Release message in small data transmission procedure

1. A method comprising:

receiving, by a first base station from a second base station, a request message indicating a small data transmission (SDT) procedure of a wireless device;

sending, to the second base station, an indication that the first base station keeps a context of the wireless device;

receiving, from the wireless device via the second base station, uplink data associated with the SDT procedure; and

sending, to the second base station and based on completion of the SDT procedure, a radio resource control (RRC) release message for the wireless device.

2. The method of claim 1 , wherein the request message indicating the SDT procedure comprises assistance information of the SDT procedure.

3. The method of claim 2 , wherein the assistance information comprises at least one of:

a traffic pattern of the SDT procedure;

an SDT indication of the wireless device;

uplink data information; and

downlink data information.

4. The method of claim 2 , wherein the assistance information comprises release assistance information (RAI).

5. The method of claim 4 , wherein the RAI indicates at least one of that:

no further uplink data is expected;

no further downlink data is expected;

a single downlink data transmission and no further uplink data transmission is expected;

more than a single uplink or downlink data transmission is expected;

a size of uplink data is smaller than an uplink data threshold; and

a size of downlink data is smaller than a downlink data threshold.

6. The method of claim 2 , further comprising determining, by the first base station and based on the assistance information, to keep the context of the wireless device.

7. The method of claim 6 , wherein the determining to keep the context of the wireless device is based on the assistance information indicating at least one of:

that further uplink data transmission is expected; and

that further downlink data transmission is expected.

8. The method of claim 1 , wherein the indication that the first base station keeps the context of the wireless device is sent in a response message that does not include the RRC release message.

9. The method of claim 1 , further comprising determining, by the first base station, the completion of the SDT procedure.

10. The method of claim 9 , wherein the determining the completion of the SDT procedure comprises determining that one or more transmissions and/or receptions of small data that are associated with SDT procedure and to be performed by the first base station are complete.

11. A first base station comprising one or more processors and memory storing instructions that, when executed by the base station, cause the first base station to perform operations comprising:

receiving, from a second base station, a request message indicating a small data transmission (SDT) procedure of a wireless device;

sending, to the second base station, an indication that the first base station keeps a context of the wireless device;

receiving, from the wireless device via the second base station, uplink data associated with the SDT procedure; and

sending, to the second base station and based on completion of the SDT procedure, a radio resource control (RRC) release message for the wireless device.

12. The first base station of claim 11 , wherein the request message indicating the SDT procedure comprises assistance information of the SDT procedure.

13. The first base station of claim 12 , wherein the assistance information comprises at least one of:

a traffic pattern of the SDT procedure;

an SDT indication of the wireless device;

uplink data information; and

downlink data information.

14. The first base station of claim 12 , wherein the assistance information comprises release assistance information (RAI).

15. The first base station of claim 14 , wherein the RAI indicates at least one of that:

no further uplink data is expected;

no further downlink data is expected;

a single downlink data transmission and no further uplink data transmission is expected;

more than a single uplink or downlink data transmission is expected;

a size of uplink data is smaller than an uplink data threshold; and

a size of downlink data is smaller than a downlink data threshold.

16. The first base station of claim 12 , wherein the operations further comprise determining, based on the assistance information, to keep the context of the wireless device.

17. The first base station of claim 16 , wherein the determining to keep the context of the wireless device is based on the assistance information indicating at least one of:

that further uplink data transmission is expected; and

that further downlink data transmission is expected.

18. The first base station of claim 11 , wherein the indication that the first base station keeps the context of the wireless device is sent in a response message that does not include the RRC release message.

19. The first base station of claim 11 , wherein the operations further comprise determining the completion of the SDT procedure.

20. A system, comprising:

a second base station comprising: one or more processors and memory storing instructions that, when executed by the one or more processors, cause the second base station to:

receive, from a wireless device, uplink data associated with a small data transmission (SDT) procedure;

send, to a first base station, a request message indicating the SDT procedure of the wireless device;

receive, from the first base station, an indication that the first base station keeps a context of the wireless device;

send, to the first base station, the uplink data associated with the SDT procedure; and

receive, from the first base station, a radio resource control (RRC) release message for the wireless device; and

the first base station, wherein the first base station comprises: one or more processors and memory storing instructions that, when executed by the one or more processors, cause the first base station to:

receive, from the second base station, the request message indicating the SDT procedure of the wireless device;

send, to the second base station, the indication that the first base station keeps the context of the wireless device;

receive, from the wireless device via the second base station, the uplink data associated with the SDT procedure; and

send, to the second base station and based on completion of the SDT procedure, the RRC release message for the wireless device.