5g tn ntn interworking improvement by joint registration

Abstract

Systems and methods for registering a user equipment include: upon losing connection to a first network to which the UE was registered, requesting by the UE to attach to a second network; sending by the UE, to the second network, an indication to retrieve, from the first network, a set of data relating to the UE previously transmitted to the first network by the UE; verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network; and registering the UE on the second network using at least a part of the retrieved set of data relating to the UE.

Description

5G TN NTN INTERWORKING IMPROVEMENT BY JOINT REGISTRATIONFIELD OF THE INVENTION

[0001] The invention relates generally to switching between networks, in particular to signaling of user equipment capabilities between 5G terrestrial and non-terrestrial networks.BACKGROUND

[0002] Fifth generation (5G) non-terrestrial network (NTN) capability was introduced within the third-generation partnership project (3GPP) in the context of Release 17. However Release 17 was subject to time pressures and focused mainly on bug fixing for new radio (NR) issues identified in the field in addition the 5G terrestrial network was already discussed within 5G Release 15 and hence needed to be considered as stable and deployed and hence unchangeable. As a consequence 5G NTN needed to be adapted to said architecture. Accordingly, 5G NTN was introduced non- optimally by adapting 5G NR so that it is suitable for NTN and mimicking 5G functionality as far as possible, which includes duplicating the entire registration procedure as well. 5G NTN and 5G TN (terrestrial network) are separate operating networks.

[0003] As such, 5G NTN registration and 5G TN are entirely separate procedures and need to be entirely executed upon each change between NTN and TN network.

[0004] Furthermore, for NTN Release 17, non-contiguous coverage behavior was introduced, e.g. where a satellite of an NTN indicates when a next satellite of the NTN will cover a UE, which may be important as there may be long periods of time (e.g. more than 1 hour) between satellite coverage. In particular, for low Earth orbit (LEO) satellites, there may only be 2-4 minutes of coverage at a fixed point on Earth once every 12 hours. Hence, depending on the number of satellites in an NTN constellation there may be longer non-contiguous coverage times. During said non-NTN coverage time a UE that is camping on the NTN does not need to look for the NTN, for example it can deactivate related access stratum (AS) functions. However, this may present disadvantages.

[0005] Embodiments of the invention aim to address improving the interworking between NTN and TN registration procedures, such as NTN and TN registration procedures in 5G.BRIEF SUMMARY OF THE INVENTION

[0006] According to one or more embodiments of the invention, there is provided a method for registering a user equipment “UE”, the method comprising: upon losing connection to a first network to which the UE was registered, requesting by the UE to attach to a second network; sending by the UE, to the second network, an indication to retrieve, from the first network, a set of data relating to the UE previously transmitted to the first network by the UE; verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network; and registering the UE on the second network using at least a part of the retrieved set of data relating to the UE.

[0007] According to some embodiments, the first network is one of: a terrestrial network or a nonterrestrial network; and the second network is one of: a terrestrial network or a non-terrestrial network.

[0008] According to some embodiments, the set of data relating to the UE comprises UE capability information.

[0009] According to some embodiments, the UE capability information previously transmitted to the first network comprises data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network.

[0010] According to some embodiments, the indication to retrieve the set of data relating to the UE comprises sending the second network at least an identifier related to the first network, e.g. one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; and / or an identity of the UE on the first network.

[0011] According to some embodiments, the identity of the UE on the first network includes a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network.

[0012] According to some embodiments, the TIMSI is accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network.

[0013] According to some embodiments, the step of verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network, comprises: performing, by the UE and the second network, a mathematical operation on at least some of the data relating to the UE; and comparing a result of the mathematicaloperation performed by the UE and a result of the mathematical operation performed by the second network, wherein the set of data relating to the UE retrieved from the first network is verified as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network.

[0014] According to some embodiments, the mathematical operation is performed on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; and / or a secret value stored by the UE.

[0015] According to some embodiments, the mathematical operation comprises at least one of: a hash function; a modulo operation; a shift function; a least significant bit “LSB” calculation; and / or a most significant bit “MSB” calculation.

[0016] According to some embodiments, a terrestrially located core network element of the second network retrieves the set of data relating to the UE from a terrestrially located core network element of the first network.

[0017] According to one or more embodiments, there is provided a user equipment “UE” configured to: register on a first network and transmit to the first network a set of data relating to the UE; request to attach to a second network upon losing connection to the first network to which the UE was registered; indicate to the second network to retrieve from the first network the set of data relating to the UE previously transmitted to the first network by the UE; verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network; and register on the second network using at least a part of the retrieved set of data relating to the UE.

[0018] According to some embodiments, the set of data relating to the UE comprises UE capability information.

[0019] According to some embodiments, the UE capability information comprises data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network.

[0020] According to some embodiments, the UE is configured to provide the second network with at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; and / or an identity of the UE on the first network.

[0021] According to some embodiments, the identity of the UE on the first network includes a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network.

[0022] According to some embodiments, the TIMSI is accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network.

[0023] According to some embodiments, the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and compare a result of the mathematical operation performed by the UE with a result of a mathematical operation performed by the second network, wherein the user equipment is further configured to verify the set of data relating to the UE retrieved from the first network by the second network as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network.

[0024] According to some embodiments, the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and send a result of the mathematical operation performed by the UE to the second network for comparison.

[0025] According to some embodiments, the result of the mathematical operation performed by the UE is sent as part of the indication to the second network to retrieve from the first network the set of data relating to the UE.

[0026] According to some embodiments, the UE is configured to perform the mathematical operation on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; and / or a secret value stored by the UE.

[0027] According to some embodiments, the mathematical operation comprises at least one of: a hash function; a modulo operation; a shift function; a least significant bit “LSB” calculation; and / or a most significant bit “MSB” calculation.

[0028] According to one or more embodiments, there is provided a network configured to perform the role of a first network in one or more methods disclosed herein, the first network being configured to: store, as part of a registration, a set of data received from a UE registering on thenetwork, the set of data relating to the UE; and send, to a second network, the set of data relating to the UE upon a request by the second network.

