In serial networking a stream of bits is sent between devices. Generally, the addressing schemes are very simple.
RS-232 (TIA-232) is not the protocol used by modems to send signals over a telephone line. RS232 is a protocol for speaking between a computer or terminal (DTE) and modem (DCE). Two DCE's or two DTE's can be connected by a special cable called a null modem.
RS232 is a serial point-to-point protocol.