Mobile communication system

A mobile communication system in which a first relay node and a radio base station are connected via a radio bear, a second relay node and the radio base station are connected via a radio bear, wherein

• the first relay node and the second relay node comprise:
• as a radio bearer function of setting a Un interface with the radio base station, a physical layer function;
• an MAC layer function provided as an upper layer function of the physical layer function;
• an RLC layer function provided as an upper layer function of the MAC layer function;
• a PDCP layer function provided as an upper layer function of the RLC layer function;
• and
• an RRC layer function provided as an upper layer function of the PDCP layer function;
• as an upper layer function of the radio bearer function, an IP layer function;
• an SCTP layer function provided as an upper layer function of the IP layer function;
• and
• an X2AP layer function provided as an upper layer function of the SCTP layer function;
• the radio base station comprises:
• as a radio bearer function of setting a Un interface with the first relay node and the second relay node, a physical layer function;
• an MAC layer function provided as an upper layer function of the physical layer function;
• an RLC layer function provided as an upper layer function of the MAC layer function;
• a PDCP layer function provided as an upper layer function of the RLC layer function;
• and an RRC layer function provided as an upper layer function of the PDCP layer function;
• as an upper layer function of the radio bearer function, an IP layer function;
• an SCTP layer function provided as an upper layer function of the IP layer function;
• and
• an X2AP layer function provided as an upper layer function of the SCTP layer function, and
• a control signal involved in a handover process is configured to be terminated between the X2AP layer function of the first relay node and the X2AP layer function of the radio base station, and between the X2AP layer function of the second relay node and the X2AP layer function of the radio base station.