Enhanced NG-ran failure handling for NR-dc

Abstract

The embodiments herein relate to an enhanced Next Generation Radio Access Network (NG-RAN) failure handling for New Radio (NR) Dual Connectivity (DC) In some embodiments, there proposes a method (600) performed by a first network function implementing Session Management Function (SMF) (101). The method (600) may comprise the step of receiving (S601), from a s User Plane Function (UPF) (102), an error indication report associated with a first user plane connection of a split session of a dual connectivity, wherein, with the dual connectivity, a user equipment,UE, (161) is communicatively connected with the UPF (102) via the first user plane connection and a second user plane connection; transmitting (S603), to a master Radio Access Network (RAN) node (151) via an Access and Mobility Management Function (AMF) (103), a session resource management request indicating an error related to the first user plane connection of the dual connectivity.

Description

[0001] ENHANCED NG-RAN FAILURE HANDLING FOR NR-DC

[0002] Technical Field

[0003] The embodiments herein relate generally to the field of communication, and more particularly, the embodiments herein relate to enhanced Next Generation Radio Access Network (NG-RAN) failure handling for New Radio (NR) Dual Connectivity (DC).

[0004] Background

[0005] Figure 1 A is a schematic block diagram showing NR-DC scenario. As shown in Figure 1 A, a User Equipment (UE) 161 may be communicatively connected to a User Plane Function (UPF) 102 via two user plane connections, i.e., a user plane connection between a master RAN node (e.g., a master gNB 151) and the UPF 102, and a user plane connection between a secondary RAN node (e.g., a secondary gNB 152) and the UPF 102. For the NR-DC, when the UE 161 establishes a Protocol Data Unit (PDU) session, there may be split PDU sessions on both the master gNB 151 and secondary gNB 152; that is part(s) of the flows (e.g., Quality of Service (QoS) flow A) are transmitted over the user plane connection between the master gNB 151 and the UPF 102, and other part(s) of flows (e.g., QoS flow B) are transmitted over the user plane connection between the secondary gNB 152 and the UPF 102.

[0006] Figure IB is a schematic block diagram showing the problem for error indication from NG- RAN for NR-DC scenario. As shown in Figure IB, the UE 161 may establish a PDU session with split PDU sessions on both the master gNB 151 and the secondary gNB 152. If the UPF 102 receives error indication from the secondary gNB 152 for QoS flow B, the UPF 102 will report to the Session Management Function (SMF) 101. The SMF 101 will release the whole PDU session N2 resource via the Access and Mobility Management Function (AMF) 103, and as a result, the QoS flow A is also affected even though it is handled by the master-RAN and works properly.

[0007] Summary

[0008] As discussed above, the problem may be raised for current error indication from NG- RAN for NR-DC scenario. The QoS flow A may be released even though it is handled by the master-RAN and works properly. Such release of the PDU session resource in the NG-RAN for split PDU session will interrupt the UE’s payload transfer and negatively impact the UE’s 5G service perception.

[0009] The embodiments herein propose methods, network functions, computer readable medium and computer program product for an enhanced NG-RAN failure handling for NR-DC.

[0010] In some embodiments, there is proposed a method performed by a SMF. The method comprises a step of receiving, from a UPF, an error indication report associated with a first user plane connection of a split session of a dual connectivity, wherein, with the dual connectivity, a user equipment (UE) is communicatively connected with the UPF via the first user plane connection and a second user plane connection. The method comprises further transmitting, to a master RAN node via an AMF, a session resource management request indicating an error related to the first user plane connection of the dual connectivity.

[0011] In an embodiment, the session resource management request may be a session release command or a session modify command.

[0012] In an embodiment, the first user plane connection may be a user plane connection between the master RAN node and UPF; and the second user plane connection may be a user plane connection between a secondary RAN node and UPF.

[0013] In an embodiment, the first user plane connection may be a user plane connection between a secondary RAN node and the UPF; and the second user plane connection may be a user plane connection between the master RAN node and the UPF.

[0014] In an embodiment, the error indication report may comprise a first parameter indicating a remote Fully Qualified Tunnel Endpoint Identifier Data (F-TEID) for the first user plane connection.

[0015] In an embodiment, the error indication report may comprise a second parameter indicating a General Packet Radio Service (GPRS) Tunneling Protocol for the user plane (GTP-U) Peer Address for the first user plane connection.

[0016] In an embodiment, determining whether the effected session associated with the error indication report is a split session may be based on at least one of the F-TEID and the GTP-U Peer Address.

[0017] In an embodiment, the method may further comprise the step of transmitting, to the UPF, a first session modification request for buffering Downlink (DL) data transmission associated with the first user plane connection.

[0018] In an embodiment, the first session modification request may comprise a third parameter indicating that an apply action is "BUFF & NOCP".

[0019] In an embodiment, the session resource management request may comprise a fourth parameter indicating the affected session is a split session.

[0020] In an embodiment, the session resource management request may comprise a fifth parameter indicating tunnel information of the first user plane connection.

[0021] In an embodiment, the tunnel information of the first user plane connection may be Downlink (DL) Next Generation-User Plane Protocol (NG-U UP) Tunnel (TNL) information.

[0022] In an embodiment, the session resource management request may comprise a sixth parameter indicating whether to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

[0023] In an embodiment, the sixth parameter may be a swap indication indicating whether there is a swap.

[0024] In an embodiment, the first user plane connection may be to be re-established if there is no swap.

[0025] In an embodiment, the data transmission conveyed on the first user plane connection may be to be moved to the second user plane connection if there is a swap.

[0026] In an embodiment, the session resource management request may comprise a seventh parameter indicating an action reason.

[0027] In an embodiment, the action reason may comprise a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0028] In an embodiment, the method may further comprise the step of receiving, from the master RAN node via the AMF, a session resource management response indicating the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0029] In an embodiment, the session resource management response may comprise information related to a third user plane connection to be established to re-establish the first user plane connection.

[0030] In an embodiment, the information related to the third user plane connection to be established may be additional Downlink (DL) Quality of Service (QoS) Flow per Tunnel (TNL) information.

[0031] In an embodiment, the session resource management response may comprise information related to the second user plane connection to move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0032] In an embodiment, the information related to the second user plane connection may be Downlink (DL) Quality of Service (QoS) Flow per Tunnel (TNL) information.

[0033] In an embodiment, the method may comprise the step of transmitting, to the UPF, a second session modification request comprising the information related to the third user plane connection for establishing the third user plane connection.

[0034] In an embodiment, the session modification request may comprise an eighth parameter indicating N3 DL F-TEID for the third user plane connection.

[0035] In an embodiment, the second session modification request may comprise a ninth parameter indicating that an apply action is "FORW".

[0036] In an embodiment, the session release command may be a PDU session resource release command.

[0037] In an embodiment, the session modify command may be a PDU session resource modify command.

[0038] In an embodiment, the dual connectivity may be a NR-NR dual connectivity.

[0039] In some embodiments, there is proposed a method performed by a master RAN node for a dual connectivity, wherein, with the dual connectivity, a UE may be communicatively connected with a UPF via a first user plane connection and a second user plane connection. The method comprises a step of receiving, from a SMF via an AMF, a session resource management request indicating an error related to the first user plane connection of the dual connectivity. The method comprises further a step of transmitting, to the SMF via the AMF, a session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0040] In an embodiment, the session resource management request may be a session release command or a session modify command.

[0041] In an embodiment, the first user plane connection may be a user plane connection between the master RAN node and the UPF; and the second user plane connection may be a user plane connection between a secondary RAN node and the UPF.

[0042] In an embodiment, the first user plane connection may be a user plane connection between a secondary RAN node and the UPF; and the second user plane connection may be a user plane connection between the master RAN node and the UPF.

[0043] In an embodiment, the session resource management request may comprise a fourth parameter indicating the affected session is a split session.

[0044] In an embodiment, the session resource management request may comprise a fifth parameter indicating tunnel information of the first user plane connection.

[0045] In an embodiment, the tunnel information of the first user plane connection may be DL NG- U UP TNL information.

[0046] In an embodiment, the session resource management request may comprise a sixth parameter indicating whether to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

[0047] In an embodiment, the sixth parameter may be a swap indication indicating whether there is a swap.

[0048] In an embodiment, the first user plane connection may be to be re-established if there is no swap.

[0049] In an embodiment, the data transmission conveyed on the first user plane connection may be to be moved to the second user plane connection if there is a swap.

[0050] In an embodiment, the session resource management request may comprise a seventh parameter indicating an action reason.

