may transmit an RRC reconnection request with the RRC identifier to the second apparatus 120 during the time duration specified by the first timer and the second timer.

[0093] The at least one further timer may be for a further time period associated with the reconnection request. For example, expiry of the at least one further timer may indicate whether the reconnection request is encrypted. As used herein, the timer for the encryption of the reconnection request may be referred to as a “timer for a protection of the reconnection request” or a “reconnection request protection timer”.

[0094] In some embodiments, the first apparatus 110 may determine a procedure for the connection recovery based on, for example, but not limited to, the at least one timer, the at least one further timer, the list of cells, or a further list of cells for a protection of a connection request. Moreover, the first apparatus 110 may perform the connection recovery based on the procedure. In this way, the first apparatus 110 may decide to leave and use one of the provided recovery option. Specifically, the first apparatus 110 may determine the procedure based on whether the context information is valid and / or whether the reconnection request is to be protected. As an example, the first apparatus 110 may select a cell from the list of cells for the connection recovery. As another example the first apparatus 110 may determine to perform a reconnection to a previous serving cell based on the at least one timer. Further embodiments regarding the determination of the procedure will be described with respect to FIG. 3.

[0095] In some embodiments, the first apparatus 110 may transmit, to the second apparatus 120, at least one capability of the first apparatus 110. Specifically, the capability may include, for example, but not limited to, a support of the RRC identifier related to the first apparatus 110 for the RRC configuration, or a support of the RRC connection recovery based on the set of configurations. That is, the capability may indicate whether the first apparatus 110 may perform the connection recovery based on the connection recovery configuration. In some implementations, the second apparatus 120 may determine that the first apparatus 110 support the connection recovery procedure with the set of configurations based on the capability. In these cases, the second apparatus 120 may transmit the identifier and the set of configurations for connection recovery to the first apparatus 110 with the capability. That is, if a UE does not have such capability, the second apparatus 120 may not transmit the connection recovery configuration(s) to the UE. The signaling overhead can thus be reduced.

[0096] In addition, optionally, the second apparatus 120 may transmit, to the first apparatus 110, at least one updated configuration. Moreover, the first apparatus 110 may perform the connectionrecovery based on the identifier and the at least one updated configuration. Specifically, the at least one updated configuration may include at least one offset of the time period for the validation of context information. For example, the updated configuration may indicate a new time period of the validation of the context information. The new time period may be represented by the offset of the time period (that is, a difference between the previous timer and the updated timer). For another example, several timers may be predefined and indicated by respective indexes. The updated configuration may indicate an index of the updated timer. By transmitting the offset or the index instead of the timer length value, the signaling overhead may be reduced.

[0097] In some embodiments, the second apparatus 120 includes a central unit and a distributed unit. Moreover, the at least one updated configuration may be transmitted from the central unit to the first apparatus 110 via the distributed unit.

[0098] Several embodiments regarding the connection recovery configuration have been described. These embodiments configure the UE about how to perform the connection recovery. In this way, the second apparatus 120 may configure one or more recovery options for the first apparatus 110 before the connection recovery procedure. The first apparatus 110 may determine to use at least one of the options based on the validation of the context information. Thus, the efficiency of the connection recovery procedure is improved.

[0099] As briefly mentioned, in another solution, the UE may select a proper connection recovery procedure based on a timer for the context information. Such solution will be described with respect to FIG. 3, which illustrates a signaling flow 300 of a connection recovery procedure in accordance with some embodiments of the present disclosure. The signaling flow 300 involves the first apparatus 110, the second apparatus 120 and optional the third apparatus 130 in FIG. 1A. In some embodiments, the third apparatus 130 may be implemented as a network device implementing the MM NF.

[0100] In operation, the second apparatus 120 transmits (3010), to the first apparatus 110, an identifier related to the first apparatus 110. Correspondingly, the first apparatus 110 may receive (3020) the identifier from the second apparatus 120. Specifically, the identifier is associated with context information of the first apparatus 110. In some embodiments, the connection recovery may include an RRC connection recovery. By way of example, the identifier may be an RRC identifier. The context information of the first apparatus 110 stored at the second apparatus 120 may be indicated by the RRC identifier.

[0101] Furthermore, the second apparatus 120 transmits (3030), to the first apparatus 110, an indication for a connection recovery and / or a connection release. Correspondingly, the first apparatus 110 receives (3040) the indication from the second apparatus 120.

[0102] Furthermore, the first apparatus 110 determines (3050) whether a first timer for context information of the first apparatus 110 is expired upon a completion of a random access procedure. The context information is associated with the identifier related to the first apparatus 110. If the first timer is running, the first apparatus 110 transmits (3060), to the second apparatus 120, a reconnection request including the identifier. Correspondingly, the second apparatus 120 receives (3070) the reconnection request from the first apparatus 110. Alternatively, or in addition, if the first timer is expired, the first apparatus 110 releases (3080) the context information of the first apparatus 110 and initiates (3080) a connection establishment procedure to the second apparatus 120.

[0103] In some example embodiments, the first timer may be predefined, or determined by the first apparatus 110, or configured by the second apparatus 120. For example, several timers may be predefined with respective indexes. An index for a target timer to be used may be determined by the first apparatus 110 based on status of the first apparatus 110, or indicated by the second apparatus 120. In an example, the second apparatus 120 may transmit, to the first apparatus 110, a configuration for connection recovery. The configuration may include the first timer or indicate an index of the first timer. In some embodiments, the first apparatus 110 may determine whether a further timer (shorter than the first timer) for the context information is expired upon the completion of the random access procedure. After the further timer expires, the reconnection request may be transmitted.

[0104] As mentioned, the first timer may be configured by the second apparatus 120. In some embodiments, the second apparatus 120 may transmit, to the first apparatus 110, a configuration for connection recovery. The configuration may be indicative of at least one of: a level of the configuration, a time period for the first timer, at least one apparatus for which the context information is valid, a list of cells for which the context information is valid, a next hop chaining count; a configuration of a SRB1 delivering the reconnection request; a further list of cells for the reconnection request; or a second time period for a second timer associated with the reconnection request. Details of these parameters have been described with respect to FIG. 2, and will not be repeated here. It is to be understood that these example parameters or values of the recovery configuration are only for the purpose of illustration, without suggesting any limitation.

[0105] Moreover, in response to receiving, from the second apparatus 120, an indication for the connection recovery and / or a connection release, the first apparatus 110 may perform the connection recovery based on the identifier and the configuration. In some embodiments, when receiving the indication, the first apparatus 110 may start at least one of the first timer or a second timer associated with the reconnection request. The second timer may be a reconnection request protection timer.

[0106] Moreover, if the first timer is running upon the completion of the random access procedure, the first apparatus 110 may determine whether at least one condition is met. Specifically, the at least one condition may include the second timer associated with the reconnection request being running upon the completion of the random access procedure, or a target cell associated with the reconnection request being included in a list of cells associated with the reconnection request. It is to be understood that these conditions are only for the purpose of illustration, without suggesting any limitation. Any suitable condition may be applied. Embodiments of the present disclosure is not limited here.

[0107] Furthermore, if the at least one condition is met, the reconnection request may include an encrypted reconnection request. The encrypted reconnection request may include a token to authorize the first apparatus 110. In these cases, the first apparatus 110 may determine that the reconnection request is valid based on the second timer and / or the target cell.

[0108] Alternatively, or in addition, if the at least one condition is not met, the reconnection request may be transmitted to the second apparatus 120 without being encrypted. In these cases, the first apparatus 110 may determine that the reconnection request protection is invalid based on the second timer and / or the target cell. Thus, the first apparatus 110 may transmit the reconnection request to the second apparatus 120. Moreover, if the reconnection request is not encrypted, the second apparatus 120 may transmit, to the third apparatus 130, information indicating that context information of the first apparatus 110 is not encrypted. In this way, the first apparatus 110 may determine whether to encrypt the reconnection request based on the at least one condition such as the second timer.

[0109] In some implementations, the second apparatus 120 may assign a further identifier related to the first apparatus 110. The further identifier may be associated with the context information of the first apparatus 110. The further identifier may be a further RRC identifier. In these cases, the second apparatus 120 may transmit the further identifier to the first apparatus 110 and / or the third apparatus 130. Correspondingly, the first apparatus 110 may receive the further identifier from the second apparatus 120. The further identifier may be associated with the context information of the first apparatus 110.

[0110] In some embodiments, if the first timer is running upon the completion of the random access procedure, the first apparatus 110 may transmit the reconnection request and a service request to the second apparatus 120. The service request may include a multiple NAS container. Specifically, the multiple NAS container may include a mobility management message and a session management message. Furthermore, when receiving the service request, the second apparatus 120 may transmit, to the third apparatus 130, the service request.

[0111] As illustrated in FIG. 3 the second apparatus 120 transmits (3090), to the third apparatus 130, the service request for mobility management. Correspondingly, the third apparatus 130 receives (3100) the service request from the second apparatus 120.

