Method and user equipment for selecting core network

Abstract

The invention relates to a method for a user equipment operating on a first base node of a cellular network, the first base node communicatively coupled to two core networks of the cellular network, the user equipment operating in an open data exchange session by means of a data exchange context terminated in a selected one of the two core networks, the user equipment also maintains a first device identity received from said selected core network, the method comprising the following steps for the user equipment:-identifying at least one second base node of said cellular network,-checking whether said at least one second base node is able to access the selected core network,-if not,-determining that the at least one second base node is able to access the selected core network. Sending a connection reestablishment message to a second base node capable of accessing a core network (hereinafter referred to as a second core network) different from the selected core network, receiving a second device identity of the second core network by the second base node, sending an acknowledgement message to the second base node, -resuming the data exchange session with the second base node over a second core network using the second device identity.

Description

Technical Field

[0001] The present invention relates to a method for selecting a core network of a cellular network comprising at least two core networks and also to a user equipment using said method.

[0002] Furthermore, the invention relates to a base node of a cellular network. The invention also relates to a method for said base node. Background Art

[0003] With the emergence of new technical standards, especially New Radio (5G), discussions began on how to make the LTE (4G) network architecture coexist and work closely with the 5G core architecture. Accordingly, it was decided to introduce 5G in the so-called non-standalone (NSA) mode, which means that 5GgNodB (GNB) will provide a new air interface for 5G-compliant user equipment (UE), but the core network behind is using the available 4G infrastructure. However, the full deployment of 5G should also include the introduction of 5G infrastructure.

[0004] Therefore, for the user equipment, there is the following possibility: its pre-occupied gNodeB or eNodeB (hereinafter referred to as basic node) may be connected to the 4G core (Evolved Packet Core EPC) or the 5G core (Next Generation Core, NextGenCore, NGC).

[0005] Generally speaking, it is the cellular network, especially the infrastructure nodes, alone or in combination with other cellular network components, that decide which core network to select. However, in the case of NB-IoT - which is a category of LTE where user equipment supports limited bandwidth and processing power, and should also be available as a 5G category - it is the user equipment that decides which core network to select / request. This is due to the fact that the user equipment request terminates directly at the core network, so once more than one core network is available, the selection is necessary.

[0006] Especially because different core networks can be adapted to specific services, i.e. in the 5G Core, so-called slices for service provision will be available and the relevant information will be broadcast by the eNB, so that interested user equipment can choose said 5G core network accordingly. User equipment not interested in such services can choose to move towards the 4G Core to fully exploit the energy saving features specified in the EPC connection context, while legacy devices do not actually have a choice and are connected to the EPC Core anyway. In addition to the UE selection, the network can also send UEs that can support both core networks to one network or the other for load sharing purposes. Therefore, when establishing a connection with the new base node, such UEs can also decide to change the core network to their preferred core.

[0007] In ETSI 3GPP Technical Report TR23.724 V.1.10, it is proposed that the corresponding infrastructure node sends an indication about the availability of multiple core networks in the broadcasted system information, and the user equipment should perform core network selection as part of the RRC connection establishment request.

[0008] However, what is not addressed in this case is the situation where the user equipment has established a connection or data exchange context with the serving base node, and before finally terminating the connection, the user equipment leaves the coverage area or wants to recover and reuse the data exchange context of the serving base node. In NB-IoT, mobility is handled by the user equipment, not by the base node that performs the handover. The UE detects a radio link failure (RLF) and establishes an RRC-connection-reestablishment at the next neighboring base node on the grounds of "radio link failure", preferably including its used identification (such as RNTI or TMSI) and the identity of the previously used serving base node. The new base node can then obtain the context from the indicated previous serving base node and continue operation.

[0009] However, there may be situations where a neighboring infrastructure node is unable to support the same core network as the previous infrastructure node. This will result in a connection being lost and a new connection needing to be established, since no context could be acquired simply due to the fact that access to the previously used core network was unavailable.

[0010] Therefore, the object of the present invention is to overcome the above disadvantages and to propose a solution to the mobility problem for such user equipment.

[0011] As this is an idea that facilitates migration to new technology standards and the same is expected to be introduced in future generations, the issues mentioned are not limited to the 4G / 5G coexistence scenario.

[0012] Therefore, there is a need in the art for further alternative and advantageous solutions. Summary of the invention

[0013] To this end, according to a first aspect of the invention, a method of operating a user equipment according to claim 1 is proposed. According to a second aspect of the invention, a user equipment according to claim 5 is also proposed. In a third aspect of the invention, a first core network element according to claim 8 is proposed. In a fourth aspect of the invention, a second core network element according to claim 10 is proposed. In a fifth aspect of the invention, a method of operating a second core network element according to claim 15 is proposed. In a sixth aspect of the invention, a base node according to claim 17 is proposed.

[0014] According to a first aspect of the present invention, a method for a user equipment operating on a first infrastructure node of a cellular network is proposed, the first infrastructure node being communicatively coupled to two core networks of the cellular network, the user equipment operating in an open data exchange session by means of a data exchange context terminated in a selected one of the two core networks, the user equipment also maintaining a first device identity received from the selected core network, the method comprising the following steps for the user equipment:

[0015] - identifying at least one second infrastructure node of said cellular network,

[0016] - checking whether the at least one second infrastructure node can access the selected core network,

[0017] - if not, sending a connection reestablishment message to a second infrastructure node that can access a core network different from the selected core network (hereinafter referred to as the second core network),

[0018] - receiving, by the second infrastructure node, a second device identity of the second core network,

[0019] - Send a confirmation message to the second infrastructure node,

[0020] - resuming the data exchange session with the second infrastructure node via a second core network using the second device identity.

