Cooperating networks

Abstract

The invention relates to a method, carried out at a secondary mobility handling entity (220) of a secondary cellular network comprising: - receiving (S31) an establishment request from a user equipment (100) having a subscription to a primary cellular network and to the secondary cellular network, to establish a secondary data packet session, the establishment request comprising an identifier of a mobility handling entity of the primary cellular network, and a session identifier of a primary data packet session of the user equipment established in the primary cellular network, - transmitting (S32) a discovery request towards a central registration entity of the primary cellular network including at least the identifier of the mobility handling entity of the primary cellular network and the session identifier of the primary data packet session, - receiving (S33) a response to the discovery request including an address of the primary mobility handling entity of the primary cellular network, - transmitting (S34), using the received address, an address request to the primary mobility handling entity, requesting an address of a primary session management entity of the primary cellular network.

Description

[0001] Cooperating Networks

[0002] Technical Field

[0003] The present application relates to an aggregation of a data packet session through different cellular networks. The application relates in more detail to a method carried out at a secondary mobility handling entity of a secondary cellular network, to a method carried out at a secondary session management entity of the secondary cellular network, to a method carried out at a primary session management entity of a primary cellular network, to a method carried out at a primary user plane entity of the primary cellular network and to a method carried out at a user equipment having a subscription to the primary and the secondary cellular network. Furthermore the corresponding entities are provided, a system comprising at least two entities from the group of entities discussed above, a computer program comprising program code and, last but not least, a carrier comprising the computer program.

[0004] Radio access coverage depends on the chosen Mobile Operator for the contract, and the geographical location of the UE (User Equipment). The very same location might have totally different radio conditions for another UE of another Mobile Network Operator. This may depend on the Radio Access Network coverage deployment per operator or may be influenced by different physical frequency performance conditions, depending on the deployed frequency range. Different services may have different requirements, which one Mobile Network Operator may not supply in all geographical positions of the UE. As an example, an Augmented Reality (AR) application might have throughput requirements which one operator cannot fulfill alone at a given location.

[0005] Ubiquitous connectivity or having the connection from anywhere, anytime is a very relevant topic for certain group of users that would benefit extremely from the national coverage that a network service provider could bring. In this context the cooperation between Mobile operators networks will bring extra security mechanisms implicit in 5G protocols together with capacity enhancements that would not be possible to achieve by traditional roaming mechanisms. This capacity boost would bring extra value in field operations during emergencies situations or remote areas where coverage is a scarce resource and temporary networks are deployed for government entities like police, fire brigades, first responders, etc..

[0006] National and international roaming provides connectivity to UEs of operators who have roaming agreements (service level agreements, SLAs) between them. In order to offer this, it is required that proper roaming architecture is deployed in the visited and in the home network. This agreement and network configuration is planned and applied in both operator networks. The visited PLMN is enhancing the Radio Access Network coverage of the home PLMN operator in areas where the home PLMN operator is not present with Radio Access Networks.

[0007] Furthermore UEs are known having multiple SIM cards which allows the UE to connect to multiple networks at a given time. The UE can be served with radio access network capacity and quality from the home network or in case of roaming from the visited network where SLA have been established. Ever increasing bandwidth demand is applicable as well to rural deployments e.g. XR, AR, Metaverse. In rural areas thin frequency bands deployed by several MNOs cannot be aggregated.

[0008] Accordingly a need exists to cope with the ever increasing bandwidth demands and to provide a possibility to bundle data services provided by different cellular networks.

[0009] This need is met by the features of the independent claims. Further aspects are described in the dependent claims.

[0010] According to a first aspect a method is provided carried out at a secondary mobility handling entity of a secondary cellular network wherein the secondary mobility handling entity receives an establishment request from a user equipment having a subscription to a primary cellular network and to the secondary cellular network, the request requesting to establish a secondary data packet session, wherein the establishment request comprises an identifier of a mobility handling entity of the primary cellular network and a session identifier of a primary data packet session of the user equipment established in the primary cellular network. The secondary mobility handling entity transmits a discovery request towards a central registration entity of the primary cellular network including at least an identifier of the mobility handling entity of the primary cellular network and the session identifier of the primary data packet session. The secondary mobility handling entity receives a response to the discovery request including an address of the primary mobility handling entity of the primary cellular network. Furthermore, an address request is transmitted to the primary mobility handling entity using the received address wherein the address request requests an address of a primary session management entity of the primary cellular network. Furthermore the corresponding secondary mobility handling entity is provided. With the steps carried out at the secondary mobility handling entity and the pieces of information exchanged it is possible to aggregate data packet sessions transmitted through different cellular networks.

[0011] Furthermore a method is provided carried out at a secondary session management entity of the secondary cellular network comprising the step of receiving from the secondary mobility handling entity a session create request including an identifier of the mobility handling entity of the primary cellular network, the request further comprising a session identifier of the primary data packet session of the user equipment in the primary cellular network, the UE having the subscription to the primary and the secondary cellular network. Furthermore, a session create request is transmitted to a primary session management entity of the primary cellular network to create a secondary data packet session for the user equipment wherein the session create request includes the session identifier of the primary data packet session and a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and the secondary data packet session. The session create request furthermore includes an identifier of a secondary user plane entity handling the first and second data packet session in the secondary cellular network. Furthermore a response is received to the session create request from the primary session management entity wherein the response contains the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session and a network address of the user equipment in the primary data packet session. The secondary session management entity then marks the network address of the user equipment in the primary cellular network as being used. Furthermore, the corresponding secondary session management entity is provided.

[0012] Furthermore, a method is provided carried out at the primary session management entity of the primary cellular network comprising the step of receiving a session create request from the secondary session management entity to create a secondary data packet session for the user equipment having a subscription to the primary and the secondary cellular network, wherein the session create request includes a session identifier of a primary data packet session handled by the primary session management entity for the user equipment in the primary cellular network wherein the session create request furthermore includes a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and the secondary data packet session and including an identifier of a secondary user plane entity in the secondary cellular network handling the first and second data packet session. The primary session management entity furthermore initiates an interconnection of the secondary data packet session to the primary data packet session, selects a primary user plane entity handling the primary and secondary data packet session and transmits a response to the secondary session management entity, wherein the response contains the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session and a network address of the user equipment. Furthermore the corresponding primary session management entity is provided operating as discussed above or as discussed in further detail below.

[0013] Further, a method is provided carried out at a primary user plane entity of the primary cellular network comprising the step of receiving from the primary session management entity of the primary cellular network a first session establishment request for establishing the primary data packet session for the user equipment having the subscription to the primary cellular network and the secondary cellular network. The primary user plane entity furthermore receives from the primary session management entity of the primary cellular network a second session establishment request for establishing a secondary data packet session for the user equipment wherein the second session establishment request includes binding information allowing to link the primary data packet session to the secondary data packet session. The primary user plane entity then, based on the binding information, interconnects the primary and the secondary data packet session. Furthermore, the corresponding primary user plane entity is provided.

