The question is: How does the data capture work ?
displays in Web Browser ?
outputs on some port ?
stores to a file ?
???
A quick search on the Web didn't find any user manuals for Fritz!Box
modems....
You start the capture via a buton on a hidden page.
(http://fritz.box/html/capture.html). This in fact starts a download. You'll
keep "downloading" the file until you use the GUI to stop. This ends the
download. The output is a file which can be opened in our favorite tool,
wireshark.
Depending on your choise, you can see the IP frames with or without the DLS
frames. If one likes, I could send a small capture file or a screenshot of
the capture page.
Dave