Patent Description:
In a conventional radio access network (RAN), a user equipment (UE) may be operating in any one of a CONNECTED mode, an IDLE mode, and an INACTIVE mode. The CONNECTED mode corresponds with bi-directional connectivity between the UE and its serving base stations, such that the UE is able to send and receive session protocol data units (PDUs). The IDLE mode corresponds with no radio resource control (RRC) connection (and therefore no radio connectivity) between the UE and the RAN, and the RAN releases any RAN resources associated with the UE. The INACTIVE mode is similar to the IDLE mode in that there is no RRC connection between the UE and the RAN and there are no radio resources allocated to the UE, but also differs from the IDLE mode in that at least one RAN node retains UE context information (such as security association, encryption keys etc.), and so is capable of initiating communication with the UE in a relatively short period of time.

The INACTIVE mode allows a UE to enter a low energy mode of operation, and thereby conserve battery power. In order to receive information transmitted by the network, the UE transitions from the INACTIVE mode into the CONNECTED mode. However a transition from the INACTIVE mode to the CONNECTED mode results in one or more of the following:.

These operations result in additional latency and extended periods of time when the UE is not able to re-enter a low energy mode of operation due to the expected interaction with the serving RAN node. Therefore the anchor RAN node should be able to decide whether to retain its role of anchor for a UE or to relocate the role of anchor to the new serving RAN node.

When the UE initiates a transition from the INACTIVE to the CONNECTED mode or initiates a RAN location notification and/or a RAN notification area (RNA) update in INACTIVE mode, current procedures do not fully protect the control plane signalling between the UE and the RAN and delay validation of the UE which potentially results in significant network signalling and processing, if validation subsequently fails.

Accordingly, there may be a need for a system and method for location and context management in a RAN INACTIVE mode that is not subject to one or more limitations of the prior art.

This background information is intended to provide information that may be of possible relevance to the present disclosure. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present disclosure.

<CIT> discloses that a network supporting a number of client devices includes a network device that generates a context for a client device. The client device context may include network state information for the client device that enables the network to communicate with the client device. The client device may obtain, from a network device that serves a first service area of the network, information that includes a first client device context. The client device may enter a second service area of the network served by a second network device.

<CIT> discloses a method and device for obtaining security context, which relate to a communication technical field, and are invented enabling normal communication between a Machine Type Communication (MTC) device and the network side under the condition that the MTC device does not perform Tracking Area Update (TAU) / Routing Area Update (RAU).

Further implementations are disclosed in the appended dependent claims, the description and the figures. It is an object of the present disclosure to obviate or mitigate at least one disadvantage of the prior art.

Accordingly, a first aspect of the present disclosure provides an anchor node of a RAN, the anchor node comprising: a memory and at least one processor configured to: receive, from a second network node, a context retrieval request comprising an identifier of a UE operating in an INACTIVE mode and a first message, the first message being protected with a first cryptographic key; validate the first message using a stored cryptographic key associated with a UE context indicated by the identifier of the UE; and send a context retrieval response to the second network node, the context retrieval response containing a relocation indication of whether the UE context is to be relocated to the second network node.

In an embodiment, the relocation indication is responsive to validating the first message in accordance with the stored cryptographic key.

In an embodiment, the relocation indication is responsive to a determination of whether to relocate the UE context to the second network node.

In an embodiment, the context retrieval response can comprise a second message protected with a second cryptographic key.

In an embodiment, the second message can be a radio resource control (RRC) message.

In an embodiment, the second message can comprise at least one of: an identifier to be used by the UE for further operations in the INACTIVE mode; an indication of an RNA where the UE can receive service while operating in the INACTIVE mode; and a maximum time between location notifications initiated by the UE.

In an embodiment, the context retrieval response can comprise the UE context and a second cryptographic key.

A further aspect of the present disclosure provides a serving node of a RAN, the serving node comprising: a memory and at least one processor configured to: receive, from a UE, an identifier of a UE operating in an INACTIVE mode and a first message, the first message being protected with a first cryptographic key; send the identifier of the UE and the first message to a second network node; receive, from the second network node, a second message protected with a second cryptographic key; and send the second message to the UE.

In an embodiment, the second network node can be determined in accordance with the identifier of the UE.

A further aspect of the present disclosure provides a serving node of a RAN, the serving node comprising: a memory and at least one processor configured to: receive, from a UE, an identifier of a UE operating in an INACTIVE mode and a first message, the first message being protected with a first cryptographic key; send the identifier of the UE and the first message to a second network node; receive from the second network node, a context associated with the UE; derive, based on the context, a second cryptographic key; and send a second message to the UE protected with the second cryptographic key.

In an embodiment, the second message can comprise any one or more of: an identifier to be used by the UE for further operations in the INACTIVE mode; an indication of an RNA where the UE can receive service while operating in the INACTIVE mode; and a maximum time between location notifications initiated by the UE.

In the following description, features of the present disclosure are described by way of examples. For convenience of description, these examples make use of features and terminology known from <NUM> and <NUM> networks as defined by the Third Generation Partnership Project (3GPP). However, it shall be understood that the present disclosure is not limited to such networks. Rather, methods and systems in accordance with the present disclosure may be implemented in any network in which a mobile device may connect to the network through at least one access point, and subsequently be handed-over to at least one other access point during the course of a communications session.

<FIG> is a block diagram of an electronic device (ED) <NUM> illustrated within a computing and communications environment <NUM> that may be used for implementing the devices and methods disclosed herein. In some examples, the ED <NUM> may be an element of communications network infrastructure, such as a base station (for example a NodeB, an enhanced Node B (eNB), a next generation NodeB (sometimes referred to as ng-eNB or gNB), a home subscriber server (HSS), a gateway (GW) such as a packet gateway (PGW) or a serving gateway (SGW) or a user plane gateway (UPGW), a user plane function (UPF), or various other nodes or functions within a CN. In other examples, the ED <NUM> may be a device that couples to network infrastructure over a radio interface, such as a mobile phone, smart phone or other such wireless device that may be classified as a UE. In some examples, ED <NUM> may be a Machine Type Communications (MTC) device (also referred to as a machine-to-machine (m2m) device), or another such device that may be categorized as a UE <NUM> despite not providing a direct service to a user. In some references, an ED <NUM> may also be referred to as a mobile device (MD), a term intended to reflect devices that couple to a mobile network, regardless of whether the device itself is designed for, or capable of, mobility. Specific devices may utilize all of the components shown or only a subset of the components, and levels of integration may vary from device to device. Furthermore, a device may contain multiple instances of a component, such as multiple processors, memories, transmitters, receivers, etc. The ED <NUM> typically includes a processor <NUM>, such as a Central Processing Unit (CPU), and may further include specialized processors such as a Graphics Processing Unit (GPU) or other such processor, a memory <NUM>, a network interface <NUM> and a bus <NUM> to couple the components of ED <NUM>. ED <NUM> may optionally also include components such as a mass storage device <NUM>, a video adapter <NUM>, and an I/O interface <NUM> (shown in dashed lines).