[0051] In an embodiment, the action reason comprises a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0052] In an embodiment, the session resource management response may comprise information related to a third user plane connection to be established to re-establish the first user plane connection.

[0053] In an embodiment, the information related to the third user plane connection to be established may be additional DL QoS Flow per TNL information.

[0054] In an embodiment, the session resource management response may comprise information related to the second user plane connection to move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0055] In an embodiment, the information related to the second user plane connection may be DL QoS Flow per TNL information.

[0056] In an embodiment, the session release command may be a PDU session resource release command.

[0057] In an embodiment, the session modify command may be a PDU session resource modify command.

[0058] In an embodiment, the dual connectivity may be a NR-NR dual connectivity.

[0059] In some embodiments, there is proposed a network function, comprising: at least one processor; and a non-transitory computer readable medium coupled to the at least one processor. In an embodiment, the non-transitory computer readable medium may store instructions executable by the at least one processor, whereby the at least one processor may be configured to perform the above methods related to the above network functions. In an embodiment, the network function may be configured as the above SMF. In some embodiments, there is proposed a RAN node, comprising: at least one processor; and a non-transitory computer readable medium coupled to the at least one processor. In an embodiment, the non-transitory computer readable medium may store instructions executable by the at least one processor, whereby the at least one processor may be configured to perform the above methods related to the above RAN node. In an embodiment, the RAN node may be configured as the above master RAN node.

[0060] In some embodiments, there is proposed a system comprising a SMF, a master RAN node and an AMF. The SMF is configured to perform the method according to any one of the above methods performed by a SMF. The master RAN node is configured to perform a method according to any one of the above methods performed by the master RAN node. The AMF is configured to receive, from the SMF, a session resource management request indicating an error related to the first user plane connection of the dual connectivity. The AMF is further configured to send, to the master RAN node, the session resource management request. The AMF is further configured to receive, from the master RAN node, a session resource management response. The AMF is further configured to send, to the SMF, the session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0061] In some embodiments, there is proposed a computer readable medium stores computer readable code, which when run on an apparatus, may cause the apparatus to perform any of the above methods.

[0062] In some embodiments, there is proposed a computer program product stores computer readable code, which when run on an apparatus, may cause the apparatus to perform any of the above methods.

[0063] The embodiments herein may continue to provide the service for a split PDU session when receiving an error indication from NG-RAN, when detecting one user plane path failure from NG-RAN, or when detecting one NG-RAN restarted. As a result, the embodiments herein, may provide good user experience and good network KPI.

[0064] Brief Description of the Drawings

[0065] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the present disclosure and, together with the description, further serve to explain the principles of the disclosure and to enable a person skilled in the pertinent art to make and use the embodiments disclosed herein. In the drawings, like reference numbers indicate identical or functionally similar elements, and in which:

[0066] Figure 1 A is a schematic block diagram showing NR DC scenario;

[0067] Figure IB is a schematic block diagram showing the problem for error indication from NG- RAN for NR-DC scenario;

[0068] Figure 2A is a schematic signaling chart showing the messages in PDU session split at UPF during PDU session resource setup;

[0069] Figure 2B is a schematic signaling chart showing the messages in PDU session split at UPF during PDU session resource modify;

[0070] Figure 3 is a schematic signaling chart showing the messages in an example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein;

[0071] Figure 4 is a schematic signaling chart showing the messages in another example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein;

[0072] Figure 5 is a schematic signaling chart showing the messages in yet another example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein;

[0073] Figure 6 is a schematic flow chart showing an example method in the first network function, according to the embodiments herein;

[0074] Figure 7 is a schematic flow chart showing an example method in the master RAN node, according to the embodiments herein;

[0075] Figure 8 is a schematic block diagram showing an example first network function, according to the embodiments herein;

[0076] Figure 9 is a schematic block diagram showing an example master RAN node, according to the embodiments herein; and

[0077] Figure 10 is a schematic block diagram showing an example computer-implemented apparatus, according to the embodiments herein.

[0078] Detailed Description of Embodiments

[0079] Embodiments herein will be described in detail hereinafter with reference to the accompanying drawings, in which embodiments are shown. These embodiments herein may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. The elements of the drawings are not necessarily to scale relative to each other.

[0080] Reference to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in an embodiment" appearing in various places throughout the specification are not necessarily all referring to the same embodiment.

[0081] The term "A, B, or C" used herein means "A" or "B" or "C"; the term "A, B, and C" used herein means "A" and "B" and "C"; the term "A, B, and / or C" used herein means "A", "B", "C", "A and B", "A and C", "B and C" or "A, B, and C".

[0082] Error Indication

[0083] When a GTP-U node receives a G-PDU for which no Evolved Packet System (EPS) bearer context, Packet Data Protocol (PDP) context, PDU session, Multimedia Broadcast Multicast Service (MBMS) bearer context, or Radio Access Bearer (RAB) exists, the GTP-U node shall discard the G-PDU. If the Tunnel End Point identifier (TEID) of the incoming G-PDU is different from the value 'all zeros', the GTP-U node shall also return a GTP error indication to the originating node. GTP entities may include the "UDP Port" extension header (Type 0x40), in order to simplify the implementation of mechanisms that can mitigate the risk of Denial-of- Service attacks in some scenarios.

[0084] Handling of the received Error Indication and the Recovery Time Stamp is specified in 3GPP TS 23.007 Rel 18.2.1 and 3GPP TS 23.527 Rel 18.2.0.

[0085] The information element Tunnel Endpoint Identifier Data I shall be the TEID fetched from the G-PDU that triggered this procedure.

[0086] The information element GTP-U Peer Address shall be the destination address (e.g. destination IP address, MBMS Bearer Context) fetched from the original user data message that triggered this procedure. A GTP-U Peer Address can be a Gateway GPRS Support Node (GGSN), Serving GPRS Support Node (SGSN), Radio Network Controller (RNC), PDN Gateway (PGW), Serving Gateway (SGW), evolved Packet Data Gateway (ePDG), evolved Node B (eNodeB), Trusted Wireless Local Area Network (WLAN) Access Network (TWAN), Mobility Management Entity (MME), next Generation Node B (gNB), Non-3GPP Interworking Function (N3IWF), or UPF address. The TEID and GTP-U peer address together uniquely identify the related PDP context, RAB, PDU session or EPS bearer in the receiving node. The optional private extension contains vendor or operator specific information.

[0087] Table 1 : Information Elements in an Error Indication

[0088] Error Indication Received from 5G-AN:

[0089] Upon receiving an error indication from 5G-Access Network (AN), the UPF shall identify the session and send an error indication report to SMF. The error indication report includes the remote F-TEID (fully qualified tunnel endpoint identifier).

[0090] For a GTP-U error indication received from a 5G-AN, the SMF shall modify the Packet Forwarding Control Protocol (PFCP) session to instruct the UPF to buffer downlink packets.

[0091] If the user plane connection of the PDU session is seen as activated by the SMF, the SMF shall initiate an Namf_Communication_NlN2MessageTransfer service operation to request the 5G-AN to release the PDU session's resources.

[0092] PDU Session Split at UPF

[0093] (1) PDU Session Split at UPF during PDU session resource setup

[0094] Figure 2A is a schematic signaling chart showing the messages in PDU session split at UPF during PDU session resource setup.

[0095] When a new PDU session needs to be established, the 5GC may provide two Uplink (UL) TEID addresses during PDU session resource setup in order to allow for PDU session split. The Master Node (MN) may perform the Secondary Node (SN) addition or the MN-initiated SN modification procedure. If the MN decides to split the PDU session, the MN provides two Downlink (DL) TEID addresses and also the QoS flows associated with each tunnel.

[0096] (2) PDU Session Split at UPF during PDU session resource modify (5GC initiated)

[0097] Figure 2B is a schematic signaling chart showing the messages in PDU session split at UPF during PDU session resource modify.

[0098] The 5GC may provide an additional UL TEID address during PDU session resource modify in order to allow the MN to split the PDU session. The MN may perform the SN addition or the MN-initiated SN modification procedure. If the MN decides to split the PDU session, the MN provides a DL TEID address to be applied as the additional DL tunnel address and the QoS flows associated with that tunnel. As discussed above, a problem may occur with the current error indication from NG- RAN for NR-DC scenario. The QoS flow A (Figs. 1 A, IB) may be released even though it is handled by the master-RAN and works properly. Such release of the PDU session resource in the NG-RAN for split PDU session will interrupt the UE’s payload transfer and thus badly impact the UE’s 5G service perception.