[0029] According to one or more embodiments, there is provided a network configured to perform the role of a second network in one or more methods disclosed herein, the second network being configured to: retrieve, from a first network, by way of a request, a set of data relating to a UE requesting to attach to the second network; verify, with the UE, that the correct set of data relating to the UE has been retrieved from the first network; and register the UE on the second network using the retrieved set of data relating to the UE.

[0030] According to one or more embodiments, there is provided a system comprising the user equipment disclosed herein, the network configured to perform the role of a first network disclosed herein, and the network configured to perform the role of a second network disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Non-limiting examples of embodiments of the disclosure are described below with reference to figures attached hereto. Dimensions of features shown in the figures are chosen for convenience and clarity of presentation and are not necessarily shown to scale. The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may be understood by reference to the following detailed description when read with the accompanied drawings. Embodiments are illustrated without limitation in the figures, in which like reference numerals indicate corresponding, analogous, or similar elements, and in which:

[0032] Fig. 1 shows an example of a problem which may be solved by some embodiments of the invention;

[0033] Fig. 2 shows a flowchart of a method for registering a user equipment “UE”, according to some embodiments of the invention;

[0034] Figs. 3A-3D show example network scenarios according to some embodiments of the invention;

[0035] Figs. 4A and 4B show example communication flows between a UE, a first network and a second network, according to some embodiments of the invention; and

[0036] Fig. 5 shows a block diagram of an exemplary computing device which may be used with some embodiments of the present invention.

[0037] It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.DETAILED DESCRIPTION

[0038] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention can be practiced without these specific details. In other instances, well-known methods, procedures, components, modules, units and / or circuits have not been described in detail so as not to obscure the invention.

[0039] A UE camping on NTN may end up in the situation that NTN may have discontinuous coverage, e.g. a satellite may not always be available to serve the UE. In these times the UE could try to regain coverage towards TN networks to ensure its reachability. On the other hand a UE being in TN coverage could experience a coverage hole and change for a short time to NTN coverage to ensure continuous service availability if needed. However, in any of these cases the UE behavior is not specified and there can be a trade off between ensuring continuous reachability / service availability versus energy (e.g. battery power) that needs to be spent for short time network change especially caused by registration procedure and sending the UE capability set to each of the networks. Short coverage holes or service gaps may occur when NTN is in discontinuous coverage or TN has a coverage hole such scenarios can occur repeatedly back-to- back and hence energy that is spent for those changes may need to be carefully considered especially with respect to power required for subsequent UE capability signaling when changing back and forth between the networks as these situations may occur several times at the same or different locations. Hence for realizing a solution ensuring continuous coverage by network change an efficient procedure for said change needs to be invented which is one of the subjects of this invention.

[0040] Fig. 1 shows an example of a problem which may be solved by some embodiments of the invention. NTN / TN switching (non-terrestrial network / terrestrial network switching) for a UE isconsidered to be a problem due to subsequent (e.g. repeated) UE capability signalling. As used herein NTN / TN switching may refer to switching from a terrestrial network to a non-terrestrial network, or switching from a non-terrestrial network to a terrestrial network. For example, when a UE 100 (e.g. a UE running a tracking application such as GPS in a moving vehicle, shown moving left to right) enters a coverage hole 105 of a terrestrial network 110, the UE may switch to a non-terrestrial network 120, for example because it has lost connection to network 110 to which it was attached. However, NTN 120 may have non-continuous coverage, for example a satellite in an NTN constellation may not be visible for hours due to rotation about the Earth. Thus, staying on NTN 120 may not be a practical option, and yet subsequent switching also has its drawbacks, for example negatively impacting power consumption of the UE.

[0041] A non-terrestrial network (NTN), such as network 120, may be comprised of a number of satellites, which may be referred to as a constellation of satellites. The satellites may include one or more low earth orbit (LEO) satellites, geosynchronous orbit (GEO) satellites, and / or very low earth orbit (VLEO) satellites. A particular satellite of the NTN may have a coverage area on Earth, such as coverage area 121.

[0042] A terrestrial network (TN), such as network 110, may be comprised of a number of base stations. Each base station may have a respective coverage area (e.g. a cell in a cellular network, see coverage areas 111) which may partially overlap to form a coverage area larger than any single individual coverage area. The overlap of coverage areas may not be entirely complete, and thus coverage holes (e.g. dead spots) may arise in the network.

[0043] Also shown in Fig. 1 is a terrestrially located core network element of NTN 120, labelled as 125. Terrestrially located core network element 125 may include a data storage such as a server, which may store data relating to the UE, such as UE capability information. Whilst not shown in Fig. 1, a TN may also be associated with one or more data storages for storing data such as UE capability information.

[0044] A TN / NTN UE in non-continuous satellite coverage may suspend NTN access stratum activities (AS) but TN AS may remain to the individual UE implementation. A UE may conduct a change to a TN network. However the required signalling of UE capabilities costs some energy (e.g. battery power). On the other hand, the UE may also rest without momentary connection possibility and just wait for next NTN satellite to occur. The same procedure or problem may arise when a TN camping UE enters a TN coverage hole, e.g. the UE could change to NTN spendingregistration energy or just wait until it has passed the coverage hole thereby being unreachable for a certain time.

[0045] One action which may be performed when a UE connects to a new network may be to transmit or otherwise send to the network a set of data relating to the UE. This set of data may include, for example, UE capability information as will be understood by a person skilled in the art. The UE capability information (which may be sent as an RRC, “radio resource control”, message) may include, for example, supported frequency bands for communication. Typically, the set of data relating to the UE is large (e.g. several kilobit) compared to the size of other messages transmitted on the network. Especially for tracking and trace devices this may bring the problem of sending large capability information versus small position information when changing the network or being unable to send a location report for a certain time, and said situation may repeatedly occur e.g. several coverage holes or continuous non-contiguous coverage by NTN. Accordingly, it is inefficient to repeatedly transmit data such as the capability information every time the UE has to change networks due to coverage holes or lack of satellite visibility. It is also a drain on UE resources, such as battery power. Embodiments of the invention may provide a solution to the above problem which avoids repeated transmission / re-registration of the set of data relating to the UE (e.g. the UE capability information).

