The physical layer is the hardware level of the protocol model that is concerned with electronic signals. Physical layer protocols send and receive data in the form of packets.
A packet contains a source address, the transmission itself, and a destination address.
TCP/IP supports a number of physical layer protocols, including Ethernet. Ethernet is an example of a packet-switching network; its communications channels are occupied only for the duration of the transmission of a packet. On the other hand, the telephone network is an example of a circuit-switching network.