Patent Description:
The following abbreviations and acronyms are herewith defined, at least some of which are referred to within the following description.

Third Generation Partnership Project ("3GPP"), Access and Mobility Management Function ("AMF"), Access Point Name ("APN"), Access Stratum ("AS"), Carrier Aggregation ("CA"), Clear Channel Assessment ("CCA"), Control Channel Element ("CCE"), Channel State Information ("CSI"), Common Search Space ("CSS"), Data Network Name ("DNN"), Data Radio Bearer ("DRB"), Downlink Control Information ("DCI"), Downlink ("DL"), Enhanced Clear Channel Assessment ("eCCA"), Enhanced Mobile Broadband ("eMBB"), Evolved Node-B ("eNB"), Evolved Packet Core ("EPC"), Evolved UMTS Terrestrial Radio Access Network ("E-UTRAN"), European Telecommunications Standards Institute ("ETSI"), Frame Based Equipment ("FBE"), Frequency Division Duplex ("FDD"), Frequency Division Multiple Access ("FDMA"), Globally Unique Temporary UE Identity ("GUTI"), Hybrid Automatic Repeat Request ("HARQ"), Home Subscriber Server ("HSS"), Internet-of-Things ("IoT"), Key Performance Indicators ("KPI"), Licensed Assisted Access ("LAA"), Load Based Equipment ("LBE"), Listen-Before-Talk ("LBT"), Long Term Evolution ("LTE"), LTE Advanced ("LTE-A"), Medium Access Control ("MAC"), Multiple Access ("MA"), Modulation Coding Scheme ("MCS"), Machine Type Communication ("MTC"), Massive MTC ("mMTC"), Mobility Management ("MM"), Mobility Management Entity ("MME"), Multiple Input Multiple Output ("MIMO"), Multipath TCP ("MPTCP"), Multi User Shared Access ("MUSA"), Non-Access Stratum ("NAS"), Narrowband ("NB"), Network Function ("NF"), Next Generation (e.g., <NUM>) Node-B ("gNB"), Next Generation Radio Access Network ("NG-RAN"), New Radio ("NR"), Policy Control & Charging ("PCC"), Policy Control Function ("PCF"), Policy Control and Charging Rules Function ("PCRF"), Packet Data Network ("PDN"), Packet Data Unit ("PDU"), PDN Gateway ("PGW"), Quality of Service ("QoS"), Quadrature Phase Shift Keying ("QPSK"), Radio Access Network ("RAN"), Radio Access Technology ("RAT"), Radio Resource Control ("RRC"), Receive ("RX"), Switching/Splitting Function ("SSF"), Scheduling Request ("SR"), Serving Gateway ("SGW"), Session Management Function ("SMF"), System Information Block ("SIB"), Transport Block ("TB"), Transport Block Size ("TBS"), Time-Division Duplex ("TDD"), Time Division Multiplex ("TDM"), Transmission and Reception Point ("TRP"), Transmit ("TX"), Uplink Control Information ("UCI"), Unified Data Management ("UDM"), User Entity/Equipment (Mobile Terminal) ("UE"), Uplink ("UL"), User Plane ("UP"), Universal Mobile Telecommunications System ("UMTS"), Ultra-reliability and Low-latency Communications ("URLLC"), and Worldwide Interoperability for Microwave Access ("WiMAX").

The wireless communication systems, a E-UTRAN can connect to both an EPC (e.g., <NUM> or LTE core network) and a <NUM> core network ("5GC"). The combination of E-UTRAN and EPC is referred to as the evolved packet system ("EPS"). The combination of <NUM>-RAN (also referred to as NG-RAN) and 5GC is referred to as the <NUM> system ("5GS"). Additionally, during a transition period while <NUM> networks deploy, the 5GC may not support all services enabled in the EPC. For example, to support various deployment scenarios, the <NUM> system supports fallback procedures towards a E-UTRAN or towards an EPC for providing emergency services.

<CIT> discusses a method for facilitating preservation of session context information during an inter-radio access technology service retry.

Claims <NUM>, <NUM> and <NUM> each define an apparatus. Claims <NUM> and <NUM> each define a method.

Methods for suspending services in a first core network while attached to a second core network are disclosed. Apparatuses and systems also perform the functions of the methods. One method (e.g., of a user equipment) for suspending services in a first core network while attached to a second core network includes using a first service in a first core network of a mobile communication network and determining to suspend the first service in order to use a second service in the second core network. Here, using the second service in the second core network may include one of: initiating a service in the second core network that is unavailable in the first core network and transferring to the second core network a service used in the first core network. The method includes sending a first mobility management ("MM") message in response to determining to suspend the first service (in order to use the second service in the second core network) and using the second service in the second core network without using the first service. Here, the MM message indicates that the first service is to be suspended while the remote unit is attached to the second core network.

Another method (e.g., of a mobility management function) for suspending services in a first core network while attached to a second core network includes receiving a message requesting suspension of one or more services (e.g., a first set of services) associated with a remote unit registered with the apparatus and suspending the one or more services (e.g., first set of services), said one or more services remaining in a first core network in a mobile communication network. Suspending the (first set of) one or more services includes preserving data connection context corresponding to the one or more services associated with the remote unit and setting a mobility management state for the remote unit to a state that indicates the remote unit is unreachable. Here, the remote unit is unreachable due to use of a service in a second core network.

This code may be provided to a processor of a general-purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagrams.

The code may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus, or other devices to produce a computer implemented process such that the code which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the schematic flowchart diagrams and/or schematic block diagram.

Generally, the present disclosure focuses on the Interworking procedures between EPC and 5GC in case of a network supporting Dual Registration ("DR") and a UE capable of DR-mode. Further, in terms of radio capability, the UE may be capable of (<NUM>) single reception and transmission (single Rx/Tx), (<NUM>) single transmission and dual reception (single Tx, dual Rx) and (<NUM>) dual reception and dual transmission (dual Rx/Tx). Unless the UE is dual Rx/Tx capable, the UE is only able to connect to (and use services of) one RAT/system at a time, even if configured for DR-mode.

<FIG> depicts a wireless communication system <NUM> for suspending services in a first core network while attached to a second core network, according to embodiments of the disclosure. In one embodiment, the wireless communication system <NUM> includes at least one remote unit <NUM>, a first access network <NUM> containing at least one base unit <NUM>, a second access network <NUM> containing at least one base unit <NUM>, wireless communication links <NUM> between remote unit <NUM> and base unit <NUM>, a first core network <NUM>, and a second core network <NUM>. Even though a specific number of remote units <NUM>, access networks <NUM>, <NUM>, base units <NUM>, wireless communication links <NUM>, and core networks <NUM>, <NUM> are depicted in <FIG>, one of skill in the art will recognize that any number of remote units <NUM>, access networks <NUM>, <NUM>, base units <NUM>, wireless communication links <NUM>, and core networks <NUM>, <NUM> may be included in the wireless communication system <NUM>. In various embodiments, the access networks <NUM>, <NUM> may contain one or more WLAN (e.g., Wi-Fi™) access points ("APs"). Here, the first access network <NUM>, second access network <NUM>, first core network <NUM> and second core network <NUM> belong to the same mobile communication network (e.g., the same PLMN).

In one implementation, the wireless communication system <NUM> is compliant with the <NUM> system and the LTE system specified in the 3GPP specifications. More generally, however, the wireless communication system <NUM> may implement some other open or proprietary communication network, for example, WiMAX, among other networks. The present disclosure is not intended to be limited to the implementation of any particular wireless communication system architectures or protocols.

In one embodiment, the remote units <NUM> may include computing devices, such as desktop computers, laptop computers, personal digital assistants ("PDAs"), tablet computers, smart phones, smart televisions (e.g., televisions connected to the Internet), smart appliances (e.g., appliances connected to the Internet), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, modems), or the like. Moreover, the remote units <NUM> may be referred to as subscriber units, mobiles, mobile stations, users, terminals, mobile terminals, fixed terminals, subscriber stations, UEs, user terminals, a device, or by other terminology used in the art. The remote units <NUM> may communicate directly with one or more of the base units <NUM> via uplink ("UL") and downlink ("DL") communication signals. Furthermore, the UL and DL communication signals may be carried over the wireless communication links <NUM>.

In some embodiments, the remote units <NUM> communicate with a remote host <NUM> (for example, an application server) via a data path that passes through one of the core network <NUM>, <NUM> and through the data network <NUM>. For example, a remote unit <NUM> may establish a PDU session (or similar data connection) to the data network <NUM> via the first core network <NUM>. The first core network <NUM> then relays traffic between the remote unit <NUM> and the remote host <NUM> using the PDU session. As another example, a remote unit <NUM> may establish a PDN connection to the data network <NUM> via the second core network <NUM>. The second core network <NUM> then relays traffic between the remote unit <NUM> and the remote host <NUM> using the PDN connection.

The base units <NUM> may be distributed over a geographic region. In certain embodiments, a base unit <NUM> may also be referred to as an access terminal, an access point, a base, a base station, a Node-B, an eNB, a gNB, a Home Node-B, a relay node, a device, or by any other terminology used in the art. The base units <NUM> are generally part of a radio access network ("RAN"), such as the first access network <NUM> (e.g., NG-RAN) and/or the second access network <NUM> (e.g., E-UTRAN), that may include one or more controllers communicably coupled to one or more corresponding base units <NUM>. These and other elements of the radio access network are not illustrated, but are well known generally by those having ordinary skill in the art.

The base units <NUM> may serve a number of remote units <NUM> within a serving area, for example, a cell or a cell sector via a wireless communication link <NUM>. The base units <NUM> may communicate directly with one or more of the remote units <NUM> via communication signals. Generally, the base units <NUM> transmit downlink ("DL") communication signals to serve the remote units <NUM> in the time, frequency, and/or spatial domain. Furthermore, the DL communication signals may be carried over the wireless communication links <NUM>. The wireless communication links <NUM> may be any suitable carrier in licensed or unlicensed radio spectrum. The wireless communication links <NUM> facilitate communication between one or more of the remote units <NUM> and/or one or more of the base units <NUM>.