[0014] A method is provided carried out at a user equipment having a subscription to the primary cellular network and the secondary cellular network wherein the user equipment transmits a first establishment request towards a primary session management entity of the primary cellular network to establish a primary data packet session of a combined data packet session in the primary cellular network, wherein the first establishment request includes an indicator to establish a secondary data packet session of the combined data packet session in the secondary cellular network. The user equipment receives a response to the first establishment request wherein the response includes an acknowledgment that the establishment of the secondary data packet session is enabled and the response including a session identifier of the primary data packet session. The user equipment transmits a second establishment request towards a secondary session management entity of the secondary cellular network to establish the secondary data packet session wherein the establishment request comprises an identifier of a mobility handling entity of the primary cellular network and the session identifier of the primary data packet session of the user equipment in the first cellular network. Furthermore, the corresponding user equipment is provided operating as discussed above or as discussed in further detail below.

[0015] Additionally, a system is provided comprising at least two entities selected from the following group of entities wherein the group contains the secondary mobility management entity, the secondary session management entity, the primary session management entity, the primary user plane entity, and the user equipment.

[0016] Furthermore, a computer program comprising program code is provided to be executed by at least one processing unit of the secondary mobility management entity, the secondary session management entity, the primary session management entity, the primary user plane entity, or the user equipment, wherein execution of the program code causes the at least one processing unit to carry out a method as discussed above for the corresponding entities or as discussed in further detail below.

[0017] Last but not least, a carrier is provided comprising the computer program wherein the carrier is one of an electronic signal, optical signal, radio signal, and computer readable storage medium.

[0018] It is to be understood that the features mentioned above and yet to be explained below can be used not only in the respective combinations indicated, but also in other combinations or in isolation without departing from the scope of the present invention. Features of the above- mentioned aspects and embodiments described below may be combined with each other in other embodiments unless explicitly mentioned otherwise.

[0019] Brief of the

[0020] The foregoing and additional features and effects of the application will become apparent from the following detailed description when read in conjunction with the accompanying drawings in which like reference numerals refer to like elements.

[0021] Figure 1 shows a schematic view of a high level architecture for a system in which data between a UE and a server are exchanged through data packet sessions in different cellular networks. Figure 2 shows a schematic view of a message exchange between the involved entities for the establishment of a primary data packet session.

[0022] Figures 3a to 3c show the message exchange between the involved entities for the establishment of the secondary data packet session and the merging with the primary session.

[0023] Figure 4 shows the message exchange between involved entities when the primary session informs the secondary sessions about a standby SMF address.

[0024] Figure 5 shows a schematic view of the message flow between the involved entities when the primary session in the primary cellular network fails.

[0025] Figure 6 shows a decision logic carried out in the user equipment in the situations discussed in connection with Figures 2 to 5.

[0026] Figure 7 shows the decision logic carried out in the secondary mobility handling entity in the situation discussed in connection with Figures 2 to 5.

[0027] Figure 8 shows a decision logic carried out in a primary session management entity in a situation discussed in connection with Figures 2 to 5.

[0028] Figure 9 shows a decision logic carried out in the secondary session management entity in a situation discussed in connection with Figures 2 to 5.

[0029] Figure 10 shows a schematic view of the logic carried out in the secondary user plane entity in the situation discussed in connection with Figures 2 to 5.

[0030] Figure 11 shows a schematic view of the logic carried out in the primary user plane entity in a situation discussed in connection with Figures 2 to 5.

[0031] Figure 12 shows a flowchart of a method carried out at the secondary mobility handling entity in a situation where an aggregated data packet session is transmitted through different cellular networks.

[0032] Figure 13 shows an example flowchart of a method carried out at a secondary session management entity of the secondary cellular network in the situation of an aggregated data packet session through different cellular networks. Figure 14 shows an example schematic flowchart of a method carried out at a primary session management entity of the primary cellular network in a situation where an aggregated data packet session is transmitted through different cellular networks.

[0033] Figure 15 shows an example flowchart of a method carried out at a primary user plane entity of the primary cellular network in a situation when an aggregated data packet flow is transmitted through different networks.

[0034] Figure 16 shows an example flowchart of a method carried out at a user equipment in a situation where an aggregated data packet session is transmitted through different cellular networks.

[0035] Figure 17 shows an example schematic representation of a user equipment configured to exchange data of an aggregated session through different cellular networks.

[0036] Figure 18 shows an example schematic representation of a secondary session management entity involved in an aggregated session exchange over different cellular networks.

[0037] Figure 19 shows an example schematic representation of a primary session management entity involved in an aggregated data packet session transmitted through different cellular networks.

[0038] Figure 20 shows an example schematic representation of a primary user plane entity involved in an aggregated data packet session through different cellular networks.

[0039] Figure 21 shows an example schematic representation of a secondary mobility handling entity involved in an aggregated data session transmitted through different cellular networks.

[0040] Detailed Description

[0041] In the following, embodiments of the invention will be described in detail with reference to the accompanying drawings. It is to be understood that the following description of embodiments is not to be taken in a limiting sense. The scope of the invention is not intended to be limited by the embodiments described hereinafter or by the drawings, which are to be illustrative only. The drawings are to be regarded as being schematic representations, and elements illustrated in the drawings are not necessarily shown to scale. Rather, the various elements are represented such that their function and general purpose becomes apparent to a person skilled in the art. Any connection or coupling between functional blocks, devices, components of physical or functional units shown in the drawings and described hereinafter may also be implemented by an indirect connection or coupling. A coupling between components may be established over a wired or wireless connection. Functional blocks may be implemented in hardware, software, firmware, or a combination thereof.

[0042] Within the context of the present application, the term “mobile entity” or “user equipment” (UE) refers to a device for instance used by a person (i.e. a user) for his or her personal communication. It can be a telephone type of device, for example a telephone or a Session Initiating Protocol (SIP) or Voice over IP (VoIP) phone, cellular telephone, a mobile station, cordless phone, or a personal digital assistant type of device like laptop, notebook, notepad, tablet equipped with a wireless data connection. The UE may also be associated with nonhumans like animals, plants, or machines. A UE may be equipped with a SIM (Subscriber Identity Module) or electronic-SIM comprising unique identities such as IMSI (International Mobile Subscriber Identity), TMSI (Temporary Mobile Subscriber Identity), or GUTI (Globally Unique Temporary UE Identity) associated with the user using the UE. The presence of a SIM within a UE customizes the UE uniquely with a subscription of the user.

[0043] For the sake of clarity, it is noted that there is a difference but also a tight connection between a user and a subscriber. A user gets access to a network by acquiring a subscription to the network and by that becomes a subscriber within the network. The network then recognizes the subscriber (e.g. by IMSI, TMSI or GUTI or the like) and uses the associated subscription to identify related subscriber data. A user is the actual user of the UE, and the user may also be the one owning the subscription, but the user and the owner of the subscription may also be different. E.g. the subscription owner may be the parent, and the actual user of the UE could be a child of that parent.

