Extended buffering management

1. A method comprising:

receiving, by an access and mobility management function (AMF) from a session management function (SMF), a first message indicating user plane activation for a wireless device, the first message comprising:

an identifier of a packet data unit session of the wireless device; and

a subscriber permanent identifier;

determining, by the AMF, that the wireless device is unreachable;

sending, by the AMF to the SMF and in response to the wireless device being unreachable, a second message to determine an extended buffering time; and

sending, by the SMF to a user plane function (UPF), a third message comprising the extended buffering time and indicating to buffer downlink data of the wireless device.

2. The method of claim 1 , wherein the second message comprises:

the extended buffering time; and

a packet count parameter.

3. The method of claim 1 , wherein the sending of the third message is in response to receiving, but the SMF, the second message, the second message comprising:

the extended buffering time; and

a packet count parameter.

4. The method of claim 3 , further comprising, buffering, by the UPF, the downlink data based on:

the extended buffering time; and

the packet count parameter.

5. The method of claim 4 , further comprising discarding by the UPF the downlink data upon expiry of the extended buffering time.

6. The method of claim 4 , further comprising transmitting by the UPF to the wireless device the downlink data via a base station upon reactivation of user plane.

7. The method of claim 6 , further comprising sending by the AMF to the SMF, upon activation of user plane, a downlink tunneling information.

8. The method of claim 7 , further comprising sending by the SMF to the UPF, the downlink tunneling information.

9. The method of claim 1 , wherein the AMF determines, in response to the wireless device being unreachable, the extended buffering time based on at least one of:

a wireless device response time;

one or more power saving mode parameters of the wireless device; or

one or more discontinuous reception or extended idle mode discontinuous reception parameters of the wireless device.

10. The method of claim 1 , further comprising:

deriving, by the AMF and in response to the determining, a first data buffer expiration time parameter based on the extended buffering time; and

retaining, by the AMF, the first data buffer expiration time parameter.

11. The method of claim 1 , further comprising sending, by a UPF to the SMF in response to receiving the downlink data for the wireless device, a fourth message indicating a data notification for the wireless device.

12. The method of claim 1 , wherein the AMF determines the extended buffering time in response to the wireless device being unreachable.

13. The method of claim 1 , further comprising receiving, by the SMF from the AMF, an indication of wireless device reachability.

14. The method of claim 13 , further comprising sending by the SMF to the wireless device via the AMF, the downlink data.

15. The method of claim 14 , further comprising sending by the AMF to the wireless device, the downlink data over a non access stratum message.

16. The method of claim 1 , further comprising determining by the SMF, a second data buffer expiration time parameter based on the extended buffering time.

17. The method of claim 16 , further comprising retaining by the SMF, the second data buffer expiration time parameter.

18. The method of claim 17 , further comprising receiving by the SMF from a UPF, the downlink data.

19. The method of claim 18 , further comprising buffering the downlink data at the SMF for a second time duration of the extended buffering time.

20. The method of claim 18 , further comprising buffering by the SMF, the downlink data based on a packet count parameter.