Patent Description:
The Third Generation Partnership Project (3GPP) New Radio (NR) specification provides for mobility from a Fifth Generation (<NUM>) System (5GS) to an Evolved Packet System (EPS). Such mobility is provided through a transfer from a source Access and Mobility Management Function (AMF) in the <NUM> Core (5GC) of the 5GS and a target Mobility Management Entity (MME) in the Evolved Packet Core (EPC) of the EPS. In the 5GS, it is always assumed that <NUM> EBIs can be allocated for interworking with an EPS. However, supporting <NUM> EPS bearers is optional in the EPS. Thus, in some cases, the target MME will support <NUM> EPS bearers and, in other cases, the target MME will not support <NUM> EPS bearers. In other words, in some cases the target MME lacks the capability of supporting <NUM> EPS bearers. In SA2#<NUM>, the scenario that the target MME does not support <NUM> EPS bearers at 5GS to EPS mobility is addressed in S2-<NUM> on 3GPP TS <NUM> (which is to be reflected in <NUM> v16.

In the case of mobility from 5GS to EPS, if the MME lacks certain capability, e.g. MME not supporting <NUM> EPS bearers, the 5GC shall not transfer the UE EPS bearers and/or EPS PDN connections that are not supported by the EPC network.

A similar issue is addressed in 3GPP TS29. <NUM> for mobility from a source MME to a target MME where the source MME supports <NUM> EPS bearers but the target MME does not. Per 3GPP TS29. <NUM>, when the target MME does not support <NUM> EPS bearers (which in fact means that the target EPS supports only <NUM> EPS bearers), the source MME shall only transfer <NUM> EPS bearers (assigning only certain EPS Bearer Identity (EBI) values) to the target MME:.

NOTE <NUM>: The support of the <NUM> EPS Bearers shall be homogeneously supported within an MME Pool / SGW serving area. A source MME which supports the <NUM> EPS Bearers, shall know whether the target MME pool also supports that by local configuration. When the target MME is known to not support the <NUM> EPS Bearers, the source MME shall only transfer up to <NUM> EPS bearer contexts with the EBI value set between '<NUM>' and '<NUM>' to the target MME and shall delete EPS bearer(s) which are not transferred, and if the default bearer is to be deleted, the corresponding PDN connection(s) shall be deleted by the source MME.

In support of the scenario in which the target MME does not support <NUM> EPS bearers at 5GS to EPS mobility, it has been proposed that the serving Access and Mobility Management Function (AMF) provides a "non supported EBI list" to a corresponding Session Management Function (SMF) or virtual SMF (V-SMF). In SA2#<NUM>, S2-<NUM> was discussed (but not agreed) and proposed the following text:.

The provided target MME capability also includes an Indication on whether the EPS bearer ID extension is supported in EPS network. If EPS bearer ID extension is not supported, the AMF provides the non supported EBI list to V-SMF, the V-SMF notifies the target MME capability to PGW-C+SMF. The QoS flows associated with the non supported EBI are not expected to be transferred to EPS network.

Document by <NPL>, discloses a method wherein AMF indicates whether the target EPS network support <NUM> EPS bearers to PGW_C+SMF and based on that indication the PGW_C+SMF determine whether the QoS flow associated with not supported EPS Bearer ID value shall not be transferred to EPS networks and released at the 5GC side. It also discloses that if EPS bearer ID extension is not supported in EPS network, the AMF provides the non-supported EBI list to V-SMF.

There currently exist certain challenge(s). It remains unclear at 5GS to EPS mobility how the 5GC ensures that no more than <NUM> mapped EPS bearers are transferred to the EPS if the target MME does not support <NUM> EPS bearers.

The present disclosure is defined by the independent claims. Further embodiments are set forth in the description.

Certain aspects of the present disclosure and their embodiments may provide solutions to the aforementioned or other challenges. In some embodiments, at 5GS to EPS mobility (for a UE), if a target MME does not support <NUM> EPS bearers but more than <NUM> EBI values are assigned to one or more Protocol Data Unit (PDU) Sessions (of the UE) by a serving AMF, then:.

In some embodiments, when the AMF receives a new EBI allocation request, and the AMF determines that an EBI value from range <NUM>-<NUM> should be used for the new request but there is no available value from range <NUM>-<NUM>, if there is a value available from EBI range <NUM>-<NUM>, the AMF may perform EBI replacement to replace the EBI value(s) for QoS Flows(s) from value(s) in range <NUM>-<NUM> with value(s) in range <NUM>-<NUM>, and the SMF updates the UE and maybe the Next Generation Radio Access Network (NG-RAN) (i.e., the RAN of the 5GS) of the EBI replacement.