As depicted, the wireless communication system <NUM> includes both a first core network <NUM> and a second core network <NUM> and various interworking network functions for to support interworking between the user plane and certain control plane functions in the first core network <NUM> and the second core network <NUM>. The first core network <NUM> includes an Access and Mobility Management Function ("AMF") <NUM> that is not shared with the second core network <NUM>. Similarly, the second core network <NUM> includes a Mobility Management Entity ("MME") <NUM> and a Serving Gateway ("SGW") <NUM> that are note shared with the first core network <NUM>. However, there is a combined UPF and PGW-user-plane ("UPF+PGW-U") <NUM>, a combined SMF and PGW-control-plane ("SMF+PGW-C") <NUM>, a combined PCF and PCRF ("PCF+PCRF") <NUM>, and a combined HSS and UDM ("HSS+UDM") that support interworking between the first core network <NUM> and second core network <NUM>. Note that the notions "SMF+PGW-C" and "UPF+PGW-U" are used to show that the network functions used for, e.g., PDU Sessions in 5GC and PDN Connections in EPC are common, in case that IP session continuity is required during transfer of PDU Sessions to PDN Connections and vice-versa. Although specific numbers and types of network functions are depicted in <FIG>, one of skill in the art will recognize that any number and type of network functions may be included in the mobile core network <NUM>.

As depicted, the wireless communication system <NUM> includes various network interfaces that facilitate communication among the core network ("CN") elements. For example, a base unit <NUM> (or RAN) may communicate with the AMF <NUM> via the N2 interface and with the UPF+PGW-U <NUM> via the N3 interface. As another example, a base unit <NUM> may communicate with the MME <NUM> via the S1-MME interface and with the SGW via the S1-U interface. Other network interfaces are depicted, including, but not limited to, a N4 interface between the UPF+PGW-U <NUM> and the SMF+PGW-C <NUM>, a N7 interface between the SMF+PGW-C <NUM> and the PCF+PCRF <NUM>, a N8 interface between the AMF <NUM> and the HSS+UDM <NUM>, a N10 interface between the SMF+PGW-C <NUM> and the HSS+UDM <NUM>, a N11 interface between the AMF <NUM> and the SMF+PGW-C <NUM>, a N15 interface between the AMF <NUM> and the PCF+PCRF <NUM>, a S5-U interface between the SGW <NUM> and the UPF+PGW-U <NUM>, a S5-C interface between the SGW <NUM> and the SMF+PGW-C <NUM>, a S6a interface between the MME <NUM> and the HSS+UDM <NUM>, and the S11 interface between the MME <NUM> and the SGW <NUM>. Although not depicted, the wireless communication system <NUM> may support a N1 interface between the remote unit <NUM> and the AMF <NUM>.

Note, however, that there is no network interface between the AMF <NUM> and the MME <NUM>. This is because the AMF <NUM> and the MME <NUM> are not communicatively coupled. Accordingly, inter-system handover from the 5GC to EPC (or vice versa) is not supported. Disclosed herein are various mechanisms to allow a DR-capable remote unit <NUM> to fallback from the 5GC towards the EPC. Because such a remote unit <NUM> supports DR-mode operations, it is unnecessary for the remote unit <NUM> to deregister from the 5GC (e.g., first core network <NUM>) in order to register with and use services in the EPC (e.g., second core network <NUM>). However, unless the access stratum (e.g., radio layer) of the remote unit <NUM> is capable of dual Rx and dual Tx ("dual Rx/Tx"), the remote unit <NUM> cannot simultaneously use services in both the first core network <NUM> and the second core network <NUM>. Accordingly, the remote unit <NUM> is unable to receive and/or respond to paging or any other downlink signaling from a first system while connected to another system.

Moreover, when the remote unit <NUM> operates in DR-mode and is using service in a first system (e.g., first RAT and first CN), if the second system (e.g., second RAT and second CN) is unaware that the remote unit <NUM> is using services in the first system, then the second system may page the remote unit <NUM> in vain, leading to inefficient use of network/radio resources. To avoid paging a remote unit <NUM> that cannot receive/respond due to using services in another system, the first core network <NUM> and second core network <NUM> synchronize the mobility management ("MM") states of the remote unit, as described in detail below.

When a remote unit <NUM> is registered to the first core network <NUM> (e.g., a 5GC) and wants to initiate a service which is not supported by the first core network <NUM> (e.g., 5GC), then the remote unit <NUM> operating in dual-registration mode attempts to fallback to the second core network <NUM> (e.g., a EPC). One example of a fallback to the second core <NUM> is an Emergency services fallback. Where the remote unit <NUM> is not able to simultaneously transmit data in multiple RATs (e.g., the remote unit <NUM> is single Tx capable), then the remote unit <NUM> attempts to suspend services in the first core network <NUM> (e.g., suspend PDU Sessions in 5GC), as follows:.

If a remote unit <NUM> is in CM-IDLE state in the first core network <NUM> (e.g., 5GC) then the remote unit <NUM> may initiate an Attach procedure (or TAU procedure) with the second core network <NUM> (e.g., EPC) and indicates to the second core network <NUM> (e.g., EPC) that services in the first core network <NUM> (e.g., 5GC) should be suspended. The MME <NUM> forwards the suspension request to the HSS+UDM <NUM> during subscription information retrieval. In turn, the HSS+UDM <NUM> notifies the AMF <NUM> that 5GC services (e.g., in the first core network <NUM>) should be suspended for this remote unit <NUM> (e.g. because the remote unit <NUM> is unreachable until it performs Registration procedure with the first core network <NUM> (e.g., 5GC)).

If the remote unit <NUM> is in CM-CONNECTED state in the first core network <NUM> (e.g., 5GC), the remote unit <NUM> requests first suspension of the first core network <NUM> (e.g., 5GC) services using NAS signaling and the first core network <NUM> (e.g., 5GC) releases the N1 and N2 connections, and the remote unit <NUM> becomes unreachable until the remote unit <NUM> performs Registration procedure with the first core network <NUM> (e.g., 5GC). Afterwards the remote unit <NUM> initiates Attach/TAU procedure with the second core network <NUM> (e.g., EPC).

<FIG> depicts a network architecture <NUM> used for suspending services in a first core network while attached to a second core network, according to embodiments of the disclosure. The network architecture <NUM> may be a simplified embodiment of the wireless communication system <NUM>. As depicted, the network architecture <NUM> includes a UE <NUM> that communicates with a 5GC <NUM> and with a EPC <NUM> via a RAN <NUM>. The UE <NUM> may be one embodiment of the remote unit <NUM>, the 5GC <NUM> may be an embodiment of the first core network <NUM>, and the EPC <NUM> may be an embodiment of the second core network <NUM>. Additionally, the network architecture <NUM> includes multiple core interworking functions <NUM>, such as a SMF/PGW-C interworking function, a UPF/PGW-U interworking functions, etc. Although shared by the 5GC <NUM> and the EPC <NUM>, the HSS+UDM is depicted as separate from the core interworking functions <NUM>.

In the depicted embodiment, the 5GC <NUM> and EPC <NUM> belong to the same PLMN; however, inter-core handover is not supported between the AMF <NUM> and the MME <NUM>. Moreover, the RAN <NUM> broadcasts an indication in the system information (e.g., SIB) that the PLMN supports DR-mode. Here, the UE <NUM> is configured to operate in DR-mode, but is not capable of both dual Rx and dual Tx (e.g., it is a single radio UE).

The UE <NUM> initially attaches to the 5GC <NUM> by communicating with an AMF <NUM> in the 5GC <NUM> (see signaling <NUM>). The AMF <NUM> may be one embodiment of the AMF <NUM> discussed above. The AMF <NUM> retrieves subscription information for the UE <NUM> from the HSS+UDM <NUM> (e.g., an embodiment of the HSS+UDM <NUM>) and the 5GC <NUM> begins providing services to the UE <NUM>. As used herein, a core network providing "services" to a UE refers to layers above the non-access stratum ("NAS"). Each "service" is supported by a data connection or bearer, such as a PDU Session in the 5GC <NUM> or a PDN Connection in the EPC <NUM>. A single data connection or bearer may support one or more services. Thus, one or more services correspond to a PDN Connection or PDU Session.

If the 5GC <NUM> does not support specific service (e.g., Emergency services over IMS) and the UE <NUM> is registered with the 5GC <NUM> (e.g. as a data-centric UE), there is a need of fallback procedure from the 5GC <NUM> to the EPS <NUM>. If the UE <NUM> is in CM-IDLE mode in the 5GC <NUM> at the time it determines to initiate a service (e.g., emergency service) in the EPC <NUM>, then it can immediately begin an attach procedure with the EPC <NUM>. However, if the UE <NUM> is in CM-CONNECTED mode in the 5GC <NUM> at the time it determines to initiate the service in the EPC <NUM>, then it does not need to deregister with the 5GC <NUM> (due to being DR capable), but it still needs to gracefully release the connection to the AMF <NUM> prior to attaching to the EPC <NUM>.

Recall that unsynchronized states in the 5GC <NUM> and the EPC <NUM> can result in one core network, such as the 5GC <NUM>, performing MT signaling (e.g., paging) to the UE <NUM> in vain while it is using services in the EPC215 and unable to respond. To avoid unnecessary states, the UE <NUM> informs the 5GC <NUM> that it is attaching to the EPC <NUM> and to suspend the services with the 5GC <NUM>. Doing so allows the 5GC <NUM> to set the MM state of the UE <NUM> to a state that indicates the UE <NUM> is unreachable (due to using services in the EPC <NUM>). The UE <NUM> may request to suspend services in the 5GC <NUM> based on the radio capabilities from lower layers (e.g. radio layer, or based on indication from RRC layer to NAS layer).

In the depicted embodiment, the UE <NUM> registers with the EPC <NUM> in DR mode (see signaling <NUM>). DR-mode permits the UE <NUM> to simultaneously be registered in both the 5GC <NUM> and the EPC <NUM>. However, because the UE <NUM> in unable to use services in the 5GC <NUM> and the EPC <NUM> at the same time, when registering with the EPC <NUM> the UE <NUM> includes an indication to suspend services in 5GC (see block <NUM>). Here, the MME <NUM> receives the indication from the UE <NUM> and passes it to the HSS+UDM <NUM>, which in turn informs the AMF <NUM>. Note that the depicted embodiment assumes that the UE <NUM> is in CM-IDLE mode when it determines to connect to the EPC <NUM>. Where the UE <NUM> is already in the CM-CONNECTED mode, the UE <NUM> will first release the connection to the AMF <NUM> before attaching to the EPC <NUM>. Here, the UE <NUM> includes an indication to suspend services in 5GC when releasing the connection to the AMF <NUM>. When suspending the 5GC <NUM> services, the AMF <NUM> deactivates (release) UP resources (and signaling associations) for active data connections of the UE <NUM>, but does not release corresponding SMF contexts.

