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In the seven-layer OSI model of computer networking, the physical layer or layer 1 is the first (lowest) layer. The implementation of this layer is often termed PHY. The physical layer consists of the basic networking hardware transmission technologies of a network. It is a fundamental layer underlying the logical data structures of the higher level functions in a network. Due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture. The physical layer defines the means of transmitting raw bits rather than logical data packets over a physical link connecting network nodes. The bit stream may be grouped into code words or symbols and converted to a physical signal that is transmitted over a hardware transmission medium. The physical layer provides an electrical, mechanical, and procedural interface to the transmission medium. The shapes and properties of the electrical connectors, the frequencies to broadcast on, the modulation scheme to use and similar low-level parameters, are specified here. Within the semantics of the OSI network architecture, the physical layer translates logical communications requests from the data link layer into hardware-specific operations to affect transmission or reception of electronic signals. ==Physical signaling sublayer== In a local area network (LAN) or a metropolitan area network (MAN) using open systems interconnection (OSI) architecture, the ''physical signaling sublayer'' is the portion of the physical layer that:〔(【引用サイトリンク】title=physical signaling sublayer (PLS) )〕 * interfaces with the data link layer's media access control (MAC) sublayer, * performs character encoding, transmission, reception and decoding and, * performs galvanic isolation. 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「physical layer」の詳細全文を読む スポンサード リンク
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