Method and apparatus for performing random access procedures

1. A method of performing a random access procedure by a terminal, the method comprising:

setting two kinds of maximum number of Hybrid Automatic Repeat reQuest (HARQ) transmissions parameter, wherein a first kind of maximum number of HARQ transmissions parameter is used for transmitting an uplink data according to Random Access Channel (RACH) procedure and a second kind of maximum number of HARQ transmissions parameter is used for transmitting data other than Protocol Data Unit (MAC PDU) stored in a MSG3 buffer;

transmitting a random access preamble which is selected at a Medium Access Control (MAC) layer in the terminal;

receiving a random access response in response to transmitting the random access preamble; and

performing an uplink transmission using an uplink grant included in the random access response,

wherein the uplink data includes an identifier of the terminal and the uplink data transmitted using the uplink grant is a MAC PDU, and

wherein the uplink transmission is performed by using the first kind of maximum number of HARQ transmissions parameter, which is included in a System Information Block (SIB) received from a base station.

2. The method of claim 1 , wherein the uplink grant is received from a lower layer and information on the first kind of the maximum number of HARQ transmissions parameter is received from the lower layer.

3. The method of claim 1 , wherein the uplink data is RACH MSG3.

4. The method of claim 1 , wherein the random access response triggers generation of RACH MSG3 related to the uplink data.

5. The method of claim 4 , wherein the triggered RACH MSG3 is temporally stored within the MSG3 buffer.

6. The method of claim 1 , wherein the first type of the maximum number of HARQ transmissions parameter is a max-HARQ-Msg3Tx parameter.

7. A terminal comprising:

A Radio Resource Control (RRC)) layer configured to receive two kinds of maximum number of Hybrid Automatic Repeat reQuest (HARQ) transmissions parameters via system information or via a dedicated massage; and

a Medium Access Control (MAC) layer configured to receive the two kinds of maximum number of HARQ transmissions parameters from the RRC layer,

wherein a first kind of maximum number of HARQ transmissions parameter is used for transmission of data related to a RACH procedure, and a second kind of maximum number of HARQ transmissions parameter is used for transmission of data other than Protocol Data Unit (MAC PDU) stored in a MSG3 buffer.

8. The terminal of claim 7 , wherein the transmission of data related to the RACH procedure uses a RACH MSG3 message.

9. The terminal of claim 7 , wherein the first kind of maximum number of HARQ transmissions parameter is received via the system information, and the second kind of maximum number of HARQ transmission parameter is received via the dedicated message.

10. The terminal of claim 7 , wherein the transmission of data related to the RACH procedure is defined as an uplink transmission using an uplink grant received in a RACH access response.

11. The terminal of claim 10 , wherein the RACH access response triggers generation of RACH MSG3, which is temporarily stored.

12. The terminal of claim 11 , wherein the triggered RACH MSG3 is temporally stored in the MSG3 buffer.

13. The terminal of claim 7 , wherein the maximum number of HARQ transmissions parameter is used for determining when to flush a HARQ buffer in the terminal.

14. The terminal claim 7 , wherein the first type of the maximum number of HARQ transmissions parameter is a max-HARQ-Msg3Tx parameter.

15. The terminal claim 7 , wherein the second type of the maximum number of HARQ transmissions parameter is maxHARQ-TX.