Method and apparatus for indirect data forwarding

1 . A method performed by a mobility management node in a first system, the method comprising:

sending, to a serving gateway entity in the first system, a request for creating an indirect data forwarding tunnel, wherein the request comprises an indication flag indicating to the serving gateway entity that an indirect data forwarding tunnel is to be created with a user plane function entity in a second system; and

receiving a response to the request from the serving gateway entity, wherein:

the indication flag is present and set to 1, when the indirect data forwarding tunnel is required for at least one user plane route to or from the user plane function entity in the second system during an inter system handover via an N26 interface;

the indication flag is absent or is present and not set to 1, when the indirect data forwarding tunnel is required for a mobility procedure other than the inter system handover via the N26 interface;

the inter system handover is from the first system to the second system or from the second system to the first system; and

the first system is an evolved packet system (EPS) and the second system is a fifth generation system (5GS).

2 . The method according to claim 1 , wherein the request is sent during the inter system handover.

3 . The method according to claim 2 , wherein the N26 interface is between an access and mobility management function (AMF) in the 5GS and a mobility management entity (MME) in the EPS.

4 . The method according to claim 3 , wherein the indirect data forwarding tunnel is for one of the following:

indirect data forwarding from the user plane function entity in the second system to a user plane of the serving gateway entity in the first system, when the inter-system handover is from the 5GS to the EPS; or

indirect data forwarding from the user plane of the serving gateway entity in the first system to the user plane function entity in the second system, when the inter-system handover is from the EPS to the 5GS.

5 . The method according to claim 1 , wherein one or more of the following applies:

the request is a Create Indirect Data Forwarding Tunnel Request and the response is a Create Indirect Data Forwarding Tunnel Response;

the mobility management node is a mobility management entity (MME);

the serving gateway entity is a serving gateway (SGW) or an SGW control plane (SGW-C); and

the user plane function entity is a User plane Function (UPF).

6 . A method performed by a serving gateway entity in a first system, comprising:

receiving, from a mobility management node in the first system, a request for creating an indirect data forwarding tunnel, wherein the request comprises an indication flag indicating to the serving gateway entity that an indirect data forwarding tunnel is to be created with a user plane function entity in a second system;

processing the request to generate a response for the request; and

sending, to the mobility management node, the response generated for the request, wherein:

the indication flag is present and set to 1, when the indirect data forwarding tunnel is required for at least one user plane route to or from the user plane function entity in the second system during an inter system handover via an N26 interface;

the indication flag is absent or is present and not set to 1, when the indirect data forwarding tunnel is required for a mobility procedure other than the inter system handover via the N26 interface;

the inter system handover is from the first system to the second system or from the second system to the first system; and

the first system is an evolved packet system (EPS) and the second system is a fifth generation system (5GS).

7 . The method according to claim 6 , wherein the request is received during the inter system handover.

8 . The method according to claim 7 , wherein the N26 interface between an access and mobility management function (AMF) in the 5GS and a mobility management entity (MME) in the EPS.

9 . The method according to claim 8 , wherein the indirect data forwarding tunnel is for one of the following:

indirect data forwarding from the user plane function entity in the second system to a user plane of the serving gateway entity in the first system, when the inter-system handover is from the 5GS to the EPS; or

indirect data forwarding from the user plane of the serving gateway entity in the first system to the user plane function entity in the second system, when the inter-system handover is from the EPS to the 5GS.

10 . The method according to claim 6 , wherein one or more of the following applies:

the request is a Create Indirect Data Forwarding Tunnel Request and the response is a Create Indirect Data Forwarding Tunnel Response;

the mobility management node is a mobility management entity (MME);

the serving gateway entity is a serving gateway (SGW) or an SGW control plane (SGW-C); and

the user plane function entity is a User plane Function (UPF).

11 . A mobility management node in a first system, the mobility management node comprising:

a processor; and

a memory operably coupled to the processor and containing instructions executable by said processor, whereby said mobility management node is operative to:

send, to a serving gateway entity in the first system, a request for creating an indirect data forwarding tunnel, where the request comprises an indication flag indicating to the serving gateway entity that an indirect data forwarding tunnel is to be created with a user plane function entity in a second system; and

receive a response to the request from the serving gateway entity, wherein:

the indication flag is present and set to 1, when the indirect data forwarding tunnel is required for at least one user plane route to or from the user plane function entity in the second system during an inter system handover via an N26 interface;

the indication flag is absent or is present and not set to 1, when the indirect data forwarding tunnel is required for a mobility procedure other than the inter system handover via the N26 interface;

the inter system handover is from the first system to the second system or from the second system to the first system; and

the first system is an evolved packet system (EPS) and the second system is a fifth generation system (5GS).

12 . A serving gateway entity in a first system, the serving gateway entity comprising:

a processor; and

a memory operably coupled to the processor and containing instructions executable by said processor, whereby said mobility management node is operative to perform operations corresponding to the method of claim 6 .