[0099] To avoid the problem related to the release of QoS flow A in the above Figure IB, the embodiments propose that for the split PDU Session, when the secondary gNB or master gNB sends out error indication, instead of releasing the whole PDU Session N2 resource, the SMF can inform the master gNB that the UPF has received GTP-U error indication for a N3 DL F- TEID, or that the UPF has detected one of RAN nodes (identified by the IP address) has a (path) failure, i.e. no response has been received for a GTP-U echo request, or that UPF has detected one of RAN nodes (identified by the IP address) has restarted (with a changed recovery timestamp). Then the master gNB can decide to maintain the PDU resources and either reestablish the impacted QoS flow on the secondary gNB, or move the impacted QoS flow to the master gNB.

[0100] The embodiments may be implemented in the NR DC scenario as shown in Figure 1 A.

[0101] In the NR-DC scenario as shown in Figure 1 A:

[0102] □ the NR-DC can be triggered by NG-RAN, or triggered by 5GC during session establishment or session modification.

[0103] □ a split is normally triggered in RAN by a measurement report from the UE, mainly about the "mmWave" frequency band coverage.

[0104] □ control signaling in NR-DC deployment is between the Master-gNB and the 5GC (AMF / SMF).

[0105] □ secondary gNB could provide a user plane path for either all user traffic of a PDU session or for a subset of the QoS Flows associated with a PDU session (while Master-gNB handles a user plane path for remaining subset of QoS Flows if applicable).

[0106] □ SN has a signaling connection with Master-gNB.

[0107] In an embodiment, the NR DC scenario 100 may be configured in an OTT scenario. The OTT connection may be transparent in the sense that the participating communication devices through which the OTT connection passes are unaware of routing of uplink and downlink communications. For example, a base station (e.g., the gNB 151, the gNB 152) may not or needs not be informed about the past routing of an incoming downlink communication with data originating from the SMF 101, UPF 102, or AMF 103 to be forwarded (e.g., handed over) to a connected UE 161. Similarly, the base station (e.g., the gNB 151, the gNB 152) needs not be aware of the future routing of an outgoing uplink communication originating from the UE 161 towards the SMF 101, UPF 102, or AMF 103.

[0108] It should also be understood that a network function can be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., on a cloud infrastructure.

[0109] It should also be understood that, while NR NR-DC (i.e., both the master and secondary RAN nodes are gNBs) is shown in Figure 1 as an example architecture for implementing the embodiments, the embodiments may be also implemented in another architecture. As an example, either of the RAN nodes may be implemented as an eNB node, i.e., E-UTRA-NR DC (NE-DC) or NR-E-UTRA DC (EN-DC).

[0110] Figure 3 is a schematic signaling chart showing the messages in an example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein.

[0111] In an embodiment, the signaling chart in Figure 3 may include the following messages or steps:

[0112] Step 1 : the UE 161 may establish a PDU session with a split PDU session, which is split on both the master gNB 151 and secondary gNB 152. The SMF 101 knows the split PDU session.

[0113] Step 2: UL / DL payload for QoS flow A is transferred between the UPF 102 and the master gNB 151.

[0114] Step 3: UL / DL Payload for QoS flow B is transferred between the UPF 102 and the secondary gNB 152.

[0115] Step 4: One DL packet for QoS flow B (or QoS flow A) is sent to the secondary gNB 152 (or the master gNB 151).

[0116] Step 5a: The corresponding PDU session data can’t be found in the secondary gNB 152 due to error.

[0117] Step 5b: The corresponding PDU session data can’t be found in the master gNB 151 due to error.

[0118] Step 6a: The secondary gNB 151 may send an error indication (the remote F-TEID) to the UPF 102. Step 6b: The master gNB may send an error indication (the remote F-TEID) to the UPF 102.

[0119] Step 7: The UPF 102 may send a PFCP session report request (an error indication report) to the SMF 101, and the SMF 101 may send a PFCP session report response to the UPF 102.

[0120] Step 8: In an example, the SMF 101 does (if the secondary gNB 152 sent the error indication):

[0121] In a first alternative: Swap the impacted QoS flow B traffic to the available N3 tunnel of QoS flow A, to assure service continuity. This may involve sending a PFCP session modification request with update DL Forward Action Rule (FAR) of QoS Flow B (change the DL NG-RAN-N3 -F-TEID with N3-F-TEID of the Master gNB 151).

[0122] In a second alternative: Buffer the impacted QoS flow B traffic, to avoid the data loss. This may involve sending a PFCP Session modification request with update DL FAR of QoS Flow B (change the apply action with BUFF).

[0123] In another example, the SMF 101 (if the master gNB 151 sent the error indication) may:

[0124] As a first alternative: swap the impacted QoS flow A traffic to the available N3 tunnel of QoS flow B, to assure service continuity. This may involve sending a PFCP session modification request with update DL FAR of QoS Flow A (change the DL NG-RAN-N3- F-TEID with N3-F-TEID of the secondary gNB 152).

[0125] As a second alternative: Buffer the impacted QoS flow A traffic, to avoid the data loss. This may involve sending a PFCP Session modification request with update DL FAR of QoS Flow A (change the apply action with BUFF).

[0126] Step 9: Then the SMF 101 may send NlN2MessageTranfer with N2 PDU session resource modify request transfer (split session report\error indication report (NG-U UP TNL Information of QoS flow B (or QoS flow A), swap indicator, action reason) to the AMF 103.

[0127] The SMF 101 can inform the master gNB 151 that the UPF 102 has received a GTP- U error indication for a N3 DL F-TEID, or that the UPF 102 has detected one of RAN nodes (identified by the IP address) has a (path) failure, i.e. no response received for GTP- U echo request, or that UPF 102 has detected one of RAN nodes (identified by the IP address) has restarted (with a changed recovery timestamp).

[0128] The following table 2 describes information elements of the PDU session resource modify request transfer from the SMF 101 to the master gNB 151.

[0129] Table 2: PDU session resource modify request transfer

[0130] As shown in table 2, an information element "Split Session Report" may be provided in the PDU session resource modify request transfer to indicate the affected session is a split session. In addition, an information element "Error Indication Report" may be provided in the PDU session resource modify request transfer to indicate tunnel information of the user plane connection for which an error happened. For example, an information element "DL NG-U UP TNL Information" may be provided in the PDU session resource modify request transfer to indicate DL NG-U UP TNL Information for which an error happened.

[0131] In addition, an information element "Swap performed at UPF Indicator" may be provided in the PDU session resource modify request transfer to indicate whether to reestablish the user plane connection for which an error happened or move data transmission conveyed on the user plane connection for which an error happened to the other user plane connection. For example, an information element "Swap (true or false)" may be provided in the PDU session resource modify request transfer to indicate whether there is a swap.

[0132] In an example, the user plane connection for which an error happened is to be reestablished if there is no swap. In another example, the data transmission conveyed on the user plane connection for which an error happened is to be moved to the other user plane connection if there is a swap.

[0133] In addition, an information element "Action Reason" may be provided in the PDU session resource modify request transfer to indicate an action reason. For example, the action reason may be a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0134] Step 10: The AMF 103 may forward the N2 PDU session resource modify request (split session reportVDL NG-U UP TNL Information with error indication, swap indicator, action reason) to the master gNB 151, no matter there is an error on QoS flow A or QoS flow B.

[0135] Step I la: As specified in 3GPP TS37.340 10.14.3 PDU Session Split at UPF (RAN initiated QoS flows offloading from MN to SN), the master gNB 151 may re-establish the impacted QoS flow on the impacted gNB if swap indicator indicates no swap; referring to Figure 2 A and / or Figure 2B. That is, if there is an error on QoS flow A, the master gNB 151 may re-establish the QoS flow A on the master gNB 151; otherwise if there is an error on QoS flow B, the master gNB 151 may re-establish the QoS flow B on the secondary gNB 152.

[0136] Step 11b: As specified in 3GPP TS37.340 10.14.4 PDU Session Split at UPF (RAN initiates QoS flows offloading from SN to MN), the master gNB 151 may move the impacted QoS flow to the not impacted gNB if swap indicator indicates a swap; referring to Figure 2A and / or Figure 2B. That is, if there is an error on QoS flow A, the master gNB

[0137] 151 may move the QoS flow A to the secondary gNB 152; otherwise if there is an error on QoS flow B, the master gNB 151 may move the QoS flow B to the master gNB 151.

