Tunnel failure procedures

1. A method comprising:

determining, by a session management function (SMF) and based on a local configuration, a layer 2 tunneling protocol (L2TP) tunnel associated with a first protocol data unit (PDU) session of a wireless device;

selecting, by the SMF, a first user plane function (UPF) based on the first UPF supporting a L2TP service;

sending, by the SMF to the first UPF that supports the L2TP service, a request to establish the L2TP tunnel between the UPF and a L2TP network server (LNS) for the first protocol data unit (PDU) session; and

receiving, by the SMF from the first UPF, a message responding to the request to establish the L2TP tunnel, the message indicating a failure of the L2TP tunnel, the message comprising a tunnel failure cause information element indicating:

a L2TP tunnel failure of the L2TP tunnel; and

that a L2TP access concentrator (LAC) and LNS pair connection between the UPF and the LNS does not exist, wherein the UPF comprises the LAC.

2. The method of claim 1 , further comprising receiving, by the SMF from the wireless device, a first PDU session establishment message requesting the first PDU session for the wireless device.

3. The method of claim 1 , further comprising sending, by the SMF to the wireless device, a PDU session message for the first PDU session, wherein the PDU session message comprises the tunnel failure cause information element for the L2TP tunnel.

4. The method of claim 1 , further comprising sending, by the SMF to the wireless device, a PDU session release message for the first PDU session, wherein the PDU session release message comprises the tunnel failure cause information element.

5. The method of claim 1 , further comprising sending, by the SMF to the wireless device, a PDU session deactivation message for the first PDU session, wherein the PDU session deactivation message comprises the tunnel failure cause information element.

6. The method of claim 1 , further comprising receiving, by the SMF from the wireless device, a second PDU session establishment message requesting a second PDU session.

7. The method of claim 6 , further comprising determining, by the SMF and based on the tunnel failure cause information element, a second UPF for the second PDU session.

8. The method of claim 7 , further comprising sending, by the SMF to the second UPF, a N4 session request message comprising a create tunnel indication.

9. The method of claim 8 , wherein the N4 session request message further comprises a tunnel endpoint address, wherein the tunnel endpoint address comprises at least one of:

a L2TP access concentrator (LAC) address;

a L2TP network server (LNS) address;

a tunnel destination address of a generic routing encapsulation (GRE) tunnel;

a tunnel destination address of an IP-in-IP tunnel; or

a tunnel destination address of a GPRS tunnelling protocol (GTP) tunnel.

10. A session management function (SMF) comprising:

one or more processors; and

memory storing instructions that, when executed by the one or more processors, cause the SMF to perform operations comprising:

determining, based on a local configuration, a layer 2 tunneling protocol (L2TP) tunnel associated with a first protocol data unit (PDU) session of a wireless device;

selecting a first user plane function (UPF) based on the first UPF supporting a L2TP service;

sending, to the first UPF that supports the L2TP service, a request to establish the L2TP tunnel between the UPF and a L2TP network server (LNS) for the first protocol data unit (PDU) session; and

receiving, from the first UPF, a message responding to the request to establish the L2TP tunnel, the message indicating a failure of the L2TP tunnel, the message comprising a tunnel failure cause information element indicating:

a L2TP tunnel failure of the L2TP tunnel; and

that a L2TP access concentrator (LAC) and LNS pair connection between the UPF and the LNS does not exist, wherein the UPF comprises the LAC.

11. The SMF of claim 10 , wherein the operations further comprise receiving, from the wireless device, a first PDU session establishment message requesting the first PDU session for the wireless device.

12. The SMF of claim 10 , wherein the operations further comprise sending, to the wireless device, a PDU session message for the first PDU session, wherein the PDU session message comprises the tunnel failure cause information element for the L2TP tunnel.

13. The SMF of claim 10 , wherein the operations further comprise sending, to the wireless device, a PDU session release message for the first PDU session, wherein the PDU session release message comprises the tunnel failure cause information element.

14. The SMF of claim 10 , wherein the operations further comprise sending, to the wireless device, a PDU session deactivation message for the first PDU session, wherein the PDU session deactivation message comprises the tunnel failure cause information element.

15. The SMF of claim 10 , wherein the operations further comprise receiving, from the wireless device, a second PDU session establishment message requesting a second PDU session.

16. The SMF of claim 15 , wherein the operations further comprise determining, based on the tunnel failure cause information element, a second UPF for the second PDU session.

17. The SMF of claim 16 , wherein the operations further comprise sending, to the second UPF, a N4 session request message comprising a create tunnel indication.

18. The SMF of claim 17 , wherein the N4 session request message further comprises a tunnel endpoint address, wherein the tunnel endpoint address comprises at least one of:

a L2TP access concentrator (LAC) address;

a L2TP network server (LNS) address;

a tunnel destination address of a generic routing encapsulation (GRE) tunnel;

a tunnel destination address of an IP-in-IP tunnel; or

a tunnel destination address of a GPRS tunnelling protocol (GTP) tunnel.