Loadtest with mockservice fails when threads >= 196

I created a simple mockService to do some subsystem loadtesting. The service works fine, but when the number of threads reaches or passes precisely 196 in a loadtest I will only get java.net.SocketTimeoutException: Read timed out. The system has plenty of memory and processing power left. It makes no difference if it's in a testcase of its own or in a case with more steps. I also tried introducing some delays, but this has no effect either.