Preservation of emergency calls upon transfer failure

Abstract

To provide preservation of emergency calls in the event of a transfer failure.SOLUTION: Systems and methods for transferring an emergency session from a first network to a second network at a user equipment (UE). The method includes transmitting a first registration request message to a second network, receiving a registration reject message from the second network, detecting that an emergency session between the UE and the first network is ongoing, transmitting a second registration request message comprising an emergency registration request to the second network, and receiving a registration accept message for the emergency session.SELECTED DRAWING: Figure 2

Description

[Background technology]

[0001] As used herein, the term “user equipment” (alternatively, “UE”) may refer, in some cases, to a mobile or wireless device, such as a mobile phone, personal digital assistant, handheld, laptop computer, or personal computer, and similar devices having telecommunications capabilities, including text and email functionality. The terms “UE,” “mobile device,” and “wireless device” may be used interchangeably herein. Such a UE may include devices such as a universal integrated circuit card (UICC) and its associated removable memory module, including, but not limited to, a subscriber identity module (SIM) application, a universal subscriber identity module (USIM) application, or a removable user identity module (R-UIM) application. Alternatively, such a UE may include the device itself without such modules. In other cases, the term “UE” may refer to a device that has similar capabilities but is not portable, such as a desktop computer, a set-top box, or a networked appliance. The term “UE” may also refer to any component on which a communication session for a user may terminate. Additionally, the terms "user agent," "UA," "user device," and "mobile device" may be used interchangeably herein.

[0002] An emergency call or session is a special type of call or session. It typically has higher priority within the network than other calls, and its bearer has different characteristics than other calls; for example, the bearer may have one or more of a higher priority or a higher quality of service (QoS). Furthermore, a UE may not need a subscription with the network to request an emergency call. For example, an emergency call can be completed even if the UICC is absent, or if the UE is associated with an expired or invalid subscription, etc. An interruption or disruption of an emergency call can have disastrous consequences. Summary of the Invention [Means for solving the problem]

[0003] An emergency call may be established by a UE operating in a single-registration mode, i.e., the UE is registered with only a single network at any given time (the term "registered" may be considered synonymous with "attached," depending on the context of the term's use). The network may be a fifth-generation (5G) core network supported by the access network, or an older network, e.g., a typical fourth-generation (4G) core network supported by the access network. An example of an access network supporting a 4G core network is an evolved universal terrestrial radio access network (E-UTRAN), i.e., an evolved universal terrestrial radio access (E-UTRA) connected to an evolved packet core (EPC). If an emergency call is established in one network (e.g., a 5G core network supported by the access network) and there is no interworking between the two networks (e.g., a 5G core network supported by the access network and an EPC or 4G core network supported by the access network), handover of the emergency call between networks may fail and the emergency call may be dropped. Described herein are several techniques for handing over emergency calls between a 5G core network and an EPC network.

[0004] The 5G access network can be at least one of multiple access networks, including New Radio (NR) and E-UTRA. The 5G access network provides access to the 5G core network (5GC). A wireless local area network (WLAN) can also be used to access the 5GC. The UE communicates with the core network via the access network using a non-access stratum (NAS) protocol. A typical network element in the EPC for handling NAS messages is the mobility management entity (MME). A typical network element in the 5GC for handling NAS messages is the access and mobility management function (AMF) or the session management function (SMF). The AMF and SMF are 5G core network nodes.

[0005] The NAS protocol consists of a mobility (management) protocol and a session management protocol. An example of an EPC NAS mobility protocol message is an attach message, e.g., an attach request message. An example of an EPC NAS session management protocol message is a packet data network (PDN) connection request message, e.g., a PDN connection request message. An example of a 5GC NAS mobility protocol message is a registration message, e.g., a registration request message. An example of a 5GC NAS session management protocol message is a protocol data unit (PDU) session request message, e.g., a PDU session request message. The sender of these NAS messages may receive a response message to any of these NAS messages. For example, the response message may be a NAS response message, e.g., an attach reject message, an attach accept message, etc.

[0006] A UE can be in a certain mode or modes of operation. In idle mode (as opposed to connected mode, generally), the UE cannot initiate NAS procedures involving session management and involving session management protocols. NAS procedures involving mobility management and involving mobility management protocols are required to change the UE from idle mode to connected mode.

[0007] When performing the EPC NAS registration procedure, the UE can request to be jointly attached (e.g., packet switched services provided by EPC and circuit switched) by using an attach procedure (which causes the UE to transmit an attach request message to the network), or to be attached for Evolved Packet System (EPS) services using only the attach procedure, or to be attached for emergency bearer services using only the attach procedure.

[0008] When coupled attaching, the network or MME registers the UE in a circuit switched (CS) domain network node, such as a mobile switching center (MSC) or an MSC server. In other words, the network registers the UE in the CS domain network node on behalf of the UE. After successful coupled registration, the UE can obtain CS service via circuit switched fallback (CSFB). The attach request message transmitted by the UE to the network may also include a packet data network (PDN) connection request message.

[0009] When performing the 5GC NAS registration procedure, the UE can request to be registered by the registration procedure (which causes the UE to transmit a registration message to the network), or can request to be registered for emergency bearer services using only the registration procedure.

[0010] In some communication environments, a 4G access network (i.e., an access network connected to a 4G core network EPC) is more common than a 5G access network (i.e., an access network connected to a 5G core network 5GC). A UE may need to transfer an existing connection from a 5G access network to a 4G access network (e.g., when handing over from an access network that provides access to a 5GC) or vice versa (e.g., when handing over from an access network that provides access to an EPC). Systems such as EPS and 5GS include a core network and an access network. The present invention provides, for example, the following. (Item 1) 1. A method in a user equipment (UE) for transferring an ongoing emergency session from a first network to a second network, the method comprising: transmitting a first attach request message to the second network, the first attach request message comprising a PDN connectivity request message with a request type set to “handover”; receiving an attach denial message from the second network; Detecting that an ongoing emergency session between the UE and the first network is ongoing; and transmitting a second attach request message to the second network in response to detecting the ongoing emergency session, the second attach request message comprising a PDN connectivity request message having a request type set to "handover of emergency bearer services" for the ongoing emergency session; Receiving an attach acknowledgement message A method comprising: (Item 2) Item 2. The method of item 1, wherein the second attach request message is an emergency attach request message. (Item 3) 3. The method of claim 1, wherein the attach denial message comprises an Evolved Packet System (EPS) Mobility Management (EMM) cause code. (Item 4) Item 4. The method of item 3, wherein prior to transmitting the second attach request message, the method further includes determining that the EMM cause code indicates an EPS Session Management (ESM) failure. (Item 5) 10. The method of claim 9, wherein the first network is a fifth generation (5G) network and the second network is a fourth generation (4G) network. (Item 6) 2. The method of claim 1, wherein the first network is part of a fifth generation system (5GS) and the second network is part of an EPS. (Item 7) Item 3. The method of item 2, wherein the emergency attach request message has an attach type set to "EPS Emergency Attach." (Item 8) 10. The method of claim 1, wherein the second attach request message has an attach type not set to "EPS Emergency Attach." (Item 9) A user equipment (UE), a processor; a memory storing instructions that, when executed by the processor, cause the UE to: transmitting a first attach request message to a second network, the first attach request message comprising a PDN connectivity request message with a request type set to “handover”; receiving an attach denial message from the second network; Detecting that an ongoing emergency session between the UE and a first network is ongoing; and transmitting a second attach request message to the second network in response to detecting the ongoing emergency session, the second attach request message comprising a PDN connectivity request message having a request type set to "handover of emergency bearer services" for the ongoing emergency session; Receiving an attach acknowledgement message memory and UE equipped with. (Item 10) Item 10. The UE of item 9, wherein the second attach request message is an emergency attach request message. (Item 11) Item 11. The UE of item 9 or 10, wherein the attach denial message comprises an evolved packet system (EPS) mobility management (EMM) cause code. (Item 12) Item 12. The UE of item 11, wherein the instructions further cause the UE to determine that the EMM cause code indicates an EPS session management (ESM) failure. (Item 13) 13. The UE of any one of items 9-12, wherein the first network is a fifth generation (5G) network and the second network is a fourth generation (4G) network. (Item 14) 13. The UE of any one of items 9-12, wherein the first network is part of a fifth generation system (5GS) and the second network is part of an EPS. (Item 15) Item 11. The UE of item 10, wherein the emergency attach request message has an attach type set to "EPS Emergency Attach." (Item 16) 16. The UE of any one of items 9-15, wherein the second attach request message has an attach type that is not set to "EPS Emergency Attach." (Item 17) A non-transitory computer-readable storage medium comprising instructions that, when executed by a processor, cause the processor to: transmitting a first attach request message to a second network, the first attach request message comprising a PDN connectivity request message with a request type set to “handover”; receiving an attach denial message from the second network; Detecting that an ongoing emergency session between the UE and a first network is ongoing; transmitting a second attach request message to the second network in response to detecting the ongoing emergency session, the second attach request message comprising a PDN connectivity request message having a request type set to "handover of emergency bearer services" for the ongoing emergency session; Receiving an attach acknowledgement message A non-transitory computer-readable storage medium for causing (Item 18) Item 18. The non-transitory computer-readable storage medium of item 17, wherein the second attach request message is an emergency attach request message. (Item 19) Item 19. The non-transitory computer-readable storage medium of item 17 or 18, wherein the attach denial message comprises an Evolved Packet System (EPS) Mobility Management (EMM) cause code. (Item 20) 20. The non-transitory computer-readable storage medium of claim 19, wherein the instructions further cause the processor to determine that the EMM cause code indicates an EPS Session Management (ESM) failure. (Item 21) 1. A method in a user equipment (UE) for transferring an ongoing emergency session from a first network to a second network, the method comprising: transmitting a first registration request message to the second network; receiving a registration denial message from the second network; Detecting that an ongoing emergency session between the UE and the first network is ongoing; and transmitting a second registration request message to the second network in response to detecting the ongoing emergency session, the second registration request message comprising an emergency registration request; receiving a registration approval message; A method comprising: (Item 22) 22. The method of claim 21, wherein the first registration request message is a first attach request message and the second registration request message is a second attach request message. (Item 23) 23. The method of claim 22, wherein the second attach request message comprises a connection request message, and the connection request message comprises an emergency handover indication. (Item 24) 24. The method of any one of items 21-23, wherein the registration denial message comprises a cause code. (Item 25) 25. The method of claim 24, wherein prior to transmitting the second registration request message, the method further includes determining that the cause code does not indicate that one of an International Mobile Equipment Identity (IMEI) or a Permanent Equipment Identity (PEI) of the UE is not authorized. (Item 26) 26. The method of claim 25, further comprising: when the UE determines the cause code indicating that one of the IMEI or the PEI of the UE is not authorized, entering one of a state EMM-DERGISTERED.NO-IMSI or a state GMM-DEREGISTERE.NO-SUPI. (Item 27) 27. The method of any one of items 21-26, wherein the first network is a fifth generation (5G) network and the second network is a fourth generation (4G) network. (Item 28) A user equipment (UE), a processor; a memory storing instructions that, when executed by the processor, cause the UE to: transmitting a first registration request message to a second network; receiving a registration denial message from the second network; Detecting that an emergency session between the UE and a first network is ongoing; and transmitting a second registration request message to the second network in response to detecting the emergency session, the second registration request message comprising an emergency registration request; receiving a registration acknowledgment message for the emergency session; memory and A user equipment (UE) comprising: (Item 29) 29. The UE of item 28, wherein the first registration request message is a first attach request message and the second registration request message is a second attach request message. (Item 30) 30. The UE of claim 29, wherein the second attach request message comprises a connection request message, and the connection request message comprises an emergency handover indication. (Item 31) 31. The UE of any one of items 28-30, wherein the registration rejection message comprises a cause code. (Item 32) Item 32. The UE of item 31, wherein the instructions further cause the UE to determine that the cause code does not indicate that one of the UE's International Mobile Equipment Identity (IMEI) or Permanent Equipment Identity (PEI) is not authorized. (Item 33) The instructions further cause the UE to enter one of a state EMM-DERGISTERED.NO-IMSI or a state GMM-DEREGISTERE.NO-SUPI when the UE determines the cause code indicating that one of the IMEI or the PEI of the UE is not authorized. (Item 34) 34. The UE of any one of items 28-33, wherein the first network is a fifth generation (5G) network and the second network is a fourth generation (4G) network. (Item 35) A non-transitory computer-readable storage medium having instructions stored thereon that, when executed by a processor, cause the processor to: transmitting a first registration request message to a second network; receiving a registration denial message from the second network; Detecting that an emergency session between a user equipment (UE) and a first network is ongoing; transmitting a second registration request message to the second network in response to detecting the emergency session, the second registration request message comprising an emergency registration request; receiving a registration acknowledgment message for the emergency session; A non-transitory computer-readable storage medium for causing (Item 36) Item 36. The non-transitory computer-readable storage medium of item 35, wherein the first registration request message is a first attach request message and the second registration request message is a second attach request message. (Item 37) Item 37. The non-transitory computer-readable storage medium of item 36, wherein the second attach request message comprises a connection request message, the connection request message comprising an emergency handover indication. (Item 38) 38. The non-transitory computer-readable storage medium of any one of items 35-37, wherein the registration denial message comprises a cause code. (Item 39) 39. The non-transitory computer-readable storage medium of claim 38, wherein the instructions further cause the processor to determine that the cause code does not indicate that one of an International Mobile Equipment Identity (IMEI) or a Permanent Equipment Identity (PEI) of the UE is not authorized. (Item 40) 40. The non-transitory computer-readable storage medium of claim 39, wherein the instructions further cause the processor to enter one of a state EMM-DERGISTERED.NO-IMSI or a state GMM-DEREGISTERE.NO-SUPI when the UE determines the cause code indicating that one of the IMEI or the PEI of the UE is not authorized. [Brief explanation of the drawings]