[0044] In the following, a solution will be disclosed in which a UE having subscriptions to at least two networks, having by way of example multi identities like eSIM or multiple SIM, connects simultaneously to two or more cellular networks operated by different mobile network operators (MNOs). In this context multiple active data packet sessions such as PDU sessions are aggregated. This leads to a parallel use of Internet connection of each cellular network combined as one big pipe to the server located on the Internet. The aggregated carriers of the multiple MNOs hide behind a single external IP address, a virtual IP address, of the multi-SIM UE. The UE and access point in the user plane function do load balancing over the multiple sessions based on capacity and other attributes provided by the individual operator. In the following, the at least two cellular networks are specified as primary network and secondary network. The expressions primary and secondary may be considered as names in order to differentiate the networks, may be considered as first and second networks as the UE first connects to the primary and then to the secondary network. Furthermore, it may be considered as an indication that the primary network and its entities is the network coordinating the overall data exchange and which is controlling the data sessions.

[0045] Reference is now made to Figure 1 where a UE 100 having several SIM cards connects to a server 700 located in the Internet through a primary network 30, meaning through a base station 380, and mobility handling entity implemented as access and mobility management function, AMF 320, a session management entity, SMF 330 and a user plane function, UPF 340. A second connection to the server 700 is established through the secondary cellular network 20 through the corresponding base station 280, the AMF 220, the secondary SMF 230 and the UPF 240. The hatched box represents a virtual UPF containing both the physical UPFs per operator. Furthermore, the IP address or connection point 40 is indicated which plays the role of the external next hop IP address to reach the virtual or common IP address of the UE. Seen from the UE 100, the uplink traffic to the server can be load-balanced via the two networks. The downlink traffic to the UE 100 is load-balanced in the UPF 340 over the primary or secondary network. The two cellular networks 20, 30 interconnect on AMF, SMF and UPF level for signaling any user plane. In the following, function and entity are used interchangeably so that e.g. user plane function and user plane entity refer to the same node.

[0046] The external visible IP address of the UE 100 is taken from a common pool of IP addresses which is shared by different operators for this kind of service.

[0047] The multi-SIM UE 100 requests a primary data packet session such as a primary PDU session establishment which assigns the IP address to the UE. The primary data packet session, PDU session has the UPF anchor to the Internet / DNN. The UE 100 requests one or more further slave data packet sessions to add radio capacity and redundancy in the radio and core network to the primary data packet session.

[0048] In case the primary data packet session fails, one of the secondary data packet sessions takes over the new role of the primary session. The solution is discussed in further detail below, wherein it first starts with the primary session establishment as is shown in connection with Figure 2. The UE 100 transmits in step S11 a session establishment request to the primary access and mobility management entity 320. This session establishment request already contains an indication that a further data packet session should be established. In step S12 the AMF 320 transmits a session create request to the session management entity 330 of the primary network which also contains the indication to establish at least one further data packet session of a combined or aggregated session. The SMF 330 then fetches the subscription data and policy rules in steps S13 and S14. The SMF allocates in S15 an I P address for the session which may come from a special I P pool managed by all cooperating mobile network operators. In step S16 the user plane session is established and radio resources are requested from the access network in step S17 and in step S18. The accept message for the radio resources is transmitted to the UE, wherein in step S18 it is indicated to the UE that the request for the further session is allowed so that it includes an accept for the indicator to establish a further data packet session over another cellular network. In step S19 a reply message is sent back to the SMF in reply to step S17 so that the first uplink data are established in step S20, wherein in step S21 the UPF is updated to set up a tunnel to the access network providing first downlink data in step S22 and providing a user data tunnel in step S23.

[0049] A possible implementation of the figures is as follows:

[0050] S11 : PDU Session Establishment Request (Primary PDU Session Indication)

[0051] S12: Nsmf_PDU Session Create SMContextRequest (Primary PDU Session Indication)

[0052] S13: Get subscription data

[0053] S14: Get policy rules

[0054] S15: IP Allocation from Cooperating NWIP Pool

[0055] S16: Establish Session for User Plane

[0056] S17: Request Radio Resources

[0057] S18: Setup Radio Resources (PDU Session Establishment Accept) {Primary PDU Session Accept}

[0058] S19: Reply from AN

[0059] S20: First uplink data

[0060] S21 : Update UPF to setup tunnel to AN

[0061] S22: First downlink data

[0062] S23: User data

[0063] The UE 100 can now request an additional secondary data packet session from another network to aggregate. If and how many other networks could be decided by the user, the UE or network policy, such as the UE resource selection priority, depending on the decision logic. Figures 3A to 3C now show the message exchange between the involved entities, how the secondary data packet session is established and how it is merged with the primary data session. In step S31 the UE transmits a session establishment request to the AMF 220 wherein this request comprises an identifier of the primary AMF of the primary network and comprising a session identifier, such as a PDU session ID which allows the already existing data packet session to be identified. The identifier of the mobility handling entity can be implemented as the primary GUTI, the Globally Unique Temporary Identifier. In step S32 the AMF transmits a discovery request first to the secondary network repository function 270 and then to the primary network repository function 370. This discovery request includes at least the identifier of the mobility handling entity such as the primary GUTI and the GUAMI, the globally unique AMF ID. Furthermore, the request includes the session identifier of the primary data packet session. The response is transmitted back in step S33 comprising the IP address of the primary AMF. In step S34 a context transfer request is transmitted to the primary AMF 320 containing the ID of the primary data packet session. The response in step S35 contains the address of the primary SMF. Accordingly, the secondary AMF can use a roaming interface architecture to ask the secondary NRF 270 about the network function discovery with a service request for the primary AMF discovery. The secondary NRF 270 forwards the request to the roaming partner’s primary NRF 370 which responds with the primary AMF IP address. The secondary AMF 220 uses a roaming interface architecture to ask the primary AMF with the UE context transfer with details of the primary SMF address.