[0138] Step 12: The NG-RAN (i.e., the master gNB 151) may send N2 PDU session resource modify response (additional DL NG-U UP TNL information if re-establishes the impacted QoS flow on the secondary gNB 152). That is, if the QoS flow B is to be re-established on the secondary gNB 152, the master gNB 151 may provide additional DL NG-U UP TNL information for establishing a new QoS flow C between the secondary gNB 152 and the UPF 102. The additional DL NG-U UP TNL information is the tunnel information for the new QoS flow C.

[0139] Step 13: The AMF 103 may send Nsmf_PDUSession_UpdateSMContext request N2 PDU session resource modify response (additional DL NG-U UP TNL information) to the SMF 101. The SMF 101 may send Nsmf_PDUSession_UpdateSMContext response.

[0140] Step 14: The SMF 101 may send a PFCP session modification request (additional DL NG-U UP TNL information) to the UPF 102. The UPF 102 may send response.

[0141] Figure 4 is a schematic signaling chart showing the messages in another example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein.

[0142] In an embodiment, the signaling chart in Figure 4 may include the following messages or steps:

[0143] Step 1 : the UE 161 may establish a PDU session with a split PDU session, which is split on both the master gNB 151 and secondary gNB 152. The SMF 101 knows the split PDU session.

[0144] Step 2: UL / DL payload for QoS flow A is transferred between the UPF 102 and the master gNB 151.

[0145] Step 3: UL / DL Payload for QoS flow B is transferred between the UPF 102 and the secondary gNB 152.

[0146] Step 4: One DL packet for QoS flow B (or QoS flow A) is sent to the secondary gNB

[0147] 152 (or the master gNB 151).

[0148] Step 5a: The corresponding PDU session data can’t be found in the secondary gNB 152 due to error.

[0149] Step 5b: The corresponding PDU session data can’t be found in the master gNB 151 due to error.

[0150] Step 6a: The secondary gNB 151 may send an error indication (the remote F-TEID) to the UPF 102.

[0151] Step 6b: The master gNB may send an error indication (the remote F-TEID) to the UPF 102.

[0152] Step 7: The UPF 102 may send a PFCP session report request (an error indication report) to the SMF 101, the SMF 101 may send a PFCP session report response to the UPF 102.

[0153] Step 8: The SMF 101 may send a PFCP session modification request with update DL FAR of QoS flow B (change the apply action with BUFF & NOCP).

[0154] Step 9: Then the SMF 101 may send NlN2MessageTranfer with N2 PDU session resource release command transfer (error indication report (NG-U UP TNL information of QoS flow B) to the AMF 103.

[0155] The SMF 101 can inform the master gNB 151 that the UPF 102 has received a GTP- U error indication for a N3 DL F-TEID, or that the UPF 102 has detected one of RAN nodes (identified by the IP address) has a (path) failure, i.e. no response received for GTP- U Echo Request, or that UPF 102 has detected one of RAN nodes (identified by the IP address) has restarted (with a changed recovery timestamp).

[0156] The following table 3 describes information elements of the PDU session resource release request transfer from the SMF 101 to the master gNB 151.

[0157] Table 3: PDU session resource release command transfer

[0158] As shown in table 3, an information element "Split Session Report" may be provided in the PDU session resource release request transfer to indicate the affected session is a split session.

[0159] In addition, an information element "Error Indication Report" may be provided in the PDU session resource release request transfer to indicate tunnel information of the user plane connection for which an error happened. For example, an information element "DL NG-U UP TNL Information" may be provided in the PDU session resource release request transfer to indicate DL NG-U UP TNL Information for which an error happened.

[0160] In addition, an information element "Swap Indicator" may be provided in the PDU session resource release request transfer to indicate whether to re-establish the user plane connection for which an error happened or move data transmission conveyed on the user plane connection for which an error happened to the other user plane connection. For example, an information element "Swap (true or false)" may be provided in the PDU session resource release request transfer to indicate whether there is a swap.

[0161] In an example, the user plane connection for which an error happened is to be reestablished if there is no swap. In another example, the data transmission conveyed on the user plane connection for which an error happened is to be moved to the other user plane connection if there is a swap.

[0162] In addition, an information element "Action Reason" may be provided in the PDU session resource release request transfer to indicate an action reason. The action reason may be 5GC triggered QoS flow mobility due to load, error, or other factors. For example, the action reason may be a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0163] Step 10: The AMF 103 may forward the N2 PDU session resource release command (error indication report (NG-U UP TNL information of QoS flow B)) to the master gNB 151, no matter there is an error on QoS flow A or QoS flow B.

[0164] Step I la: As specified in 3GPP TS37.340 10.14.3 PDU session split at UPF (RAN initiated QoS flows offloading from MN to SN), the master gNB 151 may re-establish the impacted QoS flow on the impacted gNB if swap indicator indicates no swap; referring to Figure 2 A and / or Figure 2B. That is, if there is an error on QoS flow A, the master gNB 151 may re-establish the QoS flow A on the master gNB 151; otherwise if there is an error on QoS flow B, the master gNB 151 may re-establish the QoS flow B on the secondary gNB 152.

[0165] Step 11b: As specified in 3GPP TS37.340 10.14.4 PDU session split at UPF (RAN initiates QoS flows offloading from SN to MN), the master gNB 151 may move the impacted QoS flow to the not impacted gNB if swap indicator indicates a swap; referring to Figure 2A and / or Figure 2B. That is, if there is an error on QoS flow A, the master gNB 151 may move the QoS flow A to the secondary gNB 152; otherwise if there is an error on QoS flow B, the master gNB 151 may move the QoS flow B to the master gNB 151.

[0166] Step 12: The NG-RAN (i.e., the master gNB 151) may send N2 PDU session resource release response (additional DL NG-U UP TNL information if re-establishes the impacted QoS flow on the secondary gNB 152). That is, if the QoS flow B is to be re-established on the secondary gNB 152, the master gNB 151 may provide additional DL NG-U UP TNL information for establishing a new QoS flow C between the secondary gNB 152 and the UPF 102. The additional DL NG-U UP TNL information is the tunnel information for the new QoS flow C.

[0167] Step 13: The AMF 103 may send Nsmf_PDUSession_UpdateSMContext request N2 PDU session resource release response (additional DL NG-U UP TNL information) to the SMF 101. The SMF 101 may send Nsmf_PDUSession_UpdateSMContext response to the AMF 103.

[0168] Step 14: The SMF 101 may send a PFCP session modification request (additional DL NG-U UP TNL information) to the UPF 102. The UPF 102 may send response.

[0169] Figure 5 is a schematic signaling chart showing the messages in yet another example enhanced NG-RAN error indication handling procedure for NR-DC, according to the embodiments herein.

[0170] In an embodiment, the signaling chart in Figure 5 may include the following messages or steps:

[0171] Step 1. The user plane connection of an existing PDU session is activated. Downlink G-PDUs are sent towards the 5G-AN.

[0172] Step 2. The 5G-AN returns a GTP-U Error Indication if it does not have a corresponding GTP-U context (see clause 5.2).

[0173] Step 3. Upon receipt of a GTP-U Error Indication, the UPF shall identify the related PFCP session and send an Error Indication Report to the SMF, as specified in clause 5.10 of 3GPP TS 29.244. Step 4. For a GTP-U Error Indication received from a 5G-AN, the SMF shall modify the PFCP session to instruct the UPF to buffer downlink packets for the FAR in which the F-TEID configured is associated with the Error Indication Report.

[0174] Step 5. If the user plane connection of the PDU session is seen as activated by the SMF, the SMF shall initiate an Namf_Communication_NlN2MessageTransfer service operation to request the 5G-AN to release the PDU session's resources, as specified in clause 4.3.7 of 3GPP TS 23.502. If the affected PDU session is a split PDU session and if the SMF supports the feature, the SMF may indicate to the master 5G-AN node in the "PDU Session Resource Release Command Transfer" IE that the UPF has received GTP-U Error Indication for a N3 DL F-TEID.

[0175] Step 6. Upon receipt of an Namf_Communication_NlN2MessageTransfer request to transfer the PDU Session Resource Release Command, the AMF shall:

[0176] - proceed with the request, as specified in clause 5.2.2.3.1 of 3GPP TS 29.518, if the UE is in CM-CONNECTED state for the Access Network Type associated to the PDU session;

[0177] - otherwise, reject the request with an error indicating that the UE is in CM-IDLE state for the Access Network Type associated to the PDU session.

