Telecommunications apparatus and methods

A method of operating a second network access node in a wireless telecommunication system comprising a terminal device, a first network access node and the second network access node, wherein the method comprises:

• configuring the second network access node to act as a secondary network access node for a dual connectivity mode of operation for the terminal device in which the first network access node acts as a master network access node, wherein the first network access node is associated with a master network access node security key and the second network access node is associated with a secondary network access node security key, wherein the secondary network access node security key is derived from the master network access node security key and is established by the second network access node from information received from the first network access node;
• establishing, while the second network access node is acting as secondary network access node for the dual connectivity mode of operation for the terminal device, that the second network access node should switch to acting as a master network access node;
• deriving a new master network access node security key to be used by the second network access node when it is switched to acting as a master network access node for the terminal device;
• and
• configuring the second network access node to act a master network access node for the terminal device using the new master network access node security key, wherein the step of establishing that the second network access node should switch to acting as a master network access node for the dual connectivity mode of operation for the terminal device is based on a measurement of radio channel conditions between the terminal device and the first and/or second network access node.

Circuitry for a second network access node for use in a wireless telecommunication system comprising a terminal device, a first network access node and the second network access node, wherein the circuitry comprises controller circuitry and transceiver circuitry configured to operate together such that the circuitry is operable to:

• configure the second network access node to act as a secondary network access node for a dual connectivity mode of operation for the terminal device in which the first network access node acts as a master network access node, wherein the first network access node is associated with a master network access node security key and the second network access node is associated with a secondary network access node security key, wherein the secondary network access node security key is derived from the master network access node security key and is established by the second network access node from information received from the first network access node;
• establish, while the second network access node is acting as secondary network access node for the dual connectivity mode of operation for the terminal device, that the second network access node should switch to acting as a master network access node for the terminal device;
• derive a new master network access node security key to be used by the second network access node when it is switched to acting as a master network access node for the terminal device;
• and
• configure the second network access node to act a master network access node for the terminal device using the new master network access node security key, wherein the new master network access node security key is derived by the second network access node by combining the information received from the first network access node with a predetermined number.

A terminal device for use in a wireless telecommunication system comprising the terminal device, a first network access node and a second network access node, wherein the terminal device comprises controller circuitry and transceiver circuitry configured to operate together such that the terminal device is operable to:

• configure the terminal device to operate in a dual connectivity mode of operation with the first network access node acting as a master network access node for the dual connectivity mode of operation and the second network access node acting as a secondary network access node, wherein the first network access node is associated with a master network access node security key and the second network access node is associated with a secondary network access node security key, wherein the secondary network access node security key is derived from the master network access node security key;
• establish, while the second network access node is acting as secondary network access node for the dual connectivity mode of operation for the terminal device, that the second network access node is to switch to acting as a master network access node for the dual connectivity mode of operation for the terminal device;
• establish a new master network access node security key to be used by the second network access node when it is switched to acting as a master network access node for the dual connectivity mode of operation for the terminal device;
• and
• configure the terminal device to communicate with the second network access node using the new master network access node security key, wherein the new master network access node security key is derived by the second network access node by combining the information received from the first network access node with a predetermined number.