[0064] In step S36 the secondary AMF 220 selects the secondary and the primary SMF based on the received primary SMF address. Accordingly the SMF selection procedure selects the secondary SMF and additionally selects the primary SMF with the previously received information. In step S37 a session create request is transmitted to the secondary SMF 230 which includes the identifier of the mobility handling entity of the primary network, the primary GUTI and which includes the primary session ID. The method continues in step S38 and S39 with the obtaining of the subscription data and the policy rules so that in step S40 the user plane in the secondary UPF 240 is established. The method continues in Figure 3B in step S41 , where the secondary SMF 230 transmits a session create request to the primary SMF 330, wherein this request contains the information of the primary session ID and a tunneling downlink tunnel endpoint, TEID, from the primary SMF. This can be considered similar to the roaming and the secondary SMF may use the roaming interface architecture in this request of step S41. In step S42 the primary SMF adds this tunnel from the secondary data session to the primary data session and establishes the user plane in the UPF. Accordingly a session interconnect is triggered by the SMF in step S44, the user plane session interconnect is carried out so that the secondary data packet session is interconnected to the primary data packet session. In step S45 the first downlink data are transmitted and in step S46 the SMF responds to the request of step S41 including the primary session ID, the tunnel endpoint ID for the uplink UPF and the virtual IP address. Accordingly, the primary SMF replies with information of the chosen IP address for the UE and the tunneling uplink TEID from the primary UPF. This virtual IP address is the external visible IP address of the application and the UE. It should be marked as used in the secondary SMF so that this virtual IP address cannot be assigned a second time. As the secondary SMF 230 could well be a primary SMF for a different primary data session, another virtual IP address needs to be allocated. The marking of the virtual IP address as used avoids that the secondary SMF assigns the same IP address to a different data session. The marking of the virtual IP address as used is carried out in step S47 and in step S48, the modification session for the user plane is indicated. The method continues in step S49 of Figure 3C with the request for radio resources and the setup of radio resources in step S50 and the reply from the access network in step S51. The first uplink data are transmitted in step S52 and in step S53, the UPF is updated to set up the tunnel to the access network with the first downlink data in step S54. The N9 interconnect user data tunnel is reaching the primary UPF which combines the information out to the Internet. Accordingly, a tunnel is established between the UE and UPF 340 in steps S55 and S56. In the same way, in step S57 the other tunnel is generated between the access network 210 and the UPF 340 with the N3 interface.

[0065] The UPFs 340 and 240 of the involved cooperating networks can be interconnected according to roaming agreements. This can mean that a roaming architecture deployment is provided between the operators so that the AMF, SMF, NRF, UPF IP connectivity between all involved network operators in the cooperative networks exists with a service level agreement. VPN UPF interconnect is available to protect the user traffic from eavesdropping.

[0066] A possible implementation of the Figures is as follows:

[0067] S31 : PDU Session Establishment Request (Primary GUTI, Primary PDU Session ID)

[0068] S32: Nnrf_NFDiscovery Request {Primary GUTI contains Primary GUAMI and Primary PLMNID, Primary PDU Session ID}

[0069] S33: Nnrf_NFDiscovery_Response {Primary AMF IP address}

[0070] S34: Namf_Communication_U EContext Transfer_Request {Primary PDU Session ID} S35: Namf_Communication_U EContext Transfer_Response {Primary SMF Address} S36: SMF Selection: Secondary SMF, Primary SMF

[0071] S37: Nsmf_PDU_Session_CreateSM Context Request(Primary GUTI; Primary PDU Session ID) S38: Get subscription data

[0072] S39: Get policy rules

[0073] S40: Establish Session for User Plane

[0074] S41 : Nsmf_PDUSession_Create Request (Primary PDU Session ID, TEIDDL UPF)

[0075] S42: Trigger PDU Session Interconnect Secondary to Primary PDU Session

[0076] S43: Establish Session for User Plane

[0077] S44: User Plane PDU Session Interconnect Secondary to Primary PDU Session

[0078] S45: First downlink data

[0079] S46: Nsmf_PDUSession_Create_Response {Primary PDU Session ID, TEID UL UPF, vIP}

[0080] S47: Mark vIP as used in COOP NWvl Pool

[0081] S48: Modification Session for User Plane

[0082] S49: Request radio resources

[0083] S50: Setup Radio Resources (PDU Session Establishment Accept)

[0084] S51 : Reply from AN

[0085] S52: First uplink data

[0086] S53: Update UPF to setup tunnel to AN)

[0087] S54: First downlink data

[0088] S55: Interconnect user data N3

[0089] S56: Interconnect user data N9

[0090] S57: User Plane data N3

[0091] S61 : Session status notification

[0092] In connection with Figures 4 and 5 the situation is explained in more detail if the primary data session fails. It is possible that all the secondary PDU sessions or data sessions may introduce a supervision mechanism by which they can detect this failure and they can decide which from the involved secondary data sessions can become the new primary data session. This may be reached via a BFD (Bidirectional Forwarding Detection) or any kind of protection mechanism to detect if the primary UPF is not available or a failure indication from the primary PDU session is indicated. In Figure 4 a solution is discussed in which the primary SMF informs the involved secondary SMFs about a standby SMF and the corresponding address of the standby SMF. This standby primary SMF will take over the role of the primary SMF when the current primary SMF fails.

[0093] Figure 5 shows the situation in more detail, where in step S62 the data connection between the two UPFs fail for any reason. The secondary UPF informs the secondary SMF of the failure in step S63. Now two different options are considered, in the first option discussed in steps S64 to 66, the corresponding SMF is the standby primary SMF so that in reaction to step S63 it takes over the primary session in step S64 so that an interconnect user data over the N6 interface is established in step S65 and the UE is informed in step S66 of the modification that SMF 230 is now the new primary SMF responsible for the primary data packet session. The other option is that the secondary SMF is not the standby primary so that in step S67 a session request is created to the new primary session and in step S 68 the method continues with step S41 with the session create request to the primary SMF.

[0094] Summarizing if the primary UPF drops a new primary UPF decision is taken from the rest of the involved mobile network operators. The secondary UPF can detect the primary UPF loss and informs the secondary SM F with a session report as indicated in step S63, the new primary SMF announces the fact of the new primary session to all other secondary SMFs and UPFs. The tunnel mapping is updated to the new primary UPF and all other UPFs and an update of tunnel mappings in the new primary UPF is carried out to route data packets out to the Internet. The primary switch of tunnels may be pre-prepared to act faster in case of the primary drop.

[0095] Fig. 6 summarizes the decision logic in the UE. In step S190 the method starts and in step S191 it is checked whether the UE is capable of using the aggregated data flow mechanism discussed above. If this is not the case, the method continues as known with a PDU session establishment (S192). If the UE is capable of using the aggregated data flow mechanism, the it includes the indication for the aggregated session in the session establishment request as discussed in connection with step S11 (S193). It S194 it waits for the accept message to know whether the aggregated session is also possible in the network. When this is confirmed in S 195, it requests establishment of a session including the primary GUTI, the primary PLMN ID and the primary PDU session ID per MNO as discussed in S31 above (S196). For the aggregated session it can carry out a load balancing for the uplink traffic in S197 and the downlink traffic is routed to the virtual IP address of the US in S198.

