WECLAIM:
1. A master Radio Access Network (RAN) node comprising:
a memory; and
at least one processor coupled to the memory and configured to send, to a control plane function in a core network, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in the core network, wherein
the modification request implicitly or explicitly indicates that PDU session split is needed for the already established first PDU session, and
the modification request causes the control plane function to control the user plane function to move a specific one or more Quality of Service (QoS) flows of a plurality of QoS flows associated with the already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
2. The master RAN node according to Claim 1, wherein the at least one processor is configured to receive from the control plane function, during a procedure of establishing the first PDU session performed before transmission of the modification request, a first indication indicating, on a per-PDU session basis or a per-QoS flow basis, whether or not the PDU session split for the first PDU session is permitted.
3. The master RAN node according to Claim 2, wherein the first indication is included in a message to be sent from the control plane function to the master RAN node to request setup of PDU session resources for the first PDU session.
4. The master RAN node according to any one of Claims 1 to 3, wherein the at least one processor is configured to receive a second

indication from the control plane function during a procedure of setting up or modifying a signaling connection between the master RAN node and the control plane function, the second indication indicating whether or not the PDU session split is permitted, the procedure of setting up or modifying the signaling connection being performed before transmission of the modification request.
5. The master RAN node according to Claim 4, wherein the second indication indicates, on a per-network slice basis, whether or not the PDU session split is permitted.
6. The master RAN node according to any one of Claims 1 to 5, wherein the at least one processor is configured to receive a third indication on a per-radio terminal basis from the control plane function before transmission of the modification request, the third indication indicating whether or not the PDU session split is permitted.
7. The master RAN node according to any one of Claims 1 to 6, wherein the modification request includes PDU-session type information explicitly indicating need for the PDU session split.
8. The master RAN node according to any one of Claims 1 to 7, wherein the modification request includes an identifier of each of the one or more QoS flows, in order to implicitly or explicitly indicate that the PDU session split is needed for the first PDU session.
9. The master RAN node according to any one of Claims 1 to 8, wherein the at least one processor is configured to send an inter-node message to the secondary RAN node, the inter-node message requesting allocation of resources for dual connectivity for the radio terminal and implicitly or explicitly indicating the PDU session split.
10. The master RAN node according to Claim 9, wherein the
inter-node message includes PDU-session-establishment type

information explicitly indicating that the PDU session split is to be applied to the first PDU session or to the one or more QoS flows.
11. The master RAN node according to any one of Claims 1 to 10, wherein the at least one processor is configured to transmit an RRC connection reconfiguration message to the radio terminal, the RRC connection reconfiguration message requesting implementation of a secondary cell group configuration for dual connectivity and implicitly or explicitly indicating the PDU session split.
12. The master RAN node according to Claim 11, wherein the secondary cell group configuration includes an identifier of the first PDU session and identifiers of one or more data radio bearers to be associated with the one or more QoS flows, in order to implicitly or explicitly indicate the PDU session split.
13. The master RAN node according to Claim 1 1 or 12, wherein the secondary cell group configuration includes data-radio-bearer type information explicitly indicating that the PDU session split is to be applied to the first PDU session or to the one or more QoS flows.
14. The master RAN node according to any one of Claims 1 to 1 3, wherein
the at least one processor is configured to send a handover request message to a target RAN node to request a handover of the radio terminal from the master RAN node to the target RAN node, and
the handover request message indicates that the PDU session split has been applied to the first PDU session or to the one or more QoS flows.
15. The master RAN node according to Claim 14, wherein the
handover request message includes PDU-session type information or
QoS-flow type information explicitly indicating that the PDU session
split has been applied to the first PDU session or to the one or more

