Serial Server

Roughly speaking, a serial server is typically a lightweight single piece of hardware, like an NL100 from Campbell Scientific or an Nport from Moxa, or perhaps a bit bigger like an ARM-cpu based full computer running Debian Linux. The serial server acts as a bridge between serial devices, typically radios or data loggers communicating using RS-232 and the Internet, which is TCP-IP.
There are pros and cons to single purpose NL100 style vs full fledged small computer. It depends partially on the environment but these days I (Bob) prefer the full computer because you can control access and security to the serial port. That isn't an option on the simpler systems and it turns out UAF network is fairly wide open to curious people from around the world (see for example the BNZ NL100 last summer getting broken into. Also looking at /var/auth.log contenst on the debian servers reveals that people are trying allllllll of the time, unfortunately.