[0112] Furthermore, the third apparatus 130 transmits (3110) a response of the service request to the second apparatus 120 if at least one condition is met. The second apparatus 120 receives (3120) the response from the third apparatus 130. The response excludes an access stratum security key. In other words, if the at least one condition is met, the access stratum security key does not need to be included in the service request response. Specifically, the at least one condition may include, for example, but not limited to, a timer for context information of a first apparatus 110 being running, or an indication of no need of security context. It is to be understood that these conditions are only for the purpose of illustration, without suggesting any limitation. Any suitable condition may be applied. Embodiments of the present disclosure is not limited here.

[0113] Alternatively, or in addition, if the at least one condition is not met, the third apparatus 130 transmits (3110) the service request response including an access stratum security key to the second apparatus 120. Moreover, the second apparatus 120 receives (3120) the response from the third apparatus 130. In this way, the third apparatus 130 may determine whether to transmit the access stratum security key based on the timer for context information and / or the no need of security context indication.

[0114] Moreover, the second apparatus 120 may transmit, to the first apparatus 110, a reconfiguration message encapsulating a multiple NAS container including a response to the service request. Correspondingly, the first apparatus 110 may receive the reconfiguration message from the second apparatus 120.

[0115] Additionally, the second apparatus 120 may transmit, to the third apparatus 130, a message including a timer indicating a validation duration of the context information of the first apparatus 110. Correspondingly, the third apparatus 130 may receive, from the second apparatus 120, a message including the timer for the validation of the context information, or the indication of no need of security context.

[0116] In some embodiments, the first apparatus 110 may transmit, to the second apparatus 120, at least one capability of the first apparatus 110. Specifically, the capability may include, for example, but not limited to, a support of the RRC identifier related to the first apparatus 110 for the RRC configuration, or a support of the RRC connection recovery based on the set of configurations. In some implementations, the second apparatus 120 may determine that the first apparatus 110 support the connection recovery procedure with the set of configurations based on the capability. In these cases, the second apparatus 120 may transmit the identifier and the set of configurations forconnection recovery to the first apparatus 110 with the capability.

[0117] In this way, the first apparatus 110 may determine to transmit the reconnection request or release the context information and initiate the connection establishment procedure based on the validation of the context information. Moreover, based on the recovery configurations, the procedure with less usage of resource may be performed. Additionally, in response to the context information being invalid, the first apparatus 110 may perform the connection establishment procedure. Instead of the fixed state for the first apparatus 110, the connection recovery procedure may take less resource. Thus, the efficiency of the connection recovery procedure is improved. Additionally, the first apparatus 110 may be configured with information for the reconnection request. The effectiveness of the connection recovery procedure is improved.

[0118] In some example embodiments, the second apparatus such as the network may stop data scheduling and assist the first apparatus 110 when and what recovery is may use to resume. The mechanism for stopping data scheduling may be needed in case network needs to temporarily interrupt service for the first apparatus 110.

[0119] Several embodiments regarding the connection recovery configuration have been described with respect to FIG. 2, and several embodiments regarding the connection recovery procedure have been described with respect to FIG. 3. It is to be understood that these embodiments with respect to FIG. 2 and FIG. 3 may be used separately, or in combination. Further embodiments for connection recovery will be described with respect to FIG. 3 to FIG. 7 in which some embodiments with respect to FIG. 2 and FIG. 3 are combined. In the following discussion, the steps indicated by dashed lines in the figures are optional.

[0120] In some implementations, for the UE is provided with the RRC identifier immediately after security activation, the network may indicate that it will keep the UE capabilities stored in a set of gNBs (indicated as list of gNBs or list of cells to the UE) even the UE remains in an idle state.

[0121] In some embodiments, the RRC identifier may be enhanced with the set of configurations (also referred to as “recovery configurations”) for the UE with additional information regarding validation period for the RRC ID (also referred to as “RRC UE ID”), set of gNBs or list of cells, or the level of the configuration. These may be provided in the start of the RRC connection together with the UE identification like RRC ID. Both the UE and the network device may be able to stop data scheduling and leave the RRC_CONNECTED state any time as the UE and the network device have a set of recovery configuration ready.

[0122] Specifically, for example, the gNB / CU failure may occur and may lead to losing the context information for the connection between the UE and the gNB. In some implementations. The network device may be a monolithic RAN device. FIG. 4 illustrates an example signaling flow 400 of aconnection recovery procedure in accordance with some embodiments of the present disclosure.

[0123] As shown, the signaling flow 400 involves a UE 410, a gNB 420, and a gNB 430. The UE 410 may be an implementation of the first apparatus 110 in FIG. 1A. The gNB 420 may be implementations of the second apparatus 120 in FIG. 1A. Moreover, the UE 410 may communicate with the gNB 420 via medium access control (MAC) layer (also referred to as “MAC 422”), a cell (also referred to as “cell 422” or a serving cell), and a RRC layer (also referred to as “RRC 426”) of the gNB 420. The gNB 420 may be referred to as a serving gNB or a source gNB. Additionally, the signaling flow 400 may involve a gNB 430. For example, the UE 410 may perform the connection recovery by establishing communication with the gNB 430. The gNB 430 may also be referred to as a candidate gNB or a target gNB.

[0124] As illustrated in FIG. 4, at 4010, the gNB 420 transmits, to the UE 410, an RRC reconfiguration message including an RRC identifier related to the UE 410 and a set of configurations for connection recovery. Specifically, the RRC reconfiguration may provide the UE 410 with options for connection recovery. Recovery configuration comprises at least one of the following: different level for the recovery, serving area for the context validity and the validity time. In some embodiments, if the radio link failure occurs, the network device (that is, the gNB 420) may keep compete previous configuration for 5 seconds, for example.

[0125] By way of example, after 5 seconds, the recovery configuration in the RRC setup may be valid. Moreover, in a cell level, the context information may be kept for 10 seconds. In higher UP resources in RRCJNACTIVE state, the context information may be kept for one minute and after that minimum UE context with the RRC ID up to 10 minutes. If both UE and Network know the recovery configuration, this allows to use secured RRC reconnection request message.

[0126] Moreover, at 4020, the failure or an overload situation occurs. In the embodiment of FIG. 2, at least a part of the context information of the UE 410, the control may be lost in a plane (such as control plane C-plane) of the gNB 420. In these cases, the identifier and the context information for connection recovery may be stored in the C-plane for the connection recovery procedure.

[0127] Furthermore, at 4030, in user plane (U-plane) of the gNB 420, the data scheduling between the UE 410 and the gNB 420 is continued.

[0128] Optionally, at 4040, the gNB 420 may decide to start the connection recovery by transmitting an indication to the UE 410. Correspondingly, at 4042, the UE 410 may transmit, to the gNB 420, an acknowledgement message to the indication. The indication may be indicative of initiating MAC reset and / or an available level of the connection recovery. Specifically, the indication may be transmitted from the gNB 420 to the UE 410 via MAC control element (CE).

[0129] In some implementations, at 4050, the gNB 420 may deactivate the UE 410.Correspondingly, at 4060, the UE 410 may move to the RRCJDLE state.

[0130] In some embodiment, at 4070, the gNB 410 may start a paging process for the UE 410. Moreover, at 4080, the UE 410 selects an approach for the connection recovery. For example, the UE 410 may perform the connection recovery based on the validity time or the serving area where the gNB 420 may be able to have access to the context information of the UE 410.

[0131] Moreover, the UE 410 may perform the RRC connection recovery by using the RRC ID. Additionally, the UE 410 may use available recovery connection if the connection is needed. As illustrated, at 4090, for option 1 (also referred to as “opt.1 ” in FIG. 4), the UE 410 may transmit a return request and / or a scheduling request to the gNB 420 via MAC 422. At 4100, for option 2 (also referred to as “opt.2”), the UE 410 may initiate the random access procedure to access the gNB 420 by transmitting a preamble of the UE 410 to the gNB 420 via the MAC 422.

[0132] Alternatively, or in addition, at 4110, for option 3 (also referred to as “opt.3”), the UE 410 may initiate the random access procedure to access the gNB 420 by transmitting a preamble of the UE 410 to the gNB 420 via the cell 424. At 4120, for option 4 (also referred to as “opt.4”), the UE 410 may initiate an RRC reconnection based on the RRC ID. Correspondingly, at 4122, the gNB 420 may transmit information about the RRC reconnection via the cell.

[0133] In some embodiment, at 4130, for option 5 (also referred to as “opt.5”), the UE 410 may initiate an RRC reconnection based on the RRC ID and transmit information for RRC reconnection including the RRC ID via the RRC 426. Correspondingly, at 4132, the gNB 420 may transmit information about the RRC reconnection via the RRC 426.

[0134] In this way, the UE 410 may select the approach for the connection recovery in a flexible way. Moreover, the UE 410 may know the length of time of the validation of the context information and in which cell or gNB 420 the connection recovery may be performed. Thus, the flexibility and the efficiency of the connection recovery procedure is improved.

[0135] FIG. 5 illustrates another example signaling flow 500 of a connection recovery procedure in accordance with some embodiments of the present disclosure. The signaling flow 500 illustrates embodiments regarding disaggregated RAN deployment where gNB functionalities are split into CU and DU.

