me services such as file transfers. The transparent mode is used when the size of packet data units are known in advance, such as for broadcasting system configuration information. The RLC layer also provides sequential delivery of service data units to the upper layers and eliminates duplicate packets from being delivered to the upper layers. It may also segment the service data units. Furthermore, there are two levels of re- transmissions for providing reliability, the HARQ at the MAC layer, and ARQ at the RLC layer. The 3.3 3GPP LTE/LTE-advanced protocol structure ARQ is required to handle residual errors that are not corrected by HARQ, and is kept simple by the use of a single-bit feedback mechanism. An N-process stop-and-wait HARQ is employed that has asynchronous re-transmissions in the DL and synchronous re-transmissions in the UL. In practice, multiple stop-and-wait HARQ processes are operated in parallel, i.e., when one HARQ process is waiting for an acknowledgment another process can use the channel to send sequentially-ordered sub- packets, thus improving the throughput. The synchronous HARQ means that the re-transmissions of HARQ sub-packets occur at predefined periodic intervals. Hence, no explicit signaling is required to indicate to the receiver the re-transmission schedule. Asynchronous HARQ offers the flexibility of scheduling re-transmissions based on air interface conditions (i.e., scheduling gain) [29,32]. The services and functions provided by the MAC layer can be summarized as follows [32]: Mapping between logical channels and transport channels; Multiplexing/de-multiplexing of RLC protocol data units corresponding to one or different radio bearers into/from transport blocks delivered to/from the physical layer on transport channels; Traffic volume measurement reporting; Error correction through HARQ; Priority handling between logical channels of one UE; Priority handling between UEs through dynamic scheduling; Transport format selection. E-UTRA provides ARQ and HARQ functionalities. The ARQ