B is not the final destination, will again invoke lower-level functions. This time, the cable protocol is used to send the data to C. There, the received packet is again passed to the upper protocol, which (with C being the destination) will pass it on to a higher protocol or application on C.

In practical implementation, protocol stacks are often divided into three major sections: media, transport, and applications. A particular operating system or platform will often have two well-defined software