Patent Description:
The subject matter disclosed herein relates generally to wireless communications and more particularly relates to establishing a connection with a dual registered device. There is described herein a method in a network unit and a network unit.

The following abbreviations are herewith defined, at least some of which are referred to within the following description: Third Generation Partnership Project ("3GPP"), <NUM>th Generation ("<NUM>"), <NUM> Core Network ("5GC"), <NUM> System ("5GS"), Positive-Acknowledgment ("ACK"), Access and Mobility Management Function ("AMF"), Access Point ("AP"), Application Server ("AS"), Attribute Value Pair ("AVP"), Binary Phase Shift Keying ("BPSK"), Base Station ("BS"), Buffer Status Report ("BSR"), Bandwidth ("BW"), Bandwidth Part ("BWP"), Carrier Aggregation ("CA"), Contention-Based Random Access ("CBRA"), Clear Channel Assessment ("CCA"), Cyclic Delay Diversity ("CDD"), Code Division Multiple Access ("CDMA"), Control Element ("CE"), Contention-Free Random Access ("CFRA"), Closed-Loop ("CL"), Coordinated Multipoint ("CoMP"), Cyclic Prefix ("CP"), Cyclical Redundancy Check ("CRC"), Channel State Information ("CSI"), Common Search Space ("CSS"), Control Resource Set ("CORESET"), Discrete Fourier Transform Spread ("DFTS"), Downlink Control Information ("DCI"), Downlink ("DL"), Demodulation Reference Signal ("DMRS"), Dual Registration ("DR"), Data Radio Bearer ("DRB"), Downlink Pilot Time Slot ("DwPTS"), Enhanced Clear Channel Assessment ("eCCA"), Enhanced Mobile Broadband ("eMBB"), Evolved Node B ("eNB"), Effective Isotropic Radiated Power ("EIRP"), Evolved Packet Core Network ("EPC"), Evolved Packet System ("EPS"), European Telecommunications Standards Institute ("ETSI"), Frame Based Equipment ("FBE"), Frequency Division Duplex ("FDD"), Frequency Division Multiplexing ("FDM"), Frequency Division Multiple Access ("FDMA"), Frequency Division Orthogonal Cover Code ("FD-OCC"), Front End ("FE"), <NUM> Node B or Next Generation Node B ("gNB"), General Packet Radio Services ("GPRS"), Guard Period ("GP"), Global System for Mobile Communications ("GSM"), Globally Unique Temporary UE Identifier ("GUTI"), Home AMF ("hAMF"), Hybrid Automatic Repeat Request ("HARQ"), Home Location Register ("HLR"), Home PLMN ("HPLMN"), Home Subscriber Server ("HSS"), Identity or Identifier ("ID"), Information Element ("IE"), International Mobile Equipment Identity ("IMEI"), IP Multimedia Subsystem ("IMS"), International Mobile Subscriber Identity ("IMSI"), International Mobile Telecommunications ("IMT"), Internet-of-Things ("IoT"), Internet Protocol ("IP"), Layer <NUM> ("L2"), Licensed Assisted Access ("LAA"), Load Based Equipment ("LBE"), Listen-Before-Talk ("LBT"), Logical Channel ("LCH"), Logical Channel Prioritization ("LCP"), Long Term Evolution ("LTE"), Multiple Access ("MA"), Medium Access Control ("MAC"), Multimedia Broadcast Multicast Services ("MBMS"), Modulation Coding Scheme ("MCS"), Master Information Block ("MIB"), Multiple Input Multiple Output ("MIMO"), Mobility Management ("MM"), Mobility Management Entity ("MME"), Mobile Network Operator ("MNO"), Mobile Termination ("MT"), massive MTC ("mMTC"), Maximum Power Reduction ("MPR"), Machine Type Communication ("MTC"), Multi User Shared Access ("MUSA"), AMF to MME Interface ("N26"), Non Access Stratum ("NAS"), Narrowband ("NB"), Negative-Acknowledgment ("NACK") or ("NAK"), Network Entity ("NE"), Network Function ("NF"), Non-Orthogonal Multiple Access ("NOMA"), New Radio ("NR"), Network Repository Function ("NRF"), Network Slice Instance ("NSI"), Network Slice Selection Assistance Information ("NSSAI"), Network Slice Selection Function ("NSSF"), Network Slice Selection Policy ("NSSP"), Operation and Maintenance System ("OAM"), Orthogonal Frequency Division Multiplexing ("OFDM"), Open-Loop ("OL"), Other System Information ("OSI"), Proxy-Call Session Control Function ("P-CSCF"), P-Access-Network-Info ("PANI"), Power Angular Spectrum ("PAS"), Physical Broadcast Channel ("PBCH"), Power Control ("PC"), Primary Cell ("PCell"), Policy Control Function ("PCF"), Policy and Charging Rules Function ("PCRF"), Physical Cell ID ("PCID"), Physical Downlink Control Channel ("PDCCH"), Packet Data Convergence Protocol ("PDCP"), Packet Data Network ("PDN"), Physical Downlink Shared Channel ("PDSCH"), Pattern Division Multiple Access ("PDMA"), Packet Data Unit ("PDU"), Packet Data Network Gateway ("PGW"), Physical Hybrid ARQ Indicator Channel ("PHICH"), Power Headroom ("PH"), Power Headroom Report ("PHR"), Physical Layer ("PHY"), Public Land Mobile Network ("PLMN"), Physical Random Access Channel ("PRACH"), Physical Resource Block ("PRB"), Packet Switching ("PS"), Physical Uplink Control Channel ("PUCCH"), Physical Uplink Shared Channel ("PUSCH"), Quasi Co-Located ("QCL"), Quality of Service ("QoS"), Quadrature Phase Shift Keying ("QPSK"), Registration Area ("RA"), Radio Access Network ("RAN"), Radio Access Technology ("RAT"), Random Access Procedure ("RACH"), Random Access Response ("RAR"), Radio Link Control ("RLC"), Radio Network Temporary Identifier ("RNTI"), Reference Signal ("RS"), Remaining Minimum System Information ("RMSI"), Radio Resource Control ("RRC"), Resource Spread Multiple Access ("RSMA"), Reference Signal Received Power ("RSRP"), Round Trip Time ("RTT"), Receive ("RX"), Serving-Call Session Control Function ("S-CSCF"), Service Based Interface ("SBI"), Sparse Code Multiple Access ("SCMA"), Scheduling Request ("SR"), Sounding Reference Signal ("SRS"), Single Carrier Frequency Division Multiple Access ("SC-FDMA"), Secondary Cell ("SCell"), Shared Channel ("SCH"), Sub-carrier Spacing ("SCS"), Serving - Call Session Control Function ("S-CSCF"), Service Data Unit ("SDU"), System Information Block ("SIB"), Subscriber Identity/Identification Module ("SIM"), Signal-to-Interference-Plus-Noise Ratio ("SINR"), Service Level Agreement ("SLA"), Session Management Function ("SMF"), Short Message Service ("SMS"), Single Network Slice Selection Assistance Information ("S-NSSAI"), Synchronization Signal ("SS"), Synchronization Signal Block (" SSB"), Supplementary Uplink ("SUL"), Subscriber Permanent Identifier (" SUPI"), Terminating Access Domain Selection ("T-ADS"), Tracking Area ("TA"), TA Indicator ("TAI"), Transport Block ("TB"), Transport Block Size ("TBS"), Time-Division Duplex ("TDD"), Time Division Multiplex ("TDM"), Time Division Orthogonal Cover Code ("TD-OCC"), Transmission Power Control ("TPC"), Transmission Reception Point ("TRP"), Transmission Time Interval ("TTI"), Transmit ("TX"), Uplink Control Information ("UCI"), Unified Data Management Function ("UDM"), Unified Data Repository ("UDR"), User Entity/Equipment (Mobile Terminal) ("UE"), Uplink ("UL"), Universal Mobile Telecommunications System ("UMTS"), User Plane ("UP"), Uplink Pilot Time Slot ("UpPTS"), Ultra-reliability and Low-latency Communications ("URLLC"), UE Route Selection Policy ("URSP"), UDR Translation Function ("UTF"), Visiting AMF ("vAMF"), Visiting NSSF ("vNSSF"), Visiting PLMN ("VPLMN"), and Worldwide Interoperability for Microwave Access ("WiMAX").