The memory <NUM> may comprise any type of non-transitory system memory, readable by the processor <NUM>, such as static random-access memory (SRAM), dynamic random access memory (DRAM), synchronous DRAM (SDRAM), read-only memory (ROM), or a combination thereof. In specific examples, the memory <NUM> may include more than one type of memory, such as ROM for use at boot-up, and DRAM for program and data storage for use while executing programs.

The ED <NUM> may also include one or more network interfaces <NUM>, which may include at least one of a wired network interface and a wireless network interface. As illustrated in <FIG>, network interface <NUM> may include a wired network interface to couple to a network <NUM>, and also may include a radio access network interface <NUM> for connecting to other devices over a radio link. When ED <NUM> is network infrastructure, the radio access network interface <NUM> may be omitted for nodes or functions acting as elements of the CN other than those at the radio edge (e.g. an eNB). When ED <NUM> is infrastructure at the radio edge of a network, both wired and wireless network interfaces may be included. When ED <NUM> is a wirelessly connected device, such as a UE, radio access network interface <NUM> may be present and it may be supplemented by other wireless interfaces such as WiFi network interfaces. The network interfaces <NUM> allow the ED <NUM> to communicate with remote entities such as those coupled to network <NUM>.

The mass storage <NUM> may comprise, for example, one or more of a solid-state drive, hard disk drive, a magnetic disk drive, or an optical disk drive. In some examples, mass storage <NUM> may be remote to the ED <NUM> and accessible through use of a network interface such as interface <NUM>. In the illustrated example, mass storage <NUM> is distinct from memory <NUM> where it is included, and may generally perform storage tasks compatible with higher latency, but may generally provide lesser or no volatility. In some examples, mass storage <NUM> may be integrated with a memory <NUM> to form an heterogeneous memory.

The optional video adapter <NUM> and the I/O interface <NUM> (shown in dashed lines) provide interfaces to couple the ED <NUM> to external input and output devices. Examples of input and output devices include a display <NUM> coupled to the video adapter <NUM> and an I/O device <NUM> such as a touch-screen coupled to the I/O interface <NUM>. Other devices may be coupled to the ED <NUM>, and additional or fewer interfaces may be utilized. For example, a serial interface such as Universal Serial Bus (USB) (not shown) may be used to provide an interface for an external device. Those skilled in the art will appreciate that in examples in which ED <NUM> is part of a data center, I/O interface <NUM> and Video Adapter <NUM> may be virtualized and provided through network interface <NUM>.

In some examples, ED <NUM> may be a standalone device, while in other examples, ED <NUM> may be resident within a data center. A data center, as will be understood in the art, is a collection of computing resources (typically in the form of servers) that can be used as a collective computing and storage resource. Within a data center, a plurality of servers can be coupled together to provide a computing resource pool upon which virtualized entities can be instantiated. Data centers can be interconnected with each other to form networks consisting of pools computing and storage resources coupled to each by connectivity resources. The connectivity resources may take the form of physical connections such as Ethernet or optical communications links, and may include wireless communication channels as well. If two different data centers are coupled by a plurality of different communication channels, the links can be combined together using any of a number of techniques including the formation of link aggregation groups (LAGs). It should be understood that any or all of the computing, storage and connectivity resources (along with other resources within the network) can be divided between different sub-networks, in some cases in the form of a resource slice. If the resources across a number of coupled data centers or other collection of nodes are sliced, different network slices can be created.

<FIG> illustrates an architecture <NUM> for the implementation of a <NUM> next generation radio access network (NG-RAN) <NUM>. NG-RAN <NUM> couples a UE <NUM> to a CN <NUM>. Those skilled in the art will appreciate that CN <NUM> may be a <NUM> Core Network or a <NUM> Evolved Packet Core (EPC) network. Nodes within NG-RAN <NUM> couple to the <NUM> CN <NUM> over an NG interface. This NG interface can comprise both a control plane (CP) NG-C (N2) interface to a CN CP function (CPF) and a user plane (UP) NG-U (N3) interface to a CN UP function (UPF). NG-RAN <NUM> includes a plurality of radio access nodes where each node is referred to as a gNB. In the NG-RAN <NUM>, gNB 216A and gNB 216B are able to communicate with each other over an Xn interface. Within a single gNB 216A, the functionality of the gNB may be decomposed into a centralized unit (gNB-CU) 218A and a set of distributed units (gNB-DU 220A-<NUM> and gNB-DU 220A-<NUM>, collectively referred to as 220A). gNB-CU 218A is coupled to a gNB-DU 220A over an F1 interface. Similarly gNB 216B has a gNB-CU 218B coupling to a set of distributed units gNB-DU 220B-<NUM> and gNB-DU 220B. Each gNB-DU may be responsible for one or more cells providing radio coverage within the public land mobile network (PLMN).

A gNB is also coupled to UE <NUM> (such as, for example ED <NUM>) via a radio link (Uu) and to another gNB via an Xn interface that includes both a CP component (Xn-C) and a UP component (Xn-U).

A UE <NUM> may establish multiple PDU sessions with the CN <NUM> where different sessions may correspond to different instances of the NG-U UP interface; each instance of the NG-U interface may terminate on a different CN UPF.