[0136] As shown, the signaling flow 500 involves a UE 510, a gNB 520, a database 530. The UE 510 may be an implementation of the first apparatus 110 in FIG. 1A. The gNB 520 may be an implementation of the second apparatus 120 in FIG. 1A. Moreover, the gNB 520 may include a CU 526, a DU 522 controlling a cell, and a DU 524 controlling a further cell. In the following discussion, the cell of the DU 522 may be considered as a serving cell for the UE 510. The database 530 may be implemented as an entity storing data and communicating with the gNB 520. Specifically, thedatabase 530 may communicate with the CU 526 of the gNB 520.

[0137] As illustrated in FIG. 5, at 5002, the UE 510 may transmit, to the gNB 520, a capability report of the UE 510. For example, the capability report may include a support of an RRC ID or a support of the RRC connection recovery. Moreover, at 5004, the DU 522 may transmit the capability report to the CU 526.

[0138] At 5010, the gNB 520 may determine context information (also referred to as “UE context”) for the UE 510 based on the capability report and assign an RRC ID for the UE context. In addition, if the UE 510 supports the connection recovery based on the RRC ID and the set of configurations, the gNB 520 may determine the set of configurations for the UE 510.

[0139] Specifically, the recovery configurations may include, for example, but not limited to, a validity timer of the UE context or a configuration for a reconnection request. The reconnection request may include a message 3 in the random access procedure including an RRC reconnection request. The configuration for the reconnection request may be used as configuration for the protection of the reconnection request. For example, the configuration for the reconnection request may include at least one of: a next hop chaining count, a configuration of a SRB1 delivering the reconnection request, a list of cells for the reconnection request, or a validity timer of the reconnection request. The list of cells may include one or more physical cell identifiers (PCI) of the cells.

[0140] Moreover, 5022, the gNB 520 transmits the context information, RRC ID and the recovery configurations to the UE 510. Specifically, at 5020 and 5022, the CU 526 may transmit the context information, RRC ID and the recovery configurations to the UE 510 via the DU 522. Subsequently, at 5030 and 5032, the UE 510 may transmit a confirmation message of the context information and RRC ID to the gNB 520, e.g., to the CU 526 via the DU 522.

[0141] In some implementations, at 5040, the gNB 520 may transmit the context information and the RRC ID of the UE 510 to the database 530. At 5050, the database 530 may store the received information.

[0142] In some embodiments, at 5060, a failure may occur at the gNB 520, for example, at the CU 526. In these cases, at 5070, the CU 526 may recover from the failure. Additionally, the context information of the UE 510 in the CU 526 may be lost.

[0143] Moreover, at 5080, the CU 526 may indicate the DU 522 that a control equipment of the gNB 520 has recovered from the failure. At 5090, the DU 522 may stop scheduling U-plane data to all UEs connected to the DU 522, for example, the UE 510.

[0144] Furthermore, at 5100, the DU 522 may ask all the UEs connected to the DU 522 for their RRC ID. In addition, the DU 522 may ask the UEs connected to the DU 522 and supporting theconnection recovery based on the recovery configurations to initiate a reconnection procedure to the network. For example, the DU 522 may transmit, to the UE 510, a reconnection request indicating the UE 510 to report the RRC ID of the UE 510 and to initiate the reconnection procedure.

[0145] In some implementations, at 5110, upon receiving the reconnection request, the UE 510 starts the validity timer of the UE context, if the UE 510 has been configured with the validity timer of the UE context. Additionally, at 5120, upon receiving the reconnection request, the UE 510 may start the validity timer of the reconnection request, if the UE 510 has been configured with the validity timer of the reconnection request. In addition, at 5130, the UE 510 may perform a cell selection procedure and select the same cell to which the UE 510 was connected before the failure in the gNB 520. Alternatively or in addition, the UE 510 may select a further cell served by the DU 522 or a further DU, for example, the DU 524. In the following discussion, the DU 524 may be considered as the DU serving the cell selected by the UE 510. It is to be understood that other DU (e.g., the DU 522) may also be applied.

[0146] Furthermore, at 5140, the random access procedure may be performed between the UE 510 and the gNB 520. Specifically, the UE 510 may transmit a message 1 to the DU 524. Moreover, the DU 524 may transmit a message 2 associated with the message 1 to the UE 510.

[0147] In some implementations, upon completion of the random access procedure, the UE 510 may initiate the RRC reconnection procedure for the connection recovery. Specifically, when the UE 510 initiates the RRC reconnection procedure, at least one condition may be met. In some embodiments, the at least one condition may include the validity timer of the UE context is still running, the cell selected by the UE 510 is included in the list of cells for the reconnection request, or the validity timer of the reconnection request is still running.

[0148] At 5150, the UE 510 determines whether the at least one condition is met. Moreover, if the validity timer of the UE context is still running, the cell selected by the UE 510 is included in the list of cells for the reconnection request, and the validity timer of the reconnection request is still running, the UE 510 transmits an encrypted RRC reconnection request message to the DU 524 at 5160, as illustrated as “opt.1 ” in FIG .5. Additionally, the RRC reconnection request message may include the RRC ID of the UE 510 and a token (e.g., short message authentication code (MAC)-1 ) to authorize the UE 510.

[0149] Alternatively or in addition, at 5152, if the validity timer of the UE context is still running, but the cell selected by the UE 510 is not included in the list of cells for the reconnection request, and / or the validity timer of the reconnection request is expired, at 5162, the UE 510 transmits, to the DU 524, the plain RRC reconnection request message without encryption, as illustrated as “opt 2” in FIG .5. Additionally, the RRC reconnection request message may include the RRC ID of the UE 510.

[0150] In some embodiments, at 5154, if the validity timer of the UE context is expired, the UE 510 releases all the stored UE context and initiates a connection establishment procedure from scratch at 5164, as illustrated as “opt.3” in FIG .5.

[0151] Furthermore, if the UE 510 transmits the RRC reconnection request message (encrypted or not encrypted) to the DU 524, at 5170, the DU 524 may forward the message to the CU 526. For example, the DU 524 may initiate a UL message transmission. Moreover, upon receiving the RRC reconnection request, at 5180, the CU 526 may request the database 530 to retrieve the UE context corresponding to the RRC ID in the message. Specifically, the CU 526 may transmit a request for UE context retrieval to the database 530. At 5190, the database 530 may identify the requested UE context via the RRC ID and transmit the UE context to the CU 526.

[0152] At 5200 and 5202, the CU 526 may accept the RRC reconnection request from the UE 510 and confirm the completion of the RRC reconnection. Specifically, the CU 526 may initiate a DL message transmission and transmit a message for acknowledgement of the RRC reconnection request and confirmation of the completion of the RRC reconnection. The message may be transmitted to the UE 510 via the DU 524.

[0153] Optionally, at 5202, the CU 526 may assign a new RRC ID to the UE 510. Additionally, the CU 526 may determine updated UE context for the UE 510. The new RRC ID may be for the UE context or updated UE context. In these cases, the CU 526 may transmit the new RRC ID and / or the updated UE context to the UE 510 via the DU 524. Moreover, at 5210, the CU 526 may update the new RRC ID and / or the updated UE context to the database 530. Specifically, the CU 526 may transmit a relationship between the new RRC ID and the UE context or the updated UE context to the database 530.

[0154] In this way, the UE 510 may determine to release the connection and perform the connection recovery based on the condition associated with the recovery configurations in a flexible way Thus, the efficiency and reliability of the connection recovery procedure is improved.

[0155] In some embodiments, the UE state may be converted from the connected state to the idle state. In these cases, the connection recovery procedure may be initiated by the UE instead of the gNB.

[0156] In some implementations, an RRC connection resume request may be associated with mechanisms to enhance security of the connection recovery procedure. The network device may prepare candidates cells to identify the UE based on a cell-radio network temporary identifier (C- RNTI). Additionally, the recovery configuration may include the C-RNTI for the UE. In these cases, the UE may use security context in a new cell RRC reconnection request and the network may be expected to have access to UE’s AS security context. The RRC connection resume request may bewith security on. Network may prepare cell candidates to identify the UE 510, for example, based on C-RNTI and deliver in the recovery configuration those C-RNTIs for the UE 520. In this case UE may use security in a new cell RRC reconnection request and the network is expected to have access to UE 120’s AS security context.

[0157] FIG. 6 illustrates another example signaling flow 600 of a connection recovery procedure in accordance with some embodiments of the present disclosure. The signaling flow 600 illustrates embodiments regarding the UE state transition from the idle state.

[0158] As shown, the signaling flow 600 involves a UE 610, a gNB 620, a MM NF 630, and a SM NF 640. The UE 610 may be an implementation of the first apparatus 110 in FIG. 1A. The gNB 620 may be an implementation of the second apparatus 120 in FIG. 1A. The MM NF 630 may be an implementation of the third apparatus 130 in FIG. 1A. The SM NF 640 may be a CN device implementing the SM NF.

[0159] As shown in FIG. 6, at 6002, the UE 610 transmits, to the gNB 620, a capability report of the UE 610. For example, the capability report may include a support of an RRC ID or a support of the RRC connection recovery. At 6010, the gNB 620 may determine the context information for the UE 610 based on the capability report and assign the RRC ID for the UE context.