QoS flows.
16. The master RAN node according to Claim 15, wherein
the handover request message includes terminal context
reference information for distingui shing the radio terminal at the secondary RAN node, and
the terminal context reference information includes an indication indicating that the PDU session split has been applied to the first PDU session or to the one or more QoS flows.
17. A control plane node to be located in a core network, the
control plane node comprising:
a memory; and
at least one processor coupled to the memory and configured to receive, from a master Radio Access Network (RAN) node, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in the core network, wherein
the modification request implicitly or explicitly indicates that PDU session split is needed for the already established first PDU session, and
the at least one processor is further configured to, in response to receiving the modification request, control the user plane function to move a specific one or more Quality of Service (QoS) flows of a plurality of QoS flows associated with the already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
18. The control plane node according to Claim 17, wherein the at
least one processor is configured to send to the master RAN node,
during a procedure of establishing the first PDU session performed
before transmission of the modification request, a first indication
indicating, on a per-PDU session basis or a per-QoS flow basis,

whether or not the PDU session split for the first PDU session is permitted.
19. The control plane node according to Claim 18, wherein the al least one processor is configured to incorporate the first indication into a message to be sent to the master RAN node to request setup of PDU session resources for the first PDU session.
20. The control plane node according to any one of Claims 17 to 19, wherein the at least one processor is configured to send a second indication to the master RAN node during a procedure of setting up or modifying a signaling connection between the master RAN node and the control plane node, the second indication indicating whether or not the PDU session split is permitted, the procedure of setting up or modifying the signaling connection being performed before transmission of the modification request.
21. The control plane node according to Claim 20, the second indication indicates, on a per-network slice basis, whether or not the PDU session split is permitted.
22. The control plane node according to any one of Claims 17 to
21, wherein the at least one processor is configured to send a third
indication on a per-radio terminal basis to the master RAN node before
transmission of the modification request, the third indication
indicating whether or not the PDU session split is permitted.
23. The control plane node according to any one of Claims 17 to
22, wherein the at least one processor is configured to, in response to
receiving the modification request, control the user plane function to
move the one or more QoS flows to the second tunnel.
24. The control plane node according to any one of Claims 17 to
23, wherein the modification request includes PDU-session type

information explicitly indicating need for the PDU session split.
25. The control plane node according to Claim 24, wherein the at least one processor is configured to, when the PDU session type information indicates that the PDU session split is needed or required, recognize that the first PDU session is needed to be split over two or more RAN nodes.
26. The control plane node according to Claim 25, wherein the at least one processor is configured to, when the PDU session type information does not indicate that the PDU session split is needed or required, recognize that the first PDU session is needed to be moved to another RAN node.
27. The control plane node according to any one of Claims 17 to
26, wherein the modification request includes an identifier of each of
the one or more QoS flows, in order to implicitly or explicitly indicate
that the PDU session split is needed for the first PDU session
28. The control plane node according to any one of Claims 17 to
27, wherein
the modification request includes a downlink transport network layer (TNL) address for the first PDU session, and
the at least one processor is configured to determine whether the downlink TNL address is a new downlink address or an additional downlink address, depending on whether the modification request indicates the PDU session split is needed.
29. A secondary Radio Access Network (RAN) node comprising:
a memory; and
at least one processor coupled to the memory and configured to receive an inter-node message from a master RAN node, the inter-node message requesting allocation of resources for dual connectivity for a radio terminal, wherein

the inter-node message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows are transferred through a second tunnel between the user plane function and the secondary RAN node.
30. The secondary RAN node according to Claim 29, wherein the inter-node message includes PDU-session-establishment type information explicitly indicating that the PDU session split is to be applied to the first PDU session or to the one or more second QoS flows.
31. The secondary RAN node according to Claim 29 or 30, wherein
the at least one processor is configured to transmit to the radio terminal an RRC connection reconfiguration message indicating a secondary cell group configuration for the dual connectivity, and
the RRC connection reconfiguration message also implicitly or explicitly indicates that the PDU session split is to be applied to the first PDU session.
32. A radio terminal comprising:
a memory; and
at least one processor coupled to the memory and configured to receive an RRC connection reconfiguration message from a master Radio Access Network (RAN) node or a secondary RAN node, the RRC connection reconfiguration message indicating a secondary cell group configuration for dual connectivity, wherein

