Terminal device, infrastructure equipment and methods

1. A method of communicating data by a terminal device in a wireless telecommunication system, the wireless telecommunication system comprising a first radio access node and a second radio access node, the method comprising:

establishing a radio resource control, RRC, connection with the first radio access node and entering an RRC connected mode for communicating the data between the terminal device and the first radio access node in accordance with one or more parameters configured by the first radio access node and associated with the terminal device,

entering a dual connectivity mode of operation for the terminal device in which the first radio access node acts as a master radio access node and the second radio access node acts as a secondary radio access node,

communicating the same first data between the terminal device and the first radio access node and between the terminal device and the second radio access node,

determining that a radio link failure has been detected in respect of at least the first radio access node,

transmitting to the second radio access node a re-establishment request message,

receiving from the second radio access node a re-establishment response message, the re-establishment response message being transmitted by the second radio access node in response to the re-establishment request message and without the second radio access node requesting context information comprising the one or more parameters associated with the terminal device from the first radio access node after receiving the re-establishment request message,

communicating second data between the terminal device and the second radio access node,

before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, receiving a security key associated with the first radio access node, and

calculating an authentication token based on the security key associated with the first radio access node,

wherein the re-establishment request message comprises the authentication token.

2. A method according to claim 1 , the method comprising

in response to receiving the re-establishment response message, establishing a radio bearer for the communication of the second data between the terminal device and the second radio access node.

3. A method according to claim 1 , wherein in the dual connectivity mode of operation for the terminal device the first data is communicated in a first cell with the first radio access node and in a second cell with the second radio access node, the method comprising

before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, receiving from the first radio access node or the second radio access node a list of cells including the second cell, each cell in the list of cells being associated with a radio access node having stored the context associated with the terminal device for connection re-establishment.

4. A method according to claim 3 , wherein for each cell in the list of cells, if the terminal device receives a re-establishment response message in that cell, the terminal device may establish a radio bearer for the communication of the second data in the cell.

5. A method according to claim 3 , the method comprising

after determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, selecting the second cell,

determining that the second cell is in the list of cells, and

in response to determining that the second cell is in the list of cells, including in the re-establishment request message one or more parameters based on a parameter associated with the first access node.

6. A method according to claim 5 , wherein the parameter associated with the first access node is one of a cell identity of the first cell and a radio network temporary identifier assigned to the terminal device by the first radio access node for the transmission of data in the first cell.

7. A method according to claim 1 , the method comprising

before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, storing configuration parameters for communicating data in the first cell with the first radio access node.

8. A method according to claim 1 , the method comprising

in response to receiving the re-establishment response message, entering the dual connectivity mode of operation.

9. A method according to claim 1 , wherein the re-establishment response message comprises configuration parameters for communicating data in the second cell with the second radio access node.

10. A method of communicating data by a terminal device in a wireless telecommunication system, the wireless telecommunication system comprising a first radio access node and a second radio access node, the method comprising:

establishing a radio resource control, RRC, connection with the first radio access node and entering an RRC connected mode for communicating the data between the terminal device and the first radio access node in accordance with one or more parameters configured by the first radio access node and associated with the terminal device,

entering a dual connectivity mode of operation for the terminal device in which the first radio access node acts as a master radio access node and the second radio access node acts as a secondary radio access node,

communicating the same first data between the terminal device and the first radio access node and between the terminal device and the second radio access node,

determining that a radio link failure has been detected in respect of at least the first radio access node,

transmitting to the second radio access node a re-establishment request message,

receiving from the second radio access node a re-establishment response message, the re-establishment response message being transmitted by the second radio access node in response to the re-establishment request message and without the second radio access node requesting context information comprising the one or more parameters associated with the terminal device from the first radio access node after receiving the re-establishment request message,

communicating second data between the terminal device and the second radio access node,

before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, receiving a security key associated with the second radio access node, and

calculating an authentication token based on the security key associated with the second radio access node,

wherein the re-establishment request message comprises the authentication token.

11. A method according to claim 10 , the method comprising

before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, storing configuration parameters for communicating data in the second cell with the second radio access node.

12. A terminal device for use in a wireless telecommunication system comprising a first radio access node and a second radio access node, the terminal device comprising a controller and a transceiver configured to operate together such that the terminal device is operable

to establish a radio resource control, RRC, connection with the first radio access node and to enter an RRC connected mode for communicating the data between the terminal device and the first radio access node in accordance with one or more parameters configured by the first radio access node and associated with the terminal device,

to enter a dual connectivity mode of operation for the terminal device in which the first radio access node acts as a master radio access node and the second radio access node acts as a secondary radio access node,

to communicate the same first data between the terminal device and the first radio access node and between the terminal device and the second radio access node,

to determine that a radio link failure has been detected in respect of at least the first radio access node,

to transmit to the second radio access node a re-establishment request message,

to receive from the second radio access node a re-establishment response message, the re-establishment response message being transmitted by the second radio access node in response to the re-establishment request message and without the second radio access node requesting context information comprising the one or more parameters associated with the terminal device from the first radio access node after receiving the re-establishment request message,

to communicate second data between the terminal device and the second radio access node,

to, before determining that the radio link failure criteria are satisfied in respect of at least the first radio access node, receive a security key associated with the first radio access node, and

to calculate an authentication token based on the security key associated with the first radio access node,

wherein the re-establishment request message comprises the authentication token.