[0011] For a more complete understanding of the present disclosure, reference is now made to the following brief description taken in conjunction with the accompanying drawings and detailed description, in which like reference numerals represent like parts.

[0012] [Figure 1] FIG. 1 is a schematic diagram of an embodiment of an architecture for interworking between 5GS and EPC / U-TRAN.

[0013] [Figure 2] Figure 2 is a message flow diagram of an embodiment of preserving emergency calls during handover from 5GC to EPC.

[0014] [Figure 3] FIG. 3 is a message flow diagram of an embodiment of preserving emergency calls during handover from EPC to 5GC.

[0015] [Figure 4]FIG. 4 is a message flow diagram of an embodiment of preserving emergency calls during handover from 5GC to EPC with reduced messaging.

[0016] [Figure 5] FIG. 5 is a message flow diagram of an embodiment of preserving emergency calls during handover from EPC to 5GC with reduced messaging.

[0017] [Figure 6] Figure 6 shows the proposed changes to 3GPP TS24.301 section 5.3.11.

[0018] [Figure 7] Figure 7 shows the proposed changes to 3GPP TS24.301 section 5.3.15.

[0019] [Figure 8] FIG. 8 shows the proposed changes to 3GPP TS24.301 section 5.5.1.2.5A.

[0020] [Figure 9] FIG. 9 shows the proposed changes to 3GPP TS24.301 section 5.5.1.2.5B.

[0021] [Figure 10] FIG. 10 shows the proposed changes to 3GPP TS24.301 section 5.5.1.2.5B1.

[0022] [Figure 11A] 11A and 11B are proposed changes to 3GPP TS24.301 section 5.5.1.2.6. [Figure 11B] 11A and 11B are proposed changes to 3GPP TS24.301 section 5.5.1.2.6.

[0023] [Figure 12]FIG. 12 shows the proposed changes to 3GPP TS24.501 section 5.5.1.2.6.

[0024] [Figure 13] FIG. 13 shows the proposed changes to 3GPP TS24.501 section 5.5.1.2.6A.

[0025] [Figure 14A] 14A, 14B, and 14C are proposed changes to 3GPP TS24.501 section 5.5.1.2.7. [Figure 14B] 14A, 14B, and 14C are proposed changes to 3GPP TS24.501 section 5.5.1.2.7. [Figure 14C] 14A, 14B, and 14C are proposed changes to 3GPP TS24.501 section 5.5.1.2.7.

[0026] [Figure 15] FIG. 15 is a schematic diagram of an embodiment of a network element.

[0027] [Figure 16] FIG. 16 is a schematic diagram of an embodiment of a communication device.

[0028] [Figure 17] FIG. 17 is a schematic diagram of an embodiment of a system suitable for implementing one or more embodiments disclosed herein. DETAILED DESCRIPTION OF THE INVENTION

[0029] explanation 1 is a schematic diagram of an embodiment of an architecture 100 for interworking between 5G and EPC. The N26 interface is a core-to-core network (CN) interface between the MME and the 5G system (5GS) AMF to enable interworking between the EPC and the 5G core. Support for the N26 interface within the network is optional for interworking.

[0030] The Core PDN Gateway (PGW-C) + SMF and User Plane Function (UPF) + PDN Gateway User Plane (PGW-U) is dedicated for interworking between 5GS and EPC, which is optional and based on UE Mobility Management (MM) core network capabilities and UE subscription. UEs that do not undergo 5GS and EPC interworking may be served by entities not dedicated for interworking, i.e., either the PGW or the SMF / UPF.

[0031] There may also be another UPF (not shown) between the NG Radio Access Network (NG-RAN) and the UPF+PGW-U, i.e., the UPF+PGW-U may support an N9 interface towards an additional UPF if needed. The figures and procedures herein depicting a Serving Gateway (SGW) make no assumptions regarding whether the SGW is deployed as a monolithic SGW or as a Serving Gateway (SGW) that is split into its control plane and user plane functionality.

[0032] Unless the UE is dual-registered (e.g., registered in a 5G network and attached to a 4G network), the UE cannot be in connected mode in 5GS and EPS simultaneously. For this reason, the N26 interface may be used to provide interworking between 5GS and EPS and enable handover between the networks.

[0033] An emergency call in a limited service state occurs, for example, when the UE does not have sufficient credentials to access the network (e.g., the UE may not need a subscription with the network to request an emergency call). The network can also change the emergency call to a limited service state emergency call when the UE hands over to a cell that the UE would not otherwise be allowed to access. When the network changes an emergency call by a UE to an emergency call by a limited service state UE, the UE is in connected mode. In the limited service state, subscription-based services are not or will no longer be allowed. Subscription-based services generally include common services such as short message service (SMS), non-emergency voice calls, access to the Internet, etc.

[0034] When a UE performs an emergency attach procedure with the EPC (i.e., the attach procedure results in the transmission of an attach request message for emergency bearer services only), the UE cannot obtain non-emergency services while so attached. The UE is in a limited service state. When a UE performs a (non-emergency) attach procedure with the EPC (i.e., the attach procedure results in the transmission of an attach request message or an attach request message for EPS services only), the UE can use non-emergency services (assuming the attach request is approved by the network). In either case, the transmitted attach request message may include a PDN connection request for the emergency bearer service.

[0035] When a UE performs an emergency registration procedure with 5GC (i.e., the registration procedure results in the transmission of a registration request message for emergency services only), the UE cannot use non-emergency services while so registered. The UE is in a limited service state. When a UE performs a (non-emergency) registration procedure with 5GC (i.e., the registration procedure results in the transmission of a registration request message), the UE can obtain non-emergency services (assuming the registration request is approved by the network). In either case, the UE can send a PDU session request to establish a PDU session for emergency services following the sending of the registration request message or following the registration request being approved by the network.

[0036] There are many reasons why an attach or registration request sent by a UE may be rejected by the network. For example, the request may be rejected due to a network failure, network overload, a UE subscription limit, or a user subscription limit. Other examples also exist.

[0037] 5GS supports interworking with EPS either via the N26 interface (between AMF and MME) or without the N26 interface (i.e., via cooperation or co-location between the PDG and the SMF or UPF). The issues discussed herein relate to networks that support interworking without the N26 and UEs operating in single registration mode.

