Overview#Physical Layer defines the electrical and physical specifications of the data connection.
Physical Layer defines the relationship between a device and a physical transmission medium (e.g., a copper or fiber optical cable, radio frequency). Physical Layer includes the layout of pins, voltages, line impedance, cable specifications, signal timing and similar characteristics for connected devices and frequency (5 GHz or 2.4 GHz etc.) for wireless devices.
Physical Layer is responsible for transmission and reception of unstructured raw data in a physical medium.
Physical Layer may define transmission mode as simplex, half duplex, and full duplex. It defines the network topology as bus, mesh, or ring being some of the most common.
Physical Layer of Parallel SCSI operates in this layer, as do the Physical Layers of Ethernet and other local Area Networks, such as token ring, FDDI, ITU-T G.hn, and IEEE 802.11 (Wi-Fi), as well as Personal Area Networks such as Bluetooth and IEEE 802.15.4.
Physical Layer is the layer of low-level networking equipment, such as some hubs, cabling, and repeaters.
Physical Layer is never concerned with protocols or other such higher-layer items. Examples of hardware in this layer are network adapters, repeaters, network hubs, modems, and fiber media converters.