Indicating a packet data unit session as unavailable

1. A method comprising:

determining that at least one network slice used for a packet data unit session is unavailable;

transmitting information to a session management function or a first mobility management function indicating that the packet data unit session is to be released; and

transmitting a message to a remote unit indicating allowed network slices as a result of determining that the at least one network slice used for the packet data unit session is unavailable.

2. The method of claim 1 , wherein transmitting the information to the first mobility management function comprises determining that the remote unit has moved to a second mobility management function.

3. The method of claim 1 , wherein transmitting the information to the session management function comprises determining that the remote unit is served by the first mobility management function.

4. The method of claim 1 , wherein the information indicates that the packet data unit session is to be released without notifying a corresponding remote unit.

5. The method of claim 1 , wherein the information indicates that the packet data unit session is to be released with notification given to a corresponding remote unit.

6. The method of claim 2 , wherein the information indicates that the first mobility management function is to release the packet data unit session.

7. The method of claim 2 , wherein the first mobility management function determines based on the information whether to initiate release of the packet data unit session, the first mobility management function communicates with the session management function to release the packet data unit session, and the packet data unit session is released without providing notification to a remote unit corresponding to the packet data unit session.

8. The method of claim 1 , further comprising receiving feedback indicating that the first mobility management function released the packet data unit session.

9. The method of claim 1 , wherein the message to the remote unit further indicates a modified packet data unit session status.

10. The method of claim 9 , wherein the remote unit locally releases a packet data unit session context after receiving the packet data unit session status.

11. An apparatus comprising:

a processor that determines that at least one network slice used for a packet data unit session is unavailable; and

a transmitter that:

transmits information to a session management function or a first mobility management function indicating that the packet data unit session is to be released; and

transmits a message to a remote unit indicating allowed network slices as a result of determining that the at least one network slice used for the packet data unit session is unavailable.

12. The apparatus of claim 11 , wherein the transmitter transmitting the information to the first mobility management function comprises the processor determining that the remote unit has moved to a second mobility management function.

13. The apparatus of claim 11 , wherein the transmitter transmitting the information to the session management function comprises determining that the remote unit is served by the first mobility management function.

14. The apparatus of claim 11 , wherein the information indicates that the packet data unit session is to be released without notifying a corresponding remote unit.

15. The apparatus of claim 11 , wherein the information indicates that the packet data unit session is to be released with notification given to a corresponding remote unit.

16. The apparatus of claim 12 , wherein the information indicates that the first mobility management function is to release the packet data unit session.

17. The apparatus of claim 12 , wherein the first mobility management function determines based on the information whether to initiate release of the packet data unit session, the first mobility management function communicates with the session management function to release the packet data unit session, and the packet data unit session is released without providing notification to a remote unit corresponding to the packet data unit session.

18. The apparatus of claim 11 , further comprising a receiver that receives feedback indicating that the first mobility management function released the packet data unit session.

19. The apparatus of claim 11 , wherein the message to the remote unit further indicates a modified packet data unit session status.

20. The apparatus of claim 19 , wherein the remote unit locally releases a packet data unit session context after receiving the packet data unit session status.