[0096] Figure 7 summarizes the steps and decision logic carried out in the secondary AMF 220. In the secondary AMF the method starts in step S71 and in step S72 it is checked whether the event is detected that a session request is received with the indicator for a further session. If this is the case, the SMF selection process is carried out as discussed in step S36 with the selection of the secondary SM F as known and the selection of the primary SM F with a Discover request for discovering the primary AMF and the UE context transfer request to the primary AMF to fetch the address of the primary SMF (S73). The method then continues as known in step S74 and the method ends in step S75. Figure 8 summarizes the steps and the decision logic carried out in the primary SMF. The method starting in step S81 and in step S82 it is checked whether an event is identified. If a session request is received with an identifier of a primary PDU session which indicates that data should be aggregated in connection with other sessions through at least one other network, an IP address is allocated from a network pool, as discussed in connection with steps S12 and S15. An accept message is sent back in response to the session establishment request, a step not shown in Figure 2 as indicated in step S84 and the design base procedure continues in step S85. Furthermore, a session create request might be received as discussed in connection with step S41 which contains the primary PDU session ID and the tunnel endpoint ID for the downlink UPF (S86). In S87 the session interconnect is triggered interconnecting the secondary and the primary session and in step S88 a mapping table can be created of traffic from the TEID uplink of the primary session with the traffic from the UPF interconnect for the uplink traffic. In the same way, a mapping table can be created for the downlink traffic over all involved downlink tunnels in step S89 and the user plane connection in the primary UPF is established in step S90, wherein the session create response as discussed in step S46 is created in step S91 containing the virtual IP address, the primary PDU session ID and the ID of the tunnel endpoint for the uplink UPF. The method ends in step S92.

[0097] In connection with Figure 9, the decision lodging in the secondary SMF is discussed, the method starting step S95. The event is detected in step S96. The event can be the session create response as discussed above in step S46 so that in step S97 the virtual IP address is marked as being used in the pool of common IP addresses, and in step S98 the tunnel to the primary UPF is generated. An uplink tunnel mapping is created in step S 99, where a mapping is carried out of the TEID N3 uplink traffic info into the TEID UPF interconnect uplink tunnel. In the same way in step S100 downlink tunnel mapping is created, mapping the TEID UPF interconnect downlink traffic into the TEID N3 downlink. The user plane connection and the secondary UPF is generated as step S101 and the method continues as known in step S102. The secondary SMF may receive the information that the master or primary session is lost and in step S103 it determines the algorithm to check whether the secondary SM F will play the role of the new primary SMF which is then checked in S104. If this is the case, it informs in step S105 that it has become the new primary SMF for the previous session so that it will accept in step S106 the interconnect request received from other mobile network operators to bundle the traffic. In step S107 the own PLMN ID and the session ID gets the new primary PDU session. If the secondary SMF is not the new primary SMF it waits in step S108 for the announcement of the primaryship, creates in step S109 a GTP tunnel to the primary UPF, creates uplink tunnel mapping in step S110 which maps the TEID N3 uplink traffic into the TEID UPF interconnect uplink tunnel. In the same way, in step S111 a downlink tunnel mapping is created mapping the TEID UPF interconnected downlink traffic into the TEID N3 downlink and a user plane connection is established in the secondary UPF in step S112.

[0098] Figure 10 summarizes the events in the secondary UPF and the method starts in step S120. Different events may be detected in step S121 and the event may be a setup between the coworking networks so that a connectivity is created in step S122 to all involved user plane functions in the cooperating networks. Furthermore, a connectivity protection mechanism may be created in step S123. The event may furthermore contain the information that the primary UPF or the primary PDU session is lost. Accordingly, this is reported to the secondary SMF in step S124 ( N4 PFCP Session report) and as discussed above in connection with Figure 5 in step S63. If an aggregated session is present and the downlink traffic for the primary session is arriving, it is passed on on an N3 tunnel to the access network in step S125 and if an uplink traffic arrives, it is passed on to the primary session via interconnect in step S126, the method ending in step S127.

[0099] Figure 11 summarizes the decision logic in the primary UPF and the method starts in step S130 and an event is detected in step S131 which can be the uplink traffic for the primary PDU session. Here, the traffic is merged for all involved tunnels to forward the traffic to the server in step S132. If downlink traffic is received, a load balancing of the downlink traffic can be carried out in the UPF over all connected tunnels and the own N3 tunnel in step S133. The method ends in step S134.

[0100] Figure 12 summarizes the steps carried out at the secondary mobility handling entity 220. In step S141 an establishment request is received containing the ID of the primary AMF and the primary session ID as discussed above in step S31. In step S142 a discovery request is transmitted with the ID of the primary AMF and the primary session ID as discussed above in connection with step S32. In step S143 a response is received with the address of the primary AMF so that in step S144 an address request can be transmitted to the primary AMF requesting the address of the primary SMF.

[0101] Figure 13 summarizes the steps carried out at the secondary session management entity which receives in step S151 a session create request from the secondary mobility handling entity containing the primary session at the end of the primary AMF ID as discussed in step S37. In step S52 a session create request is transmitted to the primary session management entity including the primary session ID, the downlink endpoint used in the secondary cellular network and an identifier of the secondary user plane entity handling the session and the secondary network. This was discussed in connection with step S41. The response as received in step S46 contains the ID of the primary session, the uplink endpoint identifier of the uplink endpoint used in the primary network entity network address of the UE, S153. In step S154 the network address of the UE is marked as used as discussed above in connection with step S47.

[0102] Figure 14 summarizes the steps carried out at the primary SMF and in step S161 a session create request is received from the secondary SMF wherein this request includes the session identifier of the primary session, the downlink endpoint identifier of the downlink endpoint used in the secondary network and an identifier of the secondary user plane entity as discussed above in connection with step S41. In step S162 an interconnection of the secondary data packet session to the primary data packet session is initiated and in step S163 a primary user plane entity is selected handling the primary and secondary data packet session and a response is transmitted to the secondary SMF which contains the primary session ID, the uplink endpoint identifier of the uplink endpoint in the primary network entity network address of the UE.

[0103] Figure 15 summarizes the steps carried out at the primary user plane entity which receives in step S171 the first session establishment request for the primary session, receives in step S172 the second establishment request for the secondary data packet session including the binding information which allows the binding of the primary to the secondary session. Steps S171 and 172 were discussed above in connection with steps S16 and S43. The interconnection step S173 was discussed above in connection with step S44.

[0104] Figure 16 summarizes the steps carried out at the user equipment 100 in the method discussed above. In step S181 a first session establishment request is transmitted including the indication to establish a secondary data packet session as discussed in step S11. In step S162 a response is received to this request which includes the acknowledgment that the establishment is enabled and which also contains the session identifier of the primary data packet session. This step was not shown in detail in Figures 2 to 4. In step S183 a second establishment request is transmitted towards the secondary SMF to establish the secondary data packet session which comprises the identifier of the AMF and the session ID of the primary session.