In certain wireless communications networks, a device may be registered with two networks. In such networks, information corresponding to the device may be difficult to maintain.

<NPL>, and describes a CN-based solution for keeping IMS updated on the correct access type when the UE is dual registered.

In the following, any method and/or apparatus referred to as embodiments but nevertheless do not fall within the scope of the appended claims are to be understood as examples helpful in understanding the invention.

The subject-matter of <FIG>, <FIG> and <FIG> and their descriptions, even if described or named as "embodiment(s)", "invention(s)", "aspect(s)", "example(s)" or "disclosure(s)" etc., does not fully and thus only partly correspond to the invention as defined in the claims, since one or more features present in and required by the independent claims are missing in the "embodiment(s)", "invention(s)", "aspect(s)", "example(s)" or "disclosure(s)" etc. The subject-matter of <FIG>, <FIG> and <FIG> and their descriptions is therefore not covered by the claims and is useful to highlight specific aspects of the claims.

<FIG> depicts an embodiment of a wireless communication system <NUM> for establishing a connection with a dual registered device. In one embodiment, the wireless communication system <NUM> includes remote units <NUM> and network units <NUM>. Even though a specific number of remote units <NUM> and network units <NUM> are depicted in <FIG>, one of skill in the art will recognize that any number of remote units <NUM> and network units <NUM> may be included in the wireless communication system <NUM>.

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), set-top boxes, game consoles, security systems (including security cameras), vehicle on-board computers, network devices (e.g., routers, switches, modems), aerial vehicles, drones, or the like. The remote units <NUM> may communicate directly with one or more of the network units <NUM> via UL communication signals.

In certain embodiments, a network unit <NUM> may also be referred to as an access point, an access terminal, a base, a base station, a Node-B, an eNB, a gNB, a Home Node-B, a relay node, a device, a core network, an aerial server, a radio access node, an AP, NR, a network entity, an AMF, a UDM, a UDR, a UDM/UDR, a PCF, a RAN, an NSSF, an HSS, a UTF, an MME, an IMS AS, an S-CSCF, or by any other terminology used in the art.

In one embodiment, a network unit <NUM> may receive a first request to establish an internet protocol multimedia subsystem session with a first device, wherein the first device is dual registered to: a first network access supporting <NUM> core network connectivity; and a second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to an internet protocol multimedia subsystem via either the first network access or the second network access. In certain embodiments, the network unit <NUM> may determine first information corresponding to a network access connectivity selected from the first network access and the second network access through which the first device has internet protocol connectivity with the internet protocol multimedia subsystem. In some embodiments, the network unit <NUM> may transmit a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the internet protocol multimedia subsystem from the network access connectivity, wherein the second request comprises third information indicating a second network function for the first network function to contact to retrieve the second information. Accordingly, the network unit <NUM> may be used for establishing a connection with a dual registered device.

In another embodiment, a network unit <NUM> may receive a request at a first network function to retrieve information on voice support over an internet protocol multimedia subsystem over packet switched network from a first network access connectivity, wherein the request comprises information indicating a second network function to contact regarding the first network access connectivity of the first device. Accordingly, the network unit <NUM> may be used for retrieving information.

In one embodiment, a network unit <NUM> may receive a first request indicating that a server is unavailable. In certain embodiments, the network unit <NUM> may determine first information corresponding to a network access connectivity selected from a first network access and a second network access through which a first device has internet protocol connectivity with an internet protocol multimedia subsystem, wherein the first device is dual registered to: the first network access supporting <NUM> core network connectivity; and the second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to the internet protocol multimedia subsystem via either the first network access or the second network access. In some embodiments, the network unit <NUM> may transmit a second request to a first network function to initiate reconnection with the server, wherein the second request comprises second information indicating a second network function to contact to re-establish connection with the internet protocol multimedia subsystem. Accordingly, the network unit <NUM> may be used for establishing a connection with a dual registered device.

<FIG> depicts one embodiment of an apparatus <NUM> that may be used for establishing a dual registration. The apparatus <NUM> includes one embodiment of the remote unit <NUM>. Furthermore, the remote unit <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, a display <NUM>, a transmitter <NUM>, and a receiver <NUM>. In some embodiments, the input device <NUM> and the display <NUM> are combined into a single device, such as a touchscreen. In certain embodiments, the remote unit <NUM> may not include any input device <NUM> and/or display <NUM>. In various embodiments, the remote unit <NUM> may include one or more of the processor <NUM>, the memory <NUM>, the transmitter <NUM>, and the receiver <NUM>, and may not include the input device <NUM> and/or the display <NUM>.

In various embodiments, the processor <NUM> may: determine a configured network slice selection assistance information for a first mobile network for the apparatus in response to a change of the network slice selection policy; and use the configured network slice selection assistance information in the first mobile network.

The transmitter <NUM> is used to provide UL communication signals to the network unit <NUM> and the receiver <NUM> is used to receive DL communication signals from the network unit <NUM>, as described herein.

<FIG> depicts one embodiment of an apparatus <NUM> that may be used for establishing a connection with a dual registered device. The apparatus <NUM> includes one embodiment of the network unit <NUM>. Furthermore, the network unit <NUM> may include a processor <NUM>, a memory <NUM>, an input device <NUM>, a display <NUM>, a transmitter <NUM>, and a receiver <NUM>. As may be appreciated, the processor <NUM>, the memory <NUM>, the input device <NUM>, the display <NUM>, the transmitter <NUM>, and the receiver <NUM> may be substantially similar to the processor <NUM>, the memory <NUM>, the input device <NUM>, the display <NUM>, the transmitter <NUM>, and the receiver <NUM> of the remote unit <NUM>, respectively.

The receiver <NUM> may receive a first request to establish an internet protocol multimedia subsystem session with a first device, wherein the first device is dual registered to: a first network access supporting <NUM> core network connectivity; and a second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to an internet protocol multimedia subsystem via either the first network access or the second network access. The processor <NUM> may determine first information corresponding to a network access connectivity selected from the first network access and the second network access through which the first device has internet protocol connectivity with the internet protocol multimedia subsystem. The transmitter <NUM> may transmit a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the internet protocol multimedia subsystem from the network access connectivity, wherein the second request comprises third information indicating a second network function for the first network function to contact to retrieve the second information.

The receiver <NUM> may receive a request at a first network function to retrieve information on voice support over an internet protocol multimedia subsystem over packet switched network from a first network access connectivity, wherein the request comprises information indicating a second network function to contact regarding the first network access connectivity of the first device.

The receiver <NUM> may receive a first request indicating that a server is unavailable. In various embodiments, the processor <NUM> may determine first information corresponding to a network access connectivity selected from a first network access and a second network access through which a first device has internet protocol connectivity with an internet protocol multimedia subsystem, wherein the first device is dual registered to: the first network access supporting <NUM> core network connectivity; and the second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to the internet protocol multimedia subsystem via either the first network access or the second network access. In certain embodiments, the transmitter <NUM> may transmit a second request to a first network function to initiate reconnection with the server, wherein the second request comprises second information indicating a second network function to contact to re-establish connection with the internet protocol multimedia subsystem.

Although only one transmitter <NUM> and one receiver <NUM> are illustrated, the network unit <NUM> may have any suitable number of transmitters <NUM> and receivers <NUM>.

In certain embodiments, a UE (e.g., remote unit <NUM>) may have and/or be in a dual registration mode (e.g., including networks that do not support N26 reference points). When the UE is in DR mode, the UE has simultaneous connections to an MME (e.g., in an EPS core network) and to an AMF (e.g., in a <NUM> core network). Accordingly, both the MME and the AMF hold UE context information for the UE.

In various embodiments, if a UE is in a DR mode, both an MME (e.g., in an EPS core network) and an AMF (e.g., in a <NUM> core network) provide an indication to the UE indicating that IMS over PS is supported. Both the MME and the AMF store the indication indicating that IMS over PS is supported (e.g., homogeneous support) and/or provide the indication indicating that IMS over PS is supported to an HSS and a UDM respectively. The UE uses the indication indicating that IMS over PS is supported to identify that IMS over PS is supported in accessing and/or establishing an IMS PS session.