Certain embodiments may provide one or more of the following technical advantage(s). Certain embodiments address scenarios at 5GS to EPS mobility in which a target MME does not support <NUM> EPS bearers.

Core Network Node: As used herein, a "core network node" is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing a Access and Mobility Management Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like.

Some examples of a wireless communication device include, but are not limited to: a User Equipment (UE) device in a 3GPP network, a Machine Type Communication (MTC) device, and an Internet of Things (IoT) device.

<FIG> illustrates one example of a cellular communications system <NUM> in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system <NUM> includes a <NUM> system (5GS) including a Next Generation Radio Access Network (NG-RAN) and an Evolved Packet System (EPS) including a LTE RAN (i.e., E-UTRA RAN). In this example, the NG-RAN includes one or more base stations <NUM>-<NUM>, which in <NUM> NR are referred to as NG-RAN nodes (e.g., a gNBs or gn-eNBs for LTE RAN nodes connected to a <NUM> Core (5GC) <NUM>-<NUM>), connected to the 5GC <NUM>-<NUM> and controlling corresponding (macro) cells <NUM>-<NUM>. Together, the NG-RAN node(s) (e.g., <NUM>-<NUM>) and the 5GC <NUM>-<NUM> form the 5GS. The E-UTRA RAN includes one or more base stations <NUM>-<NUM>, which in LTE are referred to as E-UTRA RAN nodes (e.g., eNBs when connected to EPC), connected to an Evolved Packet Core (EPC) <NUM>-<NUM> and controlling corresponding (macro) cells <NUM>-<NUM>. Together, the E-UTRA RAN node(s) (e.g., <NUM>-<NUM>) and the EPC <NUM>-<NUM> form the EPS.

The base stations <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as base stations <NUM> and individually as base station <NUM>. Likewise, the (macro) cells <NUM>-<NUM> and <NUM>-<NUM> are generally referred to herein collectively as (macro) cells <NUM> and individually as (macro) cell <NUM>. The base stations <NUM> provide service to one or more wireless communication devices <NUM> in the corresponding cells <NUM>. The wireless communication devices 112are generally referred to herein collectively as wireless communication devices <NUM> and individually as wireless communication device <NUM>.

<FIG> illustrates a wireless communication system represented as a <NUM> network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference point/interface. <FIG> can be viewed as one particular implementation of the 5GC <NUM>-<NUM> of the system <NUM> of <FIG>.

Seen from the access side the <NUM> network architecture shown in <FIG> comprises a plurality of User Equipment (UEs) connected to either a RAN or an Access Network (AN) as well as an Access and Mobility Management Function (AMF). Typically, the (R)AN comprises base stations, e.g. such as evolved Node Bs (eNBs) or NR base stations (gNBs) or similar. Seen from the core network side, the <NUM> core NFs shown in <FIG> include a Network Slice Selection Function (NSSF), an Authentication Server Function (AUSF), a Unified Data Management (UDM), an AMF, a Session Management Function (SMF), a Policy Control Function (PCF), and an Application Function (AF).

Reference point representations of the <NUM> network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE and AMF. The reference points for connecting between the AN and AMF and between the AN and UPF are defined as N2 and N3, respectively. There is a reference point, N11, between the AMF and SMF, which implies that the SMF is at least partly controlled by the AMF. N4 is used by the SMF and UPF so that the UPF can be set using the control signal generated by the SMF, and the UPF can report its state to the SMF. N9 is the reference point for the connection between different UPFs, and N14 is the reference point connecting between different AMFs, respectively. N15 and N7 are defined since the PCF applies policy to the AMF and SMF, respectively. N12 is required for the AMF to perform authentication of the UE. N8 and N10 are defined because the subscription data of the UE is required for the AMF and SMF.

The <NUM> core network aims at separating user plane and control plane. The user plane carries user traffic while the control plane carries signaling in the network. In <FIG>, the UPF is in the user plane and all other NFs, i.e., the AMF, SMF, PCF, AF, AUSF, and UDM, are in the control plane. Separating the user and control planes guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from control plane functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and data network for some applications requiring low latency.

The core <NUM> network architecture is composed of modularized functions. For example, the AMF and SMF are independent functions in the control plane. Separated AMF and SMF allow independent evolution and scaling. Other control plane functions like the PCF and AUSF can be separated as shown in <FIG>. Modularized function design enables the <NUM> core network to support various services flexibly.