the RRC connection reconfiguration message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows are transferred through a second tunnel between the user plane function and the secondary RAN node.
33. The radio terminal according to Claim 32, wherein the secondary cell group configuration includes an identifier of the first PDU session and identifiers of one or more data radio bearers to be associated with the one or more QoS flows, in order to implicitly or explicitly indicate the PDU session split.
34. The radio terminal according to Claim 32 or 33, wherein the secondary cell group configuration includes type information explicitly indicating that the PDU session split is to be applied to the first PDU session or to the one or more QoS flows.
35. A method performed by a master Radio Access Network (RAN) node, the method comprising:
sending, to a control plane function in the core network, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in a core network, wherein
the modification request implicitly or explicitly indicates that PDU session split is needed for the already established first PDU session, and
the modification request causes the control plane function to control the user plane function to move a specific one or more Quality

of Service (QoS) flows of a plurality of QoS flows associated with the already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
36. A method performed by a control plane node to be located in
a core network, the method comprising:
receiving, from a master Radio Access Network (RAN) node, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in the core network, the modification request implicitly or explicitly indicating that PDU session split is needed for the already established first PDU session; and
controlling the user plane function to move a specific one or more Quality of Service (QoS) flows of a plurality of QoS flows associated with the already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
37. A method performed by a secondary Radio Access Network
(RAN) node, the method comprising:
receiving an inter-node message from a master RAN node, the inter-node message requesting allocation of resources for dual connectivity for a radio terminal, wherein
the inter-node message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows

are transferred through a second tunnel between the user plane function and the secondary RAN node.
38. A method performed by a radio terminal, the method
comprising:
receiving an RRC connection reconfiguration message from a master Radio Access Network (RAN) node or a secondary RAN node, the RRC connection reconfiguration message indicating a secondary cell group configuration for dual connectivity, wherein
the RRC connection reconfiguration message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows are transferred through a second tunnel between the user plane function and the secondary RAN node.
39. A non-transitory computer readable medium storing a
program for causing a computer to perform a method for a master
Radio Access Network (RAN) node, wherein
the method comprises sending, to a control plane function in the core network, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in a core network, wherein
the modification request implicitly or explicitly indicates that PDU session split is needed for the already established first PDU session, and
the modification request causes the control plane function to control the user plane function to move a specific one or more Quality of Service (QoS) flows of a plurality of QoS flows associated with the

already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
40. A non-transitory computer readable medium storing a
program for causing a computer to perform a method for a control
plane node to be located in a core network, wherein the method
comprising:
receiving, from a master Radio Access Network (RAN) node, a modification request for modification of a first PDU session already established between a radio terminal and a user plane function in the core network, the modification request implicitly or explicitly indicating that PDU session split is needed for the already established first PDU session; and
controlling the user plane function to move a specific one or more Quality of Service (QoS) flows of a plurality of QoS flows associated with the already established first PDU session from a first tunnel between the user plane function and the master RAN node to a second tunnel between the user plane function and a secondary RAN node.
41. A non-transitory computer readable medium storing a
program for causing a computer to perform a method for a secondary
Radio Access Network (RAN) node, wherein
the method comprises receiving an inter-node message from a master RAN node, the inter-node message requesting allocation of resources for dual connectivity for a radio terminal, wherein
the inter-node message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first

tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows are transferred through a second tunnel between the user plane function and the secondary RAN node.
42. A non-transitory computer readable medium storing a program for causing a computer to perform a method for a radio terminal, wherein
the method comprises receiving an RRC connection reconfiguration message from a master Radio Access Network (RAN) node or a secondary RAN node, the RRC connection reconfiguration message indicating a secondary cell group configuration for dual connectivity, wherein
the RRC connection reconfiguration message also implicitly or explicitly indicates that PDU session split is to be applied to a first PDU session already established between the radio terminal and a user plane function in a core network, and
the PDU session split includes a configuration in which one or more first Quality of Service (QoS) flows of a plurality of QoS flows associated with the first PDU session are transferred through a first tunnel between the user plane function and the master RAN node, and in which one or more second QoS flows of the plurality of QoS flows are transferred through a second tunnel between the user plane function and the secondary RAN node.