[0021] This aspect relates to a user equipment operating in a cellular network. The user equipment is particularly equipped with a communication circuit and a processing circuit for communicating with an infrastructure node of the cellular network. The user equipment and the infrastructure node and the cellular network particularly support one of GSM (2G), UMTS (3G), LTE (4G), NR (5G) or higher cellular wireless communication technology standards. The cellular network supports at least two technical standards. This is achieved by having at least two core networks with different technical standards. In the example of LTE and NR networks, this will especially be the Evolved Packet Core (EPC) defined in 4G and the Next Generation Core (NGC) defined in 5G. The present invention certainly covers other combinations. In addition, it is also covered that the cellular network includes more than two core networks, for example, additionally includes 2G and 3G cellular networks.

[0022] Regarding the infrastructure node that the user equipment camps on, this is in the address scenario coupled to at least two core networks. This is in particular an eNodeB (which is a 4G infrastructure node) or a gNodeB (5G infrastructure node).

[0023] The proposed scenario is particularly applicable to the case of base nodes supporting subcategory Narrowband IoT (NB-IoT), which is an embedded category for user devices with lower processing capabilities, especially those designed for the Internet of Things (IoT) and which only allow addressing and decoding of a subset of the frequency range using a modulation scheme different from the rest of the frequency range of the base node.

[0024] NB-IoT is the LPWA (Low Power Wide Area) solution for both technologies and is therefore supported by both LTE and NR. It is envisaged that a UE capable of operating in NB-IoT can operate on either an eNodeB or a gNodeB in NB-IoT. This is especially true for future devices, as legacy devices will not understand the signalling and information related to NGC and the possibilities / features offered there. Therefore, the UE will always choose the EPC. However, for future user equipment, consideration of the support for connectivity to both core networks and the corresponding availability of the user equipment needs will result in requesting a connection to one network or the other.

[0025] The method starts with the situation that a user equipment is camped on the base node and is operating in an ongoing or suspended (intended to be resumed) data exchange session characterized by means of a data exchange context. This means in particular that the user equipment is in an open connection or has established such a connection, which is temporarily suspended but is intended to be resumed with another user equipment or a remote server, for example via the Internet, and data should be exchanged. The relevant control information and the necessary side conditions / parameters are part of the data exchange context. The data exchange context has an identifier, the so-called context identity, and the data exchange context can be resumed accordingly by means of the context identity while maintaining the connection to the same core network.

[0026] This data exchange environment or data exchange session terminates in one of the core networks. Termination means that the communication path is routed through the core network elements of the respective core network. Each core network comprises one or more core network elements that support the technical standards of the core network. The data exchange session is created there in particular using known methods. Alternatively, the data exchange session is suitable for different base nodes with different core network elements. In any case, the user equipment receives a first device identity from the selected core network, which identifies the device and facilitates identification of the corresponding data exchange context at the core network element.

[0027] This method is particularly suitable for the following situation: the user equipment leaves the coverage area of ​​the first base node it camps on. The coverage area is also called a cell. In this case, the user equipment will then try to identify at least one second base node with better signaling conditions or at least acceptable connection conditions because it has left the coverage area that can provide suitable services for the first base node.

[0028] According to an advantageous embodiment, it is proposed that the step of identifying at least one second infrastructure node is performed in response to detecting a radio link failure in the communication with the first infrastructure node.

[0029] Preferably, for NB-IoT, mobility management is performed in the user equipment. This means in particular that if the number of radio link failures during a data exchange session is above a predetermined threshold, the user equipment will try to identify a second infrastructure node in order to safely continue the data exchange session. This is done in that the UE operating in NB-IoT selects the second infrastructure node based on the best radio conditions belonging to the PLMN, without evaluating the connected core network.

[0030] Known methods are applied to identify the second infrastructure node and decide to change from the first infrastructure node to the second infrastructure node.When a Radio Link Failure (RLF) is detected, ie the connection is lost in the previous cell, this process is called RRC connection reestablishment.

[0031] For the case of NB-IoT, RRC connection re-establishment with the reason of “radio link failure” applies even in the case of an open data exchange session, which means that it is driven by the user equipment itself.

[0032] For other categories of user equipment, especially those supporting LTE Cat M, Cat 1, etc., mobility between cells will preferably be guaranteed by handover. In the case of handover driven by the infrastructure node, the UE measures and reports neighboring cells in advance, and the infrastructure node decides to "handover" to another suitable cell and maintain the transferred connection. However, the measurements required to maintain the connection in parallel in connected mode and perform the related signaling in the event of a degradation of the communication link quality exceed the capabilities of the NB-IoT device, so mobility is accomplished via RLF.

[0033] In any case, when the second infrastructure node is identified, it needs to be ensured that the data exchange session can be resumed, which means that the data exchange continues without establishing a new connection. This will require that the infrastructure node has access to the selected core network.

[0034] However, the second infrastructure node may be a traditional 4G eNodeB that can only access the 4G core. If the current data exchange context is operated by the selected core network of the next generation core network, the infrastructure node cannot continue the data exchange context of the data exchange session. So this situation needs to be checked.

[0035] To this end, the user equipment checks whether the second infrastructure node can access the selected core network.

[0036] The relevant information can be retrieved from the broadcast of the selected base node. As mentioned before, the connected core has no influence on the selection process, because the base node with the best radio capabilities is selected. Any search for a base node connected to a specific core network may not be successful and will take a long time and consume energy, so the connected core is not taken into account when selecting the next available base node.

[0037] When the check shows that the infrastructure node supports access to the selected core network, then the connection reestablishment message with the first device identity and context identity will succeed (RRC connection reestablishment with reason "RLF"). This means that the data exchange session on the existing data exchange context represented by the context identity can be resumed afterwards. The context and device identity are only meaningful to the one first core network and are not known in the second core network.

[0038] However, when the infrastructure node does not support access to the selected core network, a different solution is required. This is where the present invention comes into play.