In a 3GPP Long-Term Evolution (LTE) system, similar interfaces exist: an eNB is coupled to a CN <NUM> through an S1 interface and to another eNB through an X2 interface. Throughout this document, the term "RAN node" is used to refer to a RAN element that encompasses gNB, gNB-CU, gNB-DU, eNB, ng-eNB, ng-eNB-CU, ng-eNB-DU, NodeB, base station, and other forms of radio access controller. The term "RAN node" may also be understood in some contexts to include other wireless access nodes, such as WiFi access points, in which case suitable modifications to adapt to a different standard may be required.

It should be understood that any or all of the functions discussed above with respect to the NG-RAN <NUM> and CN <NUM> may be virtualized within a network, and the network itself may be provided as a network slice of a larger resource pool.

Referring to <FIG>, the Uu interface between a UE <NUM> and a RAN node may comprise several entities within the protocol stack <NUM>. Example entities include physical layer (PHY) <NUM>, medium access control (MAC) <NUM>, radio link control (RLC) <NUM>, packet data convergence protocol (PDCP) layer <NUM>, service data adaptation protocol (SDAP) layer <NUM>, and radio resource control (RRC) layer <NUM>.

CP information such as RRC <NUM> and non-access stratum (NAS) signalling may be carried over a signalling radio bearer (SRB) while UP data may be carried over a data radio bearer (DRB).

In some networks, a number of small cells may be deployed within the coverage area of a macro cell to offload traffic from the macro cell and/or to provide improved signal quality to UEs. <FIG> shows an example deployment in which a master RAN node <NUM> provides the NG connections to the CN <NUM> and maintains an SRB <NUM> to a UE <NUM> through a primary cell <NUM>. The UE <NUM> may use a DRB <NUM> to convey UP traffic through a secondary cell <NUM> to a secondary RAN node <NUM>. This traffic may be relayed between the master <NUM> and the secondary <NUM> RAN nodes over an Xn interface.

On the network side, the UP protocol stack in a dual connectivity deployment may be split between the master RAN node <NUM> and the secondary RAN node <NUM>, as may be seen in <FIG>. The master RAN node <NUM> houses the upper layer protocol stack entities (including SDAP <NUM> and PDCP <NUM>) while the secondary RAN node <NUM> houses the lower layer protocol stack entities (RLC <NUM>, MAC <NUM> and PHY <NUM>).

While the UE <NUM> is registered with the network, it may transition between multiple modes of operation, including:.

Maintaining the UE <NUM> in the INACTIVE mode reduces radio link signalling overheads and may result in commensurate battery power savings in the UE <NUM>. Keeping the UE context in the RAN <NUM> also reduces latencies and network signalling overheads.

<FIG> illustrates an example RAN model for INACTIVE mode operations. In this example RAN model:.

The example protocol stack illustrated in <FIG> is based on the dual-connectivity model shown in <FIG>. Accordingly, the upper layer SDAP <NUM> and PDCP <NUM> protocol entities and state machines are located in the anchor RAN node <NUM>, while the lower layer RLC <NUM>, MAC <NUM> and PHY <NUM> protocol entities (and any state machines used for such an implementation) are located in the serving RAN node <NUM>. However, in contrast to the dual-connectivity model illustrated in <FIG>, the serving RAN node <NUM> does not have access to the UE-specific context <NUM> for managing transmissions over the radio link (Uu) to the UE <NUM> when the UE <NUM> is coupled to the serving RAN node <NUM>. For example, the serving RAN node <NUM> may not have any one or more of:.

The lack of radio protocol information implies that the serving RAN node <NUM> retrieves the UE context <NUM> from the anchor RAN node <NUM> in order to transition a UE <NUM> from the INACTIVE to the CONNECTED mode.

3GPP Technical Specification (TS) <NUM>, "3GPP System Architecture Evolution (SAE); Security architecture" defines a UE master cryptographic key dubbed KASME that can be derived independently by the UE and a CN CPF through an authentication and key agreement procedure. From KASME, cryptographic keys used by a RAN node for encryption and integrity protection are derived from a RAN temporal master key dubbed KeNB in LTE. A similar RAN temporal master key dubbed KgNB is defined for <NUM> New Radio (NR) operations that is derived from a UE master cryptographic key dubbed KAMF. A new RAN temporal master key, dubbed KeNB* for LTE and KgNB* for NR, is derived independently by the UE <NUM> and its current serving RAN node on every inter-cell and intra-cell handover - i.e. no keys need to be transmitted over the radio link between a UE <NUM> and the nodes within the RAN <NUM>. Separate temporal keys can then be derived from the master key for encryption and integrity protection of CP traffic and UP traffic.

In 3GPP TS <NUM>, a new KeNB may be derived using either a horizontal key chain or a vertical key chain such that a new generation of the key is based on a previous generation of the key:.

The NH key used for vertical key derivation is computed independently by the UE and a CPF in the CN. A new NH key (NH*) is derived through a KDF that takes as inputs: the current NH key; and the UE master key (e.g. KASME or KAMF). The NH* key then becomes the current NH key for subsequent operations.

When a node or function within the CN <NUM> decides to generate a new NH key (e.g. following a handover to a new serving RAN node <NUM>), it increments a next-hop chaining count (NCC) and provides the NCC and new NH key to the current serving RAN node <NUM> using a secure NG-C connection (e.g. secured using IPsec). The NCC acts as a key identifier to synchronise cryptographic operations between the UE <NUM> and the RAN <NUM>.

On a subsequent handover, the current serving RAN node <NUM> provides the value of NCC to the UE <NUM> (e.g. in a handover command). If the received NCC value is different from the value currently stored in the UE <NUM>, the UE <NUM> generates a new NH key and increments its stored value of NCC; this procedure can be repeated until the stored value of NCC matches the value received from the serving RAN node <NUM>. Once the NCC values match, the corresponding NH key is used to generate a new RAN temporal master key. Using the new RAN temporal master key (e.g. KeNB or KgNB), the UE <NUM> can generate temporal keys for cryptographic operations in the new serving cell.

RAN temporal keys are derived from the RAN temporal master key (e.g. KeNB or KgNB) and are used for encryption and integrity protection of CP traffic and UP traffic. A different temporal key can be used for each cryptographic procedure:.

