Understanding this relationship is crucial. If you connect a DTE device to a DCE device, you use a "straight-through" cable (Pin 2 to Pin 2, Pin 3 to Pin 3). If you connect two DTE devices (e.g., two PCs), you must use a "null modem" cable, which crosses the transmit and receive lines so the two devices can talk.
In a world of USB, Ethernet, and wireless, is TIA/EIA-232-F still relevant? Here’s why: tia eia-232-f specification