Medium Access Control Sublayer
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Medium Access Control Sublayer book
The Medium Access Control (MAC) sublayer is the lowest sublayer that interfaces directly with the Physical sublayer. Control- and data-plane Protocol Data Unit (PDU) transmitted or received on Uplink Shared Channel or Downlink Shared Channel (DL-SCH) respectively are processed by the MAC sublayer before they are forwarded to other sublayers. When Radio link control (RLC) PDUs are received by the MAC sublayer from the RLC sublayer, they are mapped from logical channels to transport channels. Random Access (RA) procedure is one of the most important procedures at the MAC sublayer and at the User Equipment (UE) since this is the first procedure a UE initiates to connect to an eNodeB. When the UE completes the RA procedure successfully, it starts the contention resolution mechanism. A UE that moves from IDLE to CONNECTED mode needs to trigger the RA procedure. The RA procedure consists of a sequence of four messages, Msg1, Msg2, Msg3, and Msg4.