[0178] Step 7. If the AMF sent a PDU Session Resource Release Command to the 5G- AN, the PDU session's resource release is acknowledged to the SMF. If the affected PDU session is a split PDU session and if the 5G-AN supports the feature, the 5G-AN may not release the PDU session resource and may include a DL QoS Flow per TNL Information or an Additional DL QoS Flow per TNL Information in the "PDU Session Resource Release Response Transfer" to create a new N3 DL tunnel or to move the QoS flows conveyed by the failed GTP-U tunnel to the existing one.

[0179] Step 8. If the PDU session resource is released in the 5G-AN, The SMF initiates the Network Triggered Service Request procedure specified in clause 4.2.3.3 of 3GPP TS 23.502, to re-activate the user plane connection of the PDU session.

[0180] Steps 9, 10. If the PDU session resource is retained in the 5G-AN, the SMF modifies PFCP Session to provide the UPF with (new) N3 DL F-TEID(s) for the DL FARs, and the Apply Action is set to "FORW", so that user plane connection of the PDU session is reestablished.

[0181] Note that the schematic signaling chart shown in the Figures 3-5 may also be applicable for the error indication from the master gNB 151. In addition, the schematic signaling chart shown in the Figures 3-5 may also be applicable for the split PDU session handling during the following failed case:

[0182] - the UPF 102 detects user plane path failure to master gNB 151 or secondary gNB 152;

[0183] - the UPF 102 detects NG-RAN (either master gNB 151 or secondary gNB 152) restarted.

[0184] With the enhanced NG-RAN error indication handling procedure for NR-DC in the Figures 3-5, for the split PDU Session, when the secondary gNB or master gNB sends out Error Indication, instead of releasing the whole PDU Session N2 resource as standard stated, the SMF can inform the Master gNB that the UPF has received GTP-U Error Indication for a N3 DL F-TEID, or that the UPF has detected one of RAN nodes (identified by the IP address) has a (path) failure, i.e. no response received for GTP-U Echo Request, or that UPF has detected one of RAN nodes (identified by the IP address) has restarted (with a changed recovery timestamp), the Master gNB can decide to maintain the PDU resources and either reestablish impacted QoS flow on the Secondary gNB, or move impacted QoS flow to the Master gNB by using the existing TS37.340 mechanisms.

[0185] As a result, the embodiments may achieve the following technical effects:

[0186] □ Continue to provide the service for split PDU Session when receiving Error Indication from NG-RAN.

[0187] □ Continue to provide the service for split PDU Session when detecting one user plane path failure from NG-RAN.

[0188] □ Continue to provide the service for split PDU Session when detecting one NG- RAN restarted.

[0189] □ Provide good user experience.

[0190] □ Provide good network KPI.

[0191] Figure 6 is a schematic flow chart showing an example method 600 in the first network function, according to the embodiments herein. In an embodiment, the flow chart in Figure 6 may be implemented in the SMF 101 in Figures 1A-5.

[0192] The method 600 may begin with step S601, in which the SMF 101 may receive, from an UPF, an error indication report. The error indication report is associated with a first user plane connection of a split session of a dual connectivity.

[0193] In an embodiment, the error indication report may comprise a first parameter indicating a remote Fully Qualified Tunnel Endpoint Identifier Data (F-TEID) for the first user plane connection.

[0194] In an embodiment, the error indication report may comprise a second parameter indicating a General Packet Radio Service (GPRS) Tunneling Protocol for the user plane (GTP-U) Peer Address for the first user plane connection.

[0195] Then, the method 600 may proceed to an optional step S602, in which the SMF 101 may determine that an effected session associated with the error indication report is the split session. Alternatively, the step S602 may be performed by another network node, such as master RAN node.

[0196] In an embodiment, with the dual connectivity, a UE may be communicatively connected (i.e., communicatively coupled) with the UPF via the first user plane connection and a second user plane connection. Note that, the term "communicatively connected" does not mean to limit to directly communicatively connected.

[0197] In an embodiment, the first user plane connection may be a user plane connection between the master RAN node and the UPF; and the second user plane connection may be a user plane connection between a secondary RAN node and the UPF.

[0198] In an embodiment, the first user plane connection may be a user plane connection between a secondary RAN node and the UPF; and the second user plane connection may be a user plane connection between the master RAN node and the UPF.

[0199] In an embodiment, the dual connectivity may be a NR-NR dual connectivity.

[0200] In an embodiment, determining whether the effected session associated with the error indication report is a split session may be based on at least one of the F-TEID and the GTP-U Peer Address.

[0201] Then, the method 600 may proceed to step S603, the SMF 101 may transmit, to a master RAN node for the dual connectivity via the AMF, a session resource management request indicating an error related to the first user plane connection of the dual connectivity. Optionally, the session resource management request is sent for retaining the first user plane connection without releasing it. Optionally, the step S603 is performed in response to determining that the effected session is the split session. For example, the session resource management request may request re-establishing the first user plane connection or moving data transmission conveyed on the first user plane connection to the second user plane connection.

[0202] The AMF 103 may provide a transparent transmission service.

[0203] In an embodiment, the session resource management request may be a session release command or a session modify command.

[0204] In an embodiment, the session release command may be a PDU session resource release command.

[0205] In an embodiment, the session modify command may be a PDU session resource modify command.

[0206] In an embodiment, the session resource management request may comprise a fourth parameter indicating the affected session is a split session.

[0207] In an embodiment, the session resource management request may comprise a fifth parameter indicating tunnel information of the first user plane connection.

[0208] In an embodiment, the tunnel information of the first user plane connection may be Downlink (DL) Next Generation-User Plane Protocol (NG-U UP) Tunnel (TNL) information.

[0209] In an embodiment, the session resource management request may comprise a sixth parameter indicating whether to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

[0210] In an embodiment, the sixth parameter may be a swap indication indicating whether there is a swap.

[0211] In an embodiment, the first user plane connection may be to be re-established if there is no swap.

[0212] In an embodiment, the data transmission conveyed on the first user plane connection may be to be moved to the second user plane connection if there is a swap.

[0213] In an embodiment, the session resource management request may comprise a seventh parameter indicating an action reason.

[0214] In an embodiment, the action reason may comprise a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0215] Then, the method 600 may proceed to an optional step S604, in which the SMF 101 may transmit, to the UPF, a first session modification request for buffering Downlink (DL) data transmission associated with the first user plane connection.

[0216] In an embodiment, the first session modification request may comprise a third parameter indicating that an apply action is "BUFF & NOCP".

[0217] Then, the method 600 may proceed to an optional step S605, in which the SMF 101 may receive, from the master RAN node via the AMF, a session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection. In an embodiment, the session resource management response may comprise information related to a third user plane connection to be established to re-establish the first user plane connection.

[0218] In an embodiment, the information related to the third user plane connection to be established may be additional Downlink (DL) Quality of Service (QoS) Flow per Tunnel (TNL) information.

[0219] In an embodiment, the session resource management response may comprise information related to the second user plane connection to move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0220] In an embodiment, the information related to the second user plane connection may be Downlink (DL) Quality of Service (QoS) Flow per Tunnel (TNL) information.

[0221] Then, the method 600 may proceed to an optional step S606, in which the SMF 101 may transmit, to the UPF, a second session modification request comprising the information related to the third user plane connection for establishing the third user plane connection.

[0222] In an embodiment, the session modification request may comprise an eighth parameter indicating N3 DL F-TEID for the third user plane connection.

[0223] In an embodiment, the second session modification request may comprise a ninth parameter indicating that an apply action is "FORW".

[0224] The above steps are only examples, and the first network function may perform any related actions described with respect to Figures 1 A-5.

[0225] Figure 7 is a schematic flow chart showing an example method 700 in the master RAN node for a dual connectivity, according to the embodiments herein. In an embodiment, the flow chart in Figure 7 may be implemented in the master gNB 151 in Figures 1A-5.

[0226] The method 700 may begin with step S701, in which the master RAN node (such as the master gNB 151) may receive, from a SMF via the AMF, a session resource management request for retaining a user plane connection related to an error, without releasing it. For example, the session resource management request may request re-establishing the first user plane connection or moving data transmission conveyed on the first user plane connection to the second user plane connection. For example, the session resource management request may indicate an error related to the first user plane connection of the dual connectivity.

[0227] In an embodiment, with the dual connectivity, a UE may be communicatively connected with the UPF via a first user plane connection and a second user plane connection. In an embodiment, the dual connectivity may be a NR-NR dual connectivity.

[0228] In an embodiment, the session resource management request may be a session release command or a session modify command.

[0229] In an embodiment, the session release command may be a PDU session resource release command.