[0039] This method branch is suitable for sending a connection reestablishment message to the base node. The difference from the existing process is that the RRC connection reestablishment message preferably does not have a simple cause / purpose of "reestablishment due to RLF", but instead it is an RRC connection reestablishment message with a cause / purpose of "core context acquisition". The message includes in particular a first device identity and at least one context identity. The connection reestablishment message should in particular be forwarded to a second core network element of another core network to which the base node is communicatively coupled.

[0040] At least one context identity refers to the possibility that the user equipment has more than one data exchange context. Furthermore, one or more context identities that are not (any more) valid may be submitted, and only for valid data exchange contexts a get operation is performed to resume the data exchange session.

[0041] According to a preferred embodiment, it is proposed that the user equipment further maintains a context identity provided by the selected core network, wherein the connection reestablishment message comprises a core network context acquisition instruction providing the context identity and the first device identity.

[0042] The context identity identifies said data exchange context.Together with the first device identity, in particular the TMSI or RNTI provided by the first core network, the parameters for the depicted data exchange context should be easily determined within the first core network.

[0043] Preferably, it comprises or is supplemented with a core network identity, which describes which core network identity handles the context.

[0044] The core network context acquisition instruction preferably also provides information related to the core network, or more specifically to a core network element of the core network that issued or maintains the identified context.

[0045] With this embodiment, it is simplified for the addressed core network element to identify the core node element. By this, this does not necessarily mean that the addressed core network element will need to directly access the identified core network element, but rather simplifies routing. This is particularly useful when the context identity is not unique in the first core network.

[0046] In response to the connection reestablishment message, the user equipment receives a message including at least a second device identity from the second infrastructure node. The second device identity is created when a new data exchange context is created in the second core network.

[0047] Therefore, the user equipment sends a confirmation message which confirms receipt of the previous message and indicates that the data exchange session can be resumed. The confirmation message in particular includes the new second device identity for confirmation.

[0048] The data exchange session is then resumed with the second infrastructure node on the second core network by using the second device identity. In the cellular network, all necessary steps are then taken. Preferably, the context identity of the second data exchange context is also provided to the user equipment, preferably for the next connection reestablishment message.

[0049] The method of the invention is advantageous in that it removes all steps that the user equipment needs to take between core networks. Furthermore, there is only a low delay compared to the case where the infrastructure node supports access to the initially selected core network.

[0050] The biggest advantage is that the data exchange session can continue without the need for re-establishment. Re-establishment may be rejected by the communication endpoints. Therefore, the method of the present invention simplifies the processing of the user equipment, makes the connection more reliable, and ultimately leads to less cellular network signaling and less power consumption of the user equipment.

[0051] In another preferred embodiment, it is proposed that the user equipment maintains at least one first encryption key received from the first base node, thereby using the at least one first encryption key to perform the step of receiving the second device identity, and also includes the step of receiving a standard for generating at least one second encryption key from the second base node, thereby using the at least one second encryption key to perform the step of resuming the data exchange session.

[0052] By this embodiment, the important problem of protecting communications is solved. This shows that the proposed method is applicable to today's cellular networks, which need to be protected from hacking, interception or surveillance.

[0053] Known cellular networks protect the security of their communications by negotiating one or more encryption keys with the user equipment for each data exchange session. However, these encryption keys are bound to the core network. Therefore, when establishing a data exchange context, at least one first encryption key is received and maintained at the user equipment, i.e., at least one first encryption key is stored and used for messages of the data exchange context.

[0054] However, key generation may vary between the first and second core networks, so the encryption keys of the first core network are not available for serving user equipment in the second core network.Therefore, for the method steps shown, it is necessary to ensure that a new set of encryption keys are created and securely exchanged.

[0055] To this end, it is proposed that the message received at the user equipment with the new second device identity is encrypted in particular using at least one first encryption key.

[0056] However, together with this message, or in a separate message, the user equipment also receives criteria for generating at least one second encryption key to secure communications with the second infrastructure node and the second core network.

[0057] In a simple embodiment, this criterion covers the provision of a second encryption key.

[0058] Alternatively, the method steps include providing a key component, a random number and / or an authentication token, which together with a shared secret (e.g., a master key, in particular stored in a central register of a USIM card and a core network connected to the user equipment) allows the user equipment to generate a new key. Typically, this provides that the user equipment sends a key derived from the second encryption key back to the base node until both parties have the second encryption key available. This method is known and is called authentication and key agreement (AKA), which helps the user equipment and the core network establish a symmetric key to encrypt the exchanged data.

[0059] Therefore, when such negotiation of the second encryption key is performed, the following messages are encrypted using the second encryption key. This particularly relates to messages that are part of the step of resuming the data exchange session. The encryption key may be negotiated first and then the connection reestablishment process may be performed, or vice versa. Both sequences are covered in the present invention.

[0060] Furthermore, this also particularly affects confirmation messages to the base nodes.

[0061] It has been shown that the proposed method of selecting an infrastructure node and another core network can also operate with established security measures without generating too much overhead on both the user equipment and the core network.

[0062] According to a second aspect of the present invention, there is provided a user equipment operating on a first infrastructure node of a cellular network, the first infrastructure node being communicatively coupled to two core networks of the cellular network, the user equipment being configured to operate in a data exchange session by means of a data exchange context terminated in a selected one of the two core networks, and to maintain a first device identity received from the selected core network, wherein the user equipment is configured to:

[0063] - identifying at least one second infrastructure node of said cellular network,

[0064] - checking whether the at least one second infrastructure node can access the selected core network,

[0065] - if not, sending a connection reestablishment message to a second infrastructure node that can access a core network different from the selected core network (hereinafter referred to as the second core network),

[0066] - receiving, by the second infrastructure node, a second device identity of the second core network,

[0067] - Send a confirmation message to the second infrastructure node,

[0068] - resuming the data exchange session with the second infrastructure node via a second core network using the second device identity.

