<P> The physical layer is responsible for the transmission and reception of unstructured raw data between a device and a physical transmission medium . It converts the digital bits into electrical , radio , or optical signals . Layer specifications define characteristics such as voltage levels , the timing of voltage changes , physical data rates , maximum transmission distances , and physical connectors . This includes the layout of pins , voltages , line 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 , half duplex , and full duplex . The components of a physical layer can be described in terms of a network topology . Bluetooth , Ethernet , and USB all have specifications for a physical layer . </P>
which layer of the osi model defines the signal rates and voltages that are used
The physical layer