In some situations, the UP keys are applied to all DRBs associated with a UE <NUM>. In other situations, different UP keys are used for different sessions; all DRBs associated with a given session could use the same keys but DRBs associated with a different session would use a different key.

In 3GPP TS <NUM>, each of the temporal keys is generated using a KDF that takes as inputs at least one of:.

Each cryptographic operation (encryption or integrity protection) uses a pseudo-random function determined by the selected cryptographic algorithm that takes as inputs at least one of:.

In accordance with examples of the present disclosure, before initiating a transition from INACTIVE to CONNECTED mode, validation of the CP message conveying a request from the UE <NUM> to the RAN <NUM> can be performed using a message integrity check (MIC) (also known as a message authentication code for integrity (MAC-I)) computed by the UE <NUM> using cryptographic keys derived for use with the anchor RAN node <NUM>. The RAN node <NUM> currently serving the UE <NUM> can transparently forward the request to the anchor RAN node <NUM> where the MIC can be validated using information in the UE context <NUM> stored at the anchor RAN node <NUM>. If the MIC is successfully validated, the anchor RAN node <NUM> may decide to keep the UE <NUM> in the INACTIVE mode or to initiate a transition to the CONNECTED mode.

The anchor RAN node <NUM> may also decide whether to retain its role of anchor for UE <NUM> or to allow the role of anchor to be moved to the new serving RAN node <NUM>. If the anchor RAN node <NUM> decides to retain its role as anchor for UE <NUM>, configuration parameters may be updated in the UE <NUM> through a CP RRC message that is protected using keys associated with the anchor RAN node <NUM>. If the anchor RAN node <NUM> decides to relocate the anchor role to the new serving RAN node <NUM>, the anchor RAN node <NUM> can provide the serving RAN node <NUM> with UE context <NUM> allowing the generation of a new set of cryptographic keys that are associated with the new serving RAN node <NUM>.

In all cases, provision can be made for determining the validity of the UE request before UE context <NUM> is transferred to the new serving RAN node <NUM> and for securing all CP communications with the UE <NUM>.

<FIG> illustrate a generic procedure <NUM>, using a modified <NUM>-step random access procedure (as described in <NPL>"). This procedure may be implemented between the UE <NUM>, serving RAN node <NUM> and anchor RAN node <NUM> described above with reference to <FIG>, and may include the following steps.

<NUM>: The anchor RAN node <NUM> decides to transition the UE <NUM> from the CONNECTED mode to the INACTIVE mode. The anchor RAN node <NUM>, having made this determination may transmit an RRC connection release message to the UE <NUM>; this message may include:.

CP temporal keys generated for use in the serving cell of the anchor RAN node <NUM> can be used for integrity protection (KRRCint') and encryption (KRRCenc') of the RRC connection release message.

<NUM>: Following receipt of the RRC connection release message from the anchor RAN node <NUM>, the UE <NUM> may initialise a periodic location notification timer. Initialization of the periodic location notification timer may be based on the maximum time between location notifications (e.g. maxUpdateTime), which may have been indicated by the anchor RAN node <NUM> (typically indicated in the RRC connection release message transmitted to the UE <NUM>).

<NUM>: While operating in the INACTIVE mode, the UE <NUM> may move into the coverage of cells controlled by a different RAN node.

<NUM>: While in the INACTIVE mode, the UE <NUM> decides to initiate an uplink (UL) transmission. This decision may, for example, be triggered by expiry of the periodic location notification timer or by the queuing of UL data that are to be transmitted.

In response to the decision to initiate an UL transmission, the UE <NUM> begins a cell selection procedure to identify a suitable cell for re-establishing a radio link connection. The RAN node controlling the selected cell is dubbed the serving RAN node <NUM>.

<NUM>: random access request (Msg1). Based on physical random access channel (PRACH) configuration broadcast as system information by the serving cell, the UE <NUM> may select a preamble (e.g. a Zadoff-Chu sequence) and transmit the selected preamble towards the serving RAN node <NUM> using the PRACH configuration. The selection of a preamble may be a random or pseudo-random selection in some examples.

<NUM>: Following receipt of the preamble from the UE <NUM>, the serving RAN node <NUM> can schedule a DL random access response (RAR) message to be sent to the UE <NUM>.

607A and 607B: random access response (Msg2). The serving RAN node <NUM> may schedule (at 607A) a DL transmission to the UE <NUM> (using a downlink control information (DCI) message encoded with a random access radio network temporary identifier (RA-RNTI) and including a DL grant) and then transmit (at 607B) the RAR to the UE <NUM>. This RAR message may include:.

<NUM>: UE <NUM> identification and access request (Msg3). Using the UL grant provided in the RAR associated with the RAPID corresponding to the random access preamble selected by the UE <NUM>, the UE <NUM> may transmit a CP message (e.g. a RRC request) to the serving RAN node <NUM>. The RRC request message may include the INACTIVE mode identifier (ueID) assigned to the UE <NUM> by the anchor RAN node <NUM> in step <NUM>. The UE <NUM> may then start a contention resolution timer.

The RRC request may also include a MIC computed using the CP integrity protection key (KRRCint') associated with the anchor RAN node <NUM> (i.e. the same integrity protection key used for the MIC of the RRC connection release message in step <NUM>).

Optionally, the RRC request may be encrypted using the CP encryption key (KRRCenc') associated with the anchor RAN node <NUM> (i.e. the same encryption key used for protection of the RRC connection release command in step <NUM>). In this case, the INACTIVE mode identifier (ueID) can be included as cleartext in a lower layer element of Msg3, e.g. a MAC control element (CE) or PDCP information element. The existence of this information element can be interpreted by the serving RAN node <NUM> as initiation of an INACTIVE mode transaction.

609A and 609B: contention resolution (Msg4). If the serving RAN node <NUM> successfully decodes an UL transmission <NUM> according to the grant provided in step 607B, it can schedule (at 609A) a transmission to the UE <NUM> (using a DCI message encoded with the C-RNTI assigned in step <NUM> and a DL grant), followed (at 609B) by a contention resolution message (Msg4) that echoes the uelD received by the serving RAN node in Msg3. Msg4 may comprise a MAC CE containing the uelD.