[0230] In an embodiment, the session modify command may be a PDU session resource modify command.

[0231] In an embodiment, the first user plane connection may be a user plane connection between the master RAN node and the UPF; and the second user plane connection may be a user plane connection between a secondary RAN node and UPF.

[0232] In an embodiment, the first user plane connection may be a user plane connection between a secondary RAN node and the UPF; and the second user plane connection may be a user plane connection between the master RAN node and the UPF.

[0233] In an embodiment, the session resource management request may comprise a fourth parameter indicating the affected session is a split session.

[0234] In an embodiment, the session resource management request may comprise a fifth parameter indicating tunnel information of the first user plane connection.

[0235] In an embodiment, the tunnel information of the first user plane connection may be DL NG- U UP TNL information.

[0236] In an embodiment, the session resource management request may comprise a sixth parameter indicating whether to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

[0237] In an embodiment, the sixth parameter may be a swap indication indicating whether there is a swap.

[0238] In an embodiment, the first user plane connection may be to be re-established if there is no swap.

[0239] In an embodiment, the data transmission conveyed on the first user plane connection may be to be moved to the second user plane connection if there is a swap.

[0240] In an embodiment, the session resource management request may comprise a seventh parameter indicating an action reason.

[0241] In an embodiment, the action reason comprises a GPRS Tunneling Protocol for the user plane (GTP-U) error indication, a user plane path failure, or a restart of a RAN node.

[0242] Then, the method 700 may proceed to an optional step S702, in which the master RAN node (such as the master gNB 151) may re-establish or indicate the SMF 101 to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

[0243] In an embodiment, the step S702 may further comprise an optional step S711 of determining that an effected session associated with the session resource management request is a split session conveyed on the first user plane connection of the dual connectivity; and an optional step S712 of in response determining that the effected session is a split session, re-establishing or indicating to SMF 101 to re-establish the first user plane connection or moving data transmission conveyed on the first user plane connection to the second user plane connection.

[0244] Then, the method 700 may proceed to step S703, in which the master RAN node (such as the master gNB 151) transmits, to the SMF via the AMF, a session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0245] In an embodiment, the session resource management response may comprise information related to a third user plane connection to be established to re-establish the first user plane connection.

[0246] In an embodiment, the information related to the third user plane connection to be established may be additional DL QoS Flow per TNL information.

[0247] In an embodiment, the session resource management response may comprise information related to the second user plane connection to move the data transmission conveyed on the first user plane connection to the second user plane connection.

[0248] In an embodiment, the information related to the second user plane connection may be DL QoS Flow per TNL information.

[0249] The above steps are only examples, and the master RAN node may perform any related actions described with respect to Figures 1 A-5.

[0250] In some embodiments, the first network function corresponds to the SMF 101 and the first network function implementing the SMF, the second network function correspond to the UPF and the second network function implementing the UPF, and the third network function to the AMF 103 and the third network function implementing the AMF.

[0251] Figure 8 is a schematic block diagram showing an example first network function 800, according to the embodiments herein. In an embodiment, the example first network function 800 in Figure 8 may be implemented as the SMF 101 in Figures 1A-5. In an embodiment, the first network function 800 may include at least one processor 801; and a non-transitory computer readable medium 802 coupled to the at least one processor 801. The non-transitory computer readable medium 802 may store instructions executable by the at least one processor 801, whereby the at least one processor 801 is configured to perform the steps in the example method 600 as shown in the schematic flow charts of Figure 6; the details thereof are omitted here. The first network function 800 may include other software or hardware components that are not shown in Fig.8.

[0252] Note that the first network function 800 may be implemented as hardware, software, firmware and any combination thereof. For example, the first network function 800 may include a plurality of units, circuities, modules or the like, each of which may be used to perform one or more steps of the example method 600 or one or more steps shown in Figures 1A-5 related to the first network function (such as the SMF 101).

[0253] Figure 9 is a schematic block diagram showing an example master RAN node 900, according to the embodiments herein. In an embodiment, the example master RAN node 900 in Figure 9 may be implemented as the master gNB 151 in Figures 1 A-5.

[0254] In an embodiment, the master RAN node 900 may include at least one processor 901; and a non-transitory computer readable medium 902 coupled to the at least one processor 901. The non-transitory computer readable medium 902 may store instructions executable by the at least one processor 901, whereby the at least one processor 901 is configured to perform the steps in the example method 700 as shown in the schematic flow charts of Figure 7; the details thereof are omitted here. The master RAN node may include other software or hardware components that are not shown in Fig.9.

[0255] Note that the master RAN node 900 may be implemented as hardware, software, firmware and any combination thereof. For example, the master RAN node 900 may include a plurality of units, circuities, modules or the like, each of which may be used to perform one or more steps of the example method 700 or one or more steps shown in Figures 1 A-5 related to the master RAN node (such as the master gNB 151).

[0256] Figure 10 is a schematic block diagram showing an example computer-implemented apparatus 1000, according to the embodiments herein. In an embodiment, the apparatus 1000 may be configured as the above mentioned apparatus’, such as the UE 161, the gNB 151, 152, the first network function (such as the SMF 101), the second network function (such as the UPF 102), or the third network function (such as the AMF 103).

[0257] In an embodiment, the apparatus 1000 may include but not limited to at least one processor such as Central Processing Unit (CPU) 1001, a computer-readable medium 1002, and a memory 1003. The memory 1003 may comprise a volatile (e.g., Random Access Memory, RAM) and / or non-volatile memory (e.g., a hard disk or flash memory). In an embodiment, the computer- readable medium 1002 may be configured to store a computer program and / or instructions, which, when executed by the processor 1001, causes the processor 1001 to carry out any of the above mentioned methods.

[0258] In an embodiment, the computer-readable medium 1002 (such as non-transitory computer readable medium) may be stored in the memory 1003. In another embodiment, the computer program may be stored in a remote location for example computer program product 1004 (also may be embodied as computer-readable medium), and accessible by the processor 1001 via for example carrier 1005.

[0259] The computer-readable medium 1002 and / or the computer program product 1004 may be distributed and / or stored on a removable computer-readable medium, e.g. diskette, CD (Compact Disk), DVD (Digital Video Disk), flash or similar removable memory media (e.g. compact flash, SD (secure digital), memory stick, mini SD card, MMC multimedia card, smart media), HD- DVD (High Definition DVD), or Blu-ray DVD, USB (Universal Serial Bus) based removable memory media, magnetic tape media, optical storage media, magneto-optical media, bubble memory, or distributed as a propagated signal via a network (e.g. Ethernet, ATM, ISDN, PSTN, X.25, Internet, Local Area Network (LAN), or similar networks capable of transporting data packets to the infrastructure node).

[0260] Furthermore, the following amendments are proposed to amend the 3GPP Technical Specification 3GPP TS 23.527 vl 8.2.0 (2023-12).

[0261] Title: GTP-U Error Indication related to a PDU Session with Dual Connectivity

[0262] Reason for change:

[0263] As specified in clause 5.3.2 of this specification, upon receiving the GTP-U Error Indication from the NG-RAN for a PDU session, the SMF will initiate PDU Session Resource Release procedure, to cleanup the PDU session resource in the NG-RAN, and then to re-establish it upon the DL Data Notification received from the UPF. This approach would not be optimal when dual connectivity is deployed in the network. In such scenario, a split PDU session would have two DL N3 F-TEIDs allocated in the master RAN node and a secondary RAN node. When the UPF receives GTP-U Error Indication from one of RAN nodes and report it to the SMF, it would lead extra signaling if the SMF simply deletes the whole PDU session resource and then re-establishes it.

[0264] The more importantly, the payload transfer is UNNECESSARILY interrupted for the traffic pertains to QoS flows of the PDU session are conveyed by the other DL tunnel (the healthy one).

[0265] This should be enhanced.

[0266] It is proposed:

[0267] 1. Upon receiving an Error Indication Report from the UPF for one of tunnels for a split PDU session, when requesting the 5G-AN to release the PDU session's resources, the SMF may indicate to the master 5G-AN node in the "PDU Session Resource Release Command Transfer" IE that the UPF has received GTP-U Error Indication for the N3 DL F-TEID;

[0268] 2. A supporting 5G-AN would include a DL QoS Flow per TNL Information or a Additional DL QoS Flow per TNL Information in the " PDU Session Resource Release Response Transfer" to create a new N3 DL tunnel or to move the QoS flows conveyed by the failed GTP-U tunnel to the existing one. The SMF will modify the corresponding PFCP session towards the UPF.