In some embodiments, a UE in a DR mode may establish an IMS session over EPS or over <NUM> core. If an IMS AS requests from an HSS to receive T-ADS information, the HSS may not know for which access the UE has established an IMS connection because both the MME and the AMF may store information indicating that the UE supports IMS voice over PS. This may occur in systems in which a combined HSS/UDM is used or in systems that have separate HSS and UDM databases. In systems in which the HSS/UDM is combined, the system needs to identify whether the MME or the AMF needs to be queried for T-ADS information. In systems that have separate HSS and UDM databases, the HSS needs to determine if the MME or the UDM needs to be queried for T-ADS information.

In certain embodiments, if a P-CSCF fails a S-CSCF notifies an HSS to re-establish an IMS session. If a UE is dual registered, the HSS needs determine if it needs to notify an MME or an AMF (e.g., if the HSS and UDM are combined), or the MME or the UDM (e.g., if the HSS and UDM are separate) for a failure indication.

In various embodiments, a UTF allows subscription data exchange between a UDR of an HSS FE and a UDR of a UDM. The UTF may be a logical function that can be standalone or collocated with the UDM or HSS FE. In some embodiments, a UDR database of a UDM contains related <NUM> subscription data, and the UDR of a HSS FE contains related EPS and IMS subscription data.

In certain embodiments, a UTF contains a translation table that allows conversion of an Nudr (e.g., intra-PLMN interface) to a Ud (e.g., interface between PCRF and user data repositories) request and vice versa. If the UDM requires information from the EPS UDR, the UTF facilitates translation of a Nudr request to a Ud request. If the HSS FE requires information from the <NUM> UDR, the UTF is responsible to convert the Ud request to an Nudr request targeting specific subscription data. In various embodiments, a UTF implements a translation table supporting an HSS FE vendor specific Ud implementation.

In some embodiments, if an HSS FE or UDM determines that subscription data needs to be fetched from a different UDR, an Ud or Nudr message requesting subscription details may be sent to a UTF. The UTF translates the message into a corresponding message that is sent towards the HSS FE (e.g., Ud message) or the UDM (e.g., Nudr message) that is proxied towards the UDR. The UTF may also provide a translated message directly to a target UDR repository thereby bypassing the target HSS FE or the UDM.

<FIG> is a schematic block diagram illustrating one embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between an HSS <NUM>, an EPS UDR <NUM>, a UTF <NUM>, a UDM <NUM>, and a <NUM> UDR <NUM>. As may be appreciated, each communication described herein may include one or more messages.

In a first communication <NUM> transmitted to the HSS <NUM>, the HSS <NUM> receives a subscription request. The HSS <NUM> identifies <NUM> subscription data on an external UDR. Further, the HSS <NUM> constructs <NUM> a Ud message to fetch the subscription data.

In a second communication <NUM> transmitted from the HSS <NUM> to the UTF <NUM>, the HSS <NUM> transmits the Ud message to the UTF <NUM>. The UTF <NUM> translates <NUM> the Ud message to an Nudr message.

The UTF <NUM> may perform either a first option <NUM>, or a second option <NUM>. In the first option <NUM>, a third communication <NUM> is transmitted from the UTF <NUM> to the UDM <NUM>. Specifically, the UTF <NUM> transmits the Nudr message to the UDM <NUM>. The UDM <NUM> determines <NUM> a proxy Nudr message. In a fourth communication <NUM> transmitted from the UDM <NUM> to the <NUM> UDR <NUM>, the UDM <NUM> transmits the proxy Nudr message to the <NUM> UDR <NUM>. The <NUM> UDR fetches <NUM> the subscription data. In a fifth communication <NUM> transmitted from the <NUM> UDR <NUM> to the UDM <NUM>, the <NUM> UDR <NUM> transmits an Nudr response to the UDM <NUM>, and in a sixth communication <NUM> transmitted from the UDM <NUM> to the UTF <NUM>, the UDM <NUM> transmits an Nudr response to the UTF <NUM>.

In the second option <NUM>, a seventh communication <NUM> is transmitted from the UTF <NUM> to the <NUM> UDR <NUM>. Specifically, the UTF <NUM> transmits the Nudr message to the <NUM> UDR <NUM>. In an eighth communication <NUM> transmitted from the <NUM> UDR <NUM> to the UTF <NUM>, the <NUM> UDR <NUM> transmits an Nudr response to the UTF <NUM>.

The UTF <NUM> translates <NUM> the Nudr message to a Ud message. In a ninth communication <NUM> transmitted from the UTF <NUM> to the HSS <NUM>, the UTF <NUM> transmits a Ud response to the HSS <NUM>. In a tenth communication <NUM> transmitted by the HSS <NUM>, the HSS <NUM> transmits a subscription request response update location acknowledgment.

In certain embodiments, to support mobility in DR mode, support of an N26 interface between an AMF in 5GC and an MME in EPC is not required. A UE that supports a DR mode may operate in the DR mode if it receives an indication from a network that interworking without N26 is supported.

In some embodiments, for a UE operating in a DR mode the following may apply for PDU session transfer from 5GC to EPC: <NUM>) the UE operating in the DR mode may register in EPC ahead of any PDU session transfer using an attach procedure indicating that the UE is moving from 5GC without establishing a PDN connection in EPC if the EPC supports EPS attach without PDN connectivity. Support for EPS attach without PDN connectivity may be mandatory for a UE supporting DR procedures. Before attempting early registration in EPC, the UE may check whether EPC supports EPS attach without PDN connectivity by reading a related SIB in a target cell; <NUM>) the UE performs PDU session transfer from 5GC to EPC using a UE initiated PDN connection establishment procedure with a handover indication in the PDN connection request message; <NUM>) if the UE has not registered with the EPC ahead of the PDU session transfer, the UE may perform attach in the EPC with a handover indication in the PDN connection request message; <NUM>) the UE may selectively transfer certain PDU sessions to the EPC and keep other PDU sessions in 5GC; and <NUM>) the UE may maintain a registration up to date in both 5GC and EPC by re-registering periodically in both systems. If the registration in either 5GC or EPC times out (e.g., upon a mobile unit reaching a timer expiration), the corresponding network may start an implicit detach timer. Whether the UE transfers some or all PDU sessions on the EPC and whether it maintains the registration up to date in both EPC and 5GC may depend on UE capabilities that are implementation dependent. The information for determining which PDU sessions are transferred on the EPC side and the triggers may be pre-configured in the UE.

In certain embodiments, for a UE operating in a DR mode the following may apply for a PDN connection transfer from EPC to 5GC: <NUM>) the UE operating in the DR mode may register in a 5GC ahead of any PDN connection transfer using a registration procedure indicating that the UE is moving from the EPC; <NUM>) the UE performs a PDN connection transfer from the EPC to the 5GC using a UE initiated PDU session establishment procedure with an existing PDU session indication; <NUM>) the UE may selectively transfer certain PDN connections to the 5GC and keep other PDN connections in the EPC; and <NUM>) the UE may maintain the registration up to date in both the EPC and the 5GC by re-registering periodically in both systems. If the registration in either the EPC or the 5GC times out (e.g. upon a mobile unit reaching a timer expiration), the corresponding network may start an implicit detach timer. Whether the UE transfers some or all PDN connections on the 5GC side and whether it maintains the registration up to date in both the 5GC and the EPC may depend on UE capabilities that are implementation dependent. The information for determining which PDN connections are transferred on the 5GC side and the triggers may be pre-configured in the UE. If the EPC does not support EPS attach without PDN connectivity, the MME may detach the UE if the last PDN connection is released by the PGW.

In various embodiments, if sending a control plane request for MT services (e.g., MT SMS) a network may route it via either the EPC or the 5GC. In the absence of a UE response, the network may attempt routing the control plane request via the other system. The choice of the system through which the network attempts to deliver the control plane request may be left to network configuration. In some embodiments, logic of which PDU sessions are kept in which system for a DR UE with selective transfer of certain PDU sessions may be left up to UE implementation. A voice centric UE may keep a PDU session used for IMS services with a system that supports voice over IMS. The voice centric UE may re-register with the IMS if the IMS PDU session is transferred between the 5GS and the EPS.

In certain embodiments, if a UE initiates IMS registration with an IMS network, the UE may include within a registration request a PANI header field that include information corresponding to a radio access technology type that the UE may be attached to for 3GPP access.