[0038] UEs that are in dual registration mode but are not yet concurrently registered in other systems are also affected by the issues discussed herein.

[0039] A UE that is in dual registration mode and is concurrently registered in another system is affected by a subset of the problems discussed herein.

[0040] When registered in a 5GC via a cell of a 5G access network, and possibly having an emergency PDU session among other, e.g., non-emergency, PDU sessions, the UE may determine that a cell of a 4G access network is or has become more desirable. The UE may need to transfer ongoing connectivity provided by some or all of the PDU sessions to an EPC serving the cell of the 4G access network, for example, while the UE is in idle mode with the EPC.

[0041] To transfer the ongoing connectivity provided by the emergency PDU session from the 5GC to the EPC, the UE performs an attach procedure and preferably includes a PDN connection request message in the attach message, representing the connectivity provided by the emergency PDU session. However, some UEs may also include a PDN connection request message in the attach message, representing the connectivity provided by a non-emergency PDU session. In the latter case, the UE will need to transfer the connectivity provided by the emergency PDU session in a subsequent independent transmission PDN connection request message. The UE may then attempt to transfer further (non-emergency) PDU sessions.

[0042] In 4G networks, for various reasons, such as network congestion or other resource unavailability, the MME or EPC may be unable to approve an attach request. In some current approaches, if the attach request is denied, the ongoing emergency call cannot be forwarded to the network using the connectivity provided by the emergency PDU session. As a result, the ongoing emergency call may be undesirably or prematurely terminated. This may put the user of the UE whose emergency call was terminated at risk.

[0043] When attached in the EPC via a cell of a 4G access network, and possibly having emergency bearer services among other PDN connections for, e.g., non-emergency PDN connections, the UE may determine that a cell of a 5G access network is or has become more desirable. The UE may need to transfer ongoing connectivity provided by some or all of the PDN connections to a 5GC serving cell of the 5G access network, for example, while the UE is in idle mode with the 5GC.

[0044] To transfer the ongoing connectivity provided by the PDN connection for the emergency bearer service from the EPC to the 5GC, the UE performs a registration procedure and then transmits a PDU session request message representing the connectivity provided by the PDN connection for the emergency bearer service. The UE may also attempt to transfer the connectivity provided by one or more (non-emergency) PDN connections.

[0045] In 5G networks, for various reasons, such as network congestion or other resource unavailability, the AMF or 5GC may be unable to approve a registration request. In some current approaches, if the registration request is denied, the ongoing emergency call cannot be forwarded to the network using the connectivity provided by the PDN connection for the emergency bearer service. As a result, the ongoing emergency call may be undesirably or prematurely terminated. This may put the user of the UE whose emergency call was terminated at risk.

[0046] Current procedures for transferring an ongoing emergency call from 5G to EPC or from EPC to 5GC inadequately consider failure scenarios. While solutions exist for handling failure scenarios in the case of a "fallback" from one system to another, i.e., prior to establishing the emergency call, solutions for preventing unexpected and undesired termination of an ongoing emergency call during transfer from one system to another have not been considered. A more novel aspect of this problem space is the scenario in which a UE desires to transfer connectivity (including emergency connectivity) from 5GC to EPC, but the UE omits including a request for emergency connectivity in the attach request sent to the EPC.

[0047] In a first embodiment, when a UE has one or more PDU sessions to transfer from 5GC to EPS, the UE performs an attach procedure with a first network including an EPC, and the network may reject an attach request message (i.e., a first attach request message) sent by the UE due to the attach procedure. Due to the network rejecting the attach, the UE may receive an attach denial message. The network transmits the attach denial message and includes an EPS mobility management (EMM) cause value in the attach denial message. When the UE determines or detects that one or more PDU sessions include an emergency PDU session, or when the UE receives the attach denial message, or depending on the (EMM) cause value in the attach denial message, the UE performs an attach for an emergency bearer service with a second network. The attach request sent by the UE due to the attach for the emergency bearer service includes a PDN connectivity request message (i.e., a first PDN connectivity request message) requesting to activate a default bearer corresponding to a default EPS bearer context for the emergency PDU session, where the request type of the PDN connectivity request is set to "handover of emergency bearer service." The network may acknowledge the attach request sent by the UE due to the attach for the emergency bearer service and the included request to activate a default bearer corresponding to the default EPS bearer context for the emergency PDU session. Optionally, the attach request sent by the UE due to the attach procedure may also include a PDN connectivity request message, which may have the request type set to "handover of emergency bearer service." The first and second networks are each part of a public land mobile network (PLMN). The second PLMN can be either the first PLMN or a PLMN that is considered an equivalent of the first PLMN, or the second PLMN is not the first PLMN or is not considered an equivalent.A PLMN is equivalent when its PLMN identity is present in the equivalent PLMN list. A UE may be configured with the equivalent PLMN list.

[0048] A PLMN may, for example, comprise a 5GC+ access network, or an EPC+ access network, or a 5GC+ access network and an EPC+ access network. A PLMN operator operates one or more core networks+access networks.

[0049] In a first extension of the first embodiment, performing an attach for emergency bearer services with the second network is conditioned on the UE's lower layers or the UE's access stratum (AS) layer indicating to the NAS (or the UE's NAS layer) that the network supports emergency bearer services in a limited service state. Alternatively, performing an attach procedure with the network, including the EPC, is conditioned on the UE's lower layers or the UE's AS layer indicating to the NAS (or the UE's NAS layer) that the first network supports emergency bearer services in a limited service state.

[0050] In a second extension of the first embodiment, the UE performs an attach for emergency bearer services with the second network if the EMM cause value in the attach denial message from the first network is different from one or more predetermined EMM cause values. The one or more predetermined EMM cause values ​​include, for example, #5 "IMEI not authorized." If the EMM cause value is not different from the one or more predetermined EMM cause values, the UE performs one of the following: 1) enters state EMM-DEREGISTERED.NO-IMSI; or 2) attempts to attach on a second network (the second network is different from the first network from which the EMM cause value was received). The first and second networks are each part of a public land mobile network (PLMN). The second PLMN can be either the first PLMN or a PLMN considered equivalent to the first PLMN, or the second PLMN is not the first PLMN or considered equivalent. A PLMN is equivalent when its PLMN identity is present in an equivalent PLMN list. The UE may be configured with the equivalent PLMN list. The first network may set the EMM cause value to one of one or more predetermined EMM cause values ​​when an attach request sent by the UE due to the attach procedure includes a first PDN connectivity request.

[0051] In a third extension of the first embodiment, in a shared network, a UE may attempt to register with one of a plurality of PLMNs of the shared network. In the shared network, when the UE receives the attach rejection message, prior to performing the attach for the emergency bearer service, the UE performs an attach procedure with another PLMN including an EPC, where the other PLMN is one of the plurality of PLMNs of the shared network. The other PLMN may be an equivalent of the PLMN from which the EMM cause value was received.

[0052] In a fourth extension of the first embodiment, the UE shall not request the use of power saving mode (PSM) or cellular internet of things (CIoT) optimization when performing an attach procedure with the network including the EPC. The use of PSM or CIoT optimization may adversely affect emergency calls. This adverse effect may put the user of the UE at risk. The UE shall not request the use of PSM or CIoT optimization when performing an attach procedure with the network including the EPC and the UE detects that one or more PDU sessions include an emergency PDU session. The UE shall not request the use of PSM or CIoT optimization when performing an attach procedure with the network including the EPC and the attach request sent by the UE due to the attach procedure includes a PDN connectivity request message.

[0053] In a fifth enhancement of the first embodiment, the UE detects that it receives an EMM cause code set to #19, indicating an EPS Session Management (ESM) failure. The ESM failure indicates that the network detected a failure when inspecting or handling the PDN Connectivity Request message included in the first Attach Request message. Based on the detection, instead of first performing an attach for emergency bearer services with the second network (as described in the first embodiment), the UE performs another attach procedure with the network, including the EPC. The network, including the EPC, may be an equivalent of the first network. The UE transmits an Attach Request message due to the another attach procedure, where the Attach Request message includes the first PDN Connectivity Request message.

[0054] If the alternative attach procedure fails, the UE may perform and continue attach for emergency bearer services with the second network as described in the first embodiment.

[0055] 2 is a message flow diagram 200 of an embodiment for preserving an emergency call during a handover from a 5GC to an EPC. During an ongoing emergency PDU session 220 between the UE 205 and the 5GC 210, the UE 205 may decide to handover to the EPC 215. The UE 205 sends an attach message to the EPC 215 in step 230 and receives an attach denial message from the EPC 215 in step 240. The attach may be denied for various reasons, for example, the EPC 215 may be overloaded. In response to the attach denial, the UE 205 may determine or detect that an ongoing emergency call exists. In response to the determination of the ongoing emergency call, the UE 205 may submit a second attach message in step 250 indicating that the emergency session needs to be transferred. The EPC 215 may then reply with a response indicating that the second attach is acceptable or unacceptable in step 260 (the figure does not indicate that the second attach is unacceptable). The second attach may include a PDN connection request from the UE 205 to the EPC 215 to transfer the emergency session. In response to receipt of the activate default EPS bearer context request message by the UE 205, the transfer of the emergency session for the ongoing emergency call is successful. Optionally, in step 270, if the second attach is unacceptable, the UE 205 may transmit an emergency attach including a request to transfer the connectivity provided by the ongoing emergency PDU session. If the response 260 is received, another optional transmission in step 280 may be a PDN connection request from the UE 205 to the EPC 215 to transfer the emergency session. The second attach message may be an emergency attach message.

[0056] In a second embodiment, when a UE has one or more PDN connections for transferring from EPS to 5GS, the UE performs an (initial) registration procedure with a first network including 5GC, and the 5GC network may reject a registration request sent by the UE due to the registration procedure. The 5GC network sends a registration rejection message to the UE. The 5GC network includes a 5GMM cause value in the registration rejection message. The UE receives the registration rejection message. If the UE determines that one or more PDN connections include a PDN connection for an emergency bearer service and the UE receives the registration rejection message, the UE performs registration for emergency services with a second network. The UE sends a registration request message for emergency services to the second network. If the second network accepts the registration request message for emergency services, the second network sends a registration accept message to the UE. When the UE receives the registration accept message, the UE transfers the PDN connection for the emergency bearer service by sending a PDU session request message with the request type set to "existing emergency PDU session." When the UE sends the registration request, the UE includes a continuation request indicator set to "pending continuation request" in the registration request. The first and second networks are each part of a PLMN. The second PLMN can be either the first PLMN or a PLMN considered equivalent to the first PLMN, or the second PLMN is not the first PLMN or considered equivalent. A PLMN is equivalent when its PLMN identity is present in an equivalent PLMN list. The UE may be configured with an equivalent PLMN list.