<FIG> illustrates a <NUM> network architecture using service-based interfaces between the NFs in the control plane, instead of the point-to-point reference points/interfaces used in the <NUM> network architecture of <FIG>. However, the NFs described above with reference to <FIG> correspond to the NFs shown in <FIG>. The service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In <FIG> the service based interfaces are indicated by the letter "N" followed by the name of the NF, e.g. Namf for the service based interface of the AMF and Nsmf for the service based interface of the SMF etc. The Network Exposure Function (NEF) and the Network Function (NF) Repository Function (NRF) in <FIG> are not shown in <FIG> discussed above. However, it should be clarified that all NFs depicted in <FIG> can interact with the NEF and the NRF of <FIG> as necessary, though not explicitly indicated in <FIG>.

Some properties of the NFs shown in <FIG> and <FIG> may be described in the following manner. The AMF provides UE-based authentication, authorization, mobility management, etc. A UE even using multiple access technologies is basically connected to a single AMF because the AMF is independent of the access technologies. The SMF is responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF for data transfer. If a UE has multiple sessions, different SMFs may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF provides information on the packet flow to the PCF responsible for policy control in order to support Quality of Service (QoS). Based on the information, the PCF determines policies about mobility and session management to make the AMF and SMF operate properly. The AUSF supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM stores subscription data of the UE. The Data Network (DN), not part of the <NUM> core network, provides Internet access or operator services and similar.

<FIG> illustrates an LTE network architecture. <FIG> can be viewed as one particular implementation of the EPC <NUM>-<NUM> of the system <NUM> of <FIG>. As will be appreciated by one of skill in the art, core network for LTE, which is referred to as an EPC, includes a number of core network entities such as, e.g., a Serving Gateway (S-GW) <NUM>, a P-GW <NUM>, an MME <NUM>, a Home Subscriber Server (HSS) <NUM>, and a Policy and Charging Rules Function (PCRF) <NUM>. The operational details of the S-GW <NUM>, the P-GW <NUM>, the MME <NUM>, the HSS <NUM>, and the PCRF <NUM> are well known to those of skill in the art and therefore are not repeated here. (R)AN <NUM> of the LTE network includes base stations such as, e.g., eNBs.

<FIG> is a schematic diagram of a 5GS to EPS handover for single-registration mode with an N26 interface, excerpted from <FIG>. <NUM>-<NUM> of 3GPP TS <NUM>. Embodiments described herein facilitate mobility between a 5GS and an EPS, where a target MME does not support <NUM> EPS bearers (meaning that only <NUM> EPS bearers are supported). In an exemplary aspect, updates are made to 3GPP TS <NUM> clause <NUM>. <NUM>5GS to EPS handover using N26 interface as follows:.

<NUM>-<NUM> describes the handover procedure from 5GS to EPS when N26 is supported.

In the case of handover to a shared EPS network, the source NG-RAN determines a PLMN to be used in the target network as specified by TS <NUM> [<NUM>]. The source NG-RAN shall indicate the selected PLMN ID to be used in the target network to the AMF as part of the TAI sent in the HO Required message.

In the case of handover from a shared NG-RAN, the AMF may provide the MME with an indication that the 5GS PLMN is a preferred PLMN at later change of the UE to a 5GS shared networks.

During the handover procedure, as specified in clause <NUM>. <NUM>, the source AMF shall reject any PGW-C+SMF initiated N2 request received since handover procedure started and shall include an indication that the request has been temporarily rejected due to handover procedure in progress.

Upon reception of a rejection for an PGW-C+SMF initiated N2 request(s) with an indication that the request has been temporarily rejected due to handover procedure in progress, the PGW-C+SMF behaves as specified in TS <NUM> [<NUM>].

The procedure involves a handover to EPC and setup of default EPS bearer and dedicated bearers for GBR QoS Flows in EPC in steps <NUM>-<NUM> and re-activation, if required, of dedicated EPS bearers for non-GBR QoS Flows in step <NUM>. This procedure can be triggered, for example, due to new radio conditions, load balancing or in the presence of QoS Flow for normal voice or IMS emergency voice, the source NG-RAN node may trigger handover to EPC.

For Ethernet and Unstructured PDU Session Types, the PDN Type Ethernet and non-IP respectively are used, when supported, in EPS.

When EPS supports PDN Type non-IP but not PDN type Ethernet, PDN type non-IP is used also for Ethernet PDU sessions. The SMF shall also set the PDN Type of the EPS Bearer Context to non-IP in this case. After the handover to EPS, the PDN Connection will have PDN Type non-IP, but it shall be locally associated in UE and SMF to PDU Session Type Ethernet or Unstructured respectively.

In the roaming home routed case, the PGW-C+SMF always provides the EPS Bearer ID and the mapped QoS parameters to UE. The V-SMF caches the EPS Bearer ID and the mapped QoS parameters obtained from H-SMF for this PDU session. This also applies in the case that the HPLMN operates the interworking procedure without N26.