The radio access technology types that the UE indicates may include one or more of the following access-types: "3GPP-GERAN," "3GPP-UTRAN-FDD," "3GPP-UTRAN-TDD," "3GPP-E-UTRAN-FDD," "3GPP-E-UTRAN-TDD," "3GPP-E-UTRAN-ProSe-UNR," "3GPP-NR-FDD," "3GPP-NR-TDD," "3GPP2-1X," "3GPP2-1X-HRPD," "3GPP2-UMB," "3GPP2-1X-Femto," "IEEE-<NUM>," "IEEE-<NUM>. 11a," "IEEE-<NUM>. 11b," "IEEE-<NUM>," "IEEE-<NUM>. 11n," "ADSL," "ADSL2," "ADSL2+," "RADSL," "SDSL," "HDSL," "HDSL2," "G. SHDSL," "VDSL," "IDSL," "xDSL," "DOCSIS," "IEEE-<NUM>," "IEEE-<NUM>. 3a," "IEEE-<NUM>. 3e," "IEEE-<NUM>. 3i," "IEEE-<NUM>. 3j," "IEEE-<NUM>. 3u," "IEEE-<NUM>. 3ab," "IEEE-<NUM>. 3ae," "IEEE-<NUM>. 3ah," "IEEE-<NUM>. 3ak," "IEEE-<NUM>. 3aq," "IEEE-<NUM>. 3an," "IEEE-<NUM>. 3y," "IEEE-<NUM>. 3z," and "DVB-RCS2.

In one embodiment, during an IMS registration process a P-CSCF adds the access-class within a PANI header. Adding the access-class may include adding information indicating a core network technology (e.g., 5GC or EPSC) based on input from a PCRF or PCF.

The access class may be included in a field and may include one or more of the following: "3GPP-GERAN," "3GPP-UTRAN," "3GPP-E-UTRAN," "3GPP-NR," "3GPP-WLAN," "3GPP-GAN," "3GPP-HSPA," "3GPP2," "untrusted-non-3GPP-VIRTUAL-EPC," "VIRTUAL-no-PS," and "WLAN-no-PS.

In certain embodiments, an access class of 3GPP-NR may indicate that a UE is accessing IMS via a 5GC; and, in some embodiments, an access class of 3GPP-E-UTRAN may indicate that the UE is accessing IMS via EPC.

In one embodiment, an access-type may be used by an IMS node to identify a core network and a radio access technology. The access type may be a combination of the core network and radio access technology such as 3GPP-5GC-E-UTRA used to identify a 5GC with E-UTRA radio access. The access type may be 3GPP-5GC-NR used to identify a 5GC with NR radio access.

In some embodiments, if a UE initiates an IMS registration procedure, an S-CSCF and an IMS AS may receive a PANI header so that both entities know if the UE is accessing IMS via 5GC or via EPC.

In various embodiments, a UE may provide its IMS capability (e.g., such as IMS voice capability) only via a core access network the UE intends to use for IMS registration. If the UE, in DR mode, intends to create a PDN connection for IMS over an EPS access, then the UE may not provide its IMS capability to an AMF at the time the UE sends a NAS registration request (e.g., either at initial registration or due to mobility). In such embodiments, the AMF may not check whether the network supports IMS supported features (e.g., such as IMS voice over PS) in a location of the UE and does not store related information in the AMF and a UDM.

In certain embodiments, if a UE, in DR mode, intends to create a PDU session for IMS over <NUM> access, then the UE may not provide its IMS capability (e.g., such as IMS voice capability) to an MME at initial attach NAS signaling or at tracking area update NAS signaling. In such embodiments, the MME may not check whether the network supports IMS supported features (e.g., such as IMS voice over PS and/or T-ADS information) in a location of the UE and does not store related information in the MME and an HSS.

As may be appreciated, only the MME or the AMF may include information for IMS supported features (e.g., such as IMS voice over PS support) for the UE. In one embodiment, instead of a UE providing an explicit IMS voice supported capability within an NAS message, the UE may disable its radio capabilities relating to IMS voice via EPS or NAS.

In some embodiments, an MME and/or an AMF uses information provided by a UE (e.g., IMS capability or updated radio capability) to determine if the MME and/or the AMF need to determine if IMS voice over a PS session is supported. If the UE provides its IMS voice capability via one access while in DR mode then either the MME and an HSS, or the AMF and an UDM may contain information about whether IMS voice over PS session is supported at the UE.

In various embodiments, if only an MME/HSS or an AMF/UDM have IMS voice over PS supported information, then if an IMS AS sends a request to the HSS (or HSS+UDM combination) requesting T-ADS information, the HSS may check its UDR to determine whether there is an IMS over PS supported indication available or it may interrogate the MME for the indication. If the HSS UDR or the MME does not have the IMS over PS supported indication, then the HSS may query the UDM (e.g., via a new interface or via the UTF), the HSS+UDM may query the UDR of the UDM, or the HSS may interrogate the AMF to obtain the information.

In certain embodiments, an IMS system entity (e.g., such as IMS AS) may not know whether to obtain information from an AMF or an MME because at the time the UE IMS registered to the IMS network, it may have used the E-UTRA related access-type in the PANI header (e.g., which may be used for both 5GC and EPC). In such embodiments, the IMS system entities (e.g., such as IMS AS) may check in both the AMF and the MME for the information relating to IMS supported features and/or T-ADS information (e.g., such as IMS voice over PS support for the UE). If the UE has, at the time of IMS registration, used an NR related access-type in the PANI header that may only be used for 5GC, the IMS system entities (e.g., such as IMS AS) may check the AMF for the information for IMS supported features for the UE.

In some embodiments, an IMS AS may know how a UE is accessing the IMS network if the IMS AS request for T-ADS information is in a request. The request may include which core network (e.g., EPC or 5GC) may provide related information (e.g., IMS voice over PS support indication, current RAT type and last radio contact).

In certain embodiments, an IMS AS may include, in a Sh request, Requested-Nodes AVP that includes information about which node (e.g., MME and/or AMF) information is requested from. The Requested-Nodes AVP may be of a type Unsigned32 and may comprise a bit mask according to Table <NUM>.

In various embodiments, if a 3GPP subscription database node (e.g., HSS) receives a request from an IMS AS (e.g., requesting T-ADS information), the 3GPP node may check a Requested-Nodes AVP to determine if information is requested from a <NUM> subscription and/or an EPS subscription.

In some embodiments, if an operator implements a separate HSS and UDM and the HSS supports IMS subscription only and if the HSS receives a request from an IMS AS and identifies that the IMS AS is requesting T-ADS information from an AMF (e.g., because the request is set to the AMF), the HSS may be aware that the information may be available from the UDR database of the UDM. In such embodiments, the HSS either may proxy the Sh message to the UDM or request from the UDR of the UDM (e.g., via the UTF) for the T-ADS information, as illustrated in <FIG>.

<FIG> is a schematic block diagram illustrating another embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, a UDM/UDR <NUM>, a UTF <NUM>, an HSS <NUM>, and an IMS AS <NUM>. As may be appreciated, each communication described herein may include one or more messages.

In a first communication <NUM> transmitted from the UE <NUM> to the IMS AS <NUM>, the UE <NUM> may IMS register with an IMS network by including an access-type in a PANI header. In one embodiment, the content of the access-type in the PANI header may include information indicating a core network technology used (e.g., 5GC or EPC). In some embodiments, a P-CSCF may include an access-class that may further include information indicating a core network technology based on input from a PCRF or a PCF. The IMS AS <NUM> may receive the PANI header using any suitable method.

The IMS AS <NUM> may derive <NUM> from the PANI header the type of the core network the UE is connected to (e.g., EPS network or <NUM> network) by the content of the access-type field and/or access-class field of the PANI header.

In a second communication <NUM> transmitted from the IMS AS <NUM> to the HSS <NUM>, if the IMS AS <NUM> determines that it needs to obtain T-ADS information, the IMS AS <NUM> may send a request via an Sh interface to obtain the most recent T-ADS information from the HSS <NUM>. The IMS AS <NUM> may include the Requested-Nodes AVP including information about a node that the information is requested from. If the IMS AS <NUM> determines that the UE <NUM> is accessing the IMS via a <NUM> network, the IMS AS <NUM> may include in the Requested-Nodes AVP a bit mask <NUM> (e.g., indicating that the requested data applies to the AMF <NUM>). If the IMS AS <NUM> determines that the UE <NUM> is accessing the IMS via EPS, the IMS AS <NUM> may include in the Requested-Nodes AVP a bit mask <NUM> (e.g., indicating that the requested data applies to the MME <NUM>).