[0069] The user equipment according to this aspect of the invention is in particular equipped with transmitting and receiving circuits, in particular a transceiver. In addition, it comprises a processing circuit for executing control software to control the transmitting and receiving circuits. Preferably, the user equipment comprises permanent and / or volatile memory. The user equipment is also preferably connected to a subscriber identity card, in particular a USIM or an (e)UICC, which is detachable or soldered.

[0070] The user equipment operates together with at least one infrastructure node of the sixth aspect of the present invention.

[0071] The second aspect of the present invention has the same advantages as the first aspect of the present invention.

[0072] According to a third aspect of the present invention, a first core network element of a first core network is provided, the first core network being part of a cellular network comprising at least two core networks, the first core network element being communicatively coupled to at least one second core network element (SCNE) of a second core network being part of the cellular network, wherein the first core network element is configured to:

[0073] - receiving a core context retrieval message including a device identity and a context identity from one of the second core network elements,

[0074] - obtaining a first data exchange context based on the context identity, the first data exchange context comprising a set of parameters related to the first data exchange context,

[0075] - providing a context message to the second core network element, the context message comprising at least part of the set of parameters regarding the first data exchange context.

[0076] This aspect of the invention relates to a first core network element of a cellular network, wherein the cellular network has at least two core networks. Each core network comprises a pair of core network elements, wherein the first core network element is part of the first core network. Thus, the second core network element according to the fourth aspect of the invention is part of the second core network.

[0077] The first core network element is communicatively coupled to at least one second core network element, whether such coupling is direct or indirect via an intermediate or another first core network element.

[0078] The first core network element comprises communication circuitry for communicating with at least one infrastructure node, with other first core network elements, and / or for communicating with the at least one second core network element.

[0079] Furthermore, it preferably provides processing circuitry, volatile and permanent memory.

[0080] The user equipment of the first aspect of the present invention requests a data exchange session by means of a data exchange context, which is operated through a first core network. The user equipment is served by the first infrastructure node.

[0081] The first core network element may process a first data exchange context of the user equipment before leaving the cell area of ​​the first infrastructure node.

[0082] Depending on the duration of the first data exchange context and the spatial behavior of the user equipment, the first core network element may have created the first data exchange context. This includes providing the first device identity to the requesting user equipment. Preferably, it includes providing the user equipment with a context identifier.

[0083] Potentially, the first core network element has never been involved in a data exchange context, but is intended to perform the steps as depicted in this aspect of the invention.

[0084] According to this aspect, the first core network element is configured to receive a core context acquisition message including a device identity from one of the second core network elements. This occurs in particular after the user equipment leaves the cell area of ​​the first infrastructure node and sends a connection reestablishment message to the second infrastructure node, which is not directly communicatively coupled to the first core network element.

[0085] Using the device identity provided with the core context get message, the first core network element is able to retrieve a context applicable to the user equipment identified by the device identity from an accessible set of open first data exchange contexts. Such a set of first data exchange contexts is preferably available to all first core network elements of the first core network, since in this case it is not important for the second core network element to address the correct first core network element.

[0086] Preferably, the core context acquisition message also includes a context identity provided to the user equipment when establishing the data exchange context or restoring the data exchange context. With the context identity, corresponding parameters related to the first data exchange context can be easily located and retrieved.

[0087] Preferably, the core context acquisition message also includes the core node identity of the first core network element that served the user equipment before it left the cell area of ​​the first base node. In this case, the first core network element that receives the core context acquisition message may access the first core network element identified by the core node identity so that it supports or processes subsequent steps.

[0088] This first data exchange context includes a set of parameters related to the first data exchange context. Such parameters may include an indication of the device identity and a communication endpoint, such as an IP address or another user equipment in this or another (cellular) network, encryption keys, connection and / or service type information.

[0089] If the first data exchange context is not found, this fact is reported to the requesting second core network element.

[0090] Otherwise, the first core network element responds to the requesting second core network element with a context message including at least part of said set of parameters for said first data exchange context. Such a set of parameters includes at least those data required to recreate the second data exchange context.

[0091] The described process may also be initiated by another first core network element for continuing the first data exchange context.

[0092] In another preferred embodiment, it is proposed to receive a message from the second core network element indicating confirmation of creating a second data exchange context to replace the first data exchange context, and in response, at least one of closing and deleting the first data exchange context is performed.

[0093] This embodiment particularly relates to a phase in which the second core network element creates a second data exchange context.After the user equipment confirms receipt of the second device identity and related data, in particular the encryption key creation criteria, the first core network element preferably then receives a further request from the second core network element indicating said confirmation.

[0094] In this case, the first core network element is informed that the first data exchange context is no longer needed. Therefore, it takes the necessary steps to close and / or delete the first data exchange context. This may include informing the first core network and / or other components of the cellular network in this manner.

[0095] This embodiment ensures that no "zombie" data exchange contexts are maintained and fill up the database and slow down further communications.

[0096] Additionally or alternatively, a timer operates to delete the data exchange context when no operation (such as data transmission, etc.) involving the data exchange context is performed within a given time.

[0097] According to a fourth aspect of the present invention, a second core network element of a second core network is provided, the second core network being part of a cellular network comprising at least two core networks, the second core network element being communicatively coupled to at least one first core network element of a first core network being part of the cellular network, the second core network element being further communicatively coupled to at least one infrastructure node, wherein the second core network element is configured to:

[0098] - receiving a core context request message from the base node, the core context request message comprising a first device identity identifying a user equipment operating with the base node and at least one context identity,

[0099] - sending a core context acquisition message to said first core network element,

[0100] - determining that said first device identity and said context identity are for a data exchange session with a first core network element,

[0101] - receiving from the first core network element a context message comprising context parameters of a first data exchange context of the user equipment,

[0102] - generating a new device identity for said user equipment,

[0103] - creating a second data exchange context using said received context parameters, and

[0104] - providing a base node with a set of context parameters related to the second data exchange context and the second device identity.

