Method and apparatus supporting random access transmissions

A method and a wireless transmit/receive unit (WTRU) are disclosed. The WTRU comprises a transceiver and a processor. The WTRU receives a system information block (SIB) from a base station, wherein the SIB indicates random access transmission uplink resources. After receiving the SIB, the WTRU transmits a random access preamble to the base station. After transmitting the random access preamble, the WTRU transmits, using one or more of the uplink resources indicated by the SIB, a first message to the base station, wherein the first message includes a first radio network temporary identifier (RNTI) of the WTRU. After transmitting the first message, the WTRU receives a second message from the base station, wherein the second message is derived from a second RNTI, the second RNTI being different than the first RNTI. After receiving the second message, the WTRU transmits to the base station.