Please explain the meaning of :fw in documentation and examples

[RubenGarcia]

https://github.com/ar-tracking/DTrackSDK/blob/master/examples/example_universal.cpp
has the following code

		std::cout << "Usage: example_universal [<server host/ip>:]<data port>[:fw]" << std::endl;

but no explanation of what fw means.
https://github.com/ar-tracking/DTrackSDK/blob/master/doc/DTrackSDK_Programmers-Guide.pdf does not mention fw.
https://github.com/ar-tracking/DTrackSDK/blob/master/readme.txt does not mention fw.

A link to documentation about fw is enough.