[0046] Fig. 2 shows a flowchart of a method 200 for registering a user equipment “UE”, according to some embodiments of the invention. As will be understood by one skilled in the art, registering a UE with or on a network may include an attachment request from the UE, which may be accompanied by one or more credentials or authorisations of the UE. Registering a UE on a network also typically requires receiving UE capability information, so that, for example, the supported communication channels (e.g. frequency bands) of the UE are known to the network.

[0047] Method 200 may include, upon losing connection to a first network (e.g. entering a coverage hole / no longer being in coverage) to which the UE was registered (e.g. previously registered), requesting by the UE to attach to a second network (Step 202).

[0048] For example, the first network may be one of: a terrestrial network or a non-terrestrial network, and the second network may be one of: a terrestrial network or a non-terrestrial network. For example: the first network is a terrestrial network and the second network is a non-terrestrial network; the first network is a terrestrial network and the second network is a terrestrial network (e.g. different to the first network); the first network is non-terrestrial network and the secondnetwork is a terrestrial network; and / or the first network is a non-terrestrial network and the second network is a non-terrestrial network (e.g. different to the first network). Figs. 3A-3D, discussed further herein, show such example scenarios.

[0049] The first and / or second networks may be NTN or TN telecommunications networks (e.g. radio access networks), such as 5G telecommunications networks.

[0050] Method 200 may include sending by the UE, to the second network, an indication to retrieve, from the first network, a set of data relating to the UE previously transmitted to the first network by the UE (Step 204). For example, the set of data may have been previously transmitted to the first network as part of an initial registration of the UE on the first network. The set of data relating to the UE may include UE capability information. The indication to retrieve may take the form of a connection request message with indication capability already present in the first network.

[0051] In some embodiments, the UE capability information previously transmitted to the first network (e.g. comprised in the set of data relating to the UE) includes data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network. For example, the UE capability information in the first network may include a first set of supported frequency bands, and the UE capability information in the second network may include a second set of supported frequency bands (the second set may include some, all, or none of the first set of supported frequency bands). In case that the first and second networks are of a different kind, e.g. NTN and TN, this could represent the NTN frequency bands supported and the TN frequency bands supported by said device. There are frequency bands which exclusively exist only in one of the NTN / TN network.

[0052] In some embodiments, the indication to retrieve the set of data relating to the UE includes sending by the UE to the second network at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; and / or an identity of the UE on the first network.

[0053] As will be known to persons skilled in the art, an MCC / MNC tuple can be used to uniquely identify a mobile network operator, with the first digit of the mobile country code identifying the geographic region. In some embodiments, it may be sufficient to send only one of the MCC or MNC.

[0054] The identity of the UE on the first network could include, for example, a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network. This may be a (temporary, e.g. reusable) unique value identifying the UE whilst it is on the network. The TIMSI may be accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network. For example, the timestamp may be a time of initial registration / issue of the TIMSI, a time of an action performed by the UE whilst associated with the TIMSI (e.g. such as a last / most-recent action), and / or a timestamp when the TIMSI association was last used by the UE. When a TIMSI is no longer used by a device (e.g. the device may have disappeared or a new TIMSI was assigned), then after a certain elapsed time the network may re-assign the TIMSI. Hence, time stamping and maximum limitation on time lapse unless issuing UE capability fetch with previously used TIMSI may be important, which also keeps storage efforts reasonable (e.g. saving memory by not storing records of all TIMSIs assigned over a lifetime of the UE). The timestamp may include a time range, e.g. a time range from when the UE joined the network and was assigned the TIMSI, until a time the UE left the network.

[0055] A unique identifier of the UE on the first network, such as a TIMSI, may allow for devices of the same type to be distinguished.

[0056] In providing such information as an MCC, MNC, and / or TIMSI to the second network, the second network can more accurately identify the first network (e.g. based on the MNC / MCC) and more accurately instruct the first network as to the UE (e.g. based on the TIMSI) which the second network wishes to retrieve UE capability information for.

[0057] Method 200 may include verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network (Step 206). For example, the step of verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network may include: performing, by the UE and the second network, a mathematical operation on at least some of the data relating to the UE; and comparing a result of the mathematical operation performed by the UE and a result of the mathematical operation performed by the second network. The set of data relating to the UE retrieved from the first network may be verified as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network. The comparison may be performed by the UE, the second network (e.g. a server of the second network), or both.

[0058] In some embodiments, further data may be included in the mathematical operation, for example to improve the verification process by confirming that the correct UE is identified and the correct UE capability information is thereby retrieved. For example, some geographic data may be included in the verification process and / or a unique identifier of the UE on the first network may be included to help ensure that the correct UE has been identified. In some embodiments, security features may be added to the verification process such as by using a secret value (such as a private key).

[0059] Thus, in some embodiments, the mathematical operation may be performed on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; and / or or a secret value stored by the UE. A secret value may have been exchanged between the UE and the first network and may be compared by the UE or the second network when the UE capability set including the secret value is retrieved from the first network.

[0060] The MNC and / or MCC may help in confirming that the correct UE is identified based on the last known location of the UE.

[0061] The mathematical operation may be, or may include, at least one of: a hash function; a modulo operation; a shift function; and / or a least significant bit (LSB) or most significant bit (MSB) calculation. The mathematical operation could be a composite operation, for example comprising a hash followed by a modulo operation.

[0062] As an example, as part of the verification, the UE and the second network (e.g. a computing device such as a server associated with the second network) may perform a hash operation on some of the data relating to the UE (e.g. related to UE capability data). Comparing the calculated hash values may indicate that the same set of data was used if the hashes are the same, and thus may indicate that the second network has successfully retrieved the correct UE capability information from the first network.