If the ueID received by the UE <NUM> in Msg4 matches the identifier that the UE <NUM> transmitted in Msg3, the random access is deemed successful and the UE <NUM> can monitor the physical downlink control channel (PDCCH) for subsequent DCI messages encoded with the C-RNTI assigned in step <NUM>.

If the ueID received by the UE <NUM> does not match the identifier it transmitted in Msg3, or if the contention resolution timer expires, the random access is deemed unsuccessful (e.g. another UE may have selected the same preamble in step <NUM>) and the UE <NUM> restarts the random access procedure.

<NUM>: Using information extracted from the uelD received in Msg3, the serving RAN node <NUM> identifies the anchor RAN node <NUM> associated with the UE <NUM> when it entered INACTIVE mode and initiates a transaction with the anchor RAN node <NUM> to retrieve the UE context <NUM>.

As shown starting in <FIG>, the process continues to <NUM>: The serving RAN node <NUM> transmits a UE context retrieval request towards an identified anchor RAN node <NUM>. The UE context retrieval request includes the uelD and an information element that may transparently contain the RRC request and MIC received from the UE <NUM> in Msg3 (step <NUM>).

<NUM>: Using information extracted from the received uelD, the anchor RAN node <NUM> determines a current set of temporal keys associated with the UE <NUM>. This determination may be performed in accordance with stored UE context <NUM> that can be accessed by the anchor RAN node <NUM>. The anchor RAN node <NUM> can then use the CP integrity protection key (KRRCint'), which can be either stored in the UE context <NUM> or reconstituted based on the stored UE context <NUM>, to validate the MIC provided by the UE <NUM>, to the serving RAN node <NUM>, in the RRC request (step <NUM>).

<NUM>: If the MIC is successfully validated, the anchor RAN node <NUM> transmits a UE context retrieval response to the serving RAN node <NUM>, which may contain the UE context <NUM> associated with the UE <NUM> when it entered the INACTIVE mode.

If the MIC fails, the anchor RAN node <NUM> can abort the procedure by reporting an error to the serving RAN node <NUM>. In another example, the anchor RAN node <NUM> may abort the procedure by not transmitting any reply message to the serving RAN node <NUM>. The serving RAN node <NUM> can determine that the process has failed either through the receipt of the message reporting an error, or through a determination that the anchor RAN node <NUM> is alive and has not responded within a defined time period.

<NUM>: If the serving RAN node <NUM> successfully receives a UE context retrieval response from the anchor RAN node <NUM>, it uses the received information to construct a CP RRC response to the UE <NUM>:.

in some situations, the CP RRC response may be provided by the anchor RAN node <NUM>, including a MIC computed using the anchor RAN node <NUM> CP integrity protection key (KRRCint'); the prepared response is then transparently relayed to the UE <NUM> by the serving RAN node <NUM>.

in other situations, the serving RAN node <NUM> uses the UE context <NUM> provided by the anchor RAN node <NUM> to generate a new set of cryptographic keys for use within the cell serving the UE <NUM>; the serving RAN node <NUM> uses the new keys to protect CP RRC messages subsequently exchanged with the UE <NUM>.

615A and 615B: access request acknowledgement (Msg4bis). The serving RAN node <NUM> subsequently schedules (at 615A) a DL transmission to the UE <NUM> (using a DCI encoded with the C-RNTI assigned in step <NUM> and a DL grant) and transmits (at 615B) the RRC response to the RRC request sent in Msg3 (step <NUM>).

This section describes the INACTIVE to CONNECTED (i2c) mode procedure that is initiated by a UE <NUM> and follows the generic procedure described above. In this procedure:.

The steps in this procedure (<NUM>), illustrated in <FIG>, include:.

<NUM>-<NUM>: With the UE <NUM> operating in the INACTIVE mode, the UE <NUM> decides to initiate a transition to the CONNECTED mode. This decision may, for example, be triggered by the queuing of data that will be transmitted on the UL to the RAN. In response to any of these factors, or any other determination that the UE <NUM> should transition to the CONNECTED mode, the UE <NUM> can initiate a random access procedure (<NUM>) with the serving RAN node <NUM>.

The connection release, cell selection and random access procedures are similar to steps <NUM>-<NUM> of <FIG>.

<NUM>: The UE <NUM> transmits a RRC resume request message to the serving RAN node <NUM> (e.g. in Msg3 of the random access procedure). The RRC resume request message may include the INACTIVE mode identifier (ueID) assigned to the UE <NUM> by the anchor RAN node <NUM> (e.g. in step <NUM>).

The resume request message can include a MIC such as an integrity checksum or check value computed using the CP integrity protection key (KRRCint') associated with the anchor RAN node <NUM> (i.e. the same integrity protection key used for the MIC of the connection release message in step <NUM>).

Optionally, the resume request message may be encrypted using the CP encryption key (KRRCenc') associated with the anchor RAN node <NUM>. In this case, the INACTIVE mode identifier (ueID) is included as cleartext in a lower layer element of step <NUM> (Msg3), e.g. a MAC CE or PDCP information element; the existence of this information element is interpreted by the serving RAN node <NUM> as initiation of an i2c transition.

<NUM>-<NUM>: Similar to steps <NUM>-<NUM> of <FIG>, the serving RAN node <NUM> identifies the anchor RAN node <NUM> and sends a UE context <NUM> retrieval request (<NUM>) to the anchor RAN node <NUM>. The UE context <NUM> retrieval request may include any or all of the uelD, the resume request and MIC received from the UE <NUM>. Using UE context <NUM> associated with the received ueID, the anchor RAN node <NUM> can validate the MIC provided by the UE <NUM> in the resume request and, if the validation is successful, the anchor RAN node <NUM> can retrieve the requested UE context information (<NUM>).

<NUM>: If the MIC is successfully validated, the anchor RAN node <NUM> can return a UE context retrieval response to the serving RAN node <NUM> that includes any or all of :.

<NUM>: Based on the UE context <NUM> received from the anchor RAN node <NUM>, the serving RAN node <NUM> can:.

