In complicated call scenarios, I need a master who's only job is to control slaves, so I don't have to mix the scenario control with the SIP blocks. Plus, error handling would be much easier this way.
However, sipp does not allow to have a component that is neither a server or a client, i.e. does not have any send or recv commands, only sendCmd and recvCmd commands:
"Unable to determine send mode of the tool (server, client)"
even if there is no need the master to interact on SIP level at all. There is no command line parameter to specify the server/client role (as far as I have seen), so there is no workaround.