[0105] The second core network element is, like the first core network element, a core network element of a cellular network, wherein the second core network element is part of a second core network. It is communicatively coupled to a base node supporting a technical standard of the second core network. According to a third aspect of the invention, it is also communicatively coupled to at least one first core network element. It is preferably also communicatively coupled to other second core network elements of the first core network element.

[0106] Via the communication coupling, the second core network element is configured to receive a core context request message from the second infrastructure node. This occurs in particular after the user equipment of the first aspect of the invention leaves the cell area of ​​the first infrastructure node and identifies the second infrastructure node.

[0107] Preferably, it is known that the second infrastructure node cannot access the first core network, but can access the second core network. Alternatively, a core context request message is a method to solve this problem.

[0108] If this is the case, some method is needed to reestablish the first data exchange context so as to resume the data exchange session after the cell is changed from the first infrastructure node to the second infrastructure node. This process is called obtaining the data exchange context.

[0109] Preferably, the core context request message is an already defined message type, but in this case - when an acquisition of a data exchange context should be performed - the core context request message is filled with additional information elements indicating the envisaged procedure for acquiring the first data exchange context.

[0110] Thus, the second core network element receives a core context request message from the infrastructure node.

[0111] The core context message includes the first device identity. Preferably, it also includes at least one context identity. With the at least one context identity, the second core network element can determine whether the user equipment identified with the first device identity is processed in a data exchange context processed by the second core network. If this is not the case, the result can be provided to the base node. In this case, the user equipment is likely to be operated in another core network, in particular the first core network.

[0112] Upon request or on its own initiative, the second core network element is configured to obtain information of a currently open first data exchange context from the corresponding first core network element, the first data exchange context being characterized by a relevant context identity. To this end, the second core network element is configured to send a core context acquisition message to the first core network element.

[0113] Preferably, the context request message further comprises a core node identity identifying a first core network element, wherein the send core context acquisition message is addressed to the first core network element by means of the core node identity.

[0114] With this embodiment, the retrieved core node identity is used to address the first core network element. This may include directly addressing the first core network element via the core node identity. Alternatively, the second core network element can access one or more first core network elements and send a core context acquisition message to one of the core network elements, the message carrying the core node identity, in order to retrieve the first data exchange context via the addressed first core network element.

[0115] In any case, the second core network element expects to retrieve, in response, from the first core network element a set of parameters related to the depicted first data exchange context.

[0116] Furthermore, it is preferably configured to receive a set of capability information related to said user equipment from the first infrastructure node.

[0117] With the parameter set and potentially additional available information, in particular capabilities, the second core network element in particular creates a second data exchange context. This occurs together with creating a new second device identity. Preferably, the new second device identity is created first and then used to create the second data exchange context. Alternatively, the two steps are performed together, or in another order.

[0118] When the second data exchange context is created and the second device identity is available, the requesting base node is informed of the result. This includes providing a set of context parameters related to the second data exchange context and the new second device identity to the requesting base node. The context parameters also include, in particular, the context identity of the second data exchange context.

[0119] The described second core network element is a key element for solving the problem. It is configured to receive a request from a user equipment via an infrastructure node and to collect necessary parameters from the first core network in order to recreate the second data exchange context from the parameters of the first data exchange context.

[0120] This saves the user equipment from having to take extra steps to resume the data exchange session. In addition, it simplifies the migration of the cellular network to support the first core network (usually introduced later), coexisting with the access of infrastructure nodes from the first infrastructure nodes, which are capable of accessing more than one core network of different technical standards.

[0121] In another preferred embodiment, it is proposed that the second core network element is further configured to create a criterion for generating at least one second encryption key, wherein the second core network element is configured to provide the criterion to the base node together with said providing the context parameter set to the base node.

[0122] With this embodiment, the handling of encryption keys is covered by involving the second core network element. To this end, the second core network element is configured to create and provide criteria for generating at least one second encryption key to secure communications within the second data exchange context.

[0123] As indicated for the method for a user equipment according to the first aspect of the invention, the set of criteria preferably comprises a random number and / or an authentication token, and / or a shared secret, such as a master key, which allows the user equipment to create a second encryption key, and to perform further exchanges until both the user equipment and the second core network element are equipped with at least one second encryption key. This procedure follows the known AKA procedure.

[0124] In a simple embodiment, the second core network element creates at least one second encryption key and provides it to the infrastructure node and ultimately to the user equipment.

[0125] Obviously, this helps to protect the security of the communication and also helps to resume the data exchange session on the second data exchange context. Continuing to use the first encryption key is useless because it requires control of the key, which requires involving the first core network.

[0126] However, this does not exclude another preferred embodiment, wherein the core context request message further comprises at least one first encryption key, wherein the message for providing the context parameter set is encrypted by means of the at least one first encryption key.

[0127] With this embodiment, the second core network element retrieves the first encryption key using the core context request message. This is preferably used to encrypt a message with the context parameters using said first encryption key.

[0128] Alternatively, but more time consuming for the second core network element, it is also covered to first negotiate a second encryption key with the user equipment and then provide the UE with context information encrypted with the second encryption key. The second core network element will then not need to work with the first encryption key, for example if a different encryption method is defined.

[0129] With this embodiment, the retrieval of the new second data exchange context is secured from the outset.

[0130] Thereafter, the resumed data exchange session is performed by securing the data exchange session via the second data exchange context using the second encryption key.

[0131] In another preferred embodiment, it is proposed to receive a confirmation message comprising the second device identity from the base node, and in response to indicating said confirmation to the first core network element for at least one of closing and deleting the context.