NOTE <NUM>: The IP address preservation cannot be supported, if PGW-C+SMF in the HPLMN doesn't provide the mapped QoS parameters.

NOTE x: For a PDU Session, if some QoS Flows are to be transferred while others are not, the AMF can determine if the QoS Flow associated with the default QoS Rule is to be transferred based on the ARP PL and PVI value.

This step is performed with all the PGW-C+SMFs corresponding to PDU Sessions of the UE which are associated with 3GPP access and have EBI(s) allocated to them.

NOTE <NUM>: The AMF knows the MME capability to support <NUM> EPS bearers, Ethernet PDN type and/or non-IP PDN type or not through local configuration.

NOTE <NUM>: In home routed roaming scenario, the UE's SM EPS Contexts are obtained from the V-SMF.

The AMF sends a Forward Relocation Request as in Step <NUM> in clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>], with the following modifications and clarifications:.

The AMF includes the mapped SM EPS UE Contexts for PDU Sessions with and without active UP connections.

<NUM>-<NUM>. Step <NUM> and 4a respectively in clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>].

Step <NUM> (Handover Request) in clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>] with the following modification:.

<NUM>-<NUM>. Step 5a through <NUM> in clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>].

If indirect data forwarding applies, the AMF sends the Nsmf PDUSession_UpdateSMContext Request (Serving GW Address(es) and Serving GW DL TEID(s) for data forwarding) to the PGW-C+SMF, for creating indirect data forwarding tunnel. If multiple PGW-C+SMFs serves the UE, the AMF maps the EPS bearers for Data forwarding to the PGW-C+SMF address(es) based on the association between the EPS bearer ID(s) and PDU Session ID(s). In home-routed roaming case, the AMF requests the V-SMF to create indirect forwarding tunnel.

The PGW-C+SMF may select an intermediate PGW-U+UPF for data forwarding. The PGW-C+SMF maps the EPS bearers for Data forwarding to the <NUM> QoS flows based on the association between the EPS bearer ID(s) and QFI(s) for the QoS flow(s) in the PGW-C+SMF, and then sends the QFIs, Serving GW Address(es) and TEID(s) for data forwarding to the PGW-U+UPF. If CN Tunnel Info for Data Forwarding is allocated by the PGW-C+SMF, the CN Tunnel Info for Data Forwarding is provided to PGW-U+UPF in this step. The PGW-U+UPF acknowledges by sending a response. If CN Tunnel Info is allocated by the PGW-U+UPF, the CN Tunnel Info is provided to PGW-C+SMF in this response. In home-routed roaming case, the V-SMF selects the V-UPF for data forwarding.

The PGW-C+SMF returns an Nsmf PDUSession_UpdateSMContext Response (Cause, CN tunnel Info for Data Forwarding, QoS flows for Data Forwarding) for creating indirect data forwarding. Based on the correlation between QFI(s) and Serving GW Address(es) and TEID(s) for data forwarding, the PGW-U+UPF maps the QoS flow(s) into the data forwarding tunnel(s) in EPC.

The AMF sends the Handover Command to the source NG-RAN (Transparent container (radio aspect parameters that the target eNB has set-up in the preparation phase), CN tunnel info for data forwarding per PDU Session, QoS flows for Data Forwarding). The source NG-RAN commands the UE to handover to the target access network by sending the HO Command. The UE correlates the ongoing QoS Flows with the indicated EPS Bearer IDs to be setup in the HO command. The UE locally deletes the PDU Session if the QoS Flow associated with the default QoS rule in the PDU Session does not have an EPS Bearer ID assigned. If the QoS Flow associated with the default QoS rule has an EPS Bearer ID assigned, the UE keeps the PDU Session (PDN connection) and for the remaining QoS Flow(s) that do not have EPS bearer ID(s) assigned, the UE locally deletes the QoS rule(s) and the QoS Flow level QoS parameters if any associated with those QoS Flow(s) and notifies the impacted applications that the dedicated QoS resource has been released. The UE deletes any UE derived QoS rules. The EPS Bearer ID that was assigned for the QoS flow of the default QoS rule in the PDU Session becomes the EPS Bearer ID of the default bearer in the corresponding PDN connection.

For the QoS Flows indicated in the "QoS Flows for Data Forwarding", NG-RAN initiate data forwarding via to the PGW-U+UPF based on the CN Tunnel Info for Data Forwarding per PDU Session. Then the PGW-U+UPF maps data received from the data forwarding tunnel(s) in the 5GS to the data forwarding tunnel(s) in EPS, and sends the data to the target eNodeB via the Serving GW.

Step <NUM> to step <NUM> from clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>] with the following clarification:.