At some later point in time, the UE <NUM> finishes using the services in the EPC <NUM> and releases the connection to the MME <NUM> (see signaling <NUM>). In some embodiments, the UE <NUM> terminates services in the EPC <NUM> that are not available in the 5GC <NUM>. In certain embodiments, the UE <NUM> suspends services in the EPC <NUM> in order to resume service in the 5GC <NUM>. In other embodiments, the UE <NUM> transfers one or more services from the EPC <NUM> back to the 5GC <NUM> when resuming services in the 5GC <NUM>. In any case, the AMF <NUM> re-activates UP resources (and signaling associations) corresponding to the suspended services, and the UE <NUM> resumes using services in the 5GC (see signaling <NUM>).

<FIG> depicts one embodiment of a user equipment apparatus <NUM> that may be used for suspending services in a first core network while attached to a second core network, according to embodiments of the disclosure. The user equipment apparatus <NUM> may be one embodiment of the SMF <NUM>. Furthermore, the user equipment apparatus <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, a display <NUM>, and a transceiver <NUM>. In some embodiments, the input device <NUM> and the display <NUM> are combined into a single device, such as a touch screen. In certain embodiments, the user equipment apparatus <NUM> may not include any input device <NUM> and/or display <NUM>.

As depicted, the transceiver <NUM> includes at least one transmitter <NUM> and at least one receiver <NUM>. Additionally, the transceiver <NUM> may support at least one network interface <NUM>. Here, at least the network interface <NUM> facilitates communication with a eNB or gNB (e.g., using the Uu interface). Additionally, the at least one network interface <NUM> may include an interface used for communications with an AMF (e.g., using a N1 interface). The transceiver <NUM> configured to communicate with a first core network of a mobile communication network or a second core network of the mobile communication network, but only communicates one core network at a time. In various embodiments, the user equipment apparatus <NUM> is a UE capable of dual registration with the first and second core networks, but the transceiver <NUM> is incapable of both dual reception and dual transmission with the first and second core networks.

The processor <NUM> is communicatively coupled to the memory <NUM>, the input device <NUM>, the display <NUM>, and the transceiver <NUM>.

In some embodiments, the processor <NUM> determines to suspend one or more first service (e.g., a first set of services) in order to use a second service in a second core network <NUM> (e.g., a EPC), while currently attached to a first core network <NUM> (e.g., while using the at least one first service in a 5GC). Accordingly, the processor <NUM> controls the transceiver to send a first mobility management ("MM") message. Here, the MM message indicates that the first set of services (e.g., one or more first services remaining in the first core network <NUM>) are to be suspended while the user equipment apparatus <NUM> is attached to the second core network <NUM> (e.g., to the EPC <NUM>). Moreover, the processor <NUM> uses the second service in the second core network <NUM> without using the first set of services (e.g., services suspended in the 5GC <NUM>).

Here, using the second service in the second core network <NUM> includes one of: initiating a (new) service in the second core network <NUM> that is unavailable in the first core network <NUM> and transferring to the second core network <NUM> at least one third service (e.g., a third set of services) used in the first core network <NUM>. Note that the third set of services is distinct from the first set of services. Accordingly, some services may be transferred to the second core network <NUM> (e.g., EPC <NUM>) while all remaining services in the first core network <NUM> are suspended. In various embodiments, the processor <NUM> preserves data connection context associated with the one or more first services remaining in the first core network <NUM> (e.g., the first set of services) while using the second service in the second core network <NUM>. Moreover, determining to suspend the first service may include the processor <NUM> performing internal suspension of the first service. Note, that if in CONNECTED state the user equipment apparatus <NUM> needs first to receive the Suspend Ack or N1 release from the AMF <NUM> before internally suspending a <NUM> service.

In certain embodiments, the processor <NUM> receives a request for a second service (e.g., an internal request from an application running on the user equipment apparatus <NUM>) and determines to initiate the second service in the second core network. The processor <NUM> then configures the transceiver <NUM> to communicate with the second core network (e.g., in response to determining to initiate the second service in the second core network) and sends a message to initiate the second service in the second core network. Here, the message sent to the second core network indicates that communication with the first core network is to be suspended.

In some embodiments, the user equipment apparatus <NUM> is in an idle state with respect to the first core network <NUM> and the first MM message is a NAS MM message that is sent to the second core network <NUM> while in the idle state. To do so, the processor <NUM> may configure the transceiver <NUM> to communicate with the second core network <NUM> (e.g., to use a radio access technology ("RAT") of a radio access network ("RAN") connected to the second core network <NUM>). Here, the NAS MM message indicates that a registration with the first core network <NUM> is not to be cancelled. Accordingly, the user equipment apparatus <NUM> operates in DR-mode in response to the NAS MM message.

For example, a NAS MM Attach message may include a parameter indicating it is not an "initial" attach, such that the HSS+UDM <NUM> understands that the user equipment apparatus <NUM> is operating in dual registration mode. As another example, the NAS MM Attach message may lack the indication of an "initial" attach, implicitly signaling that the user equipment apparatus is operating in DR-mode. In various embodiments, the NAS MM message may be an attach request, a tracking area update request, or a service request.

In certain embodiments, the NAS MM message sent to the second core network <NUM> further includes an indication to suspend services (e.g., the first set) in the first core network <NUM>. In other embodiments, the service suspension is implied by the NAS MM message. When suspending the one or more first services, data connection contexts associated with these services (e.g., those remaining in the first core network) are preserved (e.g., are not deleted). In some embodiments, the NAS MM includes a request to transfer at least one data connection from the first core network <NUM> to the second core network <NUM>. For example, the processor <NUM> may determine to transfer the at least one data connection that does not correspond to the suspended first services.

In other embodiments, the user equipment apparatus <NUM> is in an idle state with respect to the first core network <NUM> and the MM message is a NAS MM message that is sent to the first core network <NUM> while in the connected state. Here, the NAS MM message requests suspension of the first set of services (remaining) in the first core network <NUM>. In certain embodiments, the NAS MM message includes a cause parameter which indicates that the user equipment apparatus <NUM> requires the second service in the second core network <NUM> that is unavailable in the first core network <NUM> (e.g., such as Emergency Services).

In certain embodiments, the processor <NUM> later determines to discontinue the second service (e.g., used in the second core network <NUM>). For example, if the processor <NUM> previously determined to use Emergency Services in the second core network <NUM> that were not available in the first core network <NUM>, then determining to discontinue service in the second core network <NUM> may occur in response to terminating use of the Emergency Services. Note, however, that there may be one or more remaining services in the second core network <NUM> which may be terminated or may be suspended, referred to as a fourth set of services. Here, the processor <NUM> releases connections to the second core network <NUM> while keeping DR-mode operation. With service suspension in the second core network <NUM>, the processor <NUM> may store data connection context (e.g., PDN Connection context) in the memory <NUM> (said context also kept in the second core network <NUM>).

Moreover, to resume service in the first core network <NUM> (e.g., resuming the first set of services), the processor <NUM> may send, to the first network core <NUM>, a second MM message. This second MM message may be one of: a registration request message, a tracking area update request, an attach request, and a service request message to the first core network <NUM> (e.g., to a AMF <NUM> in the first core network <NUM>). Here, the service request message indicates the services remaining in the first core network <NUM> which are to be resumed (e.g., the first set of services). In one embodiment, the registration request message also indicates (to the AMF <NUM>) which of the first set of services are to be resumed (e.g., due to the memory <NUM> storing a valid SM context). In certain embodiments, the registration/service request indicates which data connections (e.g., PDU Sessions or PDN Connections) corresponding to the first set of services are to be resumed. Further, the processor <NUM> resumes using the first set of services in response to the first core network <NUM> (e.g., the AMF <NUM>) responding to the second MM message.

In certain embodiments, the processor <NUM> requests transfer of at least one data connection from the first core network <NUM> to the second core network <NUM>, when initiating the second service in the second core network <NUM> (e.g., that is unavailable in the first core network <NUM>). Note, that the at least one data connection to be transferred correspond to the above mention third services, but does not correspond to the suspended first set of services. In one embodiment, the processor <NUM> determines to suspend at least one fourth service remaining in the second core network <NUM> in response to determining to discontinue the second service in the second core network <NUM>. Note that the at least one fourth service may include one of the third services transferred to the second core network <NUM>. In other words, the third set of services and the fourth set of service may overlap.

In another embodiment, the processor <NUM>, in response to determining to discontinue the second service in the second core network <NUM>, further determines to transfer at least one (fourth) service remaining in the second core network <NUM> to the first core network <NUM>. In such an embodiment, resuming use of the first set of services may further include using the at least one service transferred from the second core network <NUM> to the first core network <NUM>. Note, that a service transferred to the second core network <NUM> from the first core network <NUM> may be transferred back to the first core network <NUM> upon the processor <NUM> determining to discontinue the second service.

In some embodiments, the memory <NUM> stores data relating to suspending services in a core network, for example storing PDU Session contexts, PDN Connection contexts, and the like. In certain embodiments, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on the user equipment apparatus <NUM> and one or more software applications.

The transceiver <NUM> communicates with one or more network functions of a mobile communication network. The transceiver <NUM> operates under the control of the processor <NUM> to transmit messages, data, and other signals and also to receive messages, data, and other signals. For example, the processor <NUM> may selectively activate the transceiver (or portions thereof) at particular times in order to send and receive messages. The transceiver <NUM> may include one or more transmitters <NUM> and one or more receivers <NUM>.

<FIG> depicts one embodiment of a mobility management apparatus <NUM> that may be used for suspending services in a first core network, according to embodiments of the disclosure. The mobility management apparatus <NUM> may be one embodiment of the AMF <NUM>, the AMF <NUM>, the MME <NUM>, and/or the MME <NUM>. Furthermore, the mobility management apparatus <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, a display <NUM>, and a transceiver <NUM>. In some embodiments, the input device <NUM> and the display <NUM> are combined into a single device, such as a touch screen. In certain embodiments, the mobility management apparatus <NUM> may not include any input device <NUM> and/or display <NUM>.

As depicted, the transceiver <NUM> includes at least one transmitter <NUM> and at least one receiver <NUM>. Additionally, the transceiver <NUM> may support at least one network interface <NUM>. Here, the network interface <NUM> facilitates communication with one or more a network function, such as the SMF+PGW-C <NUM>, PCF+PCRF <NUM>, and HSS+UDM <NUM>. Additionally, the at least one network interface <NUM> may include an interface used for communications with an RAN, such as the NG-RAN or E-UTRAN. Specific interfaces are discussed above with reference to <FIG>.