The HSS <NUM> may perform either a first option <NUM> (e.g., using a direct interface between the UDM/UDR <NUM> and the HSS <NUM> with a new reference point between the UDM/UDR <NUM> and the HSS <NUM>; however, in some embodiments, the HSS <NUM> may proxy the Sh request to the UDM/UDR <NUM>), or a second option <NUM> (e.g., using the UTF <NUM> between the HSS <NUM> and the UDM/UDR <NUM> with no direct reference point between the HSS <NUM> and the UDM/UDR <NUM>). In the first option <NUM>, in a third communication <NUM> transmitted from the HSS <NUM> to the UDM/UDR <NUM>, if the HSS <NUM> determines that the most recent T-ADS information is located in the AMF <NUM> (e.g., based on the Requested-Node AVP), then the HSS <NUM> queries the UDM/UDR <NUM> to obtain the information. The HSS <NUM> may proxy the Sh request to the UDM/UDR <NUM> or may create a new request based on a new reference point between the HSS <NUM> and the UDM/UDR <NUM>.

The UDM/UDR <NUM> may check <NUM> with the UDR (e.g., via an Nudr message) to obtain the T-ADS information.

If the UDM/UDR <NUM> identifies <NUM> from the UDR that an IMS Voice over PS support indication is not homogeneous, the UDM/UDR <NUM> may query the AMF <NUM> for the latest information.

In a fourth communication <NUM> transmitted from the UDM/UDR <NUM> to the AMF <NUM>, the UDM/UDR <NUM> may send an Namf_MT_ProvideDomainSelectionInfo service request to the AMF <NUM>. In a fifth communication <NUM> transmitted from the AMF <NUM> to the UDM/UDR <NUM>, the AMF <NUM> may provide the information to the UDM/UDR <NUM> in a response to the Namf_MT_ProvideDomainSelectionInfo service request.

In a sixth communication <NUM> transmitted from the UDM/UDR <NUM> to the HSS <NUM>, the UDM/UDR <NUM> may send the information to the HSS <NUM> via a new interface or via an Sh reference point.

In a seventh communication <NUM> transmitted from the HSS <NUM> to the MME <NUM>, if the HSS <NUM> determines that the information requested is from the MME <NUM> the HSS <NUM> may query the MME <NUM> to obtain the most recent domain selection information (e.g., T-ADS information). In an eighth communication <NUM> transmitted from the MME <NUM> to the HSS <NUM>, the MME <NUM> may send the T-ADS information to the HSS <NUM>. In a ninth communication <NUM> transmitted from the HSS <NUM> to the IMS AS <NUM>, the HSS <NUM> may provide the information to the IMS AS <NUM> via an Sh reference point.

In the second option <NUM>, in a tenth communication <NUM> transmitted from the HSS <NUM> to the UTF <NUM>, if the HSS <NUM> determines that the information requested is from the AMF <NUM> (e.g., based on the Requested-Node AVP) the HSS <NUM> determines that it may need to query the UDR of the UDM/UDR <NUM> to obtain the information. The HSS <NUM> may construct a Ud message to retrieve the T-ADS information and may send the Ud message to the UTF <NUM>.

The UTF <NUM> may translate <NUM> the request into an Nudr request. In an eleventh communication <NUM> transmitted from the UTF <NUM> to the UDM/UDR <NUM>, the UTF <NUM> may send the Nudr request towards the UDR of the UDM/UDR <NUM>. In a twelfth communication <NUM> transmitted from the UDM/UDR <NUM> to the UTF <NUM>, the UDR of the UDM/UDR <NUM> may provide the T-ADS information in a Nudr response to the UTF <NUM>.

In a thirteenth communication <NUM> transmitted from the UTF <NUM> to the HSS <NUM>, the UTF <NUM> may translate the Nudr response into an Ud response that is transmitted to the HSS <NUM>. In a fourteenth communication <NUM> transmitted from the HSS <NUM> to the IMS AS <NUM>, the HSS <NUM> may send the T-ADS information to the IMS AS <NUM> via a Sh reference point. It should be noted that if the HSS <NUM> determines that the information requested is from the MME <NUM>, then communications <NUM> and <NUM> may take place instead.

In certain embodiments, if an operator implements a combo HSS+UDM then if the HSS+UDM receives a request from an IMS AS and identifies that the IMS AS is requesting T-ADS information and that the requested node is MME, the HSS+UDM may obtain the information from the MME.

<FIG> is a schematic block diagram illustrating an additional embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, an HSS/UDM <NUM>, and an IMS AS <NUM>. As may be appreciated, each communication described herein may include one or more messages.

In a second communication <NUM> transmitted from the IMS AS <NUM> to the HSS/UDM <NUM>, if the IMS AS <NUM> determines that it needs to obtain T-ADS information, the IMS AS <NUM> may send a request via an Sh interface to obtain the most recent T-ADS information from the HSS/UDM <NUM>. The IMS AS <NUM> may include in the Requested-Nodes AVP including information about a node that the information is requested from. If the IMS AS <NUM> determines that the UE <NUM> is accessing IMS via <NUM> network, the IMS AS <NUM> may include in the Requested-Nodes AVP a bit mask <NUM> (e.g., indicating that the requested data applies to the AMF <NUM>). If the IMS AS <NUM> determines that the UE <NUM> is accessing the IMS via EPS, the IMS AS <NUM> may include in the Requested-Nodes AVP a bit mask <NUM> (e.g., indicating that the requested data applies to the MME <NUM>).

The HSS/UDM <NUM> may check <NUM> with the UDR (via an Nudr message) to obtain the T-ADS information.

In a first option, the UE <NUM> may access the IMS via 5GC. In this first option, if the HSS/UDM <NUM> identifies <NUM> from the UDR that IMS voice over PS support indication is not homogeneous and the UE <NUM> may access the IMS via 5GC, then the HSS/UDM <NUM> may query the AMF <NUM> for the latest information. In a third communication <NUM> transmitted from the HSS/UDM <NUM> to the AMF <NUM>, the HSS/UDM <NUM> may send an Namf_MT_ProvideDomainSelectionInfo service request to the AMF <NUM>. In a fourth communication <NUM> transmitted from the AMF <NUM> to the HSS/UDM <NUM>, the AMF <NUM> may provide the information to the HSS/UDM <NUM> in a response to the Namf_MT_ProvideDomainSelectionInfo service request.

In a second option, the UE <NUM> is accessing the IMS via EPC. In this second option, if the HSS/UDM <NUM> identifies from the UDR that IMS voice over PS support indication is not homogeneous and if the UE <NUM> is accessing IMS via EPC, then in a fifth communication <NUM> transmitted from the HSS/UDM <NUM> to the MME <NUM>, the HSS/UDM <NUM> may query the MME <NUM> to obtain the most recent domain selection information (e.g., T-ADS information). In a sixth communication <NUM> transmitted from the MME <NUM> to the HSS/UDM <NUM>, the MME <NUM> may provide a response to the request for the T-ADS information.

In a seventh communication <NUM> transmitted from the HSS/UDM <NUM> to the IMS AS <NUM>, the HSS/UDM <NUM> may provide the information to the IMS AS <NUM> via an Sh reference point.

In certain embodiments, the IMS AS <NUM> may have separate interfaces with the HSS (e.g., via Sh) and with the UDM (e.g., via a new reference point based on SBI). In such embodiments, the IMS AS <NUM> derives the access via which the UE <NUM> is connected to the IMS based on the information included within the PANI header and interrogates the HSS (e.g., via Sh) or the UDM (e.g., via SBI reference point) for T-ADS information.

In an embodiment illustrated in <FIG>, the network may support separate HSS and UDM and, if the UE is DR to both EPS and 5GS, may use EPS for an IMS service such as IMS voice.

