Patent ID: 12213201

FIG.1schematically shows a user equipment UE according to the prior art. The user equipment UE is camping on a base node eNB1supporting the NB-IoT category. The base node eNB according to this embodiment might therefore be a 4G or a 5G base node, as NB-IoT is for both technology standards defined, at least backwards compatible.

The base node eNB1is connected to core network elements of at least two core networks, in this case the first core network element FCNE, which supports 5G (New Radio) and the second core network element SCNE, supporting 4G (LTE). The core networks of the respective technology standards are called for 4G Evolved Packet Core (EPC) and for 5G NextGen-Core (NGC).

Each core network provides different capabilities. E.g. the 5G core network NGC might have the capability of supporting certain slices, e.g. for ultra-reliable communication or dedicated for machine-type communication.

For a user equipment UE leaving the coverage area of the base node eNB1, it has to care for mobility when operating in an open data exchange session. For this situation the prior art offers no solution.

For doing so the inventive method is illustrated by an exemplifying embodiment inFIG.2.

The user equipment UE as shown inFIG.2is operating non-stationary, that means it is moving. It is situated in cell C1of the first base node eNB1. In the shown example after camping on the first base node eNB1it is setting up a connection at time t1with the selection of one of the core networks. The connection is in this case set up by means of the first core network element FCNE, which is indicated by a solid line as opposed to the dashed line to the second core network element SCNE of the EPC.

Then at time t2the user equipment UE moved away from the base node eNB1, that means out of cell C1into cell C2of the second base node eNB2

It turned out that the signals from base node eNB1are received that bad, that radio link failures (RLF) appear. This indicates to a user equipment UE operating in NB-IoT, that it cannot continue operating with said currently serving base node.

Hence the user equipment UE selects a better suitable base node, in this case the second base node eNB2.

However the base node eNB2does not have access to both core networks, only to the EPC, represented by the second core network element SCNE. In this situation the situation appears, that the base node eNB2has no means to retrieve the data exchange context that was setup for creating the data exchange session at time t1.

To solve that issue the message flow ofFIG.3according to an exemplifying embodiment of the invention is preferably executed.

This process flow starts with a user equipment UE which is situated in the cell area C1of a first base node eNB1. This base node has access to 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 NextGenCore (NGC) and a 4G Evolved Packet Core (EPC).

The first base node eNB1broadcasts with message M1information relating to resources for both core networks. In response for camping on the base node eNB1and setting up a data exchange session, the user equipment UE selects the 5G NextGenCore by picking the respective resources with message M2.

The first base node eNB1takes this request, forwards it to the first core network element FCNE of the 5G NGC with a request for a context ID. This includes setting up a context with message M3.

In response the first core network element provides when successful with message M4to the first base node the data exchange context parameter, in particular the device identity. More information are preferably provided, in particular the core network identity and/or the context identity identifying the established first data exchange context. The received data, are at least parts thereof, are forwarded with message M5to the user equipment.

Hence now the data exchange session over the first data exchange context is setup up and running, as indicated by message M6, which is a data exchange message that is supposed to terminate at the FCNE. This may comprise sending measurement data from a metering device.

At step M7the UE leaves the coverage area of the first base node eNB1in that way, that the signals of the first base node are that bad, that the user equipment evaluates if at least one second base node eNB2is according to the suitability criteria better suited for communication. This is in particular happening through a plurality of radio link failures. If this is the case, the user equipment decides to reselect to the second base node eNB2.

Now the user equipment has the need to continue the running data exchange session. By now the user equipment UE does not necessarily know if the second base node eNB2has access to a first core network element FCNE, which could easily retrieve the data exchange context and simply continue operating the data exchange session with it.

Alternatively the user equipment retrieves e.g. through a broadcast or any other kind of data exchange, in particular during the re-selection phase, the information from the second base node eNB2, that it is only able to access a second core network element SCNE being part of the LTE core network.

In any case the user equipment sends a connection re-establish message M8to the second base node. This message in particular comprises the retrieved device identity and in this exemplifying embodiment at least one related context identity. Preferably it also comprises an identifier of the first core network element, here called core node identity, which it in particular retrieved through message M5above.

The second base node eNB2sends this request with message M9to the accessible second core network element SCNE. There it is preferably figured out, in particular by means of the core node identity, that the user equipment was by now served by a core node element of another core network.

Consequently it uses the core node identity to send a core context fetch message M10to another first core node element of the core network, that is handling the identified data exchange context, in order to retrieve the data exchange context parameter. This does not necessarily mean that the first core network element FCNE, which is identified by the core node identity, is directly accessed. It is rather possible that any of the first core network elements of the 5G core network receives a message, wherein the first core network element which was handling the data exchange context is identified through the core node identity. The addressed first core network element FCNE will than handle within its core network all necessary steps to retrieve the data exchange context information.

These are provided to the second core network element SCNE with message M11. The second core network element SCNE creates a new data exchange context with these received information and creates a new second device identity. These information and the second device identity and the context identity of the new second data exchange context are provided with message M12to the second base node eNB2and with message M13to the user equipment. These messages are in particular encrypted with a first encryption key that was negotiated between the user equipment and the first core network element. Preferably this message also comprises criteria for generating a new set of encryption keys for the coming communication. This is necessary as the originally used keys from the first core network element FCNE cannot be reused by the second core network element.

It is likely that this key generation requires some more messaging between the user equipment and the second core network element, until both have securely retrieved the encryption key.

The user equipment then sends with message M14an acknowledgment message to base node eNB2, which then forwards this message with message M15to the second core network element SCNE. This acknowledgment in particular comprises the new second device identity.

When the second core network element SCNE receives this acknowledgment it is sure that the second data exchange context was well established. Hence it can instruct with message M16to close and/or delete the first data exchange context at the first core network element FCNE. Again it may be another component of the 5G core network which actually does the work, but the addressed first core network element confirms with message M17the deletion etc.

This information is not important for the user equipment as it may assume with the acknowledgment that it can now resume the data exchange session. This is done with message M18to the base node eNB2, respectively message M19to the second core network element. This message is in particular encrypted with the created encryption key from message M13.

Also the acknowledgement message M14may be encrypted with this key. As this has no big data which need to be secured, this is not mandatory.

Now the user equipment can continue with the data exchange session on basis of the new created second data exchange context via the second core network element SCNE.

In case that the data exchange session comprises service parameters that are not supported by the second network, e.g. 5G services like ultra-low latency operation, then there are two options.

First the related parameters will be replaced by appropriate default values. Preferably it is indicated in a message to the user equipment, that this replacement has happened. So the user equipment may decide not to continue the data exchange session under that conditions, or to accept this replacement.

Second the data exchange context is indicated as not being able to be resumed as such, i.e. the context request message sent by the device is rejected and hence a new session is set up (abnormal condition abort).

With the shown message flow it is achieved, that in a manner with low impact for the user equipment the established data exchange session can be continued although it changed to a base node which has no access to the originally used core network.

In the above detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. For example, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The above detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled.