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In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer provides multiplexing mechanisms that make it possible for several network protocols (IP, IPX, Decnet and Appletalk) to coexist within a multipoint network and to be transported over the same network medium. It can also provide flow control and automatic repeat request (ARQ) error management mechanisms. The LLC sublayer acts as an interface between the media access control (MAC) sublayer and the network layer. ==Operation== The LLC sublayer is primarily concerned with: * Multiplexing protocols transmitted over the MAC layer (when transmitting) and decoding them (when receiving). * Providing node-to-node flow and error control In today's networks, flow control and error management is typically taken care of by a transport layer protocol such as TCP, or by some application layer protocol, in an end-to-end fashion, i.e. retransmission is done from source to end destination. This implies that the need for LLC sublayer flow control and error management has reduced. LLC is consequently only a multiplexing feature in today's link layer protocols. An LLC header tells the data link layer what to do with a packet once a frame is received. It works like this: A host will receive a frame and look in the LLC header to find out to what protocol stack the packet is destined - for example, the IP protocol at the network layer or IPX. However, today most non-IP network protocols are abandoned. 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「Logical link control」の詳細全文を読む スポンサード リンク
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