The AMF acknowledges MME with Relocation Complete Ack message. A timer in AMF is started to supervise when resource in NG-RAN shall be released.

In case of home routed roaming, the AMF invokes Nsmf PDUSession_ReleaseSMContext Request(V-SMF only indication) to the V-SMF. This service operation request the V-SMF to remove only the SM context in V-SMF, i.e. not release PDU Session context in the PGW-C+SMF.

If indirect forwarding tunnel(s) were previously established, the V-SMF starts a timer and releases the SM context on expiry of the timer. If no indirect forwarding tunnel has been established, the V-SMF immediately releases the SM context and its UP resources for this PDU Session in V-UPF locally.

Step <NUM> from clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>].

Step <NUM> (Modify Bearer Request) from clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>] with the following clarification:.

NOTE <NUM>: If the QoS flow is deleted, the IP flows of the deleted QoS rules will continue flowing on the default EPS bearer if it does not have an assigned TFT. If the default EPS bearer has an assigned TFT, the IP flows of the deleted QoS Flow may be interrupted until step <NUM> when dedicated bearer activation is triggered by a request from the PCF.

The PGW-C+SMF may need to report some subscribed event to the PCF by performing an SMF initiated SM Policy Association Modification procedure as defined in clause <NUM>.

The PGW-C+SMF initiates a N4 Session Modification procedure towards the UPF+PGW-U to update the User Plane path, i.e. the downlink User Plane for the indicated PDU Session is switched to E-UTRAN. The PGW-C+SMF releases the resource of the CN tunnel for PDU Session in UPF+PGW-U.

Step 16a (Modify Bearer Response) from clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>]. At this stage the User Plane path is established for the default bearer and the dedicated EPS bearers between the UE, target eNodeB, Serving GW and the PGW-U+UPF. The PGW-C+SMF uses the EPS QoS parameters as assigned for the dedicated EPS bearers during the QoS Flow establishment. PGW-C+SMF maps all the other IP flows to the default EPS bearer (see NOTE <NUM>).

If indirect forwarding tunnel(s) were previously established, the PGW-C+SMF starts a timer, to be used to release the resource used for indirect data forwarding.

The UE initiates a Tracking Area Update procedure as specified in step <NUM> of clause <NUM>. <NUM> (S1-based handover, normal) in TS <NUM> [<NUM>].

This includes the deregistration of the old AMF for 3GPP access from the HSS+UDM as specified in clause <NUM>. Any registration associated with the non-3GPP access in the old AMF is not removed (i.e. an AMF that was serving the UE over both 3GPP and non-3GPP accesses does not consider the UE as deregistered over non 3GPP access and will remain registered and subscribed to subscription data updates in UDM).

NOTE <NUM>: The behavior whereby the HSS+UDM cancels location of CN node of the another type, i.e. AMF, is similar to HSS behavior for MME and Gn/Gp SGSN registration (see TS <NUM> [<NUM>]). The target AMF that receives the cancel location from the HSS+UDM is the one associated with 3GPP access.

When the UE decides to deregister over non-3GPP access or the old AMF decides not to maintain a UE registration for non-3GPP access anymore, the old AMF then deregisters from UDM by sending a Nudm_UECM_Deregistration service operation, unsubscribes from Subscription Data updates by sending an Nudm_SDM_Unsubscribe service operation to UDM and releases all the AMF and AN resources related to the UE.

If PCC is deployed, the PCF may decide to provide the previously removed PCC rules to the PGW-C+SMF again thus triggering the PGW-C+SMF to initiate dedicated bearer activation procedure. This procedure is specified in TS <NUM> [<NUM>], clause <NUM>. <NUM> with modification captured in clause <NUM>. This step is applicable for PDN Type IP or Ethernet, but not for non-IP PDN Type.

In the case of home routed roaming, at the expiry of the timer at V-SMF started at step 12e, the V-SMF locally releases the SM context and the UP resource for the PDU Session including the resources used for indirect forwarding tunnel(s) that were allocated at step <NUM>.

In non-roaming or local breakout roaming, if PGW-C+SMF has started a timer in step <NUM>, at the expiry of the timer, the PGW-C+SMF sends N4 Session Modification Request to PGW-U+UPF to release the resources used for the indirect forwarding tunnel(s) that were allocated at step <NUM>.

When the timer set in step 12d expires, AMF also sends a UE Context Release Command message to the source NG RAN. The source NG RAN releases its resources related to the UE and responds with a UE Context Release Complete message.

<FIG> is a schematic diagram of 5GS to EPS idle mode mobility using an N26 interface, excerpted from <FIG>. <NUM>-<NUM> of 3GPP TS <NUM>. In another exemplary aspect, updates are made to 3GPP TS <NUM> clause <NUM>. <NUM>5GS to EPS Idle mode mobility using N26 interface as follows:.

