Experts have been predicting the death of RS-232 for decades, and yet it continues to serve us well. It is a highly proven technology that is inexpensive and easy to implement. And it is well understood and widely accepted in IT and related endeavors.

The RS-232 standard refers to two classes of devices: Data Terminal Equipment (DTE) and Data Circuit Terminating Equipment (DCE). Classically, the DTE component is a computer or a terminal. These days, a router is often the DTE piece of the puzzle. In the past, the DCE component was usually a modem connected to the public, switched telephone network, but now you are likely to find a CSU/DSU instead that connects to a digital leased line (like a T1, for
instance) or maybe a Terminal Adapter (TA, for ISDN).