The primary function of this layer is to convert the bit stream onto the physical medium by converting it into electrical/optical impulses or radio signals. This layer provides the physical connection to the underlying medium and also provides the hardware means to activate, maintain, and de-activate physical connections between data link entities. This includes sequencing of the bit stream, identifying channels on the underlying medium, and optionally multiplexing. This should not be confused with the actual medium itself.
Some of the protocols that have a layer 1 component are Ethernet, G.703, FDDI, V.35, RJ45, RS232, SDH, DWDM, OTN, and so on.