[0063] As another example, as part of the verification, the UE and the second network (e.g. a computing device such as a server associated with the second network) may perform an LSB calculation on some of the data relating to the UE. Comparing the calculated LSB values may indicate that the same set of data was used, and thus that the second network has successfully retrieved the correct UE capability information from the first network.

[0064] Because the second network retrieves the UE capability information from the first network, rather than the UE transmitting the UE capability information (“retransmitting” e.g. transmitting for a second time, the UE having already transmitted to the first network) then UE resources are conserved, as well as air interface resources. It also means that for a UE travelling through areas with coverage holes, then repeat retransmission of UE capability information is avoided as the UE switches from one network to another, which also conserves UE resources and minimises network traffic. Especially for battery powered devices the saving of the energy related to a transfer or subsequent transfer of the UE capability data can yield a major improvement and increases operation time.

[0065] In the event of unsuccessful verification, e.g. the results of the mathematical operation are different indicating that the second network has not retrieved the correct set of data relating to the UE, then the second network may make a second attempt to retrieve the correct set of data from the first network. Alternatively, the second network may request further information from the UE to help identify the correct set of data relating to the UE, such as an MCC, MNC, and / or identity of the UE on the first network, such as a TIMSI. As another alternative, if the second network has not retrieved the correct set of data relating to the UE (e.g. the verification has not resulted in the same outcome from both the UE and the second network) the second network may request the UE to directly transmit the data relating to the UE to the second network. As another alternative, if the UE still has stored identifying information of a previous network other than the first network to which the UE was connected and previously sent UE capability information too (e.g. a third network), then the UE may indicate to the second network to retrieve the UE capability information from the third network: e.g. the third network may be considered as replacing the role of the first network.

[0066] In some embodiments, to reduce unnecessary back-and-forth communication, the user equipment may send a result of the mathematical operation along with (e.g. as part of) the indication to retrieve the UE capability information. The second network may then perform the mathematical operation and compare the obtained result against the already received result from the UE without, for example, requesting the UE to perform the mathematical operation and transmit the result as a separate message.

[0067] Method 200 may include registering the UE on the second network using at least a part of the retrieved set of data relating to the UE (Step 208). For example, where the UE capabilityinformation includes UE capabilities in the first network, this may not be relevant for registration on the second network. The registration may be performed following successful verification, for example that the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network.

[0068] In some embodiments, a terrestrially located core network element of the second network (such as a server) retrieves the set of data relating to the UE from a terrestrially located core network element of the first network (such as a server). For example, a core network element of the first network may share, send, or otherwise transmit the requested set of data relating to the UE (e.g. UE capability information) to a core network element of the second network over a third network, such as an internet protocol (IP) network. In cases where one of the first network or the second network is a NTN, this may conserve intersatellite resources, thereby prolonging the operational life of the satellite in the NTN. For example a terrestrially located core network element of a first non-terrestrial network, such as an AMF (Access and mobility management function), may be capable of storing UE capability information, and such terrestrially located core network element of the first non-terrestrial network may send the UE capability information to a terrestrially located core network element of a second network upon request.

[0069] Figs. 3A, 3B, 3C, and 3D show example network scenarios according to some embodiments of the invention.

[0070] In Fig. 3 A, UE 300 was previously connected to first network 310 which is a nonterrestrial network with terrestrially located core network element 315, and now UE 300 is requesting to connect to second network 320 which is a terrestrial network with terrestrially located core network element 325.

[0071] In Fig. 3B, UE 300 was previously connected to first network 310 which is a terrestrial network with terrestrially located core network element 315, and now UE 300 is requesting to connect to second network 320 which is a non-terrestrial network with terrestrially located core network element 325.

[0072] In Fig. 3C, UE 300 was previously connected to first network 310 which is a nonterrestrial network with terrestrially located core network element 315, and now UE 300 is requesting to connect to second network 320 which is also a non-terrestrial network with terrestrially located core network element 325.

[0073] In Fig. 3D, UE 300 was previously connected to first network 310 which is a terrestrial network with terrestrially located core network element 315, and now UE 300 is requesting to connect to second network 320 which is also a terrestrial network with terrestrially located core network element 325.

[0074] In Figs, 3A-3D, a terrestrially located core network element 315 of the first network and a terrestrially located core network 325 of the second network are shown as being capable of communicating with one another (335). The terrestrially located core network elements may include a data storage, such as a server, which may be capable of requesting, sending, and / or storing a set of data relating to a UE (such as UE capability information). The terrestrially located core network elements may communicate (335) via a third network such as an internet protocol network, which may be a wired or unwired connection.

[0075] According to some embodiments of the invention, UE 300, first network 310 and second network 320 communicate between one another, for example according to method 200 shown in Fig. 2, so that a set of data relating to UE 300 which was transmitted from UE 300 to first network 310 can be retrieved by second network 320 from first network 310 when requested by UE 300 upon UE 300 losing connection to first network 310. For example, UE capability information of UE 300 which was transmitted from UE 300 to first network 310 as part of registering on the first network may be retrieved by second network 320 upon UE 300 losing connection to first network 310 and requesting second network 320 to retrieve the UE capability information from first network 310.

[0076] According to one or more embodiments of the invention, there is provided a user equipment configured to carry out one or more methods or processes as described herein. For example, a user equipment according to an embodiment of the invention may be configured to: register on a first network and transmit to the first network a set of data relating to the UE; request to attach to a second network upon losing connection to the first network to which the UE was registered; indicate to the second network to retrieve from the first network the set of data relating to the UE previously transmitted to the first network by the UE; verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network; and register on the second network using at least a part of the retrieved set of data relating to the UE.

[0077] The UE may be, or may include elements of, a computing device as shown in Fig. 5 herein.

[0078] As described herein, the first network may be one of: a terrestrial network or a nonterrestrial network, and the second network may be one of: a terrestrial network or a non-terrestrial network.

