Biologically the species is the accumulation of the experiments of all its successful individuals since the beginning.
— H. G. WELLS
A protocol, like a copy center or an ice cream parlor, should be able to serve multiple clients. The clients of a protocol could be end users (as in the case of the file transfer protocol), software programs (for example, when the tool traceroute uses the Internet protocol), or even other protocols (as in the case of the email protocol SMTP, which uses TCP).
Thus when a message arrives, the receiving protocol must dispatch the received message to the appropriate client. This function is called demultiplexing. Demultiplexing is an integral part of data link, routing, and transport protocols. It ...