In case of network sharing the UE selects the target PLMN ID according to clause <NUM>. <NUM> of TS <NUM> [<NUM>].

Clause <NUM>. <NUM> covers the case of idle mode mobility from 5GC to EPC. UE performs Tracking Area Update procedure in E-UTRA/EPS when it moves from NG-RAN/5GS to E-UTRA/EPS coverage area.

The procedure involves a Tracking Area Update to EPC and setup of default EPS bearer and dedicated bearers in EPC in steps <NUM>-<NUM> and re-activation, if required.

The TAU procedure in TS <NUM> [<NUM>] is used with the following 5GS interaction:.

If the AMF knows that the target MME does not support <NUM> EPS bearers, the AMF first marks EBI values in range <NUM>-<NUM> "not to be transferred" which means the QoS Flows associated with those EBIs are not to be transferred to EPS. If there are still more than <NUM> EBI values associated with PDU Sessions, the AMF then determines EBI value(s) not to be transferred based on S-NSSAI and ARP value(s). The AMF does not retrieve the SMF context for PDU Session(s) if the QoS Flow associated with the default QoS Rule is determined not to be transferred.

This step is performed with all the PGW-C+SMFs corresponding to PDU Sessions of the UE which are associated with 3GPP access and have EBI(s) allocated to them. In this step, if the AMF correctly validates the UE, then the AMF starts a timer.

NOTE <NUM>: The AMF knows the MME capability to support <NUM> EPS bearers, Ethernet PDN Type and/or non-IP PDN type or not through local configuration.

For Non-roaming or roaming with local breakout scenario, if CN Tunnel Info is allocated by the PGW-U+UPF, the SMF sends N4 Session Modification Request to PGW-U+UPF to establish the tunnel for each EPS bearers, and PGW-U+UPF provides the PGW-U Tunnel Info for each EPS bearers to PGW-C+SMF.

NOTE <NUM>: In home routed roaming case, the CN Tunnel Info for each EPS bearer has been prepared by the PGW-C+SMF and provided to the V-SMF as specified in clause <NUM>.

For PDU Sessions that are anchored a UPF, the SMF returns mapped EPS bearer contexts, which includes PGW-C control plane tunnel information of the PDN connection corresponding to the PDU session, EBI for each EPS bearer, PGW-U tunnel information for each EPS bearer, and EPS QoS parameters for each EPS bearer. For PDU Sessions with PDU Session Type Ethernet, if the UE and target MME supports Ethernet PDN type, the SMF provides SM Context for Ethernet PDN Type, otherwise if the UE or target MME does not support Ethernet Type but support non-IP Type, the SMF provides SM Context for non-IP PDN Type. For PDU Sessions with PDU Session Type Unstructured, the SMF provides SM Context for non-IP PDN Type.

For PDU Sessions that are anchored at an NEF, the SMF returns an SCEF+NEF ID and an EBI for each PDN connection corresponding to a PDU Session.

If the PGW-C+SMF has marked that the status of one or more QoS Flows are deleted in the 5GC but not synchronized with the UE yet according to clause <NUM>. <NUM>, the PGW-C+SMF does not return to the AMF the EPS context(s) if all its associated QoS Flows are marked as deleted, that is, the PGW-C+SMF returns to the AMF the EPS bearer contexts mapped from QoS Flows where at least one of the QoS Flow for the EPS bearer is not marked as deleted.

The AMF responds with a Context Response message carrying mapped MM context (including mapped security context), Return preferred and SM EPS UE Context (default and dedicated GBR bearers) to the MME. If the verification of the integrity protection fails, the AMF returns an appropriate error cause. Return preferred is an optional indication by the AMF of a preferred return of the UE to the 5GS PLMN at a later access change to a 5GS shared network. The AMF may start an implementation specific (guard) timer for the UE context.

From the received context and the Tracking Area indicated by the RAN, the MME can determine whether the UE is performing Inter-RAT mobility to or from NB-IoT.

<NUM> - <NUM>. Steps <NUM>-<NUM> from clause <NUM>. <NUM> (Tracking Area Update procedure with Serving GW change) in TS <NUM> [<NUM>] are performed with following addition and modification:.

If the SCEF connection is to be established, the steps <NUM>-<NUM> are replaced with the steps <NUM>-<NUM> from clause <NUM>. <NUM> of TS <NUM> [<NUM>]. The SCEF+NEF ID and the EBI received from the AMF are included in the Create SCEF Connection Request.