[0079] The set of data relating to the UE may be, or may include, UE capability information. For example, the UE capability information may include data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network.

[0080] The UE may be configured to provide the second network with at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; and / or an identity of the UE on the first network. For example, the identity of the UE on the first network may be a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network.

[0081] In some embodiments, the TIMSI may be accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network, as described herein.

[0082] In some embodiments, the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and compare a result of the mathematical operation performed by the UE with a result of a mathematical operation performed by the second network. The set of data relating to the UE retrieved from the first network by the second network may be verified as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network. For example, the UE may be configured to verify the set of data as correctly retrieved if a result of the mathematical operation received from the second network matches a result of the mathematical operation performed by the UE. The UE may send a message to the second network that the results match, thereby confirming to the second network that the correct set of data (e.g. the correct UE capability information) was retrieved.

[0083] Alternatively, in some embodiments, the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and send a result of the mathematical operation performed by the UE to the second network for comparison. For example, the second network may perform the comparison, rather than the UE. This may reduce unnecessary back and forth communicationbetween the UE and the second network, and / or may mean that the UE does not need to expend computational power to compare the results of the mathematical operation, which may conserve resources (such as battery power).

[0084] Optionally, the result of the mathematical operation performed by the UE is sent as part of the indication to the second network to retrieve from the first network the set of data relating to the UE. This may have the effect of doing away with the need for the second network to send a request to the UE to perform the mathematical operation and to subsequently send back the result. Where the second network is an NTN, this has the additional benefit of reducing unnecessary use of scarce air interface resources: Note that NTN throughput is very limited and overall throughput is very limited e.g. only in Mbit area, whereas comparatively, due to the smaller distances / coupling losses involved, a TN base station throughput can be 100-1000 times higher.

[0085] In either of the two alternative embodiments discussed above (e.g. UE performing the comparison or second network performing the comparison) the UE may be configured to perform the mathematical operation on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; and / or a secret value stored by the UE. The second network would also perform the mathematical operation on the same corresponding at least some data and additional information such as the MNC etc.

[0086] As discussed herein, the mathematical operation may be, or may include, at least one of: a hash function; a modulo operation; a shift function; a least significant bit “LSB” calculation; and / or a most significant bit “MSB” calculation.

[0087] According to one or more embodiments of the invention, there may be provided a network (e.g. a telecommunications network) configured to perform the role of a first network as described herein (e.g. in method 200).

[0088] A first network as provided by embodiments of the invention may be configured to: store, as part of a registration, a set of data received from a UE registering on the network, the set of data relating to the UE; and send, to a second network, the set of data relating to the UE upon a request by the second network.

[0089] For example, the first network may include a terrestrially located core network element, such as a base station, which may have an associated data storage such as a server (see for example 315 in Figs. 3A-3D). The server may store details of user equipments registered on the firstnetwork (e.g. sets of data relating to the UEs), such as UE capability information. The server of the first network may send data to a second network upon request from the second network. The server may send the data over a network different to the first and / or second networks, for example over an internet protocol network to a server of the second network (see for example communication 335 between servers 315 and 325 in Figs. 3A-3D).

[0090] A first network provided in accordance with one or more embodiments of the invention may be a terrestrial network, or a non-terrestrial network.

[0091] According to one or more embodiments of the invention, there may be provided a network (e.g. a telecommunications network) configured to perform the role of a second network as described herein (e.g. in method 200). The second network may be configured to: retrieve, from a first network, by way of a request, a set of data relating to a UE requesting to attach to the second network; verify, with the UE, that the correct set of data relating to the UE has been retrieved from the first network; and register the UE on the second network using the retrieved set of data relating to the UE.

[0092] For example, the second network may include a terrestrially located core network element, such as a base station, which may have an associated data storage such as a server (see for example 325 in Figs. 3A-3D). The server may be configured to request a set of data relating to a UE (e.g. UE capability information) from another network. The server of the second network may send such a request upon an indication from a UE to retrieve data relating to the UE from the other network (e.g. a first network as described herein). The data may be received by the second network over a network different to the first and / or second networks, for example over an internet protocol network, thereby providing ground based “line” signaling and avoiding using first / second network resources. For example see communication 335 between servers 325 and 315 in Figs. 3A- 3D.

[0093] The server of the second network may verify that the correct set of data relating to the UE was retrieved by performing a mathematical operation as described herein and comparing the result with a result from the UE (which may be received from the UE as part of the initial indication to retrieve the data, or may be received later upon request to the UE from the second network). The set of data may be verified as correct (either by the UE or the second network) if the results of the mathematical operation are the same when performed by the UE and when performed by the second network (e.g. performed by the server of the second network).Y1

[0094] The server of the second network may be configured to store the set of data relating to the UE as received from the first network. The server may store such data if the data is verified as correctly relating to the UE. The server may register the UE on the second network using the retrieved set of data relating to the UE.

[0095] The second network as provided by embodiments of the invention may be a terrestrial network or a non-terrestrial network.

[0096] According to one or more embodiments of the invention, there is also provided a system (e.g. a telecommunications system) comprising the user equipment described herein, the network configured to perform the role of a first network described herein, and the network configured to perform the role of a second network described herein. The system may be a system as depicted in any of Figs. 3A-3D. The system, e.g. one or more elements thereof, may carry out one or more methods as described herein, such as method 200.

[0097] Fig. 4A shows an example communication flow between a UE, a first network and a second network, according to some embodiments of the invention.

[0098] In the example situation shown in Fig. 4A, first network 410 is a terrestrial network with terrestrially located core network element having a server 415, and second network 420 is a nonterrestrial network that indicates fetch support to any UE 400 attempting to register on the second network, where second network 420 has a terrestrially located core network element having a server 425.

