Mobile communication system

A mobile communication system configured to send and receive control signals between a mobile station and a mobile switching center via a first radio bearer that is set between the mobile station and a relay node, a second radio bearer that is set between the relay node and a radio base station, and a wired bearer that is set between the radio base station and the mobile switching center, wherein

• wherein the relay node comprises:
• a first radio bearer function of the relay node for setting the first radio bearer;
• a second radio bearer function of the relay node for setting the second radio bearer;
• and
• a first layer function of the relay node provided as an upper layer function of the second radio bearer function of the relay node,
• wherein the radio base station comprises:
• a second radio bearer function of the radio base station for setting the second radio bearer;
• a wired bearer function of the radio base station for setting the wired barer;
• a first layer function of the radio base station provided as an upper layer function of the second radio bearer function of the radio base station;
• and
• a second layer function of the radio base station provided as an upper layer function of the wired bearer function of the radio base station,
• wherein the mobile switching center comprises:
• a wired bearer function of the mobile switching center for setting the wired barer;
• and
• a second layer function of the mobile switching center provided as an upper layer function of the wired bearer function of the mobile switching center,
• wherein the control signals are configured to be sent and received on a first session terminating between the first layer function of the relay node and the first layer function of the radio base station and a second session terminating between the second layer function of the radio base station and the second layer function of the mobile switching center,
• wherein keep-alive processing for the first session is configured to be performed between the first layer function of the relay node and the first layer function of the radio base station,
• wherein keep-alive processing for the second session is configured to be performed between the second layer function of the radio base station and the second layer function of the mobile switching center,
• wherein security processing is configured to be performed between the first layer function of the relay node and the first layer function of the radio base station, and
• wherein security processing is configured to be performed between the second layer function of the radio base station and the second layer function of the mobile switching center.