<NUM>: The serving RAN node <NUM> transmits a message to the UE <NUM> (e.g. in Msg4bis) that includes a resume command, the cryptographic algorithm selected by the serving RAN node <NUM> and the NCC value received from the anchor RAN node <NUM>. The cryptographic algorithm and the NCC value can be provided in cleartext in a lower layer element of Msg4bis, e.g. a MAC control element (CE) or PDCP information element. The resume command can be integrity protected using the new CP integrity protection key (KRRCint) derived by the serving RAN node <NUM>. The resume command may also be encrypted using the new CP encryption key (KRRCenc) derived by the serving RAN node <NUM>. If the resume command is encrypted, the serving RAN node <NUM> may include modified RRC configuration information in this message rather than using a separate connection reconfiguration message at a later time.

<NUM>: Using the specified cryptographic algorithm, the UE <NUM> can:.

<NUM>: Using the new CP keys (KRRCenc and KRRCint), the UE <NUM> can decrypt the resume command and validate the MIC received from the serving RAN node <NUM>. In some examples, the decryption and validation may be performed separately with intervening steps.

<NUM>: If the resume command is successfully validated, the UE <NUM> sends a resume complete message (e.g. Msg5) to the serving RAN node <NUM> that can be integrity protected using the new CP integrity protection key (KRRCint) and encrypted using the new CP encryption key (KRRCenc).

<NUM>: The serving RAN node <NUM> can decrypt the received message using the CP encryption key (KRRCenc) which may have been previously derived by the serving RAN node <NUM>. The serving RAN node <NUM> can validate the MIC included in the received message using the CP integrity protection key (KRRCint).

<NUM>: If the resume complete message is successfully validated, the serving RAN node <NUM> sends a UE context retrieval complete message to the old (or previous) anchor RAN node <NUM>, confirming that the serving RAN node <NUM> has successfully assumed the role of anchor RAN node <NUM> for UE <NUM>.

<NUM>: When it receives the UE context retrieval complete message, the old anchor RAN node <NUM> may delete the stored UE context <NUM> for UE <NUM>.

The old anchor RAN node <NUM> should not delete the stored UE context <NUM> before receiving the UE context retrieval complete message because the serving RAN node <NUM> may not succeed in becoming the new anchor RAN node <NUM> for UE <NUM>, and it may be advantageous to ensure that the UE context <NUM> is not deleted until another node can assume anchor RAN node <NUM> responsibilities. For example:.

This section describes several procedures for applying the generic procedure described above to RRC messages passing between a UE <NUM> and the RAN <NUM> in order for a UE <NUM> to notify the RAN <NUM> of its current location. Location notification may be initiated by a UE <NUM> due to expiration of a periodic timer or due to mobility outside of a designated RNA <NUM>.

In both cases, location notification may or may not result in a change of anchor RAN node <NUM> and/or an update to the configuration parameters used by the UE <NUM> while operating in the INACTIVE mode. The updated configuration parameters may include:.

Relocation of the anchor role (also referred to as responsibilities of an anchor RAN node <NUM>) to the serving RAN node <NUM> is a decision made by the current anchor RAN node <NUM>. Because a change in the anchor role may involve additional processing (and consumption of battery power) in the UE <NUM> (e.g. for the generation of new cryptographic keys), the current anchor RAN node <NUM> may retain its role for UE <NUM> when the UE <NUM> moves outside the designated RNA <NUM>; retaining its role as anchor is predicated on the ability of the RAN node to communicate to the set of potential serving RAN nodes <NUM> within a new RNA <NUM>.

Similarly, the current anchor RAN node <NUM> may decide to relocate the role of anchor to the serving RAN node <NUM> following a periodic location update from the UE <NUM> even though the UE <NUM> is still within its designated RNA <NUM>. The current anchor RAN node <NUM> may make this decision based, for example, on its current load, on a projected trajectory for a mobile UE <NUM>, or on network latencies associated with the backhaul network between RAN nodes or between the RAN <NUM> and CN <NUM> nodes associated with the UE <NUM>.

In this procedure, validation of the location notification is performed by the anchor RAN node <NUM> and the updated INACTIVE mode configuration is returned by the anchor RAN node <NUM> to the serving RAN node <NUM>. UE context <NUM> is not provided to the serving RAN node <NUM>, therefore a new set of cryptographic keys is not generated at the serving RAN node <NUM>; as a consequence, the updated configuration is protected by the anchor RAN node <NUM> using the CP keys associated with the anchor RAN node <NUM>. In this procedure, the serving RAN node simply acts as a transparent relay for signalling between the UE <NUM> and the anchor RAN node <NUM>.

The steps in this procedure (<NUM>), illustrated in <FIG>, include:
<NUM>-<NUM>: With the UE <NUM> operating in the INACTIVE mode, the periodic location notification timer expires and the UE <NUM> transmits a location notification message that is received by the serving RAN node <NUM>. The serving RAN node <NUM> can act as a relay to forward or otherwise transmit this message to the anchor RAN node <NUM> indicated by the uelD received from the UE <NUM>.

This procedure is similar to steps <NUM>-<NUM> described above with reference to <FIG>.

<NUM>: If the MIC provided by the UE <NUM> is successfully validated, the anchor RAN node <NUM> may decide to not relocate the anchor role to the current serving RAN node <NUM> (e.g. the anchor RAN node <NUM> may decide to keep the anchor role instead of relocating the responsibilities to the serving RAN node <NUM>). In this case, the anchor RAN node <NUM> returns a UE context retrieval response to the serving RAN node <NUM> that may include:.

The location update response may also be encrypted using a CP encryption key (KRRCenc') associated with the anchor RAN node <NUM>.

<NUM>: Based on the received response from the anchor RAN node <NUM>, the serving RAN node <NUM> transmits a message to the UE <NUM> (e.g. Msg4bis) that includes the location notification response provided by the anchor RAN node <NUM>.

<NUM>: Using the CP keys derived for use with the anchor RAN node <NUM> (KRRCenc' and KRRCint'), the UE <NUM> decrypts the location notification response and validates the MIC.

If the location update response is successfully validated, the UE <NUM> may optionally send a location notification complete message (e.g. Msg5) to the serving RAN node <NUM> as confirmation that it is resuming INACTIVE mode operation.

