Dual connectivity mobile communication system

1 . An apparatus, comprising:

at least one processor; and

at least one non-transitory memory storing instructions that, when executed with the at least one processor, cause the apparatus to perform:

receiving a change required message from a source secondary node, wherein the change required message provides information relating to a maximum number of primary secondary cells that can be prepared for primary secondary cell change by a target secondary node;

sending, in response to said received change required message, an addition request from a master node of a dual connectivity mobile communication system to the target secondary node of the dual connectivity mobile communication system, wherein the addition request includes said information relating to the maximum number of the primary secondary cells that can be prepared for primary secondary cell change by said target secondary node; and

receiving a response to the addition request from the target secondary node, wherein said response indicates how many of the primary secondary cells have been prepared by said target secondary node in response to said addition request.

2 . The apparatus as claimed in claim 1 , wherein the response to the addition request includes radio resource control reconfiguration information for each of the primary secondary cells prepared by the target secondary node.

3 . The apparatus as claimed in claim 2 , wherein the instructions, when executed with the at least one processor, cause the apparatus to perform forwarding radio resource control reconfiguration information of the primary secondary cells prepared by said target secondary node to a user device.

4 . The apparatus as claimed in claim 1 , wherein the change required message includes a list of identifiers, wherein the list of identifiers relates to the primary secondary cells that can be prepared.

5 . The apparatus as claimed in claim 1 , wherein the information relating to the maximum number of the primary secondary cells that can be prepared comprises a list of cell identifiers.

6 . The apparatus as claimed in claim 1 , wherein the response to the addition request received from the target secondary node includes a list of cell identifiers of the prepared primary secondary cells.

7 . The apparatus as claimed in claim 6 , wherein the instructions, when executed with the at least one processor, cause the apparatus to perform sending a list of identifiers from the master node to the source secondary node of the dual connectivity system, wherein the list of identifiers includes the list of cell identifiers of the prepared primary secondary cells.

8 . The apparatus as claimed in claim 1 , wherein the instructions, when executed with the at least one processor, cause the apparatus to perform updating the maximum number of the primary secondary cells that can be prepared for primary secondary cell change by said target secondary node.

9 . The apparatus as claimed in claim 8 , wherein the instructions, when executed with the at least one processor, cause the apparatus to perform sending a modification request to the target secondary node, wherein the modification request includes information relating to the updated maximum number of the primary secondary cells that can be prepared for primary secondary cell change by said target secondary node.

10 . A method, comprising:

receiving a change required message from a source secondary node, wherein the change required message provides information relating to a maximum number of primary secondary cells that can be prepared for primary secondary cell change by a target secondary node

sending, in response to said received change required message, an addition request from a master node of a dual connectivity mobile communication system to the target secondary node of the dual connectivity mobile communication system, wherein the addition request includes said information relating to the maximum number of the primary secondary cells that can be prepared for primary secondary cell change by said target secondary node;

and receiving a response to the addition request from the target secondary node indicating how many of the primary secondary cells have been prepared by said target secondary node in response to said addition request.

11 . A non-transitory computer program storage device readable with an apparatus tangibly embodying a program of instructions executable with the apparatus for performing the method of claim 10 .