[0099] UE 400 initially accesses terrestrial network 410 and provides first (TN) network 410 with its UE capability information, which includes the TN and NTN capabilities of the UE (Stage 450). First network 410 stores the TN / NTN capability set of UE 400 in server 415 (Stage 452).[000100] If UE 400 enters a coverage hole (e.g. a coverage hole of TN network 410) UE 400 may scan for any available NTNs (Stage 454). Second (NTN) network 420 may indicate fetch support, and UE 400 may be configured to favor connection to networks that support UE capability fetching (e.g. due to the advantages described herein, such as reducing power consumption of the UE). Fetch support may be indicated in the broadcast information, e.g. the information part which describes who a device can approach and send a RACH / PRACH (random access request) to said base station. For example, when the UE receives a broadcast to perform access, e.g. frequency power and resources to be used, the UE may also retrieve information as to whether it can requestsuch a fetch procedure herein described as supported by the second network, or whether the UE needs to start the legacy UE capability signaling procedure.[000101] UE 400 may send to second (NTN) network 420 an attach request, along with for example, authorization credentials (Stage 456).[000102] Second (NTN) network 420 may check the identity of UE 400 (for example using server 425) with the home public land mobile network, “HPLMN” (Stage 458). After confirming that UE 400 may access second (NTN) network 420 (e.g. that the UE is authorized), second (NTN) network 420 may await UE capability information from UE 400.[000103] UE 400 may indicate to second (NTN) network 420 to fetch / retrieve the UE capability information from first (TN) network 410 (Stage 460). As part of the indication, UE 400 may send one or more of an MNC, an MCC and / or a previously in use TIMSI from when UE 400 was attached to first (TN) network 410. The indication received from UE 400 by second (NTN) network 420 may be processed by server 425.[000104] Server 425 may request from server 415 of first (TN) network 410 the UE capabilities of UE 400 (Stage 462). Server 425 may identify the correct network using the MNC and / or MCC provided by UE 400. Server 425 may indicate to server 415 the TIMSI received from UE 400 in order for server 415 to identify and retrieve the UE capabilities of UE 400.[000105] Server 415 may respond to server 425 with the retrieved UE capabilities (Stage 464). Server 415 may send the UE capabilities to server 425 over a third network such as an internet protocol network (not shown).[000106] Server 425 may perform a mathematical operation (such as a hash, other examples are disclosed herein) on the UE capabilities (e.g. on the set of data relating to the UE capabilities) and on the TIMSI (Stage 466). As described herein, the mathematical operation may be performed also on other data such as the MNC and / or MCC.[000107] Second (NTN) network 420 may send a verification request to UE 400 (Stage 468), for example for the purposes of verifying that server 425 has retrieved the correct set of UE capability information from server 415 (e.g. that the second network has retrieved the correct set of data relating to the UE from the first network).[000108] UE 400 may perform a mathematical operation (such as a hash, other examples are disclosed herein) on the UE capabilities (e.g. on the set of data relating to the UE capabilities) andon the TIMSI (Stage 470). As described herein, the mathematical operation may be performed also on other data such as the MNC and / or MCC.[000109] UE 400 may send a verification response, e.g. a result of the mathematical operation performed by the UE, to second (NTN) network 420 (Stage 472).[000110] Second (NTN) network 420 may, e.g. using server 425, compare the results of the mathematical operation as performed by UE 400 and server 425 (Stage 474). The set of data relating to the UE retrieved from first (TN) network 410 (e.g. retrieved from server 415) may be verified as correct if the result of the mathematical operation performed by UE 400 is the same as the result of the mathematical operation performed server 425 (e.g. performed by second network 420).[000111] Second (NTN) network 420 may send a confirmation to UE 400 that the UE capability information is verified as correctly retrieved (Stage 476). UE 400 may acknowledge the confirmation (Stage 478). UE 400 may then be registered (e.g. be attached to) second (NTN) network 420, for example using at least parts of the retrieved data relating to the UE.[000112] It should be understood that the communication flow as shown in Fig. 4A may be applicable to network scenarios different to that depicted in Fig. 4A, for example: the first network is a terrestrial network and the second network is a terrestrial network (e.g. different to the first network), see e.g. Fig. 3D; the first network is non-terrestrial network and the second network is a terrestrial network, see e.g. Fig. 3A; and / or the first network is a non-terrestrial network and the second network is a non-terrestrial network (e.g. different to the first network), see e.g. Fig. 3C.[000113] It should also be understood that such a communication flow as shown in Fig. 4A may be repeated multiple times as UE 400 moves in and out of coverage of different networks. For example if UE 400 moves out of coverage of NTN 420, UE 400 may attempt to attach to a different network (an NTN or a TN). UE 400 may indicate to this new network to retrieve the UE capabilities from original first network 410 or from second network 420 which may have stored the retrieved UE capabilities. Accordingly, repeat transmission of UE capabilities by the UE is avoided according to embodiments of the invention, instead shifting the power-intensive burden of transmitting such large data as the UE capabilities to the networks themselves through interworking between the core network elements of the TN and NTN networks. An improved telecommunication system may therefore be achieved by embodiments of the invention.[000114] Fig. 4B shows an example communication flow between a UE, a first network and a second network, according to some embodiments of the invention. Fig. 4B differs from Fig. 4A in that UE 400 performs the mathematical operation and sends the result as part of the indication to fetch / retrieve the UE capabilities, thereby resulting in a more streamlined communication flow that comprises fewer total steps because unnecessary back and forth between UE 400 and second network 420 is avoided at the verification stage.[000115] For example, in Fig. 4B, UE 400 may, after requesting to attach to second network 420, perform a mathematical operation perform a mathematical operation on at least some of the data relating to the UE (e.g. on the set of data representing the UE capabilities and TIMSI) (Stage 459). [000116] At Stage 460, as a difference from that shown in Fig. 4A, UE 400 may send a result of the mathematical operation as part of the indication to the second network to retrieve the set of data relating to the UE from the first network.[000117] At Stage 466, because second network 420 already has the result of the mathematical operation performed by UE 400, second network 420 can immediately compare this with a result of the mathematical operation as performed by the second network (e.g. performed by server 425). Thus, in Fig. 4B, if the results of the mathematical operation are the same, second network 420 can send a confirmation to UE 400 that the UE capability information is verified as correctly retrieved (Stage 467, c.f. Stage 476 in Fig. 4A).[000118] Accordingly, Fig. 4B shows that the back and forth between UE 400 and second network 420, as represented by Stages 468 and 472 in Fig. 4A, is avoided.[000119] Fig. 5 shows a block diagram of an exemplary computing device 500 which may be used with some embodiments of the present invention.[000120] As described herein, any of: a user equipment; a core network element; a satellite; a base station; and / or a server (e.g. a server in connection with a core network element), may be, or may include elements of, a computing device 500 as shown in Fig. 5.