[0160] Moreover, at 6020, the gNB 620 may transmit the context information, RRC ID, and the recovery configurations to the UE 610. At 6030, the gNB 620 may determine to release a connection to the UE 610. In these cases, at 6040, the gNB 620 may request the MM NF 630 to release the UE context of the UE 610 by sending a new radio access network (Nran) UE context release request. Furthermore, at 6050, the MM NF 630 may accept the request and transmit a Nran UE context release command for releasing the UE context of the UE 610 to the gNB 620.

[0161] In some implementations, the UE 610 may support the validity timer of the UE context for keeping the UE context when the UE 610 is in the idle state. In these cases, at 6060, the gNB 620 may determine to keep the UE context while the UE is in the idle state. Additionally, the gNB 620 may determine a length of time for keeping the UE context upon the UE 610 being in the idle state. In addition, if the UE 610 supports the connection recovery based on the RRC ID and the recovery configurations, the gNB 620 may determine the recovery configurations for the UE 610.

[0162] Specifically, the recovery configurations may include, for example, but not limited to, a validity timer of the UE context or a configuration for a reconnection request. The reconnection request may include a message 3 in the random access procedure including an RRC reconnection request. The configuration for the reconnection request may be used as configuration for the protection of the reconnection request. For example, the configuration for the reconnection request may include at least one of: a next hop chaining count, a configuration of a SRB1 delivering thereconnection request, a list of cells for the reconnection request, or a validity timer of the reconnection request. The list of cells may include one or more PCI of the cells.

[0163] In some embodiments, the recovery configurations determined at 6010 and 6060 may be different. In these cases, the recovery configurations determined at 6060 may be considered as the updated recovery configurations. Moreover, in the updated recovery configurations, the validity timer of the UE context may be different from that of the recovery configurations. The updated recovery configurations may include at least one offset of the length of time.

[0164] At 6070, the gNB 620 transmits an RRC release message to the UE 610. The RRC release message may include the validity timer of the UE context and the recovery configurations.Additionally, the RRC release message may further include a validity timer of the reconnect request.

[0165] Moreover, at 6080, upon receiving an acknowledgment of the RRC release message. The gNB 620 may transmit a release complete message of the UE context to the MM NF 630. Optionally, the release complete message may include the validity timer of the UE context to indicate the MM NF 630 about the time duration while the UE context is kept in the RAN.

[0166] Furthermore, at 6090, upon receiving the RRC release message, the UE 610 starts the validity timer of the UE context, if the UE 610 has been configured with the validity timer of the UE context. At 6100, upon receiving the RRC release message, the UE 610 may start the validity timer of the reconnection request, if the UE 610 has been configured with the validity timer of the reconnection request. In addition, the validity timers of the UE context and the reconnection request may be started simultaneously.

[0167] In some embodiments, at 6110, the UE state of the UE 610 may be converted into the idle state. Subsequently, at 6120, the UE 610 may initiate a service request and the RRC reconnection procedure.

[0168] Moreover, at 6130, the random access procedure may be performed between the UE 610 and the gNB 620. Specifically, the UE 610 may transmit a message 1 to the gNB 620. Moreover, the gNB 620 may transmit a message 2 associated with the message 1 to the UE 610.

[0169] In some implementations, upon completion of the random access procedure, the UE 610 may initiate the RRC reconnection procedure. Specifically, when the UE 610 initiates the RRC reconnection procedure, at least one condition may be met. In some embodiments, the at least one condition may include the validity timer of the UE context is still running, the cell selected by the UE 610 is included in the list of cells for the reconnection request, or the validity timer of the reconnection request is still running.

[0170] At 6140, the UE 610 determines whether the at least one condition is met. Moreover, if the validity timer of the UE context is still running, the cell selected by the UE 610 is included in the listof cells for the reconnection request, and the validity timer of the reconnection request is still running, the UE 610 initiates the service request and transmit the service request to the gNB 620 at 6150, as illustrated as “opt.1 ” in FIG. 6. Additionally, the service request may include a multiple NAS container. The multiple NAS container may include a mobility management message and a session management message.

[0171] In addition, in the “opt.1” of the FIG. 6, the UE 610 may transmit the encrypted RRC reconnection request message to the gNB 620 at 6152. The encrypted RRC reconnection request message may include, for example, but not limited to, the RRC ID of the UE 610, subscription temporary mobile subscriber identities (S-TSMI) for the MM NF 630 and the SM NF 640, and the token to authorize he UE 610 (e.g., the shortMAC-l).

[0172] Alternatively or in addition, at 6142, if the validity timer of the UE context is still running, but the cell selected by the UE 610 is not included in the list of cells for the reconnection request, and / or the validity timer of the reconnection request is expired, at 6152, the UE 610 transmits the service request including the multiple NAS container to the gNB 620 at 6154, as illustrated as “opt.2” in FIG.6. Additionally, in the “opt.2” of the FIG. 6, the UE 610 may transmit the RRC reconnection request message to the gNB 620 without encryption at 6156.

[0173] In some embodiments, at 6144, if the validity timer of the UE context is expired, the UE 610 releases all the stored UE context and initiates a connection establishment procedure from the scratch at 6158, as illustrated as “opt.3” in FIG .6.

[0174] Furthermore, at 6160, the gNB 620 may identify the UE context stored in the gNB 620 based on the RRC ID in the RRC reconnection request message (encrypted or not encrypted). Optionally, the gNB 620 may assign a new RRC ID to the UE context or updated UE context.

[0175] Moreover, at 6170, the gNB 620 may transmit an RRC connection response message to the UE 610. The RRC reconnection response message may include the new RRC ID. In some embodiments, the RRC reconnection response message may include the updated UE context.

[0176] In some implementations, at 6180, the gNB 620 may transmit, to the MM NF 630, the service request for the MM NF 630 (also referred to as “NAS MM SR”). The service request may include the S-TSMI for the MM NF 630. Additionally, the service request may include an authenticated key set identifier (aKSI-1 ).

[0177] At 6182, the gNB 620 may transmit, to the MM NF 630, a Nran notification message including the identifier of the UE, the S-TMSI for the MM NF 630. In some implementations, the Nran notification message may include an explicit indication indicating that a security context is not requested.

[0178] Furthermore, at 6190 and 6192, the MM NF 630 may reply to the service request.Specifically, the MM NF 630 may transmit, to the gNB 620, an acknowledgement message to the NAS MM SR in a DL NAS transport container. In some embodiments, if the service request is received when the validity timer of the UE context is still running, the access stratum (AS) security keys may not be sent to the gNB 620 in the transport container. Alternatively or in addition, if the RAN such as the gNB 620 does not need the security context but has it locally, the security context may include an indicator indicating that the security context is not requested. In these cases, the AS security keys may not be sent to the gNB 620.

[0179] In some embodiments, at 6200, the gNB 620 may transmit, to the SM NF 640, the service request for the SM NF 640 (also referred to as “NAS SM SR”). The service request may include the S-TSMI for the SM NF 640. Additionally, the service request may include a further authenticated key set identifier (aKSI-2) and identifications of the PDU sessions. Additionally, at 6202, the gNB 620 may transmit, to the SM NF 640, an notification message including the identifier of the UE 610 and the S-TSMI for the SM NF 640.

[0180] Moreover, at 6210 and 6212, the SM NF 640 may reply to the service request. Specifically, the SM NF 640 may transmit, to the gNB 620, a further acknowledgement message to the NAS SM SR including the S-TSMI for the SM NF 640, the identifications of the PDU sessions, and the aKSI- 2. Additionally, the SM NF 640 may transmit, to the gNB 620, a message for a Nran PDU resource setup request including the identifier of the UE 610 and the S-TSMI for the SM NF 640.

[0181] Furthermore, at 6220, the gNB 620 may transmit, to the UE 610, the RRC reconfiguration message. At 6222, the RRC reconfiguration message encapsulating the multiple NAS container may be transmitted from the gNB 620 to the UE 610.

[0182] At 6230, the UE 610 may apply the received NAS / AS configuration. Additionally, the UE 610 may transmit a reconfiguration complete message to the gNB 620. Moreover, at 6240, the gNB 620 may transmit, to the SM NF 640, a PDU resource setup response message including the identifier of the UE 610 and the S-TSMI for the SM NF 640.

[0183] In this way, the UE 610 in the idle state may perform the connection recovery procedure based on the recovery configurations. Moreover, the connection recovery procedure may be secured based on AS configuration and the security context. Thus, the efficiency and reliability of the connection recovery procedure is improved.

[0184] FIG. 7 illustrates another example signaling flow 700 of a connection recovery procedure in accordance with some embodiments of the present disclosure. The signaling flow 700 illustrates embodiments regarding disaggregated RAN deployment.

[0185] As shown, the signaling flow 700 involves a UE 710, a gNB 720, a database MM NF 730, and a SM NF 740. The UE 710 may be an implementation of the first apparatus 110 in FIG. 1A. ThegNB 720 may be an implementation of the second apparatus 120 in FIG. 1A. Moreover, the gNB 720 may include a CU 724, and a DU 722 controlling a cell. In the following discussion, the cell of the DU 722 may be considered as a serving cell for the UE 710. The MM NF 730 may be an implementation of the third apparatus 130 in FIG. 1A. The SM NF 740 may be a CN device implementing the SM NF.