In some embodiments, the transceiver <NUM> receives a message requesting suspension of one or more services associated with a remote unit <NUM>, such as the UE <NUM>, registered with the mobility management apparatus <NUM>. In response, the processor <NUM> may suspend the one or more services (e.g., the first set of services described above). Here, suspending the one or more services includes the processor <NUM> preserving data connection context corresponding to the one or more services associated with the remote unit <NUM>, said one or more services remaining in a first core network in a mobile communication network. In various embodiments, the mobility management apparatus <NUM> is located in (e.g., is a part of) the first core network.

For example, the processor <NUM> may store the data connection (e.g., PDU Session) context in a non-volatile portion of the memory <NUM>. As another example, the processor <NUM> may flag the memory locations where the data connection contexts to prevent their erasure or being overwritten. In yet another example, the processor <NUM> treats the data connection context as active contexts despite the corresponding services being suspended.

Moreover, suspending the one or more services includes the processor <NUM> setting a mobility management state for the UE <NUM> to a state that indicates the UE <NUM> is unreachable. For example, the state may be a "UE unreachable" state that is a subset of the "CM-IDLE" state. Such an "UE unreachable" state causes the mobility management apparatus <NUM> to forgo paging the UE <NUM> and other MT signaling, thereby conserving network and radio resources. Here, the UE <NUM> is unreachable due to use of a service in a second core network (e.g., EPC <NUM>). In one embodiment, the first core network is a 5GC and the second core network is a EPC. In another embodiment, the first core network is a EPC and the second core network is a 5GC.

In certain embodiments, setting the mobility management state for the UE <NUM> to the state that indicates the UE <NUM> is unreachable includes the processor <NUM> notifying a session management network function in the first core network that the remote unit is unreachable. Alternatively, the processor <NUM> may notify a SMF+PGW-C <NUM> node that the remote unit is unreachable. While the mobility management state for the UE <NUM> is set to "unreachable," the transceiver <NUM> may receive a service request message, such as from a SMF+PGW-C <NUM>, that requests activation of user plane network resources for the suspended services (of the UE <NUM>). In such embodiments, the processor <NUM> controls the transceiver <NUM> to respond to the service request with an indication that the UE <NUM> is unreachable. In certain embodiments, the indication may be a cause parameter in a response rejecting the service request. Note that upon receiving the indication, the SMF-PGW-C <NUM> may set the UE SM state of the UE <NUM> to an "UE unreachable" state or similar SM state.

In some embodiments, the processor <NUM> further releases a signaling association with the UE <NUM> and also releases user plane network resources in the first core network (e.g., 5GC <NUM>) corresponding to the one or more services associated with the UE <NUM>, in response to the message requesting suspension of the one or more services. For example, the processor <NUM> may initiate a connection release procedure, such as the "NAS signaling connection release" procedure in order to release the signaling association and user plane network resources.

In certain embodiments, the message requesting suspension of one or more services is a subscriber data update notification message from a subscription database common to the first and second core networks. For example, the HSS+UDM <NUM> may send the message to the mobility management apparatus <NUM>. Moreover, the message may invoke the "Nudm_SubscriberDataManagement_UpdateNotification" procedure in order to update the mobility management apparatus <NUM> with changes made in the subscriptions stored at the HSS+UDM <NUM>. Here, the subscriber data update notification message informs the mobility management apparatus <NUM> that the UE <NUM> has switched to the second core network (e.g., EPC <NUM>), thereby causing the processor <NUM> to suspend the services in the first core network (e.g., 5GC <NUM>). Generally, the mobility management apparatus <NUM> receives the service suspension message from the HSS+UDM <NUM> when the UE <NUM> transitions to the second core network while in an idle state for the first network core, for example where its MM state is the "CM-IDLE" state.

In certain embodiments, the message requesting suspension of one or more services is a NAS MM message from the remote unit. Here, the NAS MM message includes a cause parameter indicating that the UE <NUM> requires the service in the second core network, e.g., that is unavailable in the first core network. In certain embodiments, the message requesting suspension of one or more services is a resource release request message, such as a N2 Release Request, from a radio access network (e.g., RAN <NUM>) to which the UE <NUM> is attached. Here, the resource release request message requests the suspension due to the UE <NUM> switching to the second core network.

At a later point in time, the transceiver <NUM> may receive a second NAS MM message from the UE <NUM> causing the processor <NUM> to resume the one or more services remaining in the first core network. In one embodiment, the second NAS MM message is a registration request received from the UE <NUM> when the UE <NUM> transitions back to the first core network (e.g., 5GC <NUM>). In another embodiment, the second NAS MM message is a service request message received from the UE <NUM> when the UE <NUM> transitions back to the first core network (e.g., 5GC <NUM>). In certain embodiments, the second NAS MM message may indicate the one or more services remaining in the first core network that are to be resumed. For example, the registration request message may include a Packet Data Unit ("PDU") Session status indication for a PDU session corresponding to a suspended service in the first core network. Here, the processor <NUM> resumes (e.g., reactivates) the service remaining in the first core network corresponding to the PDU Session status indication contained in the registration request message.

In some embodiments, the memory <NUM> stores data relating to suspending services in a first core network, for example storing policy rules, service rules, service contexts, and the like. In certain embodiments, the memory <NUM> also stores program code and related data, such as an operating system or other controller algorithms operating on the mobility management apparatus <NUM> and one or more software applications.

<FIG> and <FIG> depict a network procedure <NUM> for suspending services in a first core network for a dual-registered UE, according to embodiments of the disclosure. The network procedure <NUM> involves the UE <NUM>, the AMF <NUM>, the MME <NUM>, the SMF+PGW-C <NUM>, the UPF+PGW-U <NUM>, and the HSS+UDM <NUM>. Also involved are two radio access technologies (RAT): the LTE RAT <NUM> (e.g., the EUTRAN) and the NR (<NUM>) RAT <NUM>. As discussed above, with reference to <FIG>, the AMF <NUM> is a component of the 5GC <NUM> (not depicted) and the MME <NUM> is a component of the EPC <NUM> (not depicted).

At <FIG>, the network procedure <NUM> begins as the UE <NUM> is registered with a first system, here with the 5GC <NUM> via a NR RAT <NUM>. In the network procedure <NUM>, the UE <NUM> is in a CM-IDLE state in the 5GC <NUM> (see block <NUM>). Note that the NAS layer of the UE <NUM> maintains all states for CM-IDLE state. Similarly, the AMF <NUM> also stores the UE <NUM> state in the 5GC <NUM> as CM-IDLE.

At a first point in time, the UE <NUM> determines that registration with a second system (e.g. with EPC <NUM> via the LTE RAT <NUM>) is needed. For example, the UE <NUM> may require a service (e.g., emergency services) that is available in the EPC <NUM> but is not supported in the 5GC <NUM> (see block <NUM>). As the UE <NUM> is DR-mode capable, the UE <NUM> is able to perform attach with the EPC <NUM> without deregistering with the 5GC <NUM> (e.g., in order to setup services which are not supported in the 5GC <NUM>).

Additionally, the UE <NUM> determines whether to request that the services in the first system (e.g. 5GC <NUM>) be suspended. When services are suspended the UE <NUM> is not able to receive those services temporarily, but the PDU Session contexts corresponding to the suspended services are not deleted. In one embodiment, the UE <NUM> determines to suspend services in the 5GC <NUM> because the UE <NUM> is incapable of both dual reception (e.g., simultaneous reception over two RATs, abbreviated "dual Rx") and dual transmission (e.g., simultaneous transmission over two RATs, abbreviated "dual Tx"). In another embodiment, the UE <NUM> is dual Rx/Tx capable, but determines to suspend services in the first system (here, the 5GC <NUM>), e.g., to conserve battery life.

Accordingly, the UE <NUM> configures its radio to use the LTE RAT <NUM> and initiates an Attach procedure with the MME <NUM> in the EPC <NUM> (see signaling <NUM>). When attaching to the EPC <NUM>, the UE <NUM> does not indicate an 'initial' attach (or similar indication) in order to let the MME <NUM> know that the UE <NUM> is coming from the 5GC <NUM> and that the registration at the 5GC <NUM> is not to be cancelled (thus, the UE <NUM> is operating in DR-mode). Alternatively, the UE <NUM> may instead initiate a Tracking Area Update ("TAU") procedure, for example where the UE <NUM> is connected to the 5GC <NUM> via an E-UTRAN (e.g., using the LTE RAT <NUM>). Because in the TAU procedure the UE <NUM> uses a temporary ID (e.g., a GUTI) for the EPC <NUM> derived from its temporary ID (GUTI) in the 5GC <NUM>, the MME <NUM> determines from the TAU procedure that the UE <NUM> is coming from the 5GC <NUM>.

Additionally, the UE <NUM> determines whether to include an indication that the services in the first system (e.g. 5GC) can be suspended. In the depicted embodiment, the Attach request includes a parameter (indication) labeled 'suspend <NUM> services'; however, other names expressing same/similar meanings may be used in other embodiments.

In one embodiment, the UE <NUM> includes the 'suspend <NUM> services' indication because the NAS layer is aware that the radio layer is incapable of both dual Rx and dual Tx, and thus the <NUM>/EPC NAS protocol stack decides to include the '<NUM> services suspended' indication. In another embodiment, the UE <NUM> performs attach procedure with EPC <NUM> without establishing PDN Connections in the EPC <NUM>. Here, the UE does not include the 'suspend <NUM> services' as the UE <NUM> only attaches to EPC <NUM> system, but no services are established in EPC <NUM> and after the Attach procedure the UE <NUM> would return to camp in the 5GC <NUM> system. In yet another embodiment, if the UE <NUM> determines to transfer all PDU Sessions from the first system (here, the 5GC <NUM>) to the second system (here, the EPC <NUM>). In this embodiment, the UE <NUM> decides to not suspend services in the first system as there may be no services remaining there, and thus determines to not include an indication for suspension of services.

