The Physical Layer has two responsibilities; it sends bits and receives bits.
The physical layer is usually a combination of software and hardware programming and may include electromechanical devices.
All wireing, power, cabling and connections are part of the physical layer. Without the physical layer functioning properly none of the upper layers will respond correctly.
* transmits raw bit stream over physical cable
* defines cables, cards, and physical aspects
* defines NIC attachments to hardware, how cable is attached to NIC
* defines techniques to transfer bit stream to cable