In this procedure, following validation of the location notification by the current anchor RAN node <NUM>, the anchor RAN node <NUM> decides to relocate the anchor role to the serving RAN node <NUM>. As a result, the anchor RAN node <NUM> returns the UE context <NUM> to the serving RAN node <NUM> where, following procedure <NUM>, the serving RAN node <NUM> generates a new set of cryptographic keys and instructs the UE <NUM> to return to CONNECTED mode for reconfiguration by the serving - now new anchor - RAN node.

The steps in this procedure (<NUM>), illustrated in <FIG>, include:
<NUM>-<NUM>: With the UE <NUM> operating in the INACTIVE mode, a periodic location notification timer expires and the UE <NUM> transmits a location notification message to the serving RAN node <NUM>. The serving RAN node <NUM> then relays this message to the anchor RAN node <NUM> indicated by the uelD received from the UE <NUM>.

<NUM>: If the MIC is successfully validated, the anchor RAN node <NUM> may decide to relocate the anchor role to the current serving RAN node <NUM>.

<NUM>: The anchor RAN node <NUM> returns a UE context <NUM> retrieval response to the serving RAN node <NUM> that may include any or all of:.

<NUM>-<NUM>: The UE context <NUM> returned by the anchor RAN node <NUM> is an indication to the serving RAN node <NUM> that it should assume the role of anchor RAN node for UE <NUM>. Similar to steps <NUM>-<NUM> of <FIG>, the serving RAN node <NUM> establishes a new set of temporal cryptographic keys and configures the UE <NUM> for operation with the serving - now new anchor - RAN node.

Reception of a resume command at step <NUM> rather than a location notification response is an indication to the UE <NUM> that it is being returned to the CONNECTED mode for possible reconfiguration in a new anchor RAN node.

If necessary, the new anchor RAN node <NUM> can return the UE <NUM> to the INACTIVE mode at a later time.

Turning now to <FIG>, there is shown a flow chart, shown generally at <NUM>, showing example actions taken by a network node of a RAN for managing a context of a UE operating in an inactive mode.

One example action <NUM> is to receive, from a second network node, a context retrieval request comprising a UE identifier and a first message, the first message being protected with a first cryptographic key.

One example action <NUM> is to validate the first message using a stored cryptographic key associated with a UE context indicated by the UE identifier.

The result of the validation action <NUM> may be considered in decision <NUM>. If the message is not valid <NUM>, then processing proceeds to action <NUM>. If the message is valid <NUM>, then processing proceeds to decision <NUM>.

In some non-limiting examples, one example action <NUM> may be to indicate, by the context retrieval response, that a determination has been made that the first message is not valid.

In some non-limiting examples, one example action <NUM> may be to indicate, by the relocation indication, that a determination has been made not to relocate the UE context.

In some non-limiting examples, a determination whether or not to relocate the UE context may be made at decision <NUM>. If the determination is not to relocate the UE context <NUM>, then processing proceeds to action <NUM>. If the determination is to relocate the UE context <NUM>, then processing proceeds to action <NUM>.

In some non-limiting examples, one example action <NUM> may be to include a RRC response in the context retrieval response.

In some non-limiting examples, one example action <NUM> may be to indicate, by the relocation indication, that a determination has been made to relocate the UE context.

In some non-limiting examples, one example action <NUM> may be to include the UE context and a second cryptographic key in the context retrieval response.

One example action <NUM> may be to send a context retrieval response to the second network node, the context retrieval response containing the relocation indication of whether the UE context is to be relocated to the second network node.

One example action <NUM> is to receive, from the UE, a UE identifier and a first message, the first message being protected with a first cryptographic key.

One example action <NUM> is to send the UE identifier and the first message to a second network node.

One example action <NUM> is to receive, from the second network node, a second message protected with a second cryptographic key.

One example action <NUM> is to send the second message to the UE.

Turning now to <FIG>, there is shown a flow chart, shown generally at <NUM>, showing example actions taken by a network node of a RAN for managing a context of a UE operating in an inactive mode.

One example action <NUM> is to receive, from the second network node, a context associated with the UE.

One example action <NUM> is to derive, based on the context, a second cryptographic key.

One example action <NUM> is to send a second message to the UE protected with the second cryptographic key.

Accordingly, a first aspect of the present disclosure provides a method at a network node of a RAN for managing a context of a UE operating in an INACTIVE mode, the method comprising: receiving, from a second network node, a context retrieval request comprising a UE identifier and a first message, the first message being protected with a first cryptographic key; validating the first message using a stored cryptographic key associated with a UE context indicated by the UE identifier; and sending a context retrieval response message to the second network node, the context retrieval response message containing a relocation indication of whether the UE context is to be relocated to the second network node.

A further aspect of the present disclosure provides a method at a network node of a RAN for managing a context of a UE operating in an INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; sending the UE identifier and the first message to a second network node; receiving, from the second network node, a second message protected with a second cryptographic key; and sending the second message to the UE.

A further aspect of the present disclosure provides a method at a network node of a RAN for managing a context of a UE operating in an INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; sending the UE identifier and the first message to a second network node; receiving, from the second network node, a context associated with the UE; deriving, based on the context, a second cryptographic key; and sending a second message to the UE protected with the second cryptographic key.

Accordingly, an aspect of the present disclosure provides a method at a network node of a radio access network (RAN) for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from a second network node, a context retrieval request comprising a user equipment identifier and a first message protected with a first cryptographic key; and sending a context retrieval response message to the second network node, the context retrieval response message containing an indication of whether the UE context is to be relocated to the second network node.

In an embodiment, the sending the context retrieval response if performed can be responsive to validating the first message in accordance with the first cryptographic key. In an embodiment, the sending of the context retrieval response can be performed responsive to a determination of whether to relocate the UE context to the second network node. In an embodiment, the network node can be an anchor node associated with the user equipment.

A further aspect of the present disclosure provides an anchor node of a radio access network (RAN), the anchor node comprising: at least one processor; and non-transitory computer readable software instructions configured to control the at least one processor to implement a method for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from a second network node, a context retrieval request comprising a user equipment identifier and a first message protected with a first cryptographic key; and sending a context retrieval response message to the second network node, the context retrieval response message containing an indication of whether the UE context is to be relocated to the second network node.