In some embodiments, the UE <NUM> may elect to transfer one or more PDU Sessions in the 5GC <NUM> to the EPC <NUM>. In such embodiments, the 'suspend <NUM> services' indication does not apply for the <NUM> services (PDU Sessions) transferred from 5GC to EPC, i.e. the PDU Sessions for which the UE performed PDN Connection establishment with the MME. In one embodiment, the UE <NUM> performs PDN connection establishment procedure together with the Attach procedure. In another embodiment, the UE performs PDN connection establishment (PDU Session transfer) as stand-alone procedure, e.g. by sending a PDN Connection Request message with "handover" indication (not shown).

However, the UE <NUM> may also perform a new PDN Connection establishment without including the "handover" indication. Here, the APN for such PDN Connection may be the same as the APN/DNN on an existing PDU Session in the 5GC <NUM> (for which the HSS+UDM <NUM> stores the SMF+PGW-C address). Here, the MME <NUM> may decide to assign a new PGW (e.g., a new SMF+PGW-C) for the new PDN Connection. In this case, the MME <NUM> updates the HSS+UDM <NUM> about the new SMF+PGW-C assigned to the same APN/DNN.

In response to the Attach Procedure (or TAU procedure) the MME <NUM> initiates UE subscription retrieval towards the HSS+UDM <NUM> in order to download the subscription data for the UE <NUM> (see signaling <NUM>). In the subscription retrieval request, the MME <NUM> indicates that this is not an initial attach, meaning that the UE <NUM>'s registration at the AMF <NUM> shall not be cancelled. Additionally, the MME <NUM> may indicate that 5GS services (e.g. PDU Sessions) can be suspended. As discussed above, when suspended the existing PDU Sessions established in 5GC cannot be used for data transmission. However, suspending 5GC services, the PDU Session context should be kept in the AMF <NUM> and SMF/UPF (e.g., the UPF+PGW-U <NUM> and SMF+PGW-C <NUM>). As mentioned above, one example of such in indication is the 'suspend <NUM> services' parameter; however, other indication expressing same/similar meanings may be used in other embodiments.

Recall that the UE <NUM> may request to transfer some PDU Sessions from the 5GC <NUM> to PDN Connections in the EPC <NUM>. The indication 'suspend <NUM> services' applies to services (e.g., existing PDU Sessions in 5GC <NUM>) which are NOT transferred from the first system (5GC <NUM>) to the second system (EPC <NUM>). In response to the request to transfer some PDU Sessions, the MME <NUM> requests APN-related subscription information from HSS+UDM <NUM>, for which the UE <NUM> requested PDN Connection establishment. During retrieval of the APN-related subscription information, the MME <NUM> indicates a list of one or more APNs for which the UE <NUM> performs PDN Connection establishment procedure (not shown).

In some embodiments, the UE <NUM> indicates a "handover" during the PDN Connection establishment procedure with the MME <NUM>, triggering retrieval of APN-related subscription information from the HSS+UDM <NUM>. In addition, the MME <NUM> may include, in the subscription retrieval request, a 'handover' indication for the APN for which the UE <NUM> indicated 'handover' in the PDN Connection establishment request message. Moreover, if the UE <NUM> does not indicate 'handover' during the PDN Connection establishment procedure with the MME <NUM>, then the MME <NUM> does not include 'handover' during the APN-related subscription information retrieval from HSS+UDM <NUM>.

The HSS+UDM <NUM> may keep a track in the stored APN-related subscription information for which one or more SMF+PGW-Cs <NUM> have been registered by the EPC <NUM> (e.g., the MME <NUM>) and which SMF+PGW-Cs <NUM> have been registered by the 5GC <NUM> (e.g., the SMF itself). When the MME <NUM> requests APN-related subscription information and the HSS+UDM <NUM> provides the SMF+PGW-C <NUM> address, the MME <NUM> indicates back to the HSS+UDM <NUM> whether this SMF+PGW-C <NUM> is used in the EPC <NUM>.

Accordingly, the HSS+UDM <NUM> maintains up-to-date information of which SMF+PGW-C <NUM> is used in which system (or core network). This is at least useful in case where the UE <NUM> has some PDN Connections in the EPC <NUM> and other PDU Sessions in the 5GC <NUM> (independent whether the UE <NUM> is single Tx/Rx or dual Tx/Rx capable). In certain embodiments, one SMF+PGW-C <NUM> may be used in the EPC <NUM> and another SMF+PGW-C <NUM> may be used in the 5GC <NUM> for the same APN/DNN.

When transferring the PDU Sessions, the MME <NUM> resolves the PGW address (e.g. of the common SMF+PGW-C entity <NUM>) based on the subscription information received from the HSS+UDM <NUM>. The PDN Connection Request message contains an APN, which is mapped in the MME <NUM> to the APN-related subscription information received from the HSS+UDM <NUM>, which in turn contains the co-located SMF+PGW-C <NUM> address.

In response to the MME <NUM> passing along the indication to suspend services in the 5GC <NUM>, the HSS+UDM <NUM> updates the AMF <NUM> about the UE's registration at the EPC <NUM>. In addition, the HSS+UDM <NUM> indicates that the services in 5GS (e.g. existing PDU Sessions) are suspended, i.e. the existing 5GS PDU Sessions cannot be used for data transmission. Note, however, that the PDU Session context is kept in the AMF <NUM> and SMF/UPF. Recall that the indication to suspend <NUM> services applies to existing PDU Sessions in the 5GC <NUM>, but not to any PDU Sessions transferred to the EPC <NUM>. In some embodiments, the HSS+UDM <NUM> sends a subscriber data update notification to the AMF <NUM>, for example using the "Nudm_SubscriberDataManagement_UpdateNotification" service.

Based on the 'suspend <NUM> services' indication from the HSS+UDM <NUM>, the AMF <NUM> updates the mobility management to ("MM") state of the UE <NUM> 'UE unreachable' in 5GS (see block <NUM>). In some embodiments, the 'UE unreachable' state is a sub-state of the CM-IDLE state, such that the corresponding CM-IDLE timers continue to run. For example, if any SMF requests establishment of UP resources (e.g. Downlink data notification or Paging for DL data), the AMF responds with UE unreachable.

In certain embodiments, the subscriber data update notification includes a list of one or more DNNs/APNs for which the MME <NUM> has requested APN-related subscription information. For example, the HSS+UDM <NUM> may include the indication 'EPC requested APNs' in the subscriber data update notification. The list of DNNs/APNs indicates to the AMF <NUM> that the PDU Sessions corresponding to the DNN have been transferred to PDN Connections in the EPC <NUM>.

Upon receiving the EPC requested APNs, the AMF <NUM> may internally delete the association with the SMF (e.g., SMF+PGW-C <NUM>) for the corresponding PDU Sessions (see block <NUM>). As used herein, internally deleting the SMF association refers to the AMF <NUM> performing release of N11 association to the SMF+PGW-C <NUM>. For example, the AMF <NUM> may invoke the "Nsmf_PDUSession_UpdateSMContext" service with an indication that the N11 association is to be released. Moreover, the AMF <NUM> may indicate that the PDU Session is not released as a corresponding PDN Connection is used in the EPC <NUM>. If the AMF <NUM> has context for multiple PDU Sessions established towards the same DNN/APN, then the AMF <NUM> initiates N11 signaling to the corresponding SMF+PGW-C <NUM> for all PDU Sessions associated with the particular DNN/APN.

While the UE <NUM> is in the 'UE unreachable' state, the AMF <NUM> will reject any request to establish UP resources, thereby preventing signaling (e.g., paging) the UE <NUM> from the 5GC <NUM>. There are several possible alternatives how the AMF can inform the SMFs (e.g., SMF+PGW-Cs <NUM>) about the UE unreachability state. In a first alternative (depicted as "Option (A)") the AMF <NUM> proactively informs the corresponding SMFs (e.g., SMF+PGW-Cs <NUM>) about the UE unreachability status (see signaling <NUM>). In a second alternative (depicted as "Option (B)") the AMF <NUM> informs the corresponding SMFs (e.g., SMF+PGW-Cs <NUM>) about the UE unreachability status once the SMFs (e.g., SMF+PGW-Cs <NUM>) have requested the establishment of UP resources, e.g. when DL data has arrived for the PDU Session.

In some embodiments, the AMF <NUM> may inform in advance the corresponding SMFs (e.g., SMF+PGW-Cs <NUM>) about unreachability of the UE <NUM> in response to the MM state of the UE <NUM> in the AMF <NUM> being updated to 'unreachable' (see signaling <NUM>). The 'unreachable' UE SM context means that the SMF+PGW-C <NUM> does not initiate any signaling for establishing the UP resources for DL data or MT signaling until the AMF <NUM> again updates the UE SM context upon the UE <NUM> becoming reachable. In certain embodiments, the AMF <NUM> may invoke the "Nsmf_PDUSession_UpdateSMContext" service to update the UE SM context due to the unreachability of the UE for the time being. When the UE <NUM> is again reachable, the AMF <NUM> may again invoke the "Nsmf_PDUSession_UpdateSMContext" service to update the SMF+PGW-C <NUM>.

In other embodiments, the AMF <NUM> does not proactively inform the SMF+PGW-Cs <NUM> about unreachability of the UE <NUM>. Instead, while the UE's 5GC services are suspended, if DL arrives at the UPF (see optional signaling <NUM>), the network (e.g., UPF+PGW-U would start the network-initiated Service Request procedure towards a SMF+PGW-C <NUM> to establish the UP resources. The SMF+PGW-C <NUM> invokes an AMF <NUM> service via the N11 interface to requests the establishment of UP resources. For example, the SMF+PGW-C <NUM> may invoke the "Namf_Communication_N1N2MessageTransfer" service operation to the AMF <NUM> with contents "N2 SM information (PDU Session ID, QoS Profile, Session-AMBR)" to transfer an N2 SM message towards the RAN.

However, because the UE MM state in the AMF <NUM> is 'unreachable', the AMF <NUM> replies negatively which a corresponding cause why the UP resources cannot be established (see optional signaling <NUM>). Here, the cause may be 'UE unreachable'. Thereafter, the SMF+PGW-C <NUM> updates its UE SM context to 'unreachable' and not initiate any signaling for establishing the UP resources for DL data or MT signaling until the AMF <NUM> again updates the UE SM context upon the UE <NUM> becoming reachable.

Continuing at <FIG>, the UE <NUM> establishes service in the EPC <NUM>, e.g., establishing one or more PDN Connections (see block <NUM>). Based on the UE's implementation (or on UE/network policies), the UE <NUM> may transfer particular PDU Sessions from the 5GC <NUM> to the EPC <NUM>. As discussed above, the UE <NUM> may transfer PDU Sessions by indicating 'handover' to the MME <NUM> during the PDN Connectivity establishment.

