code: public final void setHopCount(int hopCount)
  	{
  		if (hopCount < 0 || hopCount > 255)
  			throw new KNXIllegalArgumentException("hop count out of range");
  		try {
  			((MulticastSocket) socket).setTimeToLive(hopCount);
  		}
  		catch (final IOException e) {
  			logger.error("failed to set hop count", e);
  		}
  	}
docs: Sets the default hop count (TTL) used in the IP header of encapsulated cEMI
  messages.
  <p>
  This value is used to limit the multicast geographically, although this is just a
  rough estimation. The hop count value is forwarded to the underlying multicast
  socket used for communication.
  
  @param hopCount hop count value, 0 &lt;= value &lt;= 255