ded between different Access Service Classes (ASC) in order to provide different priorities of RACH usage. More than one ASC or all ASCs can get assigned to the same access slot/signature space. Each ASC will also have a set of back-off parameters associated with it, some or all of which may be broadcasted by the network. The MAC function applies the appropriate back-off and indicates to the PHY layer the RACH partition associated with a given MAC PDU transfer [9]. 3.8.3.3 RLC Services and Functions 3.8.3.3.1 Services RLC connection establishment/release. Transparent data transfer transmits higher layer PDUs without adding any pro- tocol information, but may include segmentation/re-assembly functionality. Unacknowledged data transfer transmits higher layer PDUs without guarantee- ing delivery to the peer entity. The unacknowledged data transfer mode has the fol- lowing characteristics: 10 In the TDD we represent transportable data in terms resource units sets. The UMTS Development Platform Detection of erroneous data: delivering only correct SDUs to the receiving higher layer by using the sequence-number check function. Unique delivery: delivering SDUs only once to the receiving upper layer using the duplication detection function. Immediate delivery: delivering SDUs to the higher layer receiving entity as soon as it arrives at the receiver. Acknowledged data transfer. Transmits higher layer PDUs and guarantees delivery to the peer entity. It has the following characteristics: Error-free delivery: ensured by means of retransmission. Unique delivery: delivering each SDU only once to the receiving upper layer using duplication detection function. In-sequence delivery: supports for in-order delivery of SDUs, i.e. delivering SDUs to the receiving higher layer entity in the same order as the transmitting higher layer entity submits them to the RLC sub-layer. Out-of-sequence delivery: it shall also be possible to allow the receiving RLC entity to deliver SDUs to a higher layer in a different order than submitted to RLC