<FIG> is a schematic block diagram illustrating a further embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, a UDM/UDR <NUM>, a UTF <NUM>, an HSS <NUM>, and an IMS AS <NUM>. As may be appreciated, each communication described herein may include one or more messages.

The UE <NUM> may be <NUM> DR to both EPS and 5GS and may use EPS for an IMS service, such as IMS voice.

In a first communication <NUM> transmitted from the UE <NUM> to the AMF <NUM>, the UE <NUM> may initiate a 5GS registration update with the AMF <NUM> indicating that IMS capability (e.g., such as IMS voice) is not supported. The UE <NUM> may not include its IMS capability (e.g., such as IMS voice capability) in the 5GS registration message request.

The AMF <NUM> determines <NUM> that the UE <NUM> does not support IMS capability (e.g., such as IMS voice over PS) and does not derive whether the network IMS voice is over PS in the location of the UE <NUM>. The AMF <NUM> does not store an IMS voice over PS support indication and other T-ADS information for this UE <NUM> in the UDM/UDR <NUM>.

If the IMS AS <NUM> requires <NUM> T-ADS information, the IMS AS <NUM> may not know whether to obtain this information from the AMF <NUM> or the MME <NUM>. In one embodiment, a reason may be that at the time the UE <NUM> IMS registered to the IMS network, the UE <NUM> used an E-UTRA related access-type which can be used for both 5GC and EPC. Therefore, the IMS AS <NUM> may check for the T-ADS information in both the AMF <NUM> and the MME <NUM>.

In a second communication <NUM> transmitted from the IMS AS <NUM> to the HSS <NUM>, the IMS AS <NUM> may request T-ADS information from the HSS <NUM> via a Sh reference point.

The HSS <NUM> may check <NUM> its UDR to obtain T-ADS information or may interrogate the MME <NUM>.

The HSS <NUM> may also interrogate <NUM> the UDM/UDR <NUM> for T-ADS information, and the UDM/UDR <NUM> may interrogate <NUM> the AMF <NUM> for T-ADS information.

The HSS <NUM> identifies <NUM> that T-ADS information may only be available over EPS.

In a third communication <NUM> transmitted from the HSS <NUM> to the IMS AS <NUM>, the HSS <NUM> may provide the information to the IMS AS <NUM>.

In certain embodiments, if a network supports a combo HSS+UDM then the HSS+UDM may interrogate the MME and the AMF in order to obtain the T-ADS information (only either the MME or the AMF may respond with T-ADS information).

<FIG> illustrates one embodiment in which a network may support a separate HSS and UDM, and the UE may be DR to both EPS and 5GS and may use 5GS for an IMS service such as IMS voice.

<FIG> is a flow chart diagram illustrating yet another embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, a UDM/UDR <NUM>, a UTF <NUM>, an HSS <NUM>, and an IMS AS <NUM>. As may be appreciated, each communication described herein may include one or more messages.

In a first communication <NUM> transmitted from the UE <NUM> to the MME <NUM>, the UE <NUM> may initiate a tracking area update (or an initial attach) with the MME <NUM>. The UE <NUM> may indicate that it does not support IMS capabilities (e.g., such as IMS voice capability over EPS access) by not including an indication within a request that IMS capabilities (e.g., such as IMS voice over PS) is supported.

The MME <NUM> determines <NUM> that the UE <NUM> does not support IMS capability (e.g., such as IMS voice over PS) and does not derive whether the network IMS voice is over PS in the location of the UE <NUM>. The MME <NUM> does not store an IMS voice over PS support indication and other T-ADS information for this UE <NUM> in the HSS <NUM>.

The IMS AS <NUM> identifies <NUM> that T-ADS information is required for domain selection. If the IMS AS <NUM> requires T-ADS information, the IMS AS <NUM> may know to obtain this information from the AMF <NUM> or the MME <NUM>. In one embodiment, a reason may be that at the time the UE <NUM> IMS registered to the IMS network, the UE <NUM> used an NR related access-type which can be used for 5GC.

The HSS <NUM> may also interrogate <NUM> the UDM/UDR <NUM> that may interrogate <NUM> the AMF <NUM> for T-ADS information.

The UDM/UDR <NUM> may obtain <NUM> T-ADS information from a 5GS subscription or the AMF <NUM>.

The HSS <NUM> identifies <NUM> T-ADS information from a 5GS subscription.

In certain embodiments, if the network supports a combo HSS+UDM then the HSS+UDM may interrogate the AMF to obtain the T-ADS information.

In some embodiments, if an S-CSCF determines that a P-CSCF is unavailable, the S-CSCF may trigger an HSS to re-establish a PDN connection associated with an IMS. The S-CSCF triggers the HSS to re-establish the PDN connection associated with IMS via a Cx reference point. The HSS then instructs the MME to re-establish the PDN connection used for IMS via a S6a reference point.

If a UE is DR to EPS and 5GS, the UE may either have a PDN connection for IMS over EPS or a have a PDU session for IMS over 5GS.

In one embodiment, an S-CSCF may determine an access technology via which an IMS session is established by examining a PANI header. In such embodiments, the S-CSCF may indicate to the HSS via a Cx reference point the node (e.g., MME or AMF) that needs to be triggered to re-establish the IMS connection by including a Requested-Nodes AVP in the request.

If a network supports a separate HSS and UDM architecture, the HSS may use the information provided within a Cx request to identify if the HSS triggers the MME or if it notifies the UDM to trigger the AMF as illustrated in <FIG>.

<FIG> is a flow chart diagram illustrating yet an additional embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, a UDM/UDR <NUM>, a UTF <NUM>, an HSS <NUM>, and an S-CSCF <NUM>. As may be appreciated, each communication described herein may include one or more messages.

The UE <NUM> may be registered <NUM> via IMS to either EPS or 5GS while operating in a DR mode (e.g., connected to both EPS and 5GS).

The S-CSCF <NUM> may identify <NUM> an access technology via which the UE <NUM> is IMS registered based on a PANI header.

The S-CSCF <NUM> may detect <NUM> a P-CSCF failure.

In a first communication <NUM> transmitted from the S-CSCF <NUM> to the HSS <NUM>, the S-CSCF <NUM> may send via a Cx reference point to the HSS <NUM> an indication for P-CSCF restoration. The S-CSCF <NUM> may also include information indicating the access technology via which the UE <NUM> is IMS registered. In one embodiment, the information indicating the access technology may include a Requested-Nodes AVP within the Cx request.

If the access-type and/or access-class in the PANI header identifies the IMS network that the UE <NUM> is IMS registered over as EPS, the HSS <NUM> may identify <NUM> that the MME <NUM> may need to be triggered.

The HSS <NUM> may initiate <NUM> a P-CSCF restoration indication via a transmission to the MME <NUM>.

If the access-type and/or access-class in the PANI header identifies the IMS network that the UE <NUM> is IMS registered over as 5GS, the HSS <NUM> may identify <NUM> that the UDM/UDR <NUM> may need to be notified.

In a second communication <NUM> transmitted from the HSS <NUM> to the UDM/UDR <NUM>, the HSS <NUM> may proxy a Cx request to the UDM/UDR <NUM>. In one embodiment, the HSS <NUM> may notify the UDM/UDR <NUM> via a new interface.

The UDM/UDR <NUM> may notify <NUM> the AMF <NUM> of a P-CSCF restoration indication.

In a third communication <NUM> transmitted from the UDM/UDR <NUM> to the HSS <NUM>, the UDM/UDR <NUM> may transmit an acknowledgement to the HSS <NUM>. In a fourth communication <NUM> transmitted from the HSS <NUM> to the S-CSCF <NUM>, the HSS <NUM> may transmit an acknowledgment to the S-CSCF <NUM>.

If the network supports a combo HSS+UDM, the HSS+UDM may use information provided within a Cx request to identify if the MME or the AMF needs to be triggered to re-establish a PDN connection/PDU session for IMS as illustrated in <FIG>.

<FIG> is a flow chart diagram illustrating yet a further embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, an HSS/UDM <NUM>, and an S-CSCF <NUM>. As may be appreciated, each communication described herein may include one or more messages.

The UE <NUM> may be registered <NUM> via IMS to either an EPS or an 5GS while operating in DR mode (e.g., connected to both EPS and 5GS).