[0105] Figure 17 shows a schematic architectural view of the user equipment 100 which can carry out the above discussed request for the aggregated session. The user equipment comprises an interface 110 provided for transmitting user data and control messages and provided for receiving user data and control messages to other entities as discussed above. The user equipment furthermore comprises a processing unit 120 which is responsible for the operation of the user equipment 100. The processing entity 120 comprises one or more processors and can carry out instructions stored on a memory 230, wherein the memory may include a readonly memory, a random access memory, a mass storage, a hard disk or the like. The memory can furthermore include a suitable program code to be executed by the processing unit 120 so as to implement the above-described functionalities in which the user equipment is involved.

[0106] Figure 18 shows a schematic architectural view of the secondary session management entity 230 comprising an interface 231 provided for transmitting control messages or data to other entities and provided for receiving control messages or the data from other entities. The session management entity 230 furthermore comprises a processing unit 232 which is responsible for the operation of the session management entity 230. The processing unit 232 comprises one or more processors and can carry out instructions stored on a memory 233 wherein the memory may include a read-only memory, a random access memory, a mass storage, a hard disk or the like. The memory can furthermore include a suitable program code to be executed by the processing unit 232 so as to implement the above-described functionalities in which the secondary session management entity is involved.

[0107] Figure 19 shows a schematic architectural view of the primary session management entity 330 comprising an interface 331 provided for transmitting data or control messages to other entities and for receiving data and control messages from other entities. The primary session management entity furthermore comprises a processing unit 332 which is responsible for the operation of the session management entity 330. The processing entity 332 comprises one or more processors and can carry out instructions stored on a memory 333 wherein the memory may include a read-only memory, a random access memory, a mass storage, a hard disk or the like. The memory 333 can furthermore include a suitable program code to be executed by the processing unit 332 so as to implement the above-described functionalities in which the primary session management entity is involved.

[0108] Figure 20 shows a schematic architectural view of the primary user plane entity 340 comprising an interface 341 configured to receive user data such as a data packet session from other entities or control messages from other entities and configured to transmit user data such as data packet session and control messages to other entities. The user plane entity furthermore comprises a processing unit 342 which is responsible for the operation of the user plane entity of the primary network. The processing unit 342 comprises one or more processors and can carry out instructions stored on a memory 343 wherein the memory may include a read-only memory, a random access memory, a hard disk, a mass storage or the like. The memory can include a suitable program code to be executed by the processing unit 120 so as to implement the above-described functionalities in which the primary user plane entity is involved.

[0109] Figure 21 shows a schematic architectural view of the secondary SMF 220 comprising an interface 221 configured to transmit data and control messages to other entities and configured to receive data and control messages from other entities. The secondary SMF comprises a processing unit 222 which is responsible for the operation of the mobility handling entity. The processing unit 222 comprises one or more processors and can carry out instructions stored on a memory 223 wherein the memory may include a read-only memory, a random access memory, a mass storage, a hard disk or the like. The memory can include suitable program code to be executed by the processing unit 222 so as to implement the above-described functionalities in which the secondary mobility handling entity is involved.

[0110] From the above said some general conclusions can be drawn.

[0111] As far as the secondary mobility handling entity is concerned, it may receive in response to the address request an address response from the primary mobility handling entity including a network address of the primary session management entity. This was discussed in more detail in connection with step S35.

[0112] Furthermore, it is possible that the secondary mobility handling entity selects the primary session management entity based on the received network address after primary session management entity and transmits a session create request to the secondary session management entity including the identifier of the mobility handling entity of the primary cellular network and including a session identifier of the primary data packet session. These steps were discussed above in connection with step S36 and S37.

[0113] The transmitted discovery request can comprise a network identifier identifying the primary cellular network.

[0114] As far as the secondary session management entity is concerned, it marks the network address of the user equipment as being used wherein this may be done in a common pool of common network addresses used in the primary and the secondary cellular network.

[0115] Furthermore, it is possible that two or more secondary cellular networks are provided wherein each of the two or more secondary cellular networks comprise a secondary session management entity. Here, a primary session and several of the secondary sessions are used for the data transmission. The secondary session management entity may receive from the primary session management entity a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over the role of a new primary session management entity when the primary session management entity fails. This was discussed in connection with Figures 4 and 5, especially Figure 4, step S61.

[0116] The secondary SMF may furthermore determine that the primary session management entity has failed, it may determine to take over the role of the new primary session management entity and may inform the user equipment that the own secondary data packet session has become the new primary data packet session as discussed in connection with Figure 5. Furthermore, it is possible that it determines that the primary session management entity has failed and the secondary SMF may determine the network address of the standby session management entity and may transmit a session create request to the new standby session management entity. This was discussed in the second option of Figure 5.

[0117] As far as the primary SMF is concerned, it is possible that the primary SMF transmits to each of the secondary session management entities of the two or more secondary networks a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over the role of the new primary session management entity when the primary session management entity fails.

[0118] As far as the primary user plane entity is concerned, it may merge the data packets from the primary and the secondary data packet session to a combined data packet session for an uplink traffic from the user equipment in direction of the destination and it may transmit the combined data packet session in direction of the destination using a common network address for the destination.

[0119] Furthermore, the user plane entity may receive a combined data packet session for a downlink traffic to the user equipment, may distribute the data packets of the combined data packet session into data packets for the primary data packet session and into data packets for the secondary data packet session wherein the primary data packet session is transmitted via a primary tunnel and the secondary data packet session is transmitted via a secondary tunnel in direction of the user equipment. Furthermore, it is possible to determine a load in a primary and secondary network and to distribute the combined data packet session based on the load in the primary and secondary network. As far as the user equipment is concerned, the user equipment may distribute the data packets of the combined data packet session into data packets for the primary data packet session and into packets for the secondary data packet session for an uplink traffic based on a load in the primary and secondary cellular network.

[0120] The above discussed solution has several advantages and provides a capacity boost for the radio access network for throughput enhancement of a service to the Internet. It furthermore provides an improved capacity to enable new services in remote areas needing a high bandwidth such as video or augmented or virtual reality.

[0121] It provides a redundancy on the air interface, the radio access network and / or core network to securely provide the required service and provides a seamless connectivity of the multi-SIM UE.

Claims

Claims1. A method, carried out at a secondary mobility handling entity (220) of a secondary cellular network comprising:- receiving (S31) an establishment request from a user equipment (100) having a subscription to a primary cellular network and to the secondary cellular network, to establish a secondary data packet session, the establishment request comprising an identifier of a mobility handling entity of the primary cellular network, and a session identifier of a primary data packet session of the user equipment established in the primary cellular network,- transmitting (S32) a discovery request towards a central registration entity of the primary cellular network including at least the identifier of the mobility handling entity of the primary cellular network and the session identifier of the primary data packet session,- receiving (S33) a response to the discovery request including an address of the primary mobility handling entity of the primary cellular network,- transmitting (S34), using the received address, an address request to the primary mobility handling entity, requesting an address of a primary session management entity of the primary cellular network.

2. The method of claim 1 , further comprising:- receiving (S35), in response to the address request, an address response from the primary mobility handling entity including a network address of the primary session management entity.