[0057] The PLMN may, for example, comprise a 5GC+ access network, or an EPC+ access network, or a 5GC+ access network and an EPC+ access network. A PLMN operator operates one or more core networks+access networks. In a first extension of the second embodiment, performing registration for emergency services with the second network is conditioned on the UE's lower layer or the UE's AS layer indicating to the NAS (or the UE's NAS layer) that the network supports emergency bearer services in a limited service state. Alternatively, performing a registration procedure with the network including 5GC is conditioned on the UE's lower layer or the UE's AS layer indicating to the NAS (or the UE's NAS layer) that the first network supports emergency bearer services in a limited service state if the one or more PDN connections include a PDN connection for emergency bearer services.

[0058] In a second extension of the second embodiment, the UE performs registration for emergency services with the second network if the 5GMM cause value differs from one or more predetermined 5GMM cause values. The one or more predetermined 5GMM cause values ​​include, for example, #5 "PEI not approved." If the 5GMM cause value does not differ from the one or more predetermined 5GMM cause values, the UE performs one of the following: 1) enters state 5GMM-DEREGISTERED.NO-SUPI; or 2) attempts registration on a third network (the third network is different from the first network from which the 5GMM cause value was received). The first and third networks are each part of a public land mobile network (PLMN). The third PLMN can be a PLMN considered equivalent to the first PLMN. A PLMN is equivalent when its PLMN identity is present in an equivalent PLMN list. The UE may be configured with the equivalent PLMN list. The network may set the 5GMM cause value to one of one or more predefined 5GMM cause values ​​if the registration request sent by the UE due to the registration procedure includes an indication that the UE needs to transfer an emergency session. The UE may indicate that it needs to transfer an emergency session by using the 5GS registration type to indicate that the registration request is for a transfer of an emergency session.

[0059] In a third extension of the second embodiment, in a shared network, a UE may attempt to register with one of a plurality of PLMNs of the shared network. In the shared network, when the UE receives a registration rejection message, prior to performing registration for the emergency bearer service, the UE performs a registration procedure with a fourth PLMN including 5GC, the fourth PLMN being one of the plurality of PLMNs of the shared network. The fourth PLMN may be an equivalent of the PLMN from which any of the 5GMM cause values ​​was received or from which the registration rejection message was received.

[0060] In a fourth extension of the second embodiment, the UE shall not request the use of PSM or the use of CIoT optimization when performing a registration procedure with the network including 5GC. The UE shall not request the use of PSM or the use of CIoT optimization when performing a registration procedure with the network including 5GC and the UE detects that one or more PDU sessions include an emergency PDU session. The UE shall not request the use of PSM or the use of CIoT optimization when performing a registration procedure with the network including 5GC and the registration request sent by the UE due to the registration procedure includes an indication that the UE needs to transfer the emergency session.

[0061] 3 is a message flow diagram 300 of an embodiment for preserving an emergency call during a handover from an EPC to a 5GC. During an ongoing PDN connection 320 for an emergency bearer service between the UE 305 and the EPC 310, the UE 305 may decide to handover to the 5GC 315. The UE 305 sends a registration message to the 5GC 315 in step 330 and receives a registration denial message from the 5GC 315 in step 340. The attach may be denied for various reasons, for example, the 5GC 315 may be overloaded. In response to the registration denial, the UE 305 may determine in step 350 that an ongoing emergency call exists and submit a second registration message due to the need to transfer the emergency session. The 5GC 315 may then reply in step 360 with a response (to the second registration message) indicating that the registration is acceptable or unacceptable (the figure does not indicate that the second registration is unacceptable). Following receiving a response (to the second registration message) indicating that the registration is acceptable, the UE 305 transmits a PDU session establishment request to transfer the emergency session from the UE 305 to the 5GC 315 in step 380. The PDU session establishment request may include an indication that the emergency session is an existing emergency session. The indication may indicate that the existing emergency session should be transferred. Optionally, in step 370, the UE may send an emergency registration if the second registration is unacceptable. In step 380, the UE transfers the emergency session if either the second registration is unacceptable (360) or the emergency registration (370) is acceptable.

[0062] In a third embodiment, when a UE has one or more PDU sessions to transfer from 5GC to EPS, and the one or more PDU sessions include an emergency PDU session, the UE performs an attach procedure with a network including an EPC, and the network may approve an attach request message sent by the UE due to the attach procedure. Due to the network approving the attach, the UE may receive an attach approve message. The network may send the attach approve message and include an indication that the attach is approved only for emergency services. Because the UE receives the indication that the attach is approved only for emergency services, the UE does not transfer non-emergency PDU sessions. If a PDN connectivity request message requesting activation of a default bearer corresponding to a default EPS bearer context for the emergency PDU session is not included in the attach request message sent by the UE, or a different PDN connectivity request message is included in the attach request message sent by the UE, the UE may transmit an independent PDN connectivity request message requesting activation of a default bearer corresponding to a default EPS bearer context for the emergency PDU session. The independent PDN connectivity request message is sent following receiving an indication that the attach is authorized only for emergency services.

[0063] In a first extension of the third embodiment, the PDN connectivity request message can be included in the attach request sent by the UE. Alternatively, the UE may include a different indication in the attach request to indicate that the UE intends to transfer the emergency PDU session (following sending the attach request). The UE may transfer the emergency PDU session following sending the attach request. The emergency PDU session will be transferred by using a PDN connectivity request message whose request type is set to "emergency bearer service handover". This PDN connectivity request message will be sent independently. The network determines whether to include an indication that the attach is authorized only for emergency services in the attach accept message, for example, based on receiving an indication indicating that the UE intends to transfer the emergency PDU session following sending the attach request.

[0064] 4 is a message flow diagram 400 of an embodiment for preserving an emergency call during a handover from a 5GC to an EPC with reduced messaging. During an ongoing emergency PDU session 420 between a UE 405 and a 5GC 410, the UE 405 may decide to hand over to an EPC 415. The UE 405 may send an attach message to the EPC 415 indicating that the emergency session needs to be transferred in step 430. The EPC 415 may send a response indicating an attach accept for the emergency session in step 440. Optionally, in response to the attach accept for the emergency session, the UE 405 may transmit a PDN connection request to the EPC 415 to transfer the emergency session in step 450.

[0065] In a fourth embodiment, when a UE has one or more PDN connection sessions for transfer from EPS to 5GS, and the one or more PDN connection sessions include a PDN connection session for an emergency bearer service, the UE performs a registration procedure with the network including 5GS, and the network may approve a registration message sent by the UE due to the registration procedure. Due to the network approving the registration, the UE may receive a registration approval message. The network may send the registration approval message and include an indication that the registration is approved only for emergency services. Because the UE receives the indication that the registration is approved only for emergency services, the UE does not transfer non-emergency PDN connections. A PDU session establishment request message corresponding to a default EPS bearer context of the PDN connection for the emergency bearer service is sent following receiving the indication that the registration is approved only for emergency services.

[0066] In a first extension of the fourth embodiment, the UE may include, in the registration request, an indication indicating that the UE intends to transfer the PDN connection for the emergency bearer service. The UE transfers the PDN connection for the emergency bearer service following sending the registration request. The PDN connection for the emergency bearer service is to be transferred by using a PDU Session Establishment Request message in which the request type is set to "existing emergency PDU session." The network determines whether to include an indication that the registration is approved only for emergency services in the registration accept message, for example, based on receiving the indication indicating that the UE intends to transfer the PDN connection for the emergency bearer service.

[0067] 5 is a message flow diagram 500 with reduced messaging of an embodiment that preserves an emergency call during a handover from an EPC to a 5GC. During an ongoing PDN connection 520 for emergency bearer services between the UE 505 and the EPC 510, the UE 505 may decide to handover to a 5GC 515. The UE 505 may send a registration message indicating that the emergency session needs to be transferred in step 530. The 5GC 515 may then reply with a response indicating that registration is acceptable for the emergency session in step 540. In step 550, in response to the registration approval for the emergency session, the UE 505 may transmit a PDU session establishment request to the 5GC 515 to transfer the emergency session.

[0068] In a fifth embodiment, preserving an emergency call during a handover from 5GC to EPC with reduced messaging is achieved as follows: During an ongoing emergency PDU session between the UE and 5GC, the UE may decide to handover to the EPC. The UE may have one or more additional PDU sessions to transfer from 5GC to EPS. The UE may send an emergency attach message to the EPC indicating the emergency session to be transferred. The EPC may send a response indicating an attach approval. The EPC may indicate in the message that the attach is also approved for non-emergency use. The EPC may decide to indicate that the attach is approved for non-emergency use based on a received indication that the emergency session should be transferred. Optionally, the UE may proceed with and transfer any of the one or more additional PDU sessions due to receiving a message indicating that the attach is approved for non-emergency use.

[0069] In a sixth embodiment, preserving an emergency call during a handover from an EPC to a 5GC with reduced messaging is achieved as follows: During ongoing use of a PDN connection for an emergency bearer service between the UE and the 5GC, the UE may decide to handover to the 5GC. The UE may have one or more additional PDN connection sessions to transfer from the EPS to the 5GC. The UE may send an emergency registration message. The 5GC may send a response indicating registration approval. The 5GC may indicate in the message that the registration is also approved for non-emergency use. Based on receiving a message at the UE indicating that the registration is also approved for non-emergency use, the UE may proceed and transfer any of the one or more additional PDN connection sessions in addition to transferring the PDN connection for the emergency bearer service.