If a PDU Session has been transferred from 5GC to EPC, the MME <NUM> initiates the establishment of an S5 bearer between the SGW <NUM> and the SMF+PGW-C <NUM>. With this, the UE <NUM>'s context in the SMF+PGW-C <NUM> is updated from N11 association with the AMF <NUM> to S5 bearer association with the SGW <NUM>. In such embodiments, the SMF+PGW-C <NUM> also initiates a procedure to delete/release the N11 association with the AMF <NUM> (see signaling <NUM>).

In some embodiments, the SMF+PGW-C uses a new cause value to indicate to the AMF <NUM> that the release of the N11 association is due to the transfer of the PDU Session from the 5GC <NUM> to the EPC <NUM>. Such an indication would inform the AMF <NUM> that there are no N1 SM messages to be transferred between the UE <NUM> and the SMF+PGW-C <NUM>, so that the release of the N11 association is performed without any delay. Moreover, the AMF <NUM> updates the UE's context stored in the AMF <NUM> as if this PDU Session would be released on the 5GC <NUM> and the AMF <NUM> releases this PDU Session ID and the corresponding N11 association. One example of such a new cause value can be 'inter-system PDU Session transferred" or 'PDU Session unavailable' or 'implicit PDU Session release' (meaning without N1 SM message), but other names expressing same/similar meanings may be used.

At some later point in time, the UE <NUM> determines to discontinue EPC service (see block <NUM>). In one embodiment, such as determination is due to termination of the EPC services (e.g. terminating Emergency Services). As an example, a call or a corresponding PDN connection belonging to the service for which the UE <NUM> attaches to the EPC <NUM> may terminate. In another embodiment, the UE <NUM> determines to transfer sessions a handover back to the 5GS (e.g., discontinue EPC service due to handover).

When discontinuing EPC service, the UE <NUM> may transfer to an EMM-IDLE state (e.g., with no PDN Connections established). Alternatively, the UE <NUM> may perform a Detach procedure with the MME <NUM>. When service in the EPC <NUM> is not terminated, the UE <NUM> and the MME <NUM> may retain PDN Connection context information. Accordingly, the UE <NUM> may suspend EPC service, rather than detach from the EPC <NUM>.

At this point, the UE <NUM> is in MM Registered state and CM-IDLE state in the 5GC <NUM>. To resume services in the 5GC <NUM>, the UE <NUM> sends a NAS mobility management message towards the AMF <NUM> to re-activate its registration and/or services with the 5GC <NUM> (see signaling <NUM>). Note that the UE <NUM> may configure its radio to use the NR RAT <NUM> to communicate with the AMF <NUM>.

In some embodiments, the UE <NUM> re-activates its registration and/or services with the 5GC <NUM> by sending a Registration Request message to the AMF <NUM>. Here, the Registration Request may include an indication that the registration is for 'mobility'. Additionally, the UE <NUM> may use an informational element 'PDU Session status' to indicate to the AMF <NUM> which PDU Sessions are still established in the UE <NUM>, e.g., for which PDU Sessions the UE <NUM> maintains valid PDU Session context.

The AMF <NUM> uses the 'PDU Session status' indication for several purposes, e.g. a) to align the PDU Sessions context and N11 associations stored in the AMF <NUM> with the PDU Sessions established (e.g., that remain valid) in the UE and b) to resume the PDU Sessions which are indicated in the PDU Session status informational element if those PDU Sessions have been suspended before. For example, one consequence of b) is that the AMF <NUM> initiates the signaling in step <NUM> (see signaling <NUM>). As such, the element 'PDU Session status' can be used as implicit indication for resuming the services (e.g., PDU Sessions) in the 5GC <NUM>. Note that the UE <NUM> does not include PDU Sessions which have been transferred to EPC <NUM> in the PDU Session status informational element. This is because the PDU Session which were transferred to PDN Connections in the EPC are implicitly deleted in the UE's 5GC NAS protocol stack and transferred to the UE's EPC NAS protocol stack.

In certain embodiments, the UE <NUM> re-activates its registration and/or services with the 5GC <NUM> by sending a Service Request message to the AMF <NUM>. Here, the Service Request may include the list of existing services (e.g. existing PDU Session IDs) to be resumed. For example, such a list of PDU Session IDs can be the informational element 'PDU Session status'. The handling of the element 'PDU Session status' in the AMF can be similar as described above for the Registration Request message. Note that if the UE <NUM> has established PDN Connection in the EPC <NUM> (e.g., PDN Connections not released or to be transferred to the 5GC <NUM>), then the UE <NUM> may indicate to the AMF <NUM> that the EPC service needs to be suspended. One example of such an indication is the element 'suspend EPS services' or "suspend <NUM> services', but other names expressing same/similar meanings may be used in other embodiments.

As depicted in <FIG>, the UE <NUM> may include an explicit indication in the NAS mobility management message towards the AMF <NUM> that the PDU Sessions included e.g. in the 'PDU Session status' element are to be resumed. This indication is used by the AMF <NUM> to initiate the signaling of step <NUM> (see signaling <NUM>). One example of such an indication is the element 'resume <NUM> services' or "resume services' or 'resume PDU Sessions', but other names expressing same/similar meanings may be used in other embodiments.

Similar to when the UE <NUM> established PDN Connections in the EPC <NUM>, when resuming <NUM> services the UE <NUM> may initiate PDU Sessions establishment procedure. Here, the UE <NUM> may include a 'handover' indication to indicate that the PDU Session is a transfer from a PDN Connection in the EPC <NUM>. The AMF <NUM> retrieves subscription information from the HSS+UDM <NUM> and uses the downloaded subscription information to identify which SMF+PGW-C <NUM> needs to be used for the PDU Session establishment with 'handover' indication. However, if the UE <NUM> does not indicate 'handover' during the PDU Session establishment procedure with the AMF <NUM>, then the AMF <NUM> does not include 'handover' during the APN-related subscription information retrieval from HSS+UDM <NUM>.

In response to the NAS MM message for resuming <NUM> service, the AMF <NUM> performs a location/registration update procedure with the HSS+UDM <NUM> (see signaling <NUM>). Here, the AMF <NUM> indicates this is not an initial registration so as not to cancel the UE <NUM>'s registration in the EPC. In addition, the AMF <NUM> may indicate which APNs/DNNs have been requested for transfer from the EPC <NUM> to the 5GC <NUM>. Further, if the UE <NUM> has included 'suspend EPS services' indication in the NAS MM message, then the AMF <NUM> may indicate that services in the EPC <NUM> are to be suspended.

The HSS+UDM <NUM>, in turn, performs a procedure to update the UE registration with the MME <NUM> (see signaling <NUM>). Further, the HSS+UDM <NUM> may indicate to the MME <NUM> that <NUM> services are suspended (if indicated by the AMF <NUM>). Where the UE <NUM> request transfer of one or more PDN Connections in the EPC <NUM> to PDU Session sin the 5GC <NUM>, then the HSS+UDM <NUM> may also indicate a list of APNs/DNNs for which the PDN Connections has been transferred from the EPC <NUM> to the 5GC <NUM>. As an example, this indication may be called '5GC requested APNs'; however, other names expressing same/similar meanings may be used in other embodiments. Optionally, if the MME <NUM> receives an indication '5GC requested APNs', then the MME <NUM> may trigger a release of PDN Connections corresponding to the list of APNs without EPC NAS signaling to the UE <NUM>.

Finally, the AMF <NUM> triggers an update procedure of the SM context towards the relevant SMF+PGW-Cs <NUM> (see signaling <NUM>). For example, the AMF <NUM> may use the service "Nsmf_PDUSession_UpdateSMContext (PDU Session ID, 'UE reachable')" to update the UE SM context. The cause value 'UE reachable' indicates that the SMF+PGW-C <NUM> can send a DDN/Paging request to AMF <NUM> if there is DL data.

While described as updating UE SM context in an SMF+PGW-C <NUM>, the procedure of the AMF <NUM> updating the UE's context in SMF as described with reference to signaling <NUM>, <NUM>, and <NUM> can be also applied to update the UE's context in other 5GC nodes, e.g., for delivery of control plane requests to the UE <NUM>. For example, the AMF <NUM> can update the UE <NUM>'s context in the SMSF with the indication that the UE is unreachable in the 5GC. In such a scenario, the SMSF (or other SMS-relevant entities) would perform the MT SMS delivery over the other system (e.g., over the EPC <NUM>). This approach has the advantage to save signaling (e.g. paging the UE <NUM>) in the system, where the services (e.g. PDU Sessions) are suspended.

While described as the UE <NUM> switching from the 5GC to the EPC, analogous procedures for 'suspend <NUM> services' can be applied in case that the UE <NUM> has been originally attached to the EPC <NUM> and initiates a DR-mode operation with the 5GC <NUM>. In such case the UE <NUM> sends the 'suspend <NUM> services' indication to the AMF <NUM> during mobility Registration Request procedure to the 5GC <NUM>. This operation is similar to that described in signaling steps <NUM>, <NUM>, and <NUM>. Upon discontinuing services in the 5GC <NUM>, the UE <NUM> re-attaches to the EPC <NUM>, similar to signaling steps <NUM>, <NUM>, and <NUM>. Throughout the analogous procedures, the HSS+UDM <NUM> synchronizes UE states in the 5GC <NUM> and EPC <NUM> to avoid paging the UE <NUM> in one system when it is using services in the other system.

In an analogous embodiment, a core network internal suspension of services can be performed based on the following procedure. The AMF <NUM> can use the cause to release an N11 association as per signaling <NUM> as an indication that the UE <NUM> is using services at another core network (e.g. in the EPC <NUM>). If the AMF <NUM> in addition knows the UE <NUM> radio capability, which is not able to receive or transmit simultaneously data or signaling in both systems, then the AMF <NUM> may determine to suspend the services in the 5GC <NUM>. In such an embodiment, there is no need for the UE <NUM> to request suspension of service in its message to the second core network (e.g., to the MME <NUM> in the EPC <NUM>, refer to signaling <NUM>). However, the UE <NUM> needs to inform the first core network (e.g., the AMF <NUM> in the 5GC <NUM>) about UE's radio capability and the core network maintains this UE's information in the UE's context stored in the AMF <NUM> (or MME <NUM>).