3. The method of claim 2, further- selecting (S36) the primary session management entity based on the received network address of the primary session management entity,- transmitting a session create request (S37) to the secondary session management entity including the identifier of a mobility handling entity of the primary cellular network, and a session identifier of a primary data packet session.

4. The method of any preceding claim, wherein the transmitted discovery request comprises a network identifier identifying the primary cellular network.

5. A method carried out at a secondary session management entity (230) of a secondary cellular network, comprising:- receiving (S37), from a secondary mobility handling entity (220), a session create request including an identifier of a mobility handling entity of a primary cellular network, and a sessionidentifier of a primary data packet session of a user equipment in the primary cellular network, having a subscription to the primary cellular network and to the secondary cellular network,- transmitting (S41) a session create request to a primary session management entity (330) of the primary cellular network to create a secondary data packet session for the user equipment, the session create request including the session identifier of the primary data packet session, a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and secondary data packet session, and an identifier of a secondary user plane entity handling the first and second data packet session in the secondary cellular network,- receiving (S46) a response to the session create request from the primary session management entity (330), the response containing the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session, and a network address of the user equipment in the primary data packet session,- marking (S47) the network address of the user equipment in the primary cellular network as being used.

6. The method of claim 5, wherein the network address of the user equipment is marked as used in a common pool of common network addresses used by the primary and secondary cellular network.

7. The method of claim 5 or 6, wherein two or more secondary cellular networks are provided each of the two or more secondary cellular networks comprising a secondary session management entity.

8. The method of claim 7, further receiving, from the primary session management entity, a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over a role of a new primary session management entity when the primary session management entity fails.

9. The method of claim 8, further comprising :- determining that the primary session management entity has failed,- determining to take over the role of the new primary session management entity,- informing the user equipment that the own secondary data packet session has become the new primary data packet session.

10. The method of claim 8, further comprising- determining that the primary session management entity has failed,- determining the network address of the standby session management entity,- transmitting a session create request to the standby session management entity.

11. A method carried out at a primary session management entity (330) of a primary cellular network, comprising:- receiving (S41) a session create request from a secondary session management entity (230) to create a secondary data packet session for a user equipment having a subscription to the primary cellular network and to the secondary cellular network, the session create request including a session identifier of a primary data packet session handled by the primary session management entity for the user equipment in the primary cellular network, a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and secondary data packet session, and an identifier of a secondary user plane entity in the secondary cellular network handling the first and second data packet session,- initiating (S42) an interconnection of the secondary data packet session to the primary data packet session,- selecting a primary user plane entity (340) handling the primary and secondary data packet session,- transmitting (S46) a response to the secondary session management entity, the response containing the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session, and a network address of the user equipment.

12. The method of claim 11 , wherein the secondary cellular network comprises two or more secondary cellular networks, each of the two or more secondary cellular networks comprising a secondary session management entity.

13. The method of claim 12, further transmitting, to each of the secondary session management entities of the two or more secondary cellular networks, a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over a role of a new primary session management entity when the primary session management entity fails.

14. A method carried out at a primary user plane entity (340) of a primary cellular network, comprising:- receiving (S16), from a primary session management entity of the primary cellular network, a first session establishment request for establishing a primary data packet session for a userequipment having a subscription to the primary cellular network and to a secondary cellular network,- receiving (S43), from the primary session management entity (330) of the primary cellular network, a second session establishment request for establishing a secondary data packet session for the user equipment, the second session establishment request including binding information allowing to link the primary data packet session to the secondary data packet session,- interconnecting (S44) the primary and the secondary data packet session based on the binding information.

15. The method of claim 14, further- merging data packets from the primary and secondary data packet sessions to a combined data packet session for an uplink traffic from the user equipment in direction of destination,- transmitting the combined data packet session in direction of a destination using a common network address for the destination.

16. The method of claim 14 or 15 further- receiving a combined data packet session of a downlink data traffic to the user equipment,- distributing the data packets the combined data packet session into data packets for the primary data packet session and into data packets for the secondary data packet session , and- transmitting the primary data packet session via a primary tunnel and the secondary data packet session via a secondary tunnel in direction of the user equipment.

17. The method of claim 16, further determining a load in the primary and secondary cellular network and distributing the combined data packet session based on determined load in primary and secondary cellular network.

18. A method carried out at a user equipment (100) having a subscription to a primary cellular network and to a secondary cellular network, comprising:- transmitting (S11) a first establishment request towards a primary session management entity of the primary cellular network to establish a primary data packet session of a combined data packet session in the primary cellular network, the first establishment request including an indicator to establish a secondary data packet session of the combined data packet session in the secondary cellular network,- receiving a response to the first establishment request, the response including an acknowledgement that the establishment of the secondary data packet session is enabled, and a session identifier of the primary data packet session,- transmitting a second establishment request towards a secondary session management entity of the secondary cellular network, to establish the secondary data packet session, the establishment request comprising an identifier of a mobility handling entity of the primary cellular network, and the session identifier of the primary data packet session of the user equipment in the first cellular network.

19. The method of claim 18, further distributing data packets of the combined data packet session into data packets for the primary data packet session and into data packets for the secondary data packet session for an uplink traffic in direction of the primary and secondary cellular network based on a load in the primary and secondary cellular network.

20. A secondary mobility handling entity of a secondary cellular network, comprising a memory and at least one processing unit, the memory containing instructions executable by the at least one processing unit, wherein the secondary mobility handling entity is configured to:- receive (S31) an establishment request from a user equipment (100) having a subscription to a primary cellular network and to the secondary cellular network, to establish a secondary data packet session, the establishment request comprising an identifier of a mobility handling entity of the primary cellular network, and a session identifier of a primary data packet session of the user equipment established in the primary cellular network,- transmit (S32) a discovery request towards a central registration entity of the primary cellular network including at least an identifier of a mobility handling entity of the primary cellular network and the session identifier of the primary data packet session,- receive (S33) a response to the discovery request including an address of a primary mobility handling entity of the primary cellular network,- transmit (S34), using the received address, an address request to the primary mobility handling entity, requesting an address of a primary session management entity of the primary cellular network.

21. The secondary mobility handling entity of claim 20, further being configured to receive (S35), in response to the address request, an address response from the primary mobility handling entity including a network address of the primary session management entity.

22. The secondary mobility handling entity of claim 21 , further being configured- select (S36) the primary session management entity based on the received network address of the primary session management entity,- transmit a session create request (S37) to the secondary session management entity including the identifier of a mobility handling entity of the primary cellular network, and a session identifier of a primary data packet session.

23. The secondary mobility handling entity of any of claims 20 to 22, wherein the transmitted discovery request comprises a network identifier identifying the primary cellular network.