The HSS+UDM invokes Nudm_UECM_DeregistrationNotification to notify the AMF associated with 3GPP access with reason as 5GS to EPS Mobility. If the timer started in step <NUM> is not running, the old AMF removes the UE context. Otherwise, the AMF may remove UE context when the timer expires. The AMF request the release of the PDU Session which is associated with 3GPP access, not expected to be transferred to EPC, i.e. no EBI(s) allocated to them and corresponding to the (V-)SMF which is not contacted by AMF for SM context at step 5a, or SM context retrieval failure at step 5c. The AMF requests the release of the SM context in the V-SMF only, for Home Routed PDU Session with EBIs allocated. The 5GC may also keep UE context to allow the use of native security parameters when UE moves back from EPS to 5GS later.

Registration associated with the non-3GPP access in the AMF is not removed (i.e. an AMF that was serving the UE over both 3GPP and non-3GPP accesses does not consider the UE as deregistered over non 3GPP access and will remain registered and subscribed to subscription data updates in UDM).

<NUM> - <NUM>. Steps <NUM>-<NUM> from clause <NUM>. <NUM> (Tracking Area Update procedure with Serving GW change) in TS <NUM> [<NUM>] with the following modification:.

[conditional] Step <NUM> from clause <NUM>. <NUM> applies.

If some of the QoS Flow(s) for an EPS bearer were marked as deleted, the PGW-C+SMF may initiate bearer modification as specified in clause <NUM>. <NUM> of TS <NUM> [<NUM>] to remove the TFT filter(s) corresponding to the Packet Filter Set(s) in the QoS rules.

In an alternative aspect, the AMF can indicate "EBI replacement". In this alternative, a new subclause <NUM>. <NUM> is proposed as follows:.

Following procedures are updated to revoke the EPS bearer ID(s) assigned to the QoS Flow(s):.

When the AMF receives a new EBI allocation request, and the AMF determines that EBI value from range <NUM>-<NUM> should be used for the new request but there is no available value from range <NUM>-<NUM>, if there is value available from EBI range <NUM>-<NUM>, the AMF may perform EBI replacement to replace the EBI value(s) for QoS Flows(s) from value(s) in range <NUM>-<NUM> with value(s) in range <NUM>-<NUM>, and the SMF needs to update the UE and maybe NG-RAN of the EBI replacement.

<FIG> is a flowchart illustrating a method implemented in a network node (e.g., an AMF) for transferring PDU sessions (and their associated QoS Flows) of a UE during a mobility procedure in which the UE is moved from a 5GS to an EPS is provided. This process includes at least some aspects of at least some of the embodiments described above. The method comprises one or more of the steps illustrated in <FIG>. As illustrated, the network node determines that a target MME for the mobility procedure in the EPS supports a first number of EPS bearers (e.g., supports <NUM> EPS bearers) that is less than a second number of EPS bearer identities (EBIs) (e.g., <NUM> EBIs) assigned to a number of PDU sessions (and their associated QoS Flows) of the UE that are to be transferred from the 5GS to the EPS, as described above (step <NUM>). The network node also determines which of the PDU sessions and/or which of the associated QoS Flows of the UE are not to be transferred to the target MME, as described above (step <NUM>). Again, any of the embodiments described above relating to how this determination is made may be used. The network node releases or initiates release of the PDU sessions and/or QoS Flows that are not to be transferred to the target MME, as described above (<NUM>).

It should be understood that the steps of the method illustrated in <FIG> may be implemented in the 5GS to EPS handover procedure described above with respect to <FIG> and/or the EPS idle mode mobility procedure described above with respect to <FIG>. For example, step <NUM> and <NUM> may be implemented at step <NUM> of <FIG> (e.g., thereby incorporating some or all aspects of the additions to 3GPP TS <NUM> clause <NUM>. <NUM> show above in relation to step <NUM> of <FIG>. <NUM>-<NUM>) and/or step 5a of <FIG> (e.g., thereby incorporating some or all aspects of the additions to 3GPP TS <NUM> clause <NUM>. <NUM> show above in relation to step 5a of <NUM>. <NUM>-<NUM>). Step <NUM> may be implemented at step 12a-12c of <FIG> (e.g., thereby incorporating some or all aspects of the additions to 3GPP TS <NUM> clause <NUM>. <NUM> show above in relation to steps 12a-12c of <FIG>. <NUM>-<NUM>) and/or step 15a of <FIG> (e.g., thereby incorporating some or all aspects of the additions to 3GPP TS <NUM> clause <NUM>. <NUM> show above in relation to step 15a of <NUM>. <NUM>-<NUM>). In addition, the AMF may perform some or all of the additional aspects described above with respect to steps <NUM>-14a of <FIG> and/or steps <NUM>-<NUM> of <FIG>.