[0186] As illustrated in FIG. 7, at 7002, the UE 710 may transmit, to the gNB 720, a capability report of the UE 710. For example, the capability report may include a support of an RRC ID or a support of the RRC connection recovery. Moreover, at 7004, the DU 722 may transmit the capability report to the CU 724.

[0187] At 7010, the gNB 720 may determine context information for the UE 710 based on the capability report and assign an RRC ID for the UE context. In addition, if the UE 710 supports the connection recovery based on the RRC ID and the set of configurations, the gNB 720 may determine the set of configurations for the UE 710.

[0188] Moreover, at 7020 and 7022, the CU 724 may transmit the context information, RRC ID and the recovery configurations to the UE 710 via the DU 722. For example, the CU 724 may initiate a DL message transmission and transmit the RRC reconfiguration to the UE 710. The DU 722 may transmit the RRC reconfiguration including the RRC ID and the UE context to the UE 710.

[0189] At 7030, the gNB 720 may determine to release a connection to the UE 710. In these cases, at 7040, the gNB 720 may request the MM NF 730 to release the UE context of the UE 710 by sending a Nran UE context release request. Furthermore, at 7050, the MM NF 730 may accept the request and transmit a Nran UE context release command for releasing the UE context of the UE 710 to the gNB 720.

[0190] In some implementations, the UE 710 may support the validity timer of the UE context for keeping the UE context when the UE 710 is in the idle state. In these cases, at 7060, the gNB 720 may determine to keep the UE context while the UE is in the idle state. Additionally, the gNB 720 may determine a length of time for keeping the UE context upon the UE 710 being in the idle state. In addition, if the UE 710 support the connection recovery based on the RRC ID and the recovery configurations, the gNB 720 may determine the recovery configurations for the UE 710.

[0191] Specifically, the recovery configurations may include, for example, but not limited to, a validity timer of the UE context or a configuration for a reconnection request. The reconnection request may include a message 3 in the random access procedure including an RRC reconnection request. The configuration for the reconnection request may be used as configuration for the protection of the reconnection request. For example, the configuration for the reconnection request may include at least one of: a next hop chaining count, a configuration of a SRB1 delivering thereconnection request, a list of cells for the reconnection request, or a validity timer of the reconnection request. The list of cells may include one or more PCI of the cells.

[0192] In some embodiments, the recovery configurations determined at 7010 and 7060 may be different. In these cases, the recovery configurations determined at 7060 may be considered as the updated recovery configurations. Moreover, in the updated recovery configurations, the validity timer of the UE context may be different from that of the recovery configurations. The updated recovery configurations may include at least one offset of the length of time.

[0193] At 7070 and 7080, the gNB 720 may release the connection to the UE 710. Specifically, at 7070, the CU 724 may transmit, to the DU 722, a UE context release command message. The message may include the RRC release message for the UE 710. The RRC release message may include the recovery configurations and the validity timer for the UE to keep the UE context when the UE is in the idle state. At 7080, the DU 722 transmits the RRC release message to the UE 710. The RRC release message may include the validity timer of the UE context and the recovery configurations. In some implementations, upon receiving the RRC release message, the UE 710 may transmit an ACK to the RRC release message to the DU 722, which is not shown in FIG. 7.

[0194] Furthermore, at 7090, upon receiving the ACK to the RRC release message, the DU 722 may transmit a UE context release complete message to the CU 724. Moreover, at 7100, the CU 724 may transmit a UE context release complete message to the MM NF 630. Optionally, the UE context release complete message may include a timer for the MM NF 630 to indicate the time duration while the UE context is kept in the RAN.

[0195] At 7110, upon receiving the RRC release message, the UE 710 starts the validity timer of the UE context, if the UE 710 has been configured with the validity timer of the UE context. At 7120, upon receiving the RRC release message, the UE 710 may start the validity timer of the reconnection request, if the UE 710 has been configured with the validity timer of the reconnection request. In addition, the validity timers of the UE context and the reconnection request may be started simultaneously.

[0196] In some embodiments, at 7130, the UE state of the UE 710 may be converted into the idle state. Subsequently, at 7140, the UE 710 may initiate a service request and the RRC reconnection procedure.

[0197] Moreover, at 7150, the random access procedure may be performed between the UE 710 and the gNB 720. Specifically, the UE 710 may transmit a message 1 to the gNB 720 via the DU 722. Moreover, the gNB 720 may transmit a message 2 associated with the message 1 to the UE 710 via the DU 722.

[0198] At 7160, the UE 710 determines whether the at least one condition is met. Moreover, if thevalidity timer of the UE context is still running, the cell selected by the UE 710 is included in the list of cells for the reconnection request, and the validity timer of the reconnection request is still running, the UE 710 initiates the service request and transmits the service request to the gNB 720 at 7170, as illustrated as “opt.1 ” in FIG. 7. Additionally, the service request may include a multiple NAS container. The multiple NAS container may include a mobility management message and a session management message.

[0199] Alternatively or in addition, at 7162, if the validity timer of the UE context is still running, but the cell selected by the UE 710 is not included in the list of cells for the reconnection request, and / or the validity timer of the reconnection request is expired, at 7152, the UE 710 transmits the service request including the multiple NAS container to the gNB 720 at 7174, as illustrated as “opt.2” in FIG.7. Additionally, in the “opt.2” of the FIG. 7, the UE 710 may transmit the RRC reconnection request message to the gNB 720 without encryption at 7156.

[0200] In some embodiments, at 7164, if the validity timer of the UE context is expired, the UE 710 releases all the stored UE context and initiates a connection establishment procedure from the scratch at 7178, as illustrated as “opt.3” in FIG .7.

[0201] Furthermore, at 7180, the DU 722 may transmit an initial UL message transfer to the CU 724. The initial UL message may encapsulate the multiple NAS container and the RRC connection request message (encrypted or not encrypted) received from the UE 710.

[0202] At 7190, the CU 724 may identify the UE context stored in the CU 724 based on the RRC ID in the RRC reconnection request message (encrypted or not encrypted). Optionally, the CU 724 may assign a new RRC ID to the UE context or updated UE context.

[0203] In some embodiments, at 7200, the CU 724 may transmit, to the DU 722, a DL message transfer encapsulating an RRC connection response message. The RRC connection response message may include the new RRC ID. Additionally, the RRC connection response message may include the updated UE context.

[0204] Moreover, at 7210, the DU 722 may transmit the RRC connection response message to the UE 710.

[0205] In some implementations, at 7220, the CU 724 may transmit, to the MM NF 730, the service request for the MM NF 730 (also referred to as “NAS MM SR”). The service request may include the S-TSMI for the MM NF 730. Additionally, the service request may include an authenticated key set identifier (aKSI-1 ).

[0206] At 7222, the gNB 720 may transmit, to the MM NF 730, a Nran notification message including the identifier of the UE, the S-TMSI for the MM NF 730. In some implementations, the Nran notification message may include an explicit indication indicating that a security context is notrequested.

[0207] Furthermore, at 7230 and 7232, the MM NF 730 may reply to the service request.Specifically, the MM NF 730 may transmit, to the CU 724, an acknowledgement message to the NAS MM SR in a DL NAS transport container. In some embodiments, if the service request is received when the validity timer of the UE context is still running, the access stratum (AS) security keys may not be sent to the CU 724 in the transport container. Alternatively or in addition, if the CU 724 does not need the security context but has it locally, the security context may include an indicator indicating that the security context is not requested. In these cases, the AS security keys may not be sent to the CU 724.

[0208] In some embodiments, at 7240, the CU 724 may transmit, to the SM NF 740, the service request for the SM NF 740 (also referred to as “NAS SM SR”). The service request may include the S-TSMI for the SM NF 740. Additionally, the service request may include a further authenticated key set identifier (aKSI-2) and identifications of the PDU sessions. Additionally, at 7242, the CU 724 may transmit, to the SM NF 740, a notification message including the identifier of the UE 710 and the S- TSMI for the SM NF 740.

[0209] Moreover, at 7250 and 7252, the SM NF 740 may reply to the service request. Specifically, the SM NF 740 may transmit, to the CU 724, a further acknowledgement message to the NAS SM SR including the S-TSMI for the SM NF 740, the identifications of the PDU sessions, and the aKSI- 2. Additionally, the SM NF 740 may transmit, to the CU 724, a message for a Nran PDU resource setup request including the identifier of the UE 710 and the S-TSMI for the SM NF 740.

[0210] At 7260, the CU 722 may transmit a DL message transfer encapsulating an RRC reconfiguration message to be sent to the UE 710. Subsequently, at 7270, the DU 722 may transmit, to the UE 710, the RRC reconfiguration message. At 7272, the RRC reconfiguration message encapsulating the multiple NAS container may be transmitted from the DU 722 to the UE 710.

[0211] Moreover, at 7280, the UE 710 may apply the received NAS / AS configuration. Additionally, the UE 710 may transmit a reconfiguration complete message to the DU 722. Moreover, at 7290, the DU 722 may transmit, to the CU 724, the received reconfiguration complete message via the UL message transfer. At 7300, the CU 724 may transmit, to the SM NF 740, a PDU resource setup response message including the identifier of the UE 710 and the S-TSMI for the SM NF 740.