[0070] In an extension of the sixth embodiment, preserving the emergency call during handover from EPC to 5GC with reduced messaging is achieved as follows: The UE may indicate in the emergency registration message that an existing emergency session should be transferred or that an emergency session exists. The 5GC may decide to indicate that registration is also approved for non-emergency use based on a received indication that an existing emergency session should be transferred or that an emergency session exists.

[0071] In the seventh embodiment, when a UE performs an attach procedure with a network including an EPC, the UE shall not request the use of PSM or CIoT optimization due to the transfer of certain types of PDU sessions among one or more PDU sessions to the EPC. The use of PSM or CIoT optimization may have an adverse effect on emergency calls. This adverse effect may put the user of the UE at risk. In particular, when a UE performs an attach procedure with a network including an EPC and the UE detects that one or more PDU sessions include an emergency PDU session, the UE shall not request the use of PSM or CIoT optimization. When a UE performs an attach procedure with a network including an EPC and an attach request sent by the UE due to the attach procedure is intended to be followed by a first PDN connectivity request message, the UE shall not request the use of PSM or CIoT optimization. That is, the first PDN connectivity request message shall be sent independently. That is, the attach message does not include a PDN connectivity request message, with the request type set to "handover of emergency bearer services."

[0072] In an eighth embodiment, preserving the emergency call during handover from the source core network to the target core network includes checking, by the UE, whether the target network supports handover of an existing emergency session. The target core network may comprise one of EPC or 5GC. Checking whether the target network supports handover includes, if the target core network is EPC, sending an indication that the UE supports a request type flag "handover" for the PDN connectivity request during an attach procedure. Checking whether the target network supports handover includes, if the target core network is 5GC, checking during registration and registration update. If the UE determines that the target core network does not support handover, the UE selects another PLMN (the other PLMN is an equivalent PLMN), or the UE attempts to transfer the emergency call to another Internet Protocol-Connectivity Access Network (IP-CAN). An IP-CAN is an access network that provides IP connectivity. Alternatively, the UE may attempt to forward the emergency call to the circuit-switched domain.

[0073] A UE in dual registration mode, attached or registered to both EPC and 5GS in parallel, and detecting or establishing an active emergency session in one of the two systems updates its registration information in the other of the two systems. The UE updates its registration information in the other of the two systems in anticipation of a potential transfer of the active emergency session to the other of the two systems. Updating the registration information includes disabling the use of PSM or disabling the use of CIoT optimization. Updating the registration information includes performing one of a registration update or a tracking area update, depending on whether the other system is EPS or 5GS. Performing one of the registration update or the tracking area update includes sending a NAS message to the core network. Performing the registration update includes sending a registration request message to the 5GC. Performing the tracking area update includes sending a tracking area update request message to the EPC.

[0074] Some of the embodiments described above may be combined depending on the network and / or UE. Furthermore, certain steps may be omitted from the embodiments if they are not required for handing over emergency calls.

[0075] 6 is a proposed change 600 to 3GPP TS 24.301 Section 5.3.11. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0076] The UE may request the use of power saving mode (PSM) during an attach or tracking area update procedure. The UE shall not request the use of PSM during:

[0077] - Attach procedures for emergency bearer services, or

[0078] -Attach type not set to "EPS Emergency Attach", Attach procedure

[0079] a) to initiate a PDN connection for emergency bearer services, or

[0080] b) for transmitting a PDN connectivity request message with the request type set to "handover" when the UE intends to transmit an independent PDN connectivity request message with the request type set to "handover of emergency bearer services";

[0081] - Tracking Area Update procedure for initiating PDN connection for emergency bearer services;

[0082] a tracking area update procedure when the UE has an established PDN connection for emergency bearer services, or

[0083] -Attach for access to the RLOS.

[0084] 7 is a proposed change 700 to 3GPP TS 24.301 Section 5.3.15. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0085] In NB-S1 mode, when the UE requests the use of CIoT EPS optimization,

[0086] - not requesting an attach procedure for emergency bearer services,

[0087] -Attach type is not set to "EPS Emergency Attach", no attach procedure is required,

[0088] a) to initiate a PDN connection for emergency bearer services, or

[0089] b) for transmitting a PDN connectivity request message with the request type set to "handover" when the UE intends to transmit an independent PDN connectivity request message with the request type set to "handover of emergency bearer services";

[0090] - not indicating a voice domain preference and usage setting for the UE, or

[0091] -Does not require attachment for access to the RLOS.

[0092] 8 is a proposed change 800 to 3GPP TS 24.301 Section 5.5.1.2.5A. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0093] If the attach request for the emergency bearer service fails or is denied due to receiving an attach denial, the UE proceeds to inform upper layers of the failure to access the network.

[0094] NOTE: Informing higher layers may result in higher layers requesting the establishment of a CS emergency call (if not already attempted within the CS domain), forwarding to a non-3GPP access, or other implementation-specific mechanisms. For example, the procedures specified in 3GPP TS 24.229 may result in the emergency call being attempted or forwarded to another IP-CAN...

[0095] In a shared network, upon receiving an Attach Reject message, the UE shall perform the actions described in clause 5.5.1.2.5;

[0096] a) Inform a higher layer of the failure of the procedure, or

[0097] b) To another PLMN in the shared network, if the Attach Request message does not include a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", or if the Attach Request message includes a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", and the other PLMN is an equivalent PLMN, then an attach for emergency bearer services shall be attempted.

[0098] In a shared network, if an attach request for an emergency bearer service fails due to abnormal case a) in subclause 5.5.1.2.6, the UE shall perform the actions as described in subclause 5.5.1.2.6;

[0099] a) Inform higher layers of the failure to access the network, or

[0100] b) To another PLMN in the shared network, if the Attach Request message does not include a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", or if the Attach Request message includes a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", and the other PLMN is an equivalent PLMN, then an attach for emergency bearer services shall be attempted.

[0101] In a shared network, if an attach request for an emergency bearer service fails due to abnormal cases b), c), or d) in subclause 5.5.1.2.6, the UE shall perform the actions as described in subclause 5.5.1.2.6;

[0102] a) Inform a higher layer of the failure of the procedure, or

[0103] b) To another PLMN in the shared network, if the Attach Request message does not include a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", or if the Attach Request message includes a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services", and the other PLMN is an equivalent PLMN, then an attach for emergency bearer services shall be attempted.

[0104] 9 is a proposed change 900 to 3GPP TS 24.301 Section 5.5.1.2.5B. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0105] If the network is unable to approve the attach request, including a PDN Connectivity Request message with the request type set to "emergency" and the attach type not set to "EPS Emergency Attach", the UE shall perform the procedure as described in clause 5.5.1.2.5. Then, if the UE is within the same selected PLMN where the last attach request was attempted, the UE shall:

[0106] a) Inform a higher layer of the failure of the procedure, or

[0107] b) An EPS attach for emergency bearer services shall be attempted, including a PDN Connectivity Request message.

[0108] If the network is unable to approve the attach request containing a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Services" and the attach type not set to "EPS Emergency Attach", the UE shall perform the procedure as described in clause 5.5.1.2.5. The UE shall then attempt an EPS attach for the emergency bearer service containing the PDN Connectivity Request message if the UE is within the same selected PLMN or equivalent PLMN where the last attach request was attempted.

[0109] If an attach request to initiate a PDN connection for an emergency bearer service, where the attach type is not set to "EPS Emergency Attach", fails due to abnormal case a) in subclause 5.5.1.2.6, the UE shall perform the actions as described in subclause 5.5.1.2.6 and inform higher layers of the failure to access the network.

[0110] If an attach request containing a PDN Connectivity Request message with the request type set to "emergency" and the attach type not set to "EPS Emergency Attach" fails due to abnormal cases b), c), or d) in clause 5.5.1.2.6, the UE shall perform the procedure as described in clause 5.5.1.2.6. Then, if the UE is within the same selected PLMN where the last attach request was attempted, the UE shall:

[0111] a) Inform a higher layer of the failure of the procedure, or

[0112] b) An EPS attach for emergency bearer services shall be attempted, including a PDN Connectivity Request message.

[0113] If an attach request to initiate a PDN connection for an emergency bearer service, where the attach type is not set to "EPS Emergency Attach", fails due to abnormal cases b), c), d), or o) in subclause 5.5.1.2.6, the UE shall perform the procedure as described in subclause 5.5.1.2.6. If the UE is then within the same selected PLMN or equivalent PLMN where the last attach request was attempted, the UE shall attempt an EPS attach for the emergency bearer service containing a PDN Connectivity Request message.

[0114] 10 is a proposed change 1000 to 3GPP TS 24.301 Section 5.5.1.2.5B1. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed change may enable various embodiments of preserving emergency calls described herein.

[0115] If the network is unable to approve the attach request, including a PDN Connectivity Request message with the request type set to "handover", and the UE also intends to transfer the emergency PDU session, the UE shall attempt an EPS attach for the emergency bearer service, including a PDN Connectivity Request message with the request type set to "handover of emergency bearer service" for the emergency PDU session.

[0116] If an Attach Request containing a PDN Connectivity Request message with the Request Type set to "Handover" fails due to abnormal case a) in clause 5.5.1.2.6 and the UE intends to transfer the Emergency PDU Session, the UE shall attempt an EPS Attach containing a PDN Connectivity Request message with the Request Type set to "Handover of Emergency Bearer Service" for the Emergency PDU Session.

[0117] When an Attach Request, including a PDN Connectivity Request message with the Request Type set to "Handover", fails due to abnormal cases b), c), d), or o) in clause 5.5.1.2.6, and the UE intends to transfer an Emergency PDU Session,

[0118] #19 If an EMM cause set to "ESM failure" is received, the UE shall attempt an EPS attach using an Attach Request message, including a PDN Connectivity Request message, the request type of which is set to "Handover of Emergency Bearer Service" for the emergency PDU session;

[0119] Otherwise, the UE shall attempt an EPS attach for the emergency bearer service using an Attach Request message containing a PDN Connectivity Request message with the request type set to "Handover of Emergency Bearer Service" for the emergency PDU session.