A further aspect of the present disclosure provides a method at a network node of a radio access network (RAN) for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; identifying, based on the UE identifier, a second network node; sending the UE identifier and the first message to the second network node; receiving, from the second network node, a second message protected with a second cryptographic key; and sending the second message to the UE.

In an embodiment, the second network node can be determined in accordance with the UE identifier. In an embodiment, the second message can comprise at least one of: an identifier to be used by the UE for further operations in the inactive mode; an indication of the RAN notification area where the UE can receive service while operating in the inactive mode; and a maximum time between location notifications initiated by the UE. In an embodiment, the network node can be a serving node associated with the user equipment.

A further aspect of the present disclosure provides a serving node of a radio access network (RAN), the anchor node comprising: at least one processor; and non-transitory computer readable software instructions configured to control the at least one processor to implement a method for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; identifying, based on the UE identifier, a second network node; sending the UE identifier and the first message to the second network node; receiving, from the second network node, a second message protected with a second cryptographic key; and sending the second message to the UE.

A further aspect of the present disclosure provides a method at a network node of a radio access network (RAN) for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; identifying, based on the UE identifier, a second network node; sending the UE identifier and the first message to the second network node; receiving, from the second network node, a context associated with the UE; deriving, based on the context, a second cryptographic key; and sending a second message to the UE protected with the second cryptographic key.

In an embodiment, the second network node can be determined in accordance with the UE identifier. In an embodiment, the second cryptographic key can be determined in accordance with the context associated with the UE. In an embodiment, the network node can be a serving node associated with the UE. In an embodiment, the second message can comprise any one or more of: an identifier to be used by the UE for further operations in the inactive mode; an indication of the RAN notification area where the UE can receive service while operating in the inactive mode; and a maximum time between location notifications initiated by the UE.

A further aspect of the present disclosure provides a serving node of a radio access network (RAN), the anchor node comprising: at least one processor; and non-transitory computer readable software instructions configured to control the at least one processor to implement a method for managing a UE context of a user equipment (UE) operating in the INACTIVE mode, the method comprising: receiving, from the UE, a UE identifier and a first message protected with a first cryptographic key; identifying, based on the UE identifier, a second network node; sending the UE identifier and the first message to the second network node; receiving, from the second network node, a context associated with the UE; deriving, based on the context, a second cryptographic key; and sending a second message to the UE protected with the second cryptographic key.

As will be appreciated by those skilled in the art, the above disclosure teaches a method for execution by a RAN node comprising: receiving, by a node in a RAN, from a second network node, a context retrieval request comprising an identifier of a user equipment, UE, operating in an inactive mode and a first message, the first message being protected with a first cryptographic key; validating, by the node, the first message using a stored cryptographic key associated with a UE context indicated by the identifier of the UE; and sending, by the node, a context retrieval response to the second network node, the context retrieval response containing a relocation indication of whether the UE context is to be relocated to the second network node.

In an embodiment of this method the relocation indication is responsive to validating the first message in accordance with the stored cryptographic key. In embodiments of the above methods, the relocation indication is responsive to a determination of whether to relocate the UE context to the second network node. In other embodiments of the above methods the context retrieval response comprises a second message protected with a second cryptographic key. Optionally, the second message is a radio resource control, RRC, message. In another embodiment, the second message comprises at least one of an identifier to be used by the UE for further operations in the inactive mode; an indication of a RAN notification area,RNA, where the UE can receive service while operating in the inactive mode; and a maximum time between location notifications initiated by the UE. In embodiments of the above method, the context retrieval response comprises the UE context and a second cryptographic key. In embodiments of the above methods the node is an anchor node.

As will be appreciated by those skilled in the art, the above disclosure teaches a method for execution by a RAN node comprising receiving, by a node in a radio access network (RAN) from a user equipment (UE), an identifier of a UE operating in an inactive mode and a first message, the first message being protected with a first cryptographic key; sending, by the node, the identifier of the UE and the first message to a second network node; receiving, by the node, from the second network node, a second message protected with a second cryptographic key; and sending, by the node, the second message to the UE.

In an embodiment of the above method, the second network node is determined in accordance with the identifier of the UE. In embodiments of the above methods, the second message comprises at least one of an identifier to be used by the UE for further operations in the inactive mode; an indication of a RAN notification area (RNA) where the UE can receive service while operating in the inactive mode; and a maximum time between location notifications initiated by the UE. In embodiments of the above methods, the node is a serving node in the RAN.

As will be appreciated by those skilled in the art, the above disclosure teaches a method for execution by a RAN node comprising receiving, by a node in a radio access network (RAN) from a user equipment (UE), an identifier of a UE operating in an inactive mode and a first message, the first message being protected with a first cryptographic key; sending, by the node, the identifier of the UE and the first message to a second network node; receiving, by the node, from the second network node, a context associated with the UE; deriving, by the node based on the context, a second cryptographic key; and sending, by the node, a second message to the UE protected with the second cryptographic key.

In an embodiment of the above method the second network node is determined in accordance with the identifier of the UE. In embodiments of the above methods, the second message comprises any one or more of: an identifier to be used by the UE for further operations in the inactive mode; an indication of a RAN notification area (RNA) where the UE can receive service while operating in the inactive mode; and a maximum time between location notifications initiated by the UE. In embodiments of the above methods the node is a serving node in the RAN.

Claim 1:
An anchor node of a radio access network, RAN, the anchor node comprising a memory (<NUM>) and at least one processor (<NUM>) configured to:
receive (<NUM>), from a second network node, a context retrieval request comprising an identifier of a user equipment, UE, operating in an inactive mode and a first message, the first message being protected with a first cryptographic key;
validate (<NUM>) the first message using a stored cryptographic key associated with a UE context indicated by the identifier of the UE; and
send (<NUM>) a context retrieval response to the second network node, the context retrieval response containing a relocation indication of whether the UE context is to be relocated to the second network node;
wherein the context retrieval response comprises a second message protected with a second cryptographic key, and the second message comprises:
an identifier to be used by the UE for further operations in the inactive mode;
an indication of a RAN notification area, RNA, where the UE can receive service while operating in the inactive mode; and
a maximum time between location notifications initiated by the UE.