[0212] In this way, the UE 710 in the idle state may perform the connection recovery procedure based on the recovery configurations in a disaggregated network environment. Moreover, the connection recovery procedure may be secured based on AS configuration and the security context. Thus, the flexibility and reliability of the connection recovery procedure is improved.

[0213] Example embodiments for connection recovery procedure have been described withrespect to monolithic RAN deployment and disaggregated RAN deployment in FIG. 3 to FIG. 7. It is to be understood that these RAN deployments are only for the purpose of illustration, without suggesting any limitation. The present connection recovery configuration and / or connection recovery procedure may be applied for any suitable RAN deployments.

[0214] FIG. 8 shows a flowchart of an example method 800 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 800 will be described from the perspective of the first apparatus 110 in FIG. 1A.

[0215] At block 810, the first apparatus 110 receives, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid, and,

[0216] At block 820, the first apparatus 110 performs the connection recovery based on the identifier and the set of configurations. In this way, the first apparatus may perform the connection recovery based on the configuration(s) from the second apparatus.

[0217] In some example embodiments, the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request. These details of the configuration may be applied by the first apparatus 110 for the connection recovery.

[0218] In some example embodiments, the method 800 further comprises: in response to receiving, from the second apparatus, an indication for at least one of: the connection recovery, or a connection release, performing the connection recovery based on the identifier and a target configuration of the set of configurations. Thus, the connection recovery can be triggering by the connection recovery indication and / or the connection release indication.

[0219] In some example embodiments, the method 800 further comprises: perform the connection recovery based on the identifier and the target configuration. The first apparatus 110 may thus select a target configuration for the connection recovery.

[0220] In some example embodiments, the method 800 further comprises: in response to receiving the indication, starting at least one of: at least one timer for a time period for the validation of the context information, or at least one further timer for a further time period associated with thereconnection request. The at least one timer or further timer can thus be started.

[0221] In some example embodiments, the method 800 further comprises: determining a procedure for the connection recovery based on at least one of: the at least one timer, the at least one further timer, the list of cells, or a further list of cells for a protection of a connection request; and performing the connection recovery based on the procedure. In this way, the first apparatus 110 may select a proper procedure for the connection recovery.

[0222] In some example embodiments, the at least one timer comprises a first timer and a second timer, and the connection recovery is initiated after expiry of the first timer and before expiry of the second timer. The initiating time of the connection recovery may be determined based on the timer(s).

[0223] In some example embodiments, first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information. In this way, a different recovery level with a different context validation timer period can be configured.

[0224] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier related to the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration. In this way, the RRC connection recovery can be achieved.

[0225] In some example embodiments, the method 800 further comprises: transmitting, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations. In this way, the second apparatus may be informed about the capability of the first apparatus 110.

[0226] In some example embodiments, the method 800 further comprises: receiving, from the second apparatus, at least one updated configuration; and performing the connection recovery based on the identifier and the at least one updated configuration. In this way, the connection recovery configuration can be updated.

[0227] In some example embodiments, at least one updated configuration comprises at least one offset of the time period for the validation of context information. The signaling overhead can thus be reduced.

[0228] In some example embodiments, the first apparatus comprises a terminal device and the second apparatus comprises a network device.

[0229] FIG. 9 shows a flowchart of an example method 900 implemented at a second apparatus inaccordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 900 will be described from the perspective of the second apparatus 120 in FIG. 1A.

[0230] At block 910, the second apparatus 120 transmits, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid. In this way, the second apparatus 120 can configure the connection recovery for the first apparatus 110.

[0231] In some example embodiments, the method 900 further comprises: transmitting, to the first apparatus, an indication for at least one of: the connection recovery, or a connection release. The connection recovery can thus be triggered.

[0232] In some example embodiments, the indication indicates at least one of: a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level. The first apparatus can thus use the target configuration for the connection recovery.

[0233] In some example embodiments, first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information.

[0234] In some example embodiments, the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

[0235] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0236] In some example embodiments, the method 900 further comprises: receiving, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus configuration, or a support of the RRC connection recovery based on the set of configurations; and transmitting, to the first apparatus, context information of the first apparatus. The second apparatus 120 can thus transmit the context information to the first apparatus 110 with the connection recovery capability.

[0237] In some example embodiments, the method 900 further comprises: transmitting, to the firstapparatus, at least one updated configuration comprising at least one offset of the time period for the validation of context information.

[0238] In some example embodiments, the second apparatus comprises a central unit and a distributed unit, and the at least one updated configuration is transmitted from the central unit to the first apparatus via the distributed unit.

[0239] In some example embodiments, the method 900 further comprises: receiving, from the first apparatus, an acknowledgement message to an indication for a connection release; and transmitting, to a third apparatus, a release complete message, the release complete message comprising a third timer to indicate a time period during which the context information is stored in the second apparatus. The third apparatus thus can be informed about the release complete and the validation time duration of the context information.

[0240] In some example embodiments, the first apparatus comprises a terminal device and the second apparatus comprises a network device.

[0241] FIG. 10 shows a flowchart of an example method 1000 implemented at a first apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1000 will be described from the perspective of the first apparatus 110 in FIG. 1A.

[0242] At block 1010, the first apparatus 110 determines whether a first timer for context information of the first apparatus is expired upon a completion of a random access procedure, the context information being associated with an identifier related to the first apparatus.

[0243] If the first timer is running, at block 1020, the first apparatus 110 transmits to a second apparatus, a reconnection request comprising the identifier.

[0244] If the first timer is expired, at block 1030, the first apparatus 110 releases the context information of the first apparatus and initiates a connection establishment procedure to the second apparatus. In this way, the first apparatus 110 may decide to perform a reconnection or release a connection based on the first timer.

[0245] In some example embodiments, the method 1000 further comprises: in accordance with a determination that the first timer is running upon the completion of the random access procedure, determining whether at least one condition is met, the at least one condition comprising at least one of: a second timer associated with the reconnection request being running upon the completion of the random access procedure, or a target cell associated with the reconnection request being comprised in a list of cells associated with the reconnection request.

[0246] In some example embodiments, based on the at least one condition being met, the reconnection request comprises an encrypted reconnection request, the encrypted reconnectionrequest comprising a token to authorize the first apparatus. In some example embodiments, based on the at least one condition being not met, the reconnection request is transmitted to the second apparatus without being encrypted. In this way, the first apparatus 110 may determine whether the reconnection request is encrypted based on the at least one condition.

[0247] In some example embodiments, the method 1000 further comprises: in accordance with a determination that the first timer is running upon the completion of the random access procedure, transmitting the reconnection request and a service request to the second apparatus, the service request comprising a multiple non-access stratum (NAS) container, the multiple NAS container comprising a mobility management message and a session management message. In some example embodiments, the method 1000 further comprises: receiving, from the second apparatus, a reconfiguration message encapsulating a multiple NAS container including a response to the service request. In this way, if the first timer is running, the first apparatus may transmit the service request to the second apparatus and receives the response.

[0248] In some example embodiments, the method 1000 further comprises: receiving, from the second apparatus, a further identifier related to the first apparatus, the further identifier being associated with the context information of the first apparatus. In this way, the second apparatus may assign a new identifier for the first apparatus 110.

[0249] In some example embodiments, the method 1000 further comprises: receiving, from the second apparatus, the identifier related to the first apparatus and a configuration for connection recovery, the configuration indicative of at least one of the following: a level of the configuration, a time period for the first timer, at least one apparatus for which the context information is valid, a list of cells for which the context information is valid, area information indicative of at least one apparatus for which the context information is valid, a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a further list of cells for the reconnection request; or a second time period for a second timer associated with the reconnection request. In this way, the first apparatus may be configured about the connection recovery.

[0250] In some example embodiments, the method 1000 further comprises: in response to receiving, from the second apparatus, an indication for at least one of: the connection recovery, or a connection release, performing the connection recovery based on the identifier and the configuration. The connection recovery can thus be triggered.

[0251] In some example embodiments, the method 1000 further comprises: in response to receiving the indication, starting at least one of the first timer or a second timer associated with the reconnection request. The timer(s) may thus be started.

[0252] In some example embodiments, the connection recovery comprises a radio resourcecontrol (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration. The RRC connection recovery may thus be achieved.

[0253] In some example embodiments, the method 1000 further comprises: transmitting, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations. In this way, the second apparatus may be informed about the capability of the first apparatus.

[0254] In some example embodiments, the first apparatus comprises a terminal device and the second apparatus comprises a network device.

[0255] FIG. 11 shows a flowchart of an example method 1100 implemented at a second apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1100 will be described from the perspective of the second apparatus 120 in FIG. 1A.

[0256] At block 1110, the second apparatus 120 transmits, to a first apparatus, an identifier related to the first apparatus, the identifier being associated with context information of the first apparatus.

[0257] At block 1120, the second apparatus 120 transmits, to the first apparatus, an indication for at least one of: a connection recovery, or a connection release.

[0258] At block 1130, the second apparatus 120 receives, from the first apparatus, a reconnection request comprising the identifier of the first apparatus.

