ZF (Rithmic) do not allow their data or orders or risk management servers to be pinged - so as not to interfere anyway with what they are there to do - provide data and executions with the smallest response/delay time.
See this thread starting at post #14 and then in particular post #18 - #20.
So just to follow up my posting above: I changed from Mirus with Zenfire to AMP with CQG and had never a single interruption since then (nearly four weeks now). Same trading software (Multicharts), same hardware and software on the PC, same trading instrument. The problem simply disappeared.
This questions the thought that Telekom (I am trading from Germany) was the cause for the reconnections - or CQG "streams" the data in a completely differend manner than Zenfire - after all I am not a technican.
So I am more than happy as of now and would like to thank everybody for his/ her contributions trying to get to the reason for those sad data interruptions.