[0120] 11A and 11B are proposed changes 1100 to 3GPP TS 24.301 section 5.5.1.2.6. Proposed deletions are indicated by strikethrough text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0121] The following unusual cases can be identified:

[0122] a) Access denied by the network without an "extended wait time" received from a lower layer, Access Class Restricted EAB, ACDC, or NAS signaling restricted for connection establishment.

[0123] In WB-S1 mode, if access is barred for "originating signaling", the attach procedure shall not be initiated. The UE shall remain in the current serving cell and apply the normal cell reselection process. The attach procedure shall be initiated as soon as possible, i.e., when access for "originating signaling" is allowed on the current cell, or when the UE moves to a cell where access for "originating signaling" is allowed...

[0124] b) A lower layer failure or release of the NAS signaling connection without an "extended wait time" being received from the lower layer and without "extended wait time CP data" before the Attach Accept or Attach Reject message is received.

[0125] The attach procedure shall be aborted and the UE shall proceed as described below.

[0126] c) T3410 timeout.

[0127] The UE shall abort the attach procedure and proceed as described below: The NAS signalling connection (if applicable) shall be released locally.

[0128] d) Attach Denial, any other EMM cause value other than those covered in Section 5.5.1.2.5, and EMM cause values ​​#22, #25, and #31 for cases that are considered abnormal cases according to Section 5.5.1.2.5.

[0129] In response to receiving EMM cause #19 "ESM failure", if the UE is not configured for NAS signaling low priority and the ESM cause value received in the PDN connectivity denial message is not #54 "PDN connection does not exist", the UE may set the attach attempt counter to 5. If the UE subsequently needs to retransmit the attach request message to request PDN connectivity towards a different APN, the UE may stop T3411 or T3402 if awake and send an attach request message. If the UE needs to attempt an EPS attach to request a transfer of a PDN connection for an emergency bearer service by including a PDN connectivity request message with the request type set to "handover of emergency bearer service", the UE shall stop T3411 or T3402 if awake and send an attach request message.

[0130] NOTE 3. When receiving EMM cause #19 "ESM failed", coordination is required between the EMM and ESM sublayers in the UE to determine whether the attach attempt counter should be set to 5.

[0131] If the attach request is not for an emergency bearer service or the attach type is not set to "EPS Emergency Attach", and the attach request is not for initiating a PDN connection for an emergency bearer service, then in response to receiving EMM causes #95, #96, #97, #99, and #111, the UE should set the attach attempt counter to 5.

[0132] The UE shall proceed as described below...

[0133] o) Timer T3447 is running.

[0134] The UE shall not initiate the attach procedure unless:

[0135] The UE is configured to use AC11-15 in a selected PLMN;

[0136] The UE attempts to attach for an emergency bearer service, or

[0137] The UE attempts to attach without a PDN connection request.

[0138] The UE remains in the current serving cell and applies the normal cell reselection process. An attach request procedure, if still necessary, is initiated upon expiry of timer T3447.

[0139] For cases b, c, d, l, la, and m, timer T3410 shall be stopped if it is still running. For cases b, c, d, l when "Extended Waiting Time" is ignored, and la when "Extended Waiting Time CP Data" is ignored, if the attach request is not for an emergency bearer service or the attach type is not set to "EPS Emergency Attach", and is not for initiating a PDN connection for an emergency bearer service, the attach attempt counter shall be incremented unless it is already set to 5.

[0140] If the attach attempt counter is less than 5...

[0141] In the cases of b, c, d, l when "Extended Waiting Time" is ignored and la when "Extended Waiting Time CP Data" is ignored, if the attach request is not for an emergency bearer service or the attach type is not set to "EPS Emergency Attach" and is not for initiating a PDN connection for an emergency bearer service, timer T3411 is started and the state is changed to EMM-DEREGISTERED.ATTEMPTING-TO-ATTACH. When timer T3411 expires, the attach procedure shall be restarted if still requested by the ESM sub-layer.

[0142] 12 is another proposed change 1200 to 3GPP TS 24.501 section 5.5.1.2.6. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed change may enable various embodiments of preserving emergency calls described herein.

[0143] In response to receiving a Registration Reject message or a failed registration request, the UE shall perform the actions as described in clause 5.5.1.2.5, with the following additions:

[0144] The UE shall inform higher layers of the failure of the procedure.

[0145] NOTE: This may result in higher layers requesting transfer to non-3GPP access or implementation specific mechanisms, e.g. the procedures specified in 3GPP TS 24.229 may result in the emergency call being attempted to another IP-CAN...

[0146] In a shared network, upon receipt of a Registration Reject message, the UE shall perform the actions described in clause 5.5.1.2.5;

[0147] a) Inform a higher layer of the failure of the procedure, or

[0148] b) Perform PLMN selection within the shared network and attempt to initiate initial registration for emergency services to the selected PLMN if the registration request message is not for sending a PDU session establishment message with the request type set to "existing emergency PDU session" or if the registration request message is for sending a PDU session establishment message with the request type set to "existing emergency PDU session" and the other PLMN is an equivalent PLMN.

[0149] In a shared network, if the initial registration request for emergency services fails due to an abnormal event, the UE shall perform the actions described in clause 5.5.1.2.7;

[0150] a) Inform a higher layer of the failure of the procedure, or

[0151] b) If the registration request message is not for sending a PDU session establishment message with the request type set to "existing emergency PDU session" to another PLMN in the shared network, or if the registration request message is for sending a PDU session establishment message with the request type set to "existing emergency PDU session" to another PLMN in the shared network, and that other PLMN is an equivalent PLMN, attempt initial registration for emergency services.

[0152] 13 is a proposed change 1300 to 3GPP TS 24.501 Section 5.5.1.2.6A. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed change may enable various embodiments of preserving emergency calls described herein.

[0153] If the network is unable to accept the initial registration request to send a PDU session establishment message with the request type set to "initial urgent request" and the 5GS registration type IE set to "initial registration", the UE shall implement the procedure as described in clause 5.5.1.2.5. Then, if the UE is within the same selected PLMN where the last initial registration request was attempted, the UE shall:

[0154] a) Inform a higher layer of the failure of the procedure, or

[0155] b) Initial registration for emergency services shall be attempted.

[0156] If the network cannot accept an initial registration request to initiate a PDU session for emergency services with the 5GS Registration Type IE set to "Initial Registration" and the PDU session needs to be established due to a handover of an existing PDN connection for emergency bearer services, the UE shall perform the procedure as described in clause 5.5.1.2.5. The UE shall then attempt initial registration for emergency services if it is within the same selected PLMN or equivalent PLMN where the last initial registration request was attempted.

[0157] If an initial registration request to initiate a PDU session for an emergency service, with the 5GS Registration Type IE set to "Initial Registration", fails due to abnormal cases c), d), or e) in clause 5.5.1.2.7, and a PDU session does not need to be established due to a handover of an existing PDN connection for the emergency bearer service, the UE shall perform the actions as described in clause 5.5.1.2.7. Then, if the UE is within the same selected PLMN where the last initial registration request was attempted, the UE shall:

[0158] a) Inform a higher layer of the failure of the procedure, or

[0159] b) Initial registration for emergency services shall be attempted.

[0160] If an initial registration request to initiate a PDU session for emergency services, with the 5GS Registration Type IE set to "Initial Registration", fails due to abnormal cases c), d), or e) in clause 5.5.1.2.7 and a PDU session needs to be established due to handover of an existing PDN connection for emergency bearer services, the UE shall perform the procedure as described in clause 5.5.1.2.7. The UE shall then attempt initial registration for emergency services if it is within the same selected PLMN or equivalent PLMN where the last initial registration request was attempted.

[0161] 14A, 14B, and 14C are proposed changes 1400 to 3GPP TS 25.301 Section 5.5.1.2.7. Proposed deletions are indicated by strike-through text and proposed additions are indicated by underlined text. The proposed changes may enable various embodiments of preserving emergency calls described herein.

[0162] The following unusual cases can be identified:

[0163] a) Timer T3346 is running.

[0164] The UE shall not initiate the registration procedure for initial registration unless:

[0165] 1) The UE is configured for high priority access within the selected PLMN;

[0166] 2) The UE needs to perform a registration procedure for initial registration for emergency services;

[0167] 3) The UE receives a Deregistration Request message with a "Re-registration Request" indication, or

[0168] 4) A UE in NB-N1 mode is requested by higher layers to transmit user data related to an exception event.

[0169] The UE may send exception data reports, e.g., NAS configuration management objects or USIM file EFs. NASCONFIG ExceptionDataReportingAllowed is enabled to use the leaf,

[0170] Timer T3346 was not started when the N1NAS signaling connection was established with the RRC establishment cause set to "mo-ExceptionData".

[0171] The UE remains in the current serving cell and applies the normal cell reselection process.

[0172] NOTE 1. Regardless of whether the independent timer T3346 is started due to an abnormal or unsuccessful case, it is considered an abnormal case if the UE needs to start the registration procedure for initial registration while timer T3346 is running.

[0173] b) The lower layer indicates that the access attempt is barred.

[0174] The UE shall not initiate an initial registration procedure. The UE shall remain in its current serving cell and apply the normal cell reselection process. Reception of an access barring indication shall not trigger the selection of a different core network type (EPC or 5GCN).

[0175] The initial registration procedure, if still required, is initiated when the lower layer indicates that restrictions for the access category with which the access attempt is associated are relaxed.

[0176] ba) The lower layer indicates that the access restrictions are applicable for all access categories except categories 0 and 2, and that the access category with which the access attempt is associated is other than 0 and 2.

[0177] If a Registration Request message has not been sent, the UE shall proceed as specified for case b. If a Registration Request message has been sent, the UE shall proceed as specified for case e. In addition, the registration procedure for initial registration, if still required, is initiated when lower layers indicate that restrictions are relaxed for the access category with which the access attempt is associated.

[0178] c) T3510 timeout.

[0179] The UE shall abort the registration procedure for the initial registration and the NAS signaling connection shall be locally released, if applicable, if the initial registration request is not for an emergency service or is not to initiate a PDU session for an emergency service with the request type set to "existing emergency PDU session". The UE shall proceed as described below.

