Methods for device-to-device connection re-establishment and related user equipments and radio access node

A user equipment for device-to-device connection re-establishment, the device-to-device connection being established between the user equipment and another user equipment under the control of a radio access node, the user equipment comprising:

• at least one processor;
• and
• at least one memory including computer program code;
• the at least one memory and the computer program code configured to, with the at least one processor, cause the user equipment to perform at least the following:
• receiving a first message from said another user equipment, the first message comprising a first credential which is calculated by said another user equipment;
• verifying the first credential;
• and
• sending a second message indicating acknowledgement of the device-to-device connection re-establishment to said another user equipment upon successful verification of the first credential.

A user equipment for device-to-device connection re-establishment, the device-to-device connection being established between the user equipment and another user equipment under the control of a radio access node, the user equipment comprising:

• at least one processor;
• and
• at least one memory including computer program code;
• the at least one memory and the computer program code configured to, with the at least one processor, cause the user equipment to perform at least the following:
• receiving a first message from the radio access node, the first message comprising at least a first credential which is calculated by said another user equipment, radio resource information for the re-establishment, and a process identifier for the re-establishment;
• verifying the first credential;
• sending to the radio access node a second message indicating acceptance of the re-establishment upon successful verification of the first credential;
• receiving a third message from said another user equipment, the third message comprising the process identifier;
• recognizing the re-establishment based on the process identifier;
• and
• sending to said another user equipment a fourth message indicating acknowledgement of the re-establishment.

A radio access node for device-to-device connection re-establishment, the device-to-device connection being established between a first user equipment and a second user equipment under the control of the radio access node, the radio access node comprising:

• at least one processor;
• and
• at least one memory including computer program code;
• the at least one memory and the computer program code configured to, with the at least one processor, cause the radio access node to perform at least the following:
• receiving a first message from the first user equipments, the first request comprising an indication of a device-to-device connection re-establishment, a credential calculated by the first user equipment, and an identifier of the second user equipments;
• allocating a process identifier and radio resources to the re-establishment;
• sending a second message to the second user equipment, the second message comprising the received credential, the allocated process id and radio resource information for the re-establishment;
• receiving from the second user equipment a third message indicating acceptance of the re-establishment;
• and
• sending to the first user equipment a fourth message comprising the radio resource information and the allocated process identifier, wherein the radio resource information and the process identifier are used by the first user equipment for the re-establishment.