If you do not put a "qsim" section into the config file, the system will use the default "simulation" (look there).

"qsim" is what we use for new features such as public transit or signalsystems.  "New features" implies "unstable".  Use only if you have to.

Also see www.matsim.org/javadoc/org/matsim/ptproject/qsim/package-summary.html