Distributed OSGi: Maximum number of parallel requests == 24?

Hello,

I faced another issue with my distributed OSGi application. My application
should handle hundreds of requests per second whereby each request might
need one second or more calculation time. But from my tests it seems that
the OSGi framework only accepts 24 requests in parallel and queues the
others.
I first thought that it is an error in my application so I commented out
everything, just logged each service call, and set the thread to sleep to
simulate the workload. It showed the same behaviour: 24 service calls were
logged, then some wait time while the threads were sleeping, and then the
next logs.
I although thought about a problem in my client (also an OSGi application),
so I tried to access the service by using JMeter directly on the WSDL
endpoint. The service behaved the same.
I also tested it in Felix and Equinox to see if there is any difference
between the containers, but both showed the same behaviour.

The only explanation that came in my mind so far is the size of an internal
thread pool that might be used by the OSGi container to schedule the
requests. Does anybody know if there is a threshold for the maximum number
of concurrent requests in OSGi and how I could increase it? Or do you have
an idea what else could be the source of this behaviour?

Here is the code that I used to test the behaviour:
Service endpoint:
public AtomicInteger count = new AtomicInteger(0);
public MyResponse putRequest(MyRequest request) {
   System.out.println(this.count.incrementAndGet());

   try {
      Thread.sleep(10000);
   } catch (Exception e) {
      e.printStackTrace();
   }

   this.count.decrementAndGet();
   return new MyResponse("Hello from Server!");
}

Client:
                int id = 0;
for (int repeat = 0; repeat < 10; repeat++) {
   for (int i = 0; i < 50; i++) {
      LoadGeneratingThread t = new LoadGeneratingThread(id);
      t.start();
      id++;
   }
   try {
      Thread.sleep(1000);
   } catch (InterruptedException e) {
   }
}

The LoadGeneratingThread simply looks for the service using a
ServiceTracker<S,T> and if it finds it, it calls the putRequest
method.

Many thanks in advance,
Sven