[0180] d) For Registration Denial messages, other 5GMM cause values ​​other than those covered in Section 5.5.1.2.5, and 5GMM cause values ​​#11, #22, #31, #72, #73, #74, #75, #76, and #77 in cases that are considered anomalous in accordance with Section 5.5.1.2.5.

[0181] If the registration request is not an initial registration request for an emergency service or an initial registration request for starting a PDU session for an emergency service with the request type set to "existing emergency PDU session", in response to receiving 5GMM causes #95, #96, #97, #99, and #111, the UE should set the registration attempt counter to 5.

[0182] The UE shall proceed as described below.

[0183] e)…

[0184] l) Timer T3447 is running.

[0185] The UE shall not initiate the registration procedure for an initial registration with the continuation request indicator set to "continuation request pending" unless:

[0186] 1) The UE is a UE that is configured for high priority access within the selected PLMN, or

[0187] 2) The UE needs to perform a registration procedure for initial registration for emergency services.

[0188] The UE remains in the current serving cell and applies the normal cell reselection process. The registration procedure for initial registration, if still required, is initiated upon expiration of timer T3447.

[0189] For cases c, d, and e, the UE shall proceed as follows:

[0190] Timer T3510 shall be stopped if it is still running.

[0191] If the registration procedure is not an initial registration for emergency services, the registration type is not set to "emergency registration", or it is not for establishing an emergency PDU session, the registration attempt counter shall be incremented unless it is already set to 5.

[0192] If the registration attempt counter is less than 5,

[0193] If the initial registration request is not for an emergency service, timer T3511 is started and the state is changed to 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION. Upon expiration of timer T3511, the registration procedure for initial registration shall be restarted if still required.

[0194] If the registration attempt counter is equal to 5,

[0195] The UE shall delete the 5G-GUTI, the TAI list, the last destination registration TAI, the list of equivalent PLMNs (if applicable) and the ngKSI, start timer T3502 and set the 5GS update status to 5U2 NOT UPDATED. The state is changed to 5GMM-DEREGISTERED.ATTEMPTING-REGISTRATION or optionally 5GMM-DEREGISTERED.PLMN-SEARCH to perform the PLMN selection.

[0196] If the procedure is performed via 3GPP access and the UE is operating in single registration mode,

[0197] The UE shall additionally handle the EMM parameters EPS update status, EMM state, 4G-GUTI, TAI list, last destination registration TAI, list of equivalent PLMNs, and eKSI in abnormal cases as specified in 3GPP TS 24.301 when the EPS attach procedure fails and the attach attempt counter is equal to 5;

[0198] The UE shall attempt to select the E-UTRAN radio access technology and proceed with the appropriate EMM-specific procedures. In addition, the UE may disable N1 mode capabilities as specified in clause 4.9.

[0199] A procedure for a UE to transfer one or more connections from a first access network connected to a first core network to a second access network connected to a second core network includes the steps of the UE performing a first registration procedure with the second core network and sending a registration request message; the UE receiving a registration denial message from the second core network; and the UE performing a second registration procedure with the second core network and sending one of an emergency registration request message or another registration request message following receiving the registration denial message according to one or more conditions, wherein one of the one or more conditions includes detecting an emergency connection among the one or more connections.

[0200] In some embodiments, registering comprises attaching.

[0201] In an embodiment, at least one of the attach request message, the another attach request message, and the emergency attach request message comprises a connection request message accompanied by information, the information comprising information corresponding to an emergency connection, and the connection request message comprising an emergency handover indication.

[0202] In an embodiment, the registration reject message comprises a cause code, which may be set to one of a plurality of cause codes, at least one of which indicates that one of the International Mobile Equipment Identifier (IMEI) and the Permanent Equipment Identifier (PEI) is not approved.

[0203] In an embodiment, a second condition of the one or more conditions includes detecting that the cause code is set to indicate that one of the IMEI and the PEI is not recognized.

[0204] In an embodiment, in response to detecting that the cause code is set to indicate that one of the IMEI and PEI is not authorized and determining that the UE will need to provide one of the IMEI and PEI as part of the emergency registration procedure, the UE enters one of states EMM-DEREGISTERED.NO-IMSI and 5GMM-DEREGISTERED.NO-SUPI instead of performing an emergency attach procedure.

[0205] In an embodiment, a third condition of the one or more conditions includes detecting that a timer is running.

[0206] A procedure for a UE to transfer one or more connections from a first access network connected to a first core network to a second access network connected to a second core network includes the steps of: the UE performing a first registration procedure with the second core network; the UE detecting a first condition, the first condition including one of restricted access and NAS signaling connection establishment being denied by the second access network; the UE detecting a second condition, the second condition including whether an existing emergency connection exists among the one or more connections; and the UE performing a second registration procedure with the second core network in accordance with the first and second conditions and sending a registration request message.

[0207] If the second core network comprises an MME, the second registration request message comprises a request to transfer an existing emergency connection.

[0208] If the second core network has an AMF, the second registration request message has an emergency registration.

[0209] The various methods or operations described herein may be implemented by a network element. An example network element is shown with reference to Figure 15. In Figure 15, a network element 3110 includes a processor 3120 and a communication subsystem 3130, which cooperate to perform the methods or operations described above.

[0210] Additionally, various methods or operations described herein may be implemented by a communications device (e.g., a UE, a network node, a TE, etc.). Examples of communications devices are described below with respect to FIG. 16. The communications device 3200 may comprise a two-way wireless communications device having voice and data communications capabilities. In some embodiments, voice communications capabilities are optional. The communications device 3200 may also have the capability to communicate with other computer systems over the Internet. Depending on the exact functionality provided, the communications device 3200 may be referred to as a data messaging device, a two-way pager, a wireless email device, a mobile phone with data messaging capabilities, a wireless Internet appliance, a wireless device, a smartphone, a mobile device, or a data communications device, as examples.

[0211] If the communications device 3200 is enabled for two-way communications, it may incorporate a communications subsystem 3211 including a receiver 3212 and a transmitter 3214, and associated components such as one or more antenna elements 3216 and 3218, a local oscillator (LO) 3213, and a processing module such as a digital signal processor (DSP) 3220. The particular design of the communications subsystem 3211 may depend on the communications network 3219 in which the communications device 3200 is intended to operate.

[0212] Network access may also vary depending on the type of communication network 3219. In some networks, network access is associated with a subscriber or user of the communication device 3200. The communication device 3200 may use a USIM or eUICC to operate on the network. The USIM / eUICC interface 3244 is typically similar to a card slot into which a USIM / eUICC card may be inserted. The USIM / eUICC card may have memory and may hold a number of key configurations 3251 and other information 3253, such as identification and subscriber-related information.

[0213] Once network registration or activation procedures are completed, the communications device 3200 may transmit and receive communications signals via a communications network 3219. As shown, the communications network 3219 may comprise multiple base stations that communicate with the communications device 3200.

[0214] Signals received through the communications network 3219 by the antenna element 3216 are input to the receiver 3212, which may perform common receiver functions such as signal amplification, frequency downconversion, filtering, channel selection, and the like. Analog-to-digital (A / D) conversion of the received signal allows more complex communications functions such as demodulation and decoding to be performed in the DSP 3220. In a similar manner, signals to be transmitted are processed, including modulation and encoding, by the DSP 3220, for example, and input to the transmitter 3214 for digital-to-analog (D / A) conversion, frequency upconversion, filtering, amplification, and transmission over the communications network 3219 via the antenna element 3218. The DSP 3220 not only processes communications signals, but also provides receiver and transmitter control. For example, the gains applied to communications signals in the receiver 3212 and transmitter 3214 may be adaptively controlled through automatic gain control algorithms implemented in the DSP 3220.

[0215] Communications device 3200 generally includes a processor 3238 that controls the overall operation of the device. Communication functions, including data and voice communications, are performed through a communications subsystem 3211 that cooperates with processor 3238. Processor 3238 also interacts with additional device subsystems, such as a display 3222, flash memory 3224, random access memory (RAM) 3226, an auxiliary input / output (I / O) subsystem 3228, one or more user interfaces, such as a serial port 3230, a keyboard or keypad 3232, one or more other communications subsystems 3240, such as a speaker 3234, a microphone 3236, a near-field communications subsystem, and any other device subsystems generally designated 3242. While other communications subsystem 3240 and other device subsystem 3242 are depicted in FIG. 16 as separate components, it should be understood that other communications subsystem 3240 and other device subsystem 3242 (or portions thereof) may be integrated as a single component. Serial port 3230 may include a Universal Serial Bus (USB) port or other port now known or later developed.

[0216] Some of the illustrated subsystems perform communication-related functions, while other subsystems may provide "resident" or on-device functions. In particular, some subsystems, such as keyboard 3232 and display 3222, may be used for both communication-related functions, such as entering text messages for transmission over a communication network, and device-resident functions, such as a calculator or task list.

[0217] Operating system software used by processor 3238 may alternatively be stored in permanent storage, such as flash memory 3224, which may be read-only memory (ROM) or a similar storage element (not shown). The operating system, specific device applications, or portions thereof, may be temporarily loaded into volatile memory, such as RAM 3226. Received communication signals may also be stored in RAM 3226.

[0218] As shown, flash memory 3224 may be organized with different areas for both computer programs 3258 and program data storage devices 3250, 3252, 3254, and 3256. These different storage types indicate that each program may allocate a portion of flash memory 3224 for its own data storage use. In addition to its operating system functions, processor 3238 may enable the execution of software applications on communications device 3200. For example, a predetermined set of applications that control basic operations, including at least data and voice communications applications, may typically be installed on communications device 3200 during manufacture. Other applications may be installed subsequently or dynamically.

[0219] The applications and software may be stored on any computer-readable storage medium, which may be tangible or in a transitory / non-transitory medium such as optical (e.g., CD, DVD, etc.), magnetic (e.g., tape), or other memory now known or later developed.

[0220] Software applications may be loaded onto communications device 3200 through communications network 3219, auxiliary I / O subsystem 3228, serial port 3230, other near-field communications subsystem 3240, or any other suitable device subsystem 3242, and installed by a user into RAM 3226 or non-volatile storage (not shown) for execution by processor 3238. Such flexibility in application installation may increase the functionality of communications device 3200 and may provide enhanced on-device functions, communications-related functions, or both. For example, secure communications applications may enable e-commerce functions and other such financial transactions to be conducted using communications device 3200.