[0259] In some example embodiments, the reconnection request comprises an encrypted reconnection request, the encrypted reconnection request comprising a token to authorize the first apparatus. In this way, the encrypted reconnection request may be received.

[0260] In some example embodiments, the method 1100 further comprises: based on the reconnection request being not encrypted, transmitting to a third apparatus, information indicating that context information of the first apparatus is not encrypted. In this way, the third apparatus may be informed about whether the context information is encrypted.

[0261] In some example embodiments, the method 1100 further comprises: assigning a further identifier related to the first apparatus, the further identifier being associated with the context information of the first apparatus; and transmitting, to at least one of: the first apparatus or a third apparatus, the further identifier related to the first apparatus. The second apparatus may thus assign a new identifier for the first apparatus.

[0262] In some example embodiments, the method 1100 further comprises: receiving, from thefirst apparatus, the reconnection request and a service request to the second apparatus, the service request comprising a multiple non-access stratum (NAS) container, the multiple NAS container comprising a mobility management message and a session management message. The service request response may thus be transmitted to the first apparatus.

[0263] In some example embodiments, the method 1100 further comprises: in response to receiving the service request, transmitting to a third apparatus, the service request; receiving, from the third apparatus, a response to the service request; and transmitting, to the first apparatus, a reconfiguration message encapsulating the multiple NAS container including the response to the service request. The service response may thus be obtained from the third apparatus.

[0264] In some example embodiments, the method 1100 further comprises: transmitting, to the first apparatus, a configuration for connection recovery, the configuration indicative of at least one of the following: a level of the configuration, a time period for the first timer, at least one apparatus for which the context information is valid, a list of cells for which the context information is valid, a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1 ) delivering the reconnection request; a further list of cells for the reconnection request; or a second time period for a second timer associated with the reconnection request. How to perform the connection recovery is thus configured for the first apparatus.

[0265] In some example embodiments, the method 1100 further comprises: transmitting, to a third apparatus, a message comprising a timer indicating a validation duration of the context information of the first apparatus. The third apparatus may thus be informed about the validation duration of the context information of the first apparatus.

[0266] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0267] In some example embodiments, the method 1100 further comprises: receiving, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of RRC identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations. The second apparatus may be informed about the capability of RRC connection recovery of the first apparatus.

[0268] FIG. 12 shows a flowchart of an example method 1200 implemented at a third apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 1200 will be described from the perspective of the third apparatus 130 in FIG. 1A.

[0269] At block 1210, the third apparatus 130 receives, from a second apparatus, a servicerequest for mobility management.

[0270] At block 1220, the third apparatus 130 determines whether at least one condition is met. The at least one condition comprises at least one of: a timer for context information of a first apparatus being running, or an indication of no need of security context.

[0271] If the at least one condition is met, at block 1230, the third apparatus 130 transmits a response of the service request to the second apparatus, the response excluding an access stratum security key.

[0272] If the at least one condition is not met, at block 1240, the third apparatus 130 transmits the response of the service request to the second apparatus, the response including an access stratum security key. In this way, the third apparatus 130 can decide whether to include the access stratum security key in the service request response based on the at least one condition.

[0273] In some example embodiments, the method 1200 further comprises: receiving, from the second apparatus, a message comprising at least one of: the timer for the validation of the context information, or the indication of no need of security context. In this way, the determination of whether to include the access stratum security key may be based on the message from the second apparatus.

[0274] In some example embodiments, a first apparatus capable of performing any of the method 800 (for example, the first apparatus 110 in FIG. 1A) may comprise means for performing the respective operations of the method 800. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1A.

[0275] In some example embodiments, the first apparatus comprises means for receiving, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and means for performing the connection recovery based on the identifier and the set of configurations.

[0276] In some example embodiments, the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

[0277] In some example embodiments, the first apparatus further comprises: means for in response to receiving, from the second apparatus, an indication for at least one of: the connectionrecovery, or a connection release, performing the connection recovery based on the identifier and a target configuration of the set of configurations.

[0278] In some example embodiments, means for performing the connection recovery may perform the connection recovery based on the identifier and the target configuration.

[0279] In some example embodiments, the first apparatus further comprises: means for in response to receiving the indication, starting at least one of: at least one timer for a time period for the validation of the context information, or at least one further timer for a further time period associated with the reconnection request.

[0280] In some example embodiments, the first apparatus further comprises: means for determining a procedure for the connection recovery based on at least one of: the at least one timer, the at least one further timer, the list of cells, or a further list of cells for a protection of a connection request; and means for performing the connection recovery based on the procedure.

[0281] In some example embodiments, the at least one timer comprises a first timer and a second timer, and the connection recovery is initiated after expiry of the first timer and before expiry of the second timer.

[0282] In some example embodiments, first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information.

[0283] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier related to the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0284] In some example embodiments, the first apparatus further comprises: means for transmitting, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations.

[0285] In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, at least one updated configuration; and means for performing the connection recovery based on the identifier and the at least one updated configuration.

[0286] In some example embodiments, at least one updated configuration comprises at least one offset of the time period for the validation of context information.

[0287] In some example embodiments, a second apparatus capable of performing any of the method 900 (for example, the second apparatus 120 in FIG. 1 A) may comprise means for performing the respective operations of the method 900. The means may be implemented in anysuitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1A.

[0288] In some example embodiments, the second apparatus comprises means for transmitting, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid.

[0289] In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, an indication for at least one of: the connection recovery, or a connection release.

[0290] In some example embodiments, the indication indicates at least one of: a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level.

[0291] In some example embodiments, first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information.

[0292] In some example embodiments, the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

[0293] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0294] In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus configuration, or a support of the RRC connection recovery based on the set of configurations; and means for transmitting, to the first apparatus, context information of the first apparatus.

[0295] In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, at least one updated configuration comprising at least one offset of the time period for the validation of context information.

[0296] In some example embodiments, the second apparatus comprises a central unit and adistributed unit, and the at least one updated configuration is transmitted from the central unit to the first apparatus via the distributed unit.

[0297] In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, an acknowledgement message to an indication for a connection release; and means for transmitting, to a third apparatus, a release complete message, the release complete message comprising a third timer to indicate a time period during which the context information is stored in the second apparatus.

[0298] In some example embodiments, a first apparatus capable of performing any of the method 1000 (for example, the first apparatus 110 in FIG. 1A) may comprise means for performing the respective operations of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The first apparatus may be implemented as or included in the first apparatus 110 in FIG. 1A.

[0299] In some example embodiments, the first apparatus comprises means for determining whether a first timer for context information of the first apparatus is expired upon a completion of a random access procedure, the context information being associated with an identifier related to the first apparatus; means for in accordance with a determination that the first timer is running, transmitting to a second apparatus, a reconnection request comprising the identifier; and means for in accordance with a determination that the first timer is expired, releasing the context information of the first apparatus and initiating a connection establishment procedure to the second apparatus.

[0300] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that the first timer is running upon the completion of the random access procedure, determining whether at least one condition is met, the at least one condition comprising at least one of: a second timer associated with the reconnection request being running upon the completion of the random access procedure, or a target cell associated with the reconnection request being comprised in a list of cells associated with the reconnection request.

[0301] In some example embodiments, based on the at least one condition being met, the reconnection request comprises an encrypted reconnection request, the encrypted reconnection request comprising a token to authorize the first apparatus.

[0302] In some example embodiments, based on the at least one condition being not met, the reconnection request is transmitted to the second apparatus without being encrypted.

[0303] In some example embodiments, the first apparatus further comprises: means for in accordance with a determination that the first timer is running upon the completion of the random access procedure, transmitting the reconnection request and a service request to the second apparatus, the service request comprising a multiple non-access stratum (NAS) container, themultiple NAS container comprising a mobility management message and a session management message.

[0304] In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, a reconfiguration message encapsulating a multiple NAS container including a response to the service request.

[0305] In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, a further identifier related to the first apparatus, the further identifier being associated with the context information of the first apparatus.

[0306] In some example embodiments, the first apparatus further comprises: means for receiving, from the second apparatus, the identifier related to the first apparatus and a configuration for connection recovery, the configuration indicative of at least one of the following: a level of the configuration, a time period for the first timer, at least one apparatus for which the context information is valid, a list of cells for which the context information is valid, area information indicative of at least one apparatus for which the context information is valid, a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1 ) delivering the reconnection request; a further list of cells for the reconnection request; or a second time period for a second timer associated with the reconnection request.

[0307] In some example embodiments, the first apparatus further comprises: means for in response to receiving, from the second apparatus, an indication for at least one of: the connection recovery, or a connection release, performing the connection recovery based on the identifier and the configuration.

[0308] In some example embodiments, the first apparatus further comprises: means for in response to receiving the indication, starting at least one of the first timer or a second timer associated with the reconnection request.

[0309] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0310] In some example embodiments, the first apparatus further comprises: means for transmitting, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations.

[0311] In some example embodiments, a second apparatus capable of performing any of the method 1100 (for example, the second apparatus 120 in FIG. 1A) may comprise means for performing the respective operations of the method 1100. The means may be implemented in anysuitable form. For example, the means may be implemented in a circuitry or software module. The second apparatus may be implemented as or included in the second apparatus 120 in FIG. 1A.