[0269] 3. A non-supporting 5G-AN would release the PDU session resource and the SMF will re-establish the PDU session resource.

[0270] Summary of change:

[0271] Add relevant requirement for receiving GTP-U Error Indication from a 5G-AN for a split PDU session.

[0272] Consequences if not approved:

[0273] Per existing requirement, for a split PDU session, UE's payload transferring is unnecessarily interrupted and extra network signalling will be triggered when the UPF receives GTP-U Error Indication from a 5G-AN.

[0274] Proposed changes (the proposed change includes the content to be added to (shown by underline) the 3GPP TS 23.527 v!8.2.0 (2023-12)): 5.3.2 Procedure for GTP-U Error Indication received from 5G-AN

[0275] 5.3.2.1 Principles

[0276] Figure (Referring to Figure 5): GTP-U Error Indication from 5G-AN

[0277] 1. The user plane connection of an existing PDU session is activated. Downlink G- PDUs are sent towards the 5G-AN.

[0278] 2. The 5G-AN returns a GTP-U Error Indication if it does not have a corresponding GTP-U context (see clause 5.2).

[0279] 3. Upon receipt of a GTP-U Error Indication, the UPF shall identify the related PFCP session and send an Error Indication Report to the SMF, as specified in clause 5.10 of 3GPP TS 29.244 [4],

[0280] 4. For a GTP-U Error Indication received from a 5G-AN, the SMF shall modify the PFCP session to instruct the UPF to buffer downlink packets for the FAR in which the F- TEID configured is associated with the Error Indication Report.

[0281] 5. If the user plane connection of the PDU session is seen as activated by the SMF, the SMF shall initiate an Namf_Communication_NlN2MessageTransfer service operation to request the 5G-AN to release the PDU session's resources, as specified in clause 4.3.7 of 3GPP TS 23.502 [5], If the affected PDU session is a split PDU session and if the SMF supports the feature, the SMF may indicate to the master 5G-AN node in the "PDU Session Resource Release Command Transfer" IE that the UPF has received GTP-U Error Indication for a N3 DL F-TEID.

[0282] 6. Upon receipt of an Namf_Communication_NlN2MessageTransfer request to transfer the PDU Session Resource Release Command, the AMF shall:

[0283] - proceed with the request, as specified in clause 5.2.2.3.1 of 3GPP TS 29.518 [6], if the UE is in CM-CONNECTED state for the Access Network Type associated to the PDU session;

[0284] - otherwise, reject the request with an error indicating that the UE is in CM-IDLE state for the Access Network Type associated to the PDU session.

[0285] 7. If the AMF sent a PDU Session Resource Release Command to the 5G-AN, the PDU session's resource release is acknowledged to the SMF. If the affected PDU session is a split PDU session and if the 5G-AN supports the feature, the 5G-AN may not release the PDU session resource and may include a DL QoS Flow per TNL Information or an Additional DL QoS Flow per TNL Information in the "PDU Session Resource Release Response Transfer" to create a new N3 DL tunnel or to move the QoS flows conveyed by the failed GTP-U tunnel to the existing one.

[0286] 8, If the PDU session resource is released in the 5G-AN, The SMF initiates the Network Triggered Service Request procedure specified in clause 4.2.3.3 of 3GPP TS 23.502 [5], to re-activate the user plane connection of the PDU session.

[0287] 9, 10, If the PDU session resource is retained in the 5G-AN, the SMF modifies PFCP Session to provide the UPF with (new) N3 DL F-TEID(s) for the DL FARs, and the Apply Action is set to "FORW", so that user plane connection of the PDU session is re-established.

[0288] Example embodiments are described herein with reference to block diagrams and / or flowchart illustrations of computer-implemented methods, apparatus (systems and / or devices) and / or non-transitory computer program products. It is understood that a block of the block diagrams and / or flowchart illustrations, and combinations of blocks in the block diagrams and / or flowchart illustrations, may be implemented by computer program instructions that are performed by one or more computer circuits. These computer program instructions may be provided to a processor circuit of a general purpose computer circuit, special purpose computer circuit, and / or other programmable data processing circuit to produce a machine, such that the instructions, which execute via the processor of the computer and / or other programmable data processing apparatus, transform and control transistors, values stored in memory locations, and other hardware components within such circuitry to implement the functions / acts specified in the block diagrams and / or flowchart block or blocks, and thereby create means (functionality) and / or structure for implementing the functions / acts specified in the block diagrams and / or flowchart block(s).

[0289] These computer program instructions may also be stored in a tangible computer- readable medium that may direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable medium produce an article of manufacture including instructions which implement the functions / acts specified in the block diagrams and / or flowchart block or blocks. Accordingly, embodiments of present inventive concepts may be embodied in hardware and / or in software (including firmware, resident software, micro-code, etc.) that runs on a processor such as a digital signal processor, which may collectively be referred to as “circuitry,” “a module” or variants thereof.

[0290] It should also be noted that in some alternate implementations, the functions / acts noted in the blocks may occur out of the order noted in the flowcharts. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Moreover, the functionality of a given block of the flowcharts and / or block diagrams may be separated into multiple blocks and / or the functionality of two or more blocks of the flowcharts and / or block diagrams may be at least partially integrated. Finally, other blocks may be added / inserted between the blocks that are illustrated, and / or blocks / operations may be omitted without departing from the scope of inventive concepts. Moreover, although some of the diagrams include arrows on communication paths to show a primary direction of communication, it is to be understood that communication may occur in the opposite direction to the depicted arrows.

[0291] Many variations and modifications can be made to the embodiments without substantially departing from the principles of the present inventive concepts. All such variations and modifications are intended to be included herein within the scope of present inventive concepts. Accordingly, the above disclosed subject matter is to be considered illustrative, and not restrictive, and the appended examples of embodiments are intended to cover all such modifications, enhancements, and other embodiments, which fall within the spirit and scope of present inventive concepts. Thus, to the maximum extent allowed by law, the scope of present inventive concepts is to be determined by the broadest permissible interpretation of the present disclosure including the following examples of embodiments and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

[0292] Abbreviations

[0293] 3 GPP 3rd Generation Partnership Project

[0294] AMF Access and Mobility Management Function

[0295] DC Dual Connectivity

[0296] DL Downlink

[0297] E-UTRA Evolved Universal Terrestrial Radio Access

[0298] FAR Forward Action Rule

[0299] F-TEID Fully Qualified TEID

[0300] GPRS General Packet Radio Service

[0301] GTP-U GPRS Tunneling Protocol for the User plane

[0302] MN Master Node NG-RAN Next Generation Radio Access Network

[0303] NG-U UP Next Generation-User Plane Protocol

[0304] NR New Radio

[0305] OTT Over The Top QoS Quality of Service

[0306] RAN Radio Access Network

[0307] SMF Session Management Function

[0308] SN Secondary Node

[0309] TEID Fully Qualified Tunnel Endpoint Identifier Data

[0310] UE User Equipment

[0311] UL Uplink

[0312] UPF User Plane Function.

Claims

CLAIMS1. A method (600) performed by a Session Management Function, SMF, (101), comprising:- receiving (S601), from a User Plane Function, UPF, (102), an error indication report associated with a first user plane connection of a split session of a dual connectivity, wherein, with the dual connectivity, a user equipment, UE, (161) is communicatively connected with the UPF (102) via the first user plane connection and a second user plane connection;- transmitting (S603), to a master Radio Access Network, RAN, node (151, 900) via an Access and Mobility Management Function, AMF, (103), a session resource management request indicating an error related to the first user plane connection of the dual connectivity.

2. The method (600) according to claim 1, wherein the session resource management request is a session release command or a session modify command.

3. The method (600) according to claim 1 or 2, wherein the first user plane connection is a user plane connection between the master RAN node (151) and the UPF (102); and wherein the second user plane connection is a user plane connection between a secondary RAN node (152) and the UPF (102).

4. The method (600) according to claim 1 or 2, wherein the first user plane connection is a user plane connection between a secondary RAN node (152) and the UPF (102); and wherein the second user plane connection is a user plane connection between the master RAN node (151, 900) and the UPF (102).

5. The method (600) according to any of claims 1 to 4, wherein the error indication report comprises a first parameter indicating a remote Fully Qualified Tunnel Endpoint Identifier Data, F-TEID, for the first user plane connection.

6. The method (600) according to claim 5, wherein the error indication report comprises a second parameter indicating a General Packet Radio Service, GPRS, Tunneling Protocol for the user plane, GTP-U, Peer Address for the first user plane connection.