In a first communication <NUM> transmitted from the S-CSCF <NUM> to the HSS/UDM <NUM>, the S-CSCF <NUM> may send via a Cx reference point to the HSS/UDM <NUM> an indication for P-CSCF restoration. The S-CSCF <NUM> may also include information indicating the access technology via which the UE <NUM> is IMS registered. In one embodiment, the information indicating the access technology may include a Requested-Nodes AVP within the Cx request.

If the access-type and/or access-class in the PANI header identifies the IMS network that the UE <NUM> is IMS registered over as EPS, the HSS/UDM <NUM> may identify <NUM> that the MME <NUM> may need to be triggered.

The HSS/UDM <NUM> may initiate <NUM> a P-CSCF restoration indication to the MME <NUM>.

If the access-type and/or access-class in the PANI header identifies the IMS network that the UE <NUM> is IMS registered over as 5GS, the HSS/UDM <NUM> may identify <NUM> that the AMF <NUM> may need to be notified.

The HSS/UDM <NUM> may notify <NUM> the AMF <NUM> of a P-CSCF restoration indication.

In a second communication <NUM> transmitted from the HSS/UDM <NUM> to the S-CSCF <NUM>, the HSS/UDM <NUM> may transmit an acknowledgement to the S-CSCF <NUM>.

In various embodiments, if only the MME/HSS or AMF/UDM have IMS voice over PS supported information (e.g., if the UE provides its IMS capabilities within NAS messages) then if the S-CSCF sends a request to the HSS (or HSS+UDM combo) indicating P-CSCF restoration, the HSS may check its UDR to determine if there is an IMS over PS supported indication available or it may interrogate the MME. If the HSS/UDR or the MME does not have the IMS over PS supported indication, then the HSS may query the UDM (e.g., via a new interface or via the UTF), the HSS+UDM may query the UDR of the UDM, or the HSS may interrogate the AMF to obtain the information.

<FIG> illustrates one embodiment of a procedure if the network supports separate HSS and UDMs.

<FIG> is a flow chart diagram illustrating an additional embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, a UDM/UDR <NUM>, a UTF <NUM>, an HSS <NUM>, and an S-CSCF <NUM>. As may be appreciated, each communication described herein may include one or more messages.

The UE <NUM> may be registered <NUM> via IMS to either EPS or 5GS while operating in DR mode. The UE <NUM> may only NAS register its IMS capability (e.g., such as IMS voice capability) for an access technology (e.g., either EPS or 5GS) if the UE <NUM> intends to use that access technology for the IMS registration.

In a first communication <NUM> transmitted from the S-CSCF <NUM> to the HSS <NUM>, the S-CSCF <NUM> may send via a Cx reference point to the HSS <NUM> an indication for P-CSCF restoration.

The HSS <NUM> checks <NUM> if there is information regarding support of IMS capabilities (e.g., such as IMS voice over PS support) or may query such information from the MME <NUM>.

If the HSS <NUM> determines that IMS capabilities (e.g., such as IMS voice over PS) are supported (e.g., by interrogating the MME <NUM>), the HSS <NUM> initiates <NUM> a P-CSCF restoration indication transmission to the MME <NUM>. If the P-CSCF restoration is not successful, step <NUM> is performed.

If the HSS <NUM> determines that IMS voice over PS is not supported (e.g., there is no information on the UDM/UDR <NUM> or the MME <NUM>), the HSS <NUM> determines <NUM> that the UDM/UDR <NUM> needs to be triggered.

In a second communication <NUM> transmitted from the HSS <NUM> to the UDM/UDR <NUM>, the HSS <NUM> may proxy the Cx request to the UDM/UDR <NUM>. In one embodiment, the HSS <NUM> may notify the UDM/UDR <NUM> via a new interface.

As illustrated in <FIG>, the UE <NUM> IMS registers over EPS access technology and the UE <NUM> may use an E-UTRA related PANI header that may be used for both EPS and 5GS to register to the IMS system. The IMS system entities (e.g., such as IMS AS) may check in both the AMF <NUM> and the MME <NUM> for information for IMS supported features for the UE <NUM>. If the UE <NUM> IMS registers over 5GS access technology, the UE <NUM> may use an NR related PANI header that may only be used for 5GC, the IMS system entities such as IMS AS may check the AMF <NUM> for the information for IMS supported features for the UE <NUM>. Therefore, steps <NUM> and <NUM> in <FIG> may not be performed.

If the network supports a combo HSS+UDM, the HSS+UDM may use information provided within a Cx request to identify if the MME or the AMF needs to be triggered to re-establish the PDN connection/PDU session for IMS as illustrated in <FIG>.

<FIG> is a flow chart diagram illustrating a further embodiment of communications <NUM> in a wireless communication system. The communications <NUM> include messages transmitted between a UE <NUM>, an AMF <NUM>, an MME <NUM>, an HSS/UDM <NUM>, and an S-CSCF <NUM>. As may be appreciated, each communication described herein may include one or more messages.

The UE <NUM> may be registered <NUM> via IMS to either EPS or 5GS while operating in a DR mode (e.g., connected to both EPS and 5GS). The UE <NUM> may only NAS register its IMS capability (e.g., such as IMS voice capability) for an access technology (e.g., either EPS or 5GS) if the UE <NUM> intends to use that access technology for the IMS registration.

In a first communication <NUM> transmitted from the S-CSCF <NUM> to the HSS/UDM <NUM>, the S-CSCF <NUM> may send via a Cx reference point to the HSS/UDM <NUM> an indication for P-CSCF restoration.

The HSS/UDM <NUM> checks <NUM> whether there is information regarding IMS voice over PS support at the HSS/UDM <NUM> or may query the MME <NUM>.

If the HSS/UDM <NUM> determines that IMS voice over PS is supported only at the MME <NUM>, the HSS/UDM <NUM> initiates <NUM> transmission of a P-CSCF restoration indication to the MME <NUM>.

The HSS/UDM <NUM> may determine <NUM> that IMS voice over PS is supported at the AMF <NUM>.

As illustrated in <FIG>, if the UE <NUM> IMS registers over EPS access technology, the UE <NUM> may use an E-UTRA related PANI header that may be used for both EPS and 5GS to register to IMS system. The IMS system entities such as IMS AS may check in both the AMF <NUM> and the MME <NUM> for information for IMS supported features for the UE <NUM>. If the UE <NUM> IMS registers over 5GS access technology, the UE <NUM> may use an NR related PANI header that may only be used for 5GC, the IMS system entities such as IMS AS may check the AMF <NUM> for the information for IMS supported features for the UE <NUM>. Therefore, steps <NUM> and <NUM> in <FIG> may not be performed.

In certain embodiments, the S-CSCF may have separate interfaces with the HSS (e.g., via Cx) and with the UDM (e.g., via a new reference point based on SBI). In such embodiments, the S-CSCF may derive access via which the UE is connected to the IMS based on the information included within the PANI header and may inform the HSS (e.g., via Sh) or the UDM (e.g., via the SBI reference point) of a P-CSCF restoration indication.

<FIG> is a flow chart diagram illustrating one embodiment of a method <NUM> for establishing a connection with a dual registered device. The method <NUM> is performed by a network unit <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> includes receiving <NUM> a first request to establish an internet protocol multimedia subsystem session with a first device, wherein the first device is dual registered to: a first network access supporting <NUM> core network connectivity; and a second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to an internet protocol multimedia subsystem via either the first network access or the second network access. The method <NUM> includes determining <NUM> first information corresponding to a network access connectivity selected from the first network access and the second network access through which the first device has internet protocol connectivity with the internet protocol multimedia subsystem. The method <NUM> includes transmitting <NUM> a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the internet protocol multimedia subsystem from the network access connectivity, wherein the second request comprises third information indicating a second network function for the first network function to contact to retrieve the second information.

In certain embodiments, the first information is determined to decide whether the first request is to be sent to the first device via the first network access connectivity or via the second network access connectivity. The second information is determined to decide whether the first request is to be sent via the network access connectivity via circuit switched connectivity or packet switched connectivity. In various embodiments, the third information is determined based on the first information.

In one embodiment, the first information is determined from an access type included in a p access network information header of the first device. In certain embodiments, the access type indicates a type of core network. In some embodiments, the type of core network comprises an evolved packet core network or a <NUM> core network.