[000121] Computing device 500 may include a controller or computer processor 505 that may be, for example, a central processing unit processor (CPU), a chip or any suitable computing device, an operating system 515, a memory 520, a storage 530, input devices 535 and output devices 540 such as a computer display or monitor displaying for example a computer desktop system.[000122] Operating system 515 may be or may include code to perform tasks involving coordination, scheduling, arbitration, or managing operation of computing device 100, forexample, scheduling execution of programs. Memory 520 may be or may include, for example, a Random Access Memory (RAM), a read only memory (ROM), a Flash memory, a volatile or nonvolatile memory, or other suitable memory units or storage units. At least a portion of Memory 520 may include data storage housed online on the cloud. Memory 520 may be or may include a plurality of different memory units. Memory 520 may store for example, instructions (e.g., code 525) to carry out a method as disclosed herein, such as method 200. Memory 520 may use a datastore, such as a database.[000123] Executable code 525 may be any application, program, process, task, or script. Executable code 525 may be executed by controller 105 possibly under control of operating system 515. For example, executable code 525 may be, or may execute, one or more applications performing methods as disclosed herein, such as method 200. In some embodiments, more than one computing device 500 or components of device 500 may be used. One or more processor(s) 505 may be configured to carry out embodiments of the present invention by, for example, executing software or code.[000124] Storage 530 may be or may include, for example, a hard disk drive, a floppy disk drive, a compact disk (CD) drive, a universal serial bus (USB) device or other suitable removable and / or fixed storage unit. Data described herein may be stored in a storage 530 and may be loaded from storage 530 into a memory 520 where it may be processed by controller 505. Storage 530 may include cloud storage. Storage 530 may include storing data in a database.[000125] Storage 530 may store, for example, an MNC, MCC, TIMSI, secret value, UE capability information, or other data.[000126] Input devices 535 may be or may include a mouse, a keyboard, a touch screen or pad or any suitable input device or combination of devices. Input devices 535 may include a receiver, such as an antenna receiver. Output devices 540 may include one or more displays, speakers and / or any other suitable output devices or combination of output devices. Output devices 540 may include a transmitter, such as an antenna transmitter. Any applicable input / output (I / O) devices may be connected to computing device 500, for example, a wired or wireless network interface card (NIC), a modem, printer, a universal serial bus (USB) device or external hard drive may be included in input devices 535 and / or output devices 540.[000127] Embodiments of the invention may include one or more article(s) (e.g., memory 520 or storage 530) such as a computer or processor non-transitory readable medium, or a computer orprocessor non-transitory storage medium, such as for example a memory, a disk drive, or a USB flash memory encoding, including, or storing instructions, e.g., computer-executable instructions, which, when executed by a processor or controller, carry out methods disclosed herein.[000128] It is anticipated that embodiments of the invention may have an impact on existing or future non-terrestrial network telecommunications architecture and associated standards. For example, embodiments of the invention may be employed in, beyond 5G, 6G, and / or future NTN architectures. The ongoing development of these standards, and the conceptualization and implementation of future standards, may rely on systems and / or methods of the present invention. [000129] For example, embodiments of the invention may extend the capabilities of the 3 GPP, 5G, and / or 6G standards in that repeat frequent transmission (e.g. in a short period of time, such as over the course of a day) of UE capabilities by a UE is avoided, because in embodiments of the invention the UE sends a new type of indication message to a network instructing the network to retrieve UE capability information previously transmitted, thereby conserving UE resources. Embodiments of the invention may improve the interworking of, and provide a near seamless transition between, terrestrial and non-terrestrial networks.[000130] Unless specifically stated otherwise, as apparent from the foregoing discussion, it is appreciated that throughout the specification discussions utilizing terms such as "processing," "computing," "calculating," "determining," or the like, refer to the action and / or processes of a computer or computing system, or similar electronic computing device, that manipulates and / or transforms data represented as physical, such as electronic, quantities within the computing system's registers and / or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices.[000131] Embodiments of the invention may include an article such as a computer or processor readable non-transitory storage medium, such as for example a memory, a disk drive, or a USB flash memory encoding, including, or storing instructions, e.g., computer-executable instructions, which when executed by a processor or controller, cause the processor or controller to carry out methods disclosed herein.[000132] It should be recognized that embodiments of the invention may solve one or more of the objectives and / or challenges described in the background, and that embodiments of the inventionneed not meet every one of the above objectives and / or challenges to come within the scope of the present invention.[000133] In the above description, an embodiment is an example or implementation of the inventions. The various appearances of "one embodiment,” "an embodiment" or "some embodiments" do not necessarily all refer to the same embodiments.[000134] Although various features of the invention may be described in the context of a single embodiment, the features may also be provided separately or in any suitable combination. Conversely, although the invention may be described herein in the context of separate embodiments for clarity, the invention may also be implemented in a single embodiment. While the invention has been described with respect to a limited number of embodiments, it should be understood by a person of ordinary skill in the art that one or more features from one particular embodiment or group of embodiments may be combined with features of another embodiment or group of embodiments.[000135] Reference in the specification to "some embodiments", "an embodiment", "one embodiment" or "other embodiments" means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the inventions.[000136] It is to be understood that the phraseology and terminology employed herein is not to be construed as limiting and are for descriptive purposes only.[000137] It is to be understood that the details set forth herein do not construe a limitation to an application of the invention.[000138] It is to be understood that the terms “including”, “comprising”, “consisting” and grammatical variants thereof do not preclude the addition of one or more components, features, steps, or integers or groups thereof and that the terms are to be construed as specifying components, features, steps, or integers.[000139] If the specification or claims refer to "an additional" element, that does not preclude there being more than one of the additional elements.[000140] It is to be understood that where the claims or specification refer to "a" or "an" element, such reference is not to be construed that there is only one of that element.[000141] It is to be understood that where the specification states that a component, feature, structure, or characteristic "may", "might", "may" or "could" be included, that a particular component, feature, structure, or characteristic is not required to be included.[000142] Where applicable, although state diagrams, flow diagrams or both may be used to describe embodiments, the invention is not limited to those diagrams or to the corresponding descriptions. For example, flow need not move through each illustrated box or state, or in exactly the same order as illustrated and described.

