It does this through TCP, which begs the question... can I compile remotely? The answer is Yes! It's not documented, and it is a bit awkward, but...
First, you get fsc running on the server by running fsc -verbose, like this:
[Server arguments: -d C:\Users\Daniel\Documents\Programas\. -verbose]
[VM arguments: ]
[Temp directory: C:\PROGRA~1\Scala\bin\..\var\scala-devel]
[Executed command: C:\PROGRA~1\Scala\bin\..\bin\scala.bat scala.tools.nsc.CompileServer]
[Port number: 1385]
[Connected to compilation daemon at port 1385]
This will get you the port number. Next, you can compile whatever you like from a remote client like this:
$fsc -server 192.168.1.35:1385 strategy.scala
That's it. Cool, eh?