[0132] This embodiment is used to complete the phase of recreating the second data exchange context from the first data exchange context at the second core network element.

[0133] To this end, the second core network element is configured to receive an indication that the user equipment acknowledges receipt of the parameters of the second data exchange context (and possibly the second encryption key) by means of sending the second device identity.

[0134] To allow the data exchange context stored in the first core network to be cleaned up, the second core network element sends an indication to at least one first core network element. With the indication, the first core network can close and delete the first data exchange context. With the activation and operation of the new second data exchange context, the first data exchange context is no longer needed.

[0135] This aspect of the invention shows the advantages of the proposed solution to the problem being solved. Only a few components are involved and they do what they are supposed to do: communicate with other components, create data exchange contexts, create key generation criteria, etc.

[0136] If the data exchange session uses services of the first core network element, such as a dedicated 5G slice, then a decision needs to be made on how to proceed. First, it needs to be checked whether the used service is available for the second core network.

[0137] If not available, it is possible, depending on the service type, to provide a service type close to the used service in the second core network. Otherwise, the data exchange session is abandoned, in this case preferably with an exception. The first option requires intelligence of the first and / or second core network elements involved. Alternatively or additionally, further message flows with the base node and / or the user equipment are necessary in order to clarify whether there is a way to continue the data exchange session or abandon it in this case.

[0138] In a fifth aspect of the invention, a method for operating a second core network element of a cellular network is proposed, the second core network element being communicatively coupled to at least one first core network element of the cellular network, the second core network element also being communicatively coupled to at least one infrastructure node, the method comprising the following steps for the second core network element:

[0139] - receiving from the infrastructure node a core context request message including a first device identity identifying a user equipment operating with the infrastructure node,

[0140] - determining by means of a first data exchange context of a first core network element that said first device identity is operating in a data exchange session,

[0141] If this is the case, a core context acquisition message is sent to the first core network element,

[0142] - receiving from the first core network element a context message comprising context parameters of a first data exchange context of the user equipment,

[0143] - generating a new device identity for said user equipment,

[0144] - creating a second data exchange context using said received context parameters, and

[0145] - providing a base node with a set of context parameters related to the second data exchange context and the second device identity.

[0146] The fifth aspect of the present invention has the same advantages as the fourth aspect of the present invention.

[0147] According to a sixth aspect of the present invention, a base node of a cellular network is provided, which is communicatively coupled to at least one second core network element of a core network of the cellular network and is configured to serve a plurality of user equipments, wherein the base node is configured to:

[0148] - receiving a connection re-establishment message from one of the served user equipments, wherein the connection re-establishment message comprises an indication of a second core network element belonging to a core network different from the core network to which the base node is connected, and a device identity and at least one context identity of the user equipment,

[0149] - sending a core context request message comprising a device identity and at least one context identity to a second core network element,

[0150] - receiving in response a set of context parameters associated with the second data exchange context and the new device identity,

[0151] - Forwarding the new device identity to said served user equipment.

[0152] This aspect relates to an infrastructure node of a cellular network communicatively coupled to a second core network element according to the fourth aspect of the invention. The infrastructure node is in particular not directly capable of communicating with the first core network element according to the third aspect of the invention.

[0153] When a user equipment according to the second aspect of the invention decides to camp on an infrastructure node after an open data exchange session with the infrastructure node operable with a first core network element, it should send a connection reestablishment message to the infrastructure node. This includes identifying a device identity of the user equipment in a first data exchange context of the first core network.

[0154] It also includes an indication that the user equipment is operating with a core network element belonging to a core network different from the core network to which the base node is connected. This occurs in particular after the user equipment has sent a first connection re-establishment message but has received a response that the data exchange context is not available in a second core network to which the base node is communicatively coupled (in particular only communicatively coupled).

[0155] In response to receiving the message, the base node is configured to send a core context request message to a second core network element to which the base node is communicatively coupled. The core context message includes at least a device identity and preferably a context identity. With the message, the first data exchange context is intended to be obtained.

[0156] It will instruct the second core network element to retrieve the parameters of the first data exchange context from the first core network and create a new second data exchange context.

[0157] Therefore, the base node then retrieves the set of context parameters associated with the second data exchange context that is then created. This includes in particular the new device identity.

[0158] The information is forwarded to the requesting user device.

[0159] Preferably, parameters for creating a second encryption key are also retrieved from the second core network element and forwarded to the user equipment.

[0160] According to another preferred embodiment, the base node is further configured to provide a confirmation message including said new device identity to the second core network element in response to receiving a confirmation message from said serving user equipment.

[0161] This step enables the infrastructure node to complete the data exchange context re-creation phase by receiving and forwarding the confirmation message with the new device identity.

[0162] Thereafter, the user equipment resumes the data exchange session using the infrastructure node via a new second data exchange context terminated at the second core network element.

[0163] As shown, the present invention advantageously solves the depicted problem and proposes a message flow between the involved elements that integrates seamlessly in the existing structure and allows all involved entities to continue the data exchange session with another core network of the cellular network with low impact. BRIEF DESCRIPTION OF THE DRAWINGS

[0164] The following description and drawings set forth certain illustrative aspects in detail and indicate some of the various ways in which the principles of the embodiments may be employed. The features and advantages of the present invention will become apparent when reading the following description and drawings of advantageous embodiments given as illustrative and non-limiting examples.

[0165] Figure 1 shows a user equipment of the type to which the present invention is applicable as an embodiment in combination with a base node according to the prior art;

[0166] Figure 2 In an exemplary embodiment, a user device is shown operating non-statically with two base nodes;

[0167] Figure 3 A sequence diagram showing a preferred embodiment of the method of the present invention. DETAILED DESCRIPTION

[0168] Figure 1 A user equipment UE according to the prior art is schematically shown. The user equipment UE pre-occupies an infrastructure node eNB1 supporting the NB-IoT category. Therefore, the infrastructure node eNB according to this embodiment may be a 4G or 5G infrastructure node, because NB-IoT is at least backward compatible with both defined technical standards.