[0221] In data communication mode, received signals, such as text messages or web page downloads, may be processed by communication subsystem 3211 and input to processor 3238, which may further process the received signals for output to display 3222 or, alternatively, to auxiliary I / O device 3228.

[0222] With respect to voice communications, the overall operation of communication device 3200 is similar, except that received signals may typically be output to speaker 3234 and signals for transmission may be generated by microphone 3236. Alternative voice or audio I / O subsystems, such as a voice message recording subsystem, may also be implemented on communication device 3200. While voice or audio signal output may be accomplished primarily through speaker 3234, display 3222 may also be used to provide indications, for example, of the identity of the calling party, the duration of the voice call, or other voice call related information.

[0223] The serial port 3230 may be implemented in a personal digital assistant (PDA) type device where synchronization with a user's desktop computer (not shown) may be desirable, although such a port is an optional device component. Such a serial port 3230 may allow a user to set preferences through an external device or software application, and may extend the capabilities of the communication device 3200 by providing information or software downloads to the communication device 3200 other than through the wireless communication network 3219. An alternative download path may be used, for example, to load encryption keys onto the communication device 3200 through a direct, and therefore reliable, connection, thereby enabling secure device communications. The serial port 3230 may also be used to connect the device to a computer to act as a modem.

[0224] Other communications subsystems 3240, such as a near-field communications subsystem, are further optional components that may provide communications between communications device 3200 and different systems or devices, not necessarily similar devices. For example, one or more other communications subsystems 3240 may include an infrared device and associated circuits and components or a Bluetooth® communications module to provide communications with similarly enabled systems and devices. Other communications subsystems 3240 may also include non-cellular communications, such as Wi-Fi, WiMAX, near field communication (NFC), BLUETOOTH®, ProSe (proximity services) (e.g., sidelink, PC5, D2D, etc.), and / or radio frequency identification (RFID). Other communications subsystems 3240 and / or other device subsystems 3242 may also be used to communicate with auxiliary devices, such as a tablet display, keyboard, or projector.

[0225] The communications device 3200 and other components described above may include a processing component capable of executing instructions related to the actions described above. FIG. 17 illustrates an example of a system 3300 including a processing component 3310 suitable for implementing one or more embodiments disclosed herein. In addition to the processor 3310 (which may be referred to as a central processing unit or CPU), the system 3300 may include a network connectivity device 3320, a random access memory (RAM) 3330, a read-only memory (ROM) 3340, a secondary storage device 3350, and input / output (I / O) devices 3360. These components may communicate with each other via a bus 3370. In some cases, some of these components may not be present or may be combined in various combinations with each other or with other components not shown. These components may be located within a single physical entity or within more than one physical entity. Any action described herein as being taken by the processor 3310 may be taken by the processor 3310 alone or by the processor 3310 in conjunction with one or more components, which may or may not be shown in the figures, such as a digital signal processor (DSP) 3380. Although the DSP 3380 is shown as a separate component, the DSP 3380 may be incorporated into the processor 3310.

[0226] The processor 3310 executes instructions, code, computer programs, or scripts that it may access from the network connectivity device 3320, RAM 3330, ROM 3340, or secondary storage 3350 (which may include various disk-based systems such as a hard disk, floppy disk, or optical disk). Although only one CPU 3310 is shown, multiple processors may be present. Thus, while instructions may be discussed as being executed by one processor, the instructions may be executed simultaneously, serially, or otherwise by one or more processors. The processor 3310 may be implemented as one or more CPU chips.

[0227] The network connectivity devices 3320 may take the form of a modem, a modem bank, an Ethernet device, a Universal Serial Bus (USB) interface device, a serial interface, a token ring device, a wireless local area network (WLAN) device, a code division multiple access (CDMA) device, a wireless transceiver device such as a Global System for Mobile Communications (GSM) wireless transceiver device, a Universal Mobile Telecommunications System (UMTS) wireless transceiver device, an LTE wireless transceiver device, a new generation wireless transceiver device, a Worldwide Interoperable Microwave Access (WiMAX) device, and / or other well-known devices for connecting to a network. These network connectivity devices 3320 may enable the processor 3310 to communicate with the Internet or one or more telecommunications networks or other networks from which the processor 3310 may receive information or to which the processor 3310 may output information. The network connectivity devices 3320 may also include one or more transceiver components 3325 capable of transmitting and / or receiving data wirelessly.

[0228] RAM 3330 stores volatile data and may be used to store instructions executed by processor 3310. ROM 3340 is a non-volatile memory device that typically has a smaller memory capacity than that of secondary storage 3350. ROM 3340 may be used to store instructions and possibly data read during execution of instructions. Access to both RAM 3330 and ROM 3340 is typically faster than access to secondary storage 3350. Secondary storage 3350 typically consists of one or more disk drives or tape drives and may be used for non-volatile storage of data or as an overflow data storage device if RAM 3330 is not large enough to hold all working data. Secondary storage 3350 may also be used to store programs that are loaded into RAM 3330 when such programs are selected for execution.

[0229] The I / O devices 3360 may include a liquid crystal display (LCD), a touch screen display, a keyboard, a keypad, switches, dials, a mouse, a trackball, a voice recognition device, a card reader, a paper tape reader, a printer, a video monitor, or other well-known input / output devices. Also, the transceiver component 3325 may be considered to be a component of the I / O devices 3360 instead of, or in addition to, being a component of the network connectivity device(s) 3320.

[0230] The following are hereby incorporated by reference for all purposes: 3GPP TS.24.301 and 3GPP TS24.501.

[0231] While several embodiments are provided in this disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the scope of the present disclosure. The examples are to be considered illustrative rather than restrictive, and the intention is not to be limited to the details provided herein. For example, various elements or components may be combined or integrated in another system, or certain features may be omitted, or not implemented.

[0232] Additionally, techniques, systems, subsystems, and methods described and illustrated in various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as being coupled or directly coupled or in communication with each other may also be indirectly coupled or in communication through some interface, device, or intermediate component, whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by those skilled in the art and could be made without departing from the spirit and scope disclosed herein.

Claims

1. A method for transferring an ongoing emergency session from a first network to a second network, the method comprising: a network component in the second network receiving a first attach request message from a user equipment (UE), the first attach request message comprising a PDN connectivity request message with a request type set to "handover"; transmitting an attach denial message from the network component to the UE; receiving, by the network component, a second Attach Request message from the UE in response to the Attach Reject message, the second Attach Request message comprising a PDN Connectivity Request message with a request type set to "Handover of Emergency Bearer Services" for the ongoing emergency session; and the network component transmitting to the UE an attach accept message for transferring the ongoing emergency session from the first network to the second network; A method comprising:

2. The method described in claim 1, wherein the second attach request message is an emergency attach request message.

3. The method of claim 1, wherein the attach denial message includes an Evolved Packet System (EPS) Mobility Management (EMM) cause code.

4. The method described in claim 3, wherein the EMM cause code is #19 and indicates an EPS Session Management (ESM) failure.

5. The method of claim 1, wherein the first network is a fifth generation (5G) network and the second network is a fourth generation (4G) network.

6. The method of claim 1, wherein the first network is part of a fifth generation system (5GS) and the second network is part of an EPS.

7. The method of claim 2, wherein the emergency attach request message includes an attach type that is set to "EPS Emergency Attach."

8. The method described in claim 1, wherein the second attach request message includes an attach type that is not set to "EPS Emergency Attach." 9. A network component in a first network, the network component comprising: a processor; Memory that stores instructions Equipped with The instructions, when executed by the processor, receiving, by the network component, a first attach request message from a user equipment (UE), the first attach request message comprising a PDN connectivity request message with a request type set to "handover"; transmitting an attach denial message from the network component to the UE; receiving, by the network component, a second Attach Request message from the UE in response to the Attach Reject message, the second Attach Request message comprising a PDN Connectivity Request message with a request type set to "Handover of Emergency Bearer Services" for the ongoing emergency session; and the network component transmitting to the UE an attach accept message for transferring the ongoing emergency session from a second network to the first network; a network component that causes the network component to perform the following:

10. The network component of claim 9, wherein the second attach request message is an emergency attach request message.

11. The network component of claim 9, wherein the attach denial message includes an Evolved Packet System (EPS) Mobility Management (EMM) cause code.

12. The network component of claim 11, wherein the EMM cause code is #19 and indicates an EPS Session Management (ESM) failure.

13. The network component of claim 9, wherein the second network is a fifth generation (5G) network and the first network is a fourth generation (4G) network.

14. The network component of claim 9, wherein the second network is part of a fifth generation system (5GS) and the first network is part of an EPS.

15. The network component of claim 10, wherein the emergency attach request message includes an attach type that is set to "EPS Emergency Attach." 16. The network component of claim 9, wherein the second attach request message includes an attach type that is not set to "EPS Emergency Attach." 17. A non-transitory computer-readable storage medium comprising instructions that, when executed by a processor, a network component in a second network receiving a first attach request message from a user equipment (UE), the first attach request message comprising a PDN connectivity request message with a request type set to "handover"; transmitting an attach denial message from the network component to the UE; receiving, by the network component, a second Attach Request message from the UE in response to the Attach Reject message, the second Attach Request message comprising a PDN Connectivity Request message with a request type set to "Handover of Emergency Bearer Services" for the ongoing emergency session; and the network component transmitting to the UE an attach accept message for transferring the ongoing emergency session from the first network to the second network; a non-transitory computer-readable storage medium that causes the processor to perform the steps of:

18. The non-transitory computer-readable storage medium of claim 17, wherein the second attach request message is an emergency attach request message.

19. The non-transitory computer-readable storage medium of claim 17, wherein the attach denial message includes an Evolved Packet System (EPS) Mobility Management (EMM) cause code.

20. The non-transitory computer-readable storage medium of claim 19, wherein the EMM cause code is #19 and indicates an EPS Session Management (ESM) failure.

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