Communication system

1. A first base station comprising:

a controller; and

a transceiver,

wherein the controller is configured to:

support a user equipment (UE) configured to perform optimization for a Cellular Internet of Things (CIoT) operation;

control the transceiver to receive, from the UE, a radio resource control (RRC) message for re-establishing an RRC connection suspended between the UE and a second base station storing a UE context for the UE through a suspend procedure,

wherein the RRC message includes a Radio Network Temporary Identifier (RNTI), and

wherein the RNTI identifies the second base station

retrieve the UE context based on the RNTI by controlling the transceiver to send a first signaling message including the RNTI to the second base station and controlling the transceiver to receive a second signaling message including the UE context from the second base station; and

re-establish the RRC connection with the UE using the UE context.

2. The first base station according to claim 1 , wherein the RNTI is an ID supplied to the UE by the second base station upon suspending the RRC connection.

3. The first base station according to claim 1 , wherein the suspend procedure requires interaction between a core network node for control plane and a core network node for user plane.

4. The first base station according claim 1 , wherein the controller is configured to determine that the RRC connection is suspended.

5. The first base station according to claim 1 , wherein the RNTI is made based on an ID of the second base station.

6. The first base station according to claim 1 , wherein the controller is configured to control the transceiver to send, after reception of the second signaling message, a request to the second base station for releasing the UE context at the second base station.

7. The first base station according to claim 1 , wherein the RRC connection is a connection for an Internet of Things (IoT) device.

8. The first base station according to claim 1 , wherein the controller is configured to control the transceiver to receive the RRC message in a case where Access Stratum (AS) security has not been activated.

9. A method performed by a first base station, the method comprising:

supporting a user equipment (UE) configured to perform optimization for a Cellular Internet of Things (CIoT) operation;

receiving, from the UE, a radio resource control (RRC) message for re-establishing an RRC connection suspended between the UE and a second base station storing a UE context for the UE through a suspend procedure,

wherein the RRC message includes Radio Network Temporary Identifier (RNTI), and

wherein the RNTI identifies the second base station;

retrieving the UE context based on the RNTI by sending a first signaling message including the RNTI to the second base station and receiving a second signaling message including the UE context from the second base station; and

re-establishing the RRC connection with the UE using the UE context.

10. The method according to claim 9 , wherein the receiving is performed in a case where Access Stratum (AS) security has not been activated.

11. The method according to claim 10 , wherein the RNTI is an ID supplied to the UE by the second base station upon suspending the RRC connection.

12. The method according to claim 10 , wherein the suspend procedure requires interaction between a core network node for control plane and a core network node for user plane.

13. The method according to claim 10 , further comprising determining that the RRC connection is suspended.

14. The method according to claim 10 , wherein the RNTI is made based on an ID of the second base station.

15. The method according to claim 10 , further comprising sending, after reception of the second signaling message, a request to the second base station for releasing the UE context at the second base station.

16. The method according to claim 10 , wherein the RRC connection is a connection for an Internet of Things (IoT) device.

17. A user equipment (UE) comprising:

a controller; and

a transceiver,

wherein the controller is configured to:

perform optimization for a Cellular Internet of Things (CIoT) operation;

control the transceiver to send, to a first base station, a radio resource control (RRC) message for re-establishing an RRC connection suspended between the UE and a second base station storing a UE context for the UE through a suspend procedure,

wherein the RRC message includes a Radio Network Temporary Identifier (RNTI), and

wherein the RNTI identifies the second base station; and

re-establish the RRC connection with the first base station using the UE context,

wherein the UE context is retrieved based on the RNTI by sending a first signaling message including the RNTI from the first base station to the second base station and sending a second signaling message including the UE context from the second base station to the first base station.

18. A method for a user equipment (UE), the method comprising:

performing optimization for a Cellular Internet of Things (CIoT) operation;

sending, to a first base station, a radio resource control (RRC) message for re-establishing an RRC connection suspended between the UE and a second base station storing a UE context for the UE through a suspend procedure,

wherein the RRC message includes a Radio Network Temporary Identifier (RNTI), and

wherein the RNTI identifies the second base station; and

re-establishing the RRC connection with the first base station using the UE context,

wherein the UE context is retrieved based on the RNTI by sending a first signaling message including the RNTI from the first base station to the second base station and sending a second signaling message including the UE context from the second base station to the first base station.