In various embodiments, the first device comprises a user equipment. In one embodiment, the second request comprises a request for terminating access domain selection information. In certain embodiments, the method <NUM> further comprises receiving a message comprising a terminating access domain selection in response to transmitting the second request.

In some embodiments, the message comprises a Sh message. In various embodiments, the second network function comprises a mobility management entity, an access and mobility management function, or a combination thereof. In one embodiment, the first network function comprises a home subscriber server, a unified data management function, or a combination thereof.

<FIG> is a flow chart diagram illustrating one embodiment of a method <NUM> for retrieving information. In some embodiments, the method <NUM> is performed by an apparatus, such as the network unit <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> may include receiving <NUM> a request at a first network function to retrieve information on voice support over an internet protocol multimedia subsystem over packet switched network from a first network access connectivity, wherein the request comprises information indicating a second network function to contact regarding the first network access connectivity of the first device.

<FIG> is a flow chart diagram illustrating another embodiment of a method <NUM> for establishing a connection with a dual registered device. In some embodiments, the method <NUM> is performed by an apparatus, such as the network unit <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> may include receiving <NUM> a first request indicating that a server is unavailable. In certain embodiments, the method <NUM> includes determining <NUM> first information corresponding to a network access connectivity selected from a first network access and a second network access through which a first device has internet protocol connectivity with an internet protocol multimedia subsystem, wherein the first device is dual registered to: the first network access supporting <NUM> core network connectivity; and the second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to the internet protocol multimedia subsystem via either the first network access or the second network access. In some embodiments, the method <NUM> includes transmitting <NUM> a second request to a first network function to initiate reconnection with the server, wherein the second request comprises second information indicating a second network function to contact to re-establish connection with the internet protocol multimedia subsystem.

The following embodiments even if described or named as "embodiment(s)" do not fully and thus only partly correspond to the invention as defined in the claims, since one or more features present in and required by the independent claims are missing in the "embodiment(s)", but they are useful to highlight specific aspects of the claims.

In certain embodiments, the first information is determined from an access type included in a p access network information header of the first device. In some embodiments, the access type indicates a type of core network. In various embodiments, the type of core network comprises an evolved packet core network or a <NUM> core network.

In one embodiment, the second information is determined based on the first information. In certain embodiments, the first device comprises a user equipment. In some embodiments, the first network function comprises a home subscriber server, a unified data management function, or a combination thereof.

In various embodiments, the second network function comprises a mobility management entity, an access and mobility management function, or a combination thereof. In one embodiment, the server comprises a proxy-call session control function.

In one embodiment, a method comprises: receiving a first request to establish an internet protocol multimedia subsystem session with a first device, wherein the first device is dual registered to: a first network access supporting <NUM> core network connectivity; and a second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to an internet protocol multimedia subsystem via either the first network access or the second network access; determining first information corresponding to a network access connectivity selected from the first network access and the second network access through which the first device has internet protocol connectivity with the internet protocol multimedia subsystem; and transmitting a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the internet protocol multimedia subsystem from the network access connectivity, wherein the second request comprises third information indicating a second network function for the first network function to contact to retrieve the second information.

In certain embodiments, the first information is determined to decide whether the first request is to be sent to the first device via the first network access connectivity or via the second network access connectivity.

In some embodiments, the second information is determined to decide whether the first request is to be sent via the network access connectivity via circuit switched connectivity or packet switched connectivity.

In various embodiments, the third information is determined based on the first information.

In one embodiment, the first information is determined from an access type included in a p access network information header of the first device.

In certain embodiments, the access type indicates a type of core network.

In some embodiments, the type of core network comprises an evolved packet core network or a <NUM> core network.

In various embodiments, the first device comprises a user equipment.

In one embodiment, the second request comprises a request for terminating access domain selection information.

In certain embodiments, the method further comprises receiving a message comprising a terminating access domain selection in response to transmitting the second request.

In some embodiments, the message comprises a Sh message.

In various embodiments, the second network function comprises a mobility management entity, an access and mobility management function, or a combination thereof.

In one embodiment, the first network function comprises a home subscriber server, a unified data management function, or a combination thereof.

In one embodiment, an apparatus comprises: a receiver that receives a first request to establish an internet protocol multimedia subsystem session with a first device, wherein the first device is dual registered to: a first network access supporting <NUM> core network connectivity; and a second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to an internet protocol multimedia subsystem via either the first network access or the second network access; a processor that determines first information corresponding to a network access connectivity selected from the first network access and the second network access through which the first device has internet protocol connectivity with the internet protocol multimedia subsystem; and a transmitter that transmits a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the internet protocol multimedia subsystem from the network access connectivity, wherein the second request comprises third information indicating a second network function for the first network function to contact to retrieve the second information.

In certain embodiments, the receiver receives a message comprising a terminating access domain selection in response to transmitting the second request.

In one embodiment, a method comprises: receiving a request at a first network function to retrieve information on voice support over an internet protocol multimedia subsystem over packet switched network from a first network access connectivity, wherein the request comprises information indicating a second network function to contact regarding the first network access connectivity of the first device.

In one embodiment, an apparatus comprises: a receiver that receives a request at a first network function to retrieve information on voice support over an internet protocol multimedia subsystem over packet switched network from a first network access connectivity, wherein the request comprises information indicating a second network function to contact regarding the first network access connectivity of the first device.

In one embodiment, a method comprises: receiving a first request indicating that a server is unavailable; determining first information corresponding to a network access connectivity selected from a first network access and a second network access through which a first device has internet protocol connectivity with an internet protocol multimedia subsystem, wherein the first device is dual registered to: the first network access supporting <NUM> core network connectivity; and the second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to the internet protocol multimedia subsystem via either the first network access or the second network access; and transmitting a second request to a first network function to initiate reconnection with the server, wherein the second request comprises second information indicating a second network function to contact to re-establish connection with the internet protocol multimedia subsystem.

In certain embodiments, the first information is determined from an access type included in a p access network information header of the first device.

In some embodiments, the access type indicates a type of core network.

In various embodiments, the type of core network comprises an evolved packet core network or a <NUM> core network.

In one embodiment, the second information is determined based on the first information.

In certain embodiments, the first device comprises a user equipment.

In some embodiments, the first network function comprises a home subscriber server, a unified data management function, or a combination thereof.

In one embodiment, the server comprises a proxy-call session control function.

In one embodiment, an apparatus comprises: a receiver that receives a first request indicating that a server is unavailable; a processor that determines first information corresponding to a network access connectivity selected from a first network access and a second network access through which a first device has internet protocol connectivity with an internet protocol multimedia subsystem, wherein the first device is dual registered to: the first network access supporting <NUM> core network connectivity; and the second network access supporting evolved packet core network connectivity and circuit switched network connectivity, wherein the first device has connectivity to the internet protocol multimedia subsystem via either the first network access or the second network access; and a transmitter that transmits a second request to a first network function to initiate reconnection with the server, wherein the second request comprises second information indicating a second network function to contact to re-establish connection with the internet protocol multimedia subsystem.

Claim 1:
A method performed by a network unit (<NUM>, <NUM>), the method comprising:
receiving a first request to establish an internet protocol multimedia subsystem, IMS, session with a user equipment, UE, (<NUM>, <NUM>), wherein the UE (<NUM>, <NUM>) is dual registered to:
a first network access supporting fifth generation, <NUM>, core network connectivity; and
a second network access supporting evolved packet core, EPC, network connectivity and circuit switched network connectivity,
wherein the UE (<NUM>, <NUM>) has connectivity to an IMS via the first network access or the second network access;
determining first information corresponding to a network access connectivity selected from the first network access and the second network access, wherein the UE (<NUM>, <NUM>) has internet protocol connectivity with the IMS through the network access connectivity; and
transmitting a second request to a first network function to retrieve second information corresponding to voice support over packet switched connectivity over the IMS from the network access connectivity, wherein the second request comprises information indicating a second network function which is to be contacted by the first network function to retrieve the second information;
wherein the second information indicates whether the first request is to be received via the network access connectivity via circuit switched connectivity or packet switched connectivity;
wherein the first network function comprises a home subscriber server, HSS, or a unified data management function, UDM; and
wherein the second network function comprises a mobility management entity, MME, or an access and mobility management function, AMF.