[0169] The base node eNB1 is connected to the core network elements of at least two core networks, in this case, the first core network element FCNE supports 5G (New Radio) and the second core network element SCNE supports 4G (LTE). The core networks of the corresponding technical standards are called 4G Evolved Packet Core (EPC) and 5G Next Generation Core (NGC).

[0170] Each core network provides different capabilities. For example, the 5G core network NGC may have the ability to support certain slices, such as for ultra-reliable communications or dedicated to machine-type communications.

[0171] For a user equipment UE that leaves the coverage area of ​​the infrastructure node eNB1, when it operates in an open data exchange session, it has to be concerned about mobility. For this situation, the prior art does not provide a solution.

[0172] to this end, Figure 2 The exemplary embodiment in FIG. 1 illustrates the method of the present invention.

[0173] like Figure 2The user equipment UE shown is operating non-statically, which means that it is moving. It is located in the cell C1 of the first infrastructure node eNB1. In the example shown, after camping on the first infrastructure node eNB1, it 1 The connection is established by selecting one of the core networks. In this case, a connection is established by means of a first core network element FCNE, which is indicated by a solid line, as opposed to a dotted line to a second core network element SCNE of the EPC.

[0174] Then at time t 2 , the user equipment UE moves away from the infrastructure node eNB1, which means leaving the cell C1 and entering the cell C2 of the second infrastructure node eNB2.

[0175] It turns out that the signal from the infrastructure node eNB1 is poorly received and a radio link failure (RLF) occurs. This indicates to the user equipment UE operating in NB-IoT that it cannot continue to operate with the currently serving infrastructure node.

[0176] Therefore, the user equipment UE selects a more suitable infrastructure node, which is the second infrastructure node eNB2 in this case.

[0177] However, the infrastructure node eNB2 cannot access both core networks, but can only access the EPC represented by the second core network element SCNE. In this case, the infrastructure node eNB2 has no way to retrieve the 1 The data exchange context that is set up to create a data exchange session.

[0178] In order to solve this problem, it is preferable to perform the Figure 3 message flow.

[0179] The process flow starts with a user equipment UE located in a cell area C1 of a first infrastructure node eNB1. The infrastructure node is capable of accessing a first core network element FCNE and a second core network element SCNE of a first and a second core network, in particular a 5G Next Generation Core Network (NGC) and a 4G Evolved Packet Core Network (EPC).

[0180] The first infrastructure node eNB1 broadcasts information related to resources of the two core networks with a message M1. In response to camping on the infrastructure node eNB1 and establishing a data exchange session, the user equipment UE selects the 5G next generation core by selecting the corresponding resources with a message M2.

[0181] The first infrastructure node eNB1 receives the request, forwards it to the first core network element FCNE of the 5G NGC and requests a context ID. This includes establishing a context with a message M3.

[0182] In response, the first core network element provides the data exchange context parameters, in particular the device identity, to the first base node with a message M4 upon success. Preferably, more information is provided, in particular the core network identity and / or a context identity identifying the first data exchange context established. The received data (at least a part thereof) is forwarded to the user equipment with a message M5.

[0183] Thus, now a data exchange session on the first data exchange context is established and running, as shown by message M6, which is a data exchange message that should terminate at the FCNE. This may include sending measurement data from the metering device.

[0184] In step M7, the user equipment leaves the coverage area of ​​the first infrastructure node eNB1 in such a way that the signal of the first infrastructure node is very poor, and the user equipment evaluates whether at least one second infrastructure node eNB2 is more suitable for communication according to the suitability criteria. This occurs in particular through multiple radio link failures. If this is the case, the user equipment decides to reselect to the second infrastructure node eNB2.

[0185] Now the user equipment needs to continue operating the data exchange session.Up to now, the user equipment UE does not necessarily know whether the second infrastructure node eNB2 is accessible to the first core network element FCNE, which can easily retrieve the data exchange context and simply continue operating the data exchange session with it.

[0186] Alternatively, the user equipment retrieves information from the second infrastructure node eNB2, for example by broadcasting or any other type of data exchange, in particular during a reselection phase, which has only access to the second core network element SCNE being part of the LTE core network.

[0187] In any case, the user equipment sends a connection reestablishment message M8 to the second infrastructure node. The message comprises in particular the retrieved device identity and, in this exemplary embodiment, at least one associated context identity. Preferably, it also comprises an identifier of the first core network element, here referred to as the core node identity, which is in particular retrieved by the above message M5.

[0188] The second infrastructure node eNB2 sends this request to the accessible second core network element SCNE in a message M9. There, it is preferably discovered, in particular by means of the core node identity, that the user equipment was previously served by a core node element of another core network.

[0189] Therefore, it sends a core context acquisition message M10 to another first core node element of the core network (which is processing the identified data exchange context) using the core node identity in order to retrieve the data exchange context parameters. This does not necessarily mean that the first core network element FCNE identified by the core node identity is directly accessed. It is quite possible that any first core network element of the 5G core network receives the message, wherein the first core network element processing the data exchange context is identified by the core node identity. The addressed first core network element FCNE will then process all necessary steps for retrieving the data exchange context information within its core network.

[0190] These are provided to the second core network element SCNE with a message M11. The second core network element SCNE uses these received information to create a new data exchange context and a new second device identity. These information and the second device identity as well as the context identity of the new second data exchange context are provided to the second infrastructure node eNB2 with a message M12 and to the user equipment with a message M13. These messages are in particular encrypted with the first encryption key negotiated between the user equipment and the first core network element.