<FIG> and <FIG> depict a network procedure <NUM> for suspending services in a first core network for a dual-registered UE, according to embodiments of the disclosure. The network procedure <NUM> involves the UE <NUM>, the AMF <NUM>, the MME <NUM>, the SMF+PGW-C <NUM>, the UPF+PGW-U <NUM>, and the HSS+UDM <NUM>. Also involved are the LTE RAT <NUM> (e.g., the EUTRAN) and the NR (<NUM>) RAT <NUM>. As discussed above, the AMF <NUM> is a component of the 5GC <NUM> (not depicted) and the MME <NUM> is a component of the EPC <NUM> (not depicted).

At <FIG>, the network procedure <NUM> begins as the UE <NUM> is registered with a first system, here with the 5GC <NUM> via a NR RAT <NUM>. In the network procedure <NUM>, the (5GC) NAS layer state for the UE <NUM> is the CM-CONNECTED state (see block <NUM>), meaning that the UE <NUM> has an active RRC connection with the NR RAT <NUM> and an active NAS connection with the AMF <NUM> in the 5GC <NUM>. Similarly, the AMF <NUM> also stores the UE <NUM> state in the 5GC <NUM> as CM-CONENCTED. Over the active connections, the UE <NUM> uses services in the 5GC <NUM> (see signaling <NUM>).

At a first point in time, the UE <NUM> determines that registration with a second system (e.g. with EPC <NUM> via the LTE RAT <NUM>) is needed, e.g., to set up services that are not supported in the first system (see block <NUM>). As the UE <NUM> is DR-mode capable, the UE <NUM> is able to perform attach with the EPC <NUM> without deregistering with the 5GC <NUM> (e.g., in order to setup services which are not supported in the 5GC <NUM>). However, here the UE <NUM> is not Dual Rx/Tx capable.

Because the UE <NUM> has an active connection to the 5GC <NUM>, it cannot immediately initiate signaling (e.g. attach) to the EPC <NUM>. Rather, the UE <NUM> gracefully terminates the N1 connection (at corresponding N2 signaling association) before attaching to the EPC <NUM>. In one embodiment, the UE <NUM> sends a NAS MM message to the AMF <NUM> requesting suspension of 5GS services, e.g., due to fallback to the EPC system <NUM> (see signaling <NUM>). In another embodiment, the UE <NUM> sends a RRC release request message to the NR RAT <NUM> node (e.g., a gNB) with a new indication that system change, e.g., system fallback to the EPC system <NUM> (see signaling <NUM>).

When sending the NAS MM message to the AMF <NUM> (labeled "Option (A)"), the UE <NUM> can select from various message types. In a first embodiment, the UE <NUM> sends a new NAS MM message referred to as a "Service Suspend Request" message for clearly requesting suspension of 5GS services, e.g., due to fallback to the EPC system <NUM>. In another embodiment, the UE <NUM> sends a new corresponding indication (e.g. 'suspend service') within an existing 5GC NAS message, such as the Service Request message or other suitable NAS MM message. In various embodiments, the UE <NUM> may indicate to the AMF a cause for the service suspension, e.g. due to inability to receive services simultaneously in both systems. One example of such a cause can be called e.g. 'handover to EPC' or 'fallback to EPC', or 'emergency fallback to EPC', but other names expressing same/similar meanings may be used in other embodiments.

When sending the RRC release request message to the NR RAT <NUM> node (gNB), the UE <NUM> includes a (new) indication that system change is needed (e.g. system fallback to EPC system). Here, the gNB is aware of the radio capabilities of the UE <NUM> (e.g., single Rx or single Tx capability). Accordingly, the gNB can determine that the UE is unable to receive 5GS services while registered with the EPC. Hence, the gNB may decide to initiate the UE context release in the (R)AN. Moreover, the gNB sends an explicit indication to the AMF during the N2 context release procedure that the suspension is due to system change. For example, the gNB may indicate 'suspend due to system change' to the AMF.

Regardless of the mechanism for informing the AMF <NUM> of the service suspension request, the AMF <NUM> triggers release of UP resources/connections towards the relevant SMF+PGW-Cs <NUM> (see signaling <NUM>). For example, the AMF <NUM> may update the UE SM context in a SMF+PGW-C <NUM> using the service "Nsmf_PDUSession_UpdateSMContext" with contents (PDU Session ID, PDU Session Deactivation, Cause 'suspend PDU Session')". Note that the cause 'suspend PDU Session' indicates that the SMF+PGW-C <NUM> is not to send a DDN/Paging request to the AMF <NUM> if there is DL data.

The AMF <NUM> receives the request to suspend services in the 5GC <NUM> and sets the MM state for the UE <NUM> as 'unreachable in 5GS' (see block <NUM>). While the UE <NUM> is in the 'unreachable' state, the AMF <NUM> does not perform MT signaling towards the UE <NUM>, such as a Paging procedure. Moreover, if any SMF+PGW-C <NUM> requests establishment of UP resources (e.g. Downlink data notification or Paging for DL data), the AMF <NUM> responds with UE unreachable.

During the service suspension, the UE <NUM> keeps existing PDU Session contexts, but marks the 5GC NAS SM state as temporarily not available (or not used) service. For example, the UE internally rejects requests from the Application layer to send UL data on existing or new 5GS service. As discussed above, the UE may elect to transfer one or more PDU Sessions from the 5GC <NUM> to PDN Connections in the EPC <NUM>. In such a scenario, the corresponding EPC NAS SM contexts are created based on the existing 5GC NAS SM contexts. In one embodiment, the UE <NUM> keeps the 5GC NAS SM contexts belonging to transferred PDU Sessions, but marks them as unavailable (or not used). In another embodiment, the 5GC NAS SM contexts may be internally deleted in the UE <NUM> without explicit N1/NAS SM signaling with the corresponding SMF+PGW-C <NUM>.

In response to terminating the N2 connection, the UE <NUM> transfers to the CM-IDLE state in 5GS (see block <NUM>). Correspondingly, the UE's state in the AMF <NUM> is CM-IDLE and 'UE unreachable'.

Continuing at <FIG>, the UE <NUM> configures its radio to use the LTE RAT <NUM> and initiates an Attach procedure with the MME <NUM> in the EPC <NUM> (see signaling <NUM>). Alternatively, the UE <NUM> may instead initiate a Tracking Area Update ("TAU") procedure, for example where the UE <NUM> is connected to the 5GC <NUM> via an E-UTRAN (e.g., using the LTE RAT <NUM>). When attaching to the EPC <NUM>, the UE <NUM> does not indicate an 'initial' attach (or similar indication) in order to let the MME <NUM> know that the UE <NUM> is coming from the 5GC <NUM> and that the registration at the 5GC <NUM> is not to be cancelled (thus, the UE <NUM> is operating in DR-mode).

In certain embodiments, the UE <NUM> may elect to transfer one or more PDU Sessions in the 5GC <NUM> to the EPC <NUM>. In some embodiments, the UE <NUM> performs PDN connection establishment procedure together with the Attach procedure. In other embodiments, the UE <NUM> performs PDN connection establishment procedure as stand-alone procedure, e.g. by sending a PDN Connection Request message with "handover" indication (not shown).

In response to the Attach Procedure (or TAU procedure) the MME <NUM> initiates UE subscription retrieval towards the HSS+UDM <NUM> in order to download the subscription data for the UE <NUM> (see signaling <NUM>). In the subscription retrieval request, the MME <NUM> indicates that this is not an initial attach, meaning that the UE <NUM>'s registration at the AMF <NUM> shall not be cancelled.

In response to a request to transfer some PDU Sessions, the MME <NUM> requests APN-related subscription information from HSS+UDM <NUM>. In some embodiments, the UE <NUM> indicates a "handover" during the PDN Connection establishment procedure with the MME <NUM>, triggering retrieval of APN-related subscription information from the HSS+UDM <NUM>. In addition, the MME <NUM> may include, in the subscription retrieval request, a 'handover' indication for the APN for which the UE <NUM> indicated 'handover' in the PDN Connection establishment request message. Moreover, if the UE <NUM> does not indicate 'handover' during the PDN Connection establishment procedure with the MME <NUM>, then the MME <NUM> does not include 'handover' during the APN-related subscription information retrieval from HSS+UDM <NUM>. During retrieval of the APN-related subscription information, the MME <NUM> indicates a list of one or more APNs for which the UE <NUM> performs PDN Connection establishment procedure (not shown).

Next, the UE <NUM> establishes service in the EPC <NUM>, e.g., establishing one or more PDN Connections (see block <NUM>). Based on the UE's implementation (or on UE/network policies), the UE <NUM> may transfer particular PDU Sessions from the 5GC <NUM> to the EPC <NUM>. As discussed above, the UE <NUM> may transfer PDU Sessions by indicating 'handover' to the MME <NUM> during the PDN Connectivity establishment. Note that the MME <NUM> (or other entity in the EPC <NUM>) may determine not to transfer PDU Sessions from the 5GC <NUM> to PDN Connections in the EPC <NUM> if the reason for the UE <NUM> Attach to the EPC <NUM> is to use Emergency Services. Although it is not depicted, please note that the SMF+PGW-C <NUM> can also perform the release of N11 association with the AMF <NUM>, such as shown in signaling <NUM> of <FIG>.

At some later point in time, the UE <NUM> in DR-mode of operation determines to discontinue EPC service (see block <NUM>). In one embodiment, such as determination is due to termination of the EPC services (e.g. terminating Emergency Services). As an example, a call or a corresponding PDN connection belonging to the service for which the UE <NUM> attaches to the EPC <NUM> may terminate. In another embodiment, the UE <NUM> determines to transfer sessions a handover back to the 5GS (e.g., discontinue EPC service due to handover).

Note that in the case where the UE <NUM> initiates an Emergency Attach in the EPC <NUM> (e.g., to use Emergency Services not supported in the 5GC <NUM>) and after the emergency service is terminated (e.g., Emergency PDN Connection expiry timer set, for instance, <NUM> after UE <NUM> is in IDLE), the MME <NUM> may initiate Detach request to the UE <NUM> and optionally with indication for 5GC mobility registration.

The AMF <NUM> uses this indication to resume the PDU Sessions which are indicated in the PDU Session status informational element. Note that the UE <NUM> does not include PDU Sessions which have been transferred to EPC <NUM> in the PDU Session status informational element. This is because the PDU Session which were transferred to PDN Connections in the EPC are implicitly deleted in the UE's 5GC NAS protocol stack.

