When multiple application$-$layer processes $($e$.$g$.,$ P$1,$ P$2,...,$ Pn$)$ on a host need to send their messages out through their own sockets that are virtually connected to different remote sockets, respectively, the $\_\_\_\_\_\_\_\_\_$ service on this host handles the messages $($data$)$ from P$1$ through Pn$,$ adds transport header, and wraps the messages $($data$)$ in segments and passes them to the network$-$layer process. This is the so$-$called $\_\_\_\_\_\_\_\_\_$ on the sender side.

When multiple application$-$layer processes $($e$.$g$.,$ P$1,$ P$2,...,$ Pn$)$ on a host need to send their messages out through their own sockets that are virtually connected to different remote sockets, respectively, the $\_\_\_\_\_\_\_\_\_$ service on this host handles the messages $($data$)$ from P$1$ through Pn$,$ adds transport header, and wraps the messages $($data$)$ in segments and passes them to the network$-$layer process. This is the so$-$called $\_\_\_\_\_\_\_\_\_$ on the sender side.

tcp; de$-$multiplexing

udp; de$-$multiplexing

tcp; multiplexing

udp; multiplexing