Method and apparatus for performing random access procedure in a mobile communication system

A User Equipment (UE) apparatus for performing a random access in a mobile communication system, comprising:

• a physical layer processor for exchanging messages with an Evolved Node B (ENB);
• a Medium Access Control (MAC) controller for controlling to transmit a preamble to the ENB via a first message, acquiring uplink (UL) transmission resource information from the ENB in response to the first message via a second message that the physical layer processor received from the ENB, the UL transmission resource information being used for transmitting at least one of a transparent Radio Resource Control (RRC) message indicating that a UE having no RRC control connection transmits for the first time, and Buffer Status Report (BSR) information indicating an amount of UL data, generating a MAC control message containing therein the BSR information, and outputting a format indicator indicating whether the transparent RRC message or the BSR information is included in a third message which is transmitted using the UL transmission resource information;
• and
• a MAC multiplexer for multiplexing a MAC control message including at least one of the transparent RRC message delivered from an upper layer and the BSR information delivered from the MAC controller, and generating the third message according to a format indicator designated by MAC controller.

A method for performing a random access by an Evolved Node B (ENB) in a mobile communication system, the method comprising:

• receiving a preamble for identifying a User Equipment (UE), from the UE via a first message;
• transmitting uplink (UL) transmission resource information via a second message in response to the first message, the UL transmission resource information being used for transmitting at least one of a transparent Radio Resource Control (RRC) message indicating that a UE having no control connection transmits for the first time and a Buffer Status Report (BSR) indicating an amount of UL data;
• receiving a third message transmitted through the UL transmission resource information;
• checking a format indicator indicating if the third message includes the transparent RRC message or the BSR;
• and
• processing the third message in an RRC layer or a Medium Access Control (MAC) layer according to a set value of the format indicator.

An Evolved Node B (ENB) apparatus for performing a random access in a mobile communication system, comprising:

• a Medium Access Control (MAC) controller for receiving a preamble for identifying a User Equipment (UE) from the UE via a first message to perform the random access procedure, transmitting a second message including therein uplink (UL) transmission resource information to the UE corresponding to the preamble, and processing Buffer Status Report (BSR) information included in a third message received from the UE;
• a physical layer processor for exchanging the first message, the second message and the third message with the UE;
• and
• a MAC demultiplexer for checking a format indicator of the third message received from the physical layer processor to determine if the transparent Radio Resource Control (RRC) message is included in the third message or the BSR information is included in the third message, delivering the BSR information to the MAC controller if the BSR information is included in the third message, and delivering the transparent RRC message to a Layer 2 (L2) processor if the transparent RRC message is included in the third message,
• wherein the transparent RRC message indicates that a UE having no RRC control connection to the ENB transmits for the first time, and the BSR information indicates an amount of UL data.