Inter-radio access technology handover

1. A method of performing a handover from a source base station supporting a first Radio Access Technology (RAT) to a target base station supporting a second RAT, the method comprising a user equipment:

communicating with the source base station using a Medium Access Control entity, a Radio Link Control entity, a first Packet Data Convergence Protocol entity, and a first Service Data Adaptation Protocol entity;

receiving a first Radio Resource Control message from the source base station, the first Radio Resource Control message including a second Radio Resource Control message for the handover to the target base station;

in response to the receiving the first Radio Resource Control message or the second Radio Resource Control message, releasing the Medium Access Control entity and the Radio Link Control entity;

determining, from the second Radio Resource Control message, that a configuration type is a delta configuration; and

based on the determining that the configuration type is the delta configuration, keeping the first Packet Data Convergence Protocol entity and the first Service Data Adaptation Protocol entity.

2. The method of claim 1 , further comprising the user equipment:

transmitting an RRCConnectionConfigurationComplete message; and

communicating with the target base station using the first Packet Data Convergence Protocol entity.

3. The method of claim 2 , further comprising the user equipment:

disconnecting from the source base station.

4. The method of claim 1 , wherein the first Radio Resource Control message is an RRCConnectionReconfiguration message.

5. The method of claim 4 , wherein an indication of a configuration type is a fullConfig field in the RRCConnectionReconfiguration message.

6. The method of claim 1 , wherein the source base station is a fifth-generation new radio base station, and wherein the target base station is an Evolved Universal Terrestrial Radio Access base station.

7. A user equipment comprising:

one or more wireless transceivers;

a processor; and

a memory comprising instructions for a handover manager executable by the processor to configure the user equipment to:

communicate with a source base station using a first Radio Access Technology (RAT), a Medium Access Control entity, a Radio Link Control entity, and a first Packet Data Convergence Protocol entity;

receive a first Radio Resource Control message from the source base station, the first Radio Resource Control message including a second Radio Resource Control message for a handover to a target base station that uses a second RAT;

in response to the reception of the first Radio Resource Control message or the second Radio Resource Control message, release the Medium Access Control entity and the Radio Link Control entity;

determine a configuration type from an indication of a configuration type included in the second Radio Resource Control message;

determine that the configuration type is a delta configuration;

based on the determining that the configuration type is the delta configuration, keep the first Packet Data Convergence Protocol entity;

transmit an RRCConnectionConfigurationComplete message; and

communicate with the target base station using the first Packet Data Convergence Protocol entity.

8. The user equipment of claim 7 , wherein the target base station is connected to a fifth-generation core network, and wherein the instructions are executable to configure the user equipment to:

communicate with the source base station using the Medium Access Control entity, the Radio Link Control entity, the first Packet Data Convergence Protocol entity, and a first Service Data Adaptation Protocol entity.

9. The user equipment of claim 7 , wherein the instructions are executable to configure the user equipment to:

disconnect from the source base station.

10. A method of performing a handover from a source base station supporting a first Radio Access Technology (RAT) to a target base station supporting a second RAT, the method comprising a user equipment:

communicating with a source base station using a Medium Access Control entity, a Radio Link Control entity, and a first Packet Data Convergence Protocol entity;

receiving a first Radio Resource Control message from the source base station, the first Radio Resource Control message including a second Radio Resource Control message for a handover to a target base station;

in response to the receiving the first Radio Resource Control message or the second Radio Resource Control message, releasing the Medium Access Control entity and the Radio Link Control entity;

determining a configuration type from an indication of a configuration type included in the second Radio Resource Control message;

determining that the configuration type is a delta configuration;

based on the determining that the configuration type is the delta configuration, keeping the first Packet Data Convergence Protocol entity;

transmitting an RRCConnectionConfigurationComplete message; and

communicating with the target base station using the first Packet Data Convergence Protocol entity.

11. The method of claim 10 , wherein the target base station is connected to a fifth-generation core network, the method further comprising:

communicating with the source base station using the Medium Access Control entity, the Radio Link Control entity, the first Packet Data Convergence Protocol entity, and a first Service Data Adaptation Protocol entity.

12. The method of claim 10 , the method further comprising:

responsive to the keeping the first Packet Data Convergence Protocol entity, disconnecting from the source base station.