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In the IEEE 802 reference model of computer networking, the medium access control or media access control (MAC) layer is the lower sublayer of the data link layer (layer 2) of the seven-layer OSI model. The MAC sublayer provides addressing and channel access control mechanisms that make it possible for several terminals or network nodes to communicate within a multiple access network that incorporates a shared medium, e.g. an Ethernet network. The hardware that implements the MAC is referred to as a ''media access controller''. The MAC sublayer acts as an interface between the logical link control (LLC) sublayer and the network's physical layer. The MAC layer emulates a full-duplex logical communication channel in a multi-point network. This channel may provide unicast, multicast or broadcast communication service. == Functions performed in the MAC sublayer == According to IEEE Std 802-2001 section 6.2.3 "MAC sublayer", the primary functions performed by the MAC layer are:〔(【引用サイトリンク】title=IEEE 802-2001 (R2007) IEEE Standard for Local and Metropolitan Area Networks: Overview and Architecture )〕 * Frame delimiting and recognition * Addressing of destination stations (both as individual stations and as groups of stations) * Conveyance of source-station addressing information * Transparent data transfer of LLC PDUs, or of equivalent information in the Ethernet sublayer * Protection against errors, generally by means of generating and checking frame check sequences * Control of access to the physical transmission medium In the case of Ethernet, according to 802.3-2002 section 4.1.4, the functions required of a MAC are:〔(【引用サイトリンク】title=IEEE 802.3 )〕 * receive/transmit normal frames * half-duplex retransmission and backoff functions * append/check FCS (frame check sequence) * interframe gap enforcement * discard malformed frames * prepend(tx)/remove(rx) preamble, SFD (start frame delimiter), and padding * half-duplex compatibility: append(tx)/remove(rx) MAC address 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Media access control」の詳細全文を読む スポンサード リンク
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