Terminal apparatus, base station apparatus, and method

A terminal apparatus configured to communicate with a base station apparatus, the terminal apparatus comprising:

• reception circuitry configured to receive, from the base station apparatus, an radio resource control (RRC) message;
• and
• processing circuitry;
• wherein
• the RRC message is a message indicating mobility from a first RAT to a second RAT, the first RAT being NR, the second RAT being E-UTRA or UTRA, and
• the processing circuitry is configured to:
• determine whether the second RAT in the RRC message is E-UTRA or UTRA,
• consider that an inter RAT handover to the UTRA is triggered and forward information used for key synchronization and key freshness included in the RRC message to upper layers based on a fact that the second RAT is UTRA, and
• perform processing to notify the upper layers of release of an RRC connection in a process where the mobility from the first RAT to the second RAT is normally completed based on a fact that the second RAT is E-UTRA.

A base station apparatus configured to communicate with a terminal apparatus, the base station apparatus comprising:

• transmission circuitry configured to transmit, to the terminal apparatus, an radio resource control (RRC) message;
• and
• processing circuitry;
• wherein
• the RRC message is a message indicating mobility from a first RAT to a second RAT, the first RAT being NR, and
• the processing circuitry is configured to cause the terminal apparatus to:
• forward information used for key synchronization and key freshness included in the RRC message to upper layers based on a fact that the second RAT is UTRA, and
• perform processing to notify the upper layers of release of an RRC connection in a process where the mobility from the first RAT to the second RAT is normally completed based on a fact that the second RAT is E-UTRA.

A communication method used for a terminal apparatus, the terminal apparatus configured to communicate with a base station apparatus, the communication method comprising:

• receiving, from the base station apparatus, an radio resource control (RRC) message,
• wherein
• the RRC message is a message indicating mobility from a first RAT to a second RAT, the first RAT being NR, the second RAT being E-UTRA or UTRA, and
• determining whether the second RAT in the RRC message is E-UTRA or UTRA,
• considering that an inter RAT handover to the UTRA is triggered and forward information used for key synchronization and key freshness included in the RRC message to upper layers based on a fact that the second RAT is UTRA, and
• performing processing to notify the upper layers of release of an RRC connection in a process where the mobility from the first RAT to the second RAT is normally completed based on a fact that the second RAT is E-UTRA.

A communication method used for a base station apparatus, the base station apparatus configured to communicate with a terminal apparatus, the communication method comprising:

• transmitting, to the terminal apparatus, an radio resource control (RRC) message, wherein
• the RRC message is a message indicating mobility from a first RAT to a second RAT, the first RAT being NR, and
• forwarding information used for key synchronization and key freshness included in the RRC message to upper layers based on a fact that the second RAT is UTRA, and
• performing processing to notify the upper layers of release of an RRC connection in a process where the mobility from the first RAT to the second RAT is normally completed based on a fact that the second RAT is E-UTRA.