Editing OSI model (section)

===Layer 1: Physical layer===
{{main|Physical layer}}
The physical layer is responsible for the transmission and reception of unstructured raw data between a device, such as a [[network interface controller]], [[Ethernet hub]], or [[network switch]], and a physical [[transmission medium]]. It converts the digital bits into electrical, radio, or optical signals (analogue signals). Layer specifications define characteristics such as voltage levels, the timing of voltage changes, physical data rates, maximum transmission distances, modulation scheme, channel access method and physical connectors. This includes the layout of [[Lead (electronics)|pins]], [[voltage]]s, line [[Characteristic impedance|impedance]], cable specifications, signal timing and frequency for wireless devices. Bit rate control is done at the physical layer and may define transmission mode as [[Simplex communication|simplex]], [[half duplex]], and [[full duplex]]. The components of a physical layer can be described in terms of the [[network topology]]. Physical layer specifications are included in the specifications for the ubiquitous [[Bluetooth]], [[Ethernet physical layer|Ethernet]], and [[USB]] standards. An example of a less well-known physical layer specification would be for the [[CAN bus|CAN]] standard.

The physical layer also specifies how encoding occurs over a physical signal, such as electrical voltage or a light pulse. For example, a 1 bit might be represented on a copper wire by the transition from a 0-volt to a 5-volt signal, whereas a 0 bit might be represented by the transition from a 5-volt to a 0-volt signal. As a result, common problems occurring at the physical layer are often related to the incorrect media termination, EMI or noise scrambling, and NICs and hubs that are misconfigured or do not work correctly.