[0191] Preferably, the message also includes criteria for generating a new set of encryption keys for the upcoming communication. This is necessary because the initially used keys from the first core network element FCNE cannot be reused by the second core network element.

[0192] Such key generation may require more messaging between the user equipment and the second core network element until both securely retrieve the encryption key.

[0193] The user equipment then sends a confirmation message to the infrastructure node eNB2 with a message M14, which the infrastructure node eNB2 then forwards to the second core network element SCNE with a message M15. The confirmation comprises in particular the new second device identity.

[0194] When the second core network element SCNE receives this confirmation, it determines that the second data exchange context has been well established. Therefore, it can instruct the first core network element FCNE with a message M16 to close and / or delete the first data exchange context. Again, it may be that another component of the 5G core network actually does this work, but the addressed first core network element confirms the deletion with a message M17, etc.

[0195] This information is not important for the user equipment, since with this confirmation the user equipment can assume that it can now resume the data exchange session. This is done with a message M18 to the base node eNB2, or a message M19 to the second core network element. This message is in particular encrypted with the encryption key created from the message M13.

[0196] The confirmation message M14 can also be encrypted with this key. This is not mandatory as there is no data that specifically needs to be protected.

[0197] Now, the user equipment can continue the data exchange session based on the newly created second data exchange context through the second core network element SCNE.

[0198] If the data exchange session includes service parameters that are not supported by the second network, for example 5G services like ultra-low latency operation, there are two options.

[0199] One is that the relevant parameters will be replaced by appropriate default values. Preferably, the message to the user equipment indicates that the replacement has taken place. Therefore, the user equipment can decide not to continue the data exchange session in this case or accept this replacement.

[0200] Another is that the data exchange context is indicated as not being recoverable such that a context request message sent by the device is rejected and a new session is established (abnormal case abort).

[0201] By means of the message flow shown, it is achieved in a manner with low impact on the user equipment that an established data exchange session can continue despite it being changed to not being able to access the infrastructure node of the core network originally used.

[0202] In the above detailed description, reference is made to the accompanying drawings, which illustrate in a diagrammatic manner specific embodiments in which the present invention may be implemented. These embodiments are described in sufficient detail to enable those skilled in the art to implement the present invention. It should be understood that the various embodiments of the present invention, although different, are not necessarily mutually exclusive. For example, without departing from the scope of the present invention, the specific features, structures or characteristics described herein in conjunction with one embodiment may be implemented in other embodiments. In addition, it should be understood that the position or arrangement of each element in each disclosed embodiment may be modified without departing from the scope of the present invention. Therefore, the above detailed description is not intended to be limiting, and the scope of the present invention is limited only by the appended claims properly interpreted and the full range of equivalents given by the claims.

Claims

1. a first core network element of a first core network, the first core network being part of a cellular network comprising at least two core networks, the first core network element being communicatively coupled to a second core network element of a second core network being part of the cellular network, in, The first core network element is configured to: - receiving a core context acquisition message including a device identity and a context identity from a second core network element, - obtaining a first data exchange context based on the context identity, the first data exchange context comprising a set of parameters related to the first data exchange context, and - providing a context message to the second core network element, the context message comprising at least part of the set of parameters regarding the first data exchange context.

2. The first core network element according to claim 1, is further configured to receive a message from the second core network element, the message indicating a message confirming creation of a second data exchange context to replace the first data exchange context, In response, at least one of closing and deleting the first data exchange context is performed.

3. a second core network element of a second core network, the second core network being part of a cellular network comprising at least two core networks, the second core network element being communicatively coupled to a first core network element of a first core network being part of the cellular network, the second core network element being further communicatively coupled to the base node, in, The second core network element is configured to: - receiving a core context request message from the base node, the core context request message comprising a first device identity identifying a user equipment operating with the base node and at least one context identity, - sending a core context acquisition message to said first core network element, - determining the first device identity, and the context identity is used for a data exchange session of a first core network element, - receiving from the first core network element a context message comprising context parameters of a first data exchange context of the user equipment, - generating a new device identity for said user equipment, - creating a second data exchange context using said received context parameters, and - providing a base node with a set of context parameters related to the second data exchange context and the second device identity.

4. The second core network element according to claim 3, in, The context request message also includes a core node identity identifying the first core network element, Therein, the sending of the core context acquisition message is addressed to the first core network element by means of the core node identity.

5. The second core network element according to claim 3, is also configured to create criteria for generating at least one second encryption key, in, The second core network element is configured to provide the criteria to the base node together with providing the context parameter set to the base node.

6. The second core network element according to claim 5, in, The core context request message further includes at least one first encryption key, Therein, the message for providing the context parameter set is encrypted by means of the at least one first encryption key.

7. The second core network element according to claim 3, is further configured to receive a confirmation message from the base node, the confirmation message indicating confirmation of creation of the second data exchange context and including the second device identity, and In response, the confirmation is indicated to the first core network element to at least one of close and delete the first data context.

8. A method for operating a second core network element of a second core network of a cellular network comprising at least two core networks, the second core network element being communicatively coupled to a first core network element of the cellular network, the second core network element being further communicatively coupled to an infrastructure node, The method comprises the following steps for the second core network element: - receiving from the infrastructure node a core context request message including a first device identity identifying a user equipment operating with the infrastructure node, - determining that said first device identity is operating in a data exchange session by means of a first data exchange context of a first core network element, If this is the case, a core context acquisition message is sent to the first core network element, - receiving from the first core network element a context message comprising context parameters of a first data exchange context of the user equipment, - generating a new device identity for said user equipment, - creating a second data exchange context using said received context parameters, and - providing a base node with a set of context parameters related to the second data exchange context and the second device identity.

9. The method according to claim 8, Also comprising the step of the second core network element creating a criterion for generating at least one second encryption key, in, The criteria are provided to the base node together with the step of providing the context parameter set to the base node.

Images