Claims

CLAIMS1. A method for registering a user equipment “UE”, the method comprising: upon losing connection to a first network to which the UE was registered, requesting by the UE to attach to a second network; sending by the UE, to the second network, an indication to retrieve, from the first network, a set of data relating to the UE previously transmitted to the first network by the UE; verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network; and registering the UE on the second network using at least a part of the retrieved set of data relating to the UE.

2. The method of claim 1, wherein: the first network is one of: a terrestrial network or a non-terrestrial network; and the second network is one of: a terrestrial network or a non-terrestrial network.

3. The method of any of claims 1 or 2, wherein the set of data relating to the UE comprises UE capability information.

4. The method of claim 3, wherein the UE capability information previously transmitted to the first network comprises data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network.

5. The method of any preceding claim, wherein the indication to retrieve the set of data relating to the UE comprises sending the second network at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; or an identity of the UE on the first network.

6. The method of claim 5, wherein the identity of the UE on the first network includes a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network.

7. The method of claim 6, wherein the TIMSI is accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network.

8. The method of any preceding claim, wherein said step of verifying, between the second network and the UE, that the second network has retrieved the correct set of data relating to the UE from the first network, comprises: performing, by the UE and the second network, a mathematical operation on at least some of the data relating to the UE; and comparing a result of the mathematical operation performed by the UE and a result of the mathematical operation performed by the second network, wherein the set of data relating to the UE retrieved from the first network is verified as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network.

9. The method of claim 8, wherein the mathematical operation is performed on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; or a secret value stored by the UE.

10. The method of claim 8 or 9, wherein the mathematical operation comprises at least one of: a hash function; a modulo operation; a shift function; a least significant bit “LSB” calculation; or a most significant bit “MSB” calculation.

11. The method of any previous claim, wherein a terrestrially located core network element of the second network retrieves the set of data relating to the UE from a terrestrially located core network element of the first network.

12. A user equipment “UE” configured to: register on a first network and transmit to the first network a set of data relating to the UE; request to attach to a second network upon losing connection to the first network to which the UE was registered;indicate to the second network to retrieve from the first network the set of data relating to the UE previously transmitted to the first network by the UE; verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network; and register on the second network using at least a part of the retrieved set of data relating to the UE.

13. The user equipment of claim 12, wherein the set of data relating to the UE comprises UE capability information.

14. The user equipment of claim 13, wherein the UE capability information comprises data relating to the UE capabilities in the first network and data relating to the UE capabilities in the second network.

15. The user equipment of any preceding claim, wherein the UE is configured to provide the second network with at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; or an identity of the UE on the first network.

16. The user equipment of claim 5, wherein the identity of the UE on the first network includes a temporary international mobile subscriber identity “TIMSI” assigned to the UE by the first network.

17. The user equipment of claim 6, wherein the TIMSI is accompanied by a timestamp associating the TIMSI to a time at which the TIMSI was in use for the UE on the first network.

18. The user equipment of any of claims 12-17, wherein the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and compare a result of the mathematical operation performed by the UE with a result of a mathematical operation performed by the second network,wherein the user equipment is further configured to verify the set of data relating to the UE retrieved from the first network by the second network as correct if the result of the mathematical operation performed by the UE is the same as the result of the mathematical operation performed by the second network.

19. The user equipment of any of claims 12-17, wherein the UE is configured to verify with the second network that the second network has retrieved the correct set of data relating to the UE from the first network by being configured to: perform a mathematical operation on at least some of the data relating to the UE; and send a result of the mathematical operation performed by the UE to the second network for comparison.

20. The user equipment of claim 19, wherein the result of the mathematical operation performed by the UE is sent as part of the indication to the second network to retrieve from the first network the set of data relating to the UE.

21. The user equipment of claim 18 or 19, wherein the UE is configured to perform the mathematical operation on at least some of the data relating to the UE in addition to at least one of: a mobile network code “MNC” of the first network; a mobile country code “MCC” of the first network; an identity of the UE on the first network; or a secret value stored by the UE.

22. The user equipment of any of claims 18-21, wherein the mathematical operation comprises at least one of: a hash function; a modulo operation; a shift function; a least significant bit “LSB” calculation; or a most significant bit “MSB” calculation.

23. A network configured to perform the role of a first network in the method of any of claims 1- 11 , the first network being configured to: store, as part of a registration, a set of data received from a UE registering on the network, the set of data relating to the UE; and send, to a second network, the set of data relating to the UE upon a request by the second network.

24. A network configured to perform the role of a second network in the method of any of claims 1-11, the second network being configured to: retrieve, from a first network, by way of a request, a set of data relating to a UE requesting to attach to the second network; verify, with the UE, that the correct set of data relating to the UE has been retrieved from the first network; and register the UE on the second network using the retrieved set of data relating to the UE.

25. A system comprising the user equipment according to any of claims 12-22, the network configured to perform the role of a first network according to claim 23, and the network configured to perform the role of a second network according to claim 24.

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