[0312] In some example embodiments, the second apparatus comprises means for transmitting, to a first apparatus, an identifier related to the first apparatus, the identifier being associated with context information of the first apparatus; means for transmitting, to the first apparatus, an indication for at least one of: a connection recovery, or a connection release; and means for receiving, from the first apparatus, a reconnection request comprising the identifier of the first apparatus.

[0313] In some example embodiments, the reconnection request comprises an encrypted reconnection request, the encrypted reconnection request comprising a token to authorize the first apparatus.

[0314] In some example embodiments, the second apparatus further comprises: means for based on the reconnection request being not encrypted, transmitting to a third apparatus, information indicating that context information of the first apparatus is not encrypted.

[0315] In some example embodiments, the second apparatus further comprises: means for assigning a further identifier related to the first apparatus, the further identifier being associated with the context information of the first apparatus; and means for transmitting, to at least one of: the first apparatus or a third apparatus, the further identifier related to the first apparatus.

[0316] In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, the reconnection request and a service request to the second apparatus, the service request comprising a multiple non-access stratum (NAS) container, the multiple NAS container comprising a mobility management message and a session management message.

[0317] In some example embodiments, the second apparatus further comprises: means for in response to receiving the service request, transmitting to a third apparatus, the service request; means for receiving, from the third apparatus, a response to the service request; and means for transmitting, to the first apparatus, a reconfiguration message encapsulating the multiple NAS container including the response to the service request.

[0318] In some example embodiments, the second apparatus further comprises: means for transmitting, to the first apparatus, a configuration for connection recovery, the configuration indicative of at least one of the following: a level of the configuration, a time period for the first timer, at least one apparatus for which the context information is valid, a list of cells for which the context information is valid, a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a further list of cells for the reconnection request; or a second time period for a second timer associated with the reconnection request.

[0319] In some example embodiments, the second apparatus further comprises: means for transmitting, to a third apparatus, a message comprising a timer indicating a validation duration of the context information of the first apparatus.

[0320] In some example embodiments, the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

[0321] In some example embodiments, the second apparatus further comprises: means for receiving, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of RRC identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations.

[0322] In some example embodiments, a third apparatus capable of performing any of the method 1200 (for example, the third apparatus 120 in FIG. 1A) may comprise means for performing the respective operations of the method 1200. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The third apparatus may be implemented as or included in the third apparatus 120 in FIG. 1A.

[0323] In some example embodiments, the third apparatus comprises means for receiving, from a second apparatus, a service request for mobility management; means for based on at least one condition being met, transmitting a response of the service request to the second apparatus, the response excluding an access stratum security key; and means for based on the at least one condition being not met, transmitting the response of the service request to the second apparatus, the response including an access stratum security key, wherein the at least one condition comprises at least one of: a timer for context information of a first apparatus being running, or an indication of no need of security context.

[0324] In some example embodiments, the third apparatus further comprises: means for receiving, from the second apparatus, a message comprising at least one of: the timer for the validation of the context information, or the indication of no need of security context.

[0325] FIG. 13 is a simplified block diagram of a device 1300 that is suitable for implementing example embodiments of the present disclosure. The device 1300 may be provided to implement a communication device, for example, the first apparatus 110 or the second apparatus 120 or the third apparatus 130 as shown in FIG. 1A. As shown, the device 1300 includes one or more processors 1310, one or more memories 1320 coupled to the processor 1310, and one or more communication modules 1340 coupled to the processor 1310.

[0326] The communication module 1340 is for bidirectional communications. The communication module 1340 has one or more communication interfaces to facilitate communication with one ormore other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 1340 may include at least one antenna.

[0327] The processor 1310 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1300 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0328] The memory 1320 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 1324, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 1322 and other volatile memories that will not last in the power-down duration.

[0329] A computer program 1330 includes computer executable instructions that are executed by the associated processor 1310. The instructions of the program 1330 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 1330 may be stored in the memory, e.g., the ROM 1324. The processor 1310 may perform any suitable actions and processing by loading the program 1330 into the RAM 1322.

[0330] The example embodiments of the present disclosure may be implemented by means of the program 1330 so that the device 1300 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 12. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0331] In some example embodiments, the program 1330 may be tangibly contained in a computer readable medium which may be included in the device 1300 (such as in the memory 1320) or other storage devices that are accessible by the device 1300. The device 1300 may load the program 1330 from the computer readable medium to the RAM 1322 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0332] FIG. 14 shows an example of the computer readable medium 1400 which may be in form ofCD, DVD or other optical storage disk. The computer readable medium 1400 has the program 1330 stored thereon.

[0333] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0334] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0335] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0336] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0337] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0338] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0339] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

WHAT IS CLAIMED IS:1 . A first apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the first apparatus to: receive, from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and, perform the connection recovery based on the identifier and the set of configurations.

2. The first apparatus of claim 1 , wherein the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of: a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

3. The first apparatus of claim 1 or 2, wherein the first apparatus is further caused to: in response to receiving, from the second apparatus, an indication for at least one of: the connection recovery, or a connection release, perform the connection recovery based on the identifier and a target configuration of the set of configurations.

4. The first apparatus of claim 3, wherein the indication indicates at least one of: a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level; and wherein the first apparatus is further caused to: perform the connection recovery based on the identifier and the target configuration.

5. The first apparatus of claim 3 or claim 4, wherein the first apparatus is further caused to: in response to receiving the indication, start at least one of: at least one timer for a time period for the validation of the context information, or at least one further timer for a further time period associated with the reconnection request.

6. The first apparatus of claim 5, wherein the first apparatus is further caused to: determine a procedure for the connection recovery based on at least one of: the at least one timer, the at least one further timer, the list of cells, or a further list of cells for a protection of a connection request; and perform the connection recovery based on the procedure.

7. The first apparatus of claim 6, wherein the at least one timer comprises a first timer and a second timer, and the connection recovery is initiated after expiry of the first timer and before expiry of the second timer.

8. The first apparatus of any of claims 1 to 7, wherein first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information.

9. The first apparatus of any of claims 1 to 8, wherein the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier related to the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

10. The first apparatus of any of claims 1 to 9, wherein the first apparatus is further caused to: transmit, to the second apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus for RRC configuration, or a support of the RRC connection recovery based on the set of configurations.11 . The first apparatus of any of claims 1 to 10, wherein the first apparatus is further caused to: receive, from the second apparatus, at least one updated configuration; andperform the connection recovery based on the identifier and the at least one updated configuration.

12. The first apparatus of claim 11 , wherein at least one updated configuration comprises at least one offset of the time period for the validation of context information.

13. A second apparatus comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the second apparatus to: transmit, to a first apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid.

14. The second apparatus of claim 13, wherein the second apparatus is further caused to: transmit, to the first apparatus, an indication for at least one of: the connection recovery, or a connection release.

15. The second apparatus of claim 14, wherein the indication indicates at least one of: a target level for the connection recovery or a target configuration of the set of configurations corresponding to the target level.

16. The second apparatus of claim 13, wherein first context information associated with a first level of a first configuration is different from a second context of the first apparatus associated with a second level of a second configuration, and a first time period for a validation of the first context information is different from a second time period for a validation of the second context information.

17. The second apparatus of any of claims 13 to 16, wherein the set of configurations further comprises a configuration for a reconnection request, the configuration comprising at least one of:a next hop chaining count; a configuration of a signaling radio bearer 1 (SRB1) delivering the reconnection request; a list of cells for the reconnection request; or a second time period associated with the reconnection request.

18. The second apparatus of any of claims 13 to 17, wherein the connection recovery comprises a radio resource control (RRC) connection recovery, and the identifier of the first apparatus comprises an RRC identifier related to the first apparatus for RRC configuration.

19. The second apparatus of any of claims 13 to 18, wherein the second apparatus is further caused to: receive, from the first apparatus, a capability of the first apparatus, the capability comprising at least one of: a support of a radio resource control (RRC) identifier related to the first apparatus configuration, or a support of the RRC connection recovery based on the set of configurations; and transmit, to the first apparatus, context information of the first apparatus.

20. The second apparatus of any of claims 13 to 19, wherein the second apparatus is further caused to: transmit, to the first apparatus, at least one updated configuration comprising at least one offset of the time period for the validation of context information.21 . The second apparatus of claim 20, wherein the second apparatus comprises a central unit and a distributed unit, and the at least one updated configuration is transmitted from the central unit to the first apparatus via the distributed unit.

22. The second apparatus of any of claims 13 to 21 , wherein the second apparatus is further caused to: receive, from the first apparatus, an acknowledgement message to an indication for a connection release; and transmit, to a third apparatus, a release complete message, the release complete message comprising a third timer to indicate a time period during which the context information is stored in the second apparatus.

23. A method comprising: receiving, at a first apparatus from a second apparatus, an identifier related to the first apparatus and a set of configurations for connection recovery, a configuration of the set of configurations indicative of at least one of the following: a level of the configuration, a time period for a validation of context information of the first apparatus associated with the identifier, at least one apparatus for which the context information is valid, or a list of cells for which the context information is valid; and, performing the connection recovery based on the identifier and the set of configurations.

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