TCP⁄IP consists of a layered structure of protocols ranging from hardware-dependent programs to high-level applications. Each TCP⁄IP layer provides services to the layer above it and uses the services of the layer below it. The lowest layer, which is next to the physical layer, is not part of TCP⁄IP. This layer consists of existing protocols, such as Ethernet and token ring. TCP⁄IP uses the services of this layer to transport data across dissimilar networks, much like a gateway.