Definition in Standards and Text Books
LAN standards such as Ethernet and IEEE 802 specifications use terminology from the seven-layer OSI model rather than the TCP/IP reference model. The TCP/IP model in general does not consider physical specifications, rather it assumes a working network infrastructure that can deliver media level frames on the link. Therefore RFC 1122 and RFC 1123, the definition of the TCP/IP model, do not discuss hardware issues and physical data transmission and set no standards for those aspects, other than broadly including them as link-layer components. Some textbook authors have supported the interpretation that physical data transmission aspects are part of the link layer. That position will be held in the rest of this article. Others assumed that physical data transmission standards are not considered as communication protocols, and are not part of the TCP/IP model. These authors assume a hardware layer or physical layer below the link layer, and several of them adopt the OSI term data link layer instead of link layer in a modified description of layering. In the predecessor to the TCP/IP model, the Arpanet Reference Model (RFC 908, 1982), aspects of the link layer are referred to by several poorly defined terms, such as network-access layer, network-access protocol, as well as network layer, while the next higher layer is called internetwork layer. In some modern text books, network-interface layer, host-to-network layer and network-access layer occur as synonyms either to the link layer or the data link layer, often including the physical layer.
Read more about this topic: Link Layer
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