24. A secondary session management entity of a secondary cellular network, comprising a memory and at least one processing unit, the memory containing instructions executable by the at least one processing unit, wherein the secondary session management entity is configured to:- receive (S37), from a secondary mobility handling entity (220), a session create request including an identifier of a mobility handling entity of a primary cellular network, and a session identifier of a primary data packet session of a user equipment in the primary cellular network having a subscription to the primary cellular network and to the secondary cellular network,- transmit (S41) a session create request to a primary session management entity (330) of the primary cellular network to create a secondary data packet session for the user equipment, the session create request including the session identifier of the primary data packet session, a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and secondary data packet session, and an identifier of a secondary user plane entity handling the first and second data packet session in the secondary cellular network,- receive (S46) a response to the session create request from the primary session management entity (330), the response containing the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session, and a network address of the user equipment in the primary data packet session,- mark the network address of the user equipment in the primary cellular network as being used.

25. The secondary session management entity of claim 24, wherein the network address of the user equipment is marked as used in a common pool of common network addresses used by the primary and secondary cellular network.

26. The secondary session management entity of claim 24 or 25, wherein two or more secondary cellular networks are provided each of the two or more secondary cellular networks comprising a secondary session management entity.

27. The secondary session management entity of claim 26, further being operative to receive, from the primary session management entity, a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over a role of a new primary session management entity when the primary session management entity fails.

28. The secondary session management entity of claim 27 further being configured to- determine that the primary session management entity has failed,- determine to take over the role of the new primary session management entity,- inform the user equipment that the own secondary data packet session has become the new primary data packet session.

29. The secondary session management entity of claim 27 further being configured to- determine that the primary session management entity has failed,- determine the network address of the standby session management entity,- transmit a session create request to the standby session management entity.

30. A primary session management entity of a secondary cellular network, comprising a memory and at least one processing unit, the memory containing instructions executable by the at least one processing unit, wherein the primary session management entity is configured to:- receive (S41) a session create request from a secondary session management entity (230) to create a secondary data packet session for a user equipment having a subscription to the primary cellular network and to the secondary cellular network, the session create request including a session identifier of a primary data packet session handled by the primary session management entity for the user equipment in the primary cellular network, a downlink endpoint identifier of a downlink endpoint used in the secondary cellular network for the primary and secondary data packet session, and an identifier of a secondary user plane entity in the secondary cellular network handling the first and second data packet session,- initiate (S42) an interconnection of the secondary data packet session to the primary data packet session,- select a primary user plane entity (340) handling the primary and secondary data packet session,- transmit (S46) a response to the secondary session management entity, the response containing the session identifier of the primary data packet session, an uplink endpoint identifier of an uplink endpoint used in the primary cellular network for the primary and secondary data packet session, and a network address of the user equipment.

31. The primary session management entity of claim 30, wherein the secondary cellular network comprises two or more secondary cellular networks, each of the two or more secondary cellular networks comprising a secondary session management entity.

32. The primary session management entity of claim 31 , further being configured to transmit, to each of the secondary management entities of the two or more secondary cellular networks, a network address of one standby session management entity from the secondary session management entities of the two or more secondary cellular networks that will take over a role of a new primary session management entity when the primary session management entity fails.

33. A primary user plane entity comprising a memory and at least one processing unit, the memory containing instructions executable by the at least one processing unit, wherein the primary user plane entity is configured to:- receive (S16), from a primary session management entity of the primary cellular network, a first session establishment request for establishing a primary data packet session for a user equipment having a subscription to the primary cellular network and to a secondary cellular network,- receive (S43), from the primary session management entity (330) of the primary cellular network, a second session establishment request for establishing a secondary data packet session for the user equipment, the second session establishment request including binding information allowing to link the primary data packet session to the secondary data packet session,- interconnect (S44) the primary and the secondary data packet session based on the binding information.

34. The primary user plane entity of claim 33, further being operative to- merge data packets from the primary and secondary data packet sessions to a combined data packet session for an uplink traffic from the user equipment in direction of destination,- transmit the combined data packet session in direction of a destination using a common network address for the destination.

35. The primary user plane entity of claim 33 or 34, further being operative to- receive a combined data packet session of a downlink data traffic to the user equipment,- distribute the of the data packets the combined data packet session into first data packets for the primary data packet session and into second data packets for the secondary data packet session , and- transmit the primary data packet session via a primary tunnel and the secondary data packet session via a secondary tunnel in direction of the user equipment.

36. The primary user plane entity of claim 35, further being configured to determine a load in the primary and secondary cellular network and separate the combined data packet session based on determined load in primary and secondary cellular network.

37. A user equipment comprising a memory and at least one processing unit, the memory containing instructions executable by the at least one processing unit, wherein the user equipment is configured to:- transmit (S11) a first establishment request towards a primary session management entity of the primary cellular network to establish a primary data packet session of a combined data packet session in the primary cellular network, the first establishment request including an indicator to establish a secondary data packet session of the combined data packet session in the secondary cellular network,- receive a response to the first establishment request, the response including an acknowledgement that the establishment of the secondary data packet session is enabled, and a session identifier of the primary data packet session,- transmit a second establishment request towards a secondary session management entity of the secondary cellular network, to establish the secondary data packet session, the establishment request comprising an identifier of a mobility handling entity of the primary cellular network, and the session identifier of the primary data packet session of the user equipment in the primary cellular network.

38. The user equipment of claim 37, further being configured to distribute data packets of the combined data packet session into data packets for the primary data packet session and into data packets for the secondary data packet session for an uplink traffic in direction of the primary and secondary cellular network based on a load in the primary and secondary cellular network.

39. A system comprising at least 2 entities selected from the following group: a secondary mobility management entity as mentioned in any of claims 20 to 23, a secondary session management entity as mentioned in any of claims 24 to 29, a primary session management entity as mentioned in any of claims 30 to 32, a primary user plane entity asmentioned in any of claims 33 to 36, and a user equipment as mentioned in any of claims 37 and 38.

40. A computer program comprising program code to be executed by at least one processing unit of a secondary mobility management entity, wherein execution of the program code causes the at least one processing unit to carry out a method as mentioned in any of claims 1 to 4.

41. A computer program comprising program code to be executed by at least one processing unit of a secondary session management entity, wherein execution of the program code causes the at least one processing unit to carry out a method as mentioned in any of claims 5 to 10.

42. A computer program comprising program code to be executed by at least one processing unit of a primary session management entity, wherein execution of the program code causes the at least one processing unit to carry out a method as mentioned in any of claims 11 to 13.

43. A computer program comprising program code to be executed by at least one processing unit of a primary user plane entity, wherein execution of the program code causes the at least one processing unit to carry out a method as mentioned in any of claims 14 to 17.

44. A computer program comprising program code to be executed by at least one processing unit of a user equipment, wherein execution of the program code causes the at least one processing unit to carry out a method as mentioned in any of claims 18 to 19.

45. A carrier comprising the computer program of any of claims 40 to 44, wherein the carrier is one of an electronic signal, optical signal, radio signal, and computer readable storage medium.

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