7. The method (600) according to claim 6, wherein determining (S602) whether the effected session associated with the error indication report is a split session is based on at least one of the F-TEID and the GTP-U Peer Address.

8. The method (600) according to any of claims 1 to 7, further comprising:- transmitting (S604), to the UPF (102), a first session modification request for buffering Downlink, DL, data transmission associated with the first user plane connection.

9. The method (600) according to claim 8, wherein the first session modification request comprises a third parameter indicating that an apply action is "BUFF & NOCP".

10. The method (600) according to any of claims 1 to 9, wherein the session resource management request comprises a fourth parameter indicating the affected session is a split session.

11. The method (600) according to any of claims 1 to 10, wherein the session resource management request comprises a fifth parameter indicating tunnel information of the first user plane connection.

12. The method (600) according to claim 11, wherein the tunnel information of the first user plane connection is Downlink, DL, Next Generation-User Plane Protocol, NG-U UP, Tunnel, TNL, information.

13. The method (600) according to any of claims 1 to 12, wherein the session resource management request comprises a sixth parameter indicating whether to re-establish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

14. The method (600) according to claim 13, wherein the sixth parameter is a swap indication indicating whether there is a swap.

15. The method (600) according to claim 14, wherein the first user plane connection is to be re-established if there is no swap.

16. The method (600) according to claim 14, wherein the data transmission conveyed on the first user plane connection is to be moved to the second user plane connection if there is a swap.

17. The method (600) according to any of claims 1 to 16, wherein the session resource management request comprises a seventh parameter indicating an action reason.

18. The method (600) according to claim 17, wherein the action reason comprises a GPRS Tunneling Protocol for the user plane, GTP-U, error indication, the user plane path failure, or a restart of a RAN node (151, 152).

19. The method (600) according to any of claims 1 to 18, further comprising:- receiving (S605), from the master RAN node (151, 900) via the AMF (103), a session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

20. The method (600) according to claim 19, wherein the session resource management response comprises information related to a third user plane connection to be established to re-establish the first user plane connection.

21. The method (600) according to claim 20, wherein the information related to the third user plane connection to be established is additional Downlink, DL, Quality of Service, QoS, Flow per Tunnel, TNL, information.

22. The method (600) according to claim 19, wherein the session resource management response comprises information related to the second user plane connection to move the data transmission conveyed on the first user plane connection to the second user plane connection.

23. The method (600) according to claim 22, wherein the information related to the second user plane connection is Downlink, DL, Quality of Service, QoS, Flow per Tunnel, TNL, information.

24. The method (600) according to claim 20 or 21, further comprising:- transmitting (S606), to the UPF (102), a second session modification request comprising the information related to the third user plane connection for establishing the third user plane connection.

25. The method (600) according to claim 24, wherein the session modification request comprises an eighth parameter indicating N3 Downlink, DL, Fully Qualified Tunnel Endpoint Identifier Data, F-TEID, for the third user plane connection.

26. The method (600) according to claim 24 or 25, wherein the second session modification request comprises a ninth parameter indicating that an apply action is "FORW".

27. The method (600) according to claim 2, wherein the session release command is a Protocol Data Unit (PDU) session resource release command.

28. The method (600) according to claim 2, wherein the session modify command is a Protocol Data Unit (PDU) session resource modify command.

29. The method (600) according to any of claims 1 to 28, wherein the dual connectivity is a New Radio, NR, -NR dual connectivity.

30. A method (700) performed by a master Radio Access Network, RAN, node (151, 900) for a dual connectivity, wherein, with the dual connectivity, a user equipment, UE, (161) is communicatively connected with a User Plane Function, UPF, (102) via a first user plane connection and a second user plane connection, the method (700) comprising:- receiving (S701), from a Session Management Function, SMF, (101) via an Access and Mobility Management Function, AMF, (103) a session resource management request indicating an error related to the first user plane connection of the dual connectivity; and transmitting (S703), to the SMF (101) via the AMF (103), a session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

31. The method (700) according to claim 30, wherein the session resource management request is a session release command, particularly a Protocol Data Unit, PDU, session resource release command, or a session modify command, particularly a Protocol Data Unit, PDU, session resource modify command.

32. The method (700) according to claim 30 or 31, wherein the first user plane connection is a user plane connection between the master RAN node (151, 900) and the UPF (102); and wherein the second user plane connection is a user plane connection between a secondary RAN node (152) and the UPF (102).

33. The method (700) according to claim 30 or 31, wherein the first user plane connection is a user plane connection between a secondary RAN node (152) and the UPF (102); and wherein the second user plane connection is a user plane connection between the master RAN node (151, 900) and the UPF (102).

34. The method (700) according to any of claims 30 to 33, wherein the session resource management request comprises a fourth parameter indicating the affected session is a split session.

35. The method (700) according to any of claims 30 to 34, wherein the session resource management request comprises a fifth parameter indicating tunnel information of the first user plane connection.

36. The method (700) according to claim 36, wherein the tunnel information of the first user plane connection is Downlink, DL, Next Generation-User Plane Protocol, NG-U UP, Tunnel, TNL, information.

37. The method (700) according to any of claims 30 to 36, wherein the session resource management request comprises a sixth parameter indicating whether to reestablish the first user plane connection or move data transmission conveyed on the first user plane connection to the second user plane connection.

38. The method (700) according to claim 37, wherein the sixth parameter is a swap indication indicating whether there is a swap.

39. The method (700) according to claim 38, wherein the first user plane connection is to be re-established if there is no swap.

40. The method (700) according to claim 38, wherein the data transmission conveyed on the first user plane connection is to be moved to the second user plane connection if there is a swap.

41. The method (700) according to any of claims 30 to 40, wherein the session resource management request comprises a seventh parameter indicating an action reason.

42. The method (700) according to claim 41, wherein the action reason comprises a GPRS Tunneling Protocol for the user plane, GTP-U, error indication, a user plane path failure, or a restart of a RAN node (151, 152).

43. The method (700) according to any of claims 30 to 42, wherein the session resource management response comprises information related to a third user plane connection to be established to re-establish the first user plane connection.

44. The method (700) according to claim 43, wherein the information related to the third user plane connection to be established is additional Downlink, DL, Quality of Service, QoS, Flow per Tunnel, TNL, information.

45. The method (700) according to any of claims 30 to 43, wherein the session resource management response comprises information related to the second user plane connection, to move the data transmission conveyed on the first user plane connection to the second user plane connection.

46. The method (700) according to claim 45, wherein the information related to the second user plane connection is Downlink, DL, Quality of Service, QoS, Flow per Tunnel, TNL, information.

47. The method (700) according to any of claims 30 to 46, wherein the dual connectivity is a New Radio, NR, -NR dual connectivity.

48. A Session Management Function, SMF, (101, 800), comprising:- at least one processor (801); and- a non-transitory computer readable medium (802) coupled to the at least one processor (801), the non-transitory computer readable medium (802) contains instructions executable by the at least one processor (801), whereby the at least one processor (801) is configured to perform the method (600) according to any one of claims 1 to 29.

49. A master Radio Access Network, RAN, node (151, 900), comprising:- at least one processor (901); and- a non-transitory computer readable medium (902) coupled to the at least one processor (902), the non-transitory computer readable medium (902) contains instructions executable by the at least one processor (901), whereby the at least one processor (901) is configured to perform the method (700) according to any one of claims 30 to 47.

50. A system comprising a Session Management Function, SMF, (101, 800), a master Radio Access Network, RAN, node (151, 900), an Access and Mobility Management Function, AMF, (103), wherein the SMF (101, 800) is configured to perform the method (600) according to any one of claims 1 to 29; wherein the master RAN node (151, 900) is configured to perform a method (700) according to any one of claims 1 to 47; wherein the AMF (103) is configured to: receive, from the SMF (101, 800), a session resource management request indicating an error related to the first user plane connection of the dual connectivity; send, to the master RAN node (151, 900), the session resource management request; receive, from the master RAN node (151, 900), a session resource management response; and send, to the SMF (101, 800), the session resource management response indicating to re-establish the first user plane connection or move the data transmission conveyed on the first user plane connection to the second user plane connection.

51. A computer readable medium (1002) comprising computer readable code, which when run on an apparatus (1000), causes the apparatus (1000) to perform the method (600, 700) according to any one of claims 1-47.

52. A computer program product (1004) comprising computer readable code, which when run on an apparatus (1000), causes the apparatus (1000) to perform the method (600, 700) according to any one of claims 1-47.

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