In certain embodiments, the UE <NUM> re-activates its registration and/or services with the 5GC <NUM> by sending a Service Request message to the AMF <NUM>. Here, the Service Request may include the list of existing services (e.g. existing PDU Session IDs) to be resumed. Note that if the UE <NUM> has established PDN Connection in the EPC <NUM> (e.g., PDN Connections not released or to be transferred to the 5GC <NUM>), then the UE <NUM> may indicate to the AMF <NUM> that the EPC service needs to be suspended. One example of such an indication is the element 'suspend EPS services' or "suspend <NUM> services', but other names expressing same/similar meanings may be used in other embodiments.

While described as the UE <NUM> switching from the 5GC to the EPC, analogous procedures for Service Suspend request in EPC can be applied in case that the UE <NUM> has been originally attached to the EPC <NUM> and initiates a DR-mode operation with the 5GC <NUM>. In such case the UE <NUM> sends Service Suspend request to the MME <NUM> before initiating the mobility Registration Request procedure with the 5GC <NUM>. This operation is similar to that described in signaling steps <NUM> and <NUM>.

While described as updating UE SM context in an SMF+PGW-C <NUM>, the procedure of the AMF <NUM> updating the UE's context in SMF as described with reference to signaling <NUM> can be also applied to update the UE's context in other 5GC nodes. For example, the AMF <NUM> can update the UE <NUM>'s context in the SMSF with the indication that the UE is unreachable in the 5GC. In such a scenario, the SMSF (or other SMS-relevant entities) would perform the MT SMS delivery over the other system (e.g., over the EPC <NUM>).

<FIG> and <FIG>depict the UE <NUM> changing RAT during service fallback. Here, the assumption is that for the service fallback, the UE <NUM> transfers from NR/5GC to E-UTRAN/EPC. However, it is also possible for the UE <NUM> to be connected to the 5GC <NUM> via the LTE RAT <NUM>, e.g., a E-UTRAN/5GC combination, and the fallback is an inter-system fallback from E-UTRAN/5GC to E-UTRAN/EPC. This second scenario may be needed if the services supported in core networks are different. This would mean an intra-cell but inter-system transfer if the UE <NUM> was in CONNECTED state, and inter-system change if the UE <NUM> was in IDLE state (as the UE <NUM> needs to perform TAU procedure towards EPC <NUM> camping under the same cell).

Although not depicted in the network procedures <NUM> or <NUM>, in certain embodiments, the HSS+UDM <NUM> is aware about the UE <NUM> capability in the access stratum (e.g. single Rx/Tx). As a first example, during initial Attach (e.g., with the EPC <NUM>) or initial Registration (e.g., with the 5GC <NUM>) procedures, the MME <NUM> (or AMF <NUM>) learns the UE's capabilities, including radio capabilities (e.g. single/dual Tx/Rx), via a NAS signaling exchange. The MME <NUM> (or AMF <NUM>) may then forward these UE capabilities to the HSS+UDM <NUM>. Alternatively, the HSS+UDM <NUM> may be provisioned with UE's radio capabilities via any other means, e.g. via OMA-DM system or other systems. When the UE <NUM> performs DR-mode NAS MM procedures with, e.g., PDN Connection activation in EPC, then the HSS+UDM <NUM> determines that mobile terminated 5GC services should be suspended and the HSS+UDM <NUM> indicates to AMF <NUM> that the UE <NUM> is in the EPC system <NUM> and MT services in the 5GC <NUM> are to be suspended. However, this approach would require that the HSS+UDM <NUM> be aware about the radio capabilities of the UE <NUM> and it may not be desirable to store UE radio capabilities in the HSS+UDM.

<FIG> depicts a method <NUM> for suspending services in a first core network while attached to a second core network, according to embodiments of the disclosure. In some embodiments, the method <NUM> is performed by an apparatus, such as the remote unit <NUM>, the UE <NUM>, and/or the user equipment apparatus <NUM>. In certain embodiments, the method <NUM> may be performed by a processor executing program code, for example, a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

The method <NUM> begins with using a first service (or first set of services) in a first core network of a mobile communication network. Here, a remote unit may be using <NUM> the first service. The remote unit is configured to communicate with the first core network or a second core network of the mobile communication network. However, wherein remote unit communicates with only one core network at a time. In certain embodiments, the remote unit is a user equipment capable of dual registration with the first and second core networks, but having a transceiver incapable of both dual reception and dual transmission with the first and second core networks. In one embodiment, the first core network is a 5GC, such as the 5GC <NUM>, and the second core network is a EPC, such as the EPC <NUM>. In another embodiment, the first core network is a EPC and the second core network is a 5GC.

The method <NUM> includes determining <NUM>, at the remote unit, to suspend the first service in order to use a second service (or second set of services) in the second core network. In certain embodiments, a NAS layer in the remote unit receives an internal request (e.g., from an application running on the remote unit) to send packets (e.g., for a service) and determines a need to connect to the second core network. For example, the need to connect to the second network may be due to the requested service not being available in the first core network or due to network/UE policy.

The method <NUM> includes sending <NUM> a first mobility management ("MM") message in response to determining to suspend the first service in order to use the second service (or second set of services) in the second core network. Here, the first MM message indicates that the first service (or first set of services) are to be suspended while the remote unit is attached to the second core network. The first services do not include any services transferred to the second core network (or services corresponding to data connections transferred to the second core network).

In some embodiments, sending <NUM> the first MM message includes transmitting a non-access stratum ("NAS") MM message to the second core network while the remote unit is in an idle state with respect to the first core network. Here, the NAS MM message indicates that a registration with the first core network is not to be cancelled (e.g., due to the remote unit operating in DR-mode). In various embodiments, the first NAS MM message is one of: an attach request, a tracking area update request, and a service request.

In certain embodiments, the first NAS MM message sent to the second core network further includes an indication to suspend the first service (or first set of services) and to preserve one or more data connection contexts associated with the first service. Where determining <NUM> to suspend the first service in order to use a second service in the second core network includes determining to transfer at least one data connection from the first core network to the second core network, then the NAS MM message may include a request to transfer of the at least one data connection from the first core network to the second core network. Here, the transferred data connection(s) corresponds to a third set of services that are transferred to the second core network.

In some embodiments, sending <NUM> the first MM message includes transmitting a non-access stratum ("NAS") MM message to the first core network while the remote unit is in a connected state with respect to the first core network. Here, the NAS MM message requests suspension of the first service. In certain embodiments, the NAS MM message includes a cause parameter indicating that the apparatus requires the service in the second core network that is unavailable in the first core network.

The method <NUM> includes using <NUM> the second service (or second set of services) in the second core network without using the first service (or first set of services). In certain embodiments, using <NUM> the second service in the second core network includes initiating a (new) service in the second core network that is unavailable in the first core network and/or transferring to the second core network a third service used in the first core network. In some embodiments, using <NUM> the second service in the second core network includes preserving data connection contexts associated with the first service while using the second service in the second core network.

In certain embodiments, using <NUM> the second service in the second core network includes determining to discontinue the second service in the second core network and sending, to the first core network, a second MM message. Here, the second MM message indicates that the first service is to be resumed. In certain embodiments, the second MM message indicates which data connections corresponding to the first service is to be resumed. In various embodiments, the second MM message may be one of: a registration request, a service request, an attach request, and a tracking area update request.

In one embodiment, determining to discontinue the second service in the second core network may include determining to suspend at least one fourth service remaining in the second core network in response to determining to discontinue service in the second core network. In another embodiment, determining to discontinue the second service in the second core network may include determining to transfer at least one fourth service remaining in the second core network to the first core network. Here, resuming use of the first service may further includes using the transferred at least one fourth service in the first core network. The method <NUM> ends.

<FIG> depicts a method <NUM> for suspending services in a first core network, according to embodiments of the disclosure. In some embodiments, the method <NUM> is performed by an apparatus, such as the AMF <NUM>, the AMF <NUM>, the MME <NUM>, the MME <NUM>, and/or the mobility management apparatus <NUM>. In certain embodiments, the method <NUM> may be performed by a processor executing program code, for example, a microcontroller, a microprocessor, a CPU, a GPU, an auxiliary processing unit, a FPGA, or the like.

The method <NUM> begins and receives <NUM> a message requesting suspension of one or more services associated with a remote unit registered with the apparatus. In some embodiments, receiving <NUM> the message requesting suspension of one or more services includes receiving a subscriber data update notification message from a subscription database common to the first and second core networks.

In some embodiments, receiving <NUM> the message requesting suspension of one or more services includes receiving a mobility management message from the remote unit. Here, the mobility management message may include a cause parameter, for example, indicating that the remote unit requires a service in the second core network that is unavailable in the first core network. In some embodiments, receiving <NUM> the message requesting suspension of one or more services includes receiving a resource release request message from a radio access network to which the remote unit is attached. Here, the radio access network requests the suspension due to the remote unit switching to the second core network.

The method includes suspending <NUM> the one or more services, said one or more services remaining in a first core network in a mobile communication network. Suspending <NUM> include preserving <NUM> data connection context corresponding to the one or more services and setting <NUM> a mobility management state for the remote unit to a state that indicates the remote unit is unreachable. Here, the remote unit is unreachable due to use of a service in a second core network.

In some embodiments, suspending <NUM> the one or more services includes both releasing a signaling association with the remote unit and releasing user plane network resources in the first core network corresponding to the one or more services associated with the remote unit. These releases occur in response to the message requesting suspension of the one or more services.

In some embodiments, setting <NUM> the mobility management state for the remote unit to the state that indicates the remote unit is unreachable includes notifying a session management network function in the first core network that the remote unit is unreachable. In certain embodiments, setting <NUM> the mobility management state for the remote unit to the state that indicates the remote unit is unreachable includes receiving a service request for activating user plane network resources associated with the suspended one or more services and responding with an indication that the remote unit is unreachable. The method <NUM> ends.

Claim 1:
An apparatus (<NUM>) comprising:
a transceiver (<NUM>) configured to register with a first mobile communication network and a second mobile communication network, wherein the transceiver (<NUM>) communicates with only one mobile communication network at a time; and
a processor (<NUM>) arranged to:
use a first connection in a Connected state in the first mobile communication network; and
determine to release the Connected state to the first mobile communication network;
wherein the transceiver (<NUM>) is further arranged to:
send a first mobility management, MM, message to the first mobile communication network, the first MM message comprising a release indication that requests a release of the first connection and paging restrictions, and
receive a second message as a reply to the first MM message, the second message indicating that the first connection is successfully released.