1. Physical Layer

              The physical layer is responsible for the physical cable or wireless connection between network nodes. It defines the connector, the electrical cable or wireless technology connecting the devices, and is responsible for transmission of the raw data, which is simply a series of 0s and 1s, while taking care of bit rate control.

                The lowest layer of the OSI reference model is the physical layer. It is responsible for the actual physical connection between the devices. The physical layer contains information in the form of bits.

            Hub, Repeater, Modem, Cables are Physical Layer devices. 
Network Layer, Data Link Layer and Physical Layer are also known as Lower Layers or Hardware Layers. 

Examples of hardware in the physical layer are network adapters, ethernet, repeaters, networking hubs, etc.