<FIG> is a schematic block diagram of a network node <NUM> according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node <NUM> may be, for example, a core network node (e.g., a MME), a network node that implements a core network function (e.g., an AMF), or a radio access node (e.g., the base station <NUM>-<NUM> or <NUM>-<NUM>) that implements all or part of the functionality of a network node (e.g., a NG-RAN base station, a E-UTRAN base station, a MME, an AMF, an SMF, etc.) described herein. As illustrated, the network node <NUM> includes a control system <NUM> that includes one or more processors <NUM> (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory <NUM>, and a network interface <NUM>. The one or more processors <NUM> are also referred to herein as processing circuitry. In addition, if the network node <NUM> is a radio access node, the network node <NUM> may further include one or more radio units <NUM> that each includes one or more transmitters <NUM> and one or more receivers <NUM> coupled to one or more antennas <NUM>. The radio units <NUM> may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) <NUM> is external to the control system <NUM> and connected to the control system <NUM> via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) <NUM> and potentially the antenna(s) <NUM> are integrated together with the control system <NUM>. The one or more processors <NUM> operate to provide one or more functions of the network node <NUM> as described herein (e.g., one or more functions of a NG-RAN base station, a E-UTRAN base station, a MME, an AMF, an SMF, etc. described herein, e.g., with respect to <FIG>). In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory <NUM> and executed by the one or more processors <NUM>.

<FIG> is a schematic block diagram that illustrates a virtualized embodiment of the network node <NUM> according to some embodiments of the present disclosure. As used herein, a "virtualized" network node is an implementation of the network node <NUM> in which at least a portion of the functionality of the network node <NUM> is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, in this example, the radio access node <NUM> includes one or more processing nodes <NUM> coupled to or included as part of a network(s) <NUM>. Each processing node <NUM> includes one or more processors <NUM> (e.g., CPUs, ASICs, FPGAs, and/or the like), memory <NUM>, and a network interface <NUM>. If the network node <NUM> is a radio access node, the network node <NUM> may also include the control system <NUM> and/or the one or more radio units <NUM>, as described above. The control system <NUM> may be connected to the radio unit(s) <NUM> via, for example, an optical cable or the like. If present, the control system <NUM> or the radio unit(s) are connected to the processing node(s) <NUM> via the network <NUM>.

In this example, functions <NUM> of the network node <NUM> described herein (e.g., one or more functions of a NG-RAN base station, a E-UTRAN base station, a MME, an AMF, an SMF, etc. described herein, e.g., with respect to <FIG>) are implemented at the one or more processing nodes <NUM> or distributed across the one or more processing nodes <NUM> and the control system <NUM> and/or the radio unit(s) <NUM> in any desired manner. In some particular embodiments, some or all of the functions <NUM> of the network node <NUM> described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) <NUM>. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) <NUM> and the control system <NUM> is used in order to carry out at least some of the desired functions <NUM>. Notably, in some embodiments, the control system <NUM> may not be included, in which case the radio unit(s) <NUM> communicate directly with the processing node(s) <NUM> via an appropriate network interface(s).

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the network node <NUM> or a node (e.g., a processing node <NUM>) implementing one or more of the functions <NUM> of the network node <NUM> in a virtual environment according to any of the embodiments described herein is provided.

<FIG> is a schematic block diagram of the network node <NUM> according to some other embodiments of the present disclosure. The network node <NUM> includes one or more modules <NUM>, each of which is implemented in software. The module(s) <NUM> provide the functionality of the network node <NUM> described herein (e.g., one or more functions of a NG-RAN base station, a E-UTRAN base station, a MME, an AMF, an SMF, etc. described herein, e.g., with respect to <FIG>).

Claim 1:
A method for transferring Protocol Data Unit, PDU, sessions, and their associated Quality of Service, QoS, Flows, of a User Equipment, UE, during a mobility procedure in which the UE is moved from a Fifth Generation System, 5GS, to an Evolved Packet System, EPS, the method performed by an Access and Mobility Management Function, AMF, in a <NUM> Core, 5GC, of the 5GS, and comprising:
- determining (<NUM>) that a target Mobility Management Entity, MME, for the mobility procedure in the EPS supports <NUM> EPS Bearers and that more than <NUM> EPS Bearer Identities, EBIs, are assigned to PDU sessions and/or QoS Flows that are to be transferred, wherein the EBIs are assigned to the QoS Flows of one or more PDU sessions, of the UE, said one or more PDU sessions that are to be transferred from the 5GS to the EPS;
- determining (<NUM>) which of the EBIs are not to be transferred to the target MME; and
- requesting the release (<NUM>) of the one or more PDU sessions